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  #1  
Old 25-09-2017, 12:35 PM
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Brian W (Brian)
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Am I approaching the limit of what my Tamron 90mm 272E can give me.

The skies were clear and dark but the high thin started to drift in almost as soon as I was set-up. This shot has (in round numbers) 300 color frames, fifty dark and fifty bias. Shot with my Sony Alpha a58 / Tamron 90 mm 272E combo supported on a Slik Pro 700DX tripod with a three-way pan and tilt head.

No Eq mount. No auto tracking or guiding. Processing was done in Capture 1 Sony Pro and Gimp 2.9. Stacking in DSS.

Obviously my pp needs to be improved. I'm also thinking that I just might need a longer lens or a small telescope to get much more detail in M22.

A larger version can be found here.

Brian
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  #2  
Old 26-09-2017, 01:16 AM
Tony_ (Tony)
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Hello Brian,

I don't know much about your camera or lens - but there are a few processing problems with your image.
Firstly - you have severely "clipped" the black - you have darkened the sky far too much - your histogram is too much to the left.
Also I suspect your image is out of focus - but it is hard to tell because of the clipped black. You will be able to get much better images with your set-up.
Post the image straight out of dss with no processing - then it will be easier to see what it looks like. It won't look good - but it will tell more.

Tony.
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  #3  
Old 26-09-2017, 09:09 AM
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Originally Posted by Tony_ View Post
Hello Brian,

I don't know much about your camera or lens - but there are a few processing problems with your image.
Firstly - you have severely "clipped" the black - you have darkened the sky far too much - your histogram is too much to the left.
Also I suspect your image is out of focus - but it is hard to tell because of the clipped black. You will be able to get much better images with your set-up.
Post the image straight out of dss with no processing - then it will be easier to see what it looks like. It won't look good - but it will tell more.

Tony.
Hi Tony, straight out of DSS except for scaling
Brian
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  #4  
Old 26-09-2017, 05:37 PM
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There really isn't much that can be deduced from a 124kb heavy compressed file. I opened it up and compression has destroyed everything but the stars

What exposure time are you using?
If you are not using a tracking mount then increasing the focal length then you increasingly have to use shorter and shorter exposure times. I'd actually go the other way and suggest that using a 50mm lens would be wiser. With a 50mm you should be able to use ~10s without needing a tracking mount.
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  #5  
Old 26-09-2017, 06:05 PM
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There really isn't much that can be deduced from a 124kb heavy compressed file. I opened it up and compression has destroyed everything but the stars

What exposure time are you using?
If you are not using a tracking mount then increasing the focal length then you increasingly have to use shorter and shorter exposure times. I'd actually go the other way and suggest that using a 50mm lens would be wiser. With a 50mm you should be able to use ~10s without needing a tracking mount.
Tony asked I did what I could.

I was thinking about going out with my 18 - 55 the next clear night If memory serves it was about 3s.
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Old 26-09-2017, 08:36 PM
Mickoid (Michael)
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I agree with Tony, you are definitely doing something wrong with your processing. Using the 500 rule you should be able to expose for about 4 seconds without star trailing using a 90mm lens on your Sony Alpha a58. I know it's not much more than you've been giving your subs but where do you get this 3.2 seconds from? Open your lens up to f 2.8, focus using live view, set your ISO to 3200iso or 6400iso if you want to, after all, with 300 subs I doubt you should see any noise when you stack that many and expose your subs for 4 seconds.

You should be able to pull the gradient up in DSS to see many more stars than what you're achieving at the moment. The background shouldn't be jet black. You're killing the fainter stars by doing so and any nebulosity associated with them. I'd like to see one of your single subs straight from the camera. You seem keen enough, so why not have a go with the 55mm lens and try a 15 second sub, 3200iso at f2, it should reveal heaps of stars! Good luck.
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  #7  
Old 26-09-2017, 09:45 PM
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I agree with Tony, you are definitely doing something wrong with your processing. Using the 500 rule you should be able to expose for about 4 seconds without star trailing using a 90mm lens on your Sony Alpha a58. I know it's not much more than you've been giving your subs but where do you get this 3.2 seconds from? Open your lens up to f 2.8, focus using live view, set your ISO to 3200iso or 6400iso if you want to, after all, with 300 subs I doubt you should see any noise when you stack that many and expose your subs for 4 seconds.

You should be able to pull the gradient up in DSS to see many more stars than what you're achieving at the moment. The background shouldn't be jet black. You're killing the fainter stars by doing so and any nebulosity associated with them. I'd like to see one of your single subs straight from the camera. You seem keen enough, so why not have a go with the 55mm lens and try a 15 second sub, 3200iso at f2, it should reveal heaps of stars! Good luck.

Am I missing something here. I'd love to post a full size straight out of the camera shot but it is way over the size limit ?

I will be going out with the 18-55. My wife tells me I'm a dog with a bone. I'll keep at it.
Brian
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  #8  
Old 26-09-2017, 10:39 PM
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Originally Posted by Mickoid View Post
I agree with Tony, you are definitely doing something wrong with your processing. Using the 500 rule you should be able to expose for about 4 seconds without star trailing using a 90mm lens on your Sony Alpha a58. I know it's not much more than you've been giving your subs but where do you get this 3.2 seconds from? Open your lens up to f 2.8, focus using live view, set your ISO to 3200iso or 6400iso if you want to, after all, with 300 subs I doubt you should see any noise when you stack that many and expose your subs for 4 seconds.

You should be able to pull the gradient up in DSS to see many more stars than what you're achieving at the moment. The background shouldn't be jet black. You're killing the fainter stars by doing so and any nebulosity associated with them. I'd like to see one of your single subs straight from the camera. You seem keen enough, so why not have a go with the 55mm lens and try a 15 second sub, 3200iso at f2, it should reveal heaps of stars! Good luck.
I went back and had another go at the shot after stacking. Better but still a ways to go.
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  #9  
Old 27-09-2017, 08:17 AM
sil
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For such a graphical forum we do have dumb limits on file uploads.

First Tamron lenses are not exactly high quality, never have been. They have made improvements and come up with some ok lenses at specific focal lengths. You haven't reached the limit of the hardware, I don't think you've tried to stretch your limit of how to use it. I've done a lot of good shots with a 105mm lens, 90mm isnt problem. f2.8 is part of the problem here as is overexposure. You aren't capturing nebulosity here I can see. The stars are obviously way over exposed ending up with white disc cores. Lower the exposure time and/or stop the f-stop. If you're expecting nebulosity or milky way up the iso too. Try that and the stars should tighten up and the globular cluster will start to gain definition and overall stars should gain some colour back. Plus the processing is just way off overall, imo dss and gimp/photshop are the wrong tools especially for newbies. They can be used to good effect but its clear you don't, sorry.
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  #10  
Old 27-09-2017, 08:31 AM
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For such a graphical forum we do have dumb limits on file uploads.

First Tamron lenses are not exactly high quality, never have been. They have made improvements and come up with some ok lenses at specific focal lengths. You haven't reached the limit of the hardware, I don't think you've tried to stretch your limit of how to use it. I've done a lot of good shots with a 105mm lens, 90mm isnt problem. f2.8 is part of the problem here as is overexposure. You aren't capturing nebulosity here I can see. The stars are obviously way over exposed ending up with white disc cores. Lower the exposure time and/or stop the f-stop. If you're expecting nebulosity or milky way up the iso too. Try that and the stars should tighten up and the globular cluster will start to gain definition and overall stars should gain some colour back. Plus the processing is just way off overall, imo dss and gimp/photshop are the wrong tools especially for newbies. They can be used to good effect but its clear you don't, sorry.
Don't be sorry. Honesty is what's needed. What would be good tools for this newbie? I'll give your suggestions a try the next decent night we get. Just for the record the Tamron 90mm 272E is a superb lens when attached to my Sony Alpha a58.

Last edited by Brian W; 27-09-2017 at 10:58 AM.
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  #11  
Old 27-09-2017, 10:56 AM
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I got 3.2 by experimenting. I was getting noticeable trailing at 4.
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Old 27-09-2017, 11:27 AM
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Are you shooting raw?
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  #13  
Old 27-09-2017, 11:41 AM
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Are you shooting raw?
indeed I am.
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  #14  
Old 27-09-2017, 11:47 AM
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Then it is just a processing issue. Make sure you're not clipping either ends of the histogram and don't stretch too hard so you don't burn your stars. With the exposures times you've indicated you should be getting good stellar profiles along with star colors when increasing saturation. Can you dropbox one raw file and we can have a look at it.
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Old 27-09-2017, 02:30 PM
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Then it is just a processing issue. Make sure you're not clipping either ends of the histogram and don't stretch too hard so you don't burn your stars. With the exposures times you've indicated you should be getting good stellar profiles along with star colors when increasing saturation. Can you dropbox one raw file and we can have a look at it.
Okay, I'm uploading one to my dropbox. Now how do I share it here? Lets see if I figured it out? Apparently I did. You can't preview it but you can dl it. Don't know that it makes a difference but it is sony raw.
https://www.dropbox.com/s/vohu068n06...me_25.ARW?dl=0

Last edited by Brian W; 27-09-2017 at 02:49 PM.
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Old 27-09-2017, 03:40 PM
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Okay, I'm uploading one to my dropbox. Now how do I share it here? Lets see if I figured it out? Apparently I did. You can't preview it but you can dl it. Don't know that it makes a difference but it is sony raw.
https://www.dropbox.com/s/vohu068n06...me_25.ARW?dl=0
Thanks. I had a quick look at it. The focus is good, the FOV is nice and flat. You do have nice star colors as well. Nothing's wrong with your subs. They're just very noisy. So if you have a lot of them (2.5s each), stack them and do a basic data rejection, otherwise shoot for longer like a minute or so.
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Old 27-09-2017, 05:08 PM
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The problem is most likely exposure time. 3s isn’t going to be enough to get over read noise unless you’re shootings F/2 in a red zone.

A single 120s exposure is going to look better than an hour worth of 3s exposures. If you partially dither 1200x3s exposures you’ll end up with a smooth but not deep image. A single 120s exposure will not be as smooth but will look a lot better.
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Old 27-09-2017, 05:26 PM
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To gert the longer shots I'm going to need either a manual (with slow motion cables) or a powered Eq mount.
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Old 29-09-2017, 07:18 AM
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Some form of powered eq mount will open the possibilities for improvement but you can get good results with camera on tripod. I do as I can't use my eq anymore. You need to comprehend what your gear limitations means in terms of what you can get in your post processing. Step one is find your exposure limit before stars streak an unacceptable amount. Test f-stop values that give roundest stars with least distortion (this is all up to you to decide what you're happy with). Then bump up ISO to allow milky way and faint fuzzies a chance to get recorded. Then take lots of shots to process to suppress the noise and give you room to stretch the signal. That last step is not a single step, my workflow has dozens of steps for example and can take me a week or longer to work through.

My camera lets me take 100 shots at a time. So I start with a single test shot and try to pick a bright star I can see in live view to help me frame my subject. Understanding which way the stars "rotate" lets me position my target so it will pass through center of frame where distortion is least. And after each batch of 100 i check the framing and where needed I reposition the camera again.

Registration of all the shots compensates for lack of tracking mount. Then integration boosts SNR giving me a good integration frame to work with. Chuck in darks and flats too certainly helps but not essential.

I do recommend you seriously consider PixInsight to process with. Yes you can get good results with other packages and PI is not easy for newbies to get into but there is nothing as comprehensive for pure processing. No camera control though so if you want other features also check out AstroArt and Nebulosity etc as they can do awesome processing to, but dont forget YOU have to work the software so processing success depends on how capable and patient you are to learn and work at it. Astro Pixel Processor might be the program you want at this stage but its new and I can't recommend buying it due to the stabillity and lack of documentation though it does show promise and works reasonably well for newbies to get a good image out of. Many of these packages have trial periods so I recommend grabbing them all and running through tutorials and see what might suit you best.
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Old 29-09-2017, 10:15 AM
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Originally Posted by sil View Post
Some form of powered eq mount will open the possibilities for improvement but you can get good results with camera on tripod. I do as I can't use my eq anymore. You need to comprehend what your gear limitations means in terms of what you can get in your post processing. Step one is find your exposure limit before stars streak an unacceptable amount. Test f-stop values that give roundest stars with least distortion (this is all up to you to decide what you're happy with). Then bump up ISO to allow milky way and faint fuzzies a chance to get recorded. Then take lots of shots to process to suppress the noise and give you room to stretch the signal. That last step is not a single step, my workflow has dozens of steps for example and can take me a week or longer to work through.

My camera lets me take 100 shots at a time. So I start with a single test shot and try to pick a bright star I can see in live view to help me frame my subject. Understanding which way the stars "rotate" lets me position my target so it will pass through center of frame where distortion is least. And after each batch of 100 i check the framing and where needed I reposition the camera again.

Registration of all the shots compensates for lack of tracking mount. Then integration boosts SNR giving me a good integration frame to work with. Chuck in darks and flats too certainly helps but not essential.

I do recommend you seriously consider PixInsight to process with. Yes you can get good results with other packages and PI is not easy for newbies to get into but there is nothing as comprehensive for pure processing. No camera control though so if you want other features also check out AstroArt and Nebulosity etc as they can do awesome processing to, but dont forget YOU have to work the software so processing success depends on how capable and patient you are to learn and work at it. Astro Pixel Processor might be the program you want at this stage but its new and I can't recommend buying it due to the stabillity and lack of documentation though it does show promise and works reasonably well for newbies to get a good image out of. Many of these packages have trial periods so I recommend grabbing them all and running through tutorials and see what might suit you best.
I just got back from a tour of your astrobin. Impressive work. I noticed that you use a Sigma 150 - 500. Tamron makes a 150 - 600 I'm looking at. Pity Sigma doesn't still make the Sony A mount version.

I'll look into the programs.

A few day back I was cleaning out my files and not used programs and managed to delete some important stuff as well. I often have these annoying whoops moments. One of the reasons for not going tracking and guiding. I'd be forever screwing things up.

Nevertheless this will all come together in time.
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