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Shrinking videos for retroactive testing of camera adaptation

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#1 Jan_Fremerey

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Posted 10 March 2023 - 12:38 PM

Looking for some lower reasonable limit of focal length adaptation of video cameras in video astronomy I have substantially reduced image information of an existing astro video by shrinking all individual frames linearly down to 71%, ie to about 50% of original image content. By comparing final image quality (top entry) on the basis of original and reduced video data I conclude that video recording with 2.4 µm camera pitch at f/5, equivalent to f/D = 2.1*p/µm, will enable much the same image resolution and quality as 3.75 µm at f/11, or f/D = 2.9*p/µm. I don‘t expect longer focal length adaptation to do any better. On the other hand, I do expect advantage from reducing shutter times at increased fps for decreasing seeing related image blur and noise.



#2 RedLionNJ

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Posted 10 March 2023 - 01:06 PM

I'm hesitant to re-engage on this topic, because I feel a lot may be lost in translation. But here goes ... :)

 

If I interpret you correctly, you're saying you took a video recording, aligned, stacked, sharpened and arrived at a result.

Then you took the same recording, downsized all the frames to 71% (giving about 50% of the original number of pixels), then aligned, stacked, sharpened and upscaled (for a fair comparison)

 

And the image of part of the moon (tsk, tsk!) alternates between the two results, showing very little difference?

 

If all of the above is interpreted correctly by me, then yes, I would say under the precise situation where the video was captured, there is no discernable difference in the final result.

 

But this gets us no nearer to answering "is there a difference demonstrated between capturing at f/D = 2.1 vs f/D = 5 in various types of seeing?"

 

There are many situations where a faster frame rate (afforded by a brighter image in a smaller ROI) does not help - the seeing is just so poor, there is no fine detail capturable even at very high (600+ fps) frame rates.  And that faster frame rate means a faster "shutter speed", meaning each frame is noisier, too. So you need more frames to combat the higher noise, yet a very small number of frames might be sharp enough to include ...   there is no such thing as a "free lunch".


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#3 Jan_Fremerey

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Posted 10 March 2023 - 01:55 PM

There are many situations where a faster frame rate (afforded by a brighter image in a smaller ROI) does not help - the seeing is just so poor, there is no fine detail capturable even at very high (600+ fps) frame rates.  And that faster frame rate means a faster "shutter speed", meaning each frame is noisier, too. So you need more frames to combat the higher noise, yet a very small number of frames might be sharp enough to include ...

Thank you for your valuable comment. Here are my points:

 

- When discussing limiting image resolution and quality we typically are not talking about "the seeing is just so poor ..."

- A "faster shutter speed" at shorter f/D ratio will result in equivalent noise level.

- Shorter shutter times and larger fps will certainly increase the probability of catching individual frames that "might be sharp enough to include".
 



#4 dcaponeii

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Posted 12 March 2023 - 06:39 AM

Yawn



#5 Jan_Fremerey

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Posted 12 March 2023 - 09:33 AM

Sleep well ...



#6 Jan_Fremerey

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Posted 14 March 2023 - 03:41 AM

And the image of part of the moon (tsk, tsk!)

Thanks for your valuable comment, I'm still waiting for your response to my latest answers ...
 



#7 Kokatha man

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Posted 16 March 2023 - 03:29 AM

...being honest I have not absorbed any of your claims Jan in anything but their most simple foundations...and I might not even be grasping them correctly either! wink.gif

 

I've had a very quick look at your website motivated by the link to your website in the ASI224MC Vs ASI662MC thread...my briefest of understandings has me thinking that you advocate a much shorter f/l when imaging planets as opposed to the "general rule" bandied about in this forum - that is, the "general rule" of 5x pixel sizing of any specific camera. (ie, for a 2.4um camera, employing an effective f/l of f12 etc)

 

I have no axes to grind with anyone proposing abandoning such "rules" in principle (ie, I don't consider it heresy lol.gif ) but any claims must be accompanied by a lot of supportive evidence, or in this case comparative data between videos taken at greater or lesser scales. (leaving aside the difficulties trying to do so in seeing that needs to be very consistent between each set of captures etc...)

 

You have some pretty nice planetary images and although I have only looked at a few on your site so far, I do notice quite a bit of noise in some that I've seen: that's not an absolute criticism but slightly intriguing from one of the aspects I (only) "think" I glean about your claims.

 

Shorter f/l's mean brighter disks which to me means lower gain for the same exposure & fps - there can be benefits in this but makes me wonder why the images I've looked at  seem to have a noticeable amount of noise in them..?

 

I rarely shoot at 5x unless the conditions (seeing & elevation) are good (many say my partner & I always have "very good" conditions but of course that is nonsense lol.gif ) but although 4x and sometimes even a bit lower are my preferred camera pixel size multiplier ratios, I'm having a hard time accepting that shooting at the scope's native f/l is just as beneficial - if that is what you are claiming. confused1.gif

 

Despite needing lower & lower gain as the f/l is reduced, I think there comes a point where it is no longer productive to do so: Mars for example can be videoed at less than 50% gain even when using 4-5x pixel sizing at 400fps...lower the exposure/fps down to 250fps or so (still a high frame-rate!) and gain needed becomes really quite low...I should add that we rarely employ more than a 50% histogram btw.

 

On a practical note, focusing demands for a small onscreen image become harder on the eyes and I certainly wouldn't want to focus on Uranus or Neptune at our C14's native f/l being honest! shocked.gif You cannot simply magnify the onscreen image for focusing when concentrating upon uber-small scale detail whether it is Mars of a Gas Giant in my opinion due to pixelation of the image therein...

 

As far as the topic of this specific thread is concerned, perhaps I have got it wrong but it seems that you are saying that you recorded a planetary video at a certain image scale (f/l) and then down-scaled that video and processed the result to come up with your conclusion...surely anything embedded in the original video capture (with its parameters) cannot simply be used to prove something that is only consistent with said original parameters at best - or am I misinterpreting completely..?!? scratchhead2.gif

 

My own experiences point to diminishing returns beyond 5x (and certainly the 7x suggested as workable for colour cameras!) and indeed most often find 3.5x - 4x gives better results generally, with an ability to utilise drizzling on the video data also...but your "native f/l" has not convinced me tbh...

 

Anyway, just a few comments and as Grant says there does seem to be some translation peccadilloes, but I do like the images on your site that I have seen despite the noise factor...and your scope also looks pretty cool & reminds me of Paolo Lazzarotti's "Gladius" scopes that I think are no longer being made.

 

Enough from me - I'd be interested if you could expand a bit more and I may or may not comment further...don't let the rigid orthodox imagers deter you from your views, but you must be prepared to support them with hard comparative evidence! graduate.sml.gif

 

 

 

 



#8 Jan_Fremerey

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Posted 16 March 2023 - 06:52 AM

(1) I do notice quite a bit of noise in some that I've seen: that's not an absolute criticism but slightly intriguing from one of the aspects I (only) "think" I glean about your claims.

 

(2) Shorter f/l's mean brighter disks which to me means lower gain for the same exposure & fps

 

(3) You cannot simply magnify the onscreen image for focusing when concentrating upon uber-small scale detail whether it is Mars of a Gas Giant in my opinion due to pixelation of the image therein...

 

(4) surely anything embedded in the original video capture (with its parameters) cannot simply be used to prove something that is only consistent with said original parameters at best - or am I misinterpreting completely..?!?

 

(5) Paolo Lazzarotti's "Gladius" scopes that I think are no longer being made.

 

(6) don't let the rigid orthodox imagers deter you from your views, but you must be prepared to support them with hard comparative evidence!

Thanks for your kind and detailed comments, I just try to answer some that I think might be of general interest:

 

(1) Please note that video cameras at times when the elder images were taken still operated at 30 fps maximum. With current cameras you may have ten times as many frames to stack for better noise supression.

 

(2) I usually work at standard gain setting, so shutter times will reduce by square of focal length and frame rates will increase accordingly.

 

(3) Focusing via live screen hasn't been an issue for me so far.

 

(4) Comparing on the basis of identical video material in fact appears more consistent than comparing consecutive videos taken at varying seeing conditions.

 

(5) Not to forget Russell Porter's Garden Telescope of the 1920s.

 

(6) Thanks for your encouragement, I'm rather trying to reach newcomers in the field ...

 

CS Jan



#9 Jan_Fremerey

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Posted 21 March 2023 - 07:59 AM

downsized all the frames to 71% (giving about 50% of the original number of pixels), then aligned, stacked, sharpened and upscaled (for a fair comparison)

Correction: I upsize before sharpening and then follow exactly the same sharpening procedure as with the original video.
 




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