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07-29-2016, 12:37 PM   #1
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50mm f1.2 autofocus lens

Is there a reason why a 50mm f1.2 has never been produced as an autofocus lens, even though Pentax produced the A 50mm f1.2 manual focus lens?

07-29-2016, 12:43 PM   #2
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Read some reviews of the Canon 50mm f/1.2 L.
07-29-2016, 01:27 PM   #3
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At f1.2 and 50mm the DoF is so shallow that the AF module struggles. And even if it gets it right, you move the camera by 2mm before taking the shot, and the focus is already wrong! F1.2 lenses are very niche and difficult to work.
And yes, there is a difference between f1.4 and f1.2. I remember reading somewhere that DSLRs are optimized for 2.8 lenses, and everything faster can show you the wrong DoF in the viewfinder (focusing screen is not made for ultra fast lenses) and risk misfocusing. F1.8 already requires some skills, and f1.4 even more.

tl;dr: a) DoF is shallow, difficult to work with, b) AF will have trouble nailing it at that shallow DoF, c) f1.2 lens would be very expensive d) besides technology, AF also requires some skill, and at f1.2 you need quite a bit of it.
All of these come together and say "too much work, not enough return profit"

Last edited by Na Horuk; 07-29-2016 at 02:22 PM.
07-29-2016, 02:50 PM   #4
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Thanks for the replies, I doubt if I could ever afford such a lens but I was curious given there was a manual focus version back in the analog days and so many new zooms seem to be coming out with wider than before apertures

07-29-2016, 03:59 PM   #5
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QuoteOriginally posted by Na Horuk Quote
I remember reading somewhere that DSLRs are optimized for 2.8 lenses
...well, something like that...

Most AF points on PDAF systems have a focus sensitivity of f/5.6, meaning that the ability to detect an out-of-focus condition is the same at f/5.6 as at wider apertures. Higher end models often have one or more AF points with a focus sensitivity of f/2.8 and are more appropriate for use with fast lenses. On the K-3/K-3II and K-1 those points are in the center column. In practice, accuracy with fast lenses is fine. What suffers is precision, i.e. how broadly the attained focus is scattered around the desired point-of-focus on multiple attempts. Missed focus becomes more common than not.

That is why PDAF sort of sucks for fine focus with fast lenses.


Steve

Last edited by stevebrot; 07-29-2016 at 04:28 PM.
07-29-2016, 05:19 PM   #6
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Canon use to make an AF 50 1.0
07-29-2016, 08:50 PM   #7
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I think that Canon only made the 1.0 lens so that they could claim that their cameras worked in one stop dimmer light than Nikon Cameras. The advertisements had a small disclaimer that said "with 50mm f/1.0 lens, not yet available".
07-30-2016, 07:43 AM   #8
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It is an expensive and super niche item for a brand (Pentax) which is already niche. I imagine the size of the market is so small that it just isnt cost effective to cater to the demand.

07-30-2016, 10:13 AM   #9
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QuoteOriginally posted by boriscleto Quote
Read some reviews of the Canon 50mm f/1.2 L.
they even make a great 85mm f1.2 with shallower dof ^^
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