First light with new Altair 585c - M81 and M82

[Astronomist]

Here are the fruits of my first session with my new Altair Hypercam 585c. In the absence of anything brighter and more spectacular I went for M81 and 82 (separately, my FOV is too small to get them both at the same time). Both are ~300 x 300ms exposures at prime focus on my 10" dob, at the camera's maximum gain of 136500. Capture and stacking done in Sharpcap. Annoyingly, the use of a high gain has made the results very noisy, but this is still way better than the eyepiece view from my Bortle 6 location.

 

 

 

While there is lots of room for improvement, I'm quite happy with this for a first go! 

Edited April 21 by Astronomist

[PeterC65]

That's great for a first attempt. I'd suggest lowering the gain and increasing the exposure time. I operate my IMX585 based camera at half the maximum gain (decided after doing test shots at different gain settings) and I use between 4s and 15s exposures. The 10" aperture probably accounts for why you have such good images.

 

[Astronomist]

59 minutes ago, PeterC65 said:

I'd suggest lowering the gain and increasing the exposure time.

I can't really increase the exposure time much as the scope has no tracking, but I might be able to get up to 400ms without too much star trailing. This should allow me to lower the gain quite a bit. I will attempt to give M81 another go tonight, but with longer exposures and more of them. I also see Sharpcap has the option to use darks; is that likely to make much difference?

[PeterC65]

Ah, OK, that will limit you to short exposures. I find that for a given total exposure I can see more detail the longer I make the individual frame exposures.

I'd expect the background noise to reduce significantly as you reduce the gain. My camera's maximum gain is 800 and that's unusable, but it gets much better by 600, OK by 500 and optimal at 400.

The hot pixel removal feature in SharpCap is almost as good as taking darks, and a lot less hassle. I wouldn't both with darks or flats for now. I've only recently started using them, and then only sometimes. They seem to be most useful when pushing the optics at higher magnifications.

 

[happy-kat]

M82 has worked particularly well. For reduced trailing and rotation in the northern hemisphere aiming E or W ideally lower altitudes will help eek out the exposure time you may find you can use

[Fir Chlis]

Another 585 user here - ZWO ASI585MC. Like you, I picked M81 and M82 on my first session with my new camera in January. You are right to be happy with your first go. Your M82 is really nice but, as I found as I learned more each session, you should be able to get better images of M81 as you progress.

You could try using the SharpCap Brain function to calculate exposure time and gain - but set the maximum exposure time and get it to calculate a gain/offset setting. I now have fairly standard settings, but do use the Brain regularly to check things. For my camera it almost always comes out at gain 300 with 4s or 8s (gain range for the ASI585MC is 0-600).

For myself, I find that darks do help, but I usually only need to do one set in an evening, unless the temperature changes very much, as I generally use the same exposure /gain all night long. At the exposure times I use, a dark only takes a couple of minutes to generate. I normally do a flat while it's still light, but I'm undecided about whether it is useful. I've still yet to try @PeterC65's suggestion of just using hot pixel removal. I now always use satellite trail removal and the automated brightness filtering, and am going to start trying FWHM filtering (though this may not be so relevant for a non-tracking mount).

If you have a look at my recent thread on the SharpCap forum, I'd sorted out a procedure for myself to find the longest exposure that I could run before stars started trailing too much. How good is my mount? – improving EAA images - SharpCap Forums

Exciting times ahead for you. After just doing visual, EAA opens up a whole new world.

 

Geoff

Edited April 21 by Fir Chlis

[Astronomist]

Thanks for your advice everyone, Last night I had another session on M81, with dramatically better results. Gain was half the camera's maximum. 

1272 x 380ms exposures: still noisy but better than my previous attempt by a long shot. 

[Martin Meredith]

Excellent results, especially given the absence of tracking. I'm interested in your prime focus arrangement. Do you mean that you are foregoing the secondary altogether?

I'm planning to try out EEVA with my 10 dob on an equatorial platform and your results suggest that great things are possible...

Martin

[Astronomist]

17 hours ago, Martin Meredith said:

I'm interested in your prime focus arrangement. Do you mean that you are foregoing the secondary altogether?

No, I am using the camera in the normal focuser on the side of the tube, with no reducer or barlow. I'd definitely give it a go with your 10"; you should be able to do much better than me since you have tracking. I'm not sure how accurate StarSense is but I'm guessing it would help with getting the target on the sensor, which I have found to be tricky with the dob.