Double Cluster

[Davide Simonetti]

The Double Cluster: one of my favourite objects to observe with an eyepiece in the telescope as photographs rarely do it justice. It isn't possible to capture with my 1500mm scope because of its size and proximity to us so this image was made with the equivalent of a 400mm lens in slightly murky conditions.

16 x 2 minute exposures at 400mm f11 - 800 ISO (32 minutes)
11 x dark frames
 8 x flat frames

Captured with APT
Guided with PHD2
Processed in Nebulosity and Photoshop

Equipment:
Skywatcher EQ5 Mount
Orion 50mm Mini Guide Scope
ZWO ASI120 MC imaging and guiding camera
Canon 500D DSLR
Takumar 70-200mm lens with x2 TeleConverter

[alacant]

1 hour ago, Davide Simonetti said:

photographs rarely do it justice

Yeah, I noticed that too, even top APOs struggle to make anything of it/them. Nice shot. I noticed that dark frames add more noise with my Canon, a 700d. I reckon you could get even better by taking bias frames and leaving out the darks -lmost a free lunch as it's less work-. Also with your setup it's just two clicks to add dither; that really does help. Thanks for posting. 

[Davide Simonetti]

1 hour ago, alacant said:

Yeah, I noticed that too, even top APOs struggle to make anything of it/them. Nice shot. I noticed that dark frames add more noise with my Canon, a 700d. I reckon you could get even better by taking bias frames and leaving out the darks -lmost a free lunch as it's less work-. Also with your setup it's just two clicks to add dither; that really does help. Thanks for posting. 

Usually I do take bias frames (in conjunction with darks) and I have a library of them at different ISOs but they are for my 700d and I forgot to take any for the 500d which was the only camera I could make the lens work with for some reason. I may shoot a few bias frames and reprocess to see if there's an improvement. I like the idea of using bias frames without darks...I haven't tried that before. I did dither between shots but only by a small amount because everything seemed to drift downwards with the larger number I usually use. I don't understand why...it only seems to happen when using camera lenses rather than the scope. Thanks for the tips

[alacant]

Hi. With lenses I turn off the PHD2 dither and use APT dither only, so for 400mm, make sure you've set the focal length in APT and set say 15 for the dither. It's random so shouldn't be just in one direction. So: light, bias and flat frames yes. Dark frames, no. Worth a try? HTH.

[Davide Simonetti]

9 hours ago, alacant said:

Hi. With lenses I turn off the PHD2 dither and use APT dither only, so for 400mm, make sure you've set the focal length in APT and set say 15 for the dither. It's random so shouldn't be just in one direction. So: light, bias and flat frames yes. Dark frames, no. Worth a try? HTH.

Thanks for that. Yes, definitely worth a try. I'll give it a go next time I use lenses. The cradle for the camera and guide scope needs a bit of a redesign because there is some movement in it that needs to be eliminated but that should happen quite soon (hopefully in time to capture the Orion and Running Man nebulae  ).