How to test the focus of your lense?

Hey friends,

I hope this is the correct subforum.

I need some tips on how to test your manual lenses focus.
I have an Olympus Trip laying around that I just opened up to repair the aperture. It seems to work fine now but I am not sure if the lense is adjusted correctly. It seems off on my test photos.
How can I find out?
I can only find test charts (like this: http://www.traumflieger.de/desktop/fokusdetektor/fokusdetektor_ls.pdf) for auto focus systems. Can I use them too by just moving them away from the camera depending on what distance I put the lense on and see if it's in focus? Or how would you go about it?
I have another lense that I would like to test as well so I need a reliable method.


Thanks!

C.

For rough calibration, I will take a piece of cheap scotch tape (the kind that's clear, but has a foggy adhesive) and place that over the film plane. This acts as a temporary ground glass. When the focus is set to infinity, an object about a mile or two away should be in focus. Use a loupe to get a better idea of focus.

There ware two recent threads that may be relevant for you:
https://www.photrio.com/forum/threads/am-i-expecting-too-much-of-my-nettar-515-16.167101/
https://www.photrio.com/forum/threads/folder-distance-scale-origin-point.160778/

Of course the Oly trip is not a folder, but the optics principles and methods are valid for all cameras, wit or without bellows.

If your house has a long exterior wall, tape some pieces of cardboard or posterboard so they stick out, perpendicular to the wall. Put the camera on a tripod and measure the distance to each card, start with the minimum focus distance (3'?) and mark a card every 3 feet or so - and mark the distance on each card with a sharpie (so through the vioewfinder, when you focus you'll see the distance printed on each card). Stagger them so they can all be seen through the VF. Focus on the first card, shoot, focus on the next, etc. You can do this out to like 20 feet. Make sure you do it in order so it's clear on the film which shot was supposed to be focused on which card. Or do them at 1' intervals, shoot 10 or 15, move the camera back 10 feet, re shoot and keep in mind you've add 10' to each card. Use a long fence or a wall or set up something similar indoors. That's a basic concept you can adapt to suit.

To check close focusing, mark a piece of cardboard with straight lines like 1/8" apart - a "stack" of straight lines, like 6" worth (or do one on a printer and tape/mount to a card). Take the center line and make it fatter with a marker and ruler or print it out like that. Set the card at a 45° angle to your lens and focus on the thick center line. Put your camera on a tripod and shoot at all apertures - it's smart to use post-it notes or a white board to write each aperture so they're in-focus in the frame. When you run the film, the center line should be in focus. If not, you can tell if your camera is back or front focusing.

I recently got one of these ground glass focus screens on the evil auction site.

https://www.ebay.com/itm/35mm-Groun...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Clarimort said:

Hey friends,

I hope this is the correct subforum.

I need some tips on how to test your manual lenses focus.
I have an Olympus Trip laying around that I just opened up to repair the aperture. It seems to work fine now but I am not sure if the lense is adjusted correctly. It seems off on my test photos.
How can I find out?
I can only find test charts (like this: http://www.traumflieger.de/desktop/fokusdetektor/fokusdetektor_ls.pdf) for auto focus systems. Can I use them too by just moving them away from the camera depending on what distance I put the lense on and see if it's in focus? Or how would you go about it?
I have another lense that I would like to test as well so I need a reliable method.


Thanks!

C.

Click to expand...

I'm happy to contribute the attached.

And I'll contribute this, recently used to troubleshoot and repair (modify AF corrections in EEPROM) a Yashica T4.
The "25" mark is at 35.3mm, so that when the chart is at 45°, "25" is the distance from the "0" mark as seen from camera. For AF cameras, you need another target, either with a pattern (passive AF) or a gray card (active IR AF). For MF cameras, just measure from camera to "0". I won't return to the difference between the distance conventions, origin at film versus lens, which some members discount as useless theory.

Due to the way that the light from the white strips "leaks" into the dark strips in the out-of-focus areas, the in-focus spot is obvious as having higher "macroscopic" transmission, even with the naked eye looking at a 35mm negative.

Here's how we did it at Olympus (assuming you don't have a collimator!). You'll need a spare focus screen or ground glass that will fit across the film rails inside the open back of the camera.

With the top cover off, find the pawl next to the brass wind gear (the one the big black thumb wheel turns) that keeps the wind from turning backwards. Carefully hold this pawl away from the brass gear and turn the thumbwheel _backwards_ -- this will open the shutter blades. Set the aperture to f/2.8, cover the cells, and/or set a low iso, press and hold the shutter release down to open the aperture.

Put the ground glass or focus screen across the film rails and point the lens out any convenient window with something at least several hundred meters away. Turn the lens until it's at it's sharpest. Let's call that "infinity". If needed, loosen the set screws around the lens and adjust, then tighten.