Avoid 2x TC on A7Riv. Too much "empty" magnification!

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Beatsy
Beatsy Contributing Member • Posts: 648
Avoid 2x TC on A7Riv. Too much "empty" magnification!
10

If you're planning to use (only) A7R4 with zooms or long primes on teleconverters, don't bother getting the 2x TC.

For pixel-level sharpness on A7Riv using a 2x TC (ignoring bayer matrix factors) a lens has to resolve the equivalent of 244 megapixels on FF! Sony claims "100-megapixel-ready" for GM lenses so clearly this is way out of spec and borne out by results. Here's a couple of 100% crops, one shot with A7Riv and a "naked" 400GM, the other with a 2x TC added. Each is the best result selected from several handheld shots. The 2x TC version isn't properly sharp anywhere - as expected from the numbers.

100% crop with 2x TC

100% crop, no TC

The 1.4x TC fares much better. When used on A7Riv it "only" requires the lens to resolve the equivalent of about 120 megapixels. This is still over the claimed capability, but not by much. Again, this is reflected in real-world results. Images taken with the 1.4x TC are acceptably sharp, though not *quite* as sharp as they are without the TC. Here's a snap taken this morning to prove the point - when viewed "original size" the inset is a 100% pixel-for-pixel crop.

1.4x TC (inset 100% when "viewed original size")

The above is all related to A7Riv only. The larger pixels of the A9 mean the issue is not so bad as the lens doesn't need to resolve anywhere near as much for pixel level sharpness on the 24MP sensor (96MP for 2x and 47MP for 1.4x). Hence why most TC users report good results on that camera.

A7Rii/iii fall somewhere between (lens needs to resolve 168MP and 82MP for 2x and 1.4x respectively). So the 2x doesn't look very good at all and the 1.4x is fine. Again - matched by real world results and reports.

Finally, a related observation. When I first used the 1.4x TC with my shiny new 400/2.8GM, I was disappointed with the results. Nothing was properly sharp. Turned out it wasn't the glass, just that I wasn't allowing for how much *more* steady my handheld technique needed to be at the longer FL. A little more concentration nailed sharp shots thereafter. I wonder if this could contribute to the apparent majority view that TCs perform poorly? If I hadn't figured out it was me at fault, I'd probably be another contributor to the "TCs are rubbish" meme now.

 Beatsy's gear list:Beatsy's gear list
Sony a7R II Sony a9 Sony a7R IV Canon MP-E 65mm f/2.5 1-5x Macro Sony Carl Zeiss Planar T* 50mm F1.4 ZA SSM +13 more
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