Wednesday, February 17, 2021

A few quartz flourite UV lenses on the bench for lens transmission measurements II

A few years ago I was taking transmission measurements of some special quartz-fluorite lenses for reflected UV photography. This included the then Coastal Optics UV-VIS-NIR Apo 60mm lens, after the merger now called Jenoptik CoastalOpt® UV-VIS-IR 60 mm 1:4 APO Macro. 

So since I just recently bought that CoastalOpt® lens, I measured it (amongst others) with my newer spectrometric setup and compared my results with their published data. Surprisingly enough, my older and newer measurements of that CoastalOpt® 60mm Apo lens correlate very well - but not with their now officially published data on their site which shows much lower transmission values. Their formerly published data however showed much better spectral transmission, which correlated well with my own measurements.

[click on image to see a larger one]

Here in comparison the former (white) and now published data (magenta) superimposed:

My own measurements back then were these (amongst some other lenses):

[validity: approx 310 - 750nm]

and my newer current measurements (reaching deeper into UV) are these:

[validity: approx 300 - 750nm]

The differences in transmission of both my measurements are rather small. It is beyond my understanding how these new and quite different measurements (about 20% less) happened; I am just wondering why such an excellent lens is not represented well enough....

I have written about this lens before HERE.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site