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My Zeiss Standard Prime Mk II - T2.1 - 8mm lens for 16mm


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Hi all....just received a beautiful condition (looks barely unused!!!!!!) and what I think is a Zeiss Standard Prime Mk II 8mm T2.1 lens for 16mm format which I bought on Ebay. I was hoping someone could tell me a bit about it. It has Arri bayonet mount and I have it on my Aaton XTR XC via the original adapter Aaton makes. Looking through the viewfinder I note some 'positive field curvature' which I expected.....here's info on them from the cinematechnic.com site. What I don't understand is in bold and am hoping someone will explain.....

Detailed Notes on Optical Performance

The optical design of these lenses is considered classic. Wide open, contrast is lower than what a modern prime lens (S4, Ultra Prime) can deliver. There is a “spacing” between the 10, 20 and 40 lp/mm MTF curves that is characteristic of a vintage lens. This means that progressively finer details get rendered with less contrast. This is true of all lenses, but the effect is more pronounced with older optical designs. This type of detail response is considered pleasing by many, especially when these lenses are used in conjunction with a high resolution digital cinema camera. Comparing the Distagon T* 2/16 to the Cooke Speed Panchro 2/18 wide open there is a similar spread between the 10, 20 and 40 lp/mm MTF curves, but the Distagon’s overall contrast is higher 87% vs 75% at 10 lp/mm on-axis. At the f-stop for peak on-axis MTF @40c, (f 5.6 for the Distagon and 3.7 for the Speed Panchro), the difference is more pronounced. The Distagons’ overall contrast is significantly higher and the 10/20/40 lp/mm curves are much more symmetrical and have a smoother transition from center to edge. Peak sharpness for the Distagon occurs at image height I’=4, whereas for the Speed Panchro it occurs at I’=12.

Question from me.....WHAT DOES THIS MEAN???

All Zeiss Standard Prime lenses (both the older and newer designs) exhibit some positive focus shift when stopping down. This is indicative of a “relaxed” correction of spherical aberration, especially on the older designs, which is associated with pleasing bokeh. For this reason it is recommended to stop down to the aperture you are going to shoot at and then adjust the focus for best results.
All lenses in the set exhibit positive field curvature, except for the Distagon 2/28 (which is widely considered the best of the Standard Primes for optical performance). Testing these lenses on a very accurate T-stop tester, the 16mm (which is marked T2.2) measures T2.2. The 24mm is marked T2.1 but also measured T2.2. However, both lenses are within Carl Zeiss’ tolerance spec for T2.1 marked lenses. The 50 and 85mm are both marked T2.1 and both measured exactly T2.1 Both the 50 and 85mm ST Planars cover Full Frame 24 x 36mm with some corner falloff. This excess coverage is lost when stopping down past T5.6
These lenses use the Zeiss Planar symmetrical design. The Planars are knows for high sharpness, high contrast, very good flatness of field (focus does not fall off in the corners) and very pleasing bokeh due to the simple symmetrical lens design. The 85, 100 and 135mm Standard Primes are superb close-up/portrait lens. 
As a general rule, T* coated Standard Primes can be intercut with modern cine lenses, with a good match in perceived image sharpness, as long as the ST’s are stopped down to T4. Many cinematographers feel the bokeh of the Zeiss Standard Primes is more pleasing than that of the Zeiss High Speed primes.

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This is a good example of why MTF graphs and numbers are often more confusing than helpful.

Is 75% contrast at 10lp/mm a good value? How much worse is it than 86%? What does 10lp/mm actually measure compared to 40lp/mm anyway? Is it surprising that the Distagon at f/5.6 has better contrast than the Panchro at f/3.7? Is it surprising that a 70’s Zeiss lens will have generally better MTF than a 50’s Speed Panchro? Etc, etc. 

Normally image height is the distance in mm from the centre, and MTF almost always drops from centre to edge, so why the Panchro would have peak sharpness at “12” (mms from the centre?) is anyone’s guess. I would disregard all those technical notes (which are talking about 35mm format lenses anyway and specifically just comparing a 16mm Distagon to an 18mm Speed Panchro) and simply focus on shooting with your lens. You can then analyse the images it makes directly. With older lenses there are plenty of individual factors that can influence how the lens renders an image, so generic MTF tests may not tell you anything useful about your particular lens even if you could decipher the numbers.

The usual rules of lenses apply - wide open your image will be a bit softer and fall off more at the edges, stop down too far and diffraction will introduce softness again. The only interesting fact in all those numbers might be that peak MTF for the 16mm Distagon is f/5.6, but we don’t know how much better is is than say f/4, or whether that information has any relevance to your 8mm. Your lens was often used to expand the wide end of a Zeiss 16mm format Super Speed kit (used on countless productions over the years) so it’s quality is excellent for its age and wide angle of view.

With an older lens like this I would suggest checking more practical things like the back-focus (does the focus scale line up) or whether there is any play in the focus threads causing backlash (so focus will be different depending on which direction you turn the focus ring) or causing image shift (where the image appears to jump when you change the direction of focus). 

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nice one Dom......to be honest I've never gone by mtf charts but by 'look'...for example, in the stills world, for me the old Nikkor 80-200mm is for me a way nicer lens than the modern Nikkor 70-200mm lenses....creamy images and a distinctive look.....the 80mm Hasselblad Zeiss CF Planar lens.....beautiful roll off from the focus, distinctive.....fave lens of all time: my silver 150mm C Sonnar f4.....etc etc

Edited by Stephen Perera
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Hey Dom it's fine I like the standard 16mm format....I chose to leave my Aaton as such when I got it a few years ago.....coming from Hasselblad 6x6 I like the format....and it seems to be in fashion too hahaha.....ironic how it's the perfect format for an ipad pro for example 

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