DavidBM
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 p.3 #17 · Infrared and alt lenses (on A7) | |
timballic wrote:
Just in case someone might be interested:
I compared the OM Z 100/2.8 mc with my single coated Nikon E 100/2.8 Both lenses about equally good in colour
Just as with the OM Z 24mm mc:sc comparison earlier, the single coated Nikon E (right) is so much clearer in IR than the multi coated OM (Comparison below of 1:1 enlargements,in Lr5, no adjustments applied, from centre of pics, both F/8)
https://c5.staticflickr.com/6/5507/30696641476_37d86b5f7c_h.jpgUntitled by Timothy Ball, on Flickr
I've repeated this with the OM Z 21/3.5 mc : sc (I may get round to posting the comparison), and the result just confirms the above and those with the 24mm OMs earlier. The multi coating really does mess up the IR performance in a big way!
Stick to the earlier, single coated, OM Zs and the Nik E range
I can vouch for the Silver nose, single coated OM Z 21/3.5, 24/2.8. 28/3.5 and 50/1.8, as all being excellent performers in IR, the 35/2.8 isn't as good, but the Nik E 35/2.5 has a very good IR reputation, (from diglloyd no less)
I'm now looking for an OM Z silver nose version of the 85/2, as I find the 50mm:100mm jump a bit wide. I know the later mc version was a redesign and better, but I think the multi coating will offset that.
I'v decided to continue my report on the Kolari Modded IR A7 on a new thread, as it's much more specifically about the difference with the Kolari IR thin filter mod, than about the lenses....Show more →
Looking at your samples I'm even less sure than I was that what I'm about to suggest is the right explanation, but thanks Tim, really interesting comparison.
But I wonder if the sharpness effect is just one about focus offset in the IR being different? I know that the IR focus offset markings on lenses are rarely accurate, I need to calibrate lenses. And the difference can be very large.
I wonder if the MC versions are just focussing at a different point, and once you test what it is and work out a custom offset if all will be well. Not at all sure it’s right, but worth investigating if you haven’t already. I will post this at FM as well in case you don’t get notified here.
The hot spotting is not a surprise, I guess we know that often more recent coatings contribute to that (though someone I though trustworthy was vouching for all versions of the 24).
Personally I’m hoping it won’t matter for me: I’m using Ilford SFX film, which is really mainly responsive to to low frequency red and only the highest frequency IR, so it may not matter compared to true IR film (which you can’t get) or IR modified digital sensors.
EDIT: OOPS my hypothesis can be safely ignored. I had forgotten you are using digital, so you can actually focus the image, and you aren't relying on focusing in visible light, whacking on the filter and guessing the offset like us film IR types...
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