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Andromeda DSLR and focal reducer

Craig123

By Craig123
in Getting Started With Imaging

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Craig123

Craig123

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Hi all

I tried imaging Andromeda with my Sony A7s DSLR on a skywatcher Ed80 pro and Heq5.I was doing 2 min subs unguided and got around 100.After stacking I was not  getting much detail in the final image.Would using a focal reducer help much? ..do I just need to try longer subs with guiding.Any ideas on how to improve from my last session.TIA

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Craig123

Craig123

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1 hour ago, PeterCPC said:

Even with only 120 secs exposure I would have thought that you would have something reasonable with 100 subs. What ISO were you using? How are you stacking the subs?

Peter

Iso 1600 Peter..i will try and post it up after work.Stacked in Dss

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michael.h.f.wilkinson

michael.h.f.wilkinson

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Just now, alacant said:

I must have misunderstood -again! I thought the only way he would need a different exposure would be by changing the aperture. (?)

If you want the same number of photons per pixel, which will determine the signal-to-noise ratio in a photon-noise-limited system, reducing the focal ratio gives a similar result as extending exposure time. If you want to keep the image scale and exposure time the same, then you need to increase aperture to reduce the focal ratio (expensive), otherwise a focal reducer is needed. If the system is not photon-noise limited, but instead is limited by dark current, you need to lift the signal above the dark current noise (subtracting darks only removes the average value per pixel, not the random fluctuations), and concentrating more light onto each pixel for a given exposure time is needed, where again a fast focal ratio is needed.  

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Craig123

Craig123

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That's what I got so far..i probably stacked more like 200 images and tried dark,flats and bias for the first time but obviously I would like to improve it so if anyone can input how I would really appreciate the help..sorry for the processing!

2017-11-16_02-38-21.jpg

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cjdawson

cjdawson

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That's looking great.  So let me get this straight, that's the output from DSS without any other processing?     If so, would you be able to make the tiff or other uncompressed file available?   There much be alot more data there than DSS is showing.

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Craig123

Craig123

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12 minutes ago, cjdawson said:

That's looking great.  So let me get this straight, that's the output from DSS without any other processing?     If so, would you be able to make the tiff or other uncompressed file available?   There much be alot more data there than DSS is showing.

No that's after I had a shot at processing but I want to have another shot at it tonight starting again.

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Craig123

Craig123

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18 minutes ago, cjdawson said:

That's looking great.  So let me get this straight, that's the output from DSS without any other processing?     If so, would you be able to make the tiff or other uncompressed file available?   There much be alot more data there than DSS is showing.

Yep.I will try and find the original Tiff file tonight thanks

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Craig123

Craig123

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15 minutes ago, PeterCPC said:

Had a quick play and the result is not great but shows more detail.

Peter

ag.jpg

You've certainly pulled more out of it Peter and I suspect my ham fisted efforts in ps haven't been helpful but was first attempt.

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Craig123

Craig123

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1 hour ago, michael.h.f.wilkinson said:

First try I did at Andromeda, I used a focal reducer to F/4.8 on my F/6 scope, and got some detail in 60s and 120s subs. The ED-80 is F/7.5, so a factor of 2.44 more exposure would be needed to get the same result without a focal reducer.

Makes sense..last time I tried the reducer I couldn't see any stars through the dslr

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The Admiral

The Admiral

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Hi Craig, you should be able to get reasonable results with your 2min sub length. For us users of Alt-Az mounts we are constrained to rather shorter exposures. I use 30s on mine. I think I used roughly 150 subs on my M31. As others have said, it's the processing that can make or break an image.

Ian

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Craig123

Craig123

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20 minutes ago, The Admiral said:

Hi Craig, you should be able to get reasonable results with your 2min sub length. For us users of Alt-Az mounts we are constrained to rather shorter exposures. I use 30s on mine. I think I used roughly 150 subs on my M31. As others have said, it's the processing that can make or break an image.

Ian

Interesting to hear Ian...would be good to see your  M31.My skies are reasonably dark but I'm not sure which  one of the many factors involved I need to look at first to get a better shot

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The Admiral

The Admiral

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46 minutes ago, Craig123 said:

Interesting to hear Ian...would be good to see your  M31.My skies are reasonably dark but I'm not sure which  one of the many factors involved I need to look at first to get a better shot

It's in my album or click on the link in my post. I'm sure the info in my album is wrong, it certainly will be a lot more that just 10 subs! Well, before looking at the many factors which could improve your image, I'd suggest maximising the quality using existing data first. You could try uploading the stacked image to a file postbox and let others have a go with your data. What processing software do you use on your stacked data? You should use your RAW files in DSS if you are not already.

Ian

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Craig123

Craig123

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Well I've got PhD running with my mount and qhy5ii mono doing 5 minute subs.There doesn't seem to be trailing but for some reason there is no histograph coming up on the screen..maybe it's not actually doing any guiding!.Any ideas appreciated

20171116_213222_001.jpg

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Craig123

Craig123

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3 hours ago, The Admiral said:

It's in my album or click on the link in my post. I'm sure the info in my album is wrong, it certainly will be a lot more that just 10 subs! Well, before looking at the many factors which could improve your image, I'd suggest maximising the quality using existing data first. You could try uploading the stacked image to a file postbox and let others have a go with your data. What processing software do you use on your stacked data? You should use your RAW files in DSS if you are not already.

Ian

I'm just using photoshop Ian.Will have a look at your page thanks.

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Craig123

Craig123

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6 minutes ago, alacant said:

...because you've chosen a star but haven't hit the 'Guide' button! HTH.

I hit 3 buttons..the first three on the left starting with connect...the third of which I thought was the start guiding one...and tried it a few times.Also watched a tutorial on it beforehand.Which is the start guiding button!!

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