lens calibration

[gustav[] pEña]

hi!
i got two canon lenses a 50 1.2 and a 35 1.5 that I'm with my m8. Both lenses has different problems while focusing , the 35 being the worst.


Can some tell me how to calibrate this lenses so i can be able to focus properly with my m8.
thanks!

 

[Roger Hicks]

I agree with Fred. This is not an easy do-it-yourself job.

Cheers,

R.

 

[Sonnar Brian]

Both lenses use Shims- and they are thin diameter. Hard to make yourself. The shims on the J-3 and J-8 are wider and easier to fabricate.

The thickness of the adapter has to be spot-on the for 35mm F1.5, or any focal length other than 50mm. The thickness is not as critical for a 50mm lens.

The other factor aside from the thickness of the adapter: Canon made assumptions about film thickness when shimming their lenses. This can cause problems when using them on an M8. So likely factors: 1) adapter thickness; 2) Lens Shims; 3) Flat CCD on the M8 is different from film.

 

[sanmich]

The thickness of the adapter has to be spot-on the for 35mm F1.5, or any focal length other than 50mm. The thickness is not as critical for a 50mm lens.

.

There is something I don't understand about this adapter thing:

Lets assume that the adapter is too thick by 1/10 of a mm without any paralelism problem.
the whole lens will sit 1/10 too far from the film, INCLUDING the cam.
That means, if I get it right, that you may not get infinity, but the focusing being communicated to the camera by the cam, all intermediate distances will be right, and you should get your images in focus.

What am I missing here?

 

[John Shriver]

That's why the adapter thickness is non-critical on a 50mm lens. Heck, you can focus a 50mm lens by unscrewing it from the LTM adataper!

But on other focal lengths, the cam moves at a different rate than the lens. So the thickness of the adapter is highly critical on other focal lengths.

 

[sanmich]

Thanks for the answer, John!

It has puzzled me for a while 🙂

 

[ferider]

There is more to the adapter story:

If the adapter is too thick you will not be able to get the same resolution at infinity as with a thinner adapter, also with 50mm.

In contradiction to (at least my) intuition, for lenses other than 50mm, accurate adapter thickness is more important for wide angles than for teles.

Cheers,

Roland.

 

[sanmich]

There is more to the adapter story:

If the adapter is too thick you will not be able to get the same resolution at infinity as with a thinner adapter, also with 50mm.

In contradiction to (at least my) intuition, for lenses other than 50mm, accurate adapter thickness is more important for wide angles than for teles.

Cheers,

Roland.

That's what I think I have understood:
With a thicker than normal adapter, you can't reach infinity.
With a thinner than normal adapter, you can reach infinity, but you may focus beyond it, so you have to carefully focus at infinity.
for any other FL than 50, an out of spec adapter means out of focus pictures.
wides are more sensitive to this because of a narrower depth-of-focus (vs wider depth of field).
do I graduate? :angel:

 

[Dave Wilkinson]

A few years ago, a 'Vernier' caliper gauge was a very expensive instrument, and difficult to use - for the uninitiated!, now an adequate one with an easy digital readout can be bought very cheaply, and is a very usefull thing to have around!🙂
Dave.

 

[gustav[] pEña]

all my adapters leitz made for leica m3 and m2. I notice I'm able to focus beyond infinity and thats why i'm kind of worry with my 50 f1.2 but with the 35 1.5 is a different story, is ridiculous out of focus.


So, if i can focus beyond to infinity with my 50 1.2 those that means is ok?

is there away to make a nice focusing test? i believe my pictures a wider apertures are not that sharp with this 50 1.2 lens, but being new in this rangefinder thing and old wide lenses Im not so sure if is normal, and when i notice the focusing beyond infinity i thought it was clearly a miss alignment problem

 

[sanmich]

all my adapters leitz made for leica m3 and m2. I notice I'm able to focus beyond infinity and thats why i'm kind of worry with my 50 f1.2 but with the 35 1.5 is a different story, is ridiculous out of focus.


So, if i can focus beyond to infinity with my 50 1.2 those that means is ok?

is there away to make a nice focusing test? i believe my pictures a wider apertures are not that sharp with this 50 1.2 lens, but being new in this rangefinder thing and old wide lenses Im not so sure if is normal, and when i notice the focusing beyond infinity i thought it was clearly a miss alignment problem

two tests:
1- for lens calibration only: take a metal ruler, long enough, and stick a red and round sticker at mark 50. lay the ruler at an angle (45 degrees will do), place your camera at about the min distance from the setup, focus on the sticker, and shoot. use a tripod. do it several times and refocus everytime. your perception of focus is not perfect (at least mine isn't)
If there is no shift, you will clearly see the zone of sharpness around the sticker. If you don't...
this test is pretty insensitive to the shape, color and location of the sticker. you could use a green, square sticker at mark 30 of a wooden ruler with approximately the same results.🙄

2- dirty check of a camera: use several lenses, check infinity focusing with all, then at 3m, then at 1m. put the camera on a tripod, exactly 3m or 1m from a target on the wall (measured from the camera back), focus, and read the distance on the lens (it's limited in precision, but in practice is quite sensitive to a clear RF shift)

Good luck!

 

[Dave Wilkinson]

all my adapters leitz made for leica m3 and m2. I notice I'm able to focus beyond infinity and thats why i'm kind of worry with my 50 f1.2 but with the 35 1.5 is a different story, is ridiculous out of focus.


If you are able to focus beyond infinity - you must know how far off it is!.....wish I did!😉
Dave.