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My flats are not helping

astrophotography CMOS dso imaging optics
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#1 Lite2

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Posted 07 January 2018 - 08:27 PM

This is bad and driving me crazy.

I have been playing with my spacing of FR lately along with dabbling with OAG which is on hold for the time being. I had a pretty good night out last night as far as guiding, plate solve and autofocus but everything I have seen has the "shadow" of the secondary showing up in it although it is not the 1st time I've had this lately, but it's really getting old.

I thought is was purely from my flats but it's also in stacks not using flats.

Is this a matter of spacing at all or could the scope setup be that sensitive to collimation, which I know is not perfect.

Here's a few samples.

My flats are normally taken before dark using a new run of SGP's flats cal wizard to assure the right setting, then take bias & dark while waiting on dark skys.

Could it be the flats make it worse when taken to the east but much of the imaging is "now" done to the west?

This is really becoming a major hindrance, even more than  using an AVX lol.gif

 

Attached Thumbnails

  • Basic cal no flats.jpg
  • Basic cal.jpg
  • Flat stf.jpg
  • Flame_and_HH_dss_ABE 1 6 18.jpg


#2 View2

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Posted 07 January 2018 - 08:37 PM

Is your off axis guider stuff partially in the light path or something? I don't OAG, but if all else is eliminated.....it does look like the secondary mirror, and...support? not sure why there would be the look of a reflector's secondary mirror spider support though cause its a CAT. That is bizarre. I'm pretty certain it is not from taking flats pointing in the wrong direction.moan you are reaching. Hmmmm,


Edited by View2, 07 January 2018 - 08:44 PM.

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#3 Lite2

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Posted 07 January 2018 - 08:43 PM

These were not with the OAG, I was having issues with holding a guide star and put that on hold for now.



#4 freestar8n

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Posted 07 January 2018 - 09:20 PM

I'm afraid that looks like a big image of the pupil - and that corresponds to a pupil ghost and could be impossible to remove well with a flat.

 

If it is a pupil ghost it is likely caused by a reflection up from the sensor to a concave element of the reducer that is facing the sensor.

 

If you have used the reducer before and didn't have this problem - then the new problem may be due to a change in spacing of the reducer to the sensor.  It may also be due to imaging m31 with its bright nucleus.

 

So - if it really is a pupil ghost then flats just won't help much because the pupil image won't appear the same in the flat as in the light.  You can try changing the spacing or removing the reducer.

 

Frank


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#5 Lite2

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Posted 07 January 2018 - 09:50 PM

Thanx Freestar, I may try it again without any FR, just as a test. Even then, I won't be sure if it's the FR or just plain setback because of the reducer causing it.

But I will believe your advice on the reducer causing the ghost image.

I REALLY wanted this scope to work out at reduced FL but if this is an unfixable problem I may have to go back to my 150XLT 6" till I can afford a better mount.

****, Now I have to get a new mount for the Moonlite  for the XLT



#6 Lite2

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Posted 07 January 2018 - 09:54 PM

What about the LPR i'm using, it does have a VERY "mirrored" finish to it. Could that be the culprit?

It IS at the front of the imaging train.



#7 Goofi

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Posted 07 January 2018 - 10:01 PM

I'll add to what Frank shared ...

 

I'd suggest creating a synthetic flat and try to correct it using that in PI.  David Ault has a good tutorial, see here.



#8 Ken Sturrock

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Posted 07 January 2018 - 10:05 PM

What about the LPR i'm using, it does have a VERY "mirrored" finish to it. Could that be the culprit?

It IS at the front of the imaging train.

Yes. It could be a problem. Try it without and see how she flies....



#9 Lite2

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Posted 07 January 2018 - 10:15 PM

 

What about the LPR i'm using, it does have a VERY "mirrored" finish to it. Could that be the culprit?

It IS at the front of the imaging train.

Yes. It could be a problem. Try it without and see how she flies....

 

I will certainly try it without the LP filter next time, just because it's an easier fix, thanx

 

I'll add to what Frank shared ...

 

I'd suggest creating a synthetic flat and try to correct it using that in PI.  David Ault has a good tutorial, see here.

Will read into that and hope I don't have to resort to it for every session. Thank you all for the tips!



#10 Lite2

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Posted 07 January 2018 - 10:30 PM

A question.

If the LPF "is" the cause of the reflections, and keeping in mind the spacing of the FR could I place the LPF between the FR and main Imaging camera?



#11 freestar8n

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Posted 07 January 2018 - 10:34 PM

An LPR filter may play a role - but the big issue for a pupil ghost is a curved lens that is concave toward the sensor.  Changing the spacing could have a big effect on how noticeable the pupil image is.  The light could be converging down to the LPR, then reflected up to the concave surface, then back down to the sensor.  So it would involve one flat surface - either the sensor or a filter - and a curved surface.  Changing the spacing could have a big effect.

 

I think the only way to remove it from an image is to manually create the pupil pattern in a synthetic flat so it can be removed - as described above.

 

I haven't done this myself - and it may involve subtracting the pattern rather than dividing by it - as is usually done with a flat.

 

Good luck-

Frank



#12 Lite2

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Posted 07 January 2018 - 10:53 PM

Thanx freestar, I will def attempt the synthetic removal for my existing files. I might still try the LP filter under the FR just to see what I get.

This is SO aggravating when you only get so few good chances to image.



#13 Goofi

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Posted 08 January 2018 - 12:36 AM

Yes Frank, as I understand this issue he'll want to subtract the pattern instead of diving using the synthetic flat.



#14 Goofi

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Posted 08 January 2018 - 12:37 AM

I'm busy for about a day, but if you can post a master I can take a look at it and see what I can do ... I'm sure there's a few others here who would be happy to try working on this and posting their results (and method of achieving them).



#15 View2

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Posted 08 January 2018 - 03:16 PM

If I'm not mistaken your flat look fine and showed no artifacts. Have you tried Imaging with nothing in the train no focal reducer or no field flattener? Someone said the lights would look worse than the flats but I don't see how since they're both saturated to at least one third to the left of the histogram. This is very mysterious. I've seen many images taken from cats and your scope should do just fine once you figure out this image train problem in my opinion. It could be a very simple fix or something is awfully wrong with your scope.

I too would like to see a few lights and your flat

Edited by View2, 08 January 2018 - 03:18 PM.


#16 DSO_Viewer

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Posted 08 January 2018 - 04:29 PM

If I'm not mistaken your flat look fine and showed no artifacts. Have you tried Imaging with nothing in the train no focal reducer or no field flattener? Someone said the lights would look worse than the flats but I don't see how since they're both saturated to at least one third to the left of the histogram. This is very mysterious. I've seen many images taken from cats and your scope should do just fine once you figure out this image train problem in my opinion. It could be a very simple fix or something is awfully wrong with your scope.

I too would like to see a few lights and your flat

What is your setup - scope (native focal ratio), type of reducer, spacing distance, type of LPFilter etc? If you are using a SCT then it is very strange to see any secondary holder veins unless you are using your GSO 6 " RC?

 

Just wondering if you have your focal reducing reversed? A LPFilter should be in front of the reducer but you can always place it behind as long as it if not to close to your camera.

 

Steve



#17 freestar8n

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Posted 08 January 2018 - 04:43 PM

If I'm not mistaken your flat look fine and showed no artifacts. Have you tried Imaging with nothing in the train no focal reducer or no field flattener? Someone said the lights would look worse than the flats but I don't see how since they're both saturated to at least one third to the left of the histogram. This is very mysterious. I've seen many images taken from cats and your scope should do just fine once you figure out this image train problem in my opinion. It could be a very simple fix or something is awfully wrong with your scope.

I too would like to see a few lights and your flat


It isn’t mysterious if it is a pupil ghost because that’s how they behave. It will show as a big image of the pupil centered in the view and it may not show in the flat.

They can happen with a reducer or flattener if there is a concave element at a spacing that makes the pupil image. Normally the design would factor it in to make sure it doesn’t happen.

Frank

#18 gobleb

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Posted 08 January 2018 - 05:36 PM

Yours looks almost exact to mine (https://www.cloudyni...-going-on-here/).  Mine has to do with the size of adapter and a precise back focus adjustment.  Might want to start there before going to the more expensive options. 



#19 HomerPepsi

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Posted 08 January 2018 - 08:08 PM

This was happening to me and my 8RC with the SX-AO (additional glass in the optical train). Turns out it was reflections on nose pieces and adapters. I bought a some flocking paper from scope stuff and flocked my surfaces and the problem went away

#20 Lite2

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Posted 08 January 2018 - 08:19 PM

I'm busy for about a day, but if you can post a master I can take a look at it and see what I can do ... I'm sure there's a few others here who would be happy to try working on this and posting their results (and method of achieving them).

https://www.dropbox....ING_1.xisf?dl=0

https://www.dropbox....ING_1.xisf?dl=0

 

Here ya go, thanx for trying.

 I read into the synth flats and not wanting to put that much work into what I got.

I will continue to work towards fixing the underlying problem.



#21 Lite2

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Posted 08 January 2018 - 08:51 PM

I have removed LP filter and also went to a Moonlite threaded connector for the imaging train similar to MadRatters setup.

this is a pic of the current spacing, not sure if this setup is gonna focus once I can get a clear night, the reducer used to be shoved into the focuser and of course it's now at the rim of the focuser tube.

Is there any way of testing indoors for the problem?

 

At this point, I'm SO scrambled on my spacings. Being that before the new focuser adapter the FR was inserted quite a bit into the focuser I feel it won't now go in far enough to reach focus.

Current spacing is 55mm between camera and rim of FR which I know would equal less reduction. I am limited on selection of proper fitting spacers.

Attached Thumbnails

  • Just reset spacing.jpg

Edited by Lite2, 08 January 2018 - 09:03 PM.


#22 Lite2

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Posted 09 January 2018 - 07:31 PM

 

If I'm not mistaken your flat look fine and showed no artifacts. Have you tried Imaging with nothing in the train no focal reducer or no field flattener? Someone said the lights would look worse than the flats but I don't see how since they're both saturated to at least one third to the left of the histogram. This is very mysterious. I've seen many images taken from cats and your scope should do just fine once you figure out this image train problem in my opinion. It could be a very simple fix or something is awfully wrong with your scope.

I too would like to see a few lights and your flat

What is your setup - scope (native focal ratio), type of reducer, spacing distance, type of LPFilter etc? If you are using a SCT then it is very strange to see any secondary holder veins unless you are using your GSO 6 " RC?

 

Just wondering if you have your focal reducing reversed? A LPFilter should be in front of the reducer but you can always place it behind as long as it if not to close to your camera.

 

Steve

 

Reducer is not reversed(see pic ) and everything i'm running is in my sig. Spacings my vary ATM :)



#23 Lite2

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Posted 09 January 2018 - 08:08 PM

 

If I'm not mistaken your flat look fine and showed no artifacts. Have you tried Imaging with nothing in the train no focal reducer or no field flattener? Someone said the lights would look worse than the flats but I don't see how since they're both saturated to at least one third to the left of the histogram. This is very mysterious. I've seen many images taken from cats and your scope should do just fine once you figure out this image train problem in my opinion. It could be a very simple fix or something is awfully wrong with your scope.

I too would like to see a few lights and your flat


It isn’t mysterious if it is a pupil ghost because that’s how they behave. It will show as a big image of the pupil centered in the view and it may not show in the flat.

They can happen with a reducer or flattener if there is a concave element at a spacing that makes the pupil image. Normally the design would factor it in to make sure it doesn’t happen.

Frank

 

For starters that was a single(streched) flat, the "master" or stacked flat is worse.

I have used this same reducer before without this effect. I have been recently trying to get OAG working and as such spacings have been moved around a LOT.

I guess I'm just back to waiting for a clear enough nite to do a realtime test and swap.



#24 Goofi

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Posted 09 January 2018 - 09:08 PM

You can test now just using flats.  You can pull your gear off the mount (I'd try to leave it assembled and take it off as a unit), or go out and do flats at the mount if the weather is cooperating. 

 

Flats will at least show you if the problem exists at your end, or something in the environment like a street light. Plus, if you make changes, hopefully it will show up with improved flats.



#25 rockstarbill

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Posted 09 January 2018 - 09:23 PM

Hope you get this resolved OP, first and foremost.

 

Did want to add, that this is a good example of why people are usually steered toward using refractors to image with. 




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