Dithering by hand - unguided EQ3-2 mount with RA clock drive

[KevinPSJ]

I struggled with processing my DSLR shots for a long while - could not eliminate noise despite taking plenty of dark frames. Looking on-line here and other forums it seems the recommended approach to reducing noise (walking noise especially) is using dithering. Unfortunately I don't have a goto mount - just RA clock drive. It seemed like this technique was out of my reach.

Both necessity is the mother of invention as they say so I thought I'd at least try and see if it's possible to dither manually. Turns out it's hard but not impossible. My routine now involves setting up a sequence of lights in Backyard EOS - usually something like 30x40s for prime focus work with my Skywatcher 150P and Canon DSLR 600D. Then once the sequence starts, I suspend every 4-5 subs and put my eye to the finderscope and my hand on the dec slow motion or the RA control. Carefully I nudge the scope so the stars move by a very small amount - first north, then next time west then east then south and so on. It's tricky if you are pointing at a patch of sky with only a few dim stars in the finder scope view but I'm getting better with practice. It is easier with a wider field of view - last 2 sessions I used a Takumar 200mm f/4 and it was almost easy compared with the prime focus sessions.

The main benefits are (a) I don't "waste" time taking a lot of darks and (b) satellite trails completly disappear. The downsides are (a) need to stay at the scope the whole time - no opportunity to go inside while the sequence is running and (b) lots more time squinting through the finderscope and hoping I didn't nudge too far

If you look at my gallery then all of my recent images were taken without any darks. There're not amazing by any stretch but I feel like I'm getting consistently better signal to  noise from the end product and I've eliminated the streakiness and walking noise issues from earlier images I've taken.

 

Compare: 30 x 30s subs @ ISO800 (with 10 x 30s darks) and Canon 600D at prime focus

with 15 x 60s subs at 800 ISO and no darks but with dithering 

 

Little bit tricky to find a target I can directly compare - there are sort of similar subjects but with different focal lengths.

I'll definitely be trying the Pleiades later in the year as I've not managed to get a good image of it yet that isn't spoiled by too much noise

 

 

[happy-kat]

It's great when you see change by new things you do. With a canon DSLR, I use a canon, often darks add noise and better off stacking without them.