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After taking my Sony A7III and Sony G 70-200 f/4 telephoto to a couple of hiking and camping trips, I'm looking forward to improve my equipment to get more into wildlife photography.

So I need longer reach while keeping dimensions and wheigt as low as possible, and of course trying to get as best image quality and autofocus effectiveness as possible. It must also keep at least basic moisture and dust protection, as i'm using it in nature.

I am between selling my 70-200mm f/4 and getting a Sigma 100-400mm f/5-6.3 DG DN OS, which seems to be a rather compact and light lens, or keeping the 70-200 f/4 and buying a 2x teleconverter.

Which option will better fit my needs?

edit: other possible choices are also welcomed

This is an example of the kind of photos I want to achieve more oftenly:

enter image description here

Sony A7III 70-200mm f/4 - 1/1250 sec. f/11 ISO1000 lens length:200mm focus distance:5.82mts

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2 Answers 2

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If you use x2 teleconverter this will create you lens F8. And for this combination (camera+teleconverter+lens) camera will focus only on first photo and then will lock the focus - source (if you are in Continuous Shooting). Which can be a problem for type of photos you show.

Also when add teleconverter you decrease in some degree the sharpness of the photos (add additional glass between the object and sensor).

And teleconverter will make your Sony lens F8 so Sigma will "provide" more light to the sensor. Which will help you decrease the ISO or increase the speed (which is applicable for particular case)

So my humble opinion is to use 100-400 lens.

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  • \$\begingroup\$ For the a7Riii it is apertures smaller than f/8; for the OP's a7iii it is apertures smaller than f/11 (due to diffraction limiting)... and it is the selected aperture that is the issue (i.e. continuous focus is done at the stopped down exposure aperture). \$\endgroup\$
    – Steven Kersting
    Dec 28, 2021 at 14:29
  • \$\begingroup\$ Just because the TC degrades the image quality of the 70-200mm a bit doesn't necessarily mean the 70-200mm + TC isn't still better than the Sigma 100-400mm. The Sony 70-200mm f/4 G is certainly a fairly superior lens when compared straight up with the Sigma 100-400mm f/5-6.3 C. \$\endgroup\$
    – Michael C
    Dec 29, 2021 at 15:16
  • \$\begingroup\$ @MichaelC, you are right if we talk about TC 1.4, but when it come to TC 2.0 the things escalate. The reviews i read about this TC are not so positive... \$\endgroup\$
    – Romeo Ninov
    Dec 29, 2021 at 15:42
  • \$\begingroup\$ There are two generations of Sigma TCs. The first generation 2X was horrible. The more recent newer one, though, seems to be much better. \$\endgroup\$
    – Michael C
    Dec 29, 2021 at 15:45
  • \$\begingroup\$ @MichaelC, what I see on test photos the quality of Sony is not so much better than Sigma: the-digital-picture.com/Reviews/… \$\endgroup\$
    – Romeo Ninov
    Dec 29, 2021 at 15:54
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In general, when you add optical elements that were not part of the original optical lens formula (i.e. TC's) it will have a negative impact on image quality. Quite often this shows up as a significant increase in chromatic aberrations in difficult light situations, also affecting bokeh, and adding a TC always reduces the maximum lens resolution possible (but may not be noticable).

Additionally, the difference between f/8 and f/6.3 is ~ 2/3 stop of light which will affect autofocus on a mirrorless body in lower light/backlight scenarios. It can also be significant in exposure (ISO noise).

I would say that it is very unlikely you will be any better off adding a TC to the Sony G lens... but IDK those two lenses specifically (nor the Sony 2x) so I can't actually say definitively (the Sony would have to be waaay better than the Sigma to start out).

Also not that adding a TC and using a longer telephoto lens is essentially the same thing, and both inherently reduce the maximum lens resolution capability... unless the sensor is the limiting factor there may not be a significant difference compared to cropping in post.

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  • \$\begingroup\$ Adding TC may reduce also the sharpness of resulting image (beside other things) \$\endgroup\$
    – Romeo Ninov
    Dec 28, 2021 at 15:04
  • \$\begingroup\$ @RomeoNinov, yes... a loss of resolution is also a loss of sharpness (or rather, it is increased magnification/enlargement of the same sharpness). \$\endgroup\$
    – Steven Kersting
    Dec 28, 2021 at 16:15
  • \$\begingroup\$ Well... The Sony 70-200mm f/4 G is certainly a fairly superior lens when compared straight up with the Sigma 100-400mm f/5-6.3 C. The first generation Sigma TCs were pretty bad, but the newer ones are supposed to be much better. \$\endgroup\$
    – Michael C
    Dec 29, 2021 at 15:18

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