Help with picture glow Skywatcher 130pds dslr

[si717]

Hi i was wondering if anyone could help me as regards picture glow

iam getting it alot around seems always the right hand side of my pictures and i just cant seem to figure out the problem

im using skywather pds130 and a canon 650d baddar coma corrector i believe iam well aligned with the collimation on the scope

but whatever i try i just cant seem to get rid of the picture glow any ideas or if anyone has experienced it any help would be great thanks

ive inserted a piture its norms a lot worse or an be and i have to crop most the image to acheive an even field thank

[andrew s]

Looks like amp glow from the camera. Applying flats frames should be able to remove it.

Regards Andrew 

[si717]

3 hours ago, andrew s said:

Looks like amp glow from the camera. Applying flats frames should be able to remove it.

Regards Andrew 

Thanks ive taken some new flats and tried them on this picture seems to have helped

and this image was taken under a moonlit sky ,so yes maybe iam doing my flats wrong

thanks si

[rickwayne]

Actually it's dark frames that should be used to calibrate out amp glow. I mean, I'm glad flats worked for you! But if this really was amp glow, then it should show up during an exposure of equivalent length with no light hitting the sensor, primarily from thermal effects. A flat should have much less glow, since they're almost always much shorter exposure time than your lights. If there's some light leak or other optical problem, then the flats might calibrate that out.

Turning the camera on the scope should differentiate the issues. If you turn the camera 90 degrees and the glow shows up in the same part of the frame, it's in the camera and should come out with darks. If you turn the camera and the glow is in the same part of the sky, it's light pollution, or something bizarre going on with your OTA.

Of course, if there was some systemic problem with your flat frames in the first place, rejiggering those would fix it.

[si717]

23 minutes ago, rickwayne said:

Actually it's dark frames that should be used to calibrate out amp glow. I mean, I'm glad flats worked for you! But if this really was amp glow, then it should show up during an exposure of equivalent length with no light hitting the sensor, primarily from thermal effects. A flat should have much less glow, since they're almost always much shorter exposure time than your lights. If there's some light leak or other optical problem, then the flats might calibrate that out.

Turning the camera on the scope should differentiate the issues. If you turn the camera 90 degrees and the glow shows up in the same part of the frame, it's in the camera and should come out with darks. If you turn the camera and the glow is in the same part of the sky, it's light pollution, or something bizarre going on with your OTA.

Of course, if there was some systemic problem with your flat frames in the first place, rejiggering those would fix it.

Thanks for that i havent been using darks upto now as i read that they cause more noise ,i will have a try at some dark frames on the next outing as ive tried pretty much all else ive also another camera i could try but that ones noisy images seems i cant win ,but i will try the dark frames and re align the camera see what happens thanks for the advice

[andrew s]

@rickwayne is correct I gave the wrong advice.

Regards Andrew 

[alacant]

7 hours ago, si717 said:

picture glow

It looks like light is getting into the camera. Is the glow always top right?

Have a look at:

1. Block/cover the camera viewfinder.

2. Cover the mirror end of the tube with a black shower cap.

3. Fit a dew shield to the front of the telescope.

4. Examine the tube for places where light could enter, especially around the finder holder bracket. 

5. Use ISO 800.

I do not recommend taking dark frames with a 650d.

HTH

Edited November 23, 2020 by alacant

[rickwayne]

Right, there are certainly cameras for which darks just don't contribute much (and can make things worse). It should be really simple to test whether the problem is amp glow in the camera -- just cover it up to make absolutely sure no light is leaking in (doesn't need to be attached to the scope), and take an exposure as long as the ones you do for astro. Take that "black" frame and stretch the living heck out of it, however you prefer to run up your contrast (e.g. Curves or Levels in Photoshop). If the glow is there and in the same  place as in your lights, then you'll need darks (or a new camera!). If not -- and it probably isn't, with a DSLR -- you can look elsewhere.j

[bobro]

You mention having cropped a lot of the image in the first post above. Even with cropping there is obviously something wrong with alignment as stars towards the bottom right are much less than sharp. With a coma corrector stars should be very much smaller.

I suggest going back to basics. That means removing the CC and ensuring the scope is collimated. A flat and also an image of stars will help to show this - post here if it helps. If all is well the CC can then be added and flats etc redone to check the setup. It then should be possible to find out what is causing the glow if it still appears e.g. by taking a dark/obscuring the viewfinder/turning off the screen.

[si717]

1 hour ago, alacant said:

It looks like light is getting into the camera. Is the glow always top right?

Have a look at:

1. Block/cover the camera viewfinder.

2. Cover the mirror end of the tube with a black shower cap.

3. Fit a dew shield to the front of the telescope.

4. Examine the tube for places where light could enter, especially around the finder holder bracket. 

5. Use ISO 800.

I do not recommend taking dark frames with a 650d.

HTH

Thankyou very good points i will do that cheers

[si717]

35 minutes ago, bobro said:

You mention having cropped a lot of the image in the first post above. Even with cropping there is obviously something wrong with alignment as stars towards the bottom right are much less than sharp. With a coma corrector stars should be very much smaller.

I suggest going back to basics. That means removing the CC and ensuring the scope is collimated. A flat and also an image of stars will help to show this - post here if it helps. If all is well the CC can then be added and flats etc redone to check the setup. It then should be possible to find out what is causing the glow if it still appears e.g. by taking a dark/obscuring the viewfinder/turning off the screen.

the first image wasnt too heavily cropped but yes i have noticed most imaging some stars look great and some out of focus

i was thinking was my polar alignment a little of or not quite getting sharp focus but i use a mask everytime i image

so what would you suggest try an imaging session without the coma corrector its the Baddar coma corrector

somtimes when i zoom in on a picture some stars look fine and others seem to have holes in the centre ive always found odd

Thanks alot

[bobro]

If polar alignment is well off it can result in stars showing as streaks, not as round out of focus stars. 

Holes in the centre of stars with a reflector are due to the secondary mirror becoming apparent with the image out of focus.

With the CC removed, try taking a flat before imaging again. The resultant flat will show if the scope is collimated. The illumination source doesn't have to be too complicated e.g.  an evenly illuminated ceiling without bright light directly entering the scope (what I use) or an evenly lit sky with a piece of paper or similar across the scope to diffuse the light. An exposure of something in the region of 0.5 sec will do fine as the camera shutter won't have an effect at this exposure time (too short an exposure can mean the shutter travel will affect the flat).

 

[tooth_dr]

You image reminded me very much of the one that won the Astronomy Photographer of the Year competition recently.

As bobro has indicated there is something wrong with the alignment or spacing or tilting to create stars that are in focus in one area and out of focus in another.  Post a few photos of your setup to see what could be wrong if you dont mind.

 

[si717]

50 minutes ago, bobro said:

If polar alignment is well off it can result in stars showing as streaks, not as round out of focus stars. 

Holes in the centre of stars with a reflector are due to the secondary mirror becoming apparent with the image out of focus.

With the CC removed, try taking a flat before imaging again. The resultant flat will show if the scope is collimated. The illumination source doesn't have to be too complicated e.g.  an evenly illuminated ceiling without bright light directly entering the scope (what I use) or an evenly lit sky with a piece of paper or similar across the scope to diffuse the light. An exposure of something in the region of 0.5 sec will do fine as the camera shutter won't have an effect at this exposure time (too short an exposure can mean the shutter travel will affect the flat).

 

ive taken an image of the wall as a flat looks pretty even to me but unsure what iam looking for ,and the flat was very pink before changing to jpg its a naked sensor camera

many thanks

[si717]

17 minutes ago, tooth_dr said:

You image reminded me very much of the one that won the Astronomy Photographer of the Year competition recently.

As bobro has indicated there is something wrong with the alignment or spacing or tilting to create stars that are in focus in one area and out of focus in another.  Post a few photos of your setup to see what could be wrong if you dont mind.

 

Thanks but no prize winning yet still learning and what would you mean ,take images of setup ,its basially the camera to coma corrector directlt into the focus draw tube

many thanks

[bobro]

A stretched version of the flat shows reasonably good collimation, but not quite spot-on.

@tooth_dr suggests taking a photo of the setup (camera and CC attached to focus tube). This will help with a check of spacing (someone else will need to check this as I don't use the Baader CC).

You could continue with a step-by-step check, with the camera next. When a 650D is astromodified the sensor is removed and needs to be refitted in the same alignment position. There are 3 screws holding the sensor - if they are not adjusted to the original position the sensor can be tilted, resulting in focus issues. To check this you could take a photo during daytime with a lens fitted to the camera. If sharpness of the image is good across the image the camera should be ok. Hopefully the camera will come to focus with a lens after being modified (may depend on the lens). Manual focus is probably best to use.

If the camera tests out ok, it could then be refitted to the scope without the CC and a star image made. The image should show coma on stars (like little comets) towards the 4 corners, but otherwise focus should be good across the image. 

Hope this helps.

 

[si717]

On 24/11/2020 at 10:13, bobro said:

A stretched version of the flat shows reasonably good collimation, but not quite spot-on.

@tooth_dr suggests taking a photo of the setup (camera and CC attached to focus tube). This will help with a check of spacing (someone else will need to check this as I don't use the Baader CC).

You could continue with a step-by-step check, with the camera next. When a 650D is astromodified the sensor is removed and needs to be refitted in the same alignment position. There are 3 screws holding the sensor - if they are not adjusted to the original position the sensor can be tilted, resulting in focus issues. To check this you could take a photo during daytime with a lens fitted to the camera. If sharpness of the image is good across the image the camera should be ok. Hopefully the camera will come to focus with a lens after being modified (may depend on the lens). Manual focus is probably best to use.

If the camera tests out ok, it could then be refitted to the scope without the CC and a star image made. The image should show coma on stars (like little comets) towards the 4 corners, but otherwise focus should be good across the image. 

Hope this helps.

 

Actually i went about re aligning my camera sensor yesterday ,funny as i hadnt read your post ,and i took some darks and there seems to be no glow and less than there were before. so i am hoping ive got the sensor in a better position ,im hopefully going to be able to try it out tonight on some star clusters maybe all being well with the weather ive got the scope in a better collimation ,and if all else fails ive a canon 450d to try to see if it is actually   the camera sensor on the 650d, but for now im hoping ive fixed it ,many thanks for your advice and help cheers clear skys

[Jamgood]

On 23/11/2020 at 19:37, alacant said:

It looks like light is getting into the camera. Is the glow always top right?

Have a look at:

1. Block/cover the camera viewfinder.

2. Cover the mirror end of the tube with a black shower cap.

3. Fit a dew shield to the front of the telescope.

4. Examine the tube for places where light could enter, especially around the finder holder bracket. 

5. Use ISO 800.

I do not recommend taking dark frames with a 650d.

HTH

All good points above. I too have the 130PDS and in Bortle 8 skies with lots of lights around me. Car park full of them behind me.

A dew shield helped a lot. You can make one easily. 

Cover the back of the telescope. Shower  cap or a black t-shirt and elastic band does the trick.

👍

[si717]

think my stars are looking more in focus now anyways   👍