EPL-2 Infra Red conversion questions

Started May 28, 2012 | Discussions thread
technic Veteran Member • Posts: 8,932
Re: full spectrum conversion and external IR blocker

Vasyl Tsvirkunov wrote:

technic wrote:

Is the CC1 also an interference type filter? (easily recognised because they look vibrant purple when viewed from an angle)

One could use the absortion type filters like B+W 489 (there is one from Heliopan or Schott that is a bit better) and accept the less-than-optimal IR blocking performance. Probably it depends on the sensor if the combination is acceptable; I don't have an m43 camera so can't say anything from experience. But the uncertainty alone makes the whole idea unattractive for me, better use a separate m43 body for visible light.

Regarding mounting IR blocker internally in the lens: yes, you could do that and you will have less hue shift problems. But there is no free lunch: the filter is by definition an optical element that will probably result in a lens that no longer focuses to infinity (except if the lens has a native internal filter holder, that uses a clear filter for default). Maybe for legacy lenses that could work if the focus scale extends far enough but again, this approach has its limits ...

LDP does not provide complete info on their filters but CC1 appears to be Schott BG38, absorption type. It does not show any hue shifts under any angle for sure. CC2 is also Schott, either KG2 or KG3, nobody knows for sure, also absorption. Cannot complain about CC1 IR blocking capabilities -- overlapping it with 830nm filter blocks very close to 100% of everything.

OK, BG38 is probably the best absorption filter available. But the ones that I tried until now were not fully effective, e.g. they all still had the red glow on fine fabric (e.g. black camera bag) and machined metal, and less than perfect color (although 95% of users wouldn't notice).

You are right about rear filter shifting focus. The net effect is rather small with gel filters (those have the entire host of other problems). With glass filters it may be significant. Some lenses may still work but it is hard to say for sure.

I tried using a gelatin 87c IR filter inside my full spectrum dsc-f717. That works indeed, but you can have a minor sharpness loss in some areas because the filter doesn't stay completely flat.

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