Lens adapter focus

[klompen914]

I have recently switched from a Sony APS-C sensor camera to a full-frame sensor Sony A7iii. I was using Canon FD glass lenses on the old camera using a Metabones adapter which I was able to calibrate so that infinity focus matched with the mark on the lens. I could continue to use this on theA7iii, but it is inconvenient to change the setting each time.

The tube type adapters I have tried are not calibrated so that infinity matches up. I am intrigued by the Fotodiox Pro Lens Mount Adapter because it mentions "guaranteed infinity focus", but I have seen some things about "focus past infinity" so I wonder if "guaranteed infinity focus" is what I want or if it is something else.

What I am after is an adapter where infinity on the lens is infinity focus without any need of adjustment. Is there a full-frame adapter that will do this?

[Manfred M]

I have no experience with the Canon FD series of lenses, but I understand these were mostly manual focus lenses, which means that they likely have a hard mechanical stop for infinity (this is a common feature of every manual focus lens I can ever remember using).

Having a correct infinity focus means that the adapter flange to sensor is the same as it was for the film Canon FD camera. If this is what Fotodiox has done, then their "guaranteed infinity focus" is obviously correct.

I can vouch for the quality for this company as I have one of their Hasselblad V to Nikon F shift / tilt adapters and the hard stop for infinity is bang on. The Hasselblad mount 80mm Zeiss Planar lens has the hard stop at infinity.

Any well made (i.e. correct manufacturing tolerances) should work just fine. My Novoflex Leica R to Panasonic / Olympus mFT works this way as well.

[klompen914]

Thank you, Manfred. My current adapter (left over from Sony NEX-6) is K&F Concept, which allows me to use the lens and focus to infinity, but not at the lens's infinity stop. I got burned on this and another brand when I first got the NEX-6 so I didn't want to purchase again without this kind of info.

[William W]

Note: Point #2 below was edited (26/10/2020) for clarity - this point is important.

The original published text was:"2. > Most 'tube adapters' (i.e those without optics) are made just short of the exact physical length to accommodate 'perfect' infinity focus, that at: the lens's Infinity Hard Stop - OR - smack bang in the middle of the ∞ mark."

***

I have recently switched from a Sony APS-C sensor camera to a full-frame sensor Sony A7iii. I was using Canon FD glass lenses on the old camera using a Metabones adapter which I was able to calibrate so that infinity focus matched with the mark on the lens. I could continue to use this on theA7iii, but it is inconvenient to change the setting each time.

The tube type adapters I have tried are not calibrated so that infinity matches up. I am intrigued by the Fotodiox Pro Lens Mount Adapter because it mentions "guaranteed infinity focus", but I have seen some things about "focus past infinity" so I wonder if "guaranteed infinity focus" is what I want or if it is something else.

What I am after is an adapter where infinity on the lens is infinity focus without any need of adjustment. Is there a full-frame adapter that will do this?

Short answer – Probably not.

I would like some clarification/additional information because I do not fully understand your concerns and I also especially don't understand the reason for - 'Metabones adapter which I was able to calibrate so that infinity focus matched with the mark on the lens'

Q - I assume that the “adapter” you already have is a Metabones Speedbooster?

Q – What FD lenses are you using?

A few additional comments -

1. > Focus beyond infinity ‘problems’ when introduced by using an adapter (usually always) is only an issue when using fast Normal to W/A lenses, which typically results in curvature of field issues thus inhibiting accurate focus across the (what should be) the Plane of Sharp Focus.

2. > Most 'tube adapters' (i.e those without optics) are made just short of the exact physical length to accommodate 'perfect' infinity focus, that at: the lens's Infinity Hard Stop - OR - smack bang in the middle of the ∞ mark - OR - before either.

3. > IF there is an issue using a W/A lens (1 above) and the adapter is physically short (2 above), then the fix is relatively easy for FD Lens Mount adapters because the FD Lenses are a BREECH MOUNT. The fix, usually only requiring a very minor extension of the Flange Distance, is accommodated by adding a shim underneath the face-plate at the lens's end of the adapter.

4. > “focus past infinity" – many (most?) FD, New FD and for that matter EF lenses do not have an Infinity Hard Stop and as such, already focus beyond infinity. That’s an integral part of the lens’s design. There are two main reasons for this: thermal expansion (of the optical elements) and allowances for infrared photography.

5. > The markings on a lens’s focus turret are spectacularly inefficient for accuracy and if one has (quality/premium) lenses which allow focus beyond infinity, then use that facility to accommodate precise focus, using focus peaking.

6. > If the adapter you already have is the “Speedbooster” version it would (I believe) set the A7iii to default to APS-C capture mode, so that kind of defeats the purpose of using that adapter on your new A7iii.

WW

[Manfred M]

4. > “focus past infinity" – many (most?) FD, New FD and for that matter EF lenses do not have an Infinity Hard Stop and as such, already focus beyond infinity. That’s an integral part of the lens’s design. There are two main reasons for this: thermal expansion (of the optical elements) and allowances for infrared photography.

Bill - you might want to go back and check that. On my old manual focus lenses, the IR focus mark is before one hits the hard stop for infinity, not after.

The thermal expansion issue is one that lens designers have always had to deal with and I have yet to see any detailed analysis on that particular aspect of lens design. Glass has a relatively low coefficient of thermal expansion; aluminum the primary metal used in holding the optical elements is 4 to 5 times higher, so deformation of the optical path will be highest where the glass and metal parts mate. This was also an issue in years gone by and the lenses did have a hard stop at infinity, so I'm not sure have big a factor this might be.

My understanding of why the autofocus lenses do not have a hard stop for infinity is related to the design of the autofocus mechanism. All control systems will tend to overshoot their target and will come back. It doesn't matter if this is the autofocus of the lens or the thermostat of a heating or cooling system. Potentially less of an issue with phase detect than contrast detect systems.

Having an autofocus system bang into a hard stop is potentially going to add more wear and tear into the focus mechanism. Having it overshoot and come back will be a much simpler and less expensive design solution. I suspect that this is the main reason for the "focus past infinity" feature.

[klompen914]

Short answer – Probably not.

I would like some clarification/additional information because I do not fully understand your concerns and I also especially don't understand the reason for - 'Metabones adapter which I was able to calibrate so that infinity focus matched with the mark on the lens'

Q - I assume that the “adapter” you already have is a Metabones Speedbooster?

Yes. With my NEX-6 I used a Metabones Speedbooster. Right out of the box, the infinity focus did not line up with the lens mark, but because the Speedbooster had a calibration ring I was able to set it so that I got infinity focus in the right place with all my FD lenses. This adapter also is correctly focused when I put it on my A7iii, but I don't want to change to camera settings to be able to accomodate a lens for an ASP-C camera.

Q – What FD lenses are you using?
I am using the following:
Canon Zoom Lens FD 35-105mm 1:3.5
Canon Lens FD 200mm 1:4
Canon Lens FD 50mm 1:1.4
Canon Lens FD 35mm 1:2
Canon Lens FD 28mm 1:2.8

A few additional comments -

2. > Most 'tube adapters' (i.e those without optics) are made just short of the exact physical length to accommodate 'perfect' infinity focus, that is either at the lens's Infinity Hard Stop - OR - smack bang in the middle of the ∞ mark.

All of my lenses stop with the focus mark in the middle of the ∞ mark, even if the lens is not attached to a camera. If I connect them to the tube adapters that I already have, this position is not actually in focus for distant objects and I have to continue past the ∞ mark. What I want is an adapter where this position is in focus on distant objects like I experienced with the Canon film camera that the lenses came from.

6. > If the adapter you already have is the “Speedbooster” version it would (I believe) set the A7iii to default to APS-C capture mode, so that kind of defeats the purpose of using that adapter on your new A7iii.

I think I have my A7iii set so that it does not do this automatically, but I don't want to use the camera this way. That's why I'm looking for an adapter that is made to work with the full frame sensor A7iii.

WW

[Manfred M]

Thank you, Manfred. My current adapter (left over from Sony NEX-6) is K&F Concept, which allows me to use the lens and focus to infinity, but not at the lens's infinity stop. I got burned on this and another brand when I first got the NEX-6 so I didn't want to purchase again without this kind of info.

The problem I have with a lot of these Chinese manufacturers is that we really don't know a lot about the quality of the products that they are turning out. Poor design, manufacturing tolerances or production practices could result in problems. K&F Concept appears to be out of Shenzhen China. I have had reasonably good luck with some of these unknown Chinese companies, but I have also received some garbage from them.

I have tended to stick to reputable names; if you want good quality you are going to have to pay for it. Companies like Novoflex do make high end adaptors, but you are going to pay for it. The Fotodiox adapter does not appear to be built to the same quality level as the Novoflex part, but there are a few questionable details that have more to do with design decisions than manufacturing one.

[klompen914]

BTW - I'm new here and don't know how to mark a reply as helpful. I haven't found a help section to guide me. If you can help me with that, I'd appreciate it too!

[xpatUSA]

BTW - I'm new here and don't know how to mark a reply as helpful.

Welcome!

At bottom left of the reply, click once on the thumbs-up icon. Click again to un-mark it.

Feel free to test it on this reply ...

[LenR]

The problem I have with a lot of these Chinese manufacturers is that we really don't know a lot about the quality of the products that they are turning out. Poor design, manufacturing tolerances or production practices could result in problems. K&F Concept appears to be out of Shenzhen China. I have had reasonably good luck with some of these unknown Chinese companies, but I have also received some garbage from them.

I have tended to stick to reputable names; if you want good quality you are going to have to pay for it. Companies like Novoflex do make high end adaptors, but you are going to pay for it. The Fotodiox adapter does not appear to be built to the same quality level as the Novoflex part, but there are a few questionable details that have more to do with design decisions than manufacturing one.

Agree on this score. Stick with the reputable brands.

[klompen914]

That seemed obvious, but it didn't work for me on my tablet or on two different PCs. If I hover the mouse over it, it says "javascript". Oh well, back to the original topic.

[William W]

. . .All of my lenses stop with the focus mark in the middle of the ∞ mark, even if the lens is not attached to a camera. If I connect them to the tube adapters that I already have, this position is not actually in focus for distant objects and I have to continue past the ∞ mark. What I want is an adapter where this position is in focus on distant objects like I experienced with the Canon film camera that the lenses came from. . .

Thanks for the list of lenses.

I refer to the above: I don't understand.

I understand the first underlined section to mean that all your lenses have an hard stop at the infinity mark.

I understand the second underlined section to mean that you can indeed turn the focus turret beyond the infinity mark.

That's contradictory. Please explain. Thanks.

WW

[Manfred M]

Thanks for the list of lenses.

I refer to the above: I don't understand.

I understand the first underlined section to mean that all your lenses have an hard stop at the infinity mark.

I understand the second underlined section to mean that you can indeed turn the focus turret beyond the infinity mark.

That's contradictory. Please explain. Thanks.

WW

The infrared mark on my lenses is at a point where the the focus marker for infinity rotates past it before hitting the hard stop. This means that focusing for IR is not limited by the hard stop on the lens.

[William W]

Bill - you might want to go back and check that. On my old manual focus lenses, the IR focus mark is before one hits the hard stop for infinity, not after. . .

I was referencing Canon. I was puzzled by that too, when I first read it years ago, for the same reason you raise the point now, IR focus mark is before the hard stop infinity: Canon's take, as I recall (published by Chuck Westfall, Manager Camera Division Technical Information) is the longer wavelengths of IR light come focus at a point farther than that for visible light, for some industrial and military applications having a variable infinity range allows maintaining sharp focus.

The thermal expansion issue is one that lens designers have always had to deal with and I have yet to see any detailed analysis on that particular aspect of lens design. Glass has a relatively low coefficient of thermal expansion; aluminum the primary metal used in holding the optical elements is 4 to 5 times higher, so deformation of the optical path will be highest where the glass and metal parts mate. This was also an issue in years gone by and the lenses did have a hard stop at infinity, so I'm not sure have big a factor this might be.

Again I was referencing Canon, again Chuck Westfall (my bold now for emphasis)- Compensating is for thermal expansion in the optics, and not the lens body. Materials, such as fluorite, expand and contract with ambient temperature changes and these minor movements can cause refraction of the lens surface, hence the point of infinity focus. More common in longer focal lengths but however many some Canon wide-angle zooms have inverted telephoto designs and these can be affected.

My understanding of why the autofocus lenses do not have a hard stop for infinity is related to the design of the autofocus mechanism. All control systems will tend to overshoot their target and will come back. It doesn't matter if this is the autofocus of the lens or the thermostat of a heating or cooling system. Potentially less of an issue with phase detect than contrast detect systems.

Having an autofocus system bang into a hard stop is potentially going to add more wear and tear into the focus mechanism. Having it overshoot and come back will be a much simpler and less expensive design solution. I suspect that this is the main reason for the "focus past infinity" feature.

I agree: and Canon also mentions this as a reason for why many of their Auto-focus lenses can focus beyond infinity.

However, FD Lenses (which the OP has) are Manual Focus Lenses, therefore this point is irrelevant in regard to assisting the OP, and that's why I wrote "and for that matter EF lenses", as this was only a by the way mention of Canon's Auto-focus lenses.

***

Additionally and more importantly, as I've mentioned twice, I am have difficulty in understanding the precise nature of the OP's issue.

At the moment it is my belief that the OP is concerned about something for which there should be no concern, hence my requests for clarification and more detail.

Further, technically (and now writing pedantically), many, (most) FD and nFD Lenses are ‘set’ to stop their focus turret at the infinity mark, but as I wrote “do not have an Infinity Hard Stop”. The infinity focus stop is (often) adjustable, by means of a loosening the locking screw and adjusting the Focus Turret.

The reason I did not go into that detail in my initial response was I wanted to get answers from the OP and avoid any confusion or worry for the OP.

As I have mentioned, at this point in time I can’t understand the issue and I think the OP is concerned over matters which will not be deleterious in any manner, for real world photography.

WW

[William W]

The infrared mark on my lenses is at a point where the the focus marker for infinity rotates past it before hitting the hard stop. This means that focusing for IR is not limited by the hard stop on the lens.

I don't understand why you're referencing your lenses.

The OP is not discussing the IR mark on your lenses.

I understood that the OP was referencing the infinity mark on his FD lenses and where his FD lens's focus turret stop relative to that infinity mark.

WW

[xpatUSA]

That seemed obvious, but it didn't work for me on my tablet or on two different PCs. If I hover the mouse over it, it says "javascript". Oh well, back to the original topic.

Dell-i5 Windows-7 FireFox

Hovering:


After one click:


Your system must be different - most people's do like the above as far as I know.

P.S. Sometimes it takes a while for the "1" to appear and it's tempting to click again which cancels your "like" and the "1" never appears ...

[William W]

Ernie - you wrote

All of my lenses stop with the focus mark in the middle of the ∞ mark, even if the lens is not attached to a camera. If I connect them to the tube adapters that I already have, this position is not actually in focus for distant objects and I have to continue past the ∞ mark.

Please clarify, this point is important.

Below is an image of the FD 200/4.

In my lens, the lens's Focus Turret is focused at the furthest point possible and the lens's focus hard stop is set so that the middle of the infinity mark, on the Focus Turret is in line with the orange line of the Lens Barrel.



Now on your lens -

Q1. Can you turn your lens's Focus Turret so that the middle of the infinity mark goes PAST the ORANGE LINE on the Lens Barrel, i.e. so that the letters 'm' and 'ft' move closer to the orange line on the Lens Barrel?

Q2. If yes to Q1, is it necessary to turn the Focus Turret PAST the infinity focus mark on the lens to attain infinity focus when using your tube adapter on the A7iii?

WW

[klompen914]

On my 200mm lens, with the adapter that I have, when I focus the lens to infinity the focus mark is at about 100 ft/30 m. So the infinity mark has "moved past" the marker where I want it to stop. At infinity this is no big deal, but at other distances the f-stop marks are now useless. Even though I have focus peaking and can see focus on the screen, I still use those marks for a rough-cut idea of where I want to be. So the bottom line for me is that I want to use an adapter AND have the infinity mark line up where it is supposed to be.

I have no idea what "focus beyond infinity" means or why you would want this. The original post was prompted by an adapter that said it had "guaranteed infinity focus", but running across the phrase "focus beyond infinity" as I researched this.

[xpatUSA]

On my 200mm lens, with the adapter that I have, when I focus the lens to infinity the focus mark is at about 100 ft/30 m. So the infinity mark has "moved past" the marker where I want it to stop. At infinity this is no big deal, but at other distances the f-stop marks are now useless. Even though I have focus peaking and can see focus on the screen, I still use those marks for a rough-cut idea of where I want to be. So the bottom line for me is that I want to use an adapter AND have the infinity mark line up where it is supposed to be.

Now that I think I understand the concern, I'll butt in and pass the opinion that finding an adapter that is focused exactly at infinity when your lens hits the stop under all conditions is a tall order. And that is why modern lenses allow movement of the mark past the symbol and that is also why cameras that show a focusing distance on the LCD or EVF are only vaguely accurate.

I have no idea what "focus beyond infinity" means or why you would want this.

It means that the hard stop occurs when the mark on the lens has moved past the infinity symbol, just as Bill said. Nobody here cares that much except perhaps your good self. Manufacturers like it of course - one less production step in setting up a lens -no hard stop adjustment necessary -unlike the "old" days.

[Manfred M]

finding an adapter that is focused exactly at infinity when your lens hits the stop under all conditions is a tall order

I would disagree, especially in the case of a SLR lens used on a mirrorless camera.

The adapter serves two purposes; allows a lens from one manufacturer to be used on a camera with a different lens mount and to provide the correct flange to sensor distance, which ensure focus at infinity for the old manual focus lenses with a hard stop at infinity.

Looking at the Canon FD mount, these have a 42.0mm flange focal distance whereas the Sony E mount has an 18.0 mm flange focal distance, so the adapter needs to make up for this 24.0mm difference. Not at all hard to do, as long as the manufacturer works at a high enough tolerance. I suspect that we are looking at a manufacturing tolerance of ±0.05mm or ±0.002".

The problem of adapting a lens with a shorter flange focal distance for a lens with a longer one without an optical element (which compromises image quality). Putting an Canon EF mount lens (44mm flange focal distance) on a Nikon F mount camera (46.5mm flange focal distance) could not be done as the lens would not focus at infinity.

When I went to a Nikon digital camera , I looked at converting my Leica R lenses (47.0mm flange focal distance) to the Nikon F mount. There were conversion kits on the market that took that 0.5mm off the Leica lenses, so this would have been possible.

If you look at