Infrared Conversion: 4/3 micro vs. Crop vs. FF sensor?

Started 3 months ago | Questions thread
OP nkistrup Senior Member • Posts: 2,488
Re: Tamron 28-200mm f2.8-5.6 Di III RXD - infrared hotspots?

Blueskyimages wrote:

Hi nkistrup

I would really appreciate if you expand on your comment:

“Sony E mount: Know that the Tamron 70-180 & 28-200 play very nice w. IR. And the 17-28 & 28-75 probably do.”

Had a Sony a6300 w. a Full Spectrum conversion, and tested numerous lenses, and most failed my testing.  The Sigma 18-35 f1.8 slipped through that testing, but showed hot spots in my vacation photos.  Sold it, and clamped down very hard on my testing procedures.  And that's when I tested the Tamron 70-180 & 28-200.

Both came out stellar, with no hot spot through f22.  (Beyond f22, who cares.  And given that diffraction is worse w. Infrared, should be shooting beyond f16.)  The converted a6300 died during lens testing weeks later, but was impressed w. the 2 Tamrons.

Tamron 28-75: Never actually tested this because of bad IR performance reports, but Life Pixel tech support kept badgering me to try it.  Turned out that Tamron made changes to the later copies of it, that eliminated the IR hot spot problems.  But got around to testing ... eventually I would have, since I was keen on the Tamron 70-180, and this would have been a nice complementary lens.

Based on the above, and one or two reports that the 17-28 is hot spot free, think it's worth renting to see if it is a good IR performer.

NOTE: ALL of my testing was done either at 830nm or 850mm.  You should have better luck at 720nm.

I’m interested in the Tamron 28-200mm f2.8-5.6 Di III RXD on converted Sony cameras with 665 and 720nm. Is the lens clear of hotspots to at least f8 (ideally f11) in false colour - and is that all focal lengths. Haven’t found any other mention of IR performance.

Anyone else tried this one in IR?

FWIW - just got hols of a Sony 200-600 and initial tests suggests it has no hotspot up to f8 right across the range - and then very mild from f11 onwards - which is surprising, I didn’t expect that.

All of the above, especially my tests w. the 28-200, lead me to order a brand new Sony A7 iii with a 830nm IR conversion.  Initially, I'll test the Sony 12-24 f4 & Tamron 17-28 f2.8, to see IF & WHAT my ultrawide options are.

No matter what, buying the 28-200.  IF it has hot spots, only means I bought a bad copy & need to exchange it.

In visible light, liked the 28-200, but didn't love the way some people did.  But for pure IR use, it's a winner.

For IR, renting is paramount.  Have 4 lenses for my a6400, and all of them suck in IR.


 nkistrup's gear list:nkistrup's gear list
Olympus XZ-1 Nikon D7100 Sony a7 III Sony a6400 Nikon AF-S DX Nikkor 17-55mm f/2.8G ED-IF +10 more
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