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Lens coating - mix & match?

 
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RichS



Joined: 18 Oct 2001
Posts: 1468
Location: South of Rochester, NY
PostPosted: Thu Apr 24, 2003 5:17 pm    Post subject: Reply with quote
Actually continuing from the fungus-balsam thread...

I finally got the replacement lens for the Aerostigmat. Fairly lucky. The rear element is in great shape. There's a small scratch on the front element. Luckily, the front element on my original lens is near perfect. Sounds good so far...
Now the question... The old lens has a blue coating. The new lens looks coated, but yellow. It's a pale yellow and looks to be a coating. Since the front elements are not cemented and it's not radioactive(!) and a close look with a magnifier it all comes up coated... What would be the expected result of mixing two different color coatings such as this?
I have to say that my brain has been totally consumed this week or maybe I'd be able to figure it out myself? On one side, seems like it would work, on the other not... Or would it just add up to a green coating?
Anyone got any thoughts??

Thanks, as usual...
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Dan Fromm



Joined: 14 May 2001
Posts: 2144
Location: New Jersey
PostPosted: Thu Apr 24, 2003 5:57 pm    Post subject: Reply with quote
Quote:

On 2003-04-24 10:17, RichS wrote:
Actually continuing from the fungus-balsam thread...

I finally got the replacement lens for the Aerostigmat. Fairly lucky. The rear element is in great shape. There's a small scratch on the front element. Luckily, the front element on my original lens is near perfect. Sounds good so far...
Now the question... The old lens has a blue coating. The new lens looks coated, but yellow. It's a pale yellow and looks to be a coating. Since the front elements are not cemented and it's not radioactive(!) and a close look with a magnifier it all comes up coated... What would be the expected result of mixing two different color coatings such as this?
I have to say that my brain has been totally consumed this week or maybe I'd be able to figure it out myself? On one side, seems like it would work, on the other not... Or would it just add up to a green coating?
Anyone got any thoughts??

Thanks, as usual...

Try it and see. If you don't like the results, you can always put the pieces back where they came from. What's to lose?

FWIW, the coating on the front element of the 12"/4 TTH that came Monday is blue, the coating on the rear element is deep purple. I have no idea what's in between.

Cheers,

Dan
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RichS



Joined: 18 Oct 2001
Posts: 1468
Location: South of Rochester, NY
PostPosted: Fri Apr 25, 2003 5:03 am    Post subject: Reply with quote
Quote:

On 2003-04-24 10:57, Dan Fromm wrote:
Try it and see. If you don't like the results, you can always put the pieces back where they came from. What's to lose?

FWIW, the coating on the front element of the 12"/4 TTH that came Monday is blue, the coating on the rear element is deep purple. I have no idea what's in between.

Cheers,

Dan

Somehow I kinda knew the answer would be "try it"
I suppose that unless someone is a lens coating engineer, that's the only option really. And who knows if these old coatings are even their orginal color?
Just a shame that 8x10 is so expensive to shoot. I would really need a B&W and color of both lens combinations to judge. Unfortunately, I don't have a 4x5 back yet, and of course this is the only lens I have that's mounted on a 6x6 board so I can't try it on any of the 4x5's. And the shutter is so large that I doubt it could be mounted to even the GVII 4x4 board. On the plus side, I usually only shoot B&W in LF anyway. So hopefully next week I could try a couple of shots with it and see how it(they?) look.

At least the coatings on your TTH are both 'bluish' That's a 12 inch f/4? It must be a monster!

Wait a minute here... If I put the yellow coated element behind the blue coated element, would that give me a multi-coated lens?
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45PSS



Joined: 28 Sep 2001
Posts: 4081
Location: Mid Peninsula, Ca.
PostPosted: Fri Apr 25, 2003 6:52 am    Post subject: Reply with quote
Not being an engineer or expert, I'll make an educated stab. The Yellow coating is the older and only affects 1 or 2 errors of light. The Blue coating is newer and corrects for more errors. Passing light from more corrected to less corrected then to film may reintroduce errors. Passing light from less corrected to more corrected to film may result in slight refinment of errors but not as good as both more corrected.
Many shots in many different types of light situations may tell, but it may take a lab test run.
Charles

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