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Old April 12th, 2009, 02:07 PM   #1
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IR filter behind an adapter?

Has anyone tried to sandwich an IR hot mirror type filter (like a 486) behind an adapter - b/n the camera and the achromat.

Wondering if this could be a way to avoid the wide angle green vignette issue. However its not supposed to be used after another filter (due to internal reflections from the mirror) and this probably applies to an adapter also.
This is a question for people who've actually tried it, not random speculation please.

Lenny Levy
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Old April 13th, 2009, 04:35 AM   #2
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Lenny,

I did try this exact configuration - the vignetting is still there, only more intense and darker (gray rather than green, for some reason).
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Old April 14th, 2009, 10:04 PM   #3
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Piotr ,

What adapter are you using?
I just did a sloppy test on my EX-1 with a 486 behind a Letus Extreme and on first glance I see no sign of any vignetting - other than the teeny bit that is probably normal on my set-up. This is with a 24mm Nikon!

I will try to get to more careful tests tomorrow though.

Is it possible you are seeing grey vignetting just from the "spacer effect" of the filter?

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Old April 15th, 2009, 02:56 AM   #4
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Lenny,

I sold away the 486, so I cannot repeat my experiment - however, I did see vignetting with it when put between the EX and Letus. It was different than without the adapter, as I mentioned; instead of green tint in the corners I saw gray darkening along the left and right edges (not present without the filter).

It's possible that I am mistaken as to the true reasons of the phenomenon, as I was expecting it to give artifacts and looking for them - but nevertheless, I remember it as unacceptable.

Additionally, the 486 is designed to be used as the outermost optical element, and I was about to buy a matte box anyway, so I didn't think twice and sold it on eBay.

Now I'm waiting for a better solution to arrive (in the form of a 4x5.65" filter). In the meantime, I tested another manufacturer's Hot Mirror filter, but that didn't work at all (confirming Art's observations).

If nothing better is available, I will probably buy the 486 again (this time in the rectangular form factor - the 680), as I shoot music performances mainly with people wearing all kind of black garment on the stage... I'll have to avoid wide angle shoots against plain, light surfaces, as this is when the vignetting shows its ugly face. I'm still hoping somebody will come up with a better solution (Tiffen IR without ND ???), so that vignetting is not a problem.

Whatever the outcome, this really is a pain in the [...], as most concerts I do with several EX cameras, so really all my operators would need to have and use exactly the same filters - otherwise it's useless.
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Old April 15th, 2009, 04:02 AM   #5
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I suspect what you saw on the left and right sides was vignetting due to the additional filter in the path, not IR problem due to the hot mirror. I zoomed in and it pretty much went away though perhaps it was worse than without the filter - I'll check that out again.

have you tried making using a shot of the green vignette against white and using it to color correct the vignette on a shot?
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Old April 15th, 2009, 05:13 AM   #6
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Quote:
Originally Posted by Leonard Levy View Post
have you tried making using a shot of the green vignette against white and using it to color correct the vignette on a shot?
Yes I have - but only to check whether it can be done at all (it can, sort of). With a big, multicamera project, it'd be too much hassle I'm afraid...
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