Prints appearing half black -- why?

[compur]

The black part has image in it

This is consistent with shooting above flash sync speed. The faint image in the blacked out portion is
from ambient light.

 

[CCericola]

Because there is a partial image in the darker part of the negative it was a flash sync problem.

 

[Paul Ron]

Thanks for the responses. I didn't purchase any copies of the screwed up pictures, but I took a picture of the negatives:

Since they are also messed up, I'm guessing it's what you said about the sticky shutter. I'll look into that. I appreciate the help!

Here's a picture of the camera as well if anyone cares to check it out:

But if it is a flash sync problem explain why every other frame is black? Why are there no clean frame spaces between frames?

Can you post a better pic of the negative strip backlighted please?

.

 

[Josh66]

But if it is a flash sync problem explain why every other frame is black? Why are there no clean frame spaces between frames?

Can you post a better pic of the negative strip backlighted please?

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There are only 3 frames visible in the picture the OP posted, each half black. Each also appear to have had the same shutter speed - that would explain why they are all 'cut off' at the same point.

Using flash on 3 consecutive frames with the same shutter speed doesn't seem far fetched to me.

 

[compur]

Or, to put it another way, it's not that every other frame is black. It's that every frame is half black

 

[Paul Ron]

And no clear frame spaces either? ummmm.... Where is the OP on this one?

I'd like to see a better pic of the film strip, backlited.

So what speed will cause half black image if it was a sync problem? Let's do some research and have some fun with this.

If memory serves me right, curtain shutters are a slit of varying widths flying over the film surface, 2 curtains chasing eachother. The faster the speed the smaller the slit. Now to have half frames exposed, it would be a pretty large slit or enough time for a slit to cover half a frame. Any guesses, maybe the OP can let us in on it?

Anyway, it is fun to think this through.

 

[compur]

I think there are spaces between frames on those negs -- they're just
blended in with the thin image content at the edges of the frames.

BTW, it's only a traveling slit at shutter speeds faster than the flash sync
speed. At the sync speed or below the curtains are fully open for a moment.
This is what the flash is is being synced to -- that period when it's fully open.

This is how it works on classic mechanical focal plane SLRs like the K1000
anyway. Some more modern cameras can sync at higher speeds by
using a series of flash bursts as the shutter opening travels across the
film plane. For example the last of the Olympus OM-3/4 series cameras did
this and I'm sure DSLRs can do something similar.

 

[Paul Ron]

Ah now you are seeing what I was thinking when I first saw the half black negs...

it's a slit at higher speeds over sync 1/60th, so only a black bar should be exposed (the slit), not half frames. All speeds below 1/60th are safe flash speeds because the curtains are fully open (full frame slit).

So the question is... at what speed is the curtain slit half frame to cause his problem?

*Newer focal plane camers use vertical blind shutters thus allowing higher sync speeds. Horizontal curtains all synced at 1/60 or less. Leaf shutter sync at all speeds.

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[compur]

So the question is... at what speed is the curtain slit half frame to cause his problem?

At whatever speed the OP had the K1000 set to. :mrgreen:

 

[Paul Ron]

Well not a very scientific answer. Aren't you curoius?

NIce to see you know the basic Wiki theory but how about an experiment?

Trying to reson it out... a flash burst is 1ms, so half frame exposed would mean the shutter speed was 2ms.... translates to what speed? 1/500th!



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[Josh66]

It's not possible to figure out, since, for one, we can't see the other curtain.

Only half of the frame was exposed, but the 'slit' could be much larger than that. We just know that it was 'at least' half the frame.

I would guess that the shutter speed was close to the x-sync speed though, since the slit is so large. 1/125 maybe. Just a guess though...

 

[Helen B]

Normal 'first curtain' sync fires the flash when the first curtain reaches the end of its travel - so the fully exposed part at shutter speeds shorter than the sync speed doesn't appear as a slit within the frame but always shares a common edge with the frame.

The sync speed is approximately equal to the travel time of a curtain (or a little more). Therefore the travel time of a curtain is a little under 1/60 s if the sync speed is 1/60. Therefore, if the second curtain is about half way across when the first curtain reaches the end of its travel, the exposure setting could be about 1/125 because that is how long the second curtain still has to travel. Note that this has very little to do with the flash duration if it is an electronic flash (different story for flashbulbs, especially FP - focal plane - type).

How does that sound?

Best,
Helen

 

[Paul Ron]

And I'll bet you guys are right at 1/125. and of coursew there is the BUT.....

OK here are the shutter times in ms relating to their respective 1/second parts according to my shutter tester... The ms time is how long light is hitting the film, not curtain travel times. Cutains travel at a constant velocity regardless of what the shutter speed is. The exposure is determined by the size of the slit allowing light to enter ( how soon the second curtain chases the first), not by how fast the curtains travel.

1/30-33ms
1/60-16ms
1/125-8ms
1/250-4ms
1/500-2ms
1/1000-1ms

So I figure if a flash burst is 1ms it would capture the slit in mid fleight causing a bar to appear. But since we are capturing half a frame it stands to reason the 1ms for flash plus the leftover half frame must be a total of 2ms... 1/500 is my guess.

Now for the real world test... anyone game to try on your next roll? (I don't use 35mm). Shoot using a flash marking each speed to see exactly what the captured bar will be n post the results. This might be a very enlightening experiment for basic understanding how a curtain shutters actually work. Oh and be sure you have a horizontal curtain, vertical shutters have a different sync and characteristic bars.

.

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[Helen B]

My calcs assume that the curtain travel time is constant and the distance between the curtains varies. The duration of an electronic flash has very little effect on the width of the fully exposed part of the frame, unless the duration is very long for an electronic flash.

You can estimate the curtain travel time from the sync speed.

1/60 s is 17 ms (to the nearest ms)

That means that the curtain travel time is about 13 ms or thereabouts - slightly less than the sync speed.

Here's typically what happens at 1/60 with flash, first curtain sync.

0 ms - first curtain begins to open, first strip of film begins to get exposed.
13 ms - first curtain fully open, flash triggered
13 to 17 ms - time for flash to fire and discharge
17 ms - first strip of film has had 17 ms exposure so second curtain begins to close
30 ms - second curtain closes fully 13 ms after beginning its travel = 17 ms after first curtain opened fully.

Here's what happens with the same shutter at 1/125 (8 ms)

0 ms - first curtain begins to open, first strip of film begins to get exposed
8 ms - first strip of film has had 8 ms exposure so second curtain begins to close
13 ms - first curtain fully open, flash triggered, second curtain is 5/13 (almost half) way across
13 to 14 ms - flash discharges while first curtain is fully open, second curtain is almost half closed
21 ms - second curtain now fully closed, 13 ms after opening and 8 ms after first curtain opened.

Does that make it easier to understand why the electronic flash duration is of little importance and why the curtain travel time sets the width of the fully exposed portion?

Best,
Helen

 

[Paul Ron]

I just looked at the repair manual of a Spotmatic. You are correct, a 36 millimeter wide film gate is @ 18 milliseconds 1/55th wide open. That is exactly what the constant curtain travel time is set to, 2 meters per second, regardless of shutter speeds.

I now understand what you are saying, we are stopping a half open frame at mid curtain travel within the18ms cycle, regardless of flash duration. I also felt 1/125th should be correct at first but got confused by the flash timing at 1ms thinking the frame is 2ms wide (film exposure to light duration).

Now we need to do a film test. I'm curious to see what we actually capture at different speeds.

Thanks Helen, that was fun.