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lenses suitable for infrared.


frenchie44 9 302 United Kingdom
20 Aug 2012 6:47PM
I have just had my Canon 40D converted to IR, 720nm. i have been looking at all the websites for lenses to find out what lenses are ok for IR.
my 17-85 was a big no.no. all said it was rubbish for IR, i looked to see what they say about the Sigma 10-20, which i love using for normal landscapes, the reports say that on occasions it might show a hot spot, but otherwise its good.
Well i found after testing that the Sigma is absolutely no good for IR, not sharp amd a smudged/ smear look to the highlights, no hotspots though.
the Canon 17-85 is perfect , its sharp and clean, no hotspots.
i did a simple test on sunday, about the brightest and hottest day for years. i took 12 shots standing in one place but turning in a circle for each shot. this would show up any hotspot problems, i also changed the aperature, one circle set at 28mm f5.6, then another circle at 28mm at F11, there was no problems with both lenses.
the sigma 10-20 was the lens i took to the company that converted the camera as they would set it up to suit the lens, yet the 17-85 which was not taken to the convertors out performs the sigma.
i have been out today with the camera and the canon 17-85 on it, just shooting test shots so i get used to them, no hotspot at all on 50 shots.

i expect someone out there loves the sigma for IR and most likely another would hate the canon for IR,
The moral of the story is Dont take other peoples views as Gospel, try it out for yourselves.

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MikeA 10 1.2k England
20 Aug 2012 6:53PM
This might be a useful link for you:

http://www.lensplay.com/lenses/lens_infra_red_IR.html
frenchie44 9 302 United Kingdom
20 Aug 2012 7:42PM

Quote:This might be a useful link for you:


Quote:This]http://www.lensplay.com/lenses/lens_infra_red_IR.html

Quote:This
might be a useful link for you:

I]http://www.lensplay.com/lenses/lens_infra_red_IR.html

I
looked at that site and about another 6 or 7 sites. Only 2 said the canon was suitable.thanks
RoyBoy 10 178 2 United Kingdom
20 Aug 2012 7:49PM
This is a good post!

I have a Canon 20D that I had converted about two years ago. Mostly I have a Canon 17-40 f4 L lens that stays on the camera and used for about 95% of all images taken. But I have also used 24-70, 2.8, 70-200 f4 and 100-400 IS. I have taken a LOT of images without any problems and therefore did not understand the original question. I can now see from the link that Frenchie44 has given that I have been, well lets say lucky, and that the are clearly a lot of lenses that will not work very well at all.

An interesting bit of knowledge and thank you.
MikeA 10 1.2k England
20 Aug 2012 8:11PM

Quote:This is a good post!


An interesting bit of knowledge and thank you.



Glad to have of help...Wink)
21 Aug 2012 6:32AM
Is the link helpful?
All lenses transmit less light close to the edge of the frame, particularly at wider apertures.
There is a "hot spot" with normal colour work, which more recent digital cameras tend to counteract via the in camera software.
As DSLR's generally filter out infra red they are not designed to add IR in the frame corners.
Provided lenses are used 2-3 stops down from wide open the corner optical vignetting should not be much of a problem - which probably explains why RoyBoy has, according to the link, been "lucky" Smile
Nick_w Plus
8 4.1k 99 England
21 Aug 2012 6:42AM
Len with IR it's far more pronounced with, even stopping down doesn't eliminate it (and defraction kicks in earlier), some lenses are unusable (I have a Sigma 24-70 that's very poor, it's also very poor with the big stopper).

I'm not convinced its to do with vignetting it's too regular - older lenses are often better, maybe down to lens design and/or coatings.
bmh1 Plus
9 571 1 United Kingdom
21 Aug 2012 7:31AM
I've had varying results with the Sigma 17-70 (OS/HSM version) on my IR 10D, some pictures have a very obvious hot-spot and some don't, and there doesn't seem to be any obvious combinations of aperture/zoom to use or avoid, maybe it's to something along the lines of having bright objects near the edge of the frame ?


Quote:older lenses are often better, maybe down to lens design and/or coatings

perhaps newer anti-reflective coatings are better for visible light and worse for infrared ??
Nick_w Plus
8 4.1k 99 England
21 Aug 2012 7:48PM

Quote:perhaps newer anti-reflective coatings are better for visible light and worse for infrared ??


Almost certainly the case, they are designed to minimise CA distortions in the visible light part of the spectrum.
Sooty_1 5 1.4k 214 United Kingdom
21 Aug 2012 7:57PM
IR also focusses in a different place to visible light which may be the cause of some unsharpness at wider apertures, so unless the AF module has also been converted to focus differently, you might be 'getting away with it' by using smaller apertures.

Nick

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