Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Short Exposure Time ASI 1600MM Cool?

This topic has been archived. This means that you cannot reply to this topic.
36 replies to this topic

#26 vdb

vdb

    Surveyor 1

  • -----
  • Posts: 1,618
  • Joined: 08 Dec 2009

Posted 02 June 2017 - 02:35 PM

vdb, nice image. Great star color. Only suggestion is you might want to dither more aggressively. It seems you have some correlated noise in there which would be eliminated with larger scale dithers. 

Thanks, medium dither on oag of 1100 mm focal length ... over 2 nights I had 2 sets of lights with 12 pixel difference between them, probably that can be seen.

 

Also the LP and grey night did not permit the aggressive stretch I applied.

 

/Yves



#27 NMBob

NMBob

    Surveyor 1

  • *****
  • Posts: 1,608
  • Joined: 21 Nov 2015

Posted 02 June 2017 - 03:37 PM

Why would it be any different? The sensor is the same after all. You can't compare exposure times and total exposure lengths between different scopes and different locations anyway so why try to adjust for the bayer matrix vs RGB filters? You capture in raw and look at the ADU values you get. Noise figures are the same for the color and the mono sensor so whichever advise you like regarding gain settings applies to both. Then pick an exposure setting that works for your target/sky/telescope/mount combo and take as many of these as you can. Ultimately what matters most is total exposure time. Dividing say 6 hours in 30s subs or 90s subs will result in subtle differences you will most likely not notice immediately. Because of the low read noise and super fast download times there is no or very little penalty for taking lots of short exposures and those are much much easier to take than longer ones.

 

Oh, I have no idea. It just seems like all of the really good pictures come out of mono cameras and a lot of good/hard work. I'm just wondering, qualitatively, if there's a big difference. Like...let's say I take a five minute color picture of something. Will that will be "worse" (whatever that means) than a five minute R+five minute G+five minute B+five minute L combined picture? Way worse? A little worse? Better? If I take a 20 minute color picture will that be closer or better or worse than the four five minute pictures? I just don't know how this all relates. I'd buy a 1600MM and a 1600MC, but I figure you guys are a cheaper route. :) I just glanced at the 'mono 3x' thread that just popped up. That might be getting at the stuff I'm wondering about.

 

Bob



#28 Kaos

Kaos

    Messenger

  • -----
  • topic starter
  • Posts: 409
  • Joined: 02 Dec 2015

Posted 02 June 2017 - 03:49 PM

Jon...I am sure you are right about the light pollution. The .jpeg file REALLY smoothed the grainy effect that is more than apparent in the TIFF and FIT version of the file. If you look at nice image posted by vdb, you will notice some graininess in that image, but not too bad. My FIT file multiplies the grainy noise many times compared to the noise shown in that image, as an example. Just hard to show it here because of the .jpeg conversion. I know that more subs will reduce that effect considerably, I am just not sure how many more I need or where the limit may lie. I was thinking that if I took another 3.5-4.0 hours with the Lum filter, that may be enough, just not sure as I am still learning this camera. I probably will not get rid of it totally as you noted. That and I want to bring out the faint small galaxies so they are clearly decipherable in the final image. I have a window tonight and am going to try to get 4 hours more or ~80 more subs. Once I get the RGB I will be upwards of 10.5-12.0 hours total integration. I suspect, but am not sure, that 150 3 minute L subs may be close to as good as it gets at my location. Do you agree?

 

Kaos



#29 Kaos

Kaos

    Messenger

  • -----
  • topic starter
  • Posts: 409
  • Joined: 02 Dec 2015

Posted 02 June 2017 - 04:13 PM

Jon, if I can borrow from vdb's nice work, the grainy issue is more pronounced than what his image shows here:

 

https://www.flickr.c...in/photostream/

 

What I am looking for is more like vdb's great image here:

 

https://www.flickr.c...in/photostream/

 

If that helps give you a visual to what I am talking about in the TIFF and Fit versions of the file.

 

Kaos



#30 Jon Rista

Jon Rista

    ISS

  • *****
  • Posts: 26,034
  • Joined: 10 Jan 2014

Posted 02 June 2017 - 04:24 PM

Can you share your FIT file?

 

Also, regarding the images you linked. Both are from vdb, however you have to understand that the QSI image was made from a total of 17 hours of data in total, while the QHY was made from a mere 2h31m30s of data in total. While these modern CMOS cameras have very low noise, you still need to get the necessary integration time to get a good result. Vdb's QSI image has SEVENTEEN HOURS of integration! That is almost five times as much as you currently have. ;) 

 

I think it's probably mostly just that A) you are fighting a lot of LP which is adding a ton of noise, B) you are imaging with a relatively slow scope and C) you only have 3h27m of integration with that combination of detracting factors, when you likely need three to five times that. 

 

Imaging in LP is rough, and the main reason I primarily do NB from my back yard rather than LRGB. It just isn't worth the required time investment to do LRGB from my deep red zone/white zone back yard. I, too, need umpteen gazillion hours of integration to really get the best results...and that has been true with every camera I've ever used. Conversely, if I hit up a dark site, I can get in 2-3 hours what it would take 30 hours or more from my back yard. LP is an AP killer. 



#31 Kaos

Kaos

    Messenger

  • -----
  • topic starter
  • Posts: 409
  • Joined: 02 Dec 2015

Posted 02 June 2017 - 04:39 PM

Can you share your FIT file?

 

Also, regarding the images you linked. Both are from vdb, however you have to understand that the QSI image was made from a total of 17 hours of data in total, while the QHY was made from a mere 2h31m30s of data in total. While these modern CMOS cameras have very low noise, you still need to get the necessary integration time to get a good result. Vdb's QSI image has SEVENTEEN HOURS of integration! That is almost five times as much as you currently have. wink.gif

 

I think it's probably mostly just that A) you are fighting a lot of LP which is adding a ton of noise, B) you are imaging with a relatively slow scope and C) you only have 3h27m of integration with that combination of detracting factors, when you likely need three to five times that. 

 

Imaging in LP is rough, and the main reason I primarily do NB from my back yard rather than LRGB. It just isn't worth the required time investment to do LRGB from my deep red zone/white zone back yard. I, too, need umpteen gazillion hours of integration to really get the best results...and that has been true with every camera I've ever used. Conversely, if I hit up a dark site, I can get in 2-3 hours what it would take 30 hours or more from my back yard. LP is an AP killer. 

Ok great! I think I understand your LP point now. I didn't notice the difference in his integration times! I will see how it looks after the additional subs I get tonight.

 

Thanks Jon! With you guy's help, hopefully this project will turn out nicely. I will post an updated version with the additional subs.

 

Kaos



#32 vdb

vdb

    Surveyor 1

  • -----
  • Posts: 1,618
  • Joined: 08 Dec 2009

Posted 03 June 2017 - 01:16 AM

Not only that the 17 hours where under a SQM +-21 sky where the other one is more under +-18 or even lower ... 

 

All the more impressive for the CMOS camera.

 

/Yves



#33 Jon Rista

Jon Rista

    ISS

  • *****
  • Posts: 26,034
  • Joined: 10 Jan 2014

Posted 03 June 2017 - 01:47 AM

Kaos, I'm looking forward to seeing what you end up with. ;) Once you get some solid integration time, with 100+ subs (and remember, well dithered!), I think you'll see the results with this camera can be very good. 



#34 Kaos

Kaos

    Messenger

  • -----
  • topic starter
  • Posts: 409
  • Joined: 02 Dec 2015

Posted 04 June 2017 - 12:48 AM

I managed to get some more subs last night. I was trying to get ~80 more but the moon wrecked a bunch of them. I ended up with 125 X 3 mins for a total of 6.25 hours integration time (dithered after each frame). The attached image is a cropped and resized version. It was calibrated and stacked in Maxim DL. I redid the flats and increased the median exposure of the flats from 15K to 20K and that help flatten the BG. I did some processing (not super heavy) in Photoshop CC to see what I had (exposure adjustment, levels a couple of astronomy tools and sharpened a touch). The ones from last night had a median of about 1850 (due to the moon) while the original 69 images were much lower. It appears I may be able to process the final color version with this number of subs without blowing out the bright stars and the bright core of M101 which is what I was aiming for. I am anxious to see how the small galaxy at the bottom right turns out in color, as well as the small edge on galaxy to the left of M101. I was also pleasantly surprised that the faint arms at the bottom came in with this number of subs. I will probably darken the BG just a touch in the color version.

 

Given the number of L subs, what would the minimum number of RGB subs would be recommended? I was thinking 24 per channel but I am not sure if that will be sufficient.

 

Kaos

Attached Thumbnails

  • M101-2L.jpg

Edited by Kaos, 04 June 2017 - 01:04 AM.


#35 Jon Rista

Jon Rista

    ISS

  • *****
  • Posts: 26,034
  • Joined: 10 Jan 2014

Posted 04 June 2017 - 02:57 AM

In the image I am working on now, I acquired 500x30s L subs, and 125 RGB subs (each). So I acquired about 1/4 the subs per color channel as for the L channel. The GB subs were 60s each, and the R subs were 90s. In the end, I ended up stacking 413 L subs, 109 B subs, and 106 G and R subs, after culling the bad ones. This is from a bright red zone, with some moon. The RGB data is ok, but not great. Again, though...it's not because of the camera, it's just because of the huge amount of LP. If you have similar conditions, I'd recommend getting about 1/3 of the subs for each RGB channel, minimum, and make sure you are getting the same background level for each color channel (i.e. you'll need to use longer than 3 minute subs, or use a higher gain setting). Depending on your filters, you might need to use 6 minute GB subs and 9 minute R subs, or something like that. 



#36 Mert

Mert

    Voyager 1

  • *****
  • Posts: 11,195
  • Joined: 31 Aug 2005

Posted 04 June 2017 - 03:51 AM

Here is my trial on this target, settings were 20 subs of 240 seconds each,

at unity gain, ASI1600MC-C at -15ÂșC, dithering used, darks, no flats.

Also this was shot at binning 2x2 with a 6" Maksutov at F13 aprox. 1900 FL.

No filter was used.

 

Attached Thumbnails

  • M101-20x240-Bin2x2-Mak-V3-small.jpg


#37 Kaos

Kaos

    Messenger

  • -----
  • topic starter
  • Posts: 409
  • Joined: 02 Dec 2015

Posted 06 June 2017 - 12:22 AM

In the image I am working on now, I acquired 500x30s L subs, and 125 RGB subs (each). So I acquired about 1/4 the subs per color channel as for the L channel. The GB subs were 60s each, and the R subs were 90s. In the end, I ended up stacking 413 L subs, 109 B subs, and 106 G and R subs, after culling the bad ones. This is from a bright red zone, with some moon. The RGB data is ok, but not great. Again, though...it's not because of the camera, it's just because of the huge amount of LP. If you have similar conditions, I'd recommend getting about 1/3 of the subs for each RGB channel, minimum, and make sure you are getting the same background level for each color channel (i.e. you'll need to use longer than 3 minute subs, or use a higher gain setting). Depending on your filters, you might need to use 6 minute GB subs and 9 minute R subs, or something like that. 

Thanks Jon...That gives me a great starting point!

 

Kaos




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics