Flicker in daylight

[Kristian Schumacher]

Hi everyone,

 

I have been shooting a little 16mm now with two cameras, a K-3 and a Milliken high speed camera. I am seeing some flicker on some shots that were done in sunlight. It seems to be only on the footage from the K-3, and seems to be more apparent in highlight areas. It also seems more prominent at max speed, abour 48 fps. I just uploaded this short clip from my first test roll where the fluctuations in the backlit highlights is quite visible

 

http://www.vimeo.com/6916558

 

Could anyone help me work out the cause of this?

 

Any help appreciated :-)

 

Kristian

[John Sprung]

It looks to be mostly in the lens flare from the sun. As the camera is hand held and moves, the number of tree leaves between the sun and the lens changes, which would account for substantial changes in the flare. Then, too, you have the birds passing between the camera and the sun, making big changes.

 

My guess is that the camera is OK, and if the leaves weren't there, there wouldn't have been any flicker. Try it without the leaves, and if it still flickers, then I'm wrong. But the shot itself doesn't look bad, that looks natural for what you're shooting.

 

 

 

 

-- J.S.

[Adrian Sierkowski]

totally agree with John.

[Kristian Schumacher]

Thanks to both of you!

 

I guess it could look like that - but it is quite constant. And if I go through the footage frame by frame, it is clear that the exposure fluctuates up and down exactly every frame.. i.e. one bright, one less bright and so on. It is also visible in footage where nothing is between the sunlight and the camera. I guess the pigeons flying in front of the sunlight makes it a little harder to tell apart. But have a look at the last second or so, and it should be quite clear. It is not very strong, but seems to be quite consistent throughout my 48 fps-. footage with that camera.

 

Thanks again,

 

Kristian

[John Sprung]

Unfortunately, I'm not familiar with the K-3. Does it have a two blade shutter, or a shaft somewhere that's geared to one revolution for every two frames? A small amount of dried grease or dirt on a gear might cause a once-around slowdown on a shaft like that. The extra resistance would show up more at high speeds. Can you inch the camera and feel carefully for any resistance, while watching the pulldown to see if there's something like that causing a slight slowing every other frame? Perhaps PM Olex to have a look at this thread, as he's the Russian camera expert.

 

 

 

 

-- J.S.

[Dominic Case]

I guess it could look like that - but it is quite constant.

Well it's not really constant in my view. Nor is it mainly in the highlights as you suggest. I agree with John that it seems to be in the considerable amount of flare, which is fluctuating as leaves or pigeons move across the sun. (Note that there are a couple of other hot spots from car windscreens etc reflecting the sun, that would also be contributing very slightly to the flare: so it would flicker even when one of those is obscured by a pigeon.)

 

However, there does seem to be a little bit of flicker right at the beginning, before the pigeons have really got going, and also right at the end, although that does seem to synchonise with the single pigeon still flying on the rhs of the frame. Maybe you have pigeon-induced flicker in the flare, and also a mechanical problem with the shutter. I'm not familiar with the K-3 so can't comment on that - except to ask if the shutter blades are adjustable and if so are they loose?

 

it is clear that the exposure fluctuates up and down exactly every frame

That is a much faster frequency than I'm seeing. This adds weight to the "two problem" theory.

 

If you have any more footage at the start or end of this clip, where there is less (or no) movement on the screen, it might be clearer whether you have one problem or two.

[Kristian Schumacher]

Thanks to all of you,

 

I really appreciate your input. Here is another clip, again at 48 fps, without the flare:

 

http://vimeo.com/6943544

 

The camera has a two-bladed, non- adjustable shutter, so John´s explanation could make sense with grease or some other obstruction causing speed variations. I suppose that could be difficult to locate, tough...?

[Kristian Schumacher]

OOOpps.. Because of the compression on Vimeo, it doesn´t show at all.. Here it is again:

 

http://www.kameraundervann.no/Flicker2.mov

 

 

Kristian

[John Sprung]

Yes, it's clearly there in the foliage on the lower left. It's every other frame. So , loose shutter or crud on a gear. If you don't feel competent to take it apart, you'd need someone local to do it, or you could send it to Olex in the Ukraine for a complete servicing.

 

 

 

 

-- J.S.

[Kristian Schumacher]

Thanks again, John.

 

I will have a go at taking it apart (actually, I will have a go at my second, r16 K-3 first to practice:-) and try to lube/clean up any gunk that may cause the variation. Does anyone have an idea of how to check the evenness in exposures without spending the money on a test roll, dev and tc?? Just to see if the problem is solved or not?

 

 

Thanks,

 

Kristian

[John Sprung]

My first thought would be to try a strobe light. An ordinary old time party strobe might be good enough, provided that you can adjust its rate.

 

First, borrow a known good camera without a mag and without lenses. Set up so you can see the shutter and/or pulldown in the strobe. If you can adjust it to freeze the mechanism of a good camera, then before you try any cleaning or repairs, see what it reveals about the bad one. If you see it freeze in two different positions, that'll be the test you need. In fact, it might be able to show you the claw freezing in one place while the shutter blade wanders. In that case, it's a loose shutter. If the whole thing seems to have two positions, it's more likely to be crud in the works.

 

The only other low cost test is to isolate parts of the gear train that you can turn by hand, feeling carefully for resistance or looseness.

 

Another thought -- A video camera with a very short exposure time might be a substitute for the strobe. In both cases, you're trying to grab very brief pieces of time once per frame of the film camera. It depends on what you can get.

 

 

 

 

 

-- J.S.

[Kristian Schumacher]

Thanks a bunch, John.

 

 

I will give this a go. Maybe I can set it up with my canon 5d at 30 fps and a high shutter speed. I will try that first, as it is what I have at hand.

 

 

Kristian

[John Sprung]

That should work provided that you can run the K-3 at an accurate 30 fps.

 

 

 

-- J.S.