Pages

Wednesday, March 23, 2011

The Serpent Storm on Saturn

A prominent storm erupted late 2010 in Saturn' northern hemisphere. It's called The Serpent Storm and it still rounds the planet. Its appearance changed over the last months, covering sometimes large areas of the northern hemisphere.

March 20th 2011, 21:39 GMT: The Serpent Storm is behind the planet, i.e invisible from the Earth. Photo: Mewlon 210, f/11.5, FL=2415mm, Camera=TIS DBK21USB, approx. 6000 shots, 2x digital zoom, RGB:
One day later .. March 21th 2011, 21:36 GMT: The Serpent Storm is visible from the Earth! Photo: Mewlon 210, f/11.5, FL=2415mm, Camera=TIS DBK21USB, 120 of 6000 shots stacked, 2x digital zoom, GRGB composite created from the basic RGB data with MaximDL.
In the photo above, the Serpent Storm is visible at approx. 100° of longitude. The atmosphere of Saturn mostly consists of hydrogen and helium. Its banded structure is noticeable with good amateur telescopes, since the saturnian bands look fainter than Jupiter‘s, and the planet has twice the distance of Jupiter and it is smaller than it. Observing data: Saturn: Apparent size=19,2“ / Apparent brightness=1,03mag / Distance=1.292.000.000 km

Thursday, March 17, 2011

The Marcarian Chain in Virgo

This is the star field around the Marcarian Chain in the constellation of Virgo: click here for full resolution (10 MB). The exposure time was only 2 x 100s ! The equipment used is listed below. The photographer used an unmodified Nikon d3100 DSLR camera without any light pollution filter in suburban area to shoot this photo.
The jet of the galaxy M87 is almost visible, if you zoom in the photo above. Follow the yellow lines below:
Here is a flow chart how to process your DSLR photo material:

Thursday, March 03, 2011

A Nikon d3100 camera under the stars

After five years of astrophotography with a light sensitive, mono astro camera (ST-7XME), I started looking for a more productive one with a larger color sensor. My old CCD camera had a tiny chip, my telescopes were screaming for something larger and any dedicated astro camera did not fit my camera budget.

Image 1: Nikon d3100 with solar filter

I just wanted to shoot pretty pictures in a fast and easy way without the need to spend a lot of money. Hence, I decided to attach my unmodified Nikon d3100 DSLR on the lenses I had at that time.

Image 2: These scopes were acting as lenses for the Nikon

I was wondering why astro cameras represented a long-time capital investment ;-) Although, normal astro cameras were simpler and easier to build than normal DSLRs but they were much more expensive. In the meanwhile, I have given up hope that this fact will change someday.

Image 3: H+χ Persei. (Nikon D3100 at 530mm focal length)

Anyway, at a cold clear night I had the chance to test this DSLR on the FSQ106ED equipped with the dedicated f/3.65 focal reducer. The recommended adapter train consisting of a Nikon->WideT->CA35(Sky90) has been used to mount the DSLR on the scope. This has been done in order to keep the optimal distance between the CCD sensor and the reducer. Fortunately, this adapter combination is sturdy, compact and easy to use.

I observed a hint of vignetting on the RAW photos, but it was negligible. Fortunately, the Nikon sensor was correctly built in the camera body, so there were no orthogonality issues even at f/3.8.
I used the optional remote cord to take the pictures.

Image 4: The Moon at 300mm focal length

Although the Nikon (as every consumer camera) has no active cooling, its sensor is known for its low dark noise, i.e. typical deep sky exposures of 3..5 minutes at ISO 200 are no problem in the cold winter nights. During imaging of the Moon or the Sun you may however notice mirror vibrations, especially when you are firing at long focal lengths (>1000mm). A workaround is to work with a remote cord, in silent mode settings, at ISO800.

Image 5: The Orion nebula at 386mm

If deep sky photography is your only application area, you can modify your Nikon at special shops like Optic Makkario in Germany. They set your Nikon in a so called "undefined state" by removing its internal daylight filter and making it able to register all frequencies. An IDAS LPS D1 light pollution filter is mandatory then. It is available in numerous sizes at TS.

Nikon also excels in the photography of planetary nebulas, the moons of the outer planets, and dark nebulas. An apochromatic refractor with 800..1400mm focal length and 100..150mm aperture are perfect for doing this. Example: the moons of Uranus.

My astro images are usually taken under heavy light pollution (LP). Since, I initially did not own a LP filter, I had to reduce the exposure time, increase the ISO (>400) and to process the results harder with Aperture 3 on my Mac. I captured all astro photos in NEF (Nikon's RAW) format in order to prevent data loss, a well known problem of JPG files. Nikon's NEF format offers more processing options and greater dynamics in later stages. Apple's Aperture 3 fully supports Nikon's NEF format. You can see an example here (size 3,5MB). A cropped version of M13 is shown below:


Image 6: Messier 13 - The globular cluster in Hercules captured at 385mm focal length

In August 2011, I reshot M13 at 820mm focal length (f/8). It is a crop of 3x30s stacked exposures at ISO1600 in NEF format. A high resolution photo is available here.

Image 7: Messier 13 captured with the Nikon d3100 at 820mm focal length

Photoshop users: NEF files must be converted in DNG format to be further processed in Photoshop. A good converter is here: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4923

Nikon's ViewNX software can also convert the NEF files in a photoshop readable format.

Many findings in this review can be more or less also implied on newer Nikon models. Hence, if you want to buy one, you could go for the newest model as well. The Nikon D5500 was introduced in January 2015.

More astro photos with the Nikon D3100 are available in my site at: http://dark.astrodigital.net/nikond3100

Thanks for reading

Panagiotis Xipteras