Silly question? [Imaging M31 for first time with 50mm finder and ASI185]

[AstroPhil]

In an attempt to "have a play" with the kit I already have I am trying (right now actually!) to image M31 using a very simple 50mm / 162mm FL finder/guider (Orion) hooked up to my ZWO ASI185 planetary camera... I'm not sure if this is an epic idea or a total dud. So far so good in the sense that the target is acquired but whenever I push the exposure beyond 25s (ish) is gets blown out (gain=200 / gamma=20) - is this is a limitation of the CMOS type sensors? Or am I expecting far too much, too soon? (I suspect a bit of both...!). So far I am trying stacking many many 10s subs - is this the basic way forwards or do I need to bite the bullet and get a rig more suited to the task?

[wimvb]

Nice experiment, but don't expect great results.

ASI cameras are very sensitive, using them at high gain may result in over exposure. If you lower the gain, you increase the dynamic range, which is better for dso. The finder scope has no colour correction, so expect colour issues (do you have the mono or colour version?)

If you keep exposures around 1 - 10 seconds, you can try to do lucky imaging, with LOTS of subs. And stack only the best.

As I mentioned earlier, don't expect much resultwise, but a great way to learn your gear and imaging technique.

Good luck,

(and keep us updated if you get any nice images)

[GreatAttractor]

On 7/23/2016 at 00:53, AstroPhil said:

I'm not sure if this is an epic idea or a total dud.

Well, you should get something. Some time ago I made a similar attempt with my sensitive, low-noise PGR Blackfly (IMX136) and Petri 55 mm/1.8 lens at full aperture:

271x31 s, stacked in DSS.

[uhb1966]

Well... are you positive that gain/offset are correct? theres a good article from stark labs re optimal gain and offset calibration.

[AstroPhil]

Yep, I am sure this setup wont set the world on fire, but I hope will be useful as a learning tool. So, attached are my preliminary results. 1800s total (90, 20s subs) with - I think! - darks subtracted  using Nebulosity. The second is the same, but playing with the stretch...

Not exactly great, and I am sure I have a lot to learn still...! I'm guessing that I need more exposure to get the detail, but it'll probably  have to wait for a more suitable OTA/camera combination, unless anyone has any tips?!?

[D4N]

Well it is certainly there, some flats could help it I think.

 

You have actually clipped the data when you have stretched it, there is a hint of the Galaxy extending much further out in your first image.

That gradient is probably causing the problem when you try to stretch the image so needs to be taken care of, is it a sky gradient or does it show up in flats as well?

[wimvb]

Nice start. From here on it's mostly playing with gain/offset and exposure time. As for the latter, you can either keep it short and stack several thousand (yep) subs, or increase the time and use fewer. It all depends on how much noise and dark current you have in your images.

You can also check the ZWO user forum for tips. People have used these cameras for all kinds of DSOs, with sometimes quite good results.

Here's some inspiration:

http://www.astrokraai.nl/viewimages.php?t=y&category=7

But beware, these images were taken with a 16" dob, I believe. You have a 2" scope.