Ha from 20th April

[neil phillips]

4 minutes ago, vlaiv said:

That is exactly one of the things I wanted to point out.

Sure that person in question knows that they can swamp read noise in 15ms exposures at high altitude at the site of good seeing. I just wander if that person ever recommended someone starting in lunar AP - to necessarily use 15ms as it produces excellent results for them?

Anecdotal evidence can sometimes be misleading. In average seeing, even with 8" aperture you can't really hope to have coherence time longer than say 5-6ms, let alone 15ms. Just imagine for a second that person reading advice is interested in Ha solar with internal etalon with scope that operates at F/30 while using ASI290.

That is oversampling by x3.4. Now we have x3 less exposure time and pixel is 3.4 x 3.4 = 11.56 smaller by surface than it needs to be, which makes about x35 lower signal in total. Do you still think that signal will significantly swamp read noise?

There is no harm in my advice - only benefit. While this benefit might be marginal for some setups - it is always correct and for some people it will make a difference.

It will be as full as imaging section dedicated to images taken equipment and processed with software backed by science and theory not so easily dismissed by people using them.

No i agree there is no harm in it. Its actually very helpful. But wanted to allude to what Freddie was saying. How sometimes theory and advice based solely on theory. Is not as gospel as sometimes it can appear. When in fact there are situations that might seem to contradict wisdom. I think i have highlighted such a situation here. There are situations where low gain and higher read noise do not hurt a image. And in fact under certain circumstances might actually produce the better result. Kind of what Freddie has been alluding to also i think ? Anyway your a gentleman Vlaiv. And i know how helpful you are to so many people on here. Its all good discussion. I am off TC 

[Jeff5567]

Whatever you're dong (despite the academic chat) works, & works brilliantly.  Amazing detail & something to aspire to. 

[Jeff5567]

Whatever you're dong (despite the academic chat) works, & works brilliantly.  Amazing detail & something to aspire to. 

[Freddie]

Doesn’t look like we are going to get any images that show higher gain doesn’t produce poorer quality images but never mind.

Like Neil, I absolutely respect Vlaiv’s knowledge on the theory of this and many other subjects as shown by his numerous posts across the forum. In this case however, I’m happy that I didn’t just follow theory and just maybe Neil and I have a better knowledge on what it takes to get out there, get the data and produce a high resolution image.

Enjoyed the discussion but on that note I am off to make a sandwich for lunch and yes it will contain the left over chicken from last night!!!!

[vlaiv]

20 minutes ago, Freddie said:

Doesn’t look like we are going to get any images that show higher gain doesn’t produce poorer quality images but never mind.

I can do this fairly easily - but I don't think you'll appreciate it.

In order to truly show that higher gain does not produce more noisy image - we need to conduct experiment in controlled environment, to remove any other variable that might change results.

This is very easy to do - anyone with camera can do it. Just point camera + lens to a flat wall and try to have ambient light as uniform as possible (no changing light sources like TV near by or computer screen - any kind of flicker). Alternatively - flat panel will work nicely (not sure everyone has one).

Two images should be taken at lower gain levels and two at higher. All other parameters should be kept the same (offset, exposure length ...).

All subs should be converted from ADU to electron count (divided by e/ADU for selected gain and any bit offset removed) and then each set of two images should be subtracted (subtract first from second in first group and first from second in second group).

Resulting subs should be measured for standard deviation.

One with higher standard deviation has higher noise.

As you see - experiment is very simple and very straight forward. My only concern is that you won't accept its results, because as you put it 'theory is one thing, but "hands on experience" is something completely different' (that is something that I strongly disagree with) and it might be hard for you to related above experiment with actual solar imaging.

I don't think that anyone will be able to produce sufficiently controlled experiment with actual solar images (would need two scopes with perfect or at least exactly the same figures, two cameras with the same levels of read noise and response - all manufacturing defects the same and so on ...).

[Freddie]

As you say it would be hard to relate to actual solar imaging, there seems to be no point in doing the experiment as what I want to achieve is the best quality solar image I can, not a picture of a wall.

Anyway, thanks for your input but I think it’s time for me to move on.

[vlaiv]

Physics and light itself won't behave differently depending on what you choose to image.