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r collett
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 26, 2006 - 04:45 pm: | 
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hi,
i have a nice c4, which on checking the
lens inf. appears to be out quite a bit.
when the lens is on inf.i.e viewed through the back of the camera, the r/finder
is reading 8ft.the r/finder is perfect at the
inf.setting.i don't think the r/finder
is at fault as non of the screws appear
to have been touched.
would appreciate any advice.
regards, roy. |
M Currie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 26, 2006 - 10:26 pm: |
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I'm not sure from the above just what is off, so please bear with me.
When you set the lens to infinity (i.e. turn the wheel all the way to the infinity mark, which looks like an 8 when it's actually set to infinity) what problem are you observing? You should, of course, see the correct rangefinder image at infinity, and with a ground glass or the like on the film plane, the lens itself should be focused properly.
Remember you can't just look through the back of the camera to judge the focus. You must see what is projected onto the film plane. If you don't have ground glass, you can use scotch "magic" tape on a piece of plain glass in a pinch.
I am assuming here that this is the 50 mm. f2.8 Coated Cintar lens that is standard on C-4's
A couple of quick visual checks to see if the mechanism is out of whack: The rack gear on the lens is designed so that its teeth are only just enough to go from closest focus to infinity. When you are at the infinity mark on the focus wheel, there should be no more teeth left on the lens rack, and when you go the opposite direction to three feet, you should again run out of teeth.
Now operate the focusing knob, and observe the point where the lens lengthens and shortens as it focuses. On my C4, the gap when set at 3 feet is a little under 4 1/2 millimeters, about the thickness of three US pennies stacked together. When focused to infinity, it closes to a little over 1 millimeter. If I put a dime in the gap, it will hold it tight at about half way between 50 feet and infinity. I imagine there's a little variation in individual cameras, but I'd expect that those measurements would be pretty close on any lens that's set up right. My C4, despite being a horrendously dirty, beat-up specimen bought for a dollar, focuses well.
The rangefinder of a C-4 is pretty easy to adjust, as I recall. It requires taking the top off, but this is not hard, and the parts inside are not very delicate.
If the lens itself is off in focus, it might be possible to readjust it. I note on mine that there's a setscrew which appears to control the focus adjustment of the lens itself. If you set the lens to 6 feet, the setscrew will be at the exact bottom of the lens. I have not messed with this, but it looks as if the rear part of the lens has a slot into which that setscrew goes, which turns the forward part of the lens, and that the setscrew itself is what engages the stationary brass focus helical threads beneath. Recalibrating might be as simple as unscrewing the setscrew, pulling the barrel in or out, and then screwing it back in at a different point on the helical threads. If the lens focus is truly off, and the measurements aren't close to what I observed, this might be worth a try. |
r collett
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 07:55 am: |
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hi,mr currie.
thanks for your reply.
perhaps i didn'tmake things clear.
i had the back of and a ground glass on the film plane,looking through the glass i focused the
lens on an object at least 300ft away.
when it was in perfect focus,the r/finder
wheel was reading 8ft
the funny thing is your measurements check out on my camera.
i think i'll go through the exercise again,
take some measurements,and get back to you.
thanks once again.
regards, roy |
M Currie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 08:30 am: |
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It sounds as if the lens itself is all right, then, and the rangefinder itself is all right, but just the wheel on the rangefinder is off. When I opened mine up a year or so ago to adjust the rangefinder, I don't remember just how it was all put together, so I cannot say how easy it would be to recalibrate the markings on the wheel to the actual focus point, without messing up the RF itself.
One possibility that occurs to me is that if everything is working right except that the numbers aren't lining up, it's possible that the little aluminum disc on which the numbers are printed might have fallen off and been put back on wrong. Whether or not this is the case, and how easy it might be to pry this disc off and stick it back correctly is a question only you can answer and decide on the basis of the risk to camera cosmetics. But if everything is right but the numbers, this might be one non-invasive solution. |
M Currie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 08:42 am: |
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Ii forgot to add to the above, that one reason I think the disc might simply have come unstuck and been put back wrong is the odd coincidence that it is at "8" when focused to infinity. As you've no doubt observed, the infinity mark is on end when it's correct, and looks like an "8" and the actual "8" mark is on end when it's correct, and thus looks like infinity. A person reinstalling the disk hastily might simply not have taken the time to wonder why infinity lies between 6 and 10 feet.
A second non-invasive possibility occurs to me, which is to focus it to infinity (actual, not indicated) and find where the infinity mark actually lines up. When I focus mine to 8 feet, the infinity mark lines up just about halfway up the step in the top cover. You could just stick a little piece of tape, or make a magic marker mark, there, and use that as your index point. You'd only need it when zone focusing without the rangefinder anyway, so it might be sufficient. |
r collett
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 02:42 pm: |
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hi,
again your camera and mine agree(re the last paragraph)
now consider this.all cameras when focused
at inf.come up against a positive stop.
therefore on mine when up to the stop the lens should be on inf.
but it isn't, to get sharp inf.i have to wind the lens out.then on looking at the r/finder it's
reading 8ft.which leads me to suppose
the lens is out.
anyway i'll check things again in case i've
done something stupid.
many thanks for your replies.
regards, roy |
M Currie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 03:25 pm: |
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Ok, things are becoming clearer.
As far as I can see, the only positive stop on the Argus lens is the end of the gear rack. For infinity it definitely should be at that extreme.
When you put the lens to its actual infinity focus, does the rangefinder image close at infinity, or at 8 feet? In other words, is the rangefinder optically correct for the distance or does it agree with the lens?
I'm guessing that if you have to crank the lens out for infinity focus, and if when it is correctly focused for infinity, the gap is wider than that approximate dime I measured, there is something loose or out of position in the lens itself.
I am sort of assuming that you underwent this test because the camera was not giving you well focused pictures, and that you know what you're doing with regard to the ground glass - i.e. making sure that the ground surface is facing forward, so it's on the film plane, etc. etc., so about the only thing I can come up with at this point is that the lens is damaged.
It might still be worth a try to see if you can readjust the lens using that setscrew at the bottom, but this may not work if the lens is damaged.
Here's another measurement just for possible reference. From the very front edge of the lens to the front edge of the aperture ring, I measure 7 1/2 mm. That's almost exactly 5 pennies. I wouldn't be surprised if a dropped or damaged lens might look different there.
The rear lens element of course is curved a bit, but if you look at the back side of the lens, with shutter open, you'll see a rather wide ledge to the outside of the glass. Measuring from that ledge to the film plane, with lens set at infinity, I get a measurement of a tiny bit under 39 1/2 mm (sorry, no pennies for this one, but that's about 1-17/32 inches). This portion of the lens moves back and forth with focus.
Hope that helps. If you ever do get this sorted out you'll find that the C-four is a surprisingly nice picture-taker. |
r collett
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 02:19 pm: |
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hi,
thanks for your advice once again.
i rechecked the settings, and they are
still the same.i don't think the end of the gear rack is used as an inf. stop,more like an internal
pin,though i could be wrong.
anyway,i found out that the lens module can
be moved in and out in its mounting by taking
the lens assy.off, unscrewing a very small
grub screw(looking from the back)and removing a black locking ring.
this frees the lens module which can then
be screwed in and out of its mount.
so what i shall do is put the main mount back,
set everything to inf.then screw the lens module
out until its focused on inf.therefore the
r/finder will be on inf.the lens will be on inf. the r/finder dial will be on inf.and the main mount will be against its stop.
all that remains is to lock everything up
this seems a logical way to go.
will let you know if this works.
regards, roy. |
M Currie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 03:55 pm: |
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Good luck. It sounds as if it ought to work. |
r collett
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 01, 2006 - 11:45 am: |
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hi,
have carried out the steps im my last mail,
and everything appears fine.
the lens, r/finder and dial are all on perfect
inf.when the main mount comes up against its
stop.
thanks once again for your interest.
regards, roy. |
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