Super Speed Graphic; Rangefinder Coincidence vs Perfect Focus Test

[Bart B]

Today's task with my just-acquired SSG was to check the focusing accuracy of rangefinder vs. ground glass image. I'd not yet made any critical focus tests; too busy learning about the flash and all its accessories so I can mount an old speedlight atop the Graflite tube and connect its PC cord to a suitable connecting point on the tube.

To begin with, both the fresnel field lens and ground glass were smudged with finger prints and some dust and/or lint was between these two parts. They're easily removed and cleaned with optic lens cleaner then dryed with lint-free lens cloth. Now they both look almost new. Both pieces went back in ensuring the fresnel lens grooves mated with the ground surface of the glass then installed with the field lens's smooth side towards the lens; ground glass smooth side towards the back.

With the lens all the way back at its stop, the rangefinder had good coincidence at infinity. I used a 10X loupe on the ground glass to get precice focus and had to move the lens forward about .030" or so for sharpest focus, then checked the rangefinder; 'twasn't coincident. At about 12 feet, the lens had to be moved forward about the same amount from rangefinder coincidence to sharpest focused image on the ground glass. Same thing at 4 feet. Maybe the stops got moved.

Does this mean the infinity stops need to be repositioned about .030" forward?

Bart

[rdenney]

We'll start with the assumption that the rangefinder is calibrated, and has the correct cam for your lens. We'll also assume that the focus scale is also the correct one for your lens.

Without worrying yet about the location of the lens standard, adjust the focus knob until the rangefinder indicates a subject at infinity is in focus. Then, lock the bed rail down.

Slide the loose lens standard along the locked bed rail until the ground glass shows that the infinity subject is in focus. Now, the ground glass and the rangefinder should be showing infinity focus at the same time. Adjust the pointer on the bed rail to point at infinity on the focus scale, if it isn't already. Note that the bed rail should be just extended out of the camera only a little bit--about 1/8" or so--when the rangefinder indicates a subject at infinity is in focus.

After doing all that, check that the lens and rangefinder correspond at closer distances. If they don't, check that the cam is the correct one for that lens. If it is, then rangefinder needs to be adjusted and I have to defer to others at that point. If everything looks good at this point, install the infinity stops at the current location of the standard.

This is the procedure I followed for setting the infinity stops on my top-rangefinder Pacemaker, and I'm reasonably sure it will work on a Super.

Rick "whose 127mm lens and cam were perfect after following that procedure" Denney

[BetterSense]

Note that the bed rail should be just extended out of the camera only a little bit--about 1/8" or so--when the rangefinder indicates a subject at infinity is in focus.

Why? On my pacemaker I set it up so that it hits infinity with the rail slammed all the way back. Easier that way.

[Bart B]

Note that the bed rail should be just extended out of the camera only a little bit--about 1/8" or so--when the rangefinder indicates a subject at infinity is in focus.That doesn't make sense at all. I think a coincidence rangefinder focused camera should have a hard stop at each lens' infinity setting. Ain't that how manually focused great cameras of other makes are made? My old 2x3 Graflex I had back in the 1960's focused perfect with the rail's "slammed (gently)" all the way back. That's how the guy at the camera repair shop who sold it to me told me how it's used. Maybe I'm missing something; I'll appreciate any comments/info/reasoning to convince me otherwise.


Why? On my pacemaker I set it up so that it hits infinity with the rail slammed all the way back. Easier that way.This is how I verified my Super Speed Graphic was properly set up for the rangefinder. Rangefinder coincidence happened with the rack all the way back gently.

I ended up using a .030" feeler gage to set the infinity stops that far forward from their original position. This made sharpest focus at infinity, 15 foot and 4 foot targets agree with rangefinder coincidence at those distances. So, the right cam must be in as well as the rangefinder calibrated decently. Things look pretty good to me, anyway.

If I can get a 20X loupe (or make one?) I'll check focus on the ground glass more precisly.

Bart

[Jack Dahlgren]

That doesn't make sense at all. I think a coincidence rangefinder focused camera should have a hard stop at each lens' infinity setting.
Bart

If you do that how are you ever going to focus beyond infinity?

Rick is wise to leave room to go further than man has been before.

[Bart B]

on my wanting to limit focusing to just at infinity:

"If you do that how are you ever going to focus beyond infinity?"Well, after racking the lens back to its stop, how 'bout just takin' 3 or 4 steps towards infinity with the camera pointing at it? Then it'll be focused about 10 feet or so beyond infinity.

Bart

PS: Wink.

[rdenney]

Why? On my pacemaker I set it up so that it hits infinity with the rail slammed all the way back. Easier that way.

It's nice to have a little adjustment on both side of infinity to be able to account for thermal expansion, lens movements (which have a bit of slop in them on most well-used Graflexes), and gravitational attraction of the Moon.

And that's what Graflex apparently intended, too, based on the instructions I've seen for rangefinder calibration. But that doesn't mean, of course, that it must be that way. Do it however you want.

In practice, the only time a hard stop at infinity seems that important to me is in astrophotography and night photography. When I focus, I rock the focus control back and forth around the subject on the ground glass. That allows me to split the difference when it's hard to be sure of precise focus (such as at a small aperture). But, as I say, do it however you want.

Rick "recalling CZJ lenses from the 50's that focused slightly beyond infinity to allow for thermal expansion" Denney

[Bob Salomon]

Normally the ground side of the gg and the grooved side of the fresnel both face the lens, not each other.

[BrianShaw]

Normally the ground side of the gg and the grooved side of the fresnel both face the lens, not each other.

"Normally", but not on the Graphic.

[BrianShaw]

Normally the ground side of the gg and the grooved side of the fresnel both face the lens, not each other.

p.s. "normally" doesn't the fresnel go behind the gg (toward the back of the camera)? On the graphic the fresnel goes in front of the gg (toward the lens). Odd, eh? But true!

[Bernard Kaye]

Bob Salomon & Brian Shaw may be into something:

With GG only, I thought the ground glass is located towards the film plane so that we are focusing on the ground side of the GG, not on the shiny unground surface that is closer to lens but I realize that I am guessing, may have been wrong all along..

With Fresnel glass added, I have been at a loss for half a century and ask for advice from Bob, Brian, Ole, all.

Bernie

[rdenney]

With Fresnel glass added, I have been at a loss for half a century and ask for advice from Bob, Brian, Ole, all.

Normally, the Fresnel is an accessory put behind the ground glass. But on a Graflex, the Fresnel is put in front of the ground glass.

The ground surface faces the lens, which is normal. But in addition to the Fresnel being between the ground glass and the lens, the grooves should face the rear--into the ground glass.

Rick "yes, that's different from every other camera" Denney

[Bart B]

You guys and this location issue of fresnel vs groundglass is interesting to me. My old 2x3 Graphlex of decades ago only had the one piece of glass; it was ground on the side towards the lens.

Now I've owned a Super Speed Graphic for just barely 7 days and I'm learning I gotta do some learning. Folks on graphics.org say to put the frosty glass next to the circular ridges then put the smooth side of the fresnel ridged piece towards the lens. That's how my SSG was assembled according to the notes I took when I took them out to get rid of a bunch of lint, finger prints, dirt and a few dead microbes. As long as the ground glass surface one uses to focus images on is in the same plane as the film in its holder, it doesn't matter too much, I guess, what's between it and the lens. Graflex must have spec'd good optical qualities of the Ektalite Field Lens, or fresnel lens for it to be placed between the ground glass and the lens.

To me, it's easy to use a loupe to focus precicely with the ridged and ground surfaces next to each other where the two pieces are together. This junction is the image plane. 'Tis very easy to focus ones loupe on those ridges as that'll give you the best reference to see the subject's image as it focuses on the ground surface. it prevents one from focussing their loupe at the wrong place. The ground glass surface doesn't present as sharp a point to focus my loupe on.

And if one measures the distance from the flat mating surfaces of a film holder down to the film surface, like me, they'll learn that the film's image plane is about 40/1000ths further back than the front surface of whatever's clamped into the focussing back. All I had to do was to look at a sheet of film in a holder and see it was further away from the fresnel lens surface in the focussing back.