Infinity focus with micro 4/3rds adapter question

[toobacat]

I just bought one of Rainbowimaging's Nikon to micro 4/3rds adapters for my GF1. It has a little play when mounted, but otherwise seems to work fine, except when focused at infinity. I thought I would just be able to turn the focusing ring to infinity and not have to focus when shooting at a distance, but it seems to focus past infinity and I have to back the focus off a little to be in focus at infinity. I'm wondering if this is common when mounting a lens with an adapter or if my adapter just has a problem? Would focus at infinity be more precise with one of the more expensive adapters, such as Rayqual or Novoflex?

Thanks

 

[monza]

Yes, it's normal. To design and manufacture an adapter that has a hard stop exactly at infinity requires very precise tolerances and would increase the cost. The ebay adapters are built with low cost as the primary criteria. The Rayqual and Novoflex adapters will have less play and better fitment, generally speaking, but even those will focus slightly beyond infinity. The original Novoflex Leica M adapter I bought actually was too thick and prevented infinity focus, they had to modify the design.

 

[Ron Evers]

I have adapters for both Minolta & Pentax & they both provide focus past infinity.

 

[Vivek]

Yes, it's normal. To design and manufacture an adapter that has a hard stop exactly at infinity requires very precise tolerances and would increase the cost. The ebay adapters are built with low cost as the primary criteria. The Rayqual and Novoflex adapters will have less play and better fitment, generally speaking, but even those will focus slightly beyond infinity. The original Novoflex Leica M adapter I bought actually was too thick and prevented infinity focus, they had to modify the design.

While I agree that it is normal (OP's question), I disagree on the why.

There is variation among the m4/3rds registry as CDAF and live view focusing (focusing of the sensor plane) doe not require precise tolerance of the camera registry unlike a DSLR.

This ought to make the manufacturing cheaper.

One of the reasons why I am not fond of the current prices, in general. Cams with no EVF selling for ridiculous prices and slow zooms with poor build quality priced higher than much better quality lenses.

 

[monza]

That's true, focusing at the sensor plane doesn't require as precise a tolerance of the registry (as opposed to a DSLR with optical viewfinder and focusing screen) however, this doesn't necessarily imply that there is such a variation.

Bottom line, adapters should be engineered to focus as slightly beyond infinity, but as slightly as can be. This way close focus isn't compromised.

 

[Godfrey]

That's true, focusing at the sensor plane doesn't require as precise a tolerance of the registry (as opposed to a DSLR with optical viewfinder and focusing screen) however, this doesn't necessarily imply that there is such a variation.

YES

Bottom line, adapters should be engineered to focus as slightly beyond infinity, but as slightly as can be. This way close focus isn't compromised.

All the adapters for FourThirds SLRs I've used also allow adapted manual lenses to focus slightly beyond infinity too. Including the Olympus OM to Olympus FourThirds adapter.

The issue is this: Film camera lenses and tolerances in mount registration were designed for film's characteristics. Film is not rigid, it is variable in thickness, and to make it "mostly flat" yet still allow it to pass through the camera without scuffing, peeling or dragging required quite a bit of tricky engineering, with many solutions over the year. The most common, modern solutions allow the film in a 35mm camera to curl a few tenths of a mm in the format gate so that the center is approximately at the registration distance, the acceptable variation being up to a couple of tenths of a mm plus or minus (generally plus to accommodate the thickest films). Film camera lenses were designed to accommodate this variation in film thickness and consequent registration distance. (See Norman Goldberg, "Camera Technology, The Dark Side of the Lens" for a larger discussion of this subject.)

Digital sensors are both rigid and far flatter than film ever could be. So the registration distance values in digital cameras are actually much tighter than they ever were for film cameras. Unfortunately, film camera lenses don't know this and many image best at a nominal registration +0.1mm or so distance, and that's how their infinity registration is calibrated.

As a result, when placed on a digital camera mount machined to the precise nominal registration, these lenses will not actually achieve infinity focus. The only way around that is to make the mount adapters a little short of nominal registration distance to ensure that adapted lenses will achieve infinity focus. Most achieve a little more than infinity.

There's no lack of precision in digital cameras with respect to mount register. The variability in mount register is due to lenses designed to accommodate the necessary variability in film camera mount register.

 

[pellicle]

Hi toobacat

I've found that there is variation on infinity focus from the very beginning. On my blog post here I decided that it was seldom (if ever) a real issue as I don't often want to photograph the horizon at f2.8

That said, the shorter the focal lenght is the more significant the problem is.

As Vivek points out this is related to the mismatch of close physical tolerances (required and expected with mechanical and manual focus) and fully electronic systems which can essentially re-calibrate at every powerup cycle. The electronic systems do not need to "dumbly" know, as they can communicate (camera and lens) to make things right.

I (like Vivek) have assumed that this lower tolerance in manufacture would lower prices, but had assumed that components of cameras such as the G1 with an expensive and newly developed high definition EVF as well as the sensor and great rear screen would be what keeps the prices higher. As to why the Oly EP-1 (with neither the high-def rear screen or any EVF) would be significantly more expensive than a E-510 is something which can only be attributed to Oly recognising that the market will indeed pay more for less. Good business model if you ask me.

back to the infinity issue, please read my above blog post and see if you feel comfortable with making adaptions to your adaptor as may have scope to adjust ita teeny weeny bit.

the manufactures of adaptors normally make their adaptor with their manufacturing error tolerance on the short side of things to effectively guarantee infinity and beyond

 

[duckrider]

Hi toobacat,
an adapter focusing slightly bejond infinity focus may cause a little bit of inconvenience. An adapter not able to focus to infinty is worthless to use.
So manufacturers choose for the sure way to produce: Adapters are build to foucus a little bid farer than infinity.

It's similar at speedometers for automobile industry: No Speedometer shows absolute correct speed, every speedometer shows a speed faster than actually driven.
That way manufacturers are on the secure side: Nobody can make them responsable if driver was too fast in a speed control.
Here in Germany speedometer tolerance is 10% higher plus 4km per hour (e.g. at 50km/h speedometer may indicate 50 + 10% = 55 + 4 =59km/h), but a value indicatet less than actually driven is forbidden!

need for speed
Thomas

 

[toobacat]

Thanks for the responses. It's good to know my adapter is working like it should. It doesn't seem like the expensive adapters are worth the money if they work the same. I have 3 different adapters now and they all have a little play when mounted to the camera, but it doesn't seem to affect picture quality.

I have a 400mm Tele-Astranar lens that I tried on my GF1 last night and tried taking pictures of the moon, but it didn't seem to focus to infinity. I need to test it some more.

 

[photoSmart42]

It doesn't seem like the expensive adapters are worth the money if they work the same.

If that were true in all cases, you'd be correct. Infinity focus is one aspect of functionality, fit is another. I can tell you that I've had fitting issues with all but the Kipon adapters I purchased. I've had to machine the RJ adapter for my FD lenses, as well as the M42-to-FD adapter I purchased for cheap. Next time I'll wait until I can afford the more expensive Kipon adapters.

 

[toobacat]

I can tell you that I've had fitting issues with all but the Kipon adapters I purchased. I've had to machine the RJ adapter for my FD lenses, as well as the M42-to-FD adapter I purchased for cheap. Next time I'll wait until I can afford the more expensive Kipon adapters.

Was the fit so bad they wouldn't mount on your camera or was there just a lot of play?

 

[Godfrey]

Hi toobacat,
an adapter focusing slightly bejond infinity focus may cause a little bit of inconvenience. An adapter not able to focus to infinty is worthless to use. ...

Not always. My Cosmicar 12.5mm lens, set to infinity, is focused at about 4' due to the oddities of how I boffed up the adaptation. But it is still a fine shooter for my intended purposes ...

Infinity focused is achieved by setting the focus to the infinity point and stopping down to f/9. Works like a charm. ;-)

 

[photoSmart42]

Was the fit so bad they wouldn't mount on your camera or was there just a lot of play?

Neither. It was never an issue of the adapter fitting on the camera side, but issues with lenses fitting on the adapter at the other end.

 

[larryk]

If you want some real fun, try using the Contax G1/2 autofocus lenses on a Panasonic G1 with any adapter. There is no infinity position on the focus ring because there is not focus ring! I was off shore in Puerto Vallarta trying to shoot whales at a distance (grey whales) against a grey sea and grey sky with barely a horizon. Of course, the kit lenses with autofocus on the G1 searched all over the place trying to find the whales. So, I quickly switched to an adapted Contax G1/2 90mm lens (a la 180). Perfect. I thought I'd just manually focus. I couldn't find the whales either. So, I just tried to set the lens on infinity. There is none! I could just focus away anywhere I wanted to except on the whale. By the way, the whale didn't exactly wait around for all this to happen. Meanwhile, when I attach my old Leica 50mm rigid summicron I enounter a "lock" on infinity. It locks on surprisingly close in compared to the other lenses I'm talking about and it seems well focused anywhere at or beyond that point. But I didn't have it available for the whale show. A lens with no calibrated focus ring? OT but relevant: UC Berkely is testing an experimental car on the Pikes Peak uphill race (right before the real race). The car drives itself, totally automated with GPS navigation and sensors to tell it how fast to drive and where to drive. This is the future. No focus ring on the car either.

 

[henningw]

Among various adapters I have the Leica-M and Leica-R adapters from Panasonic. Those two are right on at infinity (and, by extension, at any other focussed distance). They are the only ones. All the other adapters, from various sources including a jinfinance Leica-M adapter are off and allow focussing past infinity.

I've seen and used the Novoflex and Cosina adapters, and while they are a lot better than the other third party adapters, they are not up to the level of the Panasonic ones. You have to pay for that quality, though.

Henning