# Dark Edges on Large CCD



## nicholasuniversal (May 3, 2011)

Hi, I'm new to this forum.

I have the following camera setup:
Prosilica GE4900C
Kodak KAI-16000 CCD sensor
Nikon Nikkor AF 35mm f/2D

I can't figure out why I get dark areas on the edges of my photos.  I attached some examples.
I have tried different  kinds of F stop settings as well as shutter speed and iso, all that stuff.

Can anyone help me?
Photo 1
Photo 2


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## Patrice (May 3, 2011)

No information on aperture provided. Not familiar with that camera or sensor but your words "large CCD" lead me to think the sensor is larger than the image circle that lens was designed to illuminate. Thus, dark edges are vignetting. Try a lens for a larger format camera such as the medium format cameras or even the larger view cameras. All this assumes that the lighting was even across the scene and confirmed by light meter readings.


edit: just did a quick look up on that equipment. Full frame (135 format) with nikon mount. The lens' image circle should illuminate the sensor adequately. Check the lighting.


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## nicholasuniversal (May 3, 2011)

Thanks for the response.

Every photo we take with this camera has the dark edges.  We have not tried a large format lens before maybe that will work.  The photos were taken at F22 but the dark edges are there at all aperture settings.
Here is the spec sheet on our camera, maybe it will help: http://www.1stvision.com/cameras/Prosilica/dataman/GE4900-4900C.pdf


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## analog.universe (May 3, 2011)

Is the on camera flash firing?  To me these images look like a flash shot at a longer focal length than the lens.   The linear instead of circular pattern pretty much means the lens isn't causing it.

edit:  whoops, just saw the thing, nevermind  :lmao:


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## nicholasuniversal (May 4, 2011)

The dark edges are there under all light conditions.  We do not have a flash in the sample image we are using halogen lights.  The dark edges are there under daylight as well during aerial photography.


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## Garbz (May 4, 2011)

Take a shot and remove the lens. If it still comes out the way it does then blame the sensor itself. Otherwise it may just be an interface problem between the lens and sensor such as lens not lined up correctly.


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## nicholasuniversal (May 4, 2011)

I took some more test photos today.  I took off the lens for a couple of them.  Let me know what you guys think.

Inside of camera: photo1
Sky at F/8: photo2
Sky at F/22: photo3
The lens removed indoors (same set up as shown in original post): photo 4
Lens removed outdoors: photo5

Thanks


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## AUG19 (May 4, 2011)

nicholasuniversal said:


> Lens removed outdoors: photo5
> 
> Thanks




This is one I was hoping to see..and it's not showing up in my browser. Is it on the server?


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## AUG19 (May 4, 2011)

The splash page of your website is kinda weird. I think i'll pass.


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## nicholasuniversal (May 4, 2011)

The photo is all white.  It doesn't look like it loads on my browser either but its just a white photo.


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## Garbz (May 5, 2011)

All white and blown out. Can you do an outside shot with correct exposure? If you can't control the electronic shutterspeed then I suggest taking the photo at dusk or maybe put a polariser on the camera. A blown out photo tells you nothing.


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## nicholasuniversal (May 5, 2011)

I'll do anouther outside shot with no lens soon.  I bought a new lens yesterday its a  Zeiss 50mm f/1.4 ZF.  It made a big difference in the shading.
Check out this image, test2
Compare that to the Nikon 35mm, test1

The edge shading is still there.  I tried out this one as well, PC-E NIKKOR 24mm f/3.5D ED.  The edge shading was not present but that lens does not work for our application.  And its over $2000.

The Zeiss lens will work for now but what is a long term solution that will get rid of the shading?  I'd like to try a medium format lens or something but I can't find anything in an F mount.


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## jake337 (May 5, 2011)

have you tried a longer focal length lens? 100mm +


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## Garbz (May 6, 2011)

edwin47 said:


> Every _CCD_ camera generates a _dark_ signal that varies with exposure time and chip temperature.


 
You really didn't look at the source picture did you


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## nicholasuniversal (May 6, 2011)

Jake, I did try a Zeiss 85mm f/1.4 and it did not have any shading.  This camera is being used for aerial photography and a wider viewing angle is required.  

The tilt and shift lens allowed light to cover the whole CCD something like that would be good but the PC-E NIKKOR 24mm was very expensive.  Also the tilt and shift feature is not needed.


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## MarkF48 (May 6, 2011)

If you haven't already done it, maybe contacting Prosilica support would be an option.....
Contact Support - Allied Vision Technologies

I'm wondering if the distance from the lens mounting flange to the plane of the sensor may be be having an adverse effect on the image circle.


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## analog.universe (May 6, 2011)

This is really interesting, and it makes me think that the construction of the sensor limits the light captured based on its incidence angle.  Someone else can confirm my knowledge of optical physics here, but I think I know what I'm saying.  A theoretical lens of infinite focal length would direct light at the sensor precisely perpendicular to it.  Any shorter focal length would produce a perpendicular ray in the exact center, with gradually increasing angle toward the edges of the sensor.  It seems that your sensor has a particular incidence angle at which light begins to fall off.  The wide angle lenses reach this threshold close to the center of the sensor, and the longer lenses progressively farther out.  The 85 doesn't achieve this angle until beyond the edge of the frame.

So my suggestion is to investigate whether or not there is a filter in front of the sensor that is causing this and can be removed/replaced, or, if this a function of the construction...  employ a corrective optic to allow the lens farther from the sensor plane, resulting in more parallel light striking the sensor.


afterthought:  This explains the horizontal as opposed to circular pattern, as my guess is that whatever filter causes this light falloff is related to the R,G,B differentiation, and the pixels on that sensor are staggered horizontally and stacked vertically.. if you know what i mean.


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## nicholasuniversal (May 6, 2011)

analog.universe said:


> afterthought:  This explains the horizontal as opposed to circular pattern, as my guess is that whatever filter causes this light falloff is related to the R,G,B differentiation, and the pixels on that sensor are staggered horizontally and stacked vertically.. if you know what i mean.



Thanks, I'm not sure what you mean.


I contacted Allied Vision and this was their response:


> Yes the darkening your seeing is due to Vignetting. Vignetting - Wikipedia, the free encyclopedia
> 
> This is due to one of 2 issues. Either the off angle rays of the lens entering the column of the pixel and striking the sides of the pixel rather than the light sensitive portion at the bottom, or the lens is poorly corrected to handle those type of rays (they get worse as the aperture gets larger, so at F2 you will notice it more than at F5.6). If you adjust the exposure and aperture to match, and you dont see a difference in the vignetting, its a lens issue that can be corrected by 2 options, lens choice or software.
> 
> There is a filter that can be used to help correct this issue optically, called a center spot filter, but they are VERY expensive and do not help much as they are not optically matched to the specific lens.


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## analog.universe (May 6, 2011)

nicholasuniversal said:


> Thanks, I'm not sure what you mean.
> 
> 
> 
> > the off angle rays of the lens entering the &#8220;column&#8221; of the pixel and striking the sides of the pixel rather than the light sensitive portion at the bottom


 
^ that's what I mean.  Since the sensor has to capture each color separately, the pixels for each color are oblong, in your case narrower in the horizontal dimension.  When there are 3 next to each other you get a square pixel made up of all the colors.  So if you're hitting the pixel from the narrow side, you'll reach the opposite wall (as opposed to the bottom of the cell) sooner than you would from the long side.

The tilt shift lens worked because it had a larger image circle and was able to get to the edge of the sensor with less incidence angle.  I bet you could acquire an old medium format lens and adapter on ebay to obtain a large image circle.  I read some stuff a while back on DIY tilt/shift lenses, and Pentacon 6 lenses were really popular and fairly affordable...


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