preset the focus via the distance setting?

[analog.universe]

In all honesty, this "they are not accurate" nonsense most likely comes from poor distance estimation, not bad scales on the lens.

You are testing with reasonable quality lenses.... Most of the complaints I've heard about scale accuracy are from cheapo lenses, where either they didn't care enough to print a legit scale, or the construction tolerances are so sloppy that it's only accurate on certain copies etc. Isn't that originally how the soft infinity stop came about? They couldn't get the tolerances tight enough on more complicated autofocus designs?

 

[Josh66]

Isn't that originally how the soft infinity stop came about?

...Not sure that I'm familiar with that term.

Do you mean how the lens will go slightly past infinity? If so, I think that is built in for a number of reasons (I read something somewhere about that once, but wouldn't know where/how to find it now)...

I'm not sure if it is the "real" reason, but I always thought it was (at least in part) to allow the AF motor to overshoot infinity then come back to it - so nothing broke by having a hard stop right at infinity (like manual focus lenses, the ones I've used anyway, have). I have heard the 'thermal expansion tolerance" theory before, but I don't buy it. If it were true, it would affect manual focus lenses too.

 

[Overread]

I thought MF focus lenses had the expansion contraction gap at the infinity end as well?

 

[analog.universe]

My Zeiss lenses don't, they have a hard stop. I have an old cheap yashica manual focus lens that has the gap however.

 

[Josh66]

If you're using an adapter from one lens mount to another, or using extension rings, or in any other way changing the mount to sensor distance, then the distance scale will not be accurate.

Just for fun, and also just to see exactly what kind of difference we're talking about here - I tested a K mount lens on another crop body (Oly E-300) with a K to 4/3 adapter. (The adapter is .265" thick, BTW.)

With the camera exactly 30" (2.5', a clearly marked distance on the lens, and also right in that 'sweet range' where the focus ring has the most travel) from the target I focused, then checked the distance scale. It was off.

I then locked the focus at the 2.5 feet mark, then moved the camera till the target was in focus. The new target-to-sensor distance was 32.32".

That would be pretty far off if you were shooting wide open close-ups, but at a longer distance and stopped down (like might be typical for street shooting) it should be close enough to 'shoot from the hip', provided that you were able to estimate the distance to the subject within a foot or two. On that particular lens, at f/8 you would be safe anywhere between 5-7 feet, or about 7-13 feet if they were a little farther away.

I would say that with that lens (even with the adapter), I would be comfortable focusing without looking through the viewfinder. Composing is another story though!

 

[Overread]

My Zeiss lenses don't, they have a hard stop. I have an old cheap yashica manual focus lens that has the gap however.

Maybe its one of those things where there is a difference of opinion in the manufacturing world - with some giving it more worth than others? Or it could be linked to materials used in construction as well as the use of smaller components/changes which might be more greatly affected.

 

[Ron Evers]

My adapted legacy lenses are not accurate on my 2x crop body.

I set up on the dinning room table a subject 1.3m from the film plane & tested two M42 mount lenses & both showed 1.2m on the distance scale. I then tested two MD mount lenses & one showed 1.1m & the other 1.2m.

I know from experience that adapted lenses on my camera focus past infinity.

 

[usayit]

In regards to DOF scales....

Scales assume a circle of confusion based on full frame. The CoC for crop cameras are different.

 

[Josh66]

In regards to DOF scales....

Scales assume a circle of confusion based on full frame. The CoC for crop cameras are different.

That only applies to DOF though, not focus - correct? My own experiments seem to say so, but I am no scientist...

 

[usayit]

In regards to DOF scales....

Scales assume a circle of confusion based on full frame. The CoC for crop cameras are different.

That only applies to DOF though, not focus - correct? My own experiments seem to say so, but I am no scientist...

Yes... but when pre focusing (or hyper focus) you are depending (hoping) that the subject falls with in the DOF. You are not working focus plane as you would at eye level but estimating the subjects' distance to fall within DOF. If you are relying on the DOF scales (remember "f/8 and be there"), on the lens while mounted on a crop camera the CoC is different which means the scales are no longer totally accurate. Depending on the lens and subject distance, you may need to compensate.