• Ultraviolet Photography

Leitz 50mm f/4.5 Focotar from 1964

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#1 UlfW

    Ulf W

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Posted 19 February 2021 - 08:10

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 50mm f/4.5 Focotar from 1964

Manufacturer: Leitz Wetzlar, Germany
Manufacturer's lens designation: FOCOTAR 1:4.5/50 , 16781R
Currently manufactured: No
Lens type: Enlarger lens for film up to TBD
Design: Five element triplet optical design
Focal length: 50mm
Aperture range: f/4.5 – f/16, 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: Only by special filter adapter. See below
Introduction year: 1958
S/N of test object: 2030597
Manufacturing year: 1964

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

Transmittance Summary
Definitions of the parameters below
  • Range: The Focotar 50mm f/4.5 lens from 1964 transmits 1-79% in an increasing slope from 307nm to 400nm.
  • TVISmax (%) = 87%
  • T400nm (%) = 79%
  • T365nm (%) = 70%
    This high percentage is an indicator for relatively short exposure time under typical UV-pass filtration peaking around 360 nm or when using 365 nm UV-LED illumination.
  • λUV HMvis(nm) = 337nm
  • λUV HM400 (nm) = 335nm
  • λUV Zero (nm) = 307nm
  • These three values indicate that the lens is working well for upper UV-B photography with suitable filters and a few for this, suitable cameras.

Image of test object:

Attached Image: IMG_2575.jpg Attached Image: IMG_2576.jpg Attached Image: IMG_2577.jpg

Spectral Transmission Graphs
UV-NIR, Focotar 50mm f/4.5 from 1964
Attached Image: Focotar 50mm f:4.5 16781 Full.png
The transmission measurement accuracy into the end of NIR range is less good due to limitations in the light source.

UV, Focotar 50mm f/4.5 from 1964
Attached Image: Focotar 50mm f:4.5 16781 UV.png

UV-Log, Focotar 50mm f/4.5 from 1964
Attached Image: Focotar 50mm f:4.5 16781 UV Log.png
Numerical Spectra Data available: Yes

General comments about the UV-reach:

Filters and how to use them on this lens:
Here is an excellent description by Steve, about how make a filter mount adapter for this lens:
This method works for all versions of Focotar 50mm

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 50mm f/4.5 must be used with a helicoid or macro bellows to set desired magnification.
On mirrorless cameras the lens's 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.

Image samples:

Edited by UlfW, 06 April 2021 - 07:20.

Ulf Wilhelmson
Curious and trying to see the invisible.