do all RB67 lenses focus at the same distance?

[BetterSense]

RB67 lenses are so cheap I'm considering making a fixed focus camera that takes RB67 lenses.

RB67's focus with a bellows. That's slightly different than most SLRs where all the lenses have to focus to infinity at the same distance. If I build a fixed focus camera, with RB67 mount, and set it to infinity focus for the 90mm lens, will it also be infinity focused for all other RB67 lenses?

 

[John Koehrer]

Nope, well I don't think so anyway. I've been wrong way too many times before.
When you make the camera, are you going to set it for a hyperfocal distance like a P&S? I don't think setting at infinity will help for close or middle distance.

 

[tkamiya]

I am looking at side of my RB-SD. It has a scale that tells the user what bellows factor to use as well as distance to the subject. If I look at the very top where infinity is, it all converge to a point where bellows retracted all the way.

If you can wait until tomorrow, I can try it with lens I have and tell you what I see. If I recall correctly, I think they all focus to infinity with bellows retracted all the way in.

What focal length are you interested in?
I have 65, 90, 127, 150SF and 180mm

 

[MattKing]

The lenses each focus to infinity at a different amount of bellows extension. The chart that tkamiya refers to requires you to use the bellows extension combined with those coloured lines - a different one for each focal length - to make it work.

 

[polyglot]

They all focus to infinity at their minimum bellows stops (at least, that's what the RZ does), i.e. with the lens at the mount registration distance.

They have different maximum magnifications though because the bellows gives you the same max extension but the lenses have different focal lengths. So you can focus closer with a shorter lens.

 

[Kevin Harding]

One of my lenses, and I can't remember if it's the 50 or 250, wants a 1/10th turn of the nob before it comes to infinity, but otherwise no bellows extension is infinity for me.

 

[analoguey]

The above bellows extension clearly shows it as "0" for infinity. (see in detail)
Matt, what you are referring to is the bellows extension factor that is for macro work.
The manual clearly differentiates between the distance to film plane (represented on the extreme right of Tkamiya's pic above) and the bellows compensation factor which is the shaded bar chart.

 

[BetterSense]

I would mostly be interested in the 50mm, but now that I have picked up my 50 and hefted it, the project seems less appealing. It's too heavy. If I could afford a 38mm Grandagon I would make a camera using that.

 

[analoguey]

All RB lenses are heavy. Nature of the beast.

 

[tkamiya]

So you don't want me to test this anymore? Yes, RB lenses are heavy..... but in a good way

 

[Dan Fromm]

I would mostly be interested in the 50mm, but now that I have picked up my 50 and hefted it, the project seems less appealing. It's too heavy. If I could afford a 38mm Grandagon I would make a camera using that.

35 mm, not 38. You're still not good enough at doing your own research or correcting your typos.

I have a 35/4.5 Apo-Grandagon. It needs to be focused. If you must make an inexpensive fixed focus 6x7 or 6x9 camera, make a box with a pinhole. Nothing in the image will be sharp.

Oh and by the way, the best, IMO, inexpensive camera body for a 35/4.5 Apo-Grandagon is a Century Graphic.

 

[tkamiya]

I just tried it outside.

I used my RB-SD, 65mm K/L, 127mm K/L, and 180mm K/L. Subject distance is about 1/4 miles or 400 meters.
65mm focused with bellows racked in all the way. 127mm focused about 1/30th of a turn away from all the way in. 180mm focused 1/20th away. Essentially, they all focused at infinity all the way in or in marginal distance from it.

I'm thinking Mamiya lens may be unsuitable for OP's purposes though. The mounting plate to film plane distance is almost 5 inches. It'll be a really thick point and shoot camera.... Also, if OP plans to cover infinity focus with hyper focusing, then the film plane/lens distance where hyper focus will cover infinity will be different from lens to lens.

If there's anything I can test for you, please let me know.

 

[Ian C]

With respect to posts #6 and #12

It’s usually the case that longer lenses require a bit of extra focus distance available to attain infinity focus at the highest temperatures for which the lens is designed.

This is to compensate for the lengthening of the barrel at increasing ambient temperatures. At high temperatures, the lens has to be displaced further towards the film to attain infinity focus. That’s because the glass units are already slightly forward of their usual position due to the heat-lengthened barrel.

The additional focus travel is a function of the barrel length and is roughly proportional to the focal length. Thus, a 500mm lens might require slightly more thermal focus compensation than a 360mm lens and a 360mm lens would need more than a 180mm lens and so forth.

In very high temperatures the reserve focusing distance shrinks as the barrel lengthens due to thermal expansion. In this case, the focusing adjustment might be all the way against the stops, or nearly so, at infinity focus at the highest operating temperature for which the lens is designed.

On long helicoid-focusing lenses, the focusing ring can be turned to place the infinity mark on the focusing ring somewhat past the focusing index line on the sleeve. This extra rotation of the focusing ring is used to compensate for the thermal lengthening of the lens barrel in high temperatures. At the highest tempertures for which the lens is designed, the infinity mark might line up with the focus-index line on the sleeve at infinity focus.