Canon IV-Sb viewfinder cleaning

[ChrisN]

With the advice received recently from dexdog I managed to get the top cover off the IV-Sb to have a look underneath. I found 53 years worth of dust underneath!

The least-obvious part of the disassembly is the need to remove the small rangefinder lens and the screw mount underneath, to give the clearance to allow you to remove the top cover. The small lens (which you rotate to adjust the vertical alignment) is a press fit into its housing - it pulls straight out.

 

[ChrisN]

After using a small paintbrush and canned air to blow away most of the dirt, I tackled the optics. There's a small glass lens in the top cover, that needed cleaning for a start. Next is the interesting bit - the rotating housing that provides for the three viewfinder magnifications. This is like a cube with lenses on opposite ends, and adjacent holes to look through the other way. On the "F" and "1.5x" settings you are looking through the lenses, from either direction, and on the "1x" setting you are looking straight through the middle, no lenses.

 

[ChrisN]

In front of the rotating housing is another housing with a prism - one face of that is the front of the viewfinder. You can gently clean two of the faces without removing the housing, but if you want to clean the rearmost face, you have to remove the housing that covers the prism. Beware - if you do that you'll have a bit of work to do to get it to focus accurately again!

The housing is held by three screws; one on the left and two on the right. After removing the housing, my prism came away easily in my fingers, for a good gentle clean. Be careful here - it seems to be two prisms stuck together and I don't think you would want them to separate!

Sorry - same pics!

 

[ChrisN]

There's another small prism which is the one that moves as you focus the lens - on that one it's easy to get to both faces for careful cleaning.

Now the tricky bit - putting it all back together! After you have put the viewfinder prism carefully back into place, mount the three screws but leave the two on the right fairly loose and the one on the left only very lightly screwed down. You want to be able to rotate the prism housing slightly to get it lined up correctly again. Now screw down one of the screws on the right so there's just enough friction to stop the housing moving freely, but not enough to stop you from moving it.

I adjusted the rangefinder alignment at 3.5 feet - the shortest focus scale on my lens. (You might prefer to use infinity - I don't have infinity available in my study!) Mount the camera on a tripod, and with the lens set to 3.5ft and the camera precisely positioned so the film plane is 42inches from the target, check the rangefinder images. Wiggle the prism housing until they align precisely. After that, check the vertical alignment - if you need to adjust that do it now then check the horizontal alignment again. Finally, carefully tighten all three screws, checking as you go to make sure you don't shift the prism housing. This bit took me 30 minutes!

After that, put the rest back together carefully. My viewfider is now much brighter, and I can see the rangefinder spot!

Disclaimer - this worked for me. Please don't try to hold me responsible if it doesn't work for you. I expect I might have to do some more checking on the rangefinder alignment at infinity and some more fine tuning.

Cheers!

 

[John Shriver]

Boy, was that a dirty rangefinder! Crud city.

It is nice that there are no exposed mirrored surfaces that you need to be afraid to clean. (Unlike a Leica.)

I would recommend avoiding removing the beam-splitter prism. You can clean all sides using Q-tips. Both to avoid the hassle of re-aligning it, and to avoid any risk of a stress separating the cementing. It is quite irreplaceable.

You can make a local "infinity" by making a X and a + on a peice of paper, separated by exactly the spacing between the two windows on the front of the camera. (Well, by the spacing of their optical axes.) When you line it up at a small distance, and focus to conincide them as a star, your rangefinder is set for infinity.

The moon provides a handy infinity many nights.

 

[back alley]

chris,
where are the 'after' pics?

joe

 

[dexdog]

Canon IV-Sb cleaning

Canon IV-Sb cleaning

Chris, you are a lot braver than I am. I will have to bookmark this effort so that I can find it when/if I decide to clean the rangefinder and viewfinder of my IV-Sb or L-1. NIce effort, and well illustrated.

Dexdog

 

[jlw]

I adjusted the rangefinder alignment at 3.5 feet - the shortest focus scale on my lens. (You might prefer to use infinity - I don't have infinity available in my study!)

You can have infinity available wherever you want! (Kind of a metaphysical notion, that...)

Do the following, obviously, before you take your camera apart. Measure the EXACT physical base length (distance between the center of the RF window and the center of the VF window.) Make two bold dots or lines on a card, spaced this EXACT distance apart.

If you don't have a way to take an exact measurement, set a known-good lens to infinity and point a laser pointer forward through the viewfinder eyepiece. The rangefinder optics will split the laser beam. Mark your dots or lines at the exact locations of the two laser dots.

Once you've made this "infinity card," when you look through the rangefinder at the card, these marks will magically align when the focus is set to infinity -- regardless of the actual distance to the card!

 

[ChrisN]

John and JLW - thanks for the hints on artificial infinity. John - your advice about not removing that prism is probably very good advice, but it's nice to know how it all works!

Dexdog - thanks for the kind words, and the guidance about removing the rangefinder lens to get the top cover off.

Joe - boy you're hard to please! 🙂 OK, here's the "after" pics. Actually, while I was doing the job I was actually too worried about getting it back together & working, to take any photos as I worked! I usually take photos at the start of the job to give me a reference for re-assembly.

 

[harry01562]

Canon RF cleaning

Canon RF cleaning

Thanks Chris, for a most informative post... amazing how dust can find ways to accumulate!
I have been watching the thread with interest. One of these days I will probably "go in" and clean a couple of my own Canon's.
That's a very pretty IV-SB you have. I own a later version, and love it as a pocket shooter.

Harry

 

[back alley]

thanks chris!

hell of a difference eh?

joe

 

[Sonnar Brian]

Well Done!

Nothing nicer than a clear view through a viewfinder.

 

[ChrisN]

Thanks guys. Now, who's got a spare "P" I can practice on? 😀