Accuracy of the Index mark of the Argus C3?

[kb244]

Recently acquired a 1953 Argus C3 which needed a little bit of work but came with a cleaned up lens.

I cleaned up the other 'optics' such as behind the rangefinder view hole, back of the viewfinder glass, etc, and also adjusted the flash timing wheel so that the shutter was fully open at the moment the flash contact connects (for X-Sync once I adapt its two prong to a PC-sync of sort).

When I went to adjust the rangefinder since it seemed to be quite a bit off, so I measured out 5 feet from sheet to focus plane and adjusted, then again around 12 feet (not that much working distance inside). I used a focus screen out of an old Minolta SLR that has a split and micro-prism ring as a ground glass to check the actual focus of the lens, placed in diagonally so that it was level across the surface of where the actual film would be, fresnel facing forward where the emulsion would be. Tripoded of course.

The rangefinder and lens are pretty much paired up now by ground glass focusing, but the scale focus ring seems 'off'. It doesn't seem like the lens helicals are on incorrectly since the indexing slot wouldn't allow infinity if I had the lens any further on, and would be too far off the slot if I had it a single turn less. Where it's at now, the screw rides the slot exactly from 3ft to infinity (with the gears stopping right at each point, slightly closer than 3ft on the closer side).

The issue:
But when I focus on something that's 5 feet away measured out (focused in the rangefinder, and focused on the ground glass) it shows exactly 6 feet on the rangefinder ring. If I focus on something that's about 12 and a half feet away it shows exactly 15 on the rangefinder ring.

Was the scale focus rings not that spot on accurate?

To me it's not that huge a deal since it's not faster than f/3.5, but the scale being off that much would affect my ability to utilize some DoF guesstimates if I were going off the scale and not rangefinder.

edit
when I check the ground glass outside now that there's some daylight, the lens itself can't quite get infinity. 50~75 away is *almost* focused but I can't get the lens there where it stops at infinity.

But if I screw the lens down any further it won't reach the slot, and a turn back away is too far.

Edit #2

Seems the threading has like 3 different entry points to screw the lens onto. I went with the one that allowed me the closest-to-body position for infinity, which still doesn't get me infinity exactly, but now 50~75 ft is a little sharper at infinity.

And double-checking groundglass-vs-RF for 3ft, 6ft, 12ft, 25ft-ish seems like it's spot-on least to the pairing of the RF to the actual image captured. I just won't get crisp horizon past 50 feet at f/3.5

 

[DWThomas]

It should be able to focus at infinity. I have never counted, but was of the impression the helical had even more than three possibilities (6?). Anyway, I recall the lens is not quite "bottomed" when at infinity, so you might want to try the next thread. Normally when the idler gear is engaged and all is lined up, the end of the idler gear teeth stops things at infinity, but there might be a bit more travel available in the lens.

There are manuals on the Argus Collector Group site that might shed additional light. I have a 1957 vintage C3 I bought new that I get out at least once a year for Argus Day, an ACG event. It will be "Argust 17th" this year. It sat in a closet for about 25 years and when resurrected in 2005 or so, I was more impressed with it than I expected to be. It's rather fiddly to use, and rather limited in shutter speeds, but outdoors in good light does OK. Gad, to think I began with it shooting Kodachrome Daylight at ASA 10!!!

 

[kb244]

It should be able to focus at infinity. I have never counted, but was of the impression the helical had even more than three possibilities (6?). Anyway, I recall the lens is not quite "bottomed" when at infinity, so you might want to try the next thread. Normally when the idler gear is engaged and all is lined up, the end of the idler gear teeth stops things at infinity, but there might be a bit more travel available in the lens.

There are manuals on the Argus Collector Group site that might shed additional light. I have a 1957 vintage C3 I bought new that I get out at least once a year for Argus Day, an ACG event. It will be "Argust 17th" this year. It sat in a closet for about 25 years and when resurrected in 2005 or so, I was more impressed with it than I expected to be. It's rather fiddly to use, and rather limited in shutter speeds, but outdoors in good light does OK. Gad, to think I began with it shooting Kodachrome Daylight at ASA 10!!!

I'll see if I can find some more threads to go down. I know that if I remove the indexing screw and continue to focus down I can get infinity when checking the ground glass, I just can't find a spot where the indexing hole lines up that far back. Right now at infinity the gap between the lens and the geared collar is about 1.15mm (checked with feeler gauges).

edit: going to the next thread (ie: unscrewing while still giving some tension so it 'clicks' onto the next thread) brings me down to 1.01mm

and you're right, seems to be about 6, as I just counted back around as I went thru all of them to come back to the 1mm gap.

 

[kb244]

Lost the damn indexing screw

 

[Bill Burk]

I once tried something similar with a Kodak 35 and think I totally messed up the focusing...

I used a marked piece of glass to try to focus by parallax viewing (draw a reference mark on clear glass, then when focused on an object, move your eye back and forth and if it is in focus the subject should not appear to move from the reference mark).

After all that work, the pictures I took with it were often out of focus. This made me think maybe the focus isn't supposed to be exactly at the rails.

So I got another Kodak 35 and left the rangefinder adjustments alone (aside from setting infinity).

Its pictures are sharp.

But what I think you might try... set up an oblique test with a yardstick or some other measuring tape and check what's really in focus on a negative after you shoot film with it.

 

[kb244]

I already got it where I want it... I just lost the damn screw to keep it in place. Dog hair and wood floors, can't find the damn thing.

 

[DWThomas]

I already got it where I want it... I just lost the damn screw to keep it in place. Dog hair and wood floors, can't find the damn thing.

Oy -- hate when that happens!

For what it's worth, I made some measurements on the one out of mine:

I used vernier calipers and should perhaps mention at this moment in time I have a left eye with the cataract fixed but the old eyeglass lens and the right eye still riddled with clouds.
If a hobby shop into model railroad stuff could yield a brass #3-56 screw (a roundhead, panhead, whatever) long enough to grip the threaded end with "something" (pin vise or hand chuck) one might be able to creatively file the tip, then cut to length.

Good luck!
(If you're like me, an hour after you've finagled out a replacement, a reflective twinkle off the floor will turn out to be the original. )

 

[kb244]

I stole a focus locking screw from a Kodak Signet (that's inoperable), sanded down the front diameter of it (pointy) so that it would glide in the groove it goes into.

Which seemed to work smoothly, short of sticking out a little (I'll probably try to find a little washer cap if I can't find the original screw).

Before I lost the index screw, I locked the focus to infinity, and then removed the indexing screw putting it down in a lens cap. Turned the lens while watching on the focus screen until it hit infinity focus from some trees in a far distance (bout quarter mile or so). Once I was satisfied that infinity was achieved I loosened the 4x screws (marked in blue), and rotated the collar around so that it would line up to the slot. Tightened down the 4x screws, and then just as I was going to put the index screw in, I dropped it, and yet to be found.

Once I got that signet screw in, I re-adjusted the rangefinder calibration, first at a measured 5 ft, adjusted against a chart, then again at infinity, and then checked again at 5ft.

Now not only is the rangefinder and lens match, the distance scale actually seems accurate (measured 5 ft, focus at 5 feet, shows 5 feet on the scale).

 

[Gerald C Koch]

What the OP is experiencing is a sign that someone tinkered with the lens and did not get it back to its original configuration. Perhaps a lens element got flipped or some other problem. That the lens had been cleaned up lends credence to this assumption.

BTW focusing helicoids usually have six sets of threads. Trying to match the right set can be a rather frustrating endeavor. Professional repairmen make a scratch on the inner barrel in order to match things up correctly.

 

[EdColorado]

Karl, sounds like you may have gotten it together, but if you need the Argus indexing screw let me know. I have a goodly number of Augus spares around here and should have that screw.

 

[kb244]

Karl, sounds like you may have gotten it together, but if you need the Argus indexing screw let me know. I have a goodly number of Augus spares around here and should have that screw.

It'd be nice to have for originality, currently the screw taken from the broken signet seems to be working and I threw a dab of shellac at the base of the screw itself and tip so it wouldn't feel sharp to the touch. Just so that the screw stays where it's at since I unscrewed it a tiny bit to relieve tension off the slot, hasn't seemed to change the way focusing/etc feels compared to the original.

It's funny though that of all the parts on my "parts" black Argus, that's the one thing I didn't have. I need to get a roll thru it to see how it functions out in the real world, normally I would just throw in some cheap color roll laying around and drop it off for processing-only, but that was back when there were more places to do it and it was under $2 per roll (and that was only a year ago, now it's only one place in town, and it's $4 per roll).