• Ultraviolet Photography

Leitz 100mm f/4.5 Focotar-II

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#1 UlfW

    Ulf W

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Posted 21 February 2021 - 16:13

Finalized: Work in progress.
Last Update:
Note: Additional information or links about this lens are welcomed and will be incorporated into the first post as time permits.

Leitz 100mm f/4.5 Focotar-II

Manufacturer: Leitz Wetzlar, Germany
Manufacturer's lens designation: FOCOTAR II 1:4.5 / 100 - LEITZ WETZLAR
Currently manufactured: No
Lens type: Enlarger lens for medium format film
Design: TBD
Focal length: 100mm
Aperture range: f/4.5 – f/22, Manual, 8 blades
Format coverage: TBD
Recommended magnification range*: TBD
Optimal magnification*: TBD
*Definitions reversed from normal enlarger definition, referring to the motif not the negative-plane
Mount: M39 x 26tpi thread
Reverse mount: None.
Helicoid: No
Flange focus distance: TBD
Front filter: 49mm filter thread
Introduction year: 1974
S/N of test object: 2841030
Manufacturing year: 1977

For a short time, before I returned it, I had a lens that was slightly younger.
It had the serial #3065653 indicating that it was produced 1981.
That was the last year the Focotar-II 100mm was made.
That lens showed a similar transmission as this lens tested here.

Lens review (VIS), on the web:
Lens Manual on the web:

Transmittance Summary
Definitions of the parameters below
  • Range: The Focotar-II 100mm f/5.6 lens transmits 1-74% in an increasing slope from 322nm to 400nm.
  • TVISmax (%) = 89%
  • T400nm (%) = 74%
  • T365nm (%) = 32%
    This low percentage is an indicator for relatively long exposure time under typical UV-pass filtration and works best with filters that peaks close to 400nm like the SEU3 filter.
  • λUV HMvis(nm) = 372nm
  • λUV HM400 (nm) = 368nm
  • λUV Zero (nm) = 322nm
    These three values indicate that the lens is working only for UV-A photography with suitable filters.
    The unusually gradual slope in UV makes the performance even worse than the 1% cutoff indicates.

Image of test object:

Attached Image: IMG_2537.jpg Attached Image: IMG_2539.jpg Attached Image: IMG_2538.jpg

Spectral Transmission Graphs
UV-NIR, Focotar-II 100mm f/4.5
Attached Image: Focotar-II 100mm f:5.6 Full.png
The transmission measurement accuracy into the end of NIR range is less good due to limitations in the light source.

UV, Focotar Focotar-II 100mm f/4.5
Attached Image: Focotar-II 100mm f:5.6 UV .png

UV-Log, Focotar-II 100mm f/4.5
Attached Image: Focotar-II 100mm f:5.6 UV Log.png
Numerical Spectra Data available: Yes

Filters and how to use them on this lens:
Beside the front filter it is also possible to use rear mounted filters, either in lens mount adapters for mirrorless cameras like Sony A-series etc, or placed directly in the camera.

Handling and focussing:
This Focotar-II 100mm f/4.5 must be used with a helicoid or macro bellows to set desired magnification.
On most cameras the lens's long FFD permits focus to infinity with careful sizing of the helicoid or bellows.
However these lenses are designed and optimised for short focus distances. At infinity the result will not be optimal.

This lens is not very good for UV-photography but as a macro lens for the very top end of UV, closer to 400nm and VIS it is an excellent very sharp lens.

Image samples:

Edited by UlfW, 06 April 2021 - 07:35.

Ulf Wilhelmson
Curious and trying to see the invisible.