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Issues after modding my EOS20D

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#1 Dirk84

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Posted 03 December 2021 - 02:11 PM

Hi all,

 

I need some advice and answers because I'm a little confused. 

 

I recently did a modification to my old Canon EOS 20D. With the help of an YouTube video I removed the IR filter. 

I did not replace any glass / filter, I just removed the green looking IR glass.

 

But now I have encountered some issues and some unresolved answers.

 

1- Looking at this topic https://www.cloudyni...dslr-mod-types/ what kind of modification did I do? I don't think my 20D has a Low-pass #2 filter

 

2- I use a Canon 70-200 f2.8 but I only seem to be able to focus @+-135mm everything below and higher is blurry. Same for the 50mm f1.8, I cannot reach infinity focus.

    Is this because I did not use any clear glass to replace the IR filter. Is this giving me a backfocus issue with these lenses? 

 

3- I have attached a heavily edited sub to show you that I have a 'dark' area in the lower part of my sensor. Did I damage the sensor or is it again the issue op question #2? 
    I cant' remember having this issue before the mod because it has been too long ago since I used it. Could it be that the senor is not 100% level?

 

I have also included a picture of the North Am nebula , focus was reached at 135mm with the 70-200mm.

 

Thanks for your help!

 

 

 

Dark area in the bottom part of each image.

 

mod20d.jpg

 

 

Rather successful image:

 

mod20d.jpg

 



#2 Dirk84

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Posted 03 December 2021 - 02:50 PM

Ok I THINK I solved the black bar issue on the bottom of the pictures.

 

I have another original 20D and I thought about comparing the sensors to see if there is any visible damage on the modded on.

But I think I identified the problem.

These pictures are taking during sensor cleaning mode so the mirrors are 'locked' to the top of the camera.

The shutter on the modded 20D will not fully extent to the top.

There is a still a little bit of room and I think it is covering part of the sensor.
I can move it into place but it won't stay there. 

 

 

20dmod3.jpg

 

 

Can this be the issue? Is the top part of the sensor the bottom part of my pictures? 

 

And most importantly , is this fixable?

 

Thanks

Dirk



#3 rblackadar

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Posted 03 December 2021 - 03:27 PM

Yes, the image is upside down on the sensor so your diagnosis is probably right. I don't know what in the mod could have caused the mirror to malfunction; a good mod should not have changed the geometry in that part of the camera at all, so it shouldn't be hanging up on something. A mystery, hope you can find at least a workaround.

 

As for backfocus, yes, removing glass will cause many lenses not to reach focus at infinity. You got lucky at 135mm, it would seem. (Nice photo, by the way.) A reasonable workaround for most (but not all) backfocus issues of this kind is to shoot with a clip-in filter; Svbony UHC is the one I use for emission targets; UV/IR cut would be better for galaxies/reflection nebulae.



#4 asanmax

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Posted 03 December 2021 - 04:08 PM

You essentially now have a full spectrum modified camera. This mod is also called a 'naked sensor' or 'bare sensor' mod. 

The camera is not able to focus at infinity with your lenses because you removed the filter. This is usually compensated by moving the sensor closer to the lens flange, very precise operation requiring skills and proper equipment. Professional modification service companies do that either by re-shimming or by adjusting the 'floating' sensor mount.

Your camera has thin shims under the sensor screws. There are typically more than 1 thin shim that are either removed or replaced with the proper thickness shims to calibrate the sensor so that the camera is still able to work with lenses.

 

If you have any clip-in filter, you can try using it and it will most likely make things better but I doubt that it would be enough. 

 

Very nice image by the way, totally worth the work you did on your camera.

 

Max



#5 Dirk84

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Posted 04 December 2021 - 06:19 AM

Yes, the image is upside down on the sensor so your diagnosis is probably right. I don't know what in the mod could have caused the mirror to malfunction; a good mod should not have changed the geometry in that part of the camera at all, so it shouldn't be hanging up on something. A mystery, hope you can find at least a workaround.

 

As for backfocus, yes, removing glass will cause many lenses not to reach focus at infinity. You got lucky at 135mm, it would seem. (Nice photo, by the way.) A reasonable workaround for most (but not all) backfocus issues of this kind is to shoot with a clip-in filter; Svbony UHC is the one I use for emission targets; UV/IR cut would be better for galaxies/reflection nebulae.

 

Thanks for that up vs down confirmation. Probably the 20D already had that malfunction before. It isn't that noticeable a single image. Only when I stack you see the data loss compared to the rest of the image.

 

 

You essentially now have a full spectrum modified camera. This mod is also called a 'naked sensor' or 'bare sensor' mod. 

The camera is not able to focus at infinity with your lenses because you removed the filter. This is usually compensated by moving the sensor closer to the lens flange, very precise operation requiring skills and proper equipment. Professional modification service companies do that either by re-shimming or by adjusting the 'floating' sensor mount.

Your camera has thin shims under the sensor screws. There are typically more than 1 thin shim that are either removed or replaced with the proper thickness shims to calibrate the sensor so that the camera is still able to work with lenses.

 

If you have any clip-in filter, you can try using it and it will most likely make things better but I doubt that it would be enough. 

 

Very nice image by the way, totally worth the work you did on your camera.

 

Max

 

I have 3D printed a clip and used a clear glass (maybe too thin 1.2mm) and will need to wait uittil I have some stars visible again.

 

Is this normal too: Whenever I focus through the  viewfinder / eyepiece I seem to be able to focus at all ranges. But whenever I take a picture the focus is off. Is this again the backfocus?

Even the autofocus on the lens still works fine and the image I get trough the eyepiece is sharp.

 

Thanks for the help.

Dirk



#6 nofxrx

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Posted 04 December 2021 - 10:12 AM

The viewfinder is no longer accurate for focus after the mod due to the back focus change. Think of it this way, you have the viewfinder,AF sensor, and imaging sensor that WERE all accurately aligned together. You moved the image sensor so now neither AF sensor nor the viewfinder will focus for the image sensor any more. The only way to accurately focus for the image sensor now (with this model, since there is no LiveView), is to take short exposures and check for focus, preferably with a focus aid like a bahtinov mask.
Hope this helps!
Cheers,
Brent
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