Reasons why no Nikon 85mm f1.2?

Started Apr 11, 2013 | Discussions
Leonard Migliore
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Re: Reasons why no Nikon 85mm f1.2?
In reply to Michael Benveniste, Apr 13, 2013

Michael Benveniste wrote:

I don't know if any f/1.2 AF lens is feasible in Nikon mount, but I'm more uncertain that an 85mm f/1.2 would be less feasible than a 50mm f/1.2.  The "front focal length" determines the minimum needed size of the front element group, but when it comes to the rear element size the back focal length is of vastly more importance.  That's in part why rangefinder cameras have smaller lenses than SLR's.

Well, if you can do a 50mm f/1.2 you can do an 85mm f/1.2. Conceptually, think of putting a 1.7X teleconverter in front of a 50. What do you have?

In terms of the design, you have to put the pupil back at that 38mm distance. But, as you noted, there just isn't enough diameter to maintain f/1.2 in the corners of the sensor, which probably wouldn't pick up much light at that angle anyway.

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Photo Thoughts
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Re: Reasons why no Nikon 85mm f1.2?
In reply to Leonard Migliore, Apr 13, 2013

You'd have an 85mm, but not f/1.2.

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brightcolours
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Re: Reasons why no Nikon 85mm f1.2?
In reply to Photo Thoughts, Apr 13, 2013

Photo Thoughts wrote:

You'd have an 85mm, but not f/1.2.

Indeed, one would have to think the other way around, like a metabones speed booster. But then it only would be suable on APS-C anyway, not FF.

It would be kinda like this: a 127mm f1.8 lens, with enough space between the back element and the mount to fit a 0.666667x wide angle converter behind it. This would result in a 85mm f1.2, but with enough vignetting to be a "DX" (APS-C) only lens. Another problem will be that a 127mm f1.8 lens already will have a very big back element, maybe too big to work with the narrow F-mount. To overcome the DX-onlyness one would have to make many elements including the front ones oversized too.

I happen to have a 140mm f1.8 lens, which has enough clearance for a 0.6667x WC behind it. However, it is a very simple undercorrected design, without internal focus, without variable aperture (without anything making it suitable for 85mm f1.2 DSLR operation, actually). It is a 35-70mm film projector lens. To have it upto modern photography standards the design would have to be much more complex.

Another "possibility" would be to take a lens like a 200mm f2.8 lens and put a 0.425x wide angle converter behind it. Problems will be that a very high quality 0.425x wide angle converter will be very expensive, and that again you will have to oversize most elements of that 200mm design a lot to prevent it from being APS-C only.

For a reasonable lens design the bottleneck still remains the limited diameter of the F-mount.

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Hugowolf
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Re: Not convincing - nt
In reply to cosmicnode, Apr 14, 2013

cosmicnode wrote:

whoosh1 wrote:

Think this is an internet myth.

Grevture wrote:

whoosh1 wrote:

Other than hearsay.

Leonard Migliore wrote:

The mount's not big enough.

There's a discussion here about putting a CPU chip on a 50mm f/1.2 AI-S Nikkor and it was noted that you have to grind a piece off the rear element to get space for the contacts.

Take a look at this image and see how hard it is even with the wider EF mount ...

The rearmost lens element is so large the contacts has to invade into it.

It look's almost as if the rear elements on both lenses are flat. could this be only a protective rear filter which would not actually be the required rear element diameter ?.

A lens doesn't have to be curved on both faces. Lenses can be plano-concave or plano-convex as is the rear element of the Canon  85 f/1.2L.

Have a look at the block diagram for the Canon:
http://www.canon.com/camera-museum/camera/lens/ef/data/standard/2006_ef_85_f1.2lII_usm.html?p=2

But yes, the Nikon f.1.4 does seem to have flat glass at the rear:
http://www.nikonusa.com/en/Nikon-Products/Product/Camera-Lenses/1933/AF-NIKKOR-85mm-f%252F1.4D-IF.html#lightbox/media=/Misc/lo_1933_AF-NIKKOR-85mm-f-1.4D_Construction.jpg

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brightcolours
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No, they do not have "a protective filter"
In reply to cosmicnode, Apr 14, 2013

cosmicnode wrote:

whoosh1 wrote:

Think this is an internet myth.

Grevture wrote:

whoosh1 wrote:

Other than hearsay.

Leonard Migliore wrote:

The mount's not big enough.

There's a discussion here about putting a CPU chip on a 50mm f/1.2 AI-S Nikkor and it was noted that you have to grind a piece off the rear element to get space for the contacts.

Take a look at this image and see how hard it is even with the wider EF mount ...

The rearmost lens element is so large the contacts has to invade into it.

It look's almost as if the rear elements on both lenses are flat. could this be only a protective rear filter which would not actually be the required rear element diameter ?

Neither the 85mm f1.4 D nor the 85mm f1.4 G (AF-S) have a flat slab of glass, bot have a real optical element at the back. So does the Canon 85mm f1.2 L USM (II).

. Nikon has been known to add protective front filters as part of the optical formula of long lenses and the slip in filters are required at all times, effectively the last element. Lenses such as the 300f2.8 and 200-400f4 have these features. Just a thought, I know as much about lens design as most people here.

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Leonard Migliore
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Re: Reasons why no Nikon 85mm f1.2?
In reply to Photo Thoughts, Apr 14, 2013

Photo Thoughts wrote:

You'd have an 85mm, but not f/1.2.

Yes you would. Note that I said the teleconverter goes in front of the 50mm f/1.2. The configuration of such a converter is a 1.7X afocal telescope; such devices do not affect the f/stop of the system. Teleconverters that go between the lens and the sensor do, indeed, affect the f/stop.

My comment was only for conceptual purposes to show that if you can make a 50mm f/1.2 you can make an f/1.2 at any focal length. A hypothetical 85mm f/1.2 would be designed so that the exit pupil was 38mm from the sensor because that's where you can make it the largest (diameter of 32mm).

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whoosh1
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Re: Didn't anyone tell you f/1.2 not possible for CX mount? -nt
In reply to Grevture, Apr 17, 2013

Maybe, just maybe, it is because the CX mount have a significantly more design friendly diameter-to-sensor-size ratio?

As many has noted over the years since the 1 cameras were first introduced, the CX mount is very, very large in proportion to the sensor size.

This makes sense.

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CFynn
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Re: Reasons why no Nikon 85mm f1.2?
In reply to str8pipe, Apr 18, 2013

str8pipe wrote:

Is there technical reasons why Nikon doesn't produce this lens?

Is there any good reason, other than to match Canon, why they should?

The extra 1/3-1/2 stop is very little gain for what (if feasible) would be a large heavy and expensive lens.

Optically it would be no better than an 85mm 1.4 lens - and might be worse.

The only thing you gain is size, weight, expense, about 1/3 stop of light and a bit narrower DOF.

Does anyone need DOF that narrow? - and with today's high iso sensors how many need that extra 1/3 stop?

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Grevture
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Agree, and ...
In reply to CFynn, Apr 18, 2013

CFynn wrote:

str8pipe wrote:

Is there technical reasons why Nikon doesn't produce this lens?

Is there any good reason, other than to match Canon, why they should?

The only reasons I can think of is purely PR and marketing related

The extra 1/3-1/2 stop is very little gain for what (if feasible) would be a large heavy and expensive lens.

Optically it would be no better than an 85mm 1.4 lens - and might be worse.

The only thing you gain is size, weight, expense, about 1/3 stop of light and a bit narrower DOF.

Actually, to add insult to injury, in practice you gain almost no light at all

Does anyone need DOF that narrow? - and with today's high iso sensors how many need that extra 1/3 stop?

I agree with your sentiment. Particularly since the difference in DOF is neglible, and the difference in light is even smaller ...

I can see Nikon make some sort of "luxury 50 mm" which would line up nicely with the AF-S 24/1.4, the AF-S 35/1.4 and the AF-S 85/1.4, and which for marketing reasons alone could be a 1.2 instead of 1.4. There would be almost no technical reason, but it would make the difference to the current AF-S 50/1.4 more obvious and provide with some marketing related bragging rights as a added bonus.

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