Lens Test

[Mickoid (Michael)]

I've been trying to rid an old Pentax K mount 135mm f3.5 lens of fungus by exposing it to sunlight whenever possible. Melbourne's weather hasn't given me many opportunities to do this but it's been out for a few hours now and I do believe the fungus has been reduced. Anyway, on Sunday night I stuck it on an unmodded Canon 550d and did some test shots using the Sightron Nano Tracker.

The lens appears to be operating normally and resolves well with good colour and contrast so I'll keep going with the UV exposure for as long as I think is necessary. I'm not prepared to dismantle the lens to remove the fungus even though it appears to be on the front lens element only. Has anyone else heard that UV will kill the fungus on a lens or is it just a myth?

Here's two shots I took using the lens on Sunday night (with waxing moon nearby). Antares region 20 x 1min 800iso f5.6 and M8/M20 region 9 x 1min 800iso f5.6.

[Atmos (Colin)]

The lens looks like it's performing quite well.
Someone can correct me if I am wrong but won't the UV just kill the fungus that's there and leave the residue?

You could also get a UV lamp and forget about Melbournes lack of sunshine

[bojan]

Yes, residues will remain, they can be washed with Windex and/or vinegar (in most cases... if glass is not damaged)
Of course, you have to dismantle it to get to the internal affected parts.

I found those lenses behave much better in terms of coma and CA with external aperture... however this one seems to be quite OK (could you show us crop from one of the corners at full resolution?)

[Mickoid (Michael)]

Originally Posted by bojan

Yes, residues will remain, they can be washed with Windex and/or vinegar (in most cases... if glass is not damaged)
Of course, you have to dismantle it to get to the internal affected parts.

I found those lenses behave much better in terms of coma and CA with external aperture... however this one seems to be quite OK (could you show us crop from one of the corners at full resolution?)

Bojan, here are the 4 corners of both images as requested.

[bojan]

Hmm pretty good
Try with external aperture (f/4 of more... you can cut it out from black paper with help of compass ).
I was playing a lot with canon FD lenses (see 200mm for example), and the results with external aperture were generally the way to go to get rid of CA and coma.
Also, try to focus with Bahtinov mask, use F or G-type stars for that.

[rcheshire (Rowland)]

Originally Posted by bojan

hmm pretty good
Try with external aperture (f/4 of more... You can cut it out from black paper with help of compass ).
I was playing a lot with canon fd lenses (see 200mm for example), and the results with external aperture were generally the way to go to get rid of ca and coma.
Also, try to focus with bahtinov mask, use f or g-type stars for that.

+1