December 10, 2017, 11:06:03 PM

Author Topic: Review: Canon EF 85mm f/1.4L IS USM by TDP  (Read 7053 times)

mjg79

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Re: Review: Canon EF 85mm f/1.4L IS USM by TDP
« Reply #45 on: November 30, 2017, 07:03:22 AM »
Even if the focal length is exactly the same, I would still expect some variation in the appearance of out of focus elements just by the fact that each lens has different elements, even if the overall design is similar. I would expect different components to affect the image in different ways. In focus bits should come together similarly, but out of focus points would exhibit more variation.

That may not have anything to do with anything, but it seems a reasonable expectation on my part.

Different lens designs certainly give different results in this regard.

On Fred Miranda someone did a great test with the Zeiss ZE 21 2.8 compared to various Canon and Nikon zooms set at 21mm - at any given aperture the Zeiss had more depth of field which might explain why it is so loved by landscape photographers. And I don't just mean one is harsher than the other in terms of rendering, it really has a deeper depth of field.

An example the other way is the old Rollei and Contax Zeiss 35 1.4 which has an unusually shallow depth of field. Compared to other 35mm 1.4s, focusing to the same distance, the out of focus areas appear more out of focus which gives it that pseudo medium format look.

There must be some design elements or trade offs that are made and it's no surprise the designers of the 1.2 L went for a softer and more out of focus background.

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Re: Review: Canon EF 85mm f/1.4L IS USM by TDP
« Reply #45 on: November 30, 2017, 07:03:22 AM »

mb66energy

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Re: Review: Canon EF 85mm f/1.4L IS USM by TDP
« Reply #46 on: November 30, 2017, 02:39:13 PM »
An other reasen could be the effect "focus breathing". The focal lenght is defined for focusing to a distant point. At mfd, some lenses seems to be shorter...
At least that is how i understood it.

That seems a likely explanation.  The lenses were focused on the near water lily, less than 2 m away.

They have obviously different focal lengths: The 1.8 85mm has a slightly longer FL because it has slightly less field of view - it is much more confusing that the out of focus CoCs are smaller at the same f-stop ...
Assuming the f-stops are correct for infinity focus (even that is likely not always the case; perhaps it is actually f/1.95 in this case and canon rounded that down to f/1.8) and the absolute aperture does not change with focusing, the f-stop will also change with a change of the focal length.

Good idea! But if I just measure the diameter of the circles of confusion for both lenses at f/1.8 and calculate the relative area of these circles I see a difference of a factor 2 (in words TWO) - this is a whole f-stop so the EF 85 1.8 would show f/2.5 at the focus distance of 2m - not very plausible because 2m is ~ 25 times the focal length ...

The circle of confusion ratio between both images of the EF 85 1.2 are consistent with the f-stop numbers.

Some quick shots comparing EF 100 2.0 and EF 100 2.8 macro at the same f-stop settings show very similar circle of confusion sizes while beeing very different in optical construction at ~ 1m distance ...

But maybe this is the regime between pure optics and lens magics which needs 20 years of daily experience to be understood.
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Re: Review: Canon EF 85mm f/1.4L IS USM by TDP
« Reply #46 on: November 30, 2017, 02:39:13 PM »