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Author Topic: 24/25mm for Contax 645 & other MF cameras.  (Read 8543 times)

Theodoros

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24/25mm for Contax 645 & other MF cameras.
« on: November 26, 2015, 07:37:34 pm »

How good is the Pentax 645 25mm lens? There is a good reason for asking this, as the lens... is going to be used on a different MF camera with larger sensor than the Pentax 645... Another question (for those that know for sure) would the image circle cover the full image area of a 54X41mm MFDB? ...and do the two versions of the lense project the same image circle?

PS: Another Q (just to confirm as I'm sure from observing pictures that it does...) Is the lever on the back on the D lens to control aperture? If yes, ...does the DA has the same lever on as to control aperture?

Thanks in advance...
« Last Edit: December 06, 2015, 02:36:05 am by Theodoros »
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Theodoros

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Has somebody tried his 25mm lens on a Pentax 645 film body as to check the image circle? 
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Christoph B.

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AFAIK the new lens comes with a new lens hood which specifically designed to be used with the digital cameras, meaning the hood is longer and will produce vignetting on a full frame 645 sensor/film.

According to http://www.pentaxforums.com/lensreviews/SMC-Pentax-D-FA-645-25mm-F4-Lens.html the image circle is large enough for full frame 645 bodies and both lenses seem to be identical (except for the lens hood on the new version).

CA is supposedly pretty high in the corners, so that'll definitely become more pronounced on a full frame body but it's very sharp and has a high resolution.
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Theodoros

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AFAIK the new lens comes with a new lens hood which specifically designed to be used with the digital cameras, meaning the hood is longer and will produce vignetting on a full frame 645 sensor/film.

According to http://www.pentaxforums.com/lensreviews/SMC-Pentax-D-FA-645-25mm-F4-Lens.html the image circle is large enough for full frame 645 bodies and both lenses seem to be identical (except for the lens hood on the new version).

CA is supposedly pretty high in the corners, so that'll definitely become more pronounced on a full frame body but it's very sharp and has a high resolution.

Great, thanks! Can you (or other) please confirm that the aperture is mechanically linked with the lever on the back of the lens? ...and does the DA have the same lever linked mechanically to the aperture blades?
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Paul2660

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I don't believe you have manual control on the aperture on this lens, as is allowed on the older 645 lenses, like the 35FA.  So more than likely it will only be wide open on anything but a 645D or Z.  On the 645 lenses I have used that allow manual aperture adjustment, the ring has the aperture ranges printed on the ring.

Paul C
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Theodoros

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I don't believe you have manual control on the aperture on this lens, as is allowed on the older 645 lenses, like the 35FA.  So more than likely it will only be wide open on anything but a 645D or Z.  On the 645 lenses I have used that allow manual aperture adjustment, the ring has the aperture ranges printed on the ring.

Paul C
If the lever on the back of a Pentax lens is mechanically linked to the aperture, one will be able to control the aperture via a (fairly simple to construct) ring on the adapter. The Pentax mount is 6.87mm (this is big!) more distance than the Contax 645 mount and 7.57mm (!!!!) from the M645 mount...  Thickness is enough on both cases for one to make a sturdy adapter that will also have a ring to control the aperture (provided that the aperture is mechanically linked to the lever on the back of the lens...). There is no need for the lens to have an aperture ring, the case will be much the same as the various adapters that control the aperture on a Nikon G series lens where there is also no aperture ring, but the aperture is mechanically linked to a lever on the lens mount.
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tsjanik

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I don't have either of the 25mm lenses, but I do have the DA 28-45mm.  It too has no aperture ring, but has a mechanical lever in the rear that will change aperture; likely the 25mm is the same.  The consensus is the two 25mm lenses have the same construction other than the hood, but I've never seen a definitive statement of such.  I wonder if indeed they are identical optically, since the DA lens is 30 g lighter than the D FA despite have a larger hood.  The D FA should cover the entire 645 area, since it was listed for use on the Pentax 645 film cameras when introduced.
« Last Edit: November 27, 2015, 01:13:21 pm by tsjanik »
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Theodoros

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I don't have either of the 25mm lenses, but I do have the DA 28-45mm.  It too has no aperture ring, but has a mechanical lever in the rear that will change aperture; likely the 25mm is the same.  The consensus is the two 25mm lenses have the same construction other than the hood, but I've never seen a definitive statement of such.  I wonder if indeed they are identical optically, since the DA lens is 30 g lighter than the D FA despite have a larger hood.  The D FA should cover the entire 645 area, since it was listed for use on the Pentax 645 film cameras when introduced.

Thanks for the reply, it's exactly what I wanted to be confirmed from a Pentax user as I'm sure that the 28-45mm (and all other D-DA lenses) are the same as the 25mm in their aperture operation... So what happens is that the aperture is still mechanically coupled (despite the absence of an aperture ring) via another lever at the edge of the camera's mount and it's only the lever on the camera that is controlled electronically... Just like it happens with a Nikon G lens! Thanks again for confirming this!  :D  :-*
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alatreille

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Theodoros...what have you got planned?

I'm really intrigued.

AL
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Theodoros

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Theodoros...what have you got planned?

I'm really intrigued.

AL

I'll make an adapter as to use the Pentax 25mm f4 on Contax... Of course all Pentax lenses will then be compatible, but the 25mm & 28-45mm f4.5 should have most interest for Contax users as they can't go wider than 35mm up to now.

 I'll build the adapter by saving off the back of a Pentax 645 old extension ring and add a C645 lens mount to the back of it which I'll take off out of a Contax extension ring. As to control the aperture, I'll use two thin (1mm) rings machined so that one "just"fits in the inner diameter and the other on the outer diameter of the (what used to be) the Pentax extension ring and connect the two rings  through a slot. On the inner ring I will have a small extension at the same place as the original Pentax 645 camera mount has the lever to automatically adjust the aperture of the lens. (Any other suggestions on the matter are welcomed)

As of AF... who needs it on a 25mm f4 lens?
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chrismuc

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I am in the similar situation like Theodoros with a Contax 645 system and the efforts to mount on it what ever lens is possible (in my case in order to use with a full frame back).

I considered a conversion or adaption of the Pentax 645 25f4 lens (must be the first version D-FA where the lens shade does not reduce the usable image circle with should be full 56mmx41,5mm) for Contax 645 since quite a time for the same reason that this is the only lens for a 645 mirror reflex system which would achieve a field of view in 135 of a 16mm lens (using a 54mm x 40,5mm digital back). The flange distance of Pentax 645 is 70,87 mm, Contax 645 is 64 mm, so 6,87 mm space for the adaption.

I did not know that there is a mechanical lever to set the aperture, and due to the fact that it anyhow would require to close the lens to f11 to get an acceptable level of corner sharpness, I considered to use the lens fixed stopped down to f11 (by the common method to first attach it to a Pentax 645 camera, set the aperture to f11, press the DOF button and unmount the lens).

From the few full resolution pictures available online by this lens and the 44mmx33mm Pentax 645D/Z camera which already show the corners becoming soft and user reports about rather strong CA and purple fringing towards the corners, I have doubts that the lens corner performance at full 54mmx40,5mm (= 6,25 larger radius of image circle compared to the Pentax 645D/Z sensor) would justify the purchase of the lens and the conversion.
(I never saw a high resolution scan from a picture by the lens on a Pentax 645 film camera that would give an idea of the IQ on full frame 645.)

So my plan ... still ... is to find a Pentax 645 25f4 D-FA at a second hand dealer, go there with my FPS + IQ180 + Pentax 645 - Canon EF adapter and do some test shots. Then we would know the full frame performance of the lens. I don't expect the corner quality of the Canon TSE 24 or even the Rodenstock 23 but it should be hopefully reasonable.)

Or maybe there is an owner/user of that lens in a range of a few hundred kilometer around Munich, then we could meet and do that test together.

A year ago I also contacted the Chinese guy Steel Chen (www.jasring.com) who does Contax 645 AF conversions similar to Conorus or Metabones and asked him if he could technically imagine a full auto aperture and auto focus conversion of Pentax 645 lenses to Contax 645 and here is his answer: "I am not familiar with P645 lens, but looks like an AF adaptor shall be possible for P645 D FA lenses. Definitely and easily, but auto-aperture is a little bit trouble, need to be done with an add-in motor in the adapter to drive the aperture open/shrink. Anyway, success possibility of this mission is 70%."

So maybe after confirming the lens performance on a FPS (which has to be proven first) we should put our knowledge and efforts together to make such conversion reality :-)

(As far as I know, the new 28-45 mm lens only covers the 44mmx33mm sensor, so not usable on Contax 645 with full frame sensor.)

Christoph
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Theodoros

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Hi Chris,

The reports for this lens say that it is sharper at corners and edges than the 28-45mm being a little less sharp at the center (on 33x44mm size sensor) and it sharp across the frame. Given that the (few) reports on this lens are all on use with the Pentax which has the smaller pixels among all MF sensors available currently, should mean (if true) that it would be OK on a 37x49mm sensor too.

On a 37x49mm sensor, the AOV (on the horizontal) is equivalent to 19mm on a FF DSLR and given the 3:4 sensor ratio, it would be the same as 16mm when one shoots at "portrait" (vertical) orientation, I find that ideal for WA use more than the even wider AOV on a 54x40.5 sensor... It also makes it a perfect supplement to the Contax-Zeiss 35mm lens (but this is also true for 44x33 & 54x40.5 size sensors too...).

Given the above, I will reconsider my current thinking of adding a 54x40.5mm sensor in my system altogether as I have two 37x49 backs already and retaining the multishot ability of both of them is the main priority for me.

My other priority is to shrink equipment I have to carry as much as possible, so I had (our mutual friend) Steel Chen to make a JAS adapter for me as to use my Contax lenses on my Nikons too, but with the Nikons, I had to retain the 17-35 too as to have WA (and a couple more Nikkor lenses), so at the end, if the Pentax 25mm lens proves as promising as it looks from first site, I may as well add a Leica S 007 body and use my Contax lenses (and the Pentax 25mm) on it and abandon the use of the DSLRs altogether....
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yashima

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #12 on: November 30, 2015, 09:41:34 pm »


As a fellow Contax user, I'm looking forward to your project.

However what I'm looking forward to the most atm is a tilt shift adapter for Contax 645 lenses for Sony E mount with auto diaphragm. AF adapter has been released so with enough demand I think it might become available.
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Theodoros

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #13 on: December 01, 2015, 09:11:20 am »

As a fellow Contax user, I'm looking forward to your project.

However what I'm looking forward to the most atm is a tilt shift adapter for Contax 645 lenses for Sony E mount with auto diaphragm. AF adapter has been released so with enough demand I think it might become available.
The Pentax lens on Contax project will definitely work... I have spend most of the day yesterday as to spot a Pentax user that will help by providing a lens (other than the 25mm - he doesn't have one) whenever it is needed to check the mechanical tolerances... I did find one and we met so that I could check the aperture operation... It is exactly like in a Nikkor lens... It will work by one having an adapter made that will have an aperture ring on the adapter...

A Contax to Sony tilt shift adapter with interface will be very difficult to make as one has to house an electronics circuit in the adapter... it will cost a lot too... I think such a device exists since one can have the ALPA one made for the FPS and adapt it on the Sony... but mind the cost...

It will be much cheaper to make a full view camera with full lens interface communication and mount a mirrorless on to that... That's another project I am working on currently and it will finish in some 3 or 4 months... It is based on a Rollei xAct2 that will have the mount for Contax lenses on the front standard and the rear part of a Contax 645 camera body (with the back mounting hinges, the focal plane shutter & the CPUs included) on the rear standard and then the electronics moved on a separate (small) box that will be mounted at the edge of the rear standard.

The camera is primarily aimed for one to use a Contax mount MFDB, but there will be two film backs converted also... One with view screen and magnifier and another for mirrorless so that one may dismount the MFDB and mount the (converted) film backs instead... One will be able to do the same on other than Rollei xAct view cameras, but there are some view cameras that won't work since the Sony's sensor is 18mm deep in the body and there is some additional space needed to allow for the camera's grip.... The Rollei eXact seems ideal for the job since the front standard can "collide" with the rear standard thus using all the available space... but view cameras that don't allow the front standard to "collide" (mechanically) with the rear standard, can be a problem for using a mirrorless on them...
« Last Edit: December 01, 2015, 09:42:14 am by Theodoros »
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chiek

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #14 on: December 04, 2015, 06:04:11 pm »

How about canon 17, 24TS lenses?
In my test, 2 TS lens is good performance for medium format corners, even 54x40.
And New 11-24 lens also good corner 33x44sensor.

Both ts lenses are not expensive and custom camera body (canon - MF) is very compact and good price.
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Theodoros

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #15 on: December 05, 2015, 06:32:55 am »

How about canon 17, 24TS lenses?
In my test, 2 TS lens is good performance for medium format corners, even 54x40.
And New 11-24 lens also good corner 33x44sensor.

Both ts lenses are not expensive and custom camera body (canon - MF) is very compact and good price.

Will the Canon 24mm T-S convert mechanically Chiek?  Does the real element has enough depth? It's 20mm needed for a Canon EOS lens... The 17mm I wouldn't consider at all for MF... Too wide! The 24s are great for 37x49 sensor... 18mm FF equivalent for the horizontal and 16mm respective equivalent in "portrait" mode is just perfect supplement to an MF 35mm lens...
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chiek

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #16 on: December 06, 2015, 05:39:57 am »

Will the Canon 24mm T-S convert mechanically Chiek?  Does the real element has enough depth? It's 20mm needed for a Canon EOS lens... The 17mm I wouldn't consider at all for MF... Too wide! The 24s are great for 37x49 sensor... 18mm FF equivalent for the horizontal and 16mm respective equivalent in "portrait" mode is just perfect supplement to an MF 35mm lens...
Canon lens needs aperture preset but it has tilt/shift function.
Rear elements is very deep. Pls check TS lenses.
I made various version of this compact camera (canon lens mount / medium format digital back)
Its price (custom compact camera + 17or24 TS lens) is lower then phaseone / hasselblad H 35mm wide angle lens.

If need to aperture control, use nikkor 14-24G or 17-35ED.
Very good lenses. I made many commercial shot by 17-35ED and custom camera.
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chiek imaging, in Seoul, SOUTH-KOREA.
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Theodoros

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #17 on: December 06, 2015, 12:43:58 pm »

Canon lens needs aperture preset but it has tilt/shift function.
Rear elements is very deep. Pls check TS lenses.
I made various version of this compact camera (canon lens mount / medium format digital back)
Its price (custom compact camera + 17or24 TS lens) is lower then phaseone / hasselblad H 35mm wide angle lens.

If need to aperture control, use nikkor 14-24G or 17-35ED.
Very good lenses. I made many commercial shot by 17-35ED and custom camera.

I think you haven't understand the problem Chiek... (nothing wrong with it as English is not your mother language - mine either, but I've a British degree in MechEng and I've practiced it there...). What I am doing, is to convert a lens as to be with Contax 645 mount and be used on a Contax 645 body... The Canons don't have manual aperture control... do they? The Nikkor 17-35mm I have (my favourit WA with FF Dslrs for years...) and I used to own the (stupid - because of flare, distortion and bulk) 14-24... Both don't have enough space so that one can fit a Contax 645 mount on to them (although the image circle does widen as they are zoomed towards the long end)...

So I did some research on which lenses would do... and I found that the Canons probably would fit if one removes the rear shift mechanism, but are extremely difficult to modify as one must control the aperture manually... and then the other two I found that would work, is the Pentax 25mm f4 and the Samyang 24mm f3.5 T-S... For the first one, one has to make an adapter of 6.87mm size, that would have an aperture ring on as to control the aperture via the lens back lever which couples the aperture mechanically (I can do that but can't find the lens easy or at a reasonable price)... For the Samyang, one has to dismount the rear shift mechanism and then screw back a self made Contax mount which will shorten the lens length by 19mm from the rear... Now, because the Samyang has an image circle of 74mm, it will work with a 37x49mm image sensor just fine... and additionally it is not too difficult a modification for a skillful one... I bet you can do it too...

EDIT: Based on lens reviews of the Samyang I've read, the lens should be sharp enough with only reasonable CA and well controlled distortion towards the edges, but it should be quite sharp as well across the frame from f5.6 to f11 as it seems to work well with shifts up to 9mm.... Mind you that I'm not convinced (out of the "study" that I've done) that the Canons will be better than the Samyang (for the purpose - which doesn't involve movements or lens functioning - only wider image circle than FF)... nor I'm convinced that the Pentax will be better than the Samyang either...
« Last Edit: December 06, 2015, 12:59:38 pm by Theodoros »
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chiek

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #18 on: December 07, 2015, 09:46:50 pm »

I think you haven't understand the problem Chiek...

I had a thinking like yours. using exist lens mount, mirror up and recessed design to direct fit Mamiya 645 camera. I disassembled Mamiya 645 body and I found It's impossible.

I means for image quality, You can compare Pentax 25mm digital lens vs 24TS+custom camera for your MFDB.
24TS lens are comparable 23mm Rodenstock digital or pentax 25DFA. and plus It has T/S benefits.

Only weak point is Flange back distance. so I'm making bridge between 24/17TS and MFDB.
« Last Edit: December 07, 2015, 09:53:53 pm by chiek »
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chiek imaging, in Seoul, SOUTH-KOREA.
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Theodoros

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Re: Pentax 645 25mm lens quality & compatibility with other MF cameras.
« Reply #19 on: December 08, 2015, 03:40:51 am »

I had a thinking like yours. using exist lens mount, mirror up and recessed design to direct fit Mamiya 645 camera. I disassembled Mamiya 645 body and I found It's impossible.

I means for image quality, You can compare Pentax 25mm digital lens vs 24TS+custom camera for your MFDB.
24TS lens are comparable 23mm Rodenstock digital or pentax 25DFA. and plus It has T/S benefits.

Only weak point is Flange back distance. so I'm making bridge between 24/17TS and MFDB.

You still haven't understand the conversion Chiek.... I don't modify the camera... I modify the lens as to work on the camera! This (for the Contax 645 body) can only be done with the Pentax 25mm (by making an adapter of 6.87mm thickness), or with the Samyang 24mm f3.5 T-S where one has to remove the rear part of the lens and fit a Contax C645 mount on it, that will be 19mm recessed on the lens so that the lens can then focus to infinity.

One would probably be able to convert the Canon lens rear part of the body..., but the problem with the Canon is that there is no mechanical coupling of the aperture so that one operate it... This means that the Canon would focus to infinity (after the conversion) but one would have to shoot wide open only.... The Samyang's body can be converted (by removing the shift mechanism altogether) and it has mechanical aperture coupling... So it will be fully functional.

Another thing I suspect will happen if one converts the Samyang, is that the lens performance should improve further! My calculations show that the image circle when measured at the rear mount of an (unconverted) Samyang lens at the mount's plane, is wider than the mount. This must affect (to some degree) the circle of confusion and thus the image quality... at least towards the edges of the projected image circle.
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