Using front cell focusing lens on view camera- setting cell position?

So I have a 75mm Heliar from a Bessa 66 with bad bellows. And I have a Century Graphic 6x9. So I figured I'd play with the Heliar on the Century. Works well, covers 6x7 very evenly which surprises me.

The Heliar is set up as a front cell focusing lens for use on the Bessa folder. On the Century Graphic I can use it as a unit focusing lens.

Anyone know a method to determine the best position of the front cell? When I work with folders that have the front cell, it almost always works out that infinity is just a bit short of screwing the front cell all the way back. I base this on factory shutter position. With the Century I now have both base shutter position and front cell position as variables. I tried some targets on the wall, but small changes near full retraction don't lead to changes that I can see.

First test shots had what looked to be decent focus on ground glass. Wide open, negatives are a bit soft. Closed down, images are sharp. So I wonder if this is the front cell position being wrong.

Thanks.

Sorry, I'm not an expert to this, but it is an interesting question indeed. Just some ideas: my Bessa 66 Heliar is uncoated and it's just for 6x6. So you are pushing the limits on 2 sides, image circle and inner reflecting uncoated surfaces. Most of my uncoated lenses have to be closed down quite a bit. So maybe it isn't the front cell position...

Dan Daniel said:

First test shots had what looked to be decent focus on ground glass. Wide open, negatives are a bit soft. Closed down, images are sharp. So I wonder if this is the front cell position being wrong.

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Dan, many off-axis aberrations are sensitive to aperture. Stopping down reduces them. This is why the recommended shooting aperture for many f/4.5 and f/5.6 LF lenses is f/16 or f/22.

FWIW, I've had 2 heliar-type 105/3.7 Ektars, still have the second. Both were softer, with less coverage, aperture for aperture a decent 101/4.5 tessar type Ektar. This on film, not on the ground glass.

How do you focus on the GG? I use a 3.6x Toyo loupe, don't always get focus right.

There was recently a discussion somewhere, probably here, about front element focusing. The consensus was that the lenses were optimized for around 20'. I've shot landscapes with a couple of well-regarded folders that had well-regarded lenses. Set the lenses to infinity, stopped well down, got soft results. Never tried a lens with front element focusing on a Graphic. If I were you I'd set the thing to infinity and accept what I got. The alternative is to set the camera on a steady support, point it at a distant subject and shoot it at several distance setting and apertures.

About assessing sharpness and coverage on the GG, I've never trusted my eyes. One of my friends had a 1.75"/2.8 Elcan in barrel. He somehow stuffed it in a block of foam in the front of his Miniature Speed Graphic. He and I both looked at the image on the GG, were convinced that the lens covered 2x3. I later found an unbeatable deal on one and bought it. Skgrimes put it on a 2x3 Graphic board and I shot it on my 2x3 Pacemaker Speed. The lens was made for an aerial camera that shot 6x6 on 70 mm film. Mine covers 6x6 and not a mm more.

Yours for solidarity among Dans,

Dan

Use the front cell to focus.

ic-racer said:

Use the front cell to focus.

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The problem is that unlike when installed on a folder, I have two variables here- the position of the shutter block/lens, and the position of the front cell. I'd like to get the front cell in the best position for sharpness nd lock it down and focus by moving the whole thing back and forth on the camera rails.

I am assuming that front cell lens is the same as a unit focus lens except for the moving front cell. Maybe changes are made to the optical formula and I am making a mistake in wanting to lock the front cell in one spot.

xya said:

Sorry, I'm not an expert to this, but it is an interesting question indeed. Just some ideas: my Bessa 66 Heliar is uncoated and it's just for 6x6. So you are pushing the limits on 2 sides, image circle and inner reflecting uncoated surfaces. Most of my uncoated lenses have to be closed down quite a bit. So maybe it isn't the front cell position...

Click to expand...

I am surprised to see how well this lens covers 6x7. No light fall off. I cannot speak to focus fall off yet since I don't think that I have the lens set up for best focus no matter distance or aperture!

Dan Fromm said:

FWIW, I've had 2 heliar-type 105/3.7 Ektars, still have the second. Both were softer, with less coverage, aperture for aperture a decent 101/4.5 tessar type Ektar. This on film, not on the ground glass.

How do you focus on the GG? I use a 3.6x Toyo loupe, don't always get focus right.

There was recently a discussion somewhere, probably here, about front element focusing. The consensus was that the lenses were optimized for around 20'. I've shot landscapes with a couple of well-regarded folders that had well-regarded lenses. Set the lenses to infinity, stopped well down, got soft results. Never tried a lens with front element focusing on a Graphic. If I were you I'd set the thing to infinity and accept what I got. The alternative is to set the camera on a steady support, point it at a distant subject and shoot it at several distance setting and apertures.

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I noticed your disappointment in the 105mm Ektars. Too bad, the ones I have had have been great. But so many good lenses out there, I understand just dropping ones that didn't work out.

I use a 4x loupe. Seems to work well with other lenses.

I may try 3 feet and a fancy design to be able to read actual sharpness. Spitballing walls and trees might not be the best way to deal with the variables here.

And it may be that like you and the Ektars, I just save my time and move on to other lenses.

I've got a 10.5 cm Agnar from a folder that I sometimes use on my 4x5 Speed Graphic (yes, it barely covers the frame at f/16 or smaller and when focused to about 12 feet or closer -- conveniently hyperfocal at f/16). I set and locked the front cell at its infinity setting for convenience, so I can use the unit focusing to get the little extra distance needed to fill the corners. Different front-cell lenses will have different optimum front cell settings, but those from relatively high quality cameras like a Bessa are likely (IMO) to have this setting at or near the infinity stop.

When I read your first post my thoughts were that the front focus lenses were most likely optimized for 15 to 20 feet - because the manufacturer most likely thought the camera would be used mostly for group or single portraits at that distance. My thoughts seem to agree with the consensus that Dan Fromm mentioned.

Accordingly, maybe the best procedure would be to set the front focus distance for that distance and test it on film (or with the screen focus of a digital camera attached to the back.) And do the same with the lens set at infinity.

BTW, it surely seems to be faster and cheaper to adapt a mirrorless digital camera to the back in some way to check all this. The screen can tell you pretty quickly what the lens can resolve - particiularly in comparing resolving power of lenses - from my experience.

The Heliar is supposed to have residual aberrations, and that's part of why it's a popular portrait lens at large apertures. If you are going to test the front cell focusing version I think it's best to set the lens at different distances and focusing with the camera and take test shots with the aperture stopped down to, perhaps, f:8, and then evaluate the negatives.

Besk said:

When I read your first post my thoughts were that the front focus lenses were most likely optimized for 15 to 20 feet - because the manufacturer most likely thought the camera would be used mostly for group or single portraits at that distance.

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Those are my thoughts as well, and now Dan Daniel has the chance to prove if they are correct. There shouldn't be a big difference in image quality or they wouldn't have made front cell focusing lenses for the top of the line folding cameras.

Besk said:

BTW, it surely seems to be faster and cheaper to adapt a mirrorless digital camera to the back in some way to check all this. The screen can tell you pretty quickly what the lens can resolve - particiularly in comparing resolving power of lenses - from my experience.

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Very good idea, but risky when you compare a 80 plus year old Heliar to the lenses normally used on the modern digital camera. It will be cruel to the aberrations, especially a Heliar's.

Front cell focusing lenses operate by changing the focal length of the total lens. It is a compromise made to satisfy the mechanical limitations of a folding camera, mounting the lens to a fixed front standard. When such a lens is front-focused, you can expect some of the lens aberrations to increase off-axis. I don't think you would see much change in image quality on-axis. Stopping down will generally cover some of the aberrations up.

(For a unit-focusing lens, aberrations also change as a function of focus distance, but this change is pretty slow, so that a lens that works well at infinity will generally work well down to say 10-20x the focal length, but closer than that, bets are off unless it was designed as a macro lens or has other redeeming qualities like symmetry.)

Anyway, there is no way now to know what the original design position was, but it seems very reasonable to assume it was somewhere around 20 feet to infinity. Set the front element around that position, and use the GG to unit focus. If it's still a little soft in the center wide open, that's probably just how the lens is.

The best way to find the answer to your question is to test it yourself.

Set up the camera with the lens on a tripod in front of a scene with a near and middle ground and something at infinity to focus on and set the focus on the lens to its maximum extent, then focus the camera on the near middle and far and look at the ground glass with a good loupe and take notes on what you're seeing. Pay special attention to the corners and keep an eye out for abberation and coma and all that bad stuff that you might be able to minimize. Then set the lens to it's minimum extent and repeat the procedure. Finally set it somewhere in the middle and see if there is any improvement there. If any of the settings is better than the others you can use that or try settings near it to see if you can further improve the image.

You might find that there is a clear improvement at one setting or another, or that there are some advantages and disadvantages to each setting, or you might find out that it doesn't matter at all.

All in all it should take maybe half an hour or so to go through the whole process.

I agree with @Besk. Adapting the lens to a helicoid and mirrorless would allow you to quickly check the effects of the cell position. Check this post: http://forum.mflenses.com/focus-with-only-front-element-moving-t84713.html.