NEX-5N Astrophotography - Saturn Technique

Started May 8, 2012 | Discussions thread
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RustierOne
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NEX-5N Astrophotography - Saturn Technique
May 8, 2012

Here’s one of my first Saturn images with the NEX-5N. It’s a bit soft and has a color fringe from stacking. But I wanted to share my technique with the forum so that others can try, while Saturn is favorably placed this spring. The sky was hazy, with a tendency to form dew, and the air was not very steady. The corrector plate on the telescope has quite a bit of dust on it, since I very rarely clean it (dust is not that much of a problem, but scratches are permanent).

Here's my equipment and technique:

Celestron C-11 telescope, 2790mm f/10 w/ 9mm Plossl used eyepiece projection, Losmandy G-11 mount, Sony NEX-5N, attached to telescope with adapter (model BNEX, $58 from Telescopeadapters.com), shutter priority, 1/5 sec, speed priority continuous mode, 4 megapixel, fine, ISO 1600. Of the 410 JPEG images, the best 150 were stacked and processed with Registax 6. Resulting image was cropped with minimal post processing in Photoshop Elements.

Here's the device I made to keep the shutter release button depressed (sort of cave man style). The clamp 4-inch clamp, various screws, thread tap and bit will run less than $20.

The white nylon screw fits in a hole (in the metal plate and yellow plastic insert) threaded to match. I've found that it works just fine without the metal plate, only utilizing the threads in the yellow insert. A short section of aquarium air hose slit endwise protects the back of the camera from being scratched by the clamp bar. Here's how the whole thing looks on the camera.

With the clamp attached, access to the menu button and lower programmable button is easier using a lead pencil or other stylus. But as can be seen, the monitor can be tilted for easy viewing. To start the exposures (after carefully focusing), you just need to turn down the nylon screw until the camera begins taking images. Likewise at the end of the shots, just back the screw out until the shutter stops.

I was very pleased with how little noise was produced by the NEX-5N. Using the method described is not the best due to excessive use of the mechanical shutter. I don't know what its rated life might be. But cranking off hundreds or thousands of single shots will use up whatever life it may have at an advanced rate. While it would be better to used the 1080P HD movie mode (approx. 2 megapixels), I found that by using JPEGs (which Registax handles just fine), I didn't have to deal with converting AVCHD or MP4 movies to AVI format for Registax. Perhaps the biggest challenge is getting focus right with the live image smearing around due to atmospheric seeing. I have had some success using a Bahtinov mask to aid in focusing:

http://en.wikipedia.org/wiki/Bahtinov_mask

This mask can be purchased from various sources. I wish all who try astrophotography with the NEX cameras much success! Keep the rest of us posted as to what works for you.

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Russ

 RustierOne's gear list:RustierOne's gear list
Sony Alpha NEX-5N Sony Alpha NEX-7 Sony E 18-55mm F3.5-5.6 OSS Sigma 19mm F2.8 EX DN Samyang 8mm F2.8 UMC Fisheye +3 more
Sony Alpha NEX-5N
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