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Sigma 10-20


frenchie44 13 341 United Kingdom
29 Nov 2016 8:32AM
I do a lot of Infrared shots, I have a query about this lens, it works perfectly with normal shots, but if I use it for IR I quite often get random colours on a few shots after using the channel swap action, this swap is used for all my IR shots, it is not a hot spot. I have taken shots in 4 directions to see if its the sun, but its just random.
I have swapped back to a canon lens and it does no appear.
You will see that there is a lot of colours that should not be there, and with another lens on the Ir camera it does not happen.
Its the same problem with the converted 40D and 50D
I can only think that maybe the coatings may have something to do with it.
the leaves in the shot were all green, no bright colours,

38419_1480407994.jpg

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29 Nov 2016 11:16AM
Dont do any IR, so cant comment, but I have this lens and like it a lot.
Niknut Plus
9 2.4k 80 United Kingdom
29 Nov 2016 4:15PM
I would say it's to do with the lens components coatings within the lens ??

Maybe there's one or two elements with very curved surfaces, which would possibly
intensify or reduce the coating effect depending on the angle of the lens' surface ??

Looking at your IR shot the Magenta colours are around the outer part of the image, with
less intensity nearer the centre ??........perhaps the Canon lenses are of a different layout
internally, with different curvatures & coatings, which don't affect the image colours as in
the Sigma lens ??????

I've got this Sigma lens, but don't shoot IR, so haven't seen this phenomenon in my pics !!

Or, I'm just barking mad anyway ???????.WinkGrin
frenchie44 13 341 United Kingdom
29 Nov 2016 5:01PM
HI
thanks for the info, I thought it might be the coatings, but the 17-50 Sigma does not have the problem. it just come into my head that it does smear the image around the Edges a little bit, so could it be that where the image at the edges are hitting an element at an angle and it is then hitting the coating at an angle. because if you look at the coatings at an angle on the front of the lens you can get several different colours, does that make sense? it difficult to put it into words.
Niknut Plus
9 2.4k 80 United Kingdom
29 Nov 2016 5:11PM

Quote:HI
thanks for the info, I thought it might be the coatings, but the 17-50 Sigma does not have the problem. it just come into my head that it does smear the image around the Edges a little bit, so could it be that where the image at the edges are hitting an element at an angle and it is then hitting the coating at an angle. because if you look at the coatings at an angle on the front of the lens you can get several different colours, does that make sense? it difficult to put it into words.



Agreed.......the 17-50 lens probably doesn't have lens components with such extreme curvatures, so the effect isn't so intensified ??.Smile


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