Looking for guidance on focusing issue with Mamiya RB67 ProS

[Graham_Martin]

I recently acquired this camera and it came with the No 3 Rangefinder focusing screen. When shooting landscapes I seem to be out of focus. The closer I am to the subject the more noticeable it becomes. When viewing the subject, prior to the shot, it always seems to be sharpest when the bellows are wound all the way back. Is that typical?

Two recent images are attached. The image of the lions, shot from 8 feet away, appears to be front focused on the stonework in front of and below the lions. OTOH the one of the movie theater, shot from across the street, appears to be in focus. I use the split prism whenever there are some straight edges that I can line up.

When I owned an RB67 in the past I almost always found that the best focus was with the bellows right up against the camera body.

 

[MattKing]

Which lens are you using?

 

[gone]

I couldn't really tell anything from looking at your shots. Not having owned one of these, my suggestion is generic for most any camera like yours, but the first place I would look is the WLF/focus screen. If it's been replaced and not installed correctly, that would be my first thought. Focus on something quite far away by racking the lens/bellows to infinity, then ck to see if it appears in focus on the focus screen. By the same token, grab a tape measure, measure out a distance, set the lens distance to match, and see if you have a sharp image on the focus screen.

 

[Charles Wass]

Checking correct seating of the screen is certainly the first step. I no longer own the camera, but from what I recall, racking the bellows fully back may not guarantee infinity focus, depending on the lens. With the RZ67 that is the case. I doubt that it is possible reliably to take a distance from the scale on the side of the camera and measure out that distance on the ground, because the scale is difficult to read sufficiently accurately.

 

[Graham_Martin]

Which lens are you using?

65mm Sekor lens.

 

[Graham_Martin]

I was using a 65mm lens, and I agree that reading the focus scale on the side is difficult to read. I will double check the seating of the focusing screen.

 

[markbarendt]

As you get closer to the subject, the lens needs to move farther from the film and depth of field gets shorter.

So in practical terms, when shooting across the street it is pretty easy to get your subjects in acceptable focus and the lens should be back darn near against the body.

When shooting subjects that are closer it gets a little tougher, like for the lion statue but it should not be tough with the 65 mm lens, the shorter the distance from film to lens, the longer the depth of field. A 65 mm lens is pretty short.

When you get subject distance down to say 2 feet, depth of field becomes very short and focusing can become very finicky.

In all these cases stopping down to say f5 .6 or F8 or F11 or even F-16 can stretch out the depth of field and make focusing much easier.

Just out of curiosity was the lion shot done on a tripod or mono pod or handheld.

 

[Graham_Martin]

Thanks Mark

I was using a tripod but did not use the cable release or mirror up. On my last roll of film I used the cable release with mirror up. It will be interesting to see how much of a difference there is.

 

[pentaxuser]

Maybe it's the scans or maybe I am easily pleased but everything in the lions' shot looks to be in focus from the pool's edge all the way to the background where the "only" sign and windows look quite sharp.

A scan of a print of the size you'd normally do might be the only way to be sure but certainly the lions' manes look quite sharp and the pic appears to have a large DoF.

pentaxuser

 

[paul ron]

Everything looks great in your posted shots.

To check the screen you need to put a GG on the film plane as well. Open back, focus the view finder on a well lit target, check the FP GG with a loupe to see that it is as sharp as the view finder. If not you need to adjsut it.. Now focus the FP GG as sharp as can be.... yu have to decide if teh screen goes up or down to correct it.... Use the large brass screws under the screen with the spanner holes. Carefully scratch a reference line on each screw to the stationary part below so if you turn too much up or down, you can go back. ALso make sure you move each screw amt the same for all.. keeps the screen even.

Another thing to check before doing anything.... take the lens off the camera, now look at a white wall about 3' away.... tell me if you can see the lines of the view screen nice n sharp? If not DIOPTER is the cure.

 

[nwilkins]

Hi Graham,

clicking on the attached lion shot and resizing it to full size on my computer screen it is clear that your field of acceptable focus extends from the back of the fountain (behind the lions) to infinity. Everything from the lions and closer is out of focus. So obviously the bellows were not extended far enough.

This may be a stupid question but you do realize that you need to extend the bellows to focus on things that are closer than infinity, right? I ask that because you said you "always found that the best focus was with the bellows right up against the camera body".

Having the bellows totally closed means that the lens will be focused at infinity. You will get some things closer than infinity in focus depending on the size of the aperture and the focal length of the lens, but the plane of critical focus will be infinity. So if you want to take a picture of those lions you need to extend the bellows to move the plane of focus to the lions. Did you use the rangefinder spot on the lions, or on a line that was far away, at infinity? If you lined up something at infinity then everything is working fine with your camera. If you used the rangefinder on the lions themselves then it is a camera issue.

Apologies if you knew all that already - it just seemed from your post that maybe you were unsure.

 

[Graham_Martin]

Hi Graham,

clicking on the attached lion shot and resizing it to full size on my computer screen it is clear that your field of acceptable focus extends from the back of the fountain (behind the lions) to infinity. Everything from the lions and closer is out of focus. So obviously the bellows were not extended far enough.

This may be a stupid question but you do realize that you need to extend the bellows to focus on things that are closer than infinity, right? I ask that because you said you "always found that the best focus was with the bellows right up against the camera body".

Having the bellows totally closed means that the lens will be focused at infinity. You will get some things closer than infinity in focus depending on the size of the aperture and the focal length of the lens, but the plane of critical focus will be infinity. So if you want to take a picture of those lions you need to extend the bellows to move the plane of focus to the lions. Did you use the rangefinder spot on the lions, or on a line that was far away, at infinity? If you lined up something at infinity then everything is working fine with your camera. If you used the rangefinder on the lions themselves then it is a camera issue.

Apologies if you knew all that already - it just seemed from your post that maybe you were unsure.

No apologies necessary because, in fact, I had not extended the bellows and I was unsure. I don't recall exactly if the center spot was on the lions or behind them. I was more or less eyeballing it through the prism. Sometimes it is difficult to find any lines to use for focusing. I was using the 65mm lens, and I am also realizing now that I hadn't adjusted the FLE to the right distance. I'm going to go out and shoot another roll and see how I do.

 

[nwilkins]

okay well that's great then - if the bellows weren't extended at all on the lion shot then your camera is working correctly!

Try and use the rangefinder to find a line on whatever it is you need to focus on, or try eyeballing it - I actually find it easiest to focus using the centre spot of the plain matte screen. And I use the chimney finder, which is easier to use than the WLF (higher magnification and more light is blocked out). If using the WLF definitely employ the flip up magnifier for focusing.

 

[Graham_Martin]

That's good to hear. I have both a CDS prism and a chimney finder.