ОФ-233 / OF-233 210mm f/2.5

[ridax]

From a physics point of view, it's a lot easier to build a high-resolution lens for one specific wavelength than for the entire spectrum, and yellow seems to be the best wavelength for aerial recon. So, instead of making these with a detachable yellow filter like most US aerial lenses, they colored the glass?

Yes indeed I've put my hands on an aerial super-wide-angle (of the Roosinov type) that had one of its elements actually made of a deep yellow filter glass once. (Sorry I've never tried the ОФ-233, though.)

[monkeymon]

Could it be possible that the slight yellow tint is from lead glass?

I noticed, that my other russian aerial lens, has the same tint. Helios-53 200mm f/2.5.

I don't know why, but started googling about lead glass.. and the glass i found seem to have the same type of distinct slight yelloiwsh tint.

http://www.pnwx.com/Accessories/Lead...BarGlass_1.jpg
http://img.diytrade.com/cdimg/153563...lead_glass.jpg
http://www.wardray-premise.com/image...lead_glass.jpg

To my knowledge, lead glass was used as cheap high quality glass on photographic lenses (I know at least pentax used it). Probably nowadays considered toxic?

To my eye, this is the exact same tint that i seen in these lenses. In the lenses, the yellow tint is then multiplied by the many elements & heavy blue coating on every element.

This would also explain why on canon & pentax lead glass lenses, the coating is yellow, to compensate the slightly yellowish glass. But on russian lenses, they used the same blue coating... making it even more yellow?

[ridax]

The intense blue coating like this one



is actually enough to give the lens a prominent yellow tint on its own. With a coating like this, I would not even go into any suspicions about the glass itself. This is the 2-layer 'chemical' (according to the Soviet terminology) coating, deposited from some ester solutions. This kind of coating was the cheapest, and it's surprisingly low in its flare control ability and also has a strong color cast.

(The pale bluish coating also found on Soviet lenses (that one was called 'physical') was a single layer deposited by evaporation according to Zeiss technology. That one is of much higher quality; its flare control is way better, and the color cast is very modest to practically negligible.)

[ridax]

it's a lot easier to build a high-resolution lens for one specific wavelength than for the entire spectrum

Besides, a number of aerial lenses were corrected for a pretty wide range of wavelengths but the blue region was not a part of it. Instead, the correction started from the green zone and reached out well into the infrared, and those lenses were never meant to be used without a deep yellow, an orange or a red filter. Those pieces of glass are really sharp in the yellow and IR but make pretty soft-focus images on blue-sensitive film.

[Old-N-Feeble]

If it is yellowing due to radioavtive glass, that can usually be cleared with UV light.

EDIT: Never mind... not thorium glass, I guess.