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True pancake Minolta 45mm f2.8 - the Tessar from 1964
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PostPosted: Wed Aug 03, 2022 3:46 pm    Post subject: True pancake Minolta 45mm f2.8 - the Tessar from 1964 Reply with quote
Hi there ))

I didn't find a dedicated topic about this lens, so opened new with the link to review.



The main idea - almost the same behavior with Carl Zeiss 45/.28 with all the weaknesses of this design, but looks like a good toy for advanced guys ))


PostPosted: Wed Aug 03, 2022 4:44 pm    Post subject: Reply with quote
I have this lens.

A key feature to be aware of is that this lens is not unit focusing.

In order to keep the lens flat there is not enough room for a conventional helicoid for unit focusing with a decent MFD, so this lens focuses by only moving the first (front) element. Even then the MFD isn't great. This trick was often used with these Tessar designs as an engineering "fudge"; as the power of the first element is stronger than the rest of the lens, a usable focus range can be attained by only a very marginal movement of the front element only.

This focus topology comes with a significant drawback though: whilst aberrations are reasonably controlled at infinity (although far from perfect), for shorter focus distances the correction for aberrations becomes severely compromised due to the changing spacing of the first element relative to the other three elements.

At the MFD the lens becomes quite soft with significant SA at f/2.8, and there is also a very significant apparent focus shift near the MFD when stopping the lens down. For short focus distances it is really not recommended to do the focusing at the wide-open f/2.8, and then stop down to take the shot. Setting focus near the MFD needs to be done at f/5.6 or even smaller working apertures. Since the Minolta SR cameras were set up to do the focusing at a wide-open working aperture, I would hazard a guess that the practical focus problems of using this lens near the MFD contributed to this lens' ultimate demise in Minolta's line-up (to be "replaced" some years later in 1978 by the optically much better MD ROKKOR 45mm f/2 )


PostPosted: Wed Aug 03, 2022 5:00 pm    Post subject: Re: True pancake Minolta 45mm f2.8 - the Tessar from 1964 Reply with quote
tf wrote:
Hi there ))

I didn't find a dedicated topic about this lens, so opened new with the link to review.


The main idea - almost the same behavior with Carl Zeiss 45/.28 with all the weaknesses of this design, but looks like a good toy for advanced guys ))


Anyone knows how it stands vs an Industar 50-2 50 mm f3.5 M42 lens (that also can be mounted on Minolta bodys via the Minolta P-adapter)?

Last edited by lattesweden on Wed Aug 03, 2022 7:31 pm; edited 1 time in total


PostPosted: Wed Aug 03, 2022 6:21 pm    Post subject: Reply with quote
RokkorDoctor wrote:
I have this lens.

A key feature to be aware of is that this lens is not unit focusing.

In order to keep the lens flat there is not enough room for a conventional helicoid for unit focusing with a decent MFD, so this lens focuses by only moving the first (front) element. Even then the MFD isn't great. This trick was often used with these Tessar designs as an engineering "fudge"; as the power of the first element is stronger than the rest of the lens, a usable focus range can be attained by only a very marginal movement of the front element only.

This focus topology comes with a significant drawback though: whilst aberrations are reasonably controlled at infinity (although far from perfect), for shorter focus distances the correction for aberrations becomes severely compromised due to the changing spacing of the first element relative to the other three elements.

At the MFD the lens becomes quite soft with significant SA at f/2.8, and there is also a very significant apparent focus shift near the MFD when stopping the lens down. For short focus distances it is really not recommended to do the focusing at the wide-open f/2.8, and then stop down to take the shot. Setting focus near the MFD needs to be done at f/5.6 or even smaller working apertures. Since the Minolta SR cameras were set up to do the focusing at a wide-open working aperture, I would hazard a guess that the practical focus problems of using this lens near the MFD contributed to this lens' ultimate demise in Minolta's line-up (to be "replaced" some years later in 1978 by the optically much better MD ROKKOR 45mm f/2 )


omg.
RokkorDoctor, can I add these your words as quote to the review? With any credentials or links to your resources of course. If not - everything is OK, no questions.
I can't believe I didn't notice focusing with the front lens (twice! The first my case was with Yashika 45/2.Cool


PostPosted: Wed Aug 03, 2022 6:36 pm    Post subject: Reply with quote
RokkorDoctor wrote:
I have this lens.

A key feature to be aware of is that this lens is not unit focusing.

In order to keep the lens flat there is not enough room for a conventional helicoid for unit focusing with a decent MFD, so this lens focuses by only moving the first (front) element. Even then the MFD isn't great. This trick was often used with these Tessar designs as an engineering "fudge"; as the power of the first element is stronger than the rest of the lens, a usable focus range can be attained by only a very marginal movement of the front element only.

This focus topology comes with a significant drawback though: whilst aberrations are reasonably controlled at infinity (although far from perfect), for shorter focus distances the correction for aberrations becomes severely compromised due to the changing spacing of the first element relative to the other three elements.

At the MFD the lens becomes quite soft with significant SA at f/2.8, and there is also a very significant apparent focus shift near the MFD when stopping the lens down. For short focus distances it is really not recommended to do the focusing at the wide-open f/2.8, and then stop down to take the shot. Setting focus near the MFD needs to be done at f/5.6 or even smaller working apertures. Since the Minolta SR cameras were set up to do the focusing at a wide-open working aperture, I would hazard a guess that the practical focus problems of using this lens near the MFD contributed to this lens' ultimate demise in Minolta's line-up (to be "replaced" some years later in 1978 by the optically much better MD ROKKOR 45mm f/2 )


Very interesting- seen a few that do this before, but never this wide. Infact, slightly wider SLR lenses that are still triplets/D-Gauss seem to struggle with aberrations (see Konica 40mm f1.8 ), so pairing it with front focusing bit of a recipe for disaster. Although not as bad as I envisioned in the review, it's clearly at the limits of acceptability even for the time it was made.

Of course with modern mirrorless you could stick this on a nice helicoid and unit focus it. I would love to see someone do this and document how the performance improves...


PostPosted: Wed Aug 03, 2022 7:04 pm    Post subject: Reply with quote
tf wrote:
RokkorDoctor wrote:
I have this lens.

A key feature to be aware of is that this lens is not unit focusing.

In order to keep the lens flat there is not enough room for a conventional helicoid for unit focusing with a decent MFD, so this lens focuses by only moving the first (front) element. Even then the MFD isn't great. This trick was often used with these Tessar designs as an engineering "fudge"; as the power of the first element is stronger than the rest of the lens, a usable focus range can be attained by only a very marginal movement of the front element only.

This focus topology comes with a significant drawback though: whilst aberrations are reasonably controlled at infinity (although far from perfect), for shorter focus distances the correction for aberrations becomes severely compromised due to the changing spacing of the first element relative to the other three elements.

At the MFD the lens becomes quite soft with significant SA at f/2.8, and there is also a very significant apparent focus shift near the MFD when stopping the lens down. For short focus distances it is really not recommended to do the focusing at the wide-open f/2.8, and then stop down to take the shot. Setting focus near the MFD needs to be done at f/5.6 or even smaller working apertures. Since the Minolta SR cameras were set up to do the focusing at a wide-open working aperture, I would hazard a guess that the practical focus problems of using this lens near the MFD contributed to this lens' ultimate demise in Minolta's line-up (to be "replaced" some years later in 1978 by the optically much better MD ROKKOR 45mm f/2 )


omg.
RokkorDoctor, can I add these your words as quote to the review? With any credentials or links to your resources of course. If not - everything is OK, no questions.
I can't believe I didn't notice focusing with the front lens (twice! The first my case was with Yashika 45/2.Cool


Sure, no problem! Friends


PostPosted: Thu Aug 04, 2022 8:27 am    Post subject: Reply with quote
eggplant wrote:
RokkorDoctor wrote:
I have this lens.

A key feature to be aware of is that this lens is not unit focusing.

In order to keep the lens flat there is not enough room for a conventional helicoid for unit focusing with a decent MFD, so this lens focuses by only moving the first (front) element. Even then the MFD isn't great. This trick was often used with these Tessar designs as an engineering "fudge"; as the power of the first element is stronger than the rest of the lens, a usable focus range can be attained by only a very marginal movement of the front element only.

This focus topology comes with a significant drawback though: whilst aberrations are reasonably controlled at infinity (although far from perfect), for shorter focus distances the correction for aberrations becomes severely compromised due to the changing spacing of the first element relative to the other three elements.

At the MFD the lens becomes quite soft with significant SA at f/2.8, and there is also a very significant apparent focus shift near the MFD when stopping the lens down. For short focus distances it is really not recommended to do the focusing at the wide-open f/2.8, and then stop down to take the shot. Setting focus near the MFD needs to be done at f/5.6 or even smaller working apertures. Since the Minolta SR cameras were set up to do the focusing at a wide-open working aperture, I would hazard a guess that the practical focus problems of using this lens near the MFD contributed to this lens' ultimate demise in Minolta's line-up (to be "replaced" some years later in 1978 by the optically much better MD ROKKOR 45mm f/2 )


Very interesting- seen a few that do this before, but never this wide. Infact, slightly wider SLR lenses that are still triplets/D-Gauss seem to struggle with aberrations (see Konica 40mm f1.8 ), so pairing it with front focusing bit of a recipe for disaster. Although not as bad as I envisioned in the review, it's clearly at the limits of acceptability even for the time it was made.

Of course with modern mirrorless you could stick this on a nice helicoid and unit focus it. I would love to see someone do this and document how the performance improves...


https://www.dpreview.com/forums/thread/4505782 shows images and a discussion on intended spherical aberration effects obtained with a front cell focusing triplet Agfa Apotar 105mm 4.5 mounted on bellows.
If the aim is to get a better image quality of the front cell focusing Tessar or Triplet design by making it unit focusing then the front cell could be set at a distance of 40x the focal length of the lens and fixed there. That seems to be the object distance these front cell focusing lenses are optimised for and deliver acceptable results when focused closer or further away.
https://www.photo.net/discuss/threads/front-cell-focusing-optimal-distance-setting.58647/


PostPosted: Thu Aug 04, 2022 8:46 am    Post subject: Reply with quote
RokkorDoctor wrote:
Sure, no problem! Friends


Thank you a lot!
Posted


PostPosted: Thu Aug 04, 2022 12:38 pm    Post subject: Reply with quote
Ernst Dinkla wrote:
https://www.dpreview.com/forums/thread/4505782 shows images and a discussion on intended spherical aberration effects obtained with a front cell focusing triplet Agfa Apotar 105mm 4.5 mounted on bellows.
If the aim is to get a better image quality of the front cell focusing Tessar or Triplet design by making it unit focusing then the front cell could be set at a distance of 40x the focal length of the lens and fixed there. That seems to be the object distance these front cell focusing lenses are optimised for and deliver acceptable results when focused closer or further away.
https://www.photo.net/discuss/threads/front-cell-focusing-optimal-distance-setting.58647/


Wow, that's quite a thread! Like 1 small

Optimising the image quality like that is also affected by residual field curvature.

E.g. from the notes in the Minolta service manuals for their ROKKOR lenses it is obvious that not all their lenses have exactly the same focus/mount register, but rather the target register is "tweaked' by up to 20 microns depending on the lens model to allow for the residual field curvature. That is, for some lens models the paraxial (center) image point is allowed to focus by up to 20 microns beyond the film plane (i.e. beyond "infinity").

Obviously that correction only works with the focus set for infinity; for shorter focus distances the user is likely to set focus by means of the focus aids in the center of the focus screen anyway, thus completely "undoing" the register tweak designed to accommodate the residual field curvature.

In theory for those relevant ROKKOR lenses with significant residual field curvature, focusing for a flat subject should be done with reference to some circular band surrounding the center of the image rather than the center of the image itself. In practice it will suffice to use the center focus aids, but then turn the focus ring a minute amount towards the infinity mark in order to achieve the approximately 10-20 micron register shift. But one has to be sure first that the lens model in question needs that shift; not all of them do.

This is now getting well off-topic though..., apologies to the OP! Wink


PostPosted: Thu Aug 04, 2022 7:01 pm    Post subject: Reply with quote
RokkorDoctor wrote:
This is now getting well off-topic though..., apologies to the OP! Wink


I do not understand how such interesting and necessary information can be offtopic. Thank you very much for the explanation!


PostPosted: Sun Aug 07, 2022 5:25 pm    Post subject: Reply with quote
The Schneider Xenar 2.8/45 is a wonderful lens, as is the Zeiss Tessar 2.8/45, both were common on fixed lens cameras. the Voigtlander Color-Skopar 2.8/45 is a cracker too. So there is no reason why a 45mm lens (although I suspect most are closer to 43.2mm) shouldn't be excellent.


PostPosted: Sun Aug 07, 2022 7:28 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
The Schneider Xenar 2.8/45 is a wonderful lens, as is the Zeiss Tessar 2.8/45, both were common on fixed lens cameras. the Voigtlander Color-Skopar 2.8/45 is a cracker too. So there is no reason why a 45mm lens (although I suspect most are closer to 43.2mm) shouldn't be excellent.


Of course.

The issue with this Minolta Rokkor TD 45mm f/2.8 for the SR mount is that they clearly tried to make the form factor as flat as possible, to get a true "pancake" lens, which involved a compromise focus topology.

The same Minolta Rokkor TD 45mm f/2.8 was also used in a number of their fixed-lens rangefinder cameras. From what I have seen it performs much better there, so probably those were made unit focusing, giving a much better IQ over a wide range of focus distances. This however is conjecture rather than me knowing for sure.


PostPosted: Mon Aug 08, 2022 2:45 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
The Schneider Xenar 2.8/45 is a wonderful lens, as is the Zeiss Tessar 2.8/45, both were common on fixed lens cameras. the Voigtlander Color-Skopar 2.8/45 is a cracker too. So there is no reason why a 45mm lens (although I suspect most are closer to 43.2mm) shouldn't be excellent.


Odd, I measured several fixed 45mm lenses of compact cameras and two were a bit shorter, more with longer focal lengths though.



I love the Color Skopar 50mm 2.8 of a Vito BL on my A7RII but I was not aware that there are compact cameras with a 45mm 2.8 or 3.5 Color Skopar, could not find them either.
https://www.dpreview.com/forums/post/63926652 for some images


PostPosted: Mon Aug 08, 2022 4:32 pm    Post subject: Reply with quote
Brain fart, I should have written Color-Apotar 2.8/45, commonly seen on AGFA cameras.

Unit focussing is definitely superior, moving the front two elements apart for focussing changes the level of corrrections, especially of SA and softens the image somewhat due to a diffuse glow.


PostPosted: Mon Aug 08, 2022 4:55 pm    Post subject: Reply with quote
Pentax's take

SMC Pentax-M 40mm 1:2.8 by The lens profile, on Flickr

SMC Pentax-M 40mm 1:2.8 by The lens profile, on Flickr

It is rear focussing. Looks like an adapted tessar with extra rear element.


PostPosted: Mon Aug 08, 2022 5:50 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
Brain fart, I should have written Color-Apotar 2.8/45, commonly seen on AGFA cameras.

Unit focussing is definitely superior, moving the front two elements apart for focussing changes the level of corrrections, especially of SA and softens the image somewhat due to a diffuse glow.


That is a Triplet, not a Tessar type.


PostPosted: Mon Aug 08, 2022 7:28 pm    Post subject: Reply with quote
D1N0 wrote:
Pentax's take

SMC Pentax-M 40mm 1:2.8 by The lens profile, on Flickr

SMC Pentax-M 40mm 1:2.8 by The lens profile, on Flickr

It is rear focussing. Looks like an adapted tessar with extra rear element.


Judging from the proportions the Minolta is still quite a bit thinner than that. Hence the need for a compromised focus topology. Honestly, I'm not sure why the Minolta designers went to such extremes to try and make it that thin. I mean the end-product was obviously compromised optically...


PostPosted: Mon Aug 08, 2022 7:49 pm    Post subject: Reply with quote
1 mm difference. The minolta is 17mm, Pentax 18mm.


PostPosted: Tue Aug 09, 2022 8:27 am    Post subject: Reply with quote
D1N0 wrote:
1 mm difference. The minolta is 17mm, Pentax 18mm.


Ha!, I only just realised what I thought was part of the Pentax lens was actually part of the rear lens cap Rolling Eyes

So yes, not much difference... Wink


PostPosted: Tue Aug 09, 2022 9:35 am    Post subject: Reply with quote
Must get some low profile caps Wink


PostPosted: Wed Aug 10, 2022 3:30 pm    Post subject: Reply with quote
RokkorDoctor wrote:
A key feature to be aware of is that this lens is not unit focusing................


You ROCK, Mark! 🤘🤘🤘 You're an excellent example of a true collector who does make images with and knows the myriad technical intricacies of the gear.

Thank you for the education. RESPECT! 🙏


PostPosted: Wed Aug 10, 2022 4:39 pm    Post subject: Reply with quote
Ernst Dinkla wrote:
iangreenhalgh1 wrote:
Brain fart, I should have written Color-Apotar 2.8/45, commonly seen on AGFA cameras.

Unit focussing is definitely superior, moving the front two elements apart for focussing changes the level of corrrections, especially of SA and softens the image somewhat due to a diffuse glow.


That is a Triplet, not a Tessar type.


I have one that is a Tessar, AGFA had lots of lens names, they might not have been so strict about what was called what and used the names to denote price bands more than anything else.
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