p.1 #1 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Hi there,
I am looking for filters that allow to pass visible light while cutting IR and UV. It is to be able to take "normal" pictures with a camera converted to full spectrum (sensor filter replaced with clear glass that allows the full spectrum of light to pass).
The filters I know that can do that (BW UV/IR 486 and other similar) usually work for FOV of 35mm and above but produce color vignetting for wider FOV. I know of the existence of Xnite CC1 filters but I dont know if they have the same problem. I have tried to contact MaxMax but I havent heard back yet.
Since I know that there are some Leica users here and I guess some of them might use wide angle lenses I thought that someone might be familiar with this issue since it is my understanding that Leica cameras usually need this kind of filters.
p.1 #2 · Hot mirror (UV/IR cut) filters for wide angle lenses.
I had a Leica M8, which had IR problems, and I found that the 35 Cron (f/2) was okay with such a filter, but the 35 Lux (f/1.4) was already too wide (larger front element probably). Anything wide with an IR filter will filter the wrong wavelengths in the corners, due to the way an IR filter works (wavelength-thickness layers of coating blocking the rays; these coatings have the wrong thickness when the rays come through at an angle).
The Leica M8 and M9 solve this problem by having in-camera corrections for this, i.e. in combination with a known lens (6-bit coding) the camera will apply a reverse colour-shift. This generally works well, except that it also increases the exposure a little bit in the corners, which are therefore more noisy than the centre.
For other cameras, there is a program called CornerFix which you can use. Sandy, the author, wrote it for the Leica M8, when we discovered the IR problem over on the leica forum, but in fact the program works equally well for all cameras. The way it works is that you expose a shot with the camera/lens/(and aperture...) combination you want to correct, of an evenly lit white wall out of focus, or something similar, and then pass it to CornerFix as a template. This can then be applied to future shots with the same combination. It is a bit labour-intensive, but if you are careful, it works very well.
By the way, this problem only exists with the "hot mirror" type of filter, and you could avoid this workflow by using an IR-absorbing filter instead. I think B+W's is the 489. They are not as efficient at removing IR, but maybe overall you prefer it.
p.1 #3 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Thanks Carsten,
I am going to check that software.
I have never used IR absorbing filters because I was concerned about having blue-purple casts all over the place but maybe these color shifts are not that difficult to correct on PP
p.1 #4 · Hot mirror (UV/IR cut) filters for wide angle lenses.
BG 39 from Schott would do it. But the glass is not very perfect in regards of bubbles. Furthermore maximum transmission could be a problem. And - I do not know which consumer filter manufacturer has this filter for sale.
BW 489 seems to transmitt too much IR for my taste.
There are other alternatives, but those are very special. I think they are not sold in small numbers to consumers. Furthermore I can´t tell you - because it is part of my work.
p.1 #5 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Would a rear filter work or does the coating of the lens also produce color vignetting? My converted camera is micro four thirds and I was thinking that maybe sticking a filter in an adapter (say Nikon to M4/3) could work. I guess I will check it when my camera comes back from service.
I have seen the curve of the 489 and what you both said is totally right, it bleeds too much infrared.
@ZoneV, I wont ask you about the alternatives but dont think I wouldnt be interested in listening them
p.1 #7 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Javier Munoz wrote:
Would a rear filter work or does the coating of the lens also produce color vignetting?
Lens coatings usually are less effective under acute angles (nano structure coatings have been invented to solve this problem) but will definitely not cause noticeable color shift like a UVIR filter.
"Color vignetting" is a term you just invented? :P Vignetting just means darkening of the corners. Color shift is doesn't necessarily happen only in the corners.
p.1 #8 · Hot mirror (UV/IR cut) filters for wide angle lenses.
I have read color vignetting on many places referring to this effect of UV/IR cut filters with wide lenses. With these filters, the color cast happens mainly on the corners and it resembles vignetting. The angled light that doesnt enter the filter/lens from the edges gets lost so only the angled light from the edges produces the color shift.
p.1 #9 · Hot mirror (UV/IR cut) filters for wide angle lenses.
I have an infrared converted GH2 camera and I'm experiencing the same problems with an B+W 486 filter. I've tried the CornerFix software, but it's a hassle.
I'm wondering if anyone has had any luck finding better filters, or even rear-mounting filters on the lens?
p.1 #10 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Rear mount filters would help on retrofocus lenses - not on symmetrical designed lenses.
But back focal length is changed because of the glass path. And adding glass behind a lens normaly makes MTF ( modulation transfer function => sharpness) worse.
p.1 #14 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Mike V wrote:
Are you meaning filters similar to Schneider's True Cut range or Tiffen T1s?
Interference based filter like the Schneider 486 could be problematic. I think the True Cut is such a filter. There are ways to enlarge the usabel incident angle, don´t know wheter this filter has such or not.
The Tiffen T1 seems not to be based on interference filtering, but some colored absorbing material.
Bottom line is that Schott BG38, BG39 and BG40 filters should not introduce color cast in the corners for wide angle lenses. The CC1 filter is also suitable for this.
p.1 #17 · Hot mirror (UV/IR cut) filters for wide angle lenses.
But BG 39 without coating is reflecting much and is not very stable in terms of oxidation. Likely the other two BG filters are not much different in these problems.
p.1 #19 · Hot mirror (UV/IR cut) filters for wide angle lenses.
Yes, it is not much a problem for a filter you could change with no problem, but for example her as replacement for the original Sony A7 filter it could be a problem: https://www.fredmiranda.com/forum/topic/1340474
It could be humidity, or fingerprints, or?? The glass oxidation is nothing where one find much information about. A bit of information is in the Schott datasheets, and there the BG 39 is much more dangerous for degrading than most normal optical glass.
Quick is relative, it could be months or many years.
Lower transmittance itself is less a big problem, the reflections (~9%), or stray light is more of a problem.
