Roy Cross Posted June 16, 2021 Share Posted June 16, 2021 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 Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted June 17, 2021 Premium Member Share Posted June 17, 2021 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. Link to comment Share on other sites More sharing options...
M Joel W Posted June 17, 2021 Share Posted June 17, 2021 (edited) 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 June 17, 2021 by M Joel W Link to comment Share on other sites More sharing options...
Roy Cross Posted June 17, 2021 Author Share Posted June 17, 2021 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 Link to comment Share on other sites More sharing options...
M Joel W Posted June 17, 2021 Share Posted June 17, 2021 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. Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted June 18, 2021 Premium Member Share Posted June 18, 2021 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: 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). Link to comment Share on other sites More sharing options...
Roy Cross Posted August 1, 2021 Author Share Posted August 1, 2021 Thanks, Dom! Link to comment Share on other sites More sharing options...
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