focusing problem with mamiya RB

[menashe_soffer]

<p>hello<br>

bought a RB67 from one of the leading used camera dealers; have big troubles focising the camera.<br />I made the following experiment:<br />placed 6 targets ~2cm apart, and the camera ~1m from the targets;<br />I tried to focus on the 3rd (the one marked with arrows), I am pretty convinced that the split image converged to this one ( I made everything very slowly with tripod).<br />however the real focus seems to be somewhere between the 4th and 5th target, ~2.5% deviation.<br />my questions:<br />* since the camear is focused beyond what it seems in the focusing screen, it means that the lens-to-film distant is shorter than the lens-to-focusing-screen distant, right?<br />* is it possible that the camera is OK and i am doing something wrong, for example looking at the finder from wrong distance/angle? (never had problem in 35mm)<br />* any suggestions how I can use the camera or I should return it?<br />thanks</p><div></div>

[mag_miksch]

<p>"<em>split image</em>"<br>

Does this mean you use a split-image screen?<br>

This maybe a replacement, so look if its in place properly.<br>

I have never used split image screens on a RB, but I know from 35mm cameras that they are not that reliable with dark images, coming from a 4.5 lens.<br>

Regards<br>

Martin</p>

[jeff_livacich]

<p>Going along with what Martin said, try focusing using matte part of the screen to see if you get accurate focus that way. If not, then there is some problem other than the split image.</p>

[paul ron]

<p>Has nothing to do with lens to film. The problems usually occur with the viewscreen out of alignmnet with the focusing if the lens. One of 2 problems....<br>

1-Many people get bright screens installed and they are adgusted to focus properly wiht the film plane. Then when selling the cameras, they swap em for the standard screen but never re focus the screen to agree with the film plane and you will niotice a focus difference.<br>

2-your screen is not installed properly, may be upside down with th eground or lens side to the viewer n not towards the lens.<br>

Check the film plane to screen using a ground glass on the film plane. Focus the film plane n see if the screen agrees.</p>

[menashe_soffer]

“split image” is num. 3 “rangefinder”; it seems that the screen is placed correctly

Paul, “re-focus the screen” – how is it done?

 

when I take the screen out, I see in the corners of the base 4 screws (heads with spanner drills); it seems that theoretically I can adjust the screen height if I turn them. am I supposed to tamper with these screws?

in addition, suppose I can find ground glass, who do I manage to position it on the film plane?

[paul ron]

<p>The ground glass is tapped to the film rails so it is in the same place the emulsion would be. You can use velum (drafting paper or wax paper) to focus the film plane. Use a loupe to get the sharpest image you can, then chcek the screen to see if it has to go up or down to get the same sharp image.<br /><br />Mark a reference scratch on the spring below each screw as well as making a mark at the same point on the screw itself. This ensures you will turn each one up or down exactly the same amt or can reverese your actions if need be.</p>

<p> </p>

[menashe_soffer]

<p>paul</p>

<p>started iterating in some sort of "trial and error" (tuning - checking with film) following your guidance; need few more itterations but seems in the right direction.</p>

<p>thanks for your quick and relevant advice!</p>

[paul ron]

<p>Don't try to focus the screen using film delayed by processing as you go, it'll just get you in a hole you can't climb out of. You need to put the GG on the film plane and have it real time as you make adjustments. <br /><br />Hope it works out for ya, keep us posted?</p>

[menashe_soffer]

<p>paul<br>

using the weekend to contunue ith troubleshoot.</p>

<p>I have extra focusing screen, I have disassembled to use the glass as a reference on the film plan - it fits into the film rails.<br>

what I have found, and i didnt know before, is that the glass have "front" and "back" sides; meaning i see the imaged focussed in the film plan in one case and not in focus if I attach the other surface of the screen to the rails. in the same way I get different view if I re-assmble the focising screen into its holder in two different ways.<br>

how do i know which surface of the screen should face the mirror (or lens) and each the magnifier (or luope)? it occured to me that the only problem may be that the screen I got was assembled up-side-down, and the "calibration" I make will actualy adapt to the wrong assembly of the screen.</p>