Tuesday, March 12, 2013

Three 40mm lenses for reflected UV photography

Today about a comparison of three lenses of 40mm focal length for reflected UV, one a Cooke Triplet (C40), one a Dialyte design (D40), one a complex Sonnar design (S40) whose makers will be revealed here later - or simply contact me about it. The best of the three will also compared against the Kuribayashi 35mm. I'm using a yellow/red Phalaenopsis flower for that and my "work horse" UV filter, the Baader-U filter. Light source was an UV enhanced Xenon flash. All shots were done at f8 and are presented in a side-a-side format for easier comparison.

[click on image to see a larger one]

UV image using the Baader-U filter (approx. 320-395nm, effective peak approx. 375nm) - Cooke left, Dialyte middle, Sonnar right:

Here the three contestants present themselves side-a-side: It gets obvious, that the Sonnar is the softest of the three and has a bit less UV transmission (the latter had to be expected). The Cooke triplet lens and especially the Dialyte however show some respectable sharpness. So lets's have a closer look at the latter two.

UV image using the Baader-U filter - Cooke left, Dialyte right:

Here, the Dialyte has an edge over the Triplet, quite higher micro-contrast and higher detail reproduction, quite remarkable, considering it is an old prewar lens, and uncoated. So let's see how that Dialyte performs against the Kuribayashi 35mm.

UV image using the Baader-U filter - Dialyte lft, Kuribayashi 35mm right:

Here now it is hard to choose a winner, as both have very high sharpness and contrast, quite remarkable considering their age difference. I'm undicided honestly.

Transmission graph:

The Triplet is represented by a yellow line, the Dialyte by a reddish brown line, the Sonnar by a blue line and finally the Kuribayashi by a pink line. Transmisson of all lenses is quite high, at 365nm Sonnar: 60%, Dialyte: 64%, Triplet: 70% and finally the Kuribayashi 77%. Their reach into UV is quite remarkable, the Kuribayashi and Dialyte having the deepest, Triplet surprisingly the least, maybe caused by its bluish coating. So overall, some remarkable lenses for reflected UV.

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

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos