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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!


PostPosted: Thu Apr 14, 2022 4:55 pm    Post subject: Reply with quote
OPAL wrote:
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!


Meanwhile, I am using in addition an MC Sonnar 2,8/180mm, and an nicely compact MC Biometar 2,8/120mm, both with P-6 2x converter, on both with an adaptor on my FF Sony A7 and prefered because of the image stabilization, on my APS-C Sony A6500! The only disadavantage is the heavy metal weight, but I am used to it! No problems at all, but all with an sunshade!


PostPosted: Thu Apr 14, 2022 7:23 pm    Post subject: Reply with quote
OPAL wrote:
No problems at all, but all with an sunshade!


Indeed, when using lenses designed for one format on a smaller format camera (e.g. using medium format lenses on a full frame 35mm, or using full frame 35mm lenses on an APS-C camera), you want to shade as much of the incoming light as possible. No use having all that extraneous and contrast-reducing light bouncing around off the walls in the mirror/mirrorless box.

A really good incentive to experiment with one or more of the following:

- use the hood of a lens of a longer focal length, e.g. the hood for a 250mm lens used on a 150mm lens, as long as not vignetting
- use a rectangular hood
- use a compendium lens hood
- make a rectangular mask for a round hood; black cardboard cut to size + some sticky tape works fine, assuming a non-rotating filter/hood mount


PostPosted: Thu Apr 14, 2022 9:14 pm    Post subject: Reply with quote
OPAL wrote:
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!


To be clear, the sweet spot of the image circle is used. The entire surface of the front element continues to be used, for example, to refract light into the center of the image...

Which brings us to

RokkorDoctor wrote:
OPAL wrote:
No problems at all, but all with an sunshade!


Indeed, when using lenses designed for one format on a smaller format camera (e.g. using medium format lenses on a full frame 35mm, or using full frame 35mm lenses on an APS-C camera), you want to shade as much of the incoming light as possible. No use having all that extraneous and contrast-reducing light bouncing around off the walls in the mirror/mirrorless box.

A really good incentive to experiment with one or more of the following:

- use the hood of a lens of a longer focal length, e.g. the hood for a 250mm lens used on a 150mm lens, as long as not vignetting
- use a rectangular hood
- use a compendium lens hood
- make a rectangular mask for a round hood; black cardboard cut to size + some sticky tape works fine, assuming a non-rotating filter/hood mount



Actually it is the outgoing light -- the image circle projected from the camera side of the lens -- which needs shading. Shading the front element will reduce the f/# of the lens, and, cause vignetting, as will a longer than recomended hood. The idea is already used a a rear mask seen in some telephoto lenses, an effort to increase contrast by cropping the image circle to rectangular shape to reduce residual light in the mirror box...


PostPosted: Fri Apr 15, 2022 9:22 am    Post subject: Reply with quote
visualopsins wrote:
To be clear, the sweet spot of the image circle is used. The entire surface of the front element continues to be used, for example, to refract light into the center of the image...


Not necessarily; it depends on the lens and more importantly the relative positions of the front element and entrance pupil, which are not necessarily coincident.

visualopsins wrote:
Actually it is the outgoing light -- the image circle projected from the camera side of the lens -- which needs shading. Shading the front element will reduce the f/# of the lens, and, cause vignetting, as will a longer than recomended hood. The idea is already used a a rear mask seen in some telephoto lenses, an effort to increase contrast by cropping the image circle to rectangular shape to reduce residual light in the mirror box...


I'm afraid I have to disagree here. You can shade the front of the lens with a longer than recommended hood without affecting the f/# stop of the lens for the smaller image frame used. Whilst increasing the length of the lens hood will lead to (likely near immediate) vignetting for the original frame format for which the lens was designed, when used for a noticeably smaller frame format vignetting is unlikely to occur even under some significant lengthening of the hood.

EDIT: E.g., when using my Bronica PS 4/150 on my 35mm full frame cameras, I use the longer lens hood for the Bronica PS 5.6/250. No vignetting issues.

Shading can be done either behind the lens, or in front of the lens. Best would be be both, but shading the incoming light is more effective then shading the light coming out the back of the lens. An appropriate shade in front of the lens will be an effective field stop. Field stops can be implemented either in the subject or image space of the lens. You can sometimes see compact camera lenses with a field stop just in front of the lens, or even internal to the lens. Yes, whilst generally less effective, field stops can be internal to the lens, apart from some positions where it would be completely ineffective as a field stop. One such obvious position internal to the lens where a stop is totally ineffective as a field stop is where the variable aperture stop is located Wink .

Especially with older lenses where aperture blades may not have been blackened, allowing light rays to enter the lens that are non-image forming for the smaller frame used, can lead to loss of contrast due to internal reflections in the front cell(s) of the lens. This is where appropriately designed shading in front of the lens is especially helpful. Any internal reflections in the rear cells are indeed best served by a shading mask behind the lens, hence ideally both front and rear shading masks should be employed.

One reason a rear mask is already more often employed in telephoto lenses in particular is because of the forward position of the exit pupil in many of those lenses; that increases the angle of incidence of the extraneous light hitting the internal sides of the mirror box, a condition under which anti-reflection blacking finishes usually become less effective.

In case of any confusion, as perhaps I wasn't too clear in my comment earlier; in the suggested options I'm not talking about shading the front element with a mask just in front of the front element like you see done in some compact cameras (although that would help, esp. if rectangular). I'm talking about a deep, very deep, lens hood that forms a field stop well ahead of the lens.


PostPosted: Fri Apr 15, 2022 7:13 pm    Post subject: Reply with quote
RokkorDoctor wrote:
visualopsins wrote:
To be clear, the sweet spot of the image circle is used. The entire surface of the front element continues to be used, for example, to refract light into the center of the image...


Not necessarily; it depends on the lens and more importantly the relative positions of the front element and entrance pupil, which are not necessarily coincident.


Necessarily. Light rays from the center of the frame cover the entire front element, which rays the lens converges to the center of the image circle. That is, if the front element is not flat! Smile

RokkorDoctor wrote:
visualopsins wrote:
Actually it is the outgoing light -- the image circle projected from the camera side of the lens -- which needs shading. Shading the front element will reduce the f/# of the lens, and, cause vignetting, as will a longer than recomended hood. The idea is already used a a rear mask seen in some telephoto lenses, an effort to increase contrast by cropping the image circle to rectangular shape to reduce residual light in the mirror box...


I'm afraid I have to disagree here. You can shade the front of the lens with a longer than recommended hood without affecting the f/# stop of the lens for the smaller image frame used. Whilst increasing the length of the lens hood will lead to (likely near immediate) vignetting for the original frame format for which the lens was designed, when used for a noticeably smaller frame format vignetting is unlikely to occur even under some significant lengthening of the hood.

EDIT: E.g., when using my Bronica PS 4/150 on my 35mm full frame cameras, I use the longer lens hood for the Bronica PS 5.6/250. No vignetting issues.


Correct, the lens hood length should be matched to the angle of view; a longer hood than that will cause vignetting.

RokkorDoctor wrote:
Shading can be done either behind the lens, or in front of the lens. Best would be be both, but shading the incoming light is more effective then shading the light coming out the back of the lens.
An appropriate shade in front of the lens will be an effective field stop. Field stops can be implemented either in the subject or image space of the lens.
You can sometimes see compact camera lenses with a field stop just in front of the lens, or even internal to the lens.
Yes, whilst generally less effective, field stops can be internal to the lens, apart from some positions where it would be completely ineffective as a field stop.
One such obvious position internal to the lens where a stop is totally ineffective as a field stop is where the variable aperture stop is located Wink .


As well as a field stop, rectangular and "flower petal" hoods seek to reduce the unused light outside of the part of the image circle covering the film/sensor.

In the case where stop is positioned coincident to variable aperture, the stop acts exactly as closing the variable to the same size as the stop, i.e. f/# is higher.

RokkorDoctor wrote:
Especially with older lenses where aperture blades may not have been blackened, allowing light rays to enter the lens that are non-image forming for the smaller frame used,
can lead to loss of contrast due to internal reflections in the front cell(s) of the lens.
This is where appropriately designed shading in front of the lens is especially helpful.
Any internal reflections in the rear cells are indeed best served by a shading mask behind the lens, hence ideally both front and rear shading masks should be employed.

One reason a rear mask is already more often employed in telephoto lenses in particular is because of the forward position of the exit pupil in many of those lenses;
that increases the angle of incidence of the extraneous light hitting the internal sides of the mirror box, a condition under which anti-reflection blacking finishes usually become less effective.

In case of any confusion, as perhaps I wasn't too clear in my comment earlier;
in the suggested options I'm not talking about shading the front element with a mask just in front of the front element like you see done in some compact cameras (although that would help, esp. if rectangular).
I'm talking about a deep, very deep, lens hood that forms a field stop well ahead of the lens.


But not so deep as to cut off angle of view, which leads to vignetting.


PostPosted: Fri Apr 15, 2022 8:55 pm    Post subject: Reply with quote
visualopsins wrote:
RokkorDoctor wrote:
visualopsins wrote:
To be clear, the sweet spot of the image circle is used. The entire surface of the front element continues to be used, for example, to refract light into the center of the image...


Not necessarily; it depends on the lens and more importantly the relative positions of the front element and entrance pupil, which are not necessarily coincident.


Necessarily. Light rays from the center of the frame cover the entire front element, which rays the lens converges to the center of the image circle. That is, if the front element is not flat! Smile


I still disagree on that one; for an idealised thin lens that is the case where the entire front element constitutes the entrance pupil. But for most complex multi-element lenses that is not the case. Retrofocus wide-angles are a good example where the light rays converging to the center of the frame only pass though an often very small central area of the front lens.

A very obvious example are fish-eye lenses. Look into the front of a fish-eye lens and you will see that the entrance pupil is only a tiny fraction of the diameter of the front element. Look at some of the typical ray tracings of fisheye lenses (but the same goes for the majority of wide-angle lenses):

http://360vr.com/fisheye41/coastal-fisheyep.pdf

Consider the below coloured example (excuse the poor image quality; best I could find quickly to illustrate the point):



Here, if the lens were to be used for a much smaller image frame format that only extended to about half the size, say e.g. up to the green image point (since we are talking about using medium format lenses on much smaller frame cameras), then you could literally tape off the entire edge of the front element up to a little beyond the red rays entering, and absolutely no vignetting in the image would occur.

visualopsins wrote:
RokkorDoctor wrote:
visualopsins wrote:
Actually it is the outgoing light -- the image circle projected from the camera side of the lens -- which needs shading. Shading the front element will reduce the f/# of the lens, and, cause vignetting, as will a longer than recomended hood. The idea is already used a a rear mask seen in some telephoto lenses, an effort to increase contrast by cropping the image circle to rectangular shape to reduce residual light in the mirror box...


I'm afraid I have to disagree here. You can shade the front of the lens with a longer than recommended hood without affecting the f/# stop of the lens for the smaller image frame used. Whilst increasing the length of the lens hood will lead to (likely near immediate) vignetting for the original frame format for which the lens was designed, when used for a noticeably smaller frame format vignetting is unlikely to occur even under some significant lengthening of the hood.

EDIT: E.g., when using my Bronica PS 4/150 on my 35mm full frame cameras, I use the longer lens hood for the Bronica PS 5.6/250. No vignetting issues.


Correct, the lens hood length should be matched to the angle of view; a longer hood than that will cause vignetting.


But that is my point, when using the lens for a smaller frame format camera the angle of view is smaller so a longer hood can be used.

As a thought experiment, when we gradually lengthen the hood, vignetting will increasingly set in starting from the corners of the frame, and therefore vignetting will set in sooner for a larger image frame then it will for a smaller image frame, when we are talking about the same lens. Hence when using that same lens for a smaller image frame we can use a longer hood.


PostPosted: Fri Apr 15, 2022 9:49 pm    Post subject: Reply with quote
Those ray diagrams show diffraction of light rays arriving at different angles from the subject frame. Many/most rays from the subject frame are not shown. For example, not shown are the blue rays from the blue direction also entering where the yellow rays are shown entering from a different angle/location in the frame.

An led light as the featured subject when centered in frame casts light over the entire surface of the front lens at the same angle as the center blue rays in those ray diagrams. Only a few of the rays cast over the entire front element are shown in those ray diagrams.

Look into a fisheye lens to see the entrance pupil. Cover part of the front element. See the same part of the recessed entrance pupil now covered? Smile


PostPosted: Sat Apr 16, 2022 9:58 am    Post subject: Reply with quote
visualopsins wrote:
Those ray diagrams show diffraction of light rays arriving at different angles from the subject frame. Many/most rays from the subject frame are not shown. For example, not shown are the blue rays from the blue direction also entering where the yellow rays are shown entering from a different angle/location in the frame.


No. Those ray tracings show the entire envelope of light rays that contribute to the formation of the image.

Your suggested missing blue rays from the blue direction (central subject) entering where the yellow rays are shown entering would be marginally deflected by refraction through the front lens surface and hit the lens blacking on the straight rear surface of the front lens. That is what the lens blacking paint on the back edges of fish-eye front elements is for; to prevent the extraneous light that will not make it through the lens aperture from bouncing around inside the front cell(s).

visualopsins wrote:
An led light as the featured subject when centered in frame casts light over the entire surface of the front lens at the same angle as the center blue rays in those ray diagrams. Only a few of the rays cast over the entire front element are shown in those ray diagrams.


The entire envelope of the rays that enter the front lens surface and manage to make it through the aperture are shown (for a few selected blue, green red etc. image points). E.g. any other blue rays (i.e. from the blue direction) entering the front element outside of the blue ray envelope shown will not reach the image plane (assuming decent AR coatings / lens blackening).

visualopsins wrote:
Look into a fisheye lens to see the entrance pupil. Cover part of the front element. See the same part of the recessed entrance pupil now covered? Smile


Nope.

This is the frontal view of a Samyang 8mm f/2.8 fisheye lens at f/2.8 wide open aperture. That little white circle you see in the centre is the wide-open f/2.8 entrance pupil. It doesn't get bigger than that. Most of the front element can be covered without covering the entrance pupil for a subject central in the frame.



PostPosted: Wed May 25, 2022 5:06 pm    Post subject: Reply with quote
I understand the sonnar 180mm , initially was made for 35mm and later applied to P6, so in this case , when the sonnar lens is mounted on a FF camera should have 180mm angle view , right?


PostPosted: Wed May 25, 2022 5:37 pm    Post subject: Reply with quote
kiddo wrote:
I understand the sonnar 180mm , initially was made for 35mm and later applied to P6, so in this case , when the sonnar lens is mounted on a FF camera should have 180mm angle view , right?


Confusing enit?

Yes, 180mm lens for P6 camera on FF camera has the same angle of view as 180mm lens for any camera on FF camera.

Note 180mm lens for P6 camera on P6 camera has same angle of view as 90mm lens on FF camera.
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