Enna München 28mm f/3.5 Lithagon

[ulf]

Last Update: 03 April 2021 agb/spacing

Finalized: Work in progress.

 

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Enna München 28mm f/3.5 Lithagon

 

Manufacturer: Enna-Werk München

Lens Label: ENNA München Lithagon 1:3.5/28mm

Currently manufactured: No

 

Lens type: Manual focus, Prime, Wide-angle

Focal length: 28mm

Aperture range: f/3.5 – f/22, Manual, 7 blades, with preset

Design: TBD

Flange Focus distance: Mount dependable

Mount: M42 x 1.0**, EXA

Sensor format/coverage: up to 24mm x 36mm

Front filter: 52 mm x 0.75 mm

Introduction year: after 1965

S/N of test object: 4009022

**Mount of test object

This lens type with black case and zebra coloured rings should not be confused with the earlier, silver coloured Ultra-Lithagon 28/3.5, which uses a different lens design.

 

 

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Image of test object:

 

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Transmittance Summary

Definitions of the parameters below

• Range: The Lithagon 1:3.5 f=28mm lens transmits 1-52% in an increasing slope from 338nm to 400nm.
  
• T_VISmax (%) = 80%
  
• T_400nm (%) = 52%
  
• T_365nm (%) = 32%
  This rather low percentage is an indicator for a longer exposure time under typical UV-pass filtration peaking around 365 nm.
  
• λ_{UV HMvis}(nm) = 374nm
  
• λ_{UV HM400} (nm) = 360nm
  
• λ_{UV Zero} (nm) = 338nm
  These three values indicate that the lens is working best for UV-A photography with filters with a good transmission closer to 400nm
  

 

 

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Spectral transmission graphs:

UV-NIR, Lithagon 1:3.5 f=28mm

 

The transmission measurement accuracy into the end of NIR range is less good due to limitations in the light source.

 

UV, Lithagon 1:3.5 f=28mm

 

 

UV-Log, Lithagon 1:3.5 f=28mm

 

Numerical Spectra Data available: Pending

 

Comment about the graphs:

The long downward slope of transmission starting already at 550 nm can be seen as a faint yellow tint of the lens's glass.

The images it produce are definitely a bit warm i tone.

Even if the final UV-cutoff is reasonably deep the attenuation will make the exposure time longer.

I have a second lens of the same type, but in EXA-mount that show the same yellow tone.

 

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Filters and how to use them on this lens:

The front filter thread is 52mm standard filter thread. A step-up filter ring and bigger filters might be needed.

This wide angle makes using front mounted dichroic filters like the Baader U problematic, causing colour shifts towards the corners.

It might be possible to use such filters rear mounted instead ti decrease the problem. (tbd)

 

It is 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.

 

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Handling and focussing:

This lens has a focusing helicoid that smoothly turns almost a full turn for focus from infinity to around 0.3m.

 

Flare and sun-stars:

TBD

 

Sharpness:

TBD

 

Lens distortion:

TBD

 

Chromatic Aberration / fringing in UV:

TBD

[Andy Perrin]

That yellow tint sometimes means it’s one of the lenses with radioactivity. If it’s that, then the spectrum may change with exposure to UV over long periods.

[bvf]

Interesting!

 

I've got one of these, and the serial no. is only 50 higher than Ulf's. I can't see any yellow tint in the glass, and here is a comparison shot of a white door, same exposure, flash, WB set to flash. The Lithagon is indeed a tad warmer, but there's not much in it..

 

Lithagon:

 

Canon 50mm EF STM:

[Andy Perrin]

Interesting, if it does have radioactivity, the yellow goes away when exposed to sun or other UV. That may be why yours is different?

[ulf]

Interesting, if it does have radioactivity, the yellow goes away when exposed to sun or other UV. That may be why yours is different?

That is an interesting idea.

I am quite sensitive to seeing small differences in tone and cannot say that the tint is strong.

Just made an adjustment to the phrasing in the text above.

 

Radioactive lenses often have glass with thorium, making them yellow over time.

I have one that is like that, a very sharp early Canon FD 35/2.0 with a concave front lens element.

The radioactivity is definitely detectable but it is not very hot.

Some years ago I made it less yellow with a Convoy sitting on it at close range for some time.

 

I'll do the same now with the Lithagon and a Nemo torch to see if the Lithagon can be cured.

It can possibly go the other way around as some materials are yellowing by UV.

It could be that some internal optical resin do that.

[bvf]

Actually, in the post at https://www.ultravio...__fromsearch__1 I did say I detected a yellow cast in my Lithagon (compared to the Focotar-2) - but the same applied to many of the other lenses too. Viewed under high saturation, the Lithagon cast was stronger than some lenses (e.g. various Canons) but less than others like the Samyang 14mm and Tamron SP500 500mm (mirror lens).

[ulf]

I have seen a slight improvement in the transmission in the blue and upper UV-A region after UV-A treatment.

 

After 3 1/2 hours with a Nemo lamp-head at full power all the time, placed directly on top of the lens's front element, I got some small , but significant difference.

 

The greatest improvement was seen at 365nm where the transmission increased from 32% to 35%.

 

The change is not possible to see visually.

At least the yellowing did not get worse!

[bvf]

I've just found this video in the excellent Mathieu Stern channel:

 

 

He is doing the same as you, but he uses a much more powerful source, many more hours, and places a mirror behind the lens to reflect the transmitted UV back for a second pass. Gets very good result with a badly yellowed SMC Takumar 50mm f/1.4 (I had one of those lenses back in the day).

 

EDITED: And in this link he demonstrates the danger of radioactive lenses (no need to watch beyond 2' 50"):

[Stefano]

Does wavelength matter? Would using deeper UV give better results (taking into account the lens transmission)?

 

Also, personal opinion, if I had to choose between an old lens like this one and a modern lens like the Canon Pancake, at the same UV reach, I would choose the modern one. Buying old vintage lenses to me makes sense only if you gain significant reach, or if you like the images the lens produces.

[bvf]

Also, personal opinion, if I had to choose between an old lens like this one and a modern lens like the Canon Pancake, at the same UV reach, I would choose the modern one. Buying old vintage lenses to me makes sense only if you gain significant reach, or if you like the images the lens produces.

 

 

Truly the words of a young man! For many of us old timers, acquiring and using vintage lenses takes us back to our comfort zone when those lenses were the latest and greatest, and probably beyond our financial grasp.

 

But there is also a practical reason for hunting out vintage lenses - price. If you go for the right ones, you can get an excellent vintage lens (like the Tak 50mm f/1.4 in Stern's video) for a lot less money than an equivalent modern one. That hasn't been a motivator for me, but I am doing a little project at the moment buying some 100-year old lenses just to see if they are any use for UV - and you can only afford to play around like that because they are cheap. I have to say, though, that it's great fun trying to hunt down the lenses you want!

 

Your point about UV reach is also important. Although some modern lenses are OK for photographing through a general-purpose UV filter like a Baader U, I'm not aware of any modern lenses (apart from the multi-$000 specialist lenses) that have the UV reach of your Soligor 35mm or a Cassar S or a Focotar-2 or ...

 

I also do a lot of macro work using bellows and I cannot use my modern Canon lenses because the lack of electrical connection means the lenses cannot be stopped down. So I have to use vintage manual lenses.

 

So I maintain two distinct sets of lenses - modern ones for general visible photography and vintage ones for the nerdy stuff.

[Andy Perrin]

I have seen a slight improvement in the transmission in the blue and upper UV-A region after UV-A treatment.

 

After 3 1/2 hours with a Nemo lamp-head at full power all the time, placed directly on top of the lens's front element, I got some small , but significant difference.

 

The greatest improvement was seen at 365nm where the transmission increased from 32% to 35%.

 

The change is not possible to see visually.

At least the yellowing did not get worse!

Hah! I am glad of that, I would feel guilty. So it did make a difference. Got a geiger counter around somewhere?

[ulf]

I've just found this video in the excellent Mathieu Stern channel:

 

 

He is doing the same as you, but he uses a much more powerful source, many more hours, and places a mirror behind the lens to reflect the transmitted UV back for a second pass. Gets very good result with a badly yellowed SMC Takumar 50mm f/1.4 (I had one of those lenses back in the day).

 

EDITED: And in this link he demonstrates the danger of radioactive lenses (no need to watch beyond 2' 50"):

The light source might be three times as powerful, but the distance from the lens made the power density vastly less than what I got from the Nemo in direct contact with the lens.

His lamp is illuminating more than 100 times the area of the lens's front element and his lamp is stated to be just three times as powerful as we know for the power input of the Nemo.

 

I estimate that the actual illumination dose my lens got during 3 1/2 hours is several times bigger that the TAK in the video got.

 

There is not much gained from using the mirror either as most of the light is already absorbed by the lens.

[ulf]

Hah! I am glad of that, I would feel guilty. So it did make a difference. Got a geiger counter around somewhere?

Nope.

[ulf]

Also, personal opinion, if I had to choose between an old lens like this one and a modern lens like the Canon Pancake, at the same UV reach, I would choose the modern one. Buying old vintage lenses to me makes sense only if you gain significant reach, or if you like the images the lens produces.

If the UV-reach was the only parameter the EF 40mm pancake lens would be the one to chose before the Lithagon 28mm every time, as long as you could control the aperture of the lens.

You can do that with a suitable adapter on your EOS M, but that is not always possible.

However the main reason for getting the Lithagon lens is that it has a focal length of 28mm and is designed for 35mm size film format covering a FF-sensor.

 

When searching for suitable lenses the UV-reach is just one of the parameters to consider.

The UV-reach has to be good enough for the intended usage and "good enough" can differ very much.

IMHO the search for lenses with deep UV-reach has gotten too much priority for most UV-photography as long as you are not trying to reach UV-B with special filters and light sources.

 

If a really wide lens is needed, compromises has to be made about the reach.

You have to search among the older types of lenses to find anything usable, as no working modern alternatives are likely to exist.

[bvf]

This chart is well known on UVP. I forget the author - perhaps it was Klaus Schmitt (if not, apologies to the author).

 

Anyway, it shows the 28mm Lithagon going down to 320nm (ser. no. 4018432) or 330nm (ser. no. 3816686, 4045049). That's why I bought one. I've never been able to check this because my 345BP25 and 315BP20 filters are too small for this lens, although what I've observed using a Baader U has made me a bit suspicious of the UV reach. For example, using Focotar-2 white balancing for a Baader U image taken with this lens gives a yellow colour cast: this is similar to other poor UV performers like my modern Canons, whereas UV-friendly lenses like the El Niks, IgorOriginal, and Soligor 35mm enlarger lens don't have any colour cast when WBed for the Focotar-2.

 

[ulf]

It was 77mm

This chart is well known on UVP. I forget the author - perhaps it was Klaus Schmitt (if not, apologies to the author).

 

Anyway, it shows the 28mm Lithagon going down to 320nm (ser. no. 4018432) or 330nm (ser. no. 3816686, 4045049). That's why I bought one. I've never been able to check this because my 345BP25 and 315BP20 filters are too small for this lens, although what I've observed using a Baader U has made me a bit suspicious of the UV reach. For example, using Focotar-2 white balancing for a Baader U image taken with this lens gives a yellow colour cast: this is similar to other poor UV performers like my modern Canons, whereas UV-friendly lenses like the El Niks, IgorOriginal, and Soligor 35mm enlarger lens don't have any colour cast when WBed for the Focotar-2.

 

It was Klaus Schmitt, former member KDS that posted that chart on Photozone.

I too bought two different Lithagon 28mm based on that diagram.

Observe the -3 stops threshold for these transmission limit wavelengths.

That is giving more optimistic numbers than a propper 50% level.

 

When measuring transmission with an array spectrometer there is always some degree of offset added to the cut off spectra.

It looks from some of the spectra he has presented on his blog that he used that type of spectrometer and also had variable success of correcting for the offset.

 

That offset error adds even more false transmission range in the data.

The Lithagon 28mm seams to vary in cut-off wavelength between different items too.

 

The most important lesson to learn is that this diagram is not very good for determine how good a lens is for normal UV-photography.

(Sun and Baader U or UG11 or UG1 - stack)

For that form of photography the main parameter to look for is the transmission at around 365nm!

[Stefano]

I think Bernard's specimen is a bad version or whatever. The diagram is not very good but still Klaus did measure/see some 320 nm transmission, so his lens does have a very good reach (Bernard's color change indicates a lower reach).

[ulf]

I think Bernard's specimen is a bad version or whatever. The diagram is not very good but still Klaus did measure/see some 320 nm transmission, so his lens does have a very good reach (Bernard's color change indicates a lower reach).

Only if his measurements were correctly done and you can trust the diagram.

Do you have more detailed information about those measurements making them more trustworthy?

 

We have now three different lenses that are yellowing my #4009022 and #3816677 plus Bernhard's lens.

With that gradual slope that makes an offset error even more likely to affect the transmission cutoff value.

[Stefano]

Only if his measurements were correctly done and you can trust the diagram.

Do you have more detailed information about those measurements making them more trustworthy?

No, I don't.

 

If these lenses have the yellowing problem, than the matter is more complex.