hazed lens elements ... do they get worse with time?

norland · Joined: 10 Aug 2013 Posts: 165

When there is haze (not condensation) on inaccessible rear elements of an old lens, does it keep getting worse,
or does it stabilise at some point?
Reason for asking is I have one lens like that, a long and simple 500mm preset probably from sometime in the 1970s, but it is still sharp and not notably down on contrast or saturation despite most of the rear element assembly inner surface(s) -- no obvious way of dismantling, so presumably glued? -- having that problem.

Excalibur · Expire: 2014-04-21

Pancolart · Expire: 2013-11-18

marcusBMG · Joined: 07 Dec 2012 Posts: 1305 Location: Conwy N Wales

I can echo the preceding responses, I sold the Prinz-Galaxy 400 f6.3 that was afflicted, though it performed Ok. I have read some posts referring to "lens whitening": that's certainly what it looked like , a patchy whitish haze. I tried various solvents to see if it would shift..Is it the glass or the coating...no idea. Since it seems to be always the rear-most element that's afflicted what's particular about that?

replace the element? NWDIToT! The quality of these is in the achromat, the rear elements need to be (only) good enough, that's why the results even with the haze were acceptable. However I doubt that a custom element could be got for cheaply enough here in the UK to make it worth while given that these go for (average) 25-30 in the UK (and are often obtained for rather less by practiced MFlenses forum bargain hunters). I should consult with my neigbour who used to manage an optical factory.

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

As has been mentioned, hazing of the rear elements of this type of lens is very common. Since I have seen ones with varying degrees of hazing from barely noticeable to almost opaque, I would say it will get progressively with time.

The rear group of the lens should be separable. With all the lenses of this type that I have had it has been possible to fully dismantle the rear group. You should try running isopropyl alcohol on the threads of the lens carrier to free them.

Once you have the elements apart, you can remove the haze (and AR coating) with 0.25 micron diamond polishing (lapidary) paste on a soft cloth. Rub gently renewing the cloth and paste frequently until the haze is gone, If the hazing is not too bad, you may still have some of the AR coating left at the end as well (these lenses are just single coated so the coating is quite thick). I have cleaned up quite a lot of single coated lenses with this technique. In fact, I had a very hazed rear element from a 400mm f6.3 lens of the type you have in my junk box and used it as a practice piece with the diamond paste. It worked a treat.

Mark