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UltravioletPhotography

Zuiko Macro 38 mm f:3.5 (Olympus OM)


aphalo

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I have recently bought a Zuiko Macro 38 mm f:3.5 "bellows" lens in RMS mount from the 1970's in very good condition (the lens is described in detail at Alan Wood's website). This lens is optimized for magnifications in the range x2 to x6. Mine is an early copy described as being single coated. I did only a few tests, and as it takes 32mm push-on filters, I used for the tests a ZWB1 filter (30 mm diam x 2 mm thick from AliExpress seller Purshee) on the lens and 365 nm and 340 nm LEDs illuminating a white PTFE slab and compared it to a Soligor 35 mm f:3.5 M42 lens known good for UV (both with Baader-U and StraightedgeU filters). The Zuiko lens based on colour channel balance (in RawDigger) and exposure time seems to transmit well at 365 nm (given the difference in magnification, the EV values are not directly comparable). In contrast at 340 nm, given the extremely long exposure time and colour balance it looks like it almost completely blocks the shorter wavelengths. The images from the Soligor 35 nm f:3.5 taken with this 340 nm LED look yellow, and in RawDigger show that both green and red channels have a strong signal, while the file from the Zuiko was rather underexposed but still with the red channel dominating. As described by Enrico in his web site for the companion 20 mm objective the Zuiko 38 mm f:3.5 lens seems to be rather easily affected by diffuse flare when the objects photographed are on a white background.

 

As a further test I photographed a miniature UV-A and "UV-B" integrated sensor both in visible and 365 nm UV. These two photographs are at https://www.photo-spectrum.info/2018/08/how-small-can-a-uv-b-plus-uv-a-sensor-be-made/ The images are slightly cropped, but magnification is nearly x5 on the camera sensor, of the Olympus E-M1. I used extensions tubes and a helicoid.

 

Can anyone suggest any target with a known UV signature that could be used to test the lens at high magnification?

 

post-126-0-61810500-1534232598.jpg

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Most flowers with iridescence would do nicely. You should be able to discern the conical cells on the petals.

 

Have done this with the sibling lens, OM 38 mm f/2.8, and whilst it admittedly is not a "deep UV" lens, it does very well on flowers provided sufficient UV illumination is provided.

 

There is an old Canon "micro" lens 20mm f/3.5 in RMS mount that likewise can do duty in the near UV.

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Thanks Pedro for this write-up on the Zuiko Macro 38/3.5. I will get it into the Sticky during the next update.

 

A Rudbeckia, Helianthus (sunflower) or Bidens will be UV-absorbing on the ray (petal) base and the ray end will be UV-reflective around 350 - 360 nm. (This varies by species.) The demarcation between the UV-absorbing and UV-reflective portions of the ray might be a useful, interesting area to photograph with a UV-capable macro lens. The chromoplasts within a cell store pigments, so you might be able to see the UV-absorbing areas at a cellular level. I don't know if surface conical cells contain chromoplasts or just act as little mirrors.

 

Those ZWB filters can be leaky and some seem to have lower transmission of UV, so please be aware of this.

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There is an old Canon "micro" lens 20mm f/3.5 in RMS mount that likewise can do duty in the near UV.

 

I have this lens.

A few quick normalised transmission tests looks like this:

post-150-0-75189300-1534254582.png

 

Canon also had a Micro 35 f/2.8 in the same bellows lens family.

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Hm. Actually, better UV performance than I'd expected. I have to dig out that little Canon lens again. Like so many other sundry or small items, it is temporarily "lost" after my move out of Oslo.
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I have this lens.

A few quick normalised transmission tests looks like this:

post-150-0-75189300-1534254582.png

 

Canon also had a Micro 35 f/2.8 in the same bellows lens family.

 

Thanks for the transmission plot for the Canon 20mm lens Ulf. I've just bought one of these for a different project, and hadn't even thought about it for UV.

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The Canon 20mm lens has an old RMS microscope thread, but was sold together with a RMS to Canon FD / FL adapter.

 

I bought mine new almost 30 years ago.

It is a nice little bellows-lens with an internal iris.

 

At the same time as I measured this lens I tested a few other old low magnification microscope lenses.

I can post the results if you like.

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Yes, do that.

 

As an owner of [several] Nikon Multiphot setups, I have plenty of RMS adapters (for the Macro-Nikkor lenses).

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