Nikon FM, shutter not openning fully at high speeds

zanxion72 · Mar 17, 2022

There is a strange problem with my Nikon FM. At 1/500 and much worse at 1/1000 the shutter does not open fully. At 1/500 it opens by 2/3 and at 1/1000 by 1/3. If I work the shutter for a while it starts to open wider until full.
Does that call for a simple CLA, or the shutter calls for replacement?

shutterfinger · Mar 17, 2022

A CLA. There are 2 curtains that form a slit to achieve the speeds. The common failure is the first curtain slows and the second curtain catches up to it blocking part of the image frame.

zanxion72 · Mar 17, 2022

shutterfinger said:
A CLA. There are 2 curtains that form a slit to achieve the speeds. The common failure is the first curtain slows and the second curtain catches up to it blocking part of the image frame.

Thank you shutterfinger! CLA so be it. I love this one because it is a family camera. It might not be the fanciest of best camera ever, but it carries a ton of emotion.

Chan Tran · Mar 17, 2022

Shutter curtain tension needs to be adjusted.

Ian C · Mar 17, 2022

Re: Post #1

“There is a strange problem with my Nikon FM. At 1/500 and much worse at 1/1000 the shutter does not open fully.”

How do you know? This is too fast to see with normal human eyesight.

“At 1/500 it opens by 2/3 and at 1/1000 by 1/3.”

This sounds approximately like normal behavior for an FM shutter at these relatively fast speeds (faster than the 1/125 second flash-synchronization speed).

Do you understand how a focal-plane shutter works? The Copal SQ shutter in the Nikon FM fully opens the film gate ONLY at speeds of 1/125 second and slower.

At faster speeds, the shutter never fully opens. It “wipes” the exposure onto the film as the opening between the first and second curtains passes over the film. The faster the speed, the narrower the open gap between the two curtains.

This is why the shutter speed has to be set at the camera’s flash-synchronization speed or slower for flash photography. Otherwise, part of the frame will be unexposed due to one of shutter curtains partially covering the film and preventing the flash’s light from reaching it.

“If I work the shutter for a while it starts to open wider until full.”

This last statement is confusing. There is no way that the shutter of a properly-functioning Nikon FM should be fully open at a fast speed, such as 1/500 or 1/1000 second. Hopefully, you aren’t confusing the motion of the aperture in the lens with the shutter in the body.

If the above quote refers to the lens aperture, then your lens might have a sticky diaphragm due to seeping of the oil from the focusing helicals onto the aperture blades. If so, that is a lens problem and is unrelated to the camera body.

Chan Tran · Mar 17, 2022

Ian C said:
Re: Post #1

“There is a strange problem with my Nikon FM. At 1/500 and much worse at 1/1000 the shutter does not open fully.”

How do you know? This is too fast to see with normal human eyesight.

“At 1/500 it opens by 2/3 and at 1/1000 by 1/3.”

This sounds approximately like normal behavior for an FM shutter at these relatively fast speeds (faster than the 1/125 second flash-synchronization speed).

Do you understand how a focal-plane shutter works? The Copal SQ shutter in the Nikon FM fully opens the film gate ONLY at speeds of 1/125 second and slower.

At faster speeds, the shutter never fully opens. It “wipes” the exposure onto the film as the opening between the first and second curtains passes over the film. The faster the speed, the narrower the open gap between the two curtains.

This is why the shutter speed has to be set at the camera’s flash-synchronization speed or slower for flash photography. Otherwise, part of the frame will be unexposed due to one of shutter curtains partially covering the film and preventing the flash’s light from reaching it.

“If I work the shutter for a while it starts to open wider until full.”

This last statement is confusing. There is no way that the shutter of a properly-functioning Nikon FM should be fully open at a fast speed, such as 1/500 or 1/1000 second. Hopefully, you aren’t confusing the motion of the aperture in the lens with the shutter in the body.

If the above quote refers to the lens aperture, then your lens might have a sticky diaphragm due to seeping of the oil from the focusing helicals onto the aperture blades. If so, that is a lens problem and is unrelated to the camera body.

You're correct.

BobD · Mar 17, 2022

See Ian's post above. The shutter isn't supposed to open fully at those speeds.

__Brian · Mar 17, 2022

With the lens off the camera, back open, positioned in front of the shade of a lamp- it is very easy to see that my Nikon FM's shutter is working correctly at 1/1000th and is not capping.. The travel of the slit across the full image plane is easy to see. Using this same technique on other cameras that needed work, shutter capping- the second curtain overtaking the first before traveling the length of the exposure- is easy to see.

It sounds like your camera needs a CLA, as suggested before. The fact that you can operate the shutter and the condition clears up for a while also suggests that a CLA is required.

BrianShaw · Mar 17, 2022

https://mir.com.my/rb/photography/hardwares/classics/nikonfmseries/fm/part5.htm

https://en.wikipedia.org/wiki/Focal-plane_shutter
(see the illustrations for how the shutter blades interact at fast speeds)
"Vertical-travel focal-plane shutter firing at 1/500 of a second – the gap between the curtains is clearly visible near the bottom."

shutterfinger · Mar 17, 2022

Ian C said:
How do you know? This is too fast to see with normal human eyesight.

I have no problem seeing the slit for 1/1000 and faster. I'm 70 years young.

BrianShaw · Mar 17, 2022

And… what’s important is camera performance, like when taking pictures. Are images at fast speeds being recorded reasonably correctly?

reddesert · Mar 17, 2022

First, as Brian says what's important is whether the images on film look okay. If they are partly cut off then shutter curtain timing is off.

Next, the human vision system can only resolve motion at about 0.1 second, but effects related to the persistence of vision mean that you can perceive a light signal that is much shorter. For example, we all know you can see that an electronic flash goes off, even when the pulse is very short perhaps 1/1000 sec (like a flash in Auto mode that fires only a short burst at less than full capacity).

This is why people can see when a camera focal plane shutter slit is exposing the full frame, even at fast speeds. Just open the back, take the lens off, and look through the shutter while you fire it at 1/1000 sec. You should see light in the entire frame. It's not precise enough to tell whether the exposure is even, but if the shutter is badly capping and not exposing half of the frame, I think you would see it.

zanxion72 · Mar 18, 2022

As people said! I can see on all my cameras the shutter opening fully at all speeds and at least up to 1/1000. But on this one 1/500 and 1/1000 for sure have a problem. As suggested I will give it to some expert for CLA.

Nitroplait · Mar 18, 2022

zanxion72 said:
As people said! I can see on all my cameras the shutter opening fully at all speeds and at least up to 1/1000. But on this one 1/500 and 1/1000 for sure have a problem. As suggested I will give it to some expert for CLA.

A SLR shutter does not open fully above the flash sync shutter speed!
A slit of varying width travels across the film gate from 1/250 and above on the Nikon FM.
The important point is to establish if one curtain catches up with the other during this travel, causing part of the image to be under- or un-exposed .
If you haven't, you really need to test this with film before you send it in. Make sure you don't make the mistake of using a flash when testing 1/500 and 1/1000.

shutterfinger · Mar 18, 2022

zanxion72, is English your first language?

zanxion72 · Mar 19, 2022

Nitroplait said:
A SLR shutter does not open fully above the flash sync shutter speed!
A slit of varying width travels across the film gate from 1/250 and above on the Nikon FM.
The important point is to establish if one curtain catches up with the other during this travel, causing part of the image to be under- or un-exposed .
If you haven't, you really need to test this with film before you send it in. Make sure you don't make the mistake of using a flash when testing 1/500 and 1/1000.

Shouldn't I see an almost fully open shutter at these speeds due to that traveling slit? In front of my monitor I can see some banding, but against a bright sky it seems like a full frame opened, faint and but appears like a full frame. It had a problem with the flash sync at 1/125 where the upper third of the frame was completely black (unexposed negative).

zanxion72 · Mar 19, 2022

shutterfinger said:
zanxion72, is English your first language?

Nope! Am I that bad?

Nitroplait · Mar 19, 2022

zanxion72 said:
Shouldn't I see an almost fully open shutter at these speeds due to that traveling slit? In front of my monitor I can see some banding, but against a bright sky it seems like a full frame opened.

At 1/250, 1/500 and 1/1000 the FM shutter will never expose the entire filmgate at the same time. It will be a fixed opening which is more narrow than the filmgate that travels across the film gate opening.
It is because of this phenomenon you shouldn't use flash above 1/125, as the flash would only illuminate part of the frame.

__Brian · Mar 19, 2022

zanxion72 said:
Nope! Am I that bad?

No, I understood what you were stating. I figured you were from Athens Greece and not Athens Georgia in the USA.

It sounds like the shutter travel is uneven, and the camera needs a CLA. This is not uncommon for 40+ year old cameras.

When I tested my Nikon FM before making my post: I did the test as described. Took the lens off the camera, opened the back, and held it near the outside of a lamp shade, the lamp has an LED type bulb in it. The lighting is even. I fired the shutter at 1/500th and 1/1000th: I could see the shutter was working correctly and the light appeared even across the frame. This is a 1-minute test, I'd be interested of you did the same with your FM and describe what you see. The Nikon FM uses a copal square shutter- so having a pro do the CLA is a good decision. I've had a Nikkormat FT3 shutter "just stop working", a CLA at Essex in New Jersey, now Gone, fixed it right up.

Ian C · Mar 19, 2022

Your use of written English is perfect so far as I can see.

I suggest shooting a roll of ASA 400 film in bright outdoor light so that you can select a large enough aperture to require speeds such as 1/250, 1/500, and 1/1000 second.

Process the film. If the frames shot at such speed show significant low-exposure or no-exposure banding, then the shutter is defective. If no such banding occurs, then there is nothing wrong with the shutter.

If you do this test—and I hope that you do—then you will have settled the question one way or the other. PLEASE, report your results here so that we all may benefit from this test.

shutterfinger · Mar 19, 2022

zanxion72 said:
Nope! Am I that bad?

Thought there might be a translating error.

If you're doing the visual test and you can see the light dim as the slit crosses the image plane then the shutter needs servicing, if you are getting banding on your images at fast speed the shutter needs servicing. Banding can be blank portion of the frame or a under exposure for part of the frame.

reddesert · Mar 20, 2022

zanxion72 said:
Shouldn't I see an almost fully open shutter at these speeds due to that traveling slit? In front of my monitor I can see some banding, but against a bright sky it seems like a full frame opened, faint and but appears like a full frame. It had a problem with the flash sync at 1/125 where the upper third of the frame was completely black (unexposed negative).

Monitors/TVs aren't the perfect light source here because of the refresh rate. If you use an LCD or LED with some persistence then it will probably work fine, but a light bulb diffused by a lampshade will always work. If for some reason you still have a CRT monitor or TV, then you will absolutely see non uniform illumination due to the focal plane shutter curtains being faster than the CRT refresh. In the old days we used speeds 1/30 or slower or so to photograph monitors and TVs for this reason.

If the camera isn't exposing the full frame with the flash at 1/125, but it works with flash at slower speeds like 1/60, then there's some kind of timing problem.

Niglyn · Mar 20, 2022

zanxion72 said:
As people said! I can see on all my cameras the shutter opening fully at all speeds and at least up to 1/1000. But on this one 1/500 and 1/1000 for sure have a problem. As suggested I will give it to some expert for CLA.

Hi,

Please look at this video, it explains how a focal plane shutter works. As others have said, the shutter will only be fully open at sync speed or below. Above sync speed, the second curtain starts to close before the first has fully opened.
e.g if the camera sync speed is 1/30, the first curtain will be fully open before the second curtain starts to close. For 1/60, the second curtain will start to close when the first curtain has travelled half way. For 1/125, the second curtain will start to close when the first curtain has travelled a quarter of the way.
Interestingly, the shutter curtains always move at the same speed, no matter what the shutter speed is set to. It is the time before the second curtain starts to close, which determines the exposure.
So 'shutter speed' is a bit of a misnomer.

(175) Shutter Speed - Focal Plane Shutters - Episode 5.1 - YouTube

now look at this video, showing shutter operation in slow motion
(175) Inside a Camera at 10,000fps - The Slow Mo Guys - YouTube

Niglyn · Mar 20, 2022

zanxion72 said:
Shouldn't I see an almost fully open shutter at these speeds due to that traveling slit? In front of my monitor I can see some banding, but against a bright sky it seems like a full frame opened, faint and but appears like a full frame. It had a problem with the flash sync at 1/125 where the upper third of the frame was completely black (unexposed negative).

No.
Remove the lens & open the back and look at the shutter, from the back of the camera.
Fire the camera in bulb mode & you will see the shutter fully open whilst your finger is still pressing the shutter.
The same thing will happen, shutter fully open at all speeds up to the sync speed, 1/125 in your case, but obviously the shutter will close immediately and not stay open like bulb mode.
'the shutter' is made of two curtains, which you should have seen whilst in bulb mode. the first opens to expose & the second closes. Then winding on, they both move to the start, but staying together, so not to allow light in.
Above sync speed, the second curtain starts to close before the first is fully open, so this is the slit, which gets narrower as the speed increases.

The unexposed part of your film when using flash, shows that the second curtain had already travelled 2/3 of the way when the flash fired (I think the FM curtain travels top to bottom) so if you had the camera set to 1/125 and the sync speed is 1/125, there is a fault with the camera.

zanxion72 · Mar 21, 2022

It was a matter of CLA. I took it to a local repair shop and it has been diagnosed with a first curtain slowing down before a complete shutter release cycle. That had the effect of an uneven slit closing before crossing the entire frame. I went to the shop to get it back just an hour ago and he demonstrated me other Nikon cameras at higher than 1/250 speeds. At least up to 1/1000 you perceive a fully opened shutter as your eye cannot "catch" the slit traveling across the frame. He also told me that he found a tinny chip of wood within the clockwork of the self timer (!?).
Thanks everyone for explaining to an old dog how the shutter works at higher than flash sync speeds. I had an absolutely wrong impression of how it works for more than a decade!

Nikon FM, shutter not openning fully at high speeds

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