Off centre focusing...

[fleetwoodjazz]

Hi,

After owing the Zeiss Ikon and Leica M6 for a while. I come to wonder myself how do we focus on an off centre point since both cameras (or all rangefinders) only provide a small rangefinder patch in the centre as reference point. This is quite important as for wider aperture as a slight error will be very visible.

How do you do it? Do you focus at the centre first and then guess the dof? As a recent immigrant from SLR, things get a bit tricky at first but surely you guys have an answer for that.
Cheers

 

[awilder]

Swing the rf patch to the off center subject of interest, focus and simply recompose as intended. Very easy.

 

[Limpovitj]

Swing the rf patch to the off center subject of interest, focus and simply recompose as intended. Very easy.

No, that's how you misfocus fast, wide-open lenses. See these two (recent) threads on the subject:

http://www.rangefinderforum.com/forums/showthread.php?t=55743
and
http://www.rangefinderforum.com/forums/showthread.php?t=55823

Hope this helps!

 

[awilder]

Sorry, I've read both links and have no idea what's wrong with my advice as it seems to match what everyone is saying. As long as you or the subject don't move and you pivot the camera to aim at the subject, you've nailed the focus. Changing the camera postion to recompose doesn't alter the correct focus setting. This of course assumes no curvature of field, accurate focus and correct rf calibration. A fast lens shot wide open will have some curvature of field and focus shift and that being the case, it will take practice to figure out how to best compensate. Here's and old post demontrating the effect of curvature of field with a pre-asph. Summilux vs a flatter field Summicron: http://www.rangefinderforum.com/forums/showthread.php?t=42310

 

[lZr]

If using RF camera for street photography, there is no time to focus left and recompose again. I prefocus and shot as fast as possible. Missing the moment is critical. Focusing lenses 50 mm and wider, you don't need the SLR focusing approach.

 

[furcafe]

It depends on how off-center the subject is & how much you pivot, if by pivot you mean simply rotating the camera around the same axis. Using basic geometry, if the degree of the turn is great enough, then you do run the risk of moving the camera out of the correct focus distance (w/respect to the subject). If I'm shooting an off-center subject wide open (f/1.4 or f/1) & close up (1-1.5m), I'll slide, rather than swing, the camera (& myself, as Limpovitj suggested in the 1st thread) when recomposing to keep subject-to-film/sensor distance constant.

Sorry, I've read both links and have no idea what's wrong with my advice as it seems to match what everyone is saying. As long as you or the subject don't move and you pivot the camera to aim at the subject, you've nailed the focus. Changing the camera postion to recompose doesn't alter the correct focus setting. This of course assumes no curvature of field, accurate focus and correct rf calibration. A fast lens shot wide open will have some curvature of field and focus shift and that being the case, it will take practice to figure out how to best compensate.

 

[Limpovitj]

I tried to make a little sketch to explain the problem. The focus distance you get if you swing the camera to pick up focus is greater than what you want. It is really only a problem with wide-opne lenses close up. (The sketch is somewhat exaggerated.)

Let's see if my attachment works:

 

[Steve Bellayr]

From pratical experience the further you are from the subject the narrower the top two lines become. As previoulsly stated only at extreme close-ups and/wide open around f1.4 would this become an issue. Obviously, at extreme close-ups the subject is aware or it does not matter and one could shift the camera position if necessary. With that said, the rangefinder unlike the SLR is not designed for macro-photography. Again, a non-issue. When I shoot off center portraits I tend to f4 sometimes an f2.8. I don't think at f2.0 this would be an issue; maybe f1.4. But, I do not know and I don't think I have read about this issue anywhere. All in all a good question!

 

[lZr]

The optics lesson of high school is not implementable when focusing with lenses wide open.
With Nokton 1.4 we have negligible DOF and swinging the lens can lead to worse situation.
You can do SLR macros and miss the focus easy. RF cameras are not for this game. My 2 cents thoughts of course. Try it

 

[awilder]

Oh my Limpovitj! I see this is going to be a problem. That's what I use to believe a couple of years ago but someone else pointed out that I was wrong as seen here: http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00Cft2. Having rethought it, I came to my current position. I will conceed that if you pivot to one side to focus on an edge subject, your camera position naturally moves slightly farther back by about an inch or so compared to aiming it staight. I think this is causing the focus error because then you wind up focused somewhere between the ear and eye once the camera is aimed straight again. That being the case, you'll need to make a minor adjustment to the focus or your camera position WRT the subject.