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Using Medium Format Zeiss Lenses on Crop/35mm Cameras
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PostPosted: Wed Jan 20, 2016 4:49 am    Post subject: Using Medium Format Zeiss Lenses on Crop/35mm Cameras Reply with quote

Hello this question is about adapting Zeiss Medium Format lenses such as those used with the Pentacon Six Tl on crop sensor/full frame DSLR's as well as mirrorless cameras. I am a new user and created a profile to ask this question. I have been adapting legacy lenses to my Canon 5D MK3 and Sony Nex 7 for a while now and love their unique character, the way they render color and the interesting bokeh that some of them produce etc. I started researching medium format zeiss lenses a while back with the intention of adapting them to the Nex 7 and found a website where a director/videographer describes using them with a letus adapter on a Panasonic HVX 200 video camera. He describes how their slower max aperture values are actually misleading as the larger amount of glass lets in more light in comparison to a 35mm lens. He even posts comparison photos of a Flektogon 50mm F4 and a Nikon 50mm F 1.4 AI lens. I have done research on this before and from what I understand only the angle of view changes when a medium format lens/35mm lens is adapted to a camera with a smaller sensor/film size while the aperture remains unchanged. My reasoning for this is that even though they may let in more light, not all of that light is hitting the smaller sensor. The guy seems very knowledgeable about Zeiss lenses so I want to believe that he is correct about this and I am wrong. Any insight would be greatly appreciated. This is a quote from him in reference to the Zeiss Medium format lenses. "When you look at the numbers, they don´t seem to be real fast, but don´t be fooled.
Because of the huge diameter of those beasts they are almost twice as fast as the numbers suggest." Here is a link to his post on the matter: https://frankglencairn.wordpress.com/vintage-zeiss-glass-on-modern-cameras/


PostPosted: Wed Jan 20, 2016 5:40 am    Post subject: Reply with quote

Quote:
I have done research on this before and from what I understand only the angle of view changes when a medium format lens/35mm lens is adapted to a camera with a smaller sensor/film size while the aperture remains unchanged. My reasoning for this is that even though they may let in more light, not all of that light is hitting the smaller sensor.

This is correct. The focal length/aperture is the property of a lens. The larger the sensor, the area of illumination is needed.


PostPosted: Thu Jan 21, 2016 1:49 am    Post subject: Reply with quote

Thank you Calvin83 for your reply. Is this a universally agreed upon subject or are there people that say otherwise. I am hoping some other people will continue to confirm that aperture remains unchanged.


PostPosted: Thu Jan 21, 2016 2:20 am    Post subject: Reply with quote

See here:
https://en.wikipedia.org/wiki/F-number

The definition of the f-number is:
Quote:
The f-number N or f# is given by:

N = f/D
where f is the focal length, and D is the diameter of the entrance pupil (effective aperture).


Both f and D are properties of the lens -> N is a property of the lens. No mention of the format on which the lens is used.

This being the exact definition of the f-number there is no room for interpretations or different opinions.


PostPosted: Thu Jan 21, 2016 4:01 am    Post subject: Reply with quote

Thank you Dan for the concise reply. The science supports what I believed to be true and as you stated above, the F value is dependent on properties of the lens, not film or sensor size. Thank you for taking the time to answer my question.


PostPosted: Thu Jan 21, 2016 4:36 am    Post subject: Reply with quote

BTW, there are lenses made for 35mm and medium format. Take a look at the link http://vintage-camera-lenses.com/carl-zeiss-jena-biometar-2-8-80-for-pentacon-six-p6/ .


PostPosted: Thu Jan 21, 2016 5:04 am    Post subject: Reply with quote

What does happens sometimes is that, because of the large image circle of the medium format lenses, an important amount of light is projected inside the camera but outside the FF sensor/film. This outside light may be reflected and part of it may reach the sensor producing an impression of a brighter image. But it is a residual, unuseful light not carrying information.
The result is a brighter but less contrasty and less sharp image.
The use of a rear-baffle to cut this light is always advisable.


PostPosted: Thu Jan 21, 2016 6:51 am    Post subject: Reply with quote

dan_ wrote:
What does happens sometimes is that, because of the large image circle of the medium format lenses, an important amount of light is projected inside the camera but outside the FF sensor/film. This outside light may be reflected and part of it may reach the sensor producing an impression of a brighter image. But it is a residual, unuseful light not carrying information.
The result is a brighter but less contrasty and less sharp image.
The use of a rear-baffle to cut this light is always advisable.

Like 1


PostPosted: Thu Jan 21, 2016 7:20 am    Post subject: Reply with quote

That is good to know. Thanks for the information. I am always amazed by how much people on this forum know about photography. Do you guys know if many photographers use pentacon 6 mount medium format zeiss lenses like those mentioned above with adapters on DSLR's or mirrorless cameras or if this is uncommon. I have found posts about people adapting mamiya medium format lenses before but am wondering if people do the same with the lenses mentioned above. I am considering buying a pentacon six tl to shoot film but would want to use the lenses on digital cameras as well. I am beginning to think that it would be wiser to just buy older 35mm zeiss lenses instead as I have been looking for more affordable older zeiss lenses to add to my collection of 35mm MF lenses.


PostPosted: Sat Feb 06, 2016 10:54 pm    Post subject: Reply with quote

A Helios 44M has a big enough image circle to fill 6x6.


PostPosted: Sat Feb 06, 2016 11:04 pm    Post subject: Reply with quote

Then there is the "focal reducer" which takes the light from the larger image circle of medium format lens to focus it onto smaller sensor -- these actually do increase light transmission, for smaller f/# numbers.


PostPosted: Sat Feb 13, 2016 11:41 pm    Post subject: Reply with quote

I had P6 medium former Biometars (80mm and 120mm). I liked the colour and even the softness wide open, and preferred the 120mm over the 80mm. Both were used on a Canon 5Dii. I sold them recently as I was raising funds for a separate project. I thought long and hard about the decision to let the 120mm go.

I agree with the comment about stray light and the need to counteract it: I tried a couple of adapters (cheap off eBay), before finally going to a friend (who restores cars from scratch) to get one of the adapters modified. Without it, night shots had particular problems....took me a while to figure that out, and as ever, it was reading comments on here that did it.


PostPosted: Fri Jan 13, 2017 9:20 am    Post subject: Reply with quote

I am using with an P6/K6 adaptor, two lenses on my A7 and A6000! It's an 6x6 ARSAT C 2,8/80mm and an APO 5,6/250mm TELEAR which I had used für many years sucessfully on my 6x6 WIESE PENTASIX 636 and with special adaptor, the APO 5,6/250 TELEAR also on my CONTAX 645 AF.

Since I am using the sweet spot of these glasses only, I am fully happy with the results!