andrea tasselli avatar
I find myself in a rather odd position, that is asking for advice rather then giving some, but here it goes…

I have a Nikon D5100 with the IR cut-off filter removed and replaced with a clear filter, so IR isn't blocked anymore. So far I've used it with refractors so adding a IR filter in front of the adaptor/corrector was never an issue. Now I'm trying my hand at using it with lenses and there where the issue comes along. With small lens I can deal with the issue by using IR filter in front of the lens itself. So far so good. With bigger lens, however, this is less straightforward. My choice lens is the Nikkor 300mm f/2.8 AFS which is well up to the job IR or no IR. Problem is that the colours are essentially wiped out for broadband subjects and all you end up with getting is a mushy yellowish image. The internal stock filter is of 52mm size so there isn't much choice for AP purposes here and most might not work (one I've tried is a disaster with massive red cut-off).

Question is, how do people handle the issue with excess IR in their images, if they have no means to add an IR cut filter up front?
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Mark Germani avatar
Hi Andrea:

I had a look at your gallery (great work!) and I see you're using the Optolong L-Pro, which you could use with your camera lens if you're ok with stepping it down a bit. Purchasing a step-down ring like this one would enable you to thread your filter in front of the lens, though you'd lose a bit of aperture. You might already be stepping down your lens for the sake of rounder stars, so maybe this is fine. One caveat is that the filter would be exposed, and might get dew/sap/dust etc. on it with frequent use.

The other option is trading-in for, or purchasing the clip-in version of the L-Pro. Optolong and other manufacturers (Astronomik, Svbony, Skytech) make clip-in versions of many of their filters. If you're looking for a straight-up UV/IR cut, I'm not sure there's a clip-in version. You might have to do a bit of digging here, or use the step-down ring option.

I had my DSLR modified back in August, and there's definitely more IR bloat when I image without a filter. I plan to purchase the L-Pro as soon as I can.

I hope this was helpful!

CS,
Mark
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andrea tasselli avatar
Thanks Mark. That idea of using an adapter ring happened to me too but won't work on the front of the lens, with a 115mm front filter required (they do not even exist AFAIK). I'll experiment with the 52mm to 48mm adaptor as soon as I get one, but it might take machining out 1 mm to make it fit in the drop-in slot of the Nikkor. I think one of the issue I might have to face is that with the steep cone angle of a f/2.8 lens there might be considerable colour shift with some filters so I might not be able to use filters like L-PRO this far from the sensor. The only way is to test and see…
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