A few days ago I posted an image of the Andromeda Galaxy that was taken from a fixed tripod (no guiding or tracking) using a Nikkor 105mm telephoto lens at f/3 and a ZWO ASI178MM-Cool camera (shown here , with images of the camera and tripod setup). Then on this past Friday morning I had another clear night and decided to use the same technique to capture the Orion Nebula. However, this time I used an uncooled ASI174MM camera.
To review, by a "fixed" tripod I mean a simple unmotorized, alt-azimuth mount combined with a series of short exposures where the target is just allowed to drift across the camera's field of view. However, I manually recentered the target after each minute of drift.
Since I had changed to a camera with fairly large 5.86um pixels I allowed each sub to be exposed for 0.75 seconds (750ms) and I captured 800 subs for each of the RGB channels (800 x 750ms = 10 minutes, or 30 minutes total for the RGB result). Image capture was done with SharpCap using a gain of 189 and offset of 90 for the ASI174MM. Image processing was done with PixInsight and Photoshop CC2017.
Since I did a 2X drizzle integration to help with the star shapes I decided to increase the reproduction scale by about 1.5X and thus the image below is shown at 7.5 arc seconds per pixel (the original, 1:1 image scale with the 105mm Nikkor lens and the ASI174MM camera was 11.5 arc seconds per pixels and some of the stars had a noticeable diamond shape from the undersampling).
The image was a little noisy and the ASI174MM has a lot of pattern noise so I decided not to attempt any deconvolution, although that might have produced smaller stars and I could have used a star mask and range mask to protect the background. I also used 240 darks (at 750ms each why not?).
As for the image, I think it's not bad considering the short exposure and technique and my red zone light pollution. However, I did get some blue bloat which either came from the lens, or the filters (an inexpensive and early set from ZWO which I've never before used for DSO imaging), or a slight problem with the focus (yes, I refocused with each filter using a 52mm diameter Bahtinov mask). That said, the blue channel had the second lowest FWHM measurements (just slightly worse than green, with the blue having an undersampled FWHM of 1.47 pixels or about 17 arc seconds at the original capture scale).
I also have subs on the Pleiades which may confirm the blue bloat, although on that image I have just six minutes on each RGB channel.
Now that I've got images of a galaxy (earlier post, M31) and the Orion Nebula I guess I've shown that it is possible to image DSOs from a fixed tripod. Although, with those two very bright subjects I've almost run out of "easy" targets. Actually, back about 5 years ago I captured an image of the Orion Nebula using a series of 1/3 second exposures with a 300mm telephoto lens from a fixed camera tripod using a Nikon D5100. However, doing that kind of work with a DSLR probably isn't too smart since you can easily wear out your focal plane shutter after doing thousands of images each night.
Edited by james7ca, 13 October 2018 - 11:48 PM.