Lens coating damage

[huw_evans3]

My knowledge of optical physics is sadly limited, but perhaps someone here can help me.

 

<p>

 

I have an old Apo-Ronar with some fairly substantial damage to the coating on the front element. The damage is central, and covers about 50% of the area. The glass otherwise seems perfect. Since it is a symmetrical design I could simply swap the front and rear groups around, to make the pristine rear element into the front element.

 

<p>

 

My question is, would there be any real point? I can't quite decide whether I think a damaged front coating matters more than a damaged rear coating, or whether there would be no discernible difference. If there is even a small benefit I may as well take advantage of it.

[anthony_j._kohler]

If you feel the lens is worth it (I would, for an Apo-Ronar, but it's

up to you)there is a fellow in Lafayette, Colorado who recoats

lenses. His information escapes me at the moment, but he often has an

ad in the boxed ads near the back of Shutterbug.

[armin_seeholzer]

Hi Huw

 

<p>

 

Re. change between front and rear elements should not work at all

because the rear element is smaller in diameter! So you are loosing f

stops. Are you loosing some sharpness on the negs?

I would do a test shooting and if I would see a visible loss on the

neg. then I would buy a other one!

Good testing!

[david_rose4]

I am not an optical expert, but I believe that I have heard that the

rear surface is more important than the front.

[doug_paramore]

Huw: David is correct in that the rear element's condition is more

important than the front. I would make a few shots with it and see if

it works fine as it is. If the coating bugs you, try having it

recoated, but use the front element where it is.

 

<p>

 

Regards,

[huw_evans3]

Thanks to all who have responded.

 

<p>

 

Armin, this is the only process lens I have used, so I can't

generalise too much, but certainly this 360mm Apo-Ronar (early 60s

vintage) seems to be precisely symmetrical in every respect, so I

think the option of reversing it does apply.

 

<p>

 

As Anthony suggests I may look into getting it recoated. I'm on the

other side of the Atlantic, but I know there is a company over here

which can do the job. I haven't yet had the chance to expose any film

through this lens, but aside from the coating it looks immaculate. My

simple examination of the aerial image suggests that the lens could

well turn out to be one of the sharpest I have, so I'm sure it would

be worth it in the long run (especially since I only paid the

equivalent of about $140 for it in a compur!)

 

<p>

 

From the sound of what David and Doug are saying, it seems as though

it may be as well to leave it the way it is, although clearly it will

do no harm to try it out both ways.

 

<p>

 

Thanks again for the advice.

Huw Evans.

[pete_andrews]

Don't swap the front and rear groups over, just forget about the

coating damage and buy a lens hood. The loss of coating will reduce

the effective speed of the lens by maybe 1/5th of a stop at most, and

a lens hood will more than compensate for the slight extra tendency to

flare. Think of all the great pictures taken before lens coating was

in common use.<br>The main difficulty with having the lens re-coated

is in removing the remaining coating without causing further damage.

In effect this means having the lens re-polished. Not cheap!<br>You

could always ask if a local spectacle grinder could re-coat the lens

for you, as is. Multi layer AR coating of spectacles is so commonplace

these days that many of the larger opticians workshops have their own

coating chambers.

[cesar_barreto]

Huw,

Coatings main function is avoiding internal flare within glass

elements. The first surface, obviously, don't contribute much to

flare. So, as stated above, keep the lens and relax! And, of course,

use the shade.

 

<p>

 

Cesar B.

[huw_evans3]

It looks as though the jury is well and truly in now! Thanks again

guys. I do hereby faithfully promise that I will never again

contemplate reversing this lens, and will use a well adjusted lens

shade at all times - Scout's honour! :-)