Reasons why no Nikon 85mm f1.2?

Started Apr 11, 2013 | Discussions thread
Grevture
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Re: Not convincing - nt
In reply to whoosh1, Apr 12, 2013

whoosh1 wrote:

clarnibass wrote:

Maybe... but it is very clear from that photo that the rear lens in Canon's version is bigger than the Nikon mount and would be impossible. Whether Nikon can make an f/1.2 lens with a significantly different design that would use a samller rear lens, or whether it's even possible (maybe 85mm f/1.2 simply requires this size of lens), I have no idea.

I agree as sees from the photo that the design of Canon 85mm f/1.2 has a wider rear element than the Nikon 85mm f/1.4D - but similar to what you said none of us here on this forum have any idea whether it would be possible to have a different 85mm f/1.2 lens design where you have a smaller rear element that would fit in Nikon F mount. However I see assertions by forum members as if they were a gospel - that the Nikon mount is too small for 85mm f/1.2

Some actually have an idea

Look, this "why is there no Nikon 85/1.2 discussion" has a tendency to pop up here at least every six months or so, and has done so for many years. The issue has been discussed in length many times, and some very knowledgeable people has been involved from time to time. And yes, the rear diameter of extremely fast lenses really is an issue. A big issue (pun intended).

To be very exact, it very likely can be done - technically speaking. But from a "what makes sense" perspective, it cannot without getting and extremely expensive design. What is meant by the statement "Nikon can't make a 85/1.2 for the F mount" more precisely means "Nikon can't make a 85/1.2 for the F mount that any customer outside military entities and well funded science organisations could afford". Technically you can build almost any optical design, but what is the point of building something so horribly expensive nobody could buy it?

It is not just an internet myth.

or an autofocus f/1.2 lens of any focal length.

Nikon can however do for example a 50-60 mm lens with 1.2 without much trouble (and has done several such lenses). I do not think AF has very much to do with it - the focusing elements are most often not the rearmost ones anyway.

Similarly I don't know why the mount size does not matter for an 600mm f/4 lens (which should have 150mm aperture much larger than the mount size) and the larger aperture can be achieved with a larger front element for that lens - while the mount size matters for 85mm f/1.2 lens (70.83 mm aperture size) and the big aperture cannot be achieved using a larger front element.

Not wanting to be rude, but I think you might want to read a little about lens design

To make an over-simplistic explanation: When you calculate the aperture size, it is the diameter looking from the front end that matters (where the opening indeed is about 150 mm in a 600/4). This is what is often referred to as the "entrance pupil" in optical discussions. But after the aperture you can quite easily shrink the optical path using the built in teleconverter already in place to keep the size down (or also the other way around, like with the Metabones Speedboaster).

The irony is that it probably could be easier to build a very fast longer lens then a 85 without getting a overly complex lens design - because by virtue of the longer focal length you have more optical path to play with.

From the picture (linked by Grevture) I would think that Canon took advantage of the larger mount size for their 85mm f/1.2 design - but if Nikon were to design it they would design differently taking their own mount size into consideration. I have not checked side-by-side but from the dpreview review of Nikon 70-200 f/2.8 VR II where they show the Nikon next to the Canon - it seems to me that the Canon 70-200 f/2.8 rear element is wider but the Nikon lens is longer. May be that is related to the mount size or may be it is just a different design - but definitely different dimensions (longer/narrower vs wider/shorter). I fail to understand why similar difference in dimensions cannot be present for 85mm f/1.2 if Nikon were to decide to make one.

The real clue in that image is the fact that Canon had to put their electrical contacts inside the rearmost lens element - they would not have done that unless they really, really, desperately needed that large diameter to make it work optically. So even the wider EF mount is problematic for a 85/1.2 lens. The F narrower mount is even more problematic.

OK - peace - if folks want to believe Nikon mount is too narrow for f/1.2 lens - that's fine with me. However I find that assertion unsubstantiated and unconvincing.

Again, it is in reality not a matter of what can technically be achieved, but what can reasonably be achieved in a design who can be sold at a attainable price and at the same time produce a good image quality. Nikon probably could make also a affordable 85/1.2 - if they let the image quality slip. Or, Nikon could make a 85/1.2 that had good image quality - if they let the price slip. But who would want a crappy 85/1.2 or one that is frightfully expensive?

And the bigger issue here - for what reason? That 1/3 extra stop has almost no meaningful photographic purpose which make such a lens a bit of a non-starter anyway. Canon did it for marketing purposes and bragging rights. Nikon has wisely stayed out of that.

Look at the re-occurring 85/1.8 vs 85/1.4 discussions - where many point out the f1.8 version in practical terms deliver something like 90-95% of the usable performance of the f1.4 version at a fraction of the price. For some, the difference still is worth the money. But considering how expensive (and cumbersome, and slow focusing) a f1.2 version would be, and that it probably would deliver almost no discernible practical image quality advantage at all - it is practically pointless commercially speaking.

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