Modern Classic SLRs Series :
Nikon F3 - Frame Counter

As discussed earlier and brought up by Burt Hump: who posted this question on the Message Board... 
"..... have a Nikon F3HP and used it for some time. Quite some time ago, I found that the film counter did not reset when the film was changed. I had it repaired by an authorized Nikon dealer and it was ok for a while. It then failed again, but since I was not in the same area, I brought it to another Nikon authorized dealer and it was repaired again. I just had it happen again....." 
Looks like a US $100.00 fix was not working, perhaps some of you gurus out there may able to help him, As I explained, the pin on the camera portion and the protruding edge on the film back did the trick for film counter reset. However, solely by pressing the pin won't reset the frame counter automatically, the frame counter is far more complicated a mechanism behind the simple operation.

f3backpin.jpg

Filmback Illus.jpg (7k)

The 'mysterious' pin (B) hidden at the railing of the film back is for film counter reset. The standard or any version of the Databack will have a slight protruding edge (A). This mechanical way has been used on all Nikon since the seventies. If your frame counter won't work, check if both of these mate probably or the most likely culprit is the counter switch which would require slight adjustments.


Counter Switch Mechanism

Generally, after loading the film into the camera, you would require to make a few blank exposures before the frame counter reaches "1". However, for any AUTO camera during its time (Including Nikon own electronic auto exposure camera such as Nikkormat EL series and Nikon FE (1977) prior to the Nikon EM (1979) and F3 of 1980, if the shutter-speed dial is set to "Auto" , shutter speed becomes slow under low-light conditions, which at times, may even lock up the mirror for a minute or so and thus prevents rapid picture-taking action, one typical example is using a non-dedicated flash in AUTO mode in the dark.

countermnism.jpg
For quick and easy film loading, auto-exposure control remains cancelled until the frame counter reaches "I" as was introduced earlier by the EM in 1979, a year prior to arrival of the Nikon F3. The mechanism is: When the frame counter is advanced by the film advance operation, ON/OFF changeover of the counter switch is made by a mechanism which comprised of a combined operation of ratchet (1), Insulator (2), Conductor (3), Contact Blade B (4) and Contact Blade A (5). The Counter switch, is located just underneath the frame counter disc.

With the shutter-speed dial set to "Auto", when the frame counter is between "S" and "0". the shutter speed becomes automatically 1/80 sec. by the operation of IC circuit. At shutter-speed dial settings ranged from 1/2000 - 1/125 sec., shutter speed will become 1/80 sec. at the initial few frames.

Counter switch is turned OFF while the frame counter indication is between "0" and "1". Auto-exposure control starts working after the frame counter reaches "1".


Counter Switch Adjustment

It is not advisable for anyone to attempt to adjust the Counter Switch and this kind of task should be leave to an experienced service technician to handle it and since Burt Hump claimed two of his recent service was not able to give it a proper fixing, I, personally would still strongly suggest he should send the camera back to the Nikon service centre and naturally they should unconditionally re-adjust for him without incurring any further financial charges - even if Burt can afford it. Generally, Burt's problem could most likely be caused by the Counter Switch.
But just to highlight and stress my point, servicing a high end SLR camera such as the Nikon F3 requires a qualified service centre because the frame counter can regarded as part of the total Nikon F3 shutter mechanism. See the illustration below:

Film-advance Mechanism

The film-advance mechanism of the F3 is characterized by the one way clutch and the connecting shaft. The former serves to reduce noise, as well as provide for a series of short stroke film advancing, the latter simplifies the drive gear train or decreases the torque which the motor-drive needs to full fill film-advancing.

mechanism.jpg Symbol
countermnism.jpg

The Sprocket which in turns via conductor (c) activates the counter mechanism.
Stroking Film-advance lever (1) in the direction (A) rotates Take-up Gear (4) in the direction (B) by way of Clutch (2) and Roller (3) (One-way clutch). This power rotates Gears (5) and (7) and reaches Gear (10) through the connecting shaft. Gear (7) (Incomplete gear) rotates Gear (8) to cock the shutter. But Gear (10) drives Sprocket Gear (12), Spool Idle Gear (14) ant Spool Gear (15) to rotate Sprocket (13) and Spool (16) in the respective directions (C) and (D).

Note: Shutter cocking and Take-up Claw
(17) are referred to multiple-exposure mechanism and Shutter cocking mechanism respectively.

To check, first stroke the film-advance lever to operate the frame counter for ON/OFF timing check of the counter switch.
countersw.gif

Frame Number

S - 0

0 - 1

ON

OFF

Mode

Auto

80

User Set shutter speed

M

2000 - 125

M80

2000 - 8 - Sec.

60 - 8s

M60 - 8 - sec

For adjustment, loosen screws. Even if the task looks so simple, you need to remember you would have to disassemble the camera in order to access these few parts, requiring a lot of special tools specially design and tailor made for camera servicing. Thus this is NOT a photographer's task and one should always leave it to a professional service technician to handle it. But since a user like Bert faced such a problem despite a few attempts to get it fixed, I think maybe an open discussion here in the MB (Message Board) may draw others who are more specialized in camera repair to help him out by giving him a third opinion of what could be the likely cause. (hey, I don't want to a hero here as I am not a service technician but I am just a little curious as well and would like to find the reason why and see if my suspicion is correct..)

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Modern Classic SLRs Series : Nikon F3 - Frame Counter

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