From 7th June 2023

[M40]

Another clear bright night so a few more of the brighter targets, all using stellamira 85mm, zwo asi290mm, heq5, asiair.

M5: Gain 110 4x10 seconds. Distance about 24.4 light years away. 

M12: Gain 110, 5x10 seconds. Distance about 15.6 light years away. 

 

[PeterC65]

Two more nice images.

It looks like you're only stacking a small number of frames (4 and 5?). I find that the image improves noticeably over the first 20-30 frames and then you get in to diminishing returns where you have to wait for another 20 frames to notice any improvement. I'd be interested to see what you're getting after 20-30 frames with your monochrome camera. Generally I find that the background sky darkens considerably and the object clarity improves.

 

[M40]

5 hours ago, PeterC65 said:

Two more nice images.

It looks like you're only stacking a small number of frames (4 and 5?). I find that the image improves noticeably over the first 20-30 frames and then you get in to diminishing returns where you have to wait for another 20 frames to notice any improvement. I'd be interested to see what you're getting after 20-30 frames with your monochrome camera. Generally I find that the background sky darkens considerably and the object clarity improves.

 

Last time I tried it, it didn't seem to add anything so next playtime I shall give it a go and see what happens 👍

[PeterC65]

After every five or so frames I do an auto histogram stretch and auto colour balance (I'm using SharpCap) which usually changes the histogram and colour balance settings as a result of the data added by the new frames. I think this adds to any improvement as much as the additional frame data.

After about 30 frames, both the changes to the histogram and colour balance, and the visual changes, are tiny.

 

[M40]

15 hours ago, PeterC65 said:

After every five or so frames I do an auto histogram stretch and auto colour balance (I'm using SharpCap) which usually changes the histogram and colour balance settings as a result of the data added by the new frames. I think this adds to any improvement as much as the additional frame data.

After about 30 frames, both the changes to the histogram and colour balance, and the visual changes, are tiny.

 

Currently every picture I take is asiair software based only. The one thing I would like to achieve is a darker background to the target. One of our sons has played with a few of the pictures with photoshop and got some pretty good results but I have zero interest in trying that at the moment. 

I have tried adding darks but that doesn’t appear to do anything so my next baby step was going to be flats.....but not yet my plan is to take one of my normal pictures and then take, as you suggested, about 30 or so just to compare. 

[PeterC65]

For me, albeit using SharpCap, the biggest improvements in background darkness have come from stacking more frames and from making manual histogram adjustments.

I've only recently started using darks and they did make a difference for me, mainly reducing noise and hot pixels. With darks I took them on the night, just covering the scopes objective once all the kit had cooled down. I haven't tried taking flats.

 

[Martin Meredith]

Just a note that what is actually important is the total exposure rather than the number of frames. The two are often confused because increasing the number of frames increases the total exposure, but if your frames are very short then it doesn't make sense to stop after a specific number (eg 30); SNR will continue to improve even up to 1000s of frames.

cheers

Martin

[Ratlet]

Really nice images.  They've got a nice 'through the eyepiece' aesthetic to it.

[M40]

This is turning into a nice thought provoking challenge. Taking pictures of M13, I thought a single 10 second shot was the best I had taken, this as longer or more exposures just turned it into a blob, but I am now wondering if more and longer exposures with a lower gain will make the difference. Thanks very much for your thoughts people, it is appreciated. 

[PeterC65]

I generally observe an object for around 5 minutes when I'm doing EAA. As @Martin Meredith mentions, this is what's important, rather than the number of frames. I almost always use a 4s exposure time so I'm stacking around 75 frames. Once the image is looking OK (I've not obviously screwed up the camera paraments or framing, and there have been no satellite trails), I stack at least 50 frames (so about 3 minutes) and usually stop before I get to 100 frames. Sometimes I will collect more if the image is looking particularly good or interesting, perhaps letting the total exposure time clock up to 15 minutes. But I'm doing EAA not AP so I find waiting 15 minutes a little tedious.

The gain setting seems to be very camera specific. I almost always set the gain to 400 with my Uranus-C. My camera switches to high conversion gain mode at 180, the gain can be set as high as 800, but above 700 it is very noisy. So I'd say 400 is on the higher gain side of average. I've experimented with lower gain settings and that does reduce noise a little but greatly reduces object detail. I think lower gains might be appropriate for AP when using much longer total exposure times, but for EAA, when you're looking for a good image relatively quickly, I think the highest gain you can manage without silly amounts of noise is best.

It's interesting that you found a single 10s exposure to be the best shot and that you got more of a blob as you stacked frames. It sounds like your frame stacking may not be working correctly.