Is a *fast focusing* 20mm f1.7 pancake feasible?

correos.e

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I loved my panasonic 20mm pancake - image quality and size. However, i sold it because of its awful low light focusing speed. I shoot my kids playing indoors and it just didnt work out. Oly 17 mm f1.8 fits the bill.
But it's so much larger... I know there is a technical reason that makes the 20mm slow, my question is, is that the same reason that makes it small? Is it possible to have oly 17mm speed in a pamy 20mm size? I know the 17mm f2.8 and the 14mm... I'm asking about fast lenses, say, below f2
Thanks!
 

Jonathan F/2

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I loved my panasonic 20mm pancake - image quality and size. However, i sold it because of its awful low light focusing speed. I shoot my kids playing indoors and it just didnt work out. Oly 17 mm f1.8 fits the bill.
But it's so much larger... I know there is a technical reason that makes the 20mm slow, my question is, is that the same reason that makes it small? Is it possible to have oly 17mm speed in a pamy 20mm size? I know the 17mm f2.8 and the 14mm... I'm asking about fast lenses, say, below f2
Thanks!
I'm sure Panasonic can make it small and fast, but they'd rather you buy the upcoming Panasonic Leica 15mm 1.7 or the PL 25mm 1.4.
 
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To make it one of the faster focusing lenses the 20mm would need an internal focusing design rather than the current unit focusing design (where the whole lens group moves to focus rather than a couple of lightweight elements). That means a fundamental redesign of the lens would be required.
 

correos.e

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Thanks penguin. I understand it would be a major redesign. My question is: does the current unit focusing design contribute to the smaller size and the internal design would make it larger, or can we technically have a very small internal design?
Thanks!
 

duke

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The panasonic 14mm f2.5 is tiny and incorporates an internal focusing mechanism, so it can be done, just probably wont for a while :(
 

MAubrey

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Thanks penguin. I understand it would be a major redesign. My question is: does the current unit focusing design contribute to the smaller size and the internal design would make it larger, or can we technically have a very small internal design?
Thanks!
Probably? Without an optical designer we cannot say for sure, but the testament of the 17mm f/1.8 and the forthcoming 15mm f/1.7 suggest that it would be larger.

Minimally, you need to incorporate extra space inside the lens for focusing. You can see the space difference between the 17mm f/1.8 and the 20mm f/1.7:

20mm
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17mm
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That group of three elements in the back are the focusing group (the two asphericals and one other just before the final rear element). Internal focusing also requires more lens elements for the focusing group (and correcting the focusing group) as well, which would also contribute space--and even after those corrections, then the 20mm is still sharper. The kind of focusing in the 20mm where you move the entire lens forward and back, is extremely effective for resolution in a compact size, but not great for speed.
 

usayit

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Anything is possible with time and cost.

I am kinda hoping they leave it as is.... let the R&D costs recup and lower the price. Then maybe those that complain that MFT stuff is too expensive will stop.
 

Steven

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I've been asking that question for a long time . Based on the fact that newer lenses from both companies, like 17/1.8 and 15/1.7 are larger , I am guessing it is not possible :(
 

klee

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In my experience the 20mm's focusing motor is controlled more smoothly and quickly by panasonic bodies already.
the GH4K's new "depth of defocus" algorithm may actually improve the focus speed even more.

I don't know why Olympus hasn't bothered to make any fast aperture pancakes.
 

DekHog

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As Duke stated above, they managed it fine with the 14mm, so I can't see a reason why they couldn't do it with the 20mm with a redesign .... that doesn't mean they will. I think they would have done it before now if they were going to.

It's a very sharp little lens, but is the one I pick up less than any other due to the focus speed.
 

Steven

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I am guessing that wider angle lenses like 14mm can be kept shorter. Also , it is significantly slower aperture than 1.7.
As Duke stated above, they managed it fine with the 14mm, so I can't see a reason why they couldn't do it with the 20mm with a redesign .... that doesn't mean they will. I think they would have done it before now if they were going to.

It's a very sharp little lens, but is the one I pick up less than any other due to the focus speed.
 

MAubrey

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As Duke stated above, they managed it fine with the 14mm, so I can't see a reason why they couldn't do it with the 20mm with a redesign .... that doesn't mean they will. I think they would have done it before now if they were going to.
If we look hard enough we can see a number of reasons why.

The 14mm is only 14mm and only f/2.5. That means it only needs a entrance pupil of 5.6mm, while the 20mm f/1.7 requires 11.7mm, more than twice as large. The 14mm has the space for internal focusing because of those super tiny elements. The 20mm simply doesn't have that luxury. The 14mm also sacrifices some sharpness, too. It's nowhere near as sharp as the 20mm.
 

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