Best DSLR or ILC for Night Sky Imaging?

Started Nov 8, 2017 | Questions thread
rnclark Senior Member • Posts: 3,755
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

AstroDan wrote:

Roger, I have known the principals you described in your post for quite a few years now. This was built up largely through discussions with the astronomers I have worked with (and through a few discussions with you at various points), but I wanted to point out what a wonderful summation you provided. It can be easy to get things turned around in this hobby of ours, but I find your contributions thought provoking and well intentioned despite the cases where there may be slight disagreement. An example of this was that I recently posted an image I captured from a local observatory in my area, but spoke of the data as I would any other 'short' dataset. Roger provided the math to point out just how much light we were pulling in (despite the scope being 'only' F5), which gave me quite the chuckle.

Do you mean the scope in this thread: https://www.dpreview.com/forums/thread/4216504

72 inch (1829 mm)  aperture, 9250 mm focal length.

To turn to the discussion at hand, I find that the camera makes a contribution to the system (as many have articulated thus-far), but it typically falls third on my list. Having a proper mount and accurate tracking are at the top of the list for non-tripod based astrophography. My second is a blend between the optical design and raw aperture of the telescope. Note aperture, not f/ratio (within reason of course). If you have poor tracking it doesn't really matter how large your scope is, the stars just won't resolve correctly. Once you have the tracking down then the optical design starts to matter, as it is still fairly difficult to correctly cover even an APSC sized chip without corrected optics. Luckily for us, the always popular SCT has seen some upgrades in recent years to provide pretty clean fields. Hand in hand with this is the aperture of the telescope.

I always prefer real-world examples, and luckily I led our local club through this exact discussion recently while we were upgrading equipment. We opted to move away from a tandem setup of an 14" Meade LX200 at f10, and Televue NP127is at f5.2. We were having some issues with the mirror flopping around in the Meade, and flexure between the paired tubes, so we decided to replace them with a single tube (see, mount issues trump everything else). After doing quite a bit research we settled on a 16" Ritchey Chretien at f/8.

At times the discussion in this thread appears to suggest that as the sensor level there really isn't much of a difference between the Televue at f5.2 and the f5 scope I mentioned in the first paragraph (other than FOV), but there is. The resolution of course improves with the raw aperture until we hit the atmospheric limit. Sure, that matters, but the second feature that improves is the contrast of the object from the background sky due to the increased magnification, and higher contrast transfer from an increased aperture. We didn't exactly throw the 127 out with the bathwater, but some points in this discussion appear to suggest that the new telescope will gather less light from an object, and that overall it may be a step backwards in terms of efficiency. Well, bluntly, it won't and it isn't. We're pretty lucky that other than the rotation of the earth most of the stuff we look at stands relatively still, so if you need a wider field of view capturing panels to form a mosaic will give the benefits of both worlds. Once complete the mosaic will have more light, better contrast, and provided the seeing is good, higher resolution than a single FOV capture from the 127. I haven't had a chance to test this yet, but I plan to do a nine panel mosaic of the Pleaides using 1 minute 7 second exposures with the new tube and put it up against a single ten minute frame from the Televue. Should be interesting if nothing else.

Now, this is all fairly far afield of the initial question surrounding cameras. They matter. That being said, I have always found that pairing the camera to my optical tube is a more successful approach than trying to buy the camera in isolation. Have a huge focal length? Bigger pixels may help you, as oversampling can start to feel a bit ridiculous at 0.15"/pixel for most of our skies. Conversely, if you are shooting with a wider focal length smaller pixels may help to tease out fainter stars while also increasing resolution. For broadband work the quantum efficiency and dark current are two important features to consider, as they will impact your imaging efficiency. For narrowband work (or working with very short exposures) the read noise also matters. Luckily for us as long as the model isn't manipulating the raw data too much most modern cameras seem to provide a blend of respectable QE, dark current, and read noise.

Cheers,

Dan

Edit: added 'new' in the fourth paragraph.

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