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View Full Version : [UV, VIS] a surprising find ... and not


Dr Klaus Schmitt
October 12th, 2010, 02:26 AM
Well, I am studying lenses since quite some time and was researching the history
of some, when I noticed the same reflection pattern (which is a hint for the lens
design) in an previously overlooked, ordinary lens I have...

Well, I tested it good for 330nm in my spectrometer and in theory it should have
no focus shift (or just a tad)...

So best is always to try it out, so here some first tests, sacrificing one of my last
Rudbeckias...

VIS:
http://www.pbase.com/kds315/image/129018890/original.jpg

UV:
http://www.pbase.com/kds315/image/129018891/original.jpg

Long story short - it has hardly any visible focus shift!

Look at these mites and their fine webs!! Pretty fine resolution it has.

More about it later ... ;)

Asher Kelman
October 12th, 2010, 02:31 AM
Well, Klaus,

There's an optical company near us that makes lenses with no focus shift for DSLR's and they are very expensive. so this is a great find. what camera do you have it on?

I'm wondering as it's possible that live view might be of help in getting the focus right. Have you removed the cameras filter overlying the sensor or do you have some other system?

Asher

Dr Klaus Schmitt
October 12th, 2010, 02:37 AM
You mean Coastal Optics most likely (now part of the Jenoptic group)?
Yes, they have a 105mm (which I have) and a 60mm (very sharp lens,
but with hotspot issues, which I refused to buy). The classic UV-Nikkor
105mm (or the Tochigi Nikon 105mm which still can be bought new)
are in the $4.000 - 6.000 range indeed, this is why I constantly
search for possible candidates - and found a few.

Lifeview certainly would solve the focus shift issue, but there are
hardly any cameras sensitive enough (for UV; IR works) to see
anything life with that very dense UV transmission filter attached
(-8...10EV).

It is indeed good to have a camera with its internal filter replaced by
a clear quartz glass window (not really a "filter"), since that allows to
use the camera for UV, VIS and IR (NIR up to max. 1000 - 1100nm).

Asher Kelman
October 12th, 2010, 03:11 AM
Klaus,

Could one set the ISO for say 6400 and then focus and after that, pull down the ISO to say 800 and take the picture, on a tripod, of course!

Asher