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Sunday, May 07, 2017

Samyang 800mm Lens Review: A Night & Day Companion

The Power of Controversy

The Samyang 800mm MC IF f/8 is a manual focus, fixed aperture mirror lens made in Korea. It is a well-built metal construction styled in black and white. Having no electronics, it reaches a weight of only 946 g. Its compact size makes it easily portable. It has a good grip and lies good in the hand. Every copy of it comes with a test certificate.

The Samyang implements a closed, dust-protected catadioptric design consisting of a large corrector plate in the front, a primary and a secondary mirror and an embedded 4-lens flattener. The optics feature Multi-coated (MC) coatings ensuring high light transmission. Both lens caps are made of plastic. Its universal T2 mount is adaptable to numerous interchangeable lens cameras.

There is an optional 2x teleconverter with T2 threads on both sides, providing extreme telephoto capabilities.

A metal lens hood is also available in the market (Samyang Lens Hood 800mm f8 Mirror SH-105S). It is screwed on the 105 mm filter thread. It has been blackened and fine-textured to prevent internal reflections. It also acts as protection against damage to the front lens element.

First Impressions

If you are a stargazer, many questions are immediately answered when you see it at the first time. It behaves like your beloved Schmidt-Cassegrain telescope.

If you are new to obstructed optics, please take your time to become more familiar with it. Mirror optics differ from refractors in many respects, especially in terms of properties and handling. How the images will finally come out, will mainly depend on your shooting techniques and your photo processing skills.

Personally, I like the color rendition and the bandwidth of the Samyang very much. The photos have a rather cold, neutral look. Chromatic aberrations (CA) are negligible. Its donut bokeh is vivid and vibrant but typical for catadioptric lenses. I find it creative and inspiring but it will definitively polarize your audience. They will either love it or hate it.


Application Areas

Observational photography

The Samyang lens is suitable for shooting distant, non-moving targets. Despite its softness, its telephoto capabilities are impressive and unique once portability comes at first place.

If even more reach is required, a teleconverter might be a choice. However, the usage of inexpensive teleconverters often implies a significant loss in terms of quality and light transmission (2+ EV stops).

Wildlife

Wildlife photography is possible if:
  • the situation does not require frequent refocusing, or
  • the scenery does not presume hectic movements, and
  • enough light is available.
In many cases, you might miss here the auto-focus (AF), the vibration reduction (VR), the sharpness and the micro contrast of professional lenses.

Macros & Portraits

This Samyang can focus on to about 3.5 m which can give you acceptable macro shots. Using it for portraits is also interesting due to its distinctive bokeh. However, this long shooting distance might make the communication between you and your model difficult.

Astrophotography

It’s a Scope

Handle it in the same way you always do with your other telescopes. Put it on a parallactic motorized mount being accurately north aligned. You need a stable tripod. Try somehow to support your camera on the mount to avoid slipping, since it now holds the entire lens mass. Use a heated dew cap.

Finding your targets

Use a SLR red dot finder that is simply attached to the flash shoe of your camera, to find your targets easily at night. The viewfinder is only helpful for centering the target.

Focusing at night

You need to acclimatize the lens first; 30 minutes should be enough. Finally, focus it on a planet or a bright star using a Bahtinov Mask on the Live View display. The focusing scale on the Samyang is quite accurate, i.e. start with the infinity markings. Focusing is smooth with no backlash or mirror shift. However, the focus zone is very narrow. Be patient. The hot spot does exist.

Taking the picture

Point a bright Messier object and go with ISO2200 and 60s exposures first. After taking some pictures try to stack and process them as you usually do with your astronomy photos.

We are all perfectionists

Unfortunately, my exemplar shows triangle-shaped stars at winter temperatures below 5°C, which is an indication of tensed optics. Since the operating temperature range of my camera is 0...40°C, this issue is not a show-stopper for me. Under normal conditions (>10°C) the stars are beautifully round-shaped and the lens delivers a good image quality.

In general, all mechanics, lenses and mirrors inside a telescope asymmetrically shrink when the temperature decreases leading to unpleasant aberrations in my case. A solution would be to "relax" the optics, or to use mirror heaters, or to simply use it at normal temperatures as I do.

Let us be realistic, nobody should expect flat-field APO capabilities under all circumstances from a 183€ lens.


Usage

Thermal considerations

As every large lens, it needs to be acclimatized before usage. This step may take some minutes. Reaching thermal equilibrium is a prerequisite to achieve its maximum performance.

Contrast & Sharpness

To improve the contrast, the optional lens hood might be a little help. It reduces lens flares, halation, ghosting, and general degradation of the image caused by unwanted light sources. Unfortunately, the lens cap cannot be attached to the front lens, when the hood is mounted.

Stopping down the lens will further improve the sharpness. However, a self-made aperture tuner is required in this case.

Working on a Tripod

To get non-blurred pictures, you need:
  • a stable tripod,
  • a gimbal system,
  • activated mirror lock-up settings, and
  • a remote release.
Take your time on focusing and use the Live View at max. magnification. Turbulence in atmospheric layers significantly influences the image quality of large aperture lenses. You need to be patient to find the hot spot. Set the ISO as high as it reasonably gets and adjust the exposure time as proposed in the Live View.

Freehand Shooting

You will probably want to forget your tripod at home when going out for photo shooting in a sunny day. Even you deal with a real 800 mm non-VR lens, there is a way out:
  • Set the exposure time to 1/2000 s or faster. Depending on the situation, you might want to set the ISO at very high levels though. ISO 4500 works fine for me in most cases. A low noise camera body is always a good investment. Shoot in RAW format.
  • Put your camera on something solid, i.e. on a beanbag, a window frame, a branch, or a rock. Alternatively, you can lean against a tree or a wall.
  • Hold the lens with both hands. Focus as good as you can. Do not invest more than 5 seconds on focusing.
  • Hold your camera tight. Now, hold your breath and take 3 photos of the subject.
  • Examine quickly how they came out. Adjust the ISO. Refocus as good as you can and take 3 photos again!
  • Repeat the above steps several times.
Evaluate your images on your home PC later. Keep only the best one and delete the rest.

Usage as a Spotting Scope

After adapting the T2 mount down to Nikon/ Canon, you can put the respective lens2scope on the Samyang for using it as a high magnification (80x) spotting scope. You need a stable tripod in this case as well.

Here too, atmospheric turbulence interfering the view may be an issue depending on the weather and the acclimatization grade of the lens.



Conclusion

Having remarkable telephoto capabilities, this portable lens is a reasonable addition to your camera bag. While drawbacks like low micro contrast and the missing AF/VR in a classic package are not a secret, they can be excused when faced with its incredible price tag.

At the end of the day, it all depends on you. In any case, you get something timeless for little money. Having owned several lenses to date, this Samyang is simply the most controversial one.

Other much more expensive lenses surely offer better results and a broader applicability. But even you can afford them, they are far heavier and thus less portable.

Finally, one question still remains open:
How often would you use an 800 mm lens?”

Thanks for reading
Panagiotis Xipteras

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Photo Gallery: http://dark.astrodigital.net/samyang800
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DISCLAIMER: I have no affiliation with Samyang or any other manufacturer for that matter so I don’t really care if you buy this stuff over another. I take my time with each piece of equipment because I am always on the hunt for perfect solutions.

Tuesday, June 07, 2016

A Portable Setup for Narrowband Astrophotography: Zeiss 135mm, CCD camera, Avalon M-Zero, Gitzo GT5532s

The first three inches are the most important

In the bad old days, ambitious astrophotographers had to accept the risk of a slipped disk in order to make serious work under the stars. Corpulent flat-field scopes, noisy large format cameras, heavy mounts, car batteries, computer stuff and cable salad spiced with unfailing patience were in the menu when an astrophotographer decided to meet the competition at eye level. As time goes by, the wish to abandon the mass while keeping the class comes up.

This is a description of a fast telephoto setup for narrowband astrophotography. It consists of an ICX814-based CCD camera, a Carl Zeiss Sonnar 135mm (f/2) APO lens, a guiding subsystem, an Astroholgi MicroFocuser (AH-MF), an Avalon Zero mount and a Gitzo GT5532s tripod. Seemly invisible customized parts are placed at key positions to make those standard products work together as one system. This portable configuration offers a wide 6x5° field-of-view (FOV) and a useful resolution of 5.6".

This setup was thought up by three amateur astrophotographers. Holger Weber, Markus Noller and me had endless discussions over months how a portable astrophotographic setup should look like. Holger had the most practical answers. Markus inspired us with the smartest ideas. I had the most expensive solutions in mind. In some way, we were the perfect team for designing it.


The Classic Way
A widely used setup for astrophotography has often consisted of the legendary KAI-11000 sensor, a fast 106mm quadruplet scope, a 30kg class mount plus an adequate tripod. It has had the ability to match the common seeing conditions in Europe/ North America.

Quadruplet 106mm & KAI-11000 camera
Scope: 10.6cm aperture, 8 lenses (scope+reducer), 385mm, f/3.65
Critical Focus Zone (CFZ): 29,15μm
Camera: hosting a KAI-11000 sensor
FOV: 5° 21' 24'' x 3° 34' 16''
Resolution: 4.8"
FWC: 60000e-
Sensitivity at Hα line: 30%
Typical read noise: 11 e-
Dynamics: 9.4 mag, 5455 grayscale values
Pixel array: 11 MPixels
Focuser: integrated
Mount: 30kg class GoTo mount
Tripod: Wooden or metal tripod for 60kg load

Let's consider the system weight. The mount weights 16 kg, telescope is 8kg, counter weights 16 kg, tripod 8kg, camera incl. filter wheel 5 kg, plus the ... carrying cases.

The Future is now
The future is smart, light and flexible. We can already see how iPhones, iPads and Co. are changing our world. Our perception of a useful computer has been radically changed in the last decade. We replaced our old desktops with tablets. We drive to work with e-cars instead of using diesel trucks. We start wearing smart watches instead of mechanical chronometers. Has the time come to fundamentally re-think our telescope setups?

The game changer

Could a modern, light setup rival fat systems of the past? In certain cases, when uncompromising power plays a key role, nothing can defy the laws of physics. But if portability comes at first place, the answer might be somehow interesting or even ground-breaking.
Zeiss Sonnar 135 & ICX814-based CCD
Scope: 6.6cm aperture, 11 lenses, 135mm, f/2
Critical Focus Zone (CFZ): 8,8μm
Camera: ICX814-based CCD
FOV: 5° 17' 36'' x 4° 14' 5''
Resolution: 5.6"
FWC: 18000e-
Sensitivity at Hα line: 65%
Typical read noise: 5 e-
Dynamics: 8.7 mag, 3600 grayscale values
Pixel array: 9 MPixels
Focuser: Astroholgi
Mount: Avalon Zero  GoTo mount
Tripod: Gitzo GT5532s



May the Force be with you!
Look at the specs once again and you will know, what I am thinking about. It's not that much difference in terms of performance, isn't it? I mean, in the first case you have to carry some 60kg around. It's not the scope alone. You have to carry the mount, the heavier CCD including its pizza-like filter wheel, more counter weights, and a beefy tripod. Should there be any money left, you are well advised then to look for a fitness studio. You will need the force to carry the stuff around.

Finally, the question remains if a big system can exhaust its potential under the usual seeing conditions (Europe: 3..4") in your location. Is it reasonable to invest on such a big one under these circumstances?

A tiny world full of details
A Setup from Hell
The main challenge during the system design phase was to master the miniaturization. Unlike bigger setups, where you deal with issues such "large" and "heavy", you confront with challenges like "as small as possible" or "so light as its gets".

During designing a focussing subsystem you continuously fight in a mini world full of details. Astroholgi has already won this fight for you. The highlight of the story: The Astroholgi Telephoto Lens MicroFocuser forms a camera independent system. In contrary to conventional solutions , where the camera body, the focuser and the lens constitute a integral/monolithic system, the Astroholgi Microfocuser transforms the Zeiss lens to a sort of telescope, better said astrograph.

In addition to common DSLR bodies, high performance astronomy cameras can be mounted on the Zeiss lens, if they have short enough backfocus. In our setup, the ICX814-based CCD we used has 13mm backfocus. You can use the Zeiss Sonnar ZF.2 lens variant for Nikon instead of the ZE for Canon to gain 2mm more metal back distance (46.5mm Nikon vs. 44mm Canon -> Nikon ZF.2 wins). The ZF.2 provides you also the possibility to manually set the f-stops without needing a camera body to electronically adjust it.

An easy way to make good RGB work is to simply attach a Nikon d810a DSLR on the lens. It offers a large 35.9 × 24 mm full frame FX format CMOS sensor, small 4.88 µm pixels, special optimized filter for astrophotography and useful software functions. Even so, you are well advised to use the Astroholgi MicroFocuser mentioned above.

Since narrowband astrophotography -a domain of monochromatic cameras- was our objective, we have chosen a low-weight, ICX814-based CCD camera to catch the photons. Since, a focal length of 135mm ist short enough, the ICX814 sensor with its tiny but ultra-sensitive pixels is a good match even its sensor is not the biggest in the astrophotography scene.


Taming a Wild Horse
You might noticed Sonnar's tight CFZ of 8.8μm resulting from its ultra-fast focal ratio. You know, we are talking here about a focus zone of 9 thousandths of a millimeter! Like riding a Mustang is a no-go for novice riders, so astrophotography with this Zeiss killer lens is not recommended for greenhorns. It will kill all your images without an exception, if you can not tame it. But if you are looking for a wild workhorse, that can make you win a photography contest, you've just found it.

Can you ride it?
Apochromatic f/2 Lens
You might guess, it is a german artwork consisting of black metal with a lot of glass and two little pieces of plastic. The plastic parts are the caps :-) The Zeiss lens comes with a metal hood. The ZE version with EF mount for Canon is mainly considered in this report. It must be stated, that the Nikon ZF.2 variant offers the advantage of setting the aperture manually without the need of a DSLR body. This is something I really miss on the Canon ZE variant.


Apo Sonnar T* 2/135 Canon ZE version
Number of elements/groups 11/8
Weight=930 g
Filter thread M77 x 0,75
Dimensions (with caps) ZE: 130 mm
Aperture range f/2 – f/22


The Sonnar APO is perfect for astrophotography and it wonderfully lets the red Hα light to reach the camera sensor. Due to its apochromatic capabilities it is suitable for both RGB and narrowband work, i.e. for both color and monochrome cameras. A Nikon D810a, or an astro-modified Nikon DSLR are suitable candidates for RGB work. In that case, it is reasonable to use an IDAS LPS D1 77mm filter screwed in front of the lens in order to absorb the light pollution in your location. You can make twice longer exposures then. The IDAS Filter is approx. 1mm thin. If you already own the smaller 2" Hutech IDAS P2 filter, you can mount it on the Zeiss lens as well. Use the Geoptik adapter ring for 2" filters to M58 objective filter thread screwed on the XCSOURCE Step Up/Down Ring Filter Adapters. In that case, you deal with a smaller aperture of 50.8mm and f/2.6. Although aperture always counts -especially in astrophotography-, stopping down a lens might not be always a drawback. We achieved the most perfect star shape at f/3.5 across the field with this lens.

Thermal stability is crucial
Heater Bands
As usual, you need to acclimatize the lens before using it in the field. During the german winter, an hour is usually enough to cool down the Zeiss lens. To avoid fogging of the optics, especially at humid nights, heater-bands like those offered by Kendrick are recommended. The full metal construction of the Zeiss lens evenly conducts the heat from the barrel to the lenses. The heater-bands stabilize in some way the temperature in the lens and significantly reduce the need for refocussing during the night. This is one more reason not to undersize the power supply (see below).

Your eyes to the stars
CCD Camera

We have had solid arguments to choose an ICX814-based CCD as our main recording camera:
  • monochrome sensor that is best suited for narrowband work.
  • short metal back distance (13mm).
  • simple, comprehensible design.
  • over 65% response at line.
  • regulated cooling system.
  • low weight.
  • high resolution resulted from its small 3.69μm pixels making it a good match for short focal lengths.
  • acceptable 18000e- Full Well Capacity (FWC) and a low read noise of 5e- contributing to dynamic images.
  • no CCD chamber with Argon, i.e. 2mm less glass in the optical path.
  • supplied with stable, field-proven control software.
Several manufacturers like QSI, SBIG, ZWO, QHYCCD, or SXCCD produce excellent cameras based on this powerful CCD sensor.

Pain is temporary, glory is for ever
Our Modifications

The Zeiss lens is primarily computed to work on DSLR cameras. This fact has be taken into account during our system design. Additional glass in the optical path produces at f/2 strong comma. This fact has been seriously considered.

Cooled CCD astronomy cameras have a front window i.e. a glass plate which is 2mm thick in our case. The additional color filters you need for RGB/narrowband work have a typical thickness of 2..3mm. The filter glass we have used was 2mm thick.

The integrated filter (incl. bayer mask) on the sensor of a Canon DSLR (e.g. 5D Mk3) is approx. 1.7mm thick. Although our camera does not have any bayer mask on its sensor, we had to consider the problem of too much glass (2mm-1.7mm + 2mm = 2.3mm)  in the optical path because of the need of color filters. So, we were 2.3mm out of the specification.

Markus Noller, our award-winning astrophotographer and physicist, advised us to replace the front glass of the camera with a zero-thickness high quality Baader Turbo-Film foil. That would bring us 2mm closer to the Zeiss ZE specification. Following Markus's recommendations, we removed the 2mm thick front window and we placed a filter drawer accepting 2mm thick narrowband filters on the optical path. Our design almost matched the specified flange focal distance of the Zeiss lens. Please remember, we are dealing with f/2 and every micrometer counts!

Similar to every other cooled astronomy camera, our camera must be kept sealed. In place of its original front glass we installed a sandwich construction consisting of two metal rings and two layers of Baader-Turbo-Film foil separated by an air gap to prevent fogging. This is achieved by dry air mass between the two foils. After several field-tests, we consider the +0.3mm error as negligible for the sensor size of our camera. In our opinion, the system works Ok.
we warn you

CAUTION: All these actions void the camera warranty! You are solely responsible for undertaking these camera modifications. Probably, nobody on this planet will want to buy your modified camera if you sometime decide to sell it in the second-hand market.

My motto is No Risk No Fun! This is one more example on this planet where performance and commitment look to be fully associated. This is an evil setup and probably one the best astrographs I have experienced in the last two decades.

Please, read one of my previous CCD reviews to learn how to operate a monochrome CCD camera.


Mustang's saddle
Micro Focuser (AH-MF)

Primarily, the AH-MF is a focusing system for ultra-fast telephoto lenses. It is used in application areas where other focusers fail due to lack of precision and focusing reproducibility. It is completely designed and individually manufactured in Germany by Astroholgi.de. After years of design it had left the prototyping phase and went in production in January 2016. The production stopped in December 2017. Every AH-MF is hand-made and perfectly manufactured.

Mounting Rings
The mounting rings are part of the AH-MF. They are:
  • massive constructed to securely grab the telephoto lens. 
  • rotatable by simply unscrew two Allen screws. You can rotate the AH-MF without seriously going out-of-focus even at the extreme f/2 f-stop. 
  • offer screw holes to mount an adapter plate for an optional guider scope. 
  • offer screw holes to mount a rotatable adapter plate to support the camera in order to avoid tilting.
  • available in different colors.
The telephoto lens is only held by the first ring, that is hosted in a rotatable rail. The fixing screws should be screwed so tight as necessary to securely hold the lens! Not too tight, please! Otherwise astigmatism or other problems could be the result. This procedure should be done only once while installing the lens in the rings. I suggest to install the lens in the AH-MF, to perfectly adjust it, and to dedicate it solely for astrophotography. Buy one more Zeiss-135 for your day-time photography! Again, f/2 is not a game.

Precision is reproducible
Fine Focussing Subsystem
The Fine Focussing Subsystem is part of the AH-MF. It smoothly rotates the mounting rings to focus the Zeiss lens while displaying the focussing distance precisely. During focussing the Zeiss lens varies in length. This fact has been considered in the AH-MF, i.e. the focuser gently touches the plate and make a slight move of few millimeters during focussing.

Focusing is done by means a digital micrometer screw. Its digital display facilitates the focusing procedure since every μm counts at f/2 f-stop.

Most of the images in this review show the last AH-MF prototype for Canon ZE lenses. During the prototyping phase in 2014, a AH-MF version for the Sigma 105 mm F2,8 EX Makro DG OS HSM -a great lens in a plastic barrel- was successfully tested. The images #1, #2 are captured with it in Roque de los Muchachos, La Palma Island, at 2040m altitude. The AH-MF reached EOL (End-Of-Life) in December 2017 and it is no longer available.

I will show you the stars
Guider
Our guider is truly unconventional. It consists of:
The software MaximDL or PHD Guiding are used to control it.

The best light beams come through
Filters

  • Baader 36mm filter set for Full-Frame-CCD, consisting of three filters - H-alpha 7nm , OIII 8,5nm , SII 8nm. The filters are round, 2mm thick, without cell.
  • Baader RGB color filter set: 2mm thick, new 2015 version with steeper slope to better absorb the light pollution.
  • The following filters which are also 2mm thick are used: Red filter , Green filter , Blue filter
  • Possible filter variants could also be: Baader Highspeed Filter. Unfortunately, these are not available in 36mm size for the slim (10mm thick) filter drawer we have used.
We avoided no name filters. At diaphragm f/2, issues like halos around the stars or reflections can occur if the filter layers are not plane-parallel ground processed.

The right place for the right things
Filter Drawer
Filters are usually hosted in dust-tight filter wheels which are mostly big, thick and heavy. The short flange focal distance of the Nikon F-mount specification and our main objective to keep down the total system weight limited our options. A thin, light filter drawer was the best choice!
Our filter drawer is only 10mm thin. Other sizes with a thickness of more than 15 mm are unsuitable. The Zeiss lens is connected to the filter drawer via a Canon-M48 Adapter. The filter drawer is connected to the CCD via an adapter and 3mm long T2-extension tube.

Smart is beautyful
Mount
Only few American, Japanese and European companies are nowadays able to produce a good telescope mount. In the 8kg load class the alternatives are even more limited. One of the most suitable mounts for our system is the Italian Avalon M-Zero.

This is why we have chosen it:
  • low weight, high quality mount 
  • GoTo controller 
  • no worm backslash, because there are no worms. 
  • no counter weights required, due to its smart design. 
  • stable working software
  • mount controllable via PC or smartphone. 
  • no meridian tilt required during exposures. 
  • made in the European Union.
We have used some adaptions to customize our setup:
  • Avalon Guiding adapter is on the other axis side of the telescope so that you can install a Guider there. A smart feature of the Avalon mount that saves passive counterweight.
  • Two tiltable adjustment plates made ​​by astroholgi.de (see photo) on the Guiding Adapter.
  • Dove Tail Clamp Adaption on the adjustment plate (similar to Avalon GP clamp).
  •  Astroholgi Star Plate (see photo) to strengthen the tripod.

The Rock
Tripod
The Gitzo Systematic GT5532s is a modular tripod, with a flat centre disk that can be interchanged for centre columns, levelling bases and other components. A good example for that, is the adapter connecting the Gitzo tripod with the Avalon mount. See Astroholgi's Tripod to Mount adapter.

The Gitzo tripod has leg angle settings but they are not needed in our case. Its strong leg tubes are in 6X carbon fibre with Gitzo's efficient G-locks. Having a weight of only 2.8kg the Gitzo GT5532s can safely carry 40kg of astronomy equipment. Its reputation as "The Rock" is confirmed every time we use it.

The Gitzo reaches a max. height of 132.5 cm with its 3-section legs fully extended, which is enough for our application. There is also a longer 4-section model in Gitzo's product catalog but we suppose the 3-section version should be more stable than the 4-section one. Anyway, both of them are officially specified for a 40kg load capacity, which are good news.

Power up!
Computer and Batteries
The supplied Avalon software runs on a Windows laptop. Additionally, an Android app to control the mount via smartphone is also supplied. MaximDL Pro is used to control the CCD camera and the Guider.

Three lithium iron phosphate rechargeable batteries are connected in parallel. See LiFeEnergy LiFePO4 Accu 12V/12Ah with BMS.
They offer sufficient energy for one night.


Space photos!
Gallery and Software
A narrowband image of IC1396 with our setup

This setup is shown in gallery #1, gallery #2, video.

Astronomy photos with the setup are: North America Nebula, The Cirrus Complex, IC1396.

All telescope computations are done with my AstroDigital.Net software. The very first prototype of Astroholgi's MicroFocuser is shown here.





Conclusion
This setup addresses ambitious astrophotographers needing a high performance, portable system for narrowband work. Our ten thousand dollar baby embodies a sophisticated concept, high-grade mechanics, first-class optics and modern electronics. Its low power consumption and its adequate weight make it suitable for field use. Its resolution matches the common seeing conditions in most northern countries where useful nights are rare.

Thanks for reading
Panagiotis Xipteras



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CAUTION: All actions and modifications in this report could void the warranty or -even destroy your equipment! You are solely responsible for undertaking these actions/ modifications. DISCLAIMER: I have no affiliation with Zeiss, Avalon, Gitzo or any other manufacturer for that matter so I don’t really care if you buy this stuff over another. I take my time with each piece of equipment because I am always on the hunt for perfect solutions.

Sunday, January 18, 2015

Review: Starlight XPress SX-36 CCD camera

"Can a SX lady cause a financial crisis?"

The past and today

Elegance and power
Over a decade ago, as  I was about to enter the astrophotography scene, two companies were enjoying a high standing and a good reputation worldwide: SBIG and Starlight XPress. SBIGs were the Kodak gorillas having the power for doing everything. The Starlights were the beautiful ladies doing the same things but in a silent, elegant way. Most of the ladies were hosting a Sony sensor. If you wanted a serious camera to capture the stars, you had to choose between them, either a gorilla or a lady. End of the story. It was like the funny battle between PC and Mac in the '90s.

Her Majesty, the SX-35
Since then, two cameras dominate the upper end of the Starlight XPress product portfolio. Both of them offer full frame Kodak sensors. The heart of the first one is a legend. The KAI-11000 sensor of the Trius SX-35 camera, has been controversially discussed. Its low resolution, high dark signal, high read noise, relatively low Hα sensitivity, and its interline architecture have been criticized. Nevertheless, nothing stopped this 11MP sensor from getting the most breath-taking space photos in the last decade. Nothing is wrong on a good calibrated image from a KAI-11000 based astro camera.

Her Royal Highness, the SX-36
The second one, the "Thirty-Six" did not share the same popularity grade as her sister. For years, the 16MP camera segment was dominated by the KAI-16000 sensor. This full frame chip had a higher resolution but the same high read noise and a lower Full Well Capacity (FWC) than the practice proven KAI-11000 chip. Nothing can defy the law of physics. In that case, the price was a lower dynamic range. But even so, technology moves on and there are good news.

The "Thirty-Six" is back, and now she looks to have some say in the advanced astrophotography league. Her new heart, the modern Truesense  KAI-16070 sensor has lower read noise, higher FWC, and slightly improved sensitivity. These benefits result to a higher dynamic range. Her key advantage is still her higher resolution compared to the SX-35, making her a better match for smaller instruments. The SX-36 offers 16MP x 7.4uM square pixels vs. 11MP x 9uM of the SX-35.

Facts and features
Design is everything

However, the biggest step forward is the new Trius camera design. This is the point where both her Majesty and her Royal Highness profit of. This compact design (118mm in diameter x 102mm long) is Hyperstar capable. Light weight was always a virtue of Starlight Xpress cameras. Weighting only 1100g, the SX is light weight enough to ride atop on the focuser of a Takahashi Baby-Q without tilting it.


CCD chamber
The argon filled chamber prevents moisture under wet climatic conditions. People in northern countries look for features like that when a camera upgrade is in sight. These cameras look like a work of art. Beauty is simplicity.

CCD sensor
Unlike the KAF-16803 based beasts (even its FWC and sensitivity is a bit higher compared to the ladies), the full frame chip of both Starlight ladies is still illuminable with standard 2" filters. That means, you save thousands of Euros when small 2" filters are also doing the job. IMHO, if a 36.3x24.2mm pixel array is not large enough for your application, I wonder whether a squared 36mm array will finally satisfy you. Especially, if you look at the modern TVs, computer displays or iPads. Nothing nowadays is square.

Furthermore, if you want to use an off-axis guider this smart aspect ratio of the SX-35/36 offers you the free space you need to place an off-axis mirror above the sensor.

According to the manufacturer, dark frames are not necessary for most of the brighter deep sky objects, due to the low dark signal of the "Thirty-Six". Anyway, you can judge her by examining the master dark frame I am providing you here.

The sensor offers an effective anti-blooming (ABG) with a minimal effect on linearity and no lost active area. Although ABG architecture lacks a bit sensitivity, amateurs like me might not like to miss it particularly when having experience with light sensitive NABG (non anti-blooming) chips like the narrowband beasts Kodak KAF-402 ME und KAF-1603.

Download times
The electronic shutter of both SX sisters can take very short exposures, making them capable for solar and moon photography, although the built-in rustic USB 2.0 interface needs approx. 15 seconds to download each frame. Let be honest. Asides from marketing discussions, very fast downloads, i.e. high read-out frequencies result to unwanted high read noise. Believe me, you will want to read out your CCD chip slowly, if your are doing serious astro imaging. Hence, 15 seconds is a fair value. It's worth to download a good image slowly than getting a bad image quickly. Advanced birthday photography is not the application area of the SX. Especially, if you see her good QE (quantum efficiency): 52% at peak (green light), 31% at Hα.





USB hub
If cable salad is not your favorite dish, there are good news: the new SX Trius line has a built-in 3 port powered USB hub. That means you can directly connect your lodestar and your Starlight filter wheel on the SX-35/36. That results to a single USB cable control between your laptop and the SX for all features. Since we use an Astroholgi filter drawer on our SX-36 we don't need all three mini USB ports.

Cooling
Both SX-35 and SX-36 cameras have a three stage Peltier cooler for efficient CCD cooling. Two ventilators, one on the camera and the other inside it blow out the hot air. At room temperature we achieved -15°C to make the calibration frames available here. We think, a delta of -37°C is enough for the night use, especially in the winter and if you consider its low power consumption. It less than 1A at 12V DC - 12W at 110V/240V AC. In my opinion, these are key arguments for the field operation.


Mechanics
Both SX have a back focal distance 17mm +/-1mm. That's why I was previously talking about their useful aspect ratio. You may want to mount an off-axis guider (and adding weight) on the ladies. Especially, if you consider their acceptable weight. The circle is complete.
The input thread (72mm) is compatible with the Takahashi FSQ telescopes. We use a "WideT to 72mm" adapter to connect our SX-36 to our FSQ reducer (see images).

The tilt angle of both SX is adjustable. Although, this is a mandatory feature for a large format camera, you will probably not need it. AFAIK all their cameras are precisely adjusted with laser measuring instruments before leaving the factory. However, if you still think, you new SX has a tilt, you should first check your focuser, before trying to adjust your (probably perfectly adjusted) SX. If the focus point is far outside of the tube, this could be a possible reason for focuser tilt.

Software
Both sisters are coming with the standard Starlight XPress software package. Hence everything you need to get started is inside the box. My calibration frames are made using this software. Although, it seems to work, addicted MaximDL users like me may finally prefer the Diffraction Limited software to control the lady. Now hold on tight. Diffraction Limited, the creator of MaximDL, has recently bought SBIG!

How to use the SX-36

Mono cameras have a different handling than OSC (one-shot-color) cameras. Whenever a DSLR camera needs only one exposure to get a color image, the mono cam needs three of them => red, green and blue through a R, G, B filter respectively. See the following examples:
  • RGB image from a consumer DSLR camera Canon 7D: RGB single exposure at ISO6400 without filters (JPG).
  • Tricolor image using the SX36: Stacked exposure 10x200ms balanced 1-1-1 using Baader RGB filters (JPG).
Calibration files

Astronomical CCD cameras can be precisely calibrated. This step is mandatory in order to get the most out of the image data. You need calibrations files to do so. Please find attached the calibration files of the SX-36 we reviewed (SNR-007).

Flat fields remove artifacts caused by inhomogeneities of the CCD sensor, dust particles on both the sensor and the optics, and vignetting. You need separate Flats for each channel.

Example:
Flat field of the SX-36 on a Takahashi FSQ-85EDX with reducer f/3.9 at -15°C=> (JPG/FITS)
Dark frames remove the dark signal of the sensor. They are taken at the same binning, same temperature and at a equal time length like the light frames. A dark frame always contain a Bias frame.

Example:
Dark frame of the SX-36, 20 minutes at -15°C => (JPG/FITS)
Bias frames remove the noise of the electronics. They are useful for the calibration of the short-length L, R, G, B Flats.

Example:
Bias frame of the SX-36 at -15°C => (JPG/FITS)









FFT evaluation
The 2D Fast Fourier Transformation (FFT) of the master BIAS averaged of 30 Bias gives information about the electronics. Periodical patterns indicate badly shielded electronics. A point in the middle of the image with perfect noise around it without any pattern is a very good sign.

Example:
Read noise FFT of our SX-36 (FITS).

Links:

Read noise evaluation
Having a Bias and Master Bias frame and knowing the gain of your camera, you can try to calculate the read noise of your CCD according to the instructions in users.libero.it/mnico.

Example:
Read noise frame (FITS) of the SX-36.
Do it yourself:
Bias and Flats of our SX-36 (FITS)


Flat fields, darks, and Bias should be combined with the Median or Sigma Clip filter in MaximDL to build a master file (see screenshot). The Average filter does not remove the cosmics effectively.

How to create your calibration files

You need calibration files i.e. a master dark, a master bias, and several master flats (one for each channel) to calibrate your astro images. It is recommended to create new calibration files periodically, i.e.:
  • Darks: once a year. Like everything on this planet, CCD sensors change their characteristics over the time.
    Example: Master dark SX-36, 20min, -15°C (JPEG/FITS).
  • Bias: once a year.
    Example: Master bias SX-36, -15°C (JPEG/FITS).
  • Flats: each time you turn or mount/dismount your camera on the scope. As the time goes by, new dust particles sit on the optical path. Even in stationary setups it is advisable to periodically (once a year) make flats.
    Example: Master flat SX-36, FSQ-85(f/3.9), -15°C (JPEG/FITS). 
This procedure can be automated to a certain degree with a computer-controlled filter wheel. Download here my MaximLE sequence files on my site, to find out how I do it.
TIP: enable the check box "Group By Slot"when making flats in MaximDL to minimize filter wheel rotation!
Make your flats at the same temperature as your darks and at the same focus position as you captured the stars. Your are advised to make the flats immediately after ending your photo shooting session. Even if you can reproduce the CCD sensor temperature at the next day, the scope (especially a fast one) may not have exactly the same tube length (!) or optical characteristics (color correction, focus point, etc.) when it is operated at room temperature at the next day.


Flat field panel
Gerd Neumann's Aurora flatfield panel is a perfect tool to make your flats. Do not exceed the 2 hours time when using it. R,G,B flats can be calibrated by subtracting a Bias frame. Flats for narrowband (NB) images take longer time to expose. Hence, you must calibrate them with master darkflats having the equal exposure time as your NB flats.




The final step is to calibrate your your master flats. Download my check list. Use the Median or Sigma-Clipping filter for stacking to create the master files. For those fellows making scientific work on CCD sensors without any commercial interest, I am making available the dark, flat and bias calibration frames of our new SX-36 camera (Serial No. 007, KAI-16070 sensor): frames in JPEG for previewframes in FITS format for scientific purposes

How to process your images:

Process your RGB images strictly in the following way in MaximDL:
  1. Acquisition of red images with this monochrome camera => RRAW
  2. image calibration RRAW (using the master dark, the master bias, and a R calibrated* master flat) => RCAL 
  3. remove gradients (i.e. the light pollution) in R channel using MaximDL's "Auto remove gradient" function => Rclean
  4. align all Rclean images using MaximDL manual star alignment algorithm => Raligned 
  5. stack all Raligned  images using Sigma-Clip method => Rsum
  6. ... repeat steps 1..5 for GRAW (green) images
  7. ... repeat steps 1..5 for BRAW (blue) images
  8. align the three Rsum, Gsum, Bsum images => Rfinal, Gfinal, Bfinal
  9. color combine Rfinal, Gfinal, Bfinal => RGBfinal)
Advantages
Your RGBfinal image:
  • has an improved S/N ratio as a stack of single exposures.
  • is free of numerous artifacts due to calibration with flat fields (step 2):
    • inhomogeneities of the CCD sensor.
    • has no artifacts due to vignetting of the optics.
    • has no artifacts due to dust particles on the telescope optics or the CCD sensor.
  • is free of the bias signal (step 2).
  • is free of thermal current (step 2).
  • has no light pollution or moon glow gradients (step 3).
  • has no satellite traces, due to Sigma-Clip stacking method (step 5).
  • is in color
  • has tighter stars with accurate colors
Having now an excellent RGBfinal image your post-processing with Pixelmator, DxO OpticsPro or Photoshop is easier and leads to better results. You can better stretch your image, do good white-balance on it, etc.

Gallery and Software

Hα image of M42 with our setup
This setup is shown in gallery #1.
Astronomy photos with this setup are:
All telescope computations are done with my AstroDigital.Net software.



Conclusion

The SX-36 addresses advanced astrophotographers needing a large format astro camera, embodying a sophisticated concept with modern electronics. It nicely matches portable flat field telescopes without sacrificing the image quality in terms of resolution, dynamics and noise. Its low power consumption and its adequate weight make it suitable for field use. Its ability to interwork with numerous other components of the manufacturer´s product portfolio makes it a future-proof investment.

The Thirty-Six offers a well balanced architecture implemented in a comprehensible, upgradable product. It is made by Europeans having astronomy in mind. Good investments like this one never cause financial crises. The beauty of simplicity is timeless.

Thanks for reading.

Panagiotis Xipteras

--
Special thanks to Holger Weber for all his support during the review phase.
Gallery: http://dark.astrodigital.net/sx36


Thursday, December 25, 2014

A keyboard for stargazers - The Razer BlackWidow Chroma

Razer, a computer peripherals company, recently included an illuminated keyboard in its portfolio. Although it was primarily made for the gamer scene, it has many useful features for stargazers.

Image: The Razer BlackWidow Chroma keyboard

This keyboard is suitable for astronomy applications since the red light keeps the eyes adapted in the darkness. Each key can be separately set to a specific color  (see image). The keyboard can be dimmed.

Stargazers may want to:
  • set all alphanumeric keys in red
  • set control keys in light red
  • set often used letters (e.g. N, G, C, M, _, I, m, a, g, e) in dark red
  • turn off all keys usually not really needed (see image)
to improve the work with MaximDL, TheSky, or AstroArt at night. All these settings make things easier at night when every key stroke counts.

The keyboard can connect the personal razerzone.com internet account of the user in order to share his/her settings across other Razer devices. It supports the import / export of the settings on a hard drive. My own settings are available for download on my site.

This modern keyboard is built like a tank. It works on Mac and Windows, even on old Windows XP machines.

Some years ago, I have developed a free app (RedScreen.exe) to also protect eye adaption during your astronomy sessions. If you like, you can download it here for free.

Thanks for reading.

Panagiotis Xipteras

Friday, October 10, 2014

A fascinating image of the SH2-240 nebula

Image: SH2-240, copyright (c) 2014 by H.Weber and M. Noller

We are proud to present you a demanding target tonight. This is the Simeis 147 (SH2-240) nebula in the Taurus constellation, a large and faint celestial object mainly considered by advanced space photographers. This image is exclusively published in this blog under the permission of its authors.

Exposure:
Hα: 8x1200 sec
OIII: 4x1200 sec
SII: 5x1200 sec

Equipment:
CCD astrocamera: ICX814-based CCD bei -15°C.
Filter: Baader narrowband filters.
Lens: Sigma 105 mm f2,8 at f/4.
Guiding: Takahashi FSQ 85 with Starlight Loadstar camera.
Mount: Losmandy G11.

Astrophotographers/ authors:
Image acquisition: Holger Weber, www.astroholgi.de
Photo processing: Markus Noller, www.deep-sky-images.de

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