OMDS M.Zuiko 90mm f/3.5 macro UV capability

[dancingcat]

A quick test with new OMDS 90mm macro lens.

With all the "stuff" inside this lens, I was shocked to see it pass UV.

Maybe I am hallucinating :-), someone else please also test.

 

Camera body: Olympus EM-1mk2-broadband

Lens: OMDS M.Zuiko 90mm f/3.5 macro IS pro

Filters: Visible - KolariVision Hot Mirror 2, Ultraviolet - Baader U

Subject: Helianthus sp.  store-bought.

 

This lens is 62mm so needs a stepdown ring to fit the M48/2" Baader U.

The ISO used is a little high, but needed to keep the UV exposure time reasonable.

The Oly EM-1 tends to throw noise with long exposures.

 

These are single shots, not stacks.

 

Visible ISO 800, f/11, 1/5 sec.

 

Ultraviolet - subject painted with a KolariVision LED flashlight.  ISO 800, f/11, 10 sec.

[Stefano]

If this lens turns out to actually have good UV transmission, would it make one of the few such modern lenses? There aren't many that go below 350 nm, as I understand (speaking of modern lenses).

[colinbm]

Nice work dancingcat

[Nate]

Camera handles the noise quite well.

Lens nice and sharp too!

[dabateman]

10 seconds isn't bad. What duration would your regular UV passing lens need, 2-4 seconds? 

Its possible its passing to 380nm. 

I hope @enricosavazzi  will also test it to get a range. 

[dancingcat]

I like the 5 sec range so a stack doesnt take sort of forever.. next flower that comes up handy I will test pushing the ISO.  And if a stack then increasing the aperture.  I get stuck on f/11 sometimes out of habit.

 

I sent an inquiry to OMDS asking for the transmission data. Maybe they will answer, she said hopefully….

[enricosavazzi]

On 3/17/2023 at 6:35 PM, dabateman said:

10 seconds isn't bad. What duration would your regular UV passing lens need, 2-4 seconds? 

Its possible its passing to 380nm. 

I hope @enricosavazzi  will also test it to get a range. 

Everything outdoors is still frozen, so I have no available (living) UV subjects here. The best I can do is attempt to measure the UV transmission of the lens in a way similar to what I do with filters. It will take a little time to set up a working system.

 

I agree that what we see so far seems to indicate 380-390 nm transmission at the tail of the emission spectrum of a 365 nm LED (which typically extends a little even into VIS). LEDs are notoriously unreliable to use for evaluating lens/filter UV transmission, unless the transmission extends into the UV range where we get false-yellow.

[dabateman]

9 hours ago, enricosavazzi said:

Everything outdoors is still frozen, so I have no available (living) UV subjects here. The best I can do is attempt to measure the UV transmission of the lens in a way similar to what I do with filters. It will take a little time to set up a working system.

 

I agree that what we see so far seems to indicate 380-390 nm transmission at the tail of the emission spectrum of a 365 nm LED (which typically extends a little even into VIS). LEDs are notoriously unreliable to use for evaluating lens/filter UV transmission, unless the transmission extends into the UV range where we get false-yellow.

You can place a lens within the light path of a spectrometer and get a cut off measurement.  But you will not know the full transmission profile without an integrating sphere. 

So with correct contrls, these cut off numbers in UV and IR might be interesting to know. 

[enricosavazzi]

The following is a partial answer, but I think it tells enough of the story to allow us to fill in the blanks. Orange is the Jenoptik (formerly CoastalOpt) 60 mm Apo, blue the OM System 90 mm macro. Each series is normalized only to its own maximum (i.e. no cross-normalization between series). As illumination I used a Godox AD200 strobe without plastic window, so each series is a composite of both flash emission and lens transmission. What we see is that the 90 mm has a steeper cutoff in NUV and at the shorter wavelengths of the VIS range. The curve of the 60 mm in UV is pretty much dominated by the flash emission spectrum (the lens transmission is much flatter than suggested by this curve). As a whole, however, the transmission of the 90 mm in the VIS is more uniform than the 60 mm, which should mean the 90 mm has a better color fidelity in the 650-430 nm range. The cutoff of the 90 mm at low wavelengths starts around 430 nm and by 375-380 nm there is no usable transmission, even if one uses a low-pass filter with a sharp slope.

[dabateman]

So there is a slight edge into UV. I think my Olympus 60mm macro had nothing below 400nm. But I might be remembered wrong.

Basically you can force UV through it, but its nothing special. 

Great to know. The lens should still work for Dancingcat.

[dancingcat]

The OMDS 90mm macro has a similar working “feel” to my Olympus 30mm macro in the UV.. at least by the flower signature output.  For very small wildflower portraits the extra working distance of the 90mm is really useful. Thanks for the transmission graph @enricosavazzi, the OMDS folks still have not replied to my request for theirs.  

[Lou Jost]

Don't forget that it is really easy for anyone to make these kinds of tests using a cheap spectroscope mounted on the lens.

[nfoto]

The floral signatures begin to appear already around 390nm. Thus being able to detect their presence is no evidence of good UV transmittance.