• Ultraviolet Photography

Steinheil München 50mm f/2.8 Cassar S

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#1 UlfW

    Ulf W

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Posted 18 February 2021 - 13:33

Finalized: Work in progress.
Last Update:

Steinheil München 50mm f/2.8 Cassar S

Manufacturer: Steinheil München
Manufacturer's lens designation: Steinheil München Cassar S 1:2.8 f=50mm
Currently manufactured: No
Lens type: Manual focus, Prime, Normal
Focal length: 50mm
Aperture range: f/2.8 – f/16, Manual, 10 blades, no click stops
Design: 3 elements in 3 groups
Attached Image: Screen Shot 2021-02-18 at 14.20.36.png
Flange Focus distance: Mount dependable
Mount: M42 x 1.0**, EXA, Also as a fixed mounted lens on several cameras
Sensor format/coverage: up to 24mm x 36mm
Front filter: 40.5 mm x 0.75 mm
Introduction year: early 1950?
S/N of test object: 2020691
**Mount of test object

Lens review (VIS), on the web:

Image of test object:
Attached Image: IMG_2529.jpg Attached Image: IMG_2531.jpg Attached Image: IMG_2530.jpg

Transmittance Summary
Definitions of the parameters below
  • Range: The Cassar S 1:2.8 f=50mm lens transmits 0-74% in an increasing slope from 309nm to 400nm.
  • TVISmax (%) = 90%
  • T400nm (%) = 74%
  • T365nm (%) = 68%
    This moderate to high percentage is an indicator for a short exposure time under typical UV-pass filtration peaking around 365 nm.
  • λUV HMvis(nm) = 337nm
  • λUV HM400 (nm) = 331nm
  • λUV Zero (nm) = 309nm
    These three values indicate that the lens is working well for UV-B photography with some filters and a few for this, suitable cameras.

Spectral transmission graphs:
UV-NIR, Cassar S 1:2.8 f=50mm
Attached Image: Cassar S 50mm f:2.8 Full.png
The transmission measurement accuracy into the end of NIR range is less good due to limitations in the light source.

UV, Cassar S 1:2.8 f=50mm
Attached Image: Cassar S 50mm f:2.8 UV.png
UV-Log, Cassar S 1:2.8 f=50mm
Attached Image: Cassar S 50mm f:2.8 UV Log.png
Numerical Spectra Data available: Pending

Filters and how to use them on this lens:
The front filter thread is 40.5mm standard filter thread. A step-up filter ring might be needed.

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.

An alternative, if space in the camera allows, is to putty-mount a filter directly against the lenses rear flat parts.
The rear lens element is recessed and thus safe and the ring provides a good reference plane for orienting the filter normal to the optic axis.

My Omega 330W80 Improved Ø25mm, is mounted in a 27mm-filter ring and would work well to mount as it is.

Handling and focussing:
This lens has a focusing helicoid that smoothly turns almost a full turn for focus at infinity to around 1m.
To focus closer external bellows, focusing helicoids or extension rings are needed.
Then image quality might improve by reverse mounting the lens.

Flare and sun-stars:

The lens has a rather curved focus plane and on a full frame sensor the corners are quite soft even when stopped down.

Lens distortion:

Chromatic Aberration / fringing in UV:

Image samples:

Edited by UlfW, 02 April 2021 - 07:20.

Ulf Wilhelmson
Curious and trying to see the invisible.

#2 OlDoinyo


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  • Location: North Carolina

Posted 15 April 2021 - 02:11

Another version of this lens has a smaller front barrel with no filter threads.