IR & VariND there is difference which is first? -test added!

There is difference using vari-ND in front of IR filter, or IR filter in front of the ND?
I'm doing a couple of tests.

Thanks

Theoretically, putting the IR first makes sure it gets reflected/absorbed before it penetrates the rest of the filter stack and bounces around in there, making for a slightly better result, as well as with some VariND filters (e.g. Genius) being larger in size so as to have less chance of shading ("vingetting"). But as to the first, main point, I've not been able to find any practical tests either way to see if there is a real-life difference, so if you'd like to do some I'd love to see them.

Thank you. I made a quick test today and saw a little more red shift using the Hoya IR after the GenustechND. I also have the Heliopan IRcut.

But I have to take into account that the Genustech has a different thread outside/inside, so if one gets the IR filter for the outside thread, in the case he needs to work with available light he can't mount the IR without mounting first the GenustechND. This is a bit disappointing.

Hope to post a couple of DNGs asap.

Ok I made a more serious test. Sorry for the crappy subject but the sun is shaded most of the day in this period.

Black nylon bag, sun, 5600K 400ISO 180°, SLRM 25/.95
DNGs edited in ACDSeePro8, exposure/contrast same editing to all files, resized jpegs.

f11 no filter

f11_no_filter.JPG (258.26 KiB) Viewed 1516 times

f11 HOYA UV/IR CUT

f11_HOYA-UVIR.JPG (257.54 KiB) Viewed 1516 times

f1.4 GENUSTECH ECLIPSE at nearly max

f1.4_GENUS.JPG (187.99 KiB) Viewed 1516 times

f1.4 HOYA UV/IR CUT, GENUSTECH ECLIPSE behind (hoya/genus/lens)

f1.4_1HOYA_2GENUS.JPG (188.17 KiB) Viewed 1516 times

f1.4 GENUSTECH ECLIPSE, HOYA UV IR CUT behind (genus/hoya/lens)

f1.4_1GENUS_2HOYA.JPG (183.27 KiB) Viewed 1516 times

f1.4 GENUSTECH ECLIPSE, HELIOPAN Digital UV/IR behind (genus/heliopan/lens)

f1.4_1GENUS_2HELIOPAN.JPG (178.81 KiB) Viewed 1516 times

You can get a stepup ring to go from the larger filter size back to the size you need for the lens without the VND. But given your test results, looks like you,want to keep,the UV/IR cut behind the VND anyway. I am going to try this and see if it makes a difference with the SLR Magic VND. Thanks for the test. Cheers

Marco thanks for posting the photos.

It looks like the VND introduces IR contamination.
It now makes sense to have the IR cut the closest to the lens because you need to remove the contamination introduced by the VND.

Which is different to if one is using a hot mirror filter.
That, I believe, needs to have the hot mirror(mirror surface out) as the first filter in the stack(hot mirror/ND/lens).

I have always thought of keeping the IR cut close to the lens because it is more convenient when you do not need to use the VND, but now with your test there is actual reason to have VND/IR cut/lens.

Marco, I agree with Leon. I find the difference startling. I don't plan on using a Genustech Eclipse, but intend to use the SLR Magic Vari ND Mark 2. Now I know to keep any IR Cut closest to the lens. This question has been asked several times over the years. Nice to see a picture of the results.


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This is a little off this topic but I would like to share this video about ND and IR.
It was done some time ago and hopefully the inks in the filters have been improved by now.

Your post reminded me of this talk I went to at AbelCine in L.A.
The differences are startling.
It is important to be reminded and sometimes informed for the first time about the IR situation.

It looks like the VND introduces IR contamination.
It now makes sense to have the IR cut the closest to the lens because you need to remove the contamination introduced by the VND.

I know this is reviving the thread a little, but a few weeks isn't too bad and I thought this was worth a clarification.

Neutral Density filters do not introduce IR contamination. The IR contamination is already there. What happens is that they remove other wavelengths of light, leaving the IR contamination more dominant. It's a subtle difference, but I think an important one.

When you put a ND filter on what it is doing is blocking a certain amount of certain wavelengths of light. ND filters are tuned to specially block visible light. Different manufacturers and types use different processes, with VNDs typically leaving behind the most untouched IR (and UV, but that's usually not as big a deal). Uneven blocking of different wavelengths is why different NDs will give a slight colour cast.

For example, if you go on Hoya's site they provide transmission curves for most of their filters. If you look at their ND8 filter
http://www.hoyafilter.com/hoya/products/ndfilters/ndx8/
you can see that the transmission curve is pretty good, but not perfectly flat. It passes slightly more red that blue light with some minor wiggle in-between. Their curve cuts off at the 700 mark right where IR light starts, but I suspect if it continued further there would be a noticeable curve upwards.

This is also why combinations of different ND filters can produce quite different results in when used with different IR filters on different cameras. It's a combination of what wavelengths the ND is passing, what wavelengths the IR is blocking and what wavelengths the camera sensor is particularly sensitive to. Different manufacturers of all three are going to have different cut-off points.