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 p.1 #1 · 105 MC review by LensTip: several technical considerations they ignored | |
LensTip has recently published the 105 MC review.
As usual, their image resolution data refer to one focusing distance (I guess infinity or so), so we have no information on how good the lens is across the focusing distance range, and how it compares in close-ups to the lenses they used for comparison (90/2.8 by Tamron and Laowa).
Anyway, what surprised me was their final evaluation of focus breathing, classified as "monstrous".
They continue to forget that the angle of view (AoV) is mathematically related to the actual focal length, F, the magnification (or reproduction ratio, R), and pupil magnification, P (the ratio of the diameter of the exit pupil to the diameter of the entrance pupil of an optical system):
where x is the diagonal of the sensor/film.
Therefore, driven by curiosity, I checked the data available in photonstophotos.net, "Optical Bench" interactive section of the website.
I selected three macro lenses (MC 105, AF-S Micro-Nikkor 105/2.8G VR and the Canon RF 100/2.8 macro IS USM) and I plotted first their focal length change vs magnification:
We see that all considered macro lenses shorten their FL going from infinity (R = 0) to life size (1:1; I didn't include in the plot the 100 RF data in the 1-1.5X range). This is obviously a consequence of the floating element design. We also note that the shortening is more pronounced for the two MILC lenses (105 MC & 100 RF) than for the "old" F-mount Micro-Nikkor.
This could induce us to conclude that the larger the contraction of the focal length the more pronounced the change of AoV and, consequently, the focus breathing. Common sense often misleads us.
I then decided to plot AoV as a function of focus distance (= working distance + front element-sensor distance, the latter constant, all three lenses being IF).
Here is what I got:
We note that the Canon lens shows less breathing. The AoV changes less, going from 24° (infinity) to 23° (at 80 cm). In the same range, the AoV of the MC 105 changes from 24° to 21°. The Canon seems preferable for video at normal distances.
The two Micro-Nikkor lenses show much more pronounced focus breathing at close distances. The AoV shrinks more. Honestly, in close-ups I prefer an AoV as small as possible for better isolation of the subject from the background (see my recent pictures here: https://www.fredmiranda.com/forum/topic/1705116/81#16828165).
By looking at the two plots above, we learn that focal reduction and magnification are not sufficient to understand how much the AoV does change. In fact, according to the formula I gave at the beginning, to know the AoV we have to consider: 1) the magnification (the larger, the higher the reduction of the AoV); 2) the actual focal length (the shorter the F, the wider the AoV), AND - most important - the pupil magnification, which changes with focus distance and lens design.
In conclusion, the AoV tipically shrinks in macro lenses, and shrinks more the closer you focus. It's "normal", and this is the real reason why the actual aperture changes from infinity to closer distances (the lens collects less light from the front element). Focus breathing is absolutely unavoidable, even in normal lenses, unless you design the lens by adapting F and P so as to keep the AoV as constant as possible when R increases. This is one reason why cine lenses are expensive.
The "monstrous" focus breathing of the MC 105 is higher than, say, the Canon's. In close-ups, however, the (much) reduced AoV helps isolating the subject from the background. This cannot be considered a “flaw” (a Cons in LensTip review) but rather a feature of the lens, which can also come in handy, photographically speaking, for the macrophotographer.
Finally, let me stress that I noted some misalignment of the lens LensTip used to take Sample shots. Do you feel the same?
Edited on Jun 06, 2025 at 08:28 AM · View previous versions
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A given macro lens could be preferable at long distances, another one (e.g., a lens designed to go to 2:1) could have been optimized for close-ups.