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Lomo square front, using spherical solo, aperature


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Hi,

I have the famous NAS 35 Lomo anamorphic two-piece set. I have the 50 and 75  spherical with a square anamorphic block.

The f-stops are indicated on the spherical lens. I want to shoot with the spherical lenses without the square front, but I am wondering if the f-stop markings take into account the loss of light due to all the glass on the square block. Thus, shooting without the square front would make the f-stop markings inaccurate. Does that make sense? Does anyone have any insight. I can shoot a test. most likely the best idea. Just wondering if anyone has any thoughts or experience. I had the lenses serviced by Bernie at Super16 and would like to use them.

 

Thanks!

 

Roy

NAS 35 anamorphics R.Cross.jpeg

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If the iris marks are f stops they only relate to the geometric aperture, which is a purely mathematical relationship of focal length and aperture (or entrance pupil) size. They don't take into account any internal light loss, unless the marks are T stops. Even if the marks were T stops, typically that would only refer to the light loss of the lens itself, rather than including add-on adapters.

The anamorphic block would only lose a small amount of light due to internal light loss at any rate, probably less than a quarter of a stop.

For exposure purposes using just the prime lenses I'd probably open the aperture about a quarter stop to accommodate its own internal light loss. In case there's any confusion about whether the aperture marks on a lens are f stops or T stops, the front ring of a lens often has the maximum geometric (f stop) aperture written as a ratio - ie 1:2 for an f/2 lens.

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I think the taking lenses have the name of the lens written on them. Google that and look for the t-stop of those lenses. I think it's around t2.2 or t2.3. I think these lenses are f2.0 and t2.5 is the t stop of the entire assembly not the f stop. I'd overexpose 1/3 stop relative to the marking to be safe. Just a guess btw. I actually own a similar kit and like 4-5 50mm and 75mm Lomos and when I get a chance I can check.

Edited by M Joel W
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Thank you, Dom. Thank you, Joel.

I'm heading into my work space later this afternoon and will take a closer look. My hunch is they are f-stops.

As they are Soviet made, I am not sure if I can easily find the t-stop online. I'll check. Am I correct in recalling that t-stops are generally marked in red, while f-stops are marked in white? And if so, did the Soviet artisans making these lenses follow that convention?

Thank you, again!

Roy

 

 

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You could be right. Check the names of the taking lenses, I suspect it's OKC1-75-1 and OKC1-50-1 which, again, I think are f2. And, looking online, variously marked between t2.1 and t2.3. But not sure. 

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11 hours ago, Roy Cross said:

Am I correct in recalling that t-stops are generally marked in red, while f-stops are marked in white? And if so, did the Soviet artisans making these lenses follow that convention?

I don't think you can assume any colour conventions with a lot of vintage lenses - marks may have been repainted, and Russian stuff in particular is all over the shop I've found.

Here's some photos of an OKS1-50-1  50mm Lomo, which is the prime in a squarefront Lomo anamorphic:

91390491_Lomo50mm.jpg.2ee14a2b41eff400d497fd86a135e802.jpg

You can see on the front ring the 1:2 indicates it's an f/2 lens, while the aperture ring is marked with 2.2 as the widest aperture, which means it's a T stop (otherwise it would be marked "2"). So it is an f/2 T2.2 lens.  Most older primes tend to lose about a third of a stop, which is exactly what F/2 to T2.2 represents.

OKC1-50-1 Lomos have similar marks - 1:2 on the front ring and 2.2 as the minimum aperture mark (often written in red). So again, they are f/2 T2.2 lenses.

According to some online information from Olex Services the full anamorphic set-up with anamorphic block attached is T2.5 (as M Joel wrote above). So the anamorphic block loses a further third of a stop (from T2.2 to T2.5).

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