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Lens Glass Inspection


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#1 charles pappas

charles pappas

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Posted 24 October 2017 - 04:49 PM

Could anyone offer any tips on evaluating lens glass, especially with no means to film test this lens.

 

I have attached six photos from an Angenieux 9.5 - 95 lens (Camflex mount I have posted about earlier). At the front glass I can see at least seven or so blemishes plus a few more around the perimeter. (There is also an extremely fine scratch about 1/2 inch long no clearly visible in photos.) 

 

At the back element photos numerous specs are visible. 

 

Taking the lens outside and looking through it, a dark spec or two appear to move with the image.   

 

I know this is nebulous, and clearly the less seen on the glass the better, but any comments would be appreciated. Thank you. 

Attached Images

  • IMG_6790.jpeg
  • IMG_6791.jpeg
  • IMG_6792.jpeg
  • IMG_6812.jpeg
  • IMG_6813.jpeg
  • IMG_6814.jpeg

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#2 Dom Jaeger

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Posted 24 October 2017 - 06:25 PM

Typically, coating blemishes and fine scratches just tend to disperse light, causing veiling glare and a slight reduction in contrast. You might get some loss of fine detail as well, depending on how much of the element coating is damaged. A rear element is more crucial than a front one in that respect.

Fungus will do the same, and tends to spread, so is among the worst things to find in a lens. Often it cleans up if it hasn't been left for too long. I can't tell if your lens has fungus, it looks like fine spidery lines.

Isolated specks are usually fine unless really large, or there are too many.

Deep scratches or chips can catch and refract light, causing flares. How noticeable it is depends on the focal length and stop and lighting situation.

There could be other issues with an old zoom like this that have more impact on the image quality, such as the back-focus setting, wear to the zoom or focus mechanics, decentration of lens elements, oil on the iris blades. A film test is the only real way to check, or have a technician project the lens with a lens test projector.
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