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DKirk
8-Jun-2012, 15:29
For about 170 I recently bought an aerial reconnaissance camera, mainly to have a tinker with the 5x5 shutter and film back. It came with an Aero Ektar 7" f2.5 lens bearing a yellow dot by the serial number ER819. Can anyone shade a light on the significance of this yellow dot as opposed to other Ektars without the yellow dot. looking around there appears to be some debate, has anyone here performed a side by side test? (Mines still tanning under UV to rid it of the browning).

jcoldslabs
8-Jun-2012, 16:53
I have both yellow dot and non-yellow dot Aero-Ektars and have shot with both. To date I have not seen one whit of difference between them. The yellow dot is a 1944 lens and my other one is from 1942.

I have read that the yellow dot may indicate an optimization for daylight photography, as opposed to some other lenses (notably, in my experience, Bausch & Lomb) that are marked with both yellow and purple dots perhaps indicating daylight and night time use? I know some of the aerial lenses were used for reconnaissance and others were used to record bomb 'flashes' as they hit and exploded. Perhaps the colored dots have something to with that?

None of these explanations ever made any sense to me, though. Can a lens, either by design or coatings, be optimized for daylight or non-daylight use?

Jonathan

DKirk
9-Jun-2012, 13:19
Thought as much, or does that make it better corrected than a normal one when stopped down. Or perhaps it was merely an inventory marker system done in factory to increase sales. . .

Dan Fromm
9-Jun-2012, 14:54
Thought as much, or does that make it better corrected than a normal one when stopped down. Or perhaps it was merely an inventory marker system done in factory to increase sales. . .

There was only one customer.

Frank Petronio
9-Jun-2012, 16:16
There is a Speed with a 15" Wolly Tele on eBay now and that lens has a Yellow dot as well, so perhaps it was from the government and not the manufacturer?

75011

Mark Sawyer
9-Jun-2012, 23:49
The blue/yellow/purple dots were a code for the magnesium flouride coatings on the lenses. Different coatings were optimized for different wavelengths, which might be a day use/night use thing...

jcoldslabs
10-Jun-2012, 01:11
Mark,

I recently bought a 9" Bausch & Lomb Cinephor projection lens that has a yellow AND a purple dot on the front right next to each other. That the dots represent coatings makes sense (the Cinephor is definitely coated), but I wonder what yellow vs. purple signifies? And what does the presence of both mean? Two different coatings?

Jonathan

Mark Sawyer
10-Jun-2012, 11:40
It could be, Jonathan. I don't know whether some elements have one coating and others have another coating, or if all elements have both coatings. I have a 7.5" Cinephor with the same two dots, and it has mostly purple reflections coming through, with a single white one.

Old-N-Feeble
10-Jun-2012, 16:28
DKirk... Folks are paying big money for Aero Ektars right now. Have a look at eBay completed auctions.

Michael Cienfuegos
23-Jun-2012, 17:19
My Aero-Ektar doesn't have a yellow dot, I guess mine isn't coated. I have a large lens shade, so it does help some with flare. I tend to use it wide open, if I wanted it stopped down I could use a much lighter lens weight wise.

Martin Courtenay-Blake
16-Oct-2012, 05:32
I have one without the dot and it is definitely coated. I'm inclined to follow the day/night school of thought. I would imagine resolution is pretty much the same on all of them with the possible exception that the coating difference (if there is one) may act like a weak filter. I would guess that the film used would have made more difference and maybe the lenses were matched to a particular film type. This does bring up the interesting possibility that the non-dot lenses may actually be more useful as a general purpose lens and suited to most photographers and films.