#1  
Old 20-10-2016, 03:14 PM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline
 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
Max Image depth with ASI 174?

Unlike all the recent discussion of the benefits of stacking AVI files, I need to be able to work with the individual frames within the AVI (or SER).

I'm imaging the solar spectrum at nominated wavelengths - Ha etc.

The ASI 174 single image shows me, in 8 bit Mono setting (FireCapture/ SharpCap) that the image saturates at 256 ADU and the best absorption feature sits around 70ADU. This was at 0.55ms exposure and 70fps.
I'm working through various settings but increasing the exposure will start to impact on the frame rate - I also need the maximum frame rate possible.
(FC seems to default to SER files when set to 16bit - but no obvious improvement)
Any comment/ insight/ advice more than welcomed.....
Attached Thumbnails
Click for full-size image (102408_frame_depth.JPG)
101.2 KB26 views
Reply With Quote
  #2  
Old 21-10-2016, 10:54 AM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,474
I don't have a good answer but some thoughts, you've probably investigated already.

Assuming you need features at or below 70 is there a problem exceeding saturation if that region isn't needed?

Have you tried a hood/mask to try to ensure the first glass element in the scope is only being touched by photons direct from the sun as best as possible?

What about adding a planetary or similar filter to cut down the saturated wavelengths allowing you to boost the ones you need?

I don't know if temperature has much effect for solar but with my 120MC I added a stickon heatsink from jaycar (maybe four of them, havent used it in ages). Not much but when I first tested i got only a degree cooler sensor but more noticable was temperature fluctuation was smoother. May not help much but then you are maximising your setup.

Lastly using Region Of Interest cropping in FC can get you a better frame rate. With graphics formats making changes by powers of two is often most efficient. When I was after fastest frame rates I started with something like 480x480 then reducing this in increments of 16 pixels. Depending on target drift and how much post cropping I anticipated. So if, off the top of my head, you are capturing sunspot spectra this approach may help you with frame rate flexibility while pushing exposure settings.

16bit mode should give you more signal to play with (only 10 or 12bit vs 8bit). Are you losing the extra few bits in post processing steps before measuring?

Anyway these are approaches I'd try, maybe they'll help you with your specific process.
Reply With Quote
  #3  
Old 21-10-2016, 11:13 AM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline
 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
Sil,
Thanks for the reply.
Adding filters etc. would not influence the absorption line in the spectrum.
(The bandwidth of the "resolution" is around 0.1A and the Ha line is around 3A wide....)
I'm not too worried about the over-exposed continuum except where it starts to impact of the width of the absorption line - as I expose further it records further down into the "core" but looses the local "wing" detail.

I have tried various ROI to improve things and find under FireCapture that the ROI (1928 x 100 pixel) gives good frame rates - up to 500 fps at 2 ms exposure. (On full frame 1936 x 1216 it seems to "default" to 70 fps)
Using SER and 16 bit settings doesn't seem to make much difference.

I don't do any processing other than cropping.
The individual frames (9000!) are extracted from the video file (28-30Gb)and then processed by either Spectral Line Merge (limited to 2Gb files) or BASS Project (limited to around 3Gb files)
Reply With Quote
  #4  
Old 21-10-2016, 11:30 AM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,474
Yeah figured you'd tried most of my thoughts already. Can't imagine being of much help to someone like you mate.

Just another thought on frame rate, there do seem to be speed limits (possibly linked to a dimension or area cutoff) but keep eyes on dropped frames too. There seems to be a sweet spot where you can push exposure (holding at the maximum FPS) before you start dropping frames. Its sometimes a balancing act it seems.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 02:40 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Testar
Advertisement