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07-02-2021, 10:43 AM - 2 Likes   #1
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Contax AX Approach: Modern Version. Is it possible?

There was film camera Contax AX allowing to auto-focus on any manual lens attached. As I understand it focused by moving whole film insert inside camera body. Huge dimension (for 35 mm body) probably was the reason that such a design did not produce any successor. But could it be restored in the digital era? Digital sensor is not that big and anyway in cameras with shake reduction sensor is not fixed. Removing focusing mechanic from lenses may simplify lenses construction a lot. What do you think?


Last edited by jumbleview; 07-02-2021 at 10:50 AM.
07-02-2021, 11:36 AM - 1 Like   #2
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Yes , It is possible but the AF range would be extremely limited.
I have Pentax-F AF 1.7x adapter , love it.

it has very limited AF build in.
You must manually pre-focus attached lens to be able to utilise adapter's limited AF.

The same principle will rule your idea.
07-02-2021, 11:42 AM - 2 Likes   #3
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Alas, the physical laws of optics make the concept bulky and unfriendly. Focusing using sensor/film movement is practical only for wide-to-normal primes because:

1) Telephoto lenses would require very long sensor travel distances. For example focusing a 300mm lens at 6 feet would require a mechanism that moves the sensor back by 3 inches. The longer the lens, the deeper the camera body needs to be. Likewise, macro lenses would still need their own focusing system (e.g., a 50mm macro lens requires 2 inches of sensor shift to get to 1:1).

2) Zooms would not stay in focus when the focal length changes -- any amount of zooming would require constant refocusing.
07-02-2021, 11:48 AM - 1 Like   #4
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QuoteOriginally posted by jumbleview Quote
There was film camera Contax AX allowing to auto-focus on any manual lens attached
If users of this camera were able to look into detail of how accurate their AF was, compared to how accurately we can today by viewing an image at 100%, the novelty would have have worn off very quickly.....as it seems it did anyway.

I love using old manual focus lenses and do...a lot. But I want to focus them myself.

07-02-2021, 12:47 PM - 1 Like   #5
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To answer the question. Nope.

The Contax solution never caught on for very good reasons. A bit like doctor Frankenstein's monster if you ask me. It only had 10mm of movement so the AF couldn't have been that great. It could be made to work with Hasselblad V mount lenses for some obscure reason.

The amazing Contax AX and ‘forbidden’ photography | grumpytykepix

I also have the 1.7x AF adapter and it works very well within its limitations,

Last edited by Wasp; 07-02-2021 at 01:03 PM.
07-02-2021, 01:06 PM   #6
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QuoteOriginally posted by photoptimist Quote
Alas, the physical laws of optics make the concept bulky and unfriendly. Focusing using sensor/film movement is practical only for wide-to-normal primes because:

1) Telephoto lenses would require very long sensor travel distances. For example focusing a 300mm lens at 6 feet would require a mechanism that moves the sensor back by 3 inches. The longer the lens, the deeper the camera body needs to be. Likewise, macro lenses would still need their own focusing system (e.g., a 50mm macro lens requires 2 inches of sensor shift to get to 1:1).

2) Zooms would not stay in focus when the focal length changes -- any amount of zooming would require constant refocusing.
Both points are well understood. Regarding the first one: if there is the place for high quality camera with fixed lens why there would be no place for camera with set of simple but high quality primes: wide and normal? Regarding the second: I believe parfocal lenses is exclusion, not norm.

---------- Post added 07-02-21 at 01:08 PM ----------

QuoteOriginally posted by Wasp Quote
To answer the question. Nope.

I also have the 1.7x AF adapter and it works very well within its limitations,
Thanks, I did not know it does exist. How it works with Pentax SR? Does it provide proper focal info to the camera?
07-03-2021, 12:07 AM   #7
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For mirrorless cameras there are AF adapters for manual focus SLR and rangefiner lenses . It is just a much better more flexible solution than making a camera that do the focusing.

A camera solution like that would be super niche as it would only be users of old vintage lenses that would be interested in the camera, but as the camera would be at least twice as expensive as a standard camera few would buy it.
As the camera would be really huge there is a big disadvantage of releasing a camera like this.

I personally do not see much point in getting AF for vintage lenses as they are so easy for focus manually with focus peaking or magnification on rear screen or EVF.


Last edited by Fogel70; 07-03-2021 at 12:16 AM.
07-03-2021, 01:09 AM   #8
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Too complicated to be applied in digital camera development. Optics probably also evolved into lenses for the benefit of better focusing. It became apparent from the film era. Thatís why this concept never produced any variants... and birders would have to accept that long telephotos would rely on themselves.
And, finally, yes , manual lenses are very fun and pretty easy playing with. So why bother.....?
07-03-2021, 01:48 AM - 2 Likes   #9
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parfocal vs varifocal

QuoteOriginally posted by jumbleview Quote
Both points are well understood. Regarding the first one: if there is the place for high quality camera with fixed lens why there would be no place for camera with set of simple but high quality primes: wide and normal? Regarding the second: I believe parfocal lenses is exclusion, not norm.

All old days zooms were usually parfocal.
I used to work in Film/TV industry , was using big cameras in the Studio / Outside broadcast environments , all manual focus.
You always first fully zoomed in ,do your focus , then the image stays in focus throughout all zooming range.
Still very desirable for Cine Zoom lenses.

Unfortunately the lenses started to get smaller / lighter ( Internal zoom / focus ) and most of them nowadays are varifocal.
For still photos with very fast AF that is not a problem.
But for video "any amount of zooming would require constant refocusing" , it might not be very practical.
I still have a number of old MF zooms , like Tamrons / Vivitars / Takumars / Tokinas etc because they all are parfocal.

---------- Post added 07-03-21 at 16:59 ----------

oh and varifocal lenses suffer from "breathing" syndrome , the size of the image changes while zooming.
07-03-2021, 09:07 AM - 2 Likes   #10
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I had the opportunity, if one can call it that, to use an AX for an afternoon.
It was barely AF, even in an era where the best AF was barley AF.
It was very slow, and was really only good for fine tuning an image that was almost in focus anyway.
The modus operandi was manual focus until almost there, let the AF fine focus, and then start again because the subject would have moved in the time it took for the AF to do something.

Also, the camera was very, very thick, as the total throw on the film plane was 20mm (+- 10 mm from rest).

Zeiss said at the time that the reason for their system was because putting the onus on the lens for AF compromised the image quality of the lens by introducing design decisions that were inimical to the best lens designs.
Instead, they came up with an AF system that didn't compromise lens quality, but did deep six any ability to take pictures at all.

Last edited by Wheatfield; 07-03-2021 at 09:16 AM.
07-12-2021, 01:34 PM   #11
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QuoteOriginally posted by Wheatfield Quote
Zeiss said at the time that the reason for their system was because putting the onus on the lens for AF compromised the image quality of the lens by introducing design decisions that were inimical to the best lens designs.
Instead, they came up with an AF system that didn't compromise lens quality, but did deep six any ability to take pictures at all.
I don't buy it. From an optical perspective, there's no difference if distancing the lens' elements from the film plane is done by moving the lens' elements forward, or the film plane backwards.
This looks like an excuse, the real reason being to avoid making a set of autofocus lenses.
07-12-2021, 02:37 PM   #12
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QuoteOriginally posted by Kunzite Quote
I don't buy it. From an optical perspective, there's no difference if distancing the lens' elements from the film plane is done by moving the lens' elements forward, or the film plane backwards.
This looks like an excuse, the real reason being to avoid making a set of autofocus lenses.
That's what I thought at the time as well.
07-14-2021, 10:14 AM   #13
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QuoteOriginally posted by Kunzite Quote
I don't buy it. From an optical perspective, there's no difference if distancing the lens' elements from the film plane is done by moving the lens' elements forward, or the film plane backwards.
This looks like an excuse, the real reason being to avoid making a set of autofocus lenses.
But lenses usually move multiple elements back and forth. That could be more difficult than moving the focal plane.

Thanks,
barondla
07-14-2021, 10:21 AM   #14
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QuoteOriginally posted by barondla Quote
But lenses usually move multiple elements back and forth. That could be more difficult than moving the focal plane.
More difficult than moving the film, shutter, viewfinder system and who knows what else? I don't think so.


Edit: here's an internal diagram:

Last edited by Kunzite; 07-14-2021 at 10:27 AM.
07-14-2021, 10:56 AM   #15
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Imagine a camera like that with 12 FPS and todays standard on AF speed.
It would be like holding a jackhammer to your face.
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