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Old 26-08-2019, 06:06 PM
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Manav (Yugant)
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Moravian G3 16200 light band or amp glow help

Hi guys,

I'm new to CCD imaging and am using the G3 16200 camera with Stellarvue SVQ100.

I've noticed that all of the images I'm taking have a really bright band on the top part.

Have attached example herein:

1. https://www.flickr.c...03/48616379356/
2. https://www.flickr.c...03/48616364391/

Stretching the images shows saturation evenly starting from the top of the image.

Can anyone help point me in the right direction of how I could troubleshoot this?

Regards
Manav
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Old 26-08-2019, 06:30 PM
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What does a dark, bias and flat look like?

I take it that its not simply light pollution? Have you used the camera on another scope?

Its not amp glow. CCDs don't suffer from amp glow that is a CMOS issue as CMOS has circuitry on the sensor whereas CCD does not.

Greg.
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Old 26-08-2019, 07:52 PM
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Manav (Yugant)
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Hi Greg - First of all thanks for your prompt response. I'm new to CCD imaging so I apologise in advance.

I've linked the FITS file for Dark frame which is a 300sec exposure at -20 taken using SIPS software as well as a 0.2sec bias frame taken at -20 in the below link.

https://drive.google.com/drive/folde...hJ?usp=sharing

Unfortunately, I do not yet have a flat field generator so I did not have any flat field shots. I also do not have another scope to test on :/

I didnt even consider light pollution; I have been shooting all images at South - South West at 40deg above horizon from the backyard so that could be a possibility.

I'm using a SVQ100 so the image is inverted which could explain why the light gradient is on top of the image.

Just to confirm if this was a CCD issue we should see the same glow in the darks and bias am I right?
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Old 27-08-2019, 10:38 AM
markas (Mark)
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I would not expect to see this in dark or bias frames. If you did then you'd suspect the camera. But in fact, your dark frame looks fine!


The gradient may well be in the optical train, or possibly due to extreme light pollution. If it is in the optical train, it should show up clearly with flat frames. If all is well you should see flats possibly with a little, ideally symmetric, darkening in the corners.



Mark

Last edited by markas; 27-08-2019 at 10:56 AM.
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Old 27-08-2019, 04:47 PM
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Slawomir (Suavi)
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My bet is on light pollution causing the gradient. Try taking an image of a star field directly overhead - the gradient should lessen/go away, and/or rotate the camera by 90 deg - the gradient most likely will change to left-right direction confirming whether it is indeed light-optical and not camera related gradient. You will definitely need to use flats though to clean up the lights as there are a few dust donuts quite visible in the images you provided.
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Old 27-08-2019, 06:30 PM
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Quote:
Originally Posted by Manav View Post
Hi Greg - First of all thanks for your prompt response. I'm new to CCD imaging so I apologise in advance.

I've linked the FITS file for Dark frame which is a 300sec exposure at -20 taken using SIPS software as well as a 0.2sec bias frame taken at -20 in the below link.

https://drive.google.com/drive/folde...hJ?usp=sharing

Unfortunately, I do not yet have a flat field generator so I did not have any flat field shots. I also do not have another scope to test on :/

I didnt even consider light pollution; I have been shooting all images at South - South West at 40deg above horizon from the backyard so that could be a possibility.

I'm using a SVQ100 so the image is inverted which could explain why the light gradient is on top of the image.

Just to confirm if this was a CCD issue we should see the same glow in the darks and bias am I right?
Yes I would expect to see something in the darks, bias and the flats. Some scopes have a centre hot spot which is more common now that many have corrector lenses which can cause that effect. This is not what you have though.

It looks mostly like light pollution if the image is inverted. I discounted that at first because light pollution would be at the bottom of the image not the top.

But yes most images are reversed top/bottom and left to right.

Greg.
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Old 28-08-2019, 07:51 AM
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An old rule of electronics fault finding is the "Half split" rule (In any fault finding of multiple components, check if the system is operating properly in the middle either physically, or conceptually as per the below, and keep splitting the system in half over and over until you localise the fault) In this case the first half split would be to determine if it was in the camera or the optics (Or just sky conditions)

To do that I would rotate the camera by an arbitrary amount compared to the scope and then image the same target. If the gradient stays the same with respect to the image frame then it is in the camera, if it stays the same with regards to the orientation of the target then it is coming from the scope or light pollution/moon glow etc.

Half split again, as unlikely as it is to be in the scope/flatteners (If you are using one) etc, rotate the entire scope/camera train as an assembly (I assume as a refractor you probably have it in rings?) and image again. If the gradient stays the same with respect to the image frame then it is coming from the optics somewhere, if it stays the same with respect to the target then it is coming form the sky and there is not much that can be done about it aside from picking a different target that is not impacted unless it is a neighbors outside light or something like that.
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