jeff laitila said:
I've been shooting with fast glass recently (50mm f1.2) and have not had any trouble focusing. (Not to say that things aren't different when shooting telephoto though...)
Could I be having a problem because I am shooting a 100mm lens, but using a 90mm ltm to M mount adapter ring?
Welcome to the club! I use a 100/2 Canon on my R-D 1 and agree its performance is sensational, but also concede that getting correct focus can be a challenge.
A few responses to your points:
-- The focal length marked on the adapter ring doesn't make any difference. It only designates what frameline will be activated when you use the adapter on a camera with automatic frameline selection, such as a M Leica or a Zeiss Ikon. The framelines are selected manually with the R-D 1, so the marking on the adapter ring doesn't matter.
On the other hand, particularly if your adapter ring is a third-party brand, it's possible that its thickness is slightly off. I've encountered this on lots of third-party adapters. Usually they're slightly too thick by a couple of hundredths of a millimeter, making the lens focus closer than it should. The only way to be sure is to measure the adapter's flange thickness with a caliper or micrometer -- it should be 0.98 or 0.99mm . If you don't have a caliper and do have several adapters, you might try switching them around and seeing if there's one that gives you better focusing results than the others when used on this lens with this camera body.
-- The fact that you get good focusing with your 50/1.2 suggests your focusing technique is basically okay, but as someone else pointed out, a 100/2 lens is more demanding in terms of focusing accuracy than a 50/1.2. I find that using an eyepiece magnifier helps a lot. If you can't find or don't want to use a magnifier, you might want to try using "split-image" focusing. This means that instead of lining up the rangefinder by merging the two images in the center of the patch, find a vertical line in the subject and use the sharply-defined
edge of the patch to join the "split" in the vertical line. The eye's ability to do this accurately (which actually has a name: "vernier acuity") is considerably higher than its ability to merge two overlapping images, so this can help you focus more accurately under difficult conditions.
Your results may be a little hit-or-miss until you really get the hang of it, but I'm sure you'll agree that the optical results this lens produces are worth the effort!
