I was out last night with a new 50mm Canon lens aiming to get multiple exposures of M31 in Andromeda but i blew it on several levels. First and worst, I pointed the camera with SkyView on an iphone rather than hanging off Cassiopeia the way i did the last time.
In any event I was way off with the wrong part of Cassiopeia in frame and Andromeda off to the right. The stellarium clip below shows what i was looking for which would have put andromeda right near the center. Pointing with the phone is cute but it’s not trustworthy.
Then I was all over the map with my exposures. In the previous outing at 55mm I got a smudge at f/5.6, 10 seconds, ISO 1600. I should have started there adjusting for the faster lens. Maybe f/4 6 seconds ISO 1600. Lastly, I had only jpegs being produced which are no good for stacking.
Also, the lens may be faster but, while the center stars are pretty good, the stars near the edge are smeared – this could be a defect or just need stopping the lens down a bit.
So: Next time try to bracket Shedar in Cassiopeia and Mirach in Andromeda at 50mm. Expose for 6 sec at f/4 ISO 1600. If It’s a good evening I could try bringing my laptop and checking with the plate solver but that’s a lot of risk and setup fuss.
The two samples below were shot with the Canon T3i 50mm lens at f/2.8 ISO 1600, 4 seconds on the left and 6 on the right.
UPDATE: I accidentally found something super encouraging. The plate solving web site, shows you images uploaded by other users in the neighbourhood of your shot. One of them looked like andromeda so i clicked it and got the results below. I’d be delighted if i got anything like this and the field of view is almost identical to mine(24.8X16.6 degrees vs my 24.7X16.5). So, if i can capture enough light i can get an acceptably sized image. I don’t think it was taken with the same sort of setup i’m using(50mm lens on a canon aps-c body) because the pixel scale is different, 25.5 arcsec/pixel vs my 17.2 but still it’s very encouraging. I see another shot with similar but distinct parameters(24.4X15.7 degrees, 15.3 arcsec/pixel).
These may be done with more sophisticated setups and tracking but i suspect they are single images. I don’t think anyone would upload stacked images to a plate solver.
Well: somewhat less encouragingly I was able to identify the camera as a Sony ILCE7RM2, a $2500 full frame mirrorless camera. Also, that shot was a 401 second exposure at 85mm f/2.2. So to get that much light i would need to stack maybe 100 shots with my camera. still, image size is not the barrier i was afraid of.
Another example, below from a tutorial(for which thank you) also shows andromeda at 80mm equivalent focal length. This was made from a stack of 25 light frames. Andromeda and Half Dome – Nikon D800e, Nikon 85mm f/1.8 G – ISO 6400, f/1.8, 6 sec.
To get that much light I would need 100 shots at f/4 6 seconds ISO 6400. (Or I need to get my darned tracker working)