Sharpness of image: Tachihara 4X5

I am the original owner of a Tachihara 4X5 that is about 2 years old

and is very unused. I have questioned the image sharpness since day

one but I most often stop down so it has not been a problem. But with

my suspicions I recently compleated the Robert Zeichner test for gg

alignment using polaroid film. The test indicates the distance between

the lens and the gg is not the same as the lens and the film.

According to this test my focus screen needs to move closer to the

lens. I did a little experimenting of my own, I noted that when I

moved the lens slight ahead (away) of the ground glass and took a shot

the image was very sharp though it was now out of focus on the

gg.This would seem to confirm the results of the Zeichner test My

camera has no adjustments to move the focusing screen towards the

lens. Will the body need to be milled? Dose ianyone know if this is

covered under warranty? Any help will be usefull

You may have the ground glass installed improperly.<p>Check this recent photo.net

thread:<p>http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Dbgj

Noah-Thank you--The thread you mentioned was in responce to my question yesterday about the gg. Based on the very usefull info I recieved I do believe I have and always have had the right placement. That is gg facing lens with the fensnal towards back covered with glass

Yes, it does sound like the GG is not installed right. Is the frosted side forward ?? Also this may sound silly, but do you have a fesnel ?? I bought a camera a while back and the fresnel was installed under the GG. Of course all my test shots were all OOF. An easy fix afterward.

 

I would not mill anything.

Your question seems confusing about the direction of the focus error. Once you say that the sharpness of the Polaroids improve when you move the lens away from the ground glass. Then you say that you want to adjust the camera to move the focusing screen towards the lens. These two statements are inconsistent. If the first statement is the correct one, the adjustment is easy -- you can place shims between the focusing screen and the camera to move the screen away from the lens. This also has the advantage of being reversable, in case a mistake is made. You can either do this yourself, using photographic tests of the focus, or by measurementing, after purchasing a suitable tool (a depth micrometer), or have a specialist make the repair.

 

I would expect a LF camera to be shipped by the manufacturer with accurate focus, to a few thousandths of an inch. If one wants an specic accuracy number, the ANSI standard for 4x5 filmholders is probably a good starting point. Sources on the web say that the ANSI tolerance for the depth of a 4x5 filmholder is 0.007 inches. I don't know how long the Tachihara warranty is.

 

If the ground glass has to be moved closer to the lens, the repair is move difficult -- the seat of the ground glass (or plastic) will have to be milled. Unless you are skilled woodworker or machinist, you will probably want to have someone else do this. It is probably best to do this by measurement, measuring the depth and correcting it to thousanth of an inch accuracy. Possible repair places are S. K. Grimes, Inc. and Richard Ritter.

I'm not familiar with the Tach back, but can't you shim the GG? Of coruse, once you shim it, how do you know you've done it correctly? Read on...

 

If you're not opposed to spending a few dollars, I would suggest purchasing a digital caliper. Make a small jig out of plywood (about the same size as a lensboard) that has holes drilled through it (five holes are more than enough - one in the center, one in each corner - you could even get away with three, in a triangle form) that will fit the extension probe of the caliper. Mount your camera on the tripod, and insert a film holder (preferably one in good condition) that has a sheet of film in it (important!). Don't mount a lens, and point the camera at the ceiling.

 

The jig you made should rest on the front standard in the same way the lensboard will. It doesn't have to lock in place, just sit there. Take the caliper, and insert the probe into the center hole and measure the distance between the film and the jig. Without changing anything, zero the probe. You can now measure through the other holes and determine the differences. Write these numbers down.

 

The distances that you've measured are your reference distances, since you measured with a sheet of film in place. Your goal is of course to get the frosted surface of the GG into the same plane as the sheet of film.

 

Now, remove the film holder, and repeat the measurements without changing anything - don't re-zero the caliper, nor more the front standard. If the back is parallel to the front standard, all your measurements should be the same. If they're off, make adjustments to the GG. Of course, having to move the GG further away from the front standard is much harder than shimming it to move it closer, and will most likely mean milling if there are no adjustment screws.

 

If you have a fresnel in place this technique won't work, since my understanding of a fresnel is that it will cause a slight amount of focus shift (1/2 the depth of the grooves?).

 

I had to do this with my Master Technika, since it a) had a warped Super Screen which I removed and replaced with a plain GG, and b) the previous owner had mucked with the GG placement. I'm pretty sure I've got the GG adjusted to withing a few thou, and my negatives seem to agree.

 

This procedure does take a while, but it should work for you. If you can shim the GG, of course.

"Of course, having to move the GG further away from the front standard is much harder than shimming it to move it closer, and will most likely mean milling if there are no adjustment screws." This seems backwards to me. The easiest adjustment to make is to place thin shims between the seat of the ground glass and the ground glass. On almost all LF cameras, the seat of the ground glass is in front of the ground glass (touching the ground surface), so adding a shim moves the ground glass farther from the lens. Moving the ground glass forward requires moving the seat forward. If there is already a shim, then one can remove the shim or switch to a thiner shim. If there is an adjustment screw, then again, fairly easy. Many cameras, particuarly wooden cameras, have a fixed seat, and an adjustment will require forward will require machining the seat.

 

"If you have a fresnel in place this technique won't work, since my understanding of a fresnel is that it will cause a slight amount of focus shift (1/2 the depth of the grooves?)." The problem of a focus shift from a Fresnel is only if the Fresnel is in front of the ground glass. This causes a focus shift of approximately one third of the thickness of the Fresnel lens -- this arises from the index of refraction of the Fresnel lens and has nothing to do with the depth of the grooves. But from the answers to Jeff's previous question (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Dbgj ), Jeff's camera has a combined ground plastic / Fresnel lens with the ground suface facing the lens. He doesn't have to be concerned with the effects of a material with an index of refraction differing from air being in front of the ground surface. So a straghtforward mechanical measurement and comparison of the positions of film in filmholder and ground surface of screen, such as Ken describes, should work.

Michael, I think you're wrong. If Jeff can correct his (film) image by moving the lens forward, that means the film position is forward of the ground glass position and the ground glass needs to go forward not back. Unless I'm missing something!

Jeff and Sam are right -- better focus with lens moved forward means that the ground surface of the screen should be move forward -- my first answer was wrong. On most wooden cameras this means the difficult fix of removing material where the ground glass seats. Or perhaps you could try glueing shims where the filmholder seats to move the film backwards to align with the current position of the ground glass. This might be worth doing with paper shims and contact cement as a temporary fix to verify the amount of the correction. Or the perhaps easiest solution -- see if Tachihara will fix the camera under warranty.

Thank you all for your responses reading them has been very helpfull. I have a call to SK Grimes for there assesment. I called Mid West Photo exchange (purchase point) to see about warranty but there LF man will not be in until Friday.I really don't expect that this will be covered. This evening I am going to redo the bench testing (Zeichner) and this time I will use the ready load back instead of the polaroid back just to make sure the problem was not with the polaroid back.

Any other thoughts will be helpfull.

Hi Jeff;<p>Sorry I sent you back to your own post!<p>This seems like a screwy problem to

be having with a brand new camera.<p>The best and final way to check out your problem is

with a tool called a projection collimator.<p>It can project a target image on your film and

your ground glass and tell you exactly how 'off' your ground glass is.<p>Grimes has one, I

know that because I did work for him from time to time when he was still alive.<p>I have two

projection collimators myself....

I checked mine with a digital caliper. You can get them really cheap at Harbor Freight. Just make sure to zero it.

 

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=47257

 

You use the opposite end to go in the hole and measure the distance to the gg. Work off the hole in the lens board.

 

Then kill a piece of film, put it in the holder insert it and measure to the film. My cameras that I checked were withing a few thousandths of an inch if not dead on.

 

If its off more than that there is a problem with the camera or your holders.

 

If its dead on or very close, but still OOF, its probably a problem with the GG or the way it is installed.

 

Like I said my camera measured right on, but the fresnel was installed wrong by the previous owner (I assume) so the camera was actually focusing farther back.

 

I also received another camera and the GG was too big, but it would fit on an outer part of the frame. It focused too far back too.

Measuring the depth with a calipers is fine if you have a plain ground glass, but useless if

there's a fresnel between the ground glass and the lens.<p>The ground glass position has to

be checked and adjusted optically with a projection collimator.<p>And that's after you've

figured out the proper way to install the fresnel.

Re: Michael Briggs's comments -- you were right the first time!!!

 

He moves the lens forward, throwing the image out of focus on the ground glass, but the image on film comes out sharp.

 

Moving the lens forward *increases* the distance between lens and ground glass. THAT means that the ground glass should be shimmed, because the distance between lens and ground glass must be increased to achieve correct focus. It does NOT mean that the ground glass panel should be milled.

 

One more suggestion: Make sure that the camera is aligned properly, that all controls "zero out" correctly. Make your test shots with the front and rear standards exactly parallel. You can use various bubble levels, even laser-printed parallel lines on paper, to test this. THEN check your focus. I've seen some very nice field cameras that were off on this -- when the controls were at zero position, the standards were not parallel.

 

Of course, the easiest way is also as expressed above -- check the ground glass panel for 0.007" thickness where the glass sits. Check for "high spots". Also check to make sure it isn't warped, by laying it on a flat surface and seeing if it "rocks" from side to side, corner to corner.

 

After all, if your ground glass is calibrated properly, it doesn't matter what the cameras controls are doing, you can still ensure proper focus even when hardware is not all it's supposed to be.

 

It's surprising how many cameras come with defective ground glass panels.

Michael Hendrickson, draw yourself a diagram. When he moves the lens forward it's not to get it farther away from the ground glass - the ground glass was already in focus! - it's to get it farther away from the FILM which was CLOSER than the ground glass.

An illuminating discussion. I have been disappointed with the sharpness from my 90mm Angulon on my Tachihara, and have been assuming it was my focus error, and this thread raises other possibilities. Proves again the usefulness of this forum.

Ellis - Before worrying too much about your camera I'd first investigate your lens. The Angulons are very old lenses and Schneider's quality control back then wasn't what it is (or at least is supposed to be) today so there was a good bit of variation from one lens to the other. And considering their age there's a lot that can be wrong with them today even if they were fine when they left the factory 30 or more years ago.