Manual Focus Lenses Forum

fourmix · Joined: 29 Oct 2009 Posts: 111

Hi,

i'm looking about methods or tips for doing new coating for my Zeiss biotar 75 T* ; cause (as you see on the pictures) there's a lot of 'bubbles" on the front element.

Did you know the prices for doing that ?
Do you think zeiss or pentax could do that on this old lens ?

thanks

luisalegria · Expire: 2018-01-18

I think that should have very little or no effect on performance. I suggest you use a good hood and not worry about it.

estudleon · Joined: 15 May 2008 Posts: 3754 Location: Argentina

What's that?

1-Greasy layer by cleaning with greasy substance.

2- Greasy sediment by evaporated oil

3- Deteriorated coated.

You are sure that it's a deteriorated coated, aren't you?

indianadinos · Expire: 2011-12-05

Hi,

AFAIK, there is only one repair center in Germany that is able to coat again a lens, but their prices were not really on the cheap side ... And this is not a repair that you can do by yourself ...

I will try to find the bookmark if you are interested ...

Cheers

P.S.: Why don't you try to find a Biotar 75 "for parts or repair" and simply swap the front element ? It could be a cheaper solution ...

bob955i · Joined: 15 Apr 2007 Posts: 2495

Assuming coating damage, recoating a lens is expensive as the old coating has to be removed without altering the shape of the element in any way and the new coating is then applied by the means of heat IIRC. Arax in the Ukraine offered a recoating service at one time but I don't know if they still do.

Luis is probably right about leaving it as is and using a hood as even if the lens had perfect glass, you'd likely end up fitting one anyway to help counteract flare as the Biotar 75 was only ever single coated as standard.

kds315* · Expire: 2021-03-09

Looks more like the coating got etched by something (Lemon or orange peel??).

I now say this WITH NO LIABILITY OR GUARANTEE WHATSOEVER and it carries teh risk of damaging the lens surface even more!! But it has worked once for me to get some coating back into order. The recipe is actually simple, is consists of thinned down white vinegar (chinese + thai food stores carry that) to about 2% acidity. Mix 1 part of white vinegar (5% acid) and 1 part of purified water and moist a clean cotton pads with that (NOT dripping) and gently wipe the lens from the middle to the outside in gentle strokes. DO NOT CIRCLE with the pad and turn the pad so always a fresh part touches the lens surface. Change pad after a few strokes with a freshly moistened one. The repeat same procedure using only purified water to remove any reminders of the vinegar. Let dry in warm air. I HAVE ASSUMED THAT THE LENS HAS BEEN CLEANED BEFORE!!

But maybe it would indee best, to just leave it as is, the difference to a perfectly coated lens may just be marginal and no risk is involved!!

Wish you luck!

scsambrook · Expire: 2011-11-18

Recoating used to be easier to have done, in UK at least. But now very few firms can, or will, do it on older lenses. The last time I spoke to anyone about it - for an experiment on an old high grade binocular - the advice was that even single coating these days would only be done appropriate to the glass being coated, which meant different deposits for objectives, prisms and eyepieces. Doing a single element was "not a worthwhile proposition". Well, that's what I was told. Maybe the search for excellence prevents any good being done . . .

You have a relatively rare lens with a high reputation and if it were mine I would hesitate to do anything to it unless the performance was being really affected by the coating deterioration. As Luisalegria has already said, using a lens hood (a L O N G one, especialy on a crop format camera) might be as good a solution as any. I think the worst that can happen is a slight loss of contrast, which can be fixed in PP.

Sevo · Expire: 2012-12-03

Uncoated glass has a surface transmission and contrast loss somewhere around 5% per surface. I.e. even the best multi-coating has only an advantage of less than 5% in transmission and contrast over no coating at all. A lens with total coating loss on 10% of the front surface will have lost maybe 0.4% of its real life performance. Chances are that re-coating that lens introduces a much higher error than that by replacing the 90% good coating with a less suitable coating (the coating at the damaged spots might still be better matched to the lens than the very generic coating these companies can apply), and in any case there are few cameras whose overall tolerances sum up to less than a 5% error shot-by-shot.

Quite apart from feasibility - there are only two or three companies left which will re-coat individual lenses, at a price, and you must deliver them the element separate, uncemented and cleaned - it is rather questionable whether it is beneficial. I'd leave the coating as is...

fourmix · Joined: 29 Oct 2009 Posts: 111

Hi;

Great thanks to all, my english is not very good, so i have little difficulties to read but you give me a lot of informations.

I would take pictures to test if the IQ is affected or not; but what i could see on some shoots is that the bublles appears in the OOF, and it's not really beautiful.

I would post a picture this afternoon to see.

fourmix · Joined: 29 Oct 2009 Posts: 111

PaulC · Joined: 23 Dec 2008 Posts: 2318

Not nice at all.

I have a feeling that Hartblei/Arsenal in Kiev offer a recoating service. It's probably cheaper than in the West.

scsambrook · Expire: 2011-11-18

Well, that is a STRANGE effect ... my optical science is pretty weak, but I'm puzzled by how something actually on the front element can form a clearly defined image ... is any well-educated MF member able to give an explanation?

Fourmix - can you show us a close up of the front element itself?

fourmix · Joined: 29 Oct 2009 Posts: 111

fourmix · Joined: 29 Oct 2009 Posts: 111

damn, i just see that the back glass is affected to... Confused

fourmix · Joined: 29 Oct 2009 Posts: 111

Here are the close views

Front glass:

and... rear glass... Crying or Very sad

Spotmatic · Joined: 18 Aug 2008 Posts: 4045 Location: Netherlands

Are you sure the marks are on the front element, or only the back of the front element? It might be cleanable...

I just checked mine just to be sure and I'm happy to say it's still dead mint.

eggboy · Thu Dec 31, 2009 4:26 pm

These guys offer lens repair, that includes removal of the old coating and new coating applied. I would only do this if your Biotar's performance was visibly affected by the issues you see, since there is always risk when doing this, and the figure of the front element might change very slightly from the removal process.

I did use them to repolish the front element of a plate camera format Tessar from the 1920's that had very heavy cleaning marks. I didn't have it coated, but was very happy with their service and professionalism.
http://www.focalpointlens.com/fp_intro.html

scsambrook · Expire: 2011-11-18

Fourmix -

thanks for showing us those close-ups. Very odd, it looks to me more like a fungal growth than simply deterioration of the coating. There's so much of it that I think it must affect the performance of the lens - as indeed you've found out.

If it were my lens I would do one of two things: either ship it off to a specialist to see about getting it cleaned and re-coated, OR, sell it on eBay as it is, with the problem declared. I would favour the second, for myself.

My rationale would be this:
1: Such specialists are hard to find. I don't know of any by reputation. Recoating will be expensive and possibly risky - you could finish up with a useless lens AND a large bill.
2: Selling with a declared fault may cause you to get back less than you originally paid, but that would be better than a total loss.

I understand this will be a hard decision - you may get the lens restored to good condition if you try for the re-coating, if you sell it you certainly won't have the lens at all and finding another might be very hard.

Others on the Forum here may have more positive advice for you - I do hope so!

ikoflexer · Joined: 25 Oct 2009 Posts: 14 Location: Toronto

I would definitely check first that the marks aren't actually on the back of the front element. It is usually easy to remove the front element, I have a wrench made out of a pair of scissors which works very well; HOWEVER I would recommend that you use a proper wrench.

I removed quite a lot of ugly of back-of-the-lens marks this way, washing the element insistently with dish washing liquid and then rinsing very well with water. I would recommend distilled water.

Pancolart · Expire: 2013-11-18

Huh, after i saw your close-up it seems pretty bad situation: reminds me of some strange things growing in Praktica prisms. Well beware and before doing anything watch Star Trek: Crystal Entity (these things are impossible to kill since they are not really alive Wink

. Anyway there is still slight possibility it's only grease related like Estudleon suggested. Let the nearest photoserviceman check that for you.

Pancolart · Expire: 2013-11-18

hinnerker · Expire: 2015-08-09

Abbazz · Joined: 23 Jun 2007 Posts: 1098 Location: Jakarta

Fourmix, the damage to your lens looks like it's more than only a coating problem. Maybe you could try to contact Henry Scherer:
http://www.zeisscamera.com/services_lens.shtml

Cheers!

Abbazz

SkedAddled · Expire: 2021-08-12

I am no expert by any means, but this looks to be a result of something
having condensed on the lens(water, oil, etc), and very slowly dried off.
The very slow drying may have left minerals or other deposits behind.
Whether or not it can be corrected, I do not know, though it does appear
to have damaged the coating.

fourmix · Joined: 29 Oct 2009 Posts: 111

Guys, thanks for your advices.

I've just mailed zeiss repair service, foto service gorlitz and focalpointlens.

I would tell you the rest of the history

Surprised