*[part II of USSR 70mm wide format lenses compendium]*
OKS2-40-1 has high resolution even at the border, nice microcontrast, very good corner illuminance of 50%, absence of astigmatism, as for distortion, well, it's very reasonable 2% at edge. Datasheet for OKS2-40-1:
By the way, OKS2-40-1 is an upscaled version of OKS1-18-1 18mm f2.8 T3.2 (35mm format) lens design, compare lens diagrams:
[OKS1-18-1 Datasheet: Resolution, MTF, Vignetting, aberrations]
— OKS4-40-1 40mm f3.5 T4 lens, diagonal image field 2ω=71°14'. This is a lens from the Soviet mainstream 70mm set. Relatively widespread because of production in line at LOMO. Meant to be a replacement for OKS2-40-1 — well, I agree it's more practical to use a smaller and faster OKS4-40-1 lens on set, but strictly speaking OKS2-40-1 is optically superior: just compare every plot of both lenses and you'll see the newer 4-40-1 is a bit worse, besides, the distortion rose to 3-4% at the edge...Do not get me wrong, it is a good lens (it's better than Cooke DuoPanchro 40mm f2.8 T3.2 for instance), it's just a step back optically. Though, lens design is always a compromise of size/price to performance and Prof. D. Volosov, a chief soviet lens designer, the author of both 40mm-s, writes that 4-40-1 is a huge leap forward.
OKS4-40-1 datasheet:
Compare 2-40-1 and 4-40-1 lens designs: both use advanced MIR-1 lens design: basic 5-element Gauss lens as a core component and a negative 3-element attachment at front. Prof. D. Volosov writes that pretty high distortion of 3-4%, edge, was intentionally introduced to the OKS4-40-1 so that the awkward unusual border perspective of such a wide lens at such a wide format became less prominent. Well, I do not know, one need to test to understand what he means, but now that seems a very poor excuse making...Tell that to Bertele's Zeiss Biogon 38mm with ~0.3% distortion!
WOW just missed the last 40mm, the OKS5-40-1. It is one more (on par with OKS2-28-1) USSR Biogon! Though, Distortion is much worse than in Biogon 38mm, it is ~1.6% at image edge, — on the other hand it is considered OK number for cine lenses in USSR (below 2%):
— OKS5-40-1 40mm f4.5 T5.3 lens, diagonal image field 2ω=82°29', made to cover square wide format frame of 46.5x52.5mm size, Vario-70 cinema. Again only a CKBK production, small quantities. Datasheet:
[update] It occurs OKS5-40-1 is not the last 40mm lens! Please welcome:
— OKS8-40-1 f2.0 T2.3 (sic!) lens, 2ω=71°14'. It's late 1980-s design, quite complex computer involved design optimization, 11 lenses in 10 groups, multi-coated, was produced in very little quantities at CKBK NPO Ekran, St. Petersburg. So here the simplified datasheet with no charts on resolution, etc, sorry, the empire fall was at the gates:
— OKS1-56-1 56mm f3 T3.4 lens, 2ω=54°12'. This lens is widely spread, it's from mainstream set. Tiny lens with impressive overall IQ, mild contrast, very pleasant creamy bokeh and high center sharpness (fall-of is also minimal since the edge is 37 lp/mm). The lens has 7 elements in 4 components Double-Gauss formula, known as Aero-Ektar of George Aklin of Kodak (US Pat.2,343,627 military aerial lens). Prof. D. Volosov, a OKS1-56-1 designer, though, did not use radioactive Thorium and rare earth Lanthanum crown glass (as it was with Aero-Ektar), but employed regular optical glass with no IQ degradation.
Datasheet of OKS1-56-1:
— OKS2-56-1 56mm f2.5 T~3 lens, 2ω=54°12'. This lens was calculated to improve OKS1-56-1 with the faster f-stop and a higher IQ — yet, it has worse egde resolution, namely 26 lp/mm vs 37 lp/mm of 1-56-1. OKS2-56-1 incorporates 5/7 lens design formula, if I'm not mistaken some Leica 50-75mm glass of the mid 1970-shas the same design. Seems it is not widely spread, being replaced by OKS3-56-1 and OKS5-56-1 lenses. Though, it was produced for some little time.
Datasheet of OKS2-56-1, taken from GOI Lens Catalogue of 1970, part I:
— OKS3-56-1 56mm f3 T3.4 lens, 2ω=54°12'. This lens incorporated some new glass types so it was also meant to be an improvement over OKS1-56-1 with the higher overall IQ — well, in some aspects (egde illuminance is shocking 70% vs 45-47% of OKS1-56-1) it is, in others, it's not (edge resolution). Compare the charts. OKS3-56-1 has the same lens design formula of 5/7 as the OKS2-56-1 whilst the details like curvatures and glass are obviously different.
Seems 3-56-1 is more widespread than OKS2-56-1 since it was at run at LOMO factory, and I have one with the serial number 660474. Yet, the "Prototype" is engraved on mine and I do not know whether it went farther to the large scale prodcution.
Datasheet of OKS3-56-1 with all the nice nerdy charts:
Prof. Volosov was not quite happy with both 2-56-1 and 3-56-1 as he was planning (at late 1970-s) to reach more at 56mm with the design which uses extra heavy crown thorium glasses (like in the Aero-Ektar of Kodak). I have no data if that happened or not.
— OKS5-56-1 56mm f2.5 T2.8 lens, 2ω=54°12'. Early 1970-s calculation by CKBK (later known as EKRAN), this lens is a final OKS1-56-1 upgrade with the separated last component so the formula is 5/7, see the lens diagram. Beside the speed (I also see 84% transmission which means, for a 5/7 lens, a multicoating applied) they say that way OKS5-56-1 received higher egde resolution, but actually I do not see that at the resolution chart...
Was in production at LOMO.
Datasheet of OKS5-56-1:
And finally the top point of Soviet 56mm:
— OKS7-56-1 56mm f2.0 T2.3 lens, 2ω=54°12'. Early 1980-s calculation by CKBK, USSR Patent 1027665, applied 17.02.1982. This lens boasts impressive speed of f2.0, the T-stop is 2.3 due to MC. Advanced and original 6/8 lens design, the patent said the goal was to make a better lens than oks5-56-1, namely to get 1.5x more speed and far better field performance while retaining compactness. The lens is supposed to have high resolution and contrast with almost zero diffusion. On the other hand, edge illuminance is as low as 30%, — there's always a price for speed in Opic / Planar deriviatives. Was in production at CKBK / EKRAN since maybe 1982 (the pic on the Datasheet shows the lens and the number on the barrel is 820001, together with "Prototype" designation). I myslef have one OKS7-56-1, serial is 870003. I found an image of one more 7-56-1 here, it is #870001. That means CKBK had been making maybe a dozen of lenses per year in the 80-s. How many of them survived? Ultra rare no bullshit.
Datasheet of the speedy OKS7-56-1:
There's Flickr album of funglaukim full of OKS7-56-1 shots mounted on Sony A7RII (photo full-frame sensor 35,9x24mm):
***
— OKS4-75-1 56mm f2.8 T3.2 lens, 2ω=41°50'. This lens is widely spread, plenty of them pop up on Ebay. Lomo production. OKS4-75-1 has the same as OKS1-56-1 lens formula of 7 elements in 4 components (Kodak Aero-Ektar). At 75mm this design shows its peak and the lens is very solid performer. See the resolution graph: 4-75-1 has very flat field with almost no fall-off. This lens rocks on portraits having comfortable shooting distance, the smoothest bokeh ever, a bit of spherical aberration, absolute lack of distortion, and a touch of 50% vignette at the edge.
Datasheet of the OKS4-75-1:
[OKS4-75-1 charts: Resolution, Vignetting, aberrations]
Welcome wide format SUPERspeed!
— OKS16-75-1 75mm f1.4 T1.6 lens, 2ω=41°49'. It's CKBK made and as rare as OKS7-56-1 56mm f2.0. 7/6 Double-Gauss formula.
Datasheet of the OKS16-75-1:
Funglaukim luckily has another 70mm album shot with OKS16-75-1 on Leica S2-P body (30×45mm sensor):
And one more with a girl wide open ehhe e heh h
