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Shutter Speeds Off on RB Graflex Series B

 
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Tim Engel



Joined: 17 Oct 2002
Posts: 6
Location: Minneapolis, Minnesota, USA

PostPosted: Thu Oct 17, 2002 7:48 pm    Post subject: Reply with quote

The shutter speeds are off in my RB Graflex Series B, Ser No 154561 (it was my father's), and I could use some help/ advice. It has always produced great image's, but the exposure has been problematic. Recently I picked up a Calumet Shutter Speed Tester on ebay, so I tried it out on the Graflex.

According to the placque on the camera, the Graflex shutter speeds are supposed to be:
Slot Width __ 1/8" __ 3/8 __ 3/4 __ 1 1/2
Tension 1 ___ 350 ___ 110 __ 40 __ 10
Tension 6 ___ 1000 __ 295 __ 90 __ 35

But measured speeds were:
Tension 1 ___ 652 ___ 321 __ 133 __ 27
Tension 6 ___ 713 ___ 404 __ 170 __ 36

For each slot width, the speeds were about 3 stops fast at tension 1. But at tension 6, the speeds varied from almost right on at 35/36, to fast at 90/170 and 295/404, to slow at 1000/713. 35 and 680 are close to being correct.

I like to dabble in camera repair (hobbyist/ dangerous) and have a copy of the service manual for the Series B. I dismantled the shutter mechanism and cla'd it per the book. No appreciable difference. So I played with the amount of pre-load on the tension roller spring, but nothing made much difference.

Finally it occurred to me to check the shutter curtain material to see if it was getting stiff. While examining it, I noticed that the slot widths didn't look right. So I measured them and here's what I found.

Curtain Slot Widths
Nominal __ 1/8 ____ 3/8 ____ 3/4 ____ 1 1/2
Decimal __ 0.125 __ 0.375 __ 0.750 __ 1.500
Measured _ 0.160 __ 0.280 __ 0.545 __ 2.120
Error ____ +.035 __ -.095 __ -.205 __ +.620

None of the measured slot widths match those given on the placque on the camera. And most are off by quite a bit. And some are wider while others are narrower. I don't see any logic to the error pattern... like attempting to compensate for spindle diameter growth as curtain material winds onto it.

Are these slot widths correct? This camera went into storage when Dad went of to WW-II and didn't come out again until I inherited it after his death. It's factory original, and no one messed with it until me... and I haven't altered the curtain slots.

What are the correct slot widths that should have been cut into the curtain? Should the actual widths match the nominal widths marked on the placque?

How many turns of curtain material should be glued to the roller spindle? That will influence the effective roller diameter.

Does anyone have any other suggestions on what needs to be done to yield correct shutter speeds?

For now, I've created an alternate shutter speed placque that gives the actual shutter speed per the Calumet tester for each combination of tension and slot width.

Thanks for any and all suggestions,
Tim
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45PSS



Joined: 28 Sep 2001
Posts: 3201
Location: Mid Peninsula, Ca.

PostPosted: Thu Oct 17, 2002 8:05 pm    Post subject: Reply with quote

I suspect a fault in the tension roller/spring. If it can be dismantled do so and clean/lubericate it and reassemble and retest. If it cannot be disassembled then flush it out with a spray cleaner and lube with light oil.
If the camera has never been repaired then slot width, wraps on the rollers ect. should be factory origional and tolerances of the day come in to question.
Does this shutter assembly have a govenor? If so is there a difference in accuracy between govenor and non governed speeds?
Charles

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While a picture may be worth a thousand words, a quality photograph is worth a million.

[ This Message was edited by: 45PSS on 2002-10-17 13:07 ]
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Tim Engel



Joined: 17 Oct 2002
Posts: 6
Location: Minneapolis, Minnesota, USA

PostPosted: Thu Oct 17, 2002 9:14 pm    Post subject: Reply with quote

[quote]
On 2002-10-17 13:05, 45PSS wrote:
> I suspect a fault in the tension roller/
> spring. If it can be dismantled do so and
> clean/lubericate it and reassemble and
> retest. If it cannot be disassembled then
> flush it out with a spray cleaner and lube
> with light oil.

Charles,
Thanks for the reply.

The tension roller doesn't appear to be very sophisticated. However, I didn't see any way to dismantle it, and I didn't want to force anything since replacement parts aren't readily available. But I did flush it out as best I could. Then I applied a small droplet of light oil where the spindles exit the roller.


> If the camera has never been repaired then
> slot width, wraps on the rollers ect.
> should be factory origional and tolerances
> of the day come in to question.

Tolerances? 5/8" on a 1 1/2" slot? =8<0 I hope they had tighter tolerances than that back then. Anyone can free-hand cut better than that (I've gotta be careful where I throw stones since this camera isn't that much older than I am). IF" the nominal dimensions on the shutter speed chart are correct, then someone at the factory was having a real bad day when they made mine. Tolerances won't cover it... I hope. That's why I was guessing that there might be some attempt to compensate for roller diameter growth as the curtain winds up on it... or something like that.


> Does this shutter assembly have a
> govenor? If so is there a difference in
> accuracy between govenor and non governed
> speeds?

No govenor that I could see or detect. If it exists, it must be inside the tension roller, and as I stated above, I didn't force it open. But it doesn't move like it's governed. Actually, it moves about like a window shade.

Regards,
Tim



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bertsaunders



Joined: 20 May 2001
Posts: 577
Location: Bakersfield California

PostPosted: Thu Oct 17, 2002 10:30 pm    Post subject: Reply with quote

No adjustment except how tight the spring is wound.....no gov.....no lube points...
no disassembly possible....slots are std for all models, and after 20+ years of restorations, have never seen any variations except the number of slots! You will have to set the tension on the spring to hit a happy medium....set it to your most used settings, and check speeds at diff tension settings to compensate for some of the closer exposures!
You new fellows to these cameras must realize that these are not typically
up to "todays state of the art", and the design came along a very long time before the 35mm canned film was invented! Like all old things, they tend to slow a bit with age! And check out that $65 tester you are using, against a expensive one, and you will
find yourself doing a bit of hedging with it too, (I have a tester just like yours)
Best to take notes of results and exposures, and keep them handy....I usually find that the exposures are always kinda one sided...all slow, or all fast!
Bert
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Tim Engel



Joined: 17 Oct 2002
Posts: 6
Location: Minneapolis, Minnesota, USA

PostPosted: Fri Oct 18, 2002 12:22 am    Post subject: Reply with quote

Bert,

Thanks for the info.

And yes, I understand that the Calumet Shutter Speed Tester is more of a tape measure than a micrometer. I take what it says with a grain of salt. I don't have a "real" tester to check it against, but I have used it on several modern SLR's fresh from professional cla's, and it/they seem to correlate well.

Thanks and regards,
Tim
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45PSS



Joined: 28 Sep 2001
Posts: 3201
Location: Mid Peninsula, Ca.

PostPosted: Fri Oct 18, 2002 12:31 am    Post subject: Reply with quote

Bret, I'm well aware that the "MODEL T" is not quite a Towne Car even though it is quite durable.
Tim's measurements calculate to an adverage of + or - 25%, good enough for materials of that age?
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While a picture may be worth a thousand words, a quality photograph is worth a million.



[ This Message was edited by: 45PSS on 2002-10-17 17:51 ]
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