does it have to be a helicoid?

[gunner]

I recently posted a thread asking about salvaging a helicoid from an old lens to use on a D.I.Y camera build. I purchased a job lot of old faulty lens from E Bay and have been taking them apart to see if there is anything I could use. A couple of the salvaged helicoids look promising but its left me wondering wether a helicoid is strictly necessary. With a simple point and shoot camera where focussing is on a scale (no ground glass or rangefinder) is there any reason why the lens could not be simply mounted at the end of a tube which slides in and out of a barrel to achieve focus ( a bit like a trombone) Provided the parts fit well once the focus distance is set it shouldn't move in or out. Has anyone tried this or is there a good reason why something this simple shouldn't work?

 

[tedr1]

It worked for the first 25 years of photography until the rack-and-pinion focusing adjustment system was introduced and it can still work. One of the things about a helicoid is it is often non-rotating which can be important in some situations where there is something mounted on the lens, such as some sorts of filter. The precision of mechanical alignment provided by a helicoid is usually pretty good also.

 

[David Lyga]

gunner, there is NOTHING as precise as a focusing helicoid because there is no opportunity for wobbling or mis-alignment. In fact, I have often wondered why enlargers do not generally employ one instead of rack and pinion. - David Lyga

 

[M Carter]

gunner, there is NOTHING as precise as a focusing helicoid because there is no opportunity for wobbling or mis-alignment. In fact, I have often wondered why enlargers do not generally employ one instead of rack and pinion. - David Lyga

Never had a problem with the RB rack & pinion. My RB body is something like 25 years old and the only issues I've had were light seals. Also gets away from the problem of rotating front elements. Helicoids have their own problems - usually dried up grease, but many lenses with plastic parts have bad focusing failures.

 

[Sirius Glass]

Rack and pinon work well with my Pacemaker Speed Graphic and Graflex Model D. It worked well on my Mamiya C330.

 

[John Koehrer]

The sliding box camera design would work for you. It's probably the easiest option & will work with
any fl length lens within the physical limitation of the box. Actually you could make an extra box
if you want to expand the "system"
It's easier to googleize "sliding box camera" than for me to describe it

 

[michr]

A sliding box was one of the first (maybe the first, but I'm no expert) focusing methods employed in early cameras. I see no reason it would work quite well, especially if you had a way to lock focus.

 

[David A. Goldfarb]

My oldest trombone was made in 1924. Works just fine.

 

[Jim Jones]

The rack and pinion focusing on many enlargers is well suited for fast refocusing for a wide range of negative and print sizes. The helicoid used on many small cameras is more precise. It also provides for distance and DOF scales, and internal movement of lens cells..

 

[David A. Goldfarb]

The precision of a rack and pinion mechanism depends on the gear ratio, and that of a helical depends on the pitch of the threads, and while helicals may be more common on smaller formats requiring more precision, I don't see why one should be necessarily more precise than the other. It is true that helical mechanisms can be quite complex in allowing for floating element systems or having a variable pitch for different focus ranges, but in the original post, that's not an issue. The helical on a Kodak Medalist II is kind of coarse, while the rack and pinion mechanism on a Linhof macro rail is quite precise. Sinar cameras with rack and pinion focusing have DOF scales, and Linhof technical cameras have distance scales with rack and pinion focusing.

 

[Diapositivo]

Well, Novoflex used to manufacture photographic "rifles" which were focused with some kind of piston mechanism (sor of a pistol handle).

http://4.bp.blogspot.com/_cG5D6Gal1...uks/s1600/Novoflex+Noflexar+400mm+F5.6+01.jpg

If speed is what is required, a helicoid is probably slow.
If precision is what is required, a helicoid is better because it allows an easier fine-tuning.

 

[David A. Goldfarb]

The Canon FD long teles have rack and pinion rear group focusing with distance markings but no DOF scale. I'm often using the 600/4.5 close to wide open, and it offers a good compromise of speed and precision for bird photography, which needs to be fairly precise, since the DOF range tends to be quite narrow at good bird photo distances. There's a lever to adjust the tension in the mechanism for more precision when you've got it set to the approximate focal distance.

 

[Dan Fromm]

If precision is what is required, a helicoid is better because it allows an easier fine-tuning.

Fabrizio and Jim, 'splain me this: if helicoids are more precise why do the microscopes I use -- today's was a Wild M-5 -- use rack and pinions instead of helicals? Think dovetails.

 

[David A. Goldfarb]

And of course some enlargers have both a fine and a coarse focus knob, both rack and pinion.

 

[Diapositivo]

Fabrizio and Jim, 'splain me this: if helicoids are more precise why do the microscopes I use -- today's was a Wild M-5 -- use rack and pinions instead of helicals? Think dovetails.

You use a microscope on a table. Its weight make it stable. You have free hands. The rack and pinion system allows for great demultiplication (and thus precision of focusing) while assuring great ease of use.

In the real photographic world you cannot use a rack and pinion while hand-holding a camera, can you? You can use a rack and pinion for a lens which is since the beginning designed for exclusive tripod use. That gives you free hands, and the benefit of added demultiplication.

If the lens is designed for hand-holding, focusing is reached either the helicoid or piston mechanism, rack and pinion wouldn't be confortable to use. The helicoid is slower and more precise (demultiplied) the piston is faster but less precise (more difficult to obtain fine adjustements).

Bellows use rack and pinion as well, but they are normally used on a tripod (or, for quasi-macrophotography of live insects, flowers etc. the photographer actually focuses by moving the entire camera back and forth).

 

[Dan Fromm]

Fabrizio, thanks for trying to educate me. I don't buy it. My Graphics focus by rack and pinion. They're made to be shot hand-held. Press and technical cameras with RF focusing don't fit your scheme.

Compound microscopes made for high magnifications typically have fine and coarse focusing racks. The fine racks allow exquisitely accurate focusing to higher precision than a focusing helical will do. Incidentally, microscopes don't focus by adjusting extension, in camera terms they focus by adjusting the film-to-subject distance while holding extension constant.

Please consider that you might be mistaken.

 

[Diapositivo]

Fabrizio, thanks for trying to educate me. I don't buy it. My Graphics focus by rack and pinion. They're made to be shot hand-held. Press and technical cameras with RF focusing don't fit your scheme.

Compound microscopes made for high magnifications typically have fine and coarse focusing racks. The fine racks allow exquisitely accurate focusing to higher precision than a focusing helical will do. Incidentally, microscopes don't focus by adjusting extension, in camera terms they focus by adjusting the film-to-subject distance while holding extension constant.

Please consider that you might be mistaken.

Dan, it's not a wrong or right situation. 99% of photographic system for hand-holding are focused with helicoids. Your camera which is focused by rack and pinion, and which can be very confortable for you, represents in any case a very minoritary solution.

Please consider that your mileage may vary. It's a large world and there is a lot of place for both focusing solutions. There's not just one right way to skin a cat (or to cook it).

 

[Dan Fromm]

Fabrizio, thanks for the reply. The OP asked whether there was a good reason why not to use sliding concentric tubes for focusing. The first reply pointed out that that approach had been tried early in photography's history and that it had worked well.

And then the discussion turned into sort of a shouting match between small format photographers whose cameras' lenses come in focusing helicals and those with larger cameras whose lenses come without focusing mechanisms and whose cameras usually focus with rack and pinion. If you look at cameras' history, you'll see that cameras with bellows between front standard and their rears and that focus by sliding the front standard, with or without rack and pinion, were for quite some time in the majority.

Point is, this thread almost instantly moved away from the OP's question and turned into a argument between partisans of whatever it is that they know best. What the OP contemplates doing has worked well enough.

Oh, yeah. Since no one has mentioned them here, how about lead screws and pulley and cord arrangements? They've worked too.

 

[Jim Jones]

. . . Oh, yeah. Since no one has mentioned them here, how about lead screws and pulley and cord arrangements? They've worked too.

And a lever, as in some early Polaroids. There was no end to the ingenious engineering of cameras over the past 167 years, either to improve on earlier designs or to circumvent patents.

 

[Diapositivo]

Fabrizio, thanks for the reply. The OP asked whether there was a good reason why not to use sliding concentric tubes for focusing. The first reply pointed out that that approach had been tried early in photography's history and that it had worked well.

And then the discussion turned into sort of a shouting match between small format photographers whose cameras' lenses come in focusing helicals and those with larger cameras whose lenses come without focusing mechanisms and whose cameras usually focus with rack and pinion. If you look at cameras' history, you'll see that cameras with bellows between front standard and their rears and that focus by sliding the front standard, with or without rack and pinion, were for quite some time in the majority.

Point is, this thread almost instantly moved away from the OP's question and turned into a argument between partisans of whatever it is that they know best. What the OP contemplates doing has worked well enough.

Oh, yeah. Since no one has mentioned them here, how about lead screws and pulley and cord arrangements? They've worked too.

Yes, I agree overall.
I tend to think that standard rack-and-pinion overall would better match foldable design bellows-mounted lenses.
SLR and RF almost always used helicoids for what I know, so the bellows must, I imagine, being the limiting factor in the adoption of the helicoid. A bellows is presumably more easily coupled with a rack-and-pinion mechanism than a helicoid one.
Small formats made foldable designs less desirable/necessary (than in LF and MF) and moved the focusing preference toward helicoids.

Ultimately the "coupling" of the photographer to the camera is the most important factor. Being familiar, intimate with one's camera is an important factor in obtaining an overall high average image quality.

I suspect Graflex-endowed paparazzi would not focus at all: they would rely on DoF and decent f/ closure, large film estate, and low quality reproduction on paper. Basically I suspect most photojournalists with LF foldable cameras would probably not bother about focus at all . Those who did (landscape, architecture) would certainly reach with rack-and-pinion the same quality of focusing of a helicoid-based mechanism.

 

[dirkfletcher]

Here is a 2x3 camera I built using a rack system from a 2x3 Century Graphic that works quite well. I've never had an issue with focus but I do tend to shoot stopped down.

Morte pics and other cameras are on my Flickr:
https://www.flickr.com/photos/dirkfletcher/albums

 

[Dan Fromm]

Not to be a complete idiot or anything, but what does your cute little cut down Century Graphic do that an unmolested Century can't do? I can see full rise with a short lens, what else am I missing? I mean, the shortest lens that covers 2x3 is the 35/4.5 Apo Grandagon and an unmolested Century can focus one to infinity.

 

[dirkfletcher]

Not to be a complete idiot or anything, but what does your cute little cut down Century Graphic do that an unmolested Century can't do? I can see full rise with a short lens, what else am I missing? I mean, the shortest lens that covers 2x3 is the 35/4.5 Apo Grandagon and an unmolested Century can focus one to infinity.

Hey there,
Thanks for checking out my camera. We were using it set up with either the 35mm Rodenstock and a roll film back or the 28mm Schneider with a PhaseOne back and wanted something that was small and could be quickly pulled out, shot and and stuffed back in a camera bag as we were using it addition to digital and 4x5 cameras. Being able to focus 'inside the box' when shooting handheld is tricky and time consuming. Cutting it down made it crazy quick to shoot with and in all honesty, a heck of a lot cheaper then an Alpa which we just couldn't afford.

 

[Dan Fromm]

Thanks for the reply. I'm not sure which 28 Schneider you're using (28/2.8? 28/5.6?). I don't mean to be a nattering nabob of negativism, but a Century as delivered by Graflex Inc. will focus both of them, also a 35 Apo Grandy. I just checked, the Schneiders' flange focal distances are >= 50 mm, per Leaf, and 35.2 mm, per B&H, respectively and the Apo Grandy's is 41.1. A Century's minimum extension is 34.9 mm.

Focusing on a ground glass is focusing on a ground glass is focusing on a ground glass. One of Pacemaker Graphics' advantages over many of their press camera competitors is that the inner and outer bed rails are linked. This makes focusing with a lens that makes infinity "inside the box" simple. Set the lens to its infinity position using bed stops on the outer bed rails and a spacer to put the front standard as far behind the stops as it needs to be. Lock the standard, rack the rails back in. Drop the bed. And off you go.

If you don't have one, look for a Cambo SF-320 in-line viewer. I use one on my 2x3 Graphics, it replaces the focusing panel.

All that negativism aside, y'r adaptation is cute and clearly meets your needs. Can't ask for much more than that.

Re the Alpa, they're lovely. Absolutely lovely. But expensive, absolutely expensive. A Century Graphic will do more and is much more cost effective. For this and similar comments Andre Oldani has denounced me as an ignorant barbarian.

Cheers,

Dan

 

[dirkfletcher]

An ignorant barbarian is prolb a little much, a Ferrari and an old Ford will both get you the grocery store and back...but an Alpa or my conversion can fit in a small pouch and let me shoot a frame here and there while shooting a tornado ravaged town where a Century is just too big. Too big to fit in a bag with the bed folded out and too slow to open the bed and pull the lens out each time I want to shoot a single frame along one of the Canons I'm already shooting with.

The 28mm is the f/2.8, I got it along with a Cambo X2 Pro, thank god I didn't take a hack saw to that...I'd never hear the end of it.