Nikon Nikkor Z MC 105mm f/2.8 S Focus Breathing = 49mm FL at 1x

[RobertOToole]

Photons to Photos added the Nikon Z 105 lens on the optical bench:

https://www.photonstophotos.net//Genera ... sO,OffAxis

One interesting thing is that the FL drops from 103mm to 49mm at 1x. The older AF-S VR Micro-NIKKOR 105mm is not as bad (see below).

Nikon Nikkor Z MC 105mm f/2.8 VR S

Focal length at infinity: 102.86mm
Focal length at 1/2x: 70.46mm
Focal length at 1x: 49.28mm
WD at 1x =138mm

For comparison, the older AF-S VR 105 from Nikon:

Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED Lens
Focal length at infinity: 103.97mm
Focal length at 1/2x: 96.03mm
Focal length at 1x: 75.87mm
WD at 1x =152.47

AF-S 105 Link:
https://www.photonstophotos.net//Genera ... sO,OffAxis

Also you can see the Z 105 lens patent here: https://patentscope.wipo.int/search/en/ ... 2022097401

You will need a browser translator extension unless you can read Japanese.

Nikon claims 3 ED glass elements in the Z 105 design but there aren't any EDs element in the patent, the V-numbers are all too low. Low dispersion maybe but not ED level. The Nikon Z 105 highest Vd glass is only 69. The older Nikon Micro-Nikkor AiS 105mm f/2.8 uses glasses in the 27.6 - 54.0 range. The Printing-NIKKOR 95A uses glasses with a Vd value range from 51.35 - 82.52.

Abbe number, also known as the V-number is an approximate measure of the material's dispersion, that is the change of refractive index versus wavelength, with high values of V indicating low dispersion.

From my site:

Abbe number (Vd) value for some common optical glass types
Common glass type range: 25-65 Vd
Low-dispersion glass, ED-UD-SD: 81 + Vd
Super-ED or super-UD glass (Schott FK-51 for example): 84 Vd
Fluorite: 95 Vd

From the Nikon Nikkor Z MC 105mm f/2.8 VR S patent:

Older thread on macro lens focus breathing and Photons to Photos Optical Bench: https://www.photomacrography.net/forum/ ... 25&t=44431

[rjlittlefield]

One interesting thing I noticed was the FL change from 103mm to 49mm at 1x.

Focus breathing is funny stuff.

Common descriptions, such as at https://photographylife.com/focus-breathing , imply that changing FL is the cause of focus breathing.

But on the other hand, changing FL in exactly the right way is what's needed to prevent focus breathing. As a totally theoretical example, suppose you had a magical "thin" lens with an aperture in the lens plane and adjustable focal length. Set that lens at some FL_0, adjust extension so that it focuses at infinity that way, then further adjust focus solely by changing the focal length. What you'd find is no focus breathing at all, and FL_mag = FL_0 / (magnification+1).

So, if FL_0 at infinity focus is 100 mm, then at magnification 1x the magical no-breathing lens would have FL_1 = 50 mm. This newly posted Nikon lens has a ratio that's awfully close to that, so I was hopeful that it would not breathe.

But note, the magical no-breathing lens also leaves its entrance pupil in exactly the same spot as it changes focus. To get no focus breathing, you need exactly the right change in FL and also no movement of the entrance pupil. Without the proper change in FL you get zooming to go along with your focus changes, and without a fixed entrance pupil, you get changes in angle-of-view.

For this new lens, photonstophotos.net shows that the angle of view drops from 24.05 degrees at infinity focus to only 9.04 degrees at 1:1. That's caused by movement of the entrance pupil, which goes far back as focus gets closer. So, my hopes were dashed. This new lens still breathes quite a bit.

--Rik

[RobertOToole]

..............
For this new lens, photonstophotos.net shows that the angle of view drops from 24.05 degrees at infinity focus to only 9.04 degrees at 1:1. That's caused by movement of the entrance pupil, which goes far back as focus gets closer. So, my hopes were dashed. This new lens still breathes quite a bit.

--Rik

This is interesting, made a quick split diagram with pupil positions enabled, infinity focus and 1:1.

Illustration source: https://www.photonstophotos.net//Genera ... nchHub.htm

Edited to add: The blue P is the entrance pupil and the red P' is the exit pupil.