DIY: Calibrating/checking infinity focus

[shawn]

I took the lens off an Argus C3 to grease the helicoid. The way the lens is removed makes it fairly easy to throw off focus. As such I did a focus check to verify it went back together correctly. This method works to check focus on pretty much any camera. The Argus just makes it really easy to tweak this slightly if needed.

First you need either ground glass or tape in the camera/lens to be tested. Draw an X on it in sharpie. You can use exposed film too if desired.




Set the camera/lens to be tested (DUT) to infinity and then use another camera/lens that is focused at infinity (mirrorless is fantastic for this) and look through the DUT. Use B to hold the shutter open if needed.





Zoom in on the mirrorless to look at the X. If it is sharp the DUT is focused properly at infinity. If it isn't, you need to adjust the DUT lens to get the X sharp.





In the case of the Argus you can also tweak the rangefinder dial to be sure it is stopped right at the infinity mark and then adjust the RF itself if needed to align the RF at infinity.

 

[rfaspen]

To be most precise....should we draw the X on the "inside" side of the tape? Tape isn't terribly thick, but.....

I gave/sold away all my Argi. Kind of miss them, but not too sad because they are with loving parents now.

 

[WoodallP]

To be most precise....should we draw the X on the "inside" side of the tape? Tape isn't terribly thick, but.....

I gave/sold away all my Argi. Kind of miss them, but not too sad because they are with loving parents now.

I use the a similar technique on setting up lenses on Isolettes; in that case I have a clear glass plate that sits on the film plane across the two film rollers, held tight by elastic bands. The plate has three pieces of magic tape right along the glass plate (top bottom and middle) such that the tape face is the surface touching the rollers (the glass is just to give transparent rigidity). I put the cross on the face surface of the tape, i.e. the surface facing into the isolette, as this is the closest approximation to where the emulsion would be.

 

[Muggins]

Tape will do the job, especially for 35mm, but the bigger the format the more it distorts and the more you need a solid plane. If you have a sheet of glass of plastic it only takes a few minuties with glasspaper to have a nice ground glass you can use for setting focus.

 

[Ko.Fe.]

To be most precise....should we draw the X on the "inside" side of the tape? Tape isn't terribly thick, but.....

I gave/sold away all my Argi. Kind of miss them, but not too sad because they are with loving parents now.

Originally we used ground glass or equivalent of it. You should focus where film emulsion is going to be.

I made ground glass from tiny picture frame glass, sold in dollar store. It fits into film channel of 135 film format cameras.

 

[Nassimo]

Hi everyone! I'm a bit late to the conversation, but I have been having issues re-calibrating the focus on an Agfa 1535.

How can you use this method if the camera doesn't have a bulb mode? Slowest shutter speed is apparently 15s, but since the camera is fully automatic, I wonder what would be the preferred way to do this. Maybe : creating a dark environnement with a small light behind the Agfa just enough to light the cross mark, shooting on burst mode with my mirrorless and firing both cameras at the same time ? The only fixed speed I can put dial on the Agfa is 1/30 when in flash mode, maybe that is enough considering how fast mirrorless cameras shoot nowadays. Or should I dismantle the Agfa to trick the blades to stay open ? (which would imply having to dismantle everything again after I find the proper focusing point)

Any guidance on this matter would be really appreciated.
thanks !

Nassimo