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Lens focus The place to talk about your camera's glassware.

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MikeOxon MikeOxon is offline
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Re: m4/3 lenses for IR

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Originally Posted by Petrochemist View Post
..........Have you come up with a good way of holding the filters?.............
'fraid not - I had the lens tilted back a little and a blob of Blue-tac to form a raised ledge in the lower part of the filter ring, to raise the disk up, so that it completely covered the lens. OK for experimental 'dabbling' but not a practical field solution
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Re: m4/3 lenses for IR

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Originally Posted by MikeOxon View Post
'fraid not - I had the lens tilted back a little and a blob of Blue-tac to form a raised ledge in the lower part of the filter ring, to raise the disk up, so that it completely covered the lens. OK for experimental 'dabbling' but not a practical field solution

I guess I'll just have to keep looking then


It's probably got to the point where none of mine will be needed for work again, so I can probably get away with gluing a ring to them to make them easier to mount.
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Re: m4/3 lenses for IR

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Originally Posted by Petrochemist View Post
I guess I'll just have to keep looking then
Another thought - if you lay the small filter over the lens (while it is pointing upwards) and then gently screw a UV or protective filter over it, I've found it will hold in position. I have tried this but didn't use it for experiments, in case the additional filter affected the results (I doubt it would)
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  #19  
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Re: m4/3 lenses for IR

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Originally Posted by MikeOxon View Post
Another thought - if you lay the small filter over the lens (while it is pointing upwards) and then gently screw a UV or protective filter over it, I've found it will hold in position. I have tried this but didn't use it for experiments, in case the additional filter affected the results (I doubt it would)

It's worth a try.

It will affect some of my filters, which were brought for photographing UV, but it seems even my full spectrum converted model isn't sensitive to UV. So the difference won't be seen by the camera.
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MikeOxon MikeOxon is offline
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Re: m4/3 lenses for IR

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Originally Posted by Petrochemist View Post
............... it seems even my full spectrum converted model isn't sensitive to UV. So the difference won't be seen by the camera.

The glass types used for making most photographic lenses are, themselves, pretty opaque to UV. I've never really understood the need for a special filter, unless its cut-off extends into the short wavelength end of the visible spectrum, to reduce a blue cast in snow scenes.


I've started some experiments with the Schott WG and GG filters and will report on the results in another thread.
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Re: m4/3 lenses for IR

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Originally Posted by MikeOxon View Post
The glass types used for making most photographic lenses are, themselves, pretty opaque to UV. I've never really understood the need for a special filter, unless its cut-off extends into the short wavelength end of the visible spectrum, to reduce a blue cast in snow scenes.


I've started some experiments with the Schott WG and GG filters and will report on the results in another thread.

I've measured the spectral transmission for some of my lenses. Yes the modern MFT lenses transmit very little UV, and even reduce IR by a surprising amount. The lens I used for my trials was a El Nikkor 80mm enlarger lens that does transmit a reasonable amount of UV.
My lens data may not be very readable on-line but it summarized here


There's a similar set for some of my filters as well here though you can download data on schott glass from many suppliers such as UQG outside Cambridge. I have a GG495 somewhere, and must have tried it once or twice but I don't think I have any other WG or GG grades.

I think my best results with schott glass have been with BG3 & U330 or U340 filters which give UV, blue & NIR in various combinations. Quite a few old photographic filters work well for IR on converted bodies
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