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UltravioletPhotography

Sensor Stack Thickness


Bill De Jager

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Bill De Jager

Interesting discussion here about possible pitfalls of using film-era lenses on μ4/3 cameras: http://www.lensrenta...iii-the-summary. The basic concept is that the unusually thick cover glass on the μ4/3 (and 4/3 for that matter) sensors adds some additional optical effects which could cause problems at times, given that these lenses were designed for operating with no sensor glass. However, the information provided is not adequate to assess the degree of the problem under all common circumstances. Stopping down solves the issue on-axis but not off-axis. What is not clear is how quickly things deteriorate off-axis when the lens is stopped down, especially given the severe cropping a μ4/3 sensor does with the image from a 35mm lens.

 

I'm not sure I've actually taken UV photos on my converted broad-spectrum Panny GX1 (I've generally used my D5100), but I'll check on my past results to see if I have any samples and if so whether there are any obvious effects. My usual casual UV lens so far has been the Nikkor GN 45/2.8 which I'm not afraid of getting stolen or damaged. Its slow maximum aperture ought to protect it from the referenced on-axis effects on μ4/3, but off-axis is still a question mark.

 

One bright note is that the Metabones Speed Booster is designed to compensate for this effect, so feel free to use your old film lenses with that adapter.

 

BTW, the LIfepixel UV conversion of my Canon 600D appears to have worked. So far I've only tested it briefly on a Pentax screwmount tele-Takumar 1000mm lens (f/8, 5 elements and 5 groups, 1965-71), with very disappointing results in terms of attainable sharpness even after stopping down a bit. That one was going to be used for astrophotography. Oh well- it's still a cool lens, plus I have a older screwmount 500mm to try still. I might also just defy diffraction and try stopping down a lot more to see what happens- the aperture goes to f/45! I can always pretend the resulting blurryness is just my aging eyes. :)

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Bill, I'm going to peel this post off into its own thread.

Sensor stack thickness is a good stand alone topic.

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The filter in front of the sensor of my Canon EOS/Rebel 300D was 28,25x22,05x2,75mm.

 

My experience in converting digicams is not that big. I did some USB-webcams successfully but failed in converting the Canon DSLR.

I did some modifications on different lenses of different formats (even 9x13cm) to adapt them to APS-C cams. Sometimes it is very simple to improve contrast and overall performance of a "downsized" lens.

 

Currently I am working on a small 10Eur cam intended to become the "display unit" of my spectroscope. The HM is removed, it was part of the lens which is also removed. I fitted a M42 thread instead. Unfortunately the pics have some distortion but be assured the M42 is aligned very carefully.

 

Now the cam looks like that:

http://up.picr.de/20233495sa.jpg

 

Notice the small black shield around the sensor. To show what I mean the shield is removed here:

http://up.picr.de/20233496mh.jpg

 

And this are two pics, 1:1, made with the cam under bad conditions but equal conditions (and f5.6). the upper picture is made with, the lower without the small shield. I hope one can see the difference in sharpness and contrast (example: black spot on the letter "i"). I didn't want to modify or even fake the pics. And I made the pics "on the fly". Of course one can find better examples.

 

http://up.picr.de/20233497um.jpg

 

I made very good experience with that simple kind of shields on cams and lenses.

 

 

Here a photo of the test device with a pentacon 50mm f1.8 Lens mounted.

http://up.picr.de/20233498be.jpg

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Good luck with your digital spectroscope Stefan, they are fun to have.

The conversion looks very interesting, especially the M42 mounting.

Did the Jay-Tech have the shutter in the lens or was it an electronic shutter ?

What did you use to get the M42 mount ring ?

 

I have looked for a camera like this but mono only.

Actually, you don't need color for a digital spectroscope, once it is calibrated by using known emission & adsorption lines.

 

Looking forwards to progress on this Stefan.

Cheers

Col

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The mounting is from an old analogue cam.

 

The cam has asall sensor and only electronc shutter. Colin I tink it's possibly dangerous to the sensor if I hold the 50/1.8 towads the sun. Even here "in the north". Ok, to Bjorn it is south...

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Hi Stefan

That is good that the cam has an electronic shutter, I'll have to look out for one.

I have never found what will damage a digital sensor in photography ?

As far as the Sun goes, the lens is a magnifying glass in front of the camera & will cause things like shutter screens to get burnt holes & plastic mirror boxes to melt. Baader Solar filter film is not expensive & you can cut to size.

Col

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