Canon LTM Shiming.....

[uhoh7]

Hi,

I have a few Canon Ltm lenses which are off on my M9 in focus.

This occurs with several LTM-M adapters, so I'd like to try and increase/descrease the shims.

I can get to the shims, no problem.

1) front focus needs thicker or thinner shim?

2) what options for shim materials?

TY so much,
Charlie

 

[enero]

I cant say about thickness, as I usually just add or subtract until its right, but my go to material is always aluminium foil. I fold a piece into fours and mark the size that I need and cut, which give me 8 rings to play with. I stack as needed, and if its just a tiny bit, I break a ring into pieces and adjust the position the piece with some tweezers, as needed.

 

[peterm1]

I think you will find that front focus requires a thinner shim to correct it.

I think of it this way..........when a lens is focused on an object at a close distance you will observe that its elements move forward. Hence if an existing lens is front focussing (ie focussing to a distance which is shorter than required) its elements are too far forward and you require a thinner shim on that lens to move the point of focus back (away from the shooter) a little. This usually involves sanding an existing shim to make it thinner.

However to fabricate new shims, should that becomes necessary, I have used the kind of heavy grade aluminium foil found in disposable roasting trays (found in the supermarket). These are cheap and this grade of foil is quite rigid (making it easy to handle) and yet is thin enough to be cut with a pair of sharp scissors. Making it very convenient. However it may be too thick for some purposes.

Other people on this forum may wish to confirm this before you start fritzing about with sanding shims down.

 

[rick oleson]

I had this problem with a 135mm Canon Serenar once - no adapters, the lens itself was OK on a screw mount Leica but the rangefinder cam was short by a few thousandths and it threw the rangefinder off. I couldn't adjust it out, so I used aluminum duct tape to build up the face of the RF cam until it came up correct. It was very sharp after that....

 

[John Shriver]

Being able to borrow an M Typ 240 would make this so much easier. (Make Live View agree with the RF.) For me with only film LTM cameras, adjusting the shimming is a very slow iterative process, involving developing and scanning film. I've generally paid professionals to do this for me…