Author Topic: Mark on lens  (Read 391 times)

Mark on lens
« on: April 15, 2018, 07:30:23 pm »
I've got a lens with a couple of grey marks on the rear element about 2mm across. They seem to be damage to the surface of the glass.



They are at the edge of the lens, does that fact they are where they are affect the image less than if they were at the centre?

I think those spots wouldn't even end up on the image anyway because my camera is a crop sensor dslr and even on full frame the edges of the circle won't end up on the rectangular image.

Re: Mark on lens
« Reply #1 on: April 15, 2018, 10:55:25 pm »
No, the full lens can project to each part of the image, although it may be aperture dependent. Otoh, it probably won’t have much (or any) visible impact - ‘though rear element damage can be worse than front iirc

Mike

LEE

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Re: Mark on lens
« Reply #2 on: April 15, 2018, 11:07:48 pm »
It may be fungus.

Best way to see the impact is to photograph some 1mm graph paper at all apertures, then some plain white paper.  It may not be all that bad. You may not notice it.

What lens is it? What camera is it used on?
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Jaded

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Re: Mark on lens
« Reply #3 on: April 15, 2018, 11:30:22 pm »
Cracking sunspots!  :thumbsup:
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Re: Mark on lens
« Reply #4 on: April 16, 2018, 12:13:51 am »
I've only just got it and I don't want to say too much as I might want to return it. It's a M42 zoom, I think it's a retailer/distributor brand, made in Japan.

The postage was more than the lens!

I haven't tried it yet as I haven't got a M42 to Pentax K adapter. There wasn't any fungus when I got it. I've read that fungus can etch the glass. If it was caused by fungus, it was cleaned off before I got it.

Aunt Maud

  • Le Flâneur.
Re: Mark on lens
« Reply #5 on: May 24, 2018, 08:51:00 am »
You're right that the image on the sensor will only be a portion of the total circular image projected by the lens. It's how tilt and shift lenses work, except they project a larger image circle than a normal lens.

Why don't you give it a try and see if there are any blurry spots on the photograph ?

T42

  • Old fool in a hurry
Re: Mark on lens
« Reply #6 on: May 24, 2018, 09:56:07 am »
I haven't tried it yet as I haven't got a M42 to Pentax K adapter. There wasn't any fungus when I got it. I've read that fungus can etch the glass. If it was caused by fungus, it was cleaned off before I got it.

If it was fungus and was simply wiped off it probably wasn't eradicated and could grow back again. I would look for some kind of optics-friendly fungicide and try to kill it, because there's a faint possibility that it could migrate to any other optics put in proximity to it.
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