[gazonk]

Filter size might almost equal focal length!

That’s hard to avoid when largest aperture is 1.4!
Although the FA* has a filter size of only 67 mm (which seems as close to the physical minimum as possible).

[ffking]

I'm so glad* I don't really do portraits - that 85 looks seriously sweet - and they're no going to make it orse than the previous one, which is very nice optically.



*glad as it ill be had enoigh resisting it even when I don't need it

[reh321]

That’s hard to avoid when largest aperture is 1.4!
Although the FA* has a filter size of only 67 mm (which seems as close to the physical minimum as possible).

My Super Takumar 50mm f/1.4 has a filter size of 49mm, much smaller than the "Fat Fifty" - but it had different design objectives.

[gazonk]

My Super Takumar 50mm f/1.4 has a filter size of 49mm, much smaller than the "Fat Fifty" - but it had different design objectives.

Sure, but I was commenting on the 85mm. 49mm filter size for a 50mm is actually very close to the focal length :-)

[zapp]

Most probably. For instance the Sigma 85mm f/1.4 DG HSM | Art takes 82mm filters.

82 mm Diameter is the limit for 100x100 filters.

[RonHendriks1966]

That’s hard to avoid when largest aperture is 1.4!
Although the FA* has a filter size of only 67 mm (which seems as close to the physical minimum as possible).

anyone knowing how to calculate that?

[TwoUptons]

anyone knowing how to calculate that?

Using the Wikipedia definition of f-number as a diameter ratio, it would allow just under 61mm ignoring the physical realities of actually building something...

That’s also assuming none of the elements are larger than that for some other reason (like on the DFA 50)...

-Eric

[Kharan]

anyone knowing how to calculate that?

The entrance pupil of a lens needs to be at least (focal_length)/(maximum_f-number) to realize the desired aperture. For example, a 200mm f/2 lens can't have a front element smaller than 100mm in diameter, or else it won't count as a real f/2 lens.
Nowadays, the very ambitious design goals set for lenses means that their diameters have outgrown this simple calculation. In some cases (Sigma ARTs, most famously, but also the Zeiss Otus line) this is done to project an image circle larger than necessary, leaving the garbage edges out of the frame completely. In other cases it's done to allow the designers extra leeway in the optical design, incorporating more aggressive corrective elements that would normally just cause hard vignetting in a narrower optical pathway.

[Ontarian50]

Using the Wikipedia definition of f-number as a diameter ratio, it would allow just under 61mm ignoring the physical realities of actually building something...

That’s also assuming none of the elements are larger than that for some other reason (like on the DFA 50)...

-Eric

Sounds right. Nikon's old manual focus 85mm 1.4 had a 72mm filter size, and it had a trim ring inside the filter mount. And the Zeiss 85mm 1.4 Planar was wonderfully compact (and sharp) with just a 67mm filter.

[biz-engineer]

82 mm Diameter is the limit for 100x100 filters.

I've never had to use a 6 stops ND grad for a portrait.

[robbiec]

OT for the filter size chat going on but the knock up is nice, want one, will get one Patience is a virtue so they say.

[acoufap]

82 mm Diameter is the limit for 100x100 filters.

With the exception of the Irix filter holder Edge IFH-100 - 86 and 95mm possible.

[repaap]

I’d say that it would be a miracle if that thing is less than 82 mm diameter. I was just looking at my Sigma 85/1,4 and just by holding it out, it can’t be smaller that that.but perhaps it is just couple mm larger. My sigma will be at ’for sale’ thread when this thing will hit shelves and reviews are great(like DFA*50). But, Sigma EX HSM, is optically quite good. For what it is, it is also quite good prize ratio. I have DFA*70-200 so I’m quite confidet that this 85 is gonna be amazing. what ever is going on at lens designers laboratory, seems to be working.

[beholder3]

In other cases it's done to allow the designers extra leeway in the optical design, incorporating more aggressive corrective elements that would normally just cause hard vignetting in a narrower optical pathway.

Correct. The closer you are to the theoretical minimum of 85/1.4= 61mm the stronger the vignetting will be inevitably. Sadly it does not work the other way around (large diamater is no guarantee for low vignetting).
Pentax with the DFA* 50 has already shown that they can design a fast lens with very good low vignetting.

And let us not forget that vignetting also comes in the form of "cats eyes" bokeh highlights.

Lastly let us not forget that vignetting effectively changes DoF around the image (small cats eyes mean more DoF).

There is a price you pay for everything.

[repaap]

OT for the filter size chat going on but the knock up is nice, want one, will get one Patience is a virtue so they say.

it sure is, and with Pentax you have to be patient, that makes us virtues. Thing what most wont get