ASI294MC Pro - Pointers

[Budgie1]

I've just got my first dedicated astro CMOS camera from a member on SGL and had first light with it the other night.

The camera is the ASI294MC Pro connected to a SW Evostar 100ED Pro with field flattener (not the SW reducer/flattener) on a EQ5 mount, guided with PHD2 and capture with APT. I have a UV/IR cut filter on order but no filters are currently in use on this camera.

I'm looking for some pointers regarding the gain and exposure settings for this camera as I've only ever used Canon DSLR's before now.

For my first session I chose M31 as it's a nice big & bright target. I only set the cooling to -5°C on this first session, although I should have gone lower because the air temp got down to -6°C during the session. 

I used gain of 125 and exposure times of 60 & 120 seconds. The image below is the result of 1h 17m total ingestion of 48 frames, stacked in DSS with darks, flats & dark flats and processed in PI.

I think the bloated stars will be sorted once the UV/IR cut filter arrives and the centre is blow out a bit so, maybe a reduction in exposure or gain is required? There is some good detail in there and I'm please with the reduction in noise over my modded EOS1300D.

So, I'm open to pointers, suggestions & recommendations for the settings to try with this setup, if anyone has similar.

Thanks.

[SamAndrew]

Hi Martin,

Glad you were able to get out and test the camera. How are you focusing? manually or with an autofocuser? stars could be a bit out of focus, although the detail in Andromeda does look sharp. 

[Budgie1]

Hi Sam,

Yep, managed a good night after it arrived.

Focus is manual, using a Bahtinov Mask and the Bahtinov Mask Assistant in ATP. I think the addition of the UV/IR cut filter should sort the stars, I could have reduced them sightly in post-processing but as this was more of a test session then it made sense to leave them for comparison when the filter arrives.

I'll have to re-focus when I fit the filter, so I may use just the Focus Assist instead and see if there's that much difference.

Edited January 11, 2021 by Budgie1

[tenpinmark]

At gain 120 the camera enters in to "HCG" mode which reduces read noise. See  HERE for the graphs from the ZWO web site.

Trevor Jones gave a review of this camera a while back - worth a quick read - it's HERE - He speaks of "Unity Gain" which in turn is 117, but for the extra 3 units in gain to get in HCG mode and the reduced noise reduction, then I start there and adjust the expose time to suit.

[Budgie1]

Thanks Mark,

I've initially set the gain at 125 as it was just above the HCG level and compared to my DSLR you can really see the reduction in noise on the image.

I'll have a read through Trevor Jones review later, thanks for the link.

[Budgie1]

Just an update on how things went when the UV/IR filter arrived.

It clouded over for a couple of weeks, is what happened! 

Anyway, I managed to get a few nights out last week and I persevered with the near full Moon. The first couple weren't that great, I went back to M31 and I'm going to re-process that completely because it was just nasty and I'm not putting it on here!

Then came M33 and I took 93 x 120 sec images at -10°C and 120 gain, used darks, flats, dark-flats & bias and ended up with this:

 

You may be able to see some amp-glow on the right and the background isn't that good, although not too much noise.

Then on Sunday night I went for M81 & M82. I use 68 x 180 second subs, with darks, flats, dark flats & bias and got the amp-glow in this one too. So I did a bit of searching and found a few people mention not to use the bias frames with this camera, so I ran the stacking again in DSS using only darks, flats & dark-flats and this is the result:

The amp-glow has gone and I'm really pleased with the detail I managed to get in both galaxies. Has the UV/IR filter made any difference to the stars? I'm not sure, I think the mount may be the limiting factor with those and I'll know more when I get a chance to have a night with less Moon.

I'm still learning with the ASI294 but I'm seeing improvement.