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First Try At M31

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#1 lynnelkriver

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Posted 07 December 2017 - 02:33 PM

This is my first try at a DSO (M31) with my Stellarvue SV90TBV refractor at Prime focus on a SkyView Pro mount.  My camera is a older generation Canon Rebel XSI DSLR. I know I have a long way to go to get amazing photos that I have seen through the years on Cloudy Nights web site. I was surprised at what one could do with a simple mount, a older DSLR, and no auto-guiding. The details of the photo are as follows:

 

Lights: 91 RAW photos (60 second exposures at ISO1600, F7 through the Stellarvue refractor).

Darks: 10 RAW photos (60 second exposures at ISO1600, telescope lens covered).

Bias: 10 RAW photos (1/4000 second exposures at ISO1600).

Flats: 10 RAW photos taken of my off white colored garage wall with same imaging train.  Looking for suggestions on proper way to collecting flats!

 

The above images were stacked and initial post processing through Deep Sky Stacker (DSS) software.  Final processing with GIMP software. 

 

Appreciate any comments in advance.  Thanks! Scott

 

Compressed M31.jpg


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#2 poobie

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Posted 07 December 2017 - 02:43 PM

for a first effort, this is amazing.  Well done.  

 

For collecting flats, you don't have to ISO match your lights or darks.  I usually shoot them in the morning when I bring the rig in.  point your mount away from the sun.  Cover the end of your tube with a plain white t-shirt, secure it with a rubber band.  set your camera to aperture priority, drop the ISO until you get a reasonable shutter speed, and start clicking away.  yes, it'll be blue shifted, no (in my experience) it doesn't matter.

 

Again, well done, and keep at it!



#3 Gipht

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Posted 07 December 2017 - 03:20 PM

Very nice result.  I use a doubled up tee shirt pointing at a white garage wall panel for flats with the overhead lights on.  Be sure to smooth the tee-shirt out as much as possible and avoid seams.  The flats should peak about in the middle of the histogram.

 

One of the easier ways to start to learn processing is by using Star Tools.  If you decide to do this,  don't bother to process in DSS but save the DSS file with the embedded button selected.  Star Tools has a wipe button that would take away a lot of the light gradient on the bottom left of your picture.

 

Good job!


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#4 bobzeq25

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Posted 07 December 2017 - 03:30 PM

Pretty nice.  I did wall flats for the first 6 months, nothing very wrong with them.

 

As said, do not do _any_ postprocessing in DSS, it does a lousy job.  When you open up the DSS stack in your processing program, it should look dismayingly dark.  That is correct.

 

Among other things all important gradient reduction tools like WIPE work far better on linear, unstretched stacks.


Edited by bobzeq25, 07 December 2017 - 03:31 PM.


#5 jag32

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Posted 07 December 2017 - 06:32 PM

Really good job.  What type of skies did you do this in, was it a dark side? Also is your camera modded?



#6 lynnelkriver

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Posted 07 December 2017 - 06:56 PM

Thanks so much to all for the suggestions on post processing options and on doing "Flats"!  I really appreciate it as just scratching the surface on this and I really find it exciting!  Another question on "Flats".  Do you re-use them at all or do you find yourself collecting new "Flats" for each set-up?

 

jag32: My Canon Rebel XSI is not modified.  It is just a old Rebel that was collecting dust until now. There was a quarter moon so not the best sky conditions.

 

Thanks again to all, Scott



#7 bobzeq25

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Posted 07 December 2017 - 07:57 PM

Thanks so much to all for the suggestions on post processing options and on doing "Flats"!  I really appreciate it as just scratching the surface on this and I really find it exciting!  Another question on "Flats".  Do you re-use them at all or do you find yourself collecting new "Flats" for each set-up?

 

jag32: My Canon Rebel XSI is not modified.  It is just a old Rebel that was collecting dust until now. There was a quarter moon so not the best sky conditions.

 

Thanks again to all, Scott

Flats. 

 

It is crucial that the optical train not be rotated at all.  The usual culprit is moving the camera.

 

Dust moves.

 

So I take flats for every new image.

 

Since bias can be reused, and are trivial to do, I suggest doing 100.  Maybe 20 darks and flats.

 

Bias (especially) and darks (if the temperature is carefully matched) can be reused for at least months.


Edited by bobzeq25, 07 December 2017 - 07:58 PM.

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#8 17.5Dob

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Posted 07 December 2017 - 10:14 PM

for a first effort, this is amazing.  Well done.  

 

For collecting flats, you don't have to ISO match your lights or darks.  I usually shoot them in the morning when I bring the rig in.  point your mount away from the sun.  Cover the end of your tube with a plain white t-shirt, secure it with a rubber band.  set your camera to aperture priority, drop the ISO until you get a reasonable shutter speed, and start clicking away.  yes, it'll be blue shifted, no (in my experience) it doesn't matter.

 

Again, well done, and keep at it!

Not true. The ISO of the flats needs to match the ISO of the Lights, Darks, Bias etc, or all of the calibration frames are for naught.

But since dSLRS already have so much uncontrolled RAW firmware working in the background, no actual correct temperature information, etc.it's a rare day I bother with any of it.

I keep my sensors clean, so I don't need flats to correct the dust motes, so any vignetting can be corrected in PP.

There's no way to take a temperature calibrated darks unless you use LINR, if you camera supports it, and then you loose 1/2 your imaging time.

I've rarely, if ever, have applied calibration frames , and on the few times I have , I see little to no difference using a dSLR.

They were necessary 20 years at the very dawn of digital imaging, using CCD's , maybe 10 yrs ago with crude dSLRS, but it's not necessary with any dSLR camera made in the last 5 yrs

 


Edited by 17.5Dob, 07 December 2017 - 10:42 PM.

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#9 jag32

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Posted 07 December 2017 - 11:04 PM

 

for a first effort, this is amazing.  Well done.  

 

For collecting flats, you don't have to ISO match your lights or darks.  I usually shoot them in the morning when I bring the rig in.  point your mount away from the sun.  Cover the end of your tube with a plain white t-shirt, secure it with a rubber band.  set your camera to aperture priority, drop the ISO until you get a reasonable shutter speed, and start clicking away.  yes, it'll be blue shifted, no (in my experience) it doesn't matter.

 

Again, well done, and keep at it!

Not true. The ISO of the flats needs to match the ISO of the Lights, Darks, Bias etc, or all of the calibration frames are for naught.

 

 

Pay attention to this^^.  There is a lot of articles and other information out there on the internet on a variety of sides that indicates that darks and bias MUST be the same ISO as the lights BUT the flats can be any ISO.  So heeding this advice from what I thought were reliable people who knew more than I did, I never made the flats the same ISO as my darks, lights, and bias and I kept having issues stacking all the files in DSS.  DSS wouldn't properly stack my files and I ended up with complete rubbish, completely whited out final stacks, etc.  Then one day I got the idea to just forget ALL of the information out there that says flats can be a different ISO and shot them the same, and low and behold I got my first nice beautiful stack from DSS without a problem.  I don't know why flats do or do not need to be the same ISO as the others, but I do know that DSS literally would not produce a usable stack if the ISO on the flats were different.



#10 poobie

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Posted 07 December 2017 - 11:56 PM

hmm.  I've not had any issues with stacking non-matching flats in Siril.  could be blind luck I suppose.




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