Variable Aperture Lenses

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Ltgk20

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It's farily often that I'll see a comment on this forum or others about not liking variable aperture lenses. Based on my experience and what I've read, years ago the lower cost lenses were variable aperture and so variable aperture typically went with less sharpness, slower focusing, etc. I also think that lens design and fabrication technology wasn't what it is today. However, in the last few years I'm not sure I understand the aversion to them. Certainly a variable aperture lens may be a bit slower at the long end, but very often the variable aperture lens will be lighter, smaller, and/or lower cost than the fixed. Additionally, there are many newer variable aperture lenses which are very sharp (often requiring significant pixel peeping and side by side comparison to tell the difference between even the $10k plus super-telephotos). The Sony 100-400 and 200-600, the Tamron 35-150 f2-2.8, the Canon 100-500, the Nikon 100-400 are all very sharp and many of them take a 1.4TC quite well also.

It seems to me that wanting a faster lens may be a valid reason to avoid variable aperture, but I'm not sure sharpness is so much any more. What am I missing?
 
Have to agree with you. A quality lens on a budget, but with a couple of compromises in IQ.
 
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It's an interesting point, but I think we don't have enough current generation samples to really know. I haven't yet seen even a modern variable aperture zoom be reviewed as 'as sharp as a prime'. I have seen reviews of the Nikon (F-mount) 100-300 f2.8 and 180-400 f4 being as sharp (on in the case of the 100-300 actually sharper) as the primes in that range. I have seen some claims that the NIkon 100-400 f4.5-f.5.6 is as sharp as the 500 PF, but that's a bit of a special case, and I haven't seen creditable full reviews that support that yet. Agreed that variable aperture zooms have made strides, but I think the book is still open on how far :)
 
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i think there's two general objections. 1) the point you made about variable aperture lens typically not being as good which, as you point out, isn't a great actual predictor. 2) some folks will want to maintain the same aperture over the zoom range for <reasons>. maybe dof. maybe to maintain exposure. in those cases there are typically ways to deal with it, for example, just choosing an aperture that can be maintained across the zoom range.
 
Somewhere in my camera menu there is a choice of whether to maintain exposure as the aperture changes, and whether to use ISO or shutter speed. Never really paid attention to it to know the details.

Found it for R5 (Tv is shutter speed in Canonspeak):

C.Fn2​

Same expo. for new aperture

The maximum aperture value may decrease (the lowest f/number may increase) in [
Manual exposure
] mode (manual exposure shooting) with ISO speed set manually (except when set to ISO Auto) if you (1) Change lenses, (2) Attach an extender, or (3) Use a zoom lens with a variable maximum aperture value. This function prevents the corresponding underexposure by adjusting ISO speed or shutter speed (Tv value) automatically to maintain the same exposure as before (1), (2), or (3).

With [ISO speed/Shutter speed], the ISO speed is automatically adjusted within the ISO speed range. If exposure cannot be maintained by adjusting ISO speed, shutter speed (Tv value) is automatically adjusted.

  • OFF: Disable
  • ISO: ISO speed
  • ISO/Tv: ISO speed/Shutter speed
  • Tv: Shutter speed
 
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I doubt you will find many reviews directly comparing variable aperture zooms and primes., it would be an apples/oranges thing. I have the 100-400 f/4.5-5.6 S and the 400 TC 2.8. Even comparing 400 at 5.6 on one and 2.8 on the other, the prime lens is noticeably sharper. This is also true comparing both at f/5.6 BUT most reviewers have noted that the 100-400 is less sharp from 350 to 400 mm. At 200 mm the zoom is amazingly sharp, as sharp as my 70-200 f/2.8 fixed aperture zoom. All of these lenses are more than sharp enough for any reasonable print requirements. The main difference for me is maximum aperture. 200 mm at f/2.8 compared to f/5 is a big difference in low light capability. 400 mm at f/2.8 compared to f/2.8 is a night and day (I couldn't resist) difference. Nikon's S lenses are all very sharp over most of their range but image quality also depends on noise and dynamic range. The slower, variable aperture zooms lose out a little here but to be honest, I find the 100-400 zoom on my camera more often than the 400 TC. I am quite happy with the IQ it produces.
 
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