ASA and FPS question

[thebrowniecameraguy]

Ok, I can approximate exposure pretty well using KM25 and KMA 40, also I can make decent exposures with E125T outside and inside.

But, I am totally off on this: When I use a light meter that has ASA and Shutter speed selection I am totally lost.

Example: E125T shot in a Brownie 8mm camera at 16 fps, I dont know the shutter speed. I dont know how to change that from fps to shutter time.

I am asking 'What is the time on 16 fps, 18, 24 etc. And how can I learn to figure it out?

Thanks,
Jordan

[FourFourForty]

Try this formula:

1 / ((fps x 360) / shutter angle)

Using 24fps and a shutter angle of 180 degrees it works out as follows

1 / ((24 x 360) / 180) = 1/48sec shutter speed.

[drsanchez]

I have to think this through every time I do it but, thankfully, it only depends on 5th grade math. It all depends not only on the frame rate, but the angle of the shutter opening. 180-degree shutter is the easiest. If you shoot at 16 frames per second, each frame takes 1/16 of a second. But, for each frame, the shutter spends some time open and some time closed (to allow for the film to advance in the dark). For a 180-degree shutter, the shutter is open exactly 1/2 of the time. So, even though it took 1/16 of a second for one frame, the shutter is only open for 1/32 of a second. Setting your exposure to 1/30 will be fine. If you have an exposure meter with a frames per second setting, you might get the exact 1/32 second.

Things get a little trickier with a 220-degree shutter. I'll leave the math to you, but the exposure time is (I think) 1/26 of a second (which is a longer time than 1/32 second).

Hope it helps. Once you figure out the math, it might help to print the exposure time for every frame rate and shutter opening and tape it to your light meter.

[reedsturtevant]

Example: E125T shot in a Brownie 8mm camera at 16 fps, I dont know the shutter speed. I dont know how to change that from fps to shutter time.

I am asking 'What is the time on 16 fps, 18, 24 etc. And how can I learn to figure it out?

Do you know the angle of opening in your shutter disc? If your shutter had a 180 degree opening, for example, the "shutter speed" would be 1/32nd of a second, I believe. Imagine it spins 16 times a second and the shutter disc is open for 180 of each 360 degrees, 1/16 multiply by 180/360 = 1/32.

That's why the Canon XL cameras had 220 degree shutters, to let more light in during each rotation.

P.S. when using an external meter with a reflex camera you also have to account for light lost to the viewfinder but that shouldn't be an issue with your Brownie

[thebrowniecameraguy]

In the camera I use the most the shutter is 180'.

j

[cinecymru]

I have a Brownie Model 2 with 13mm f 1.9 lens.

I've not used it yet but will put some filmstock through it this year. I can get some R8 stock called 'Cinechrome' from Photoword here in Llandudno, Wales.

As a user of this camera - what's the picture steadiness like as I see there's no sprocket feed

[thebrowniecameraguy]

No, there is no sprocket feed because the slack film is only 2> inches from the gate.

The registration is fine, better than fine. Great!

The camera is just so simple, its hard to get bad results. Most of the Brownie cameras have sky guides on the front panel that tell you how to set the lens. But its really easy.

PM me for more detailed information, I'll send you a copy of a manual if you dont already have one.


Cheers,
Jordan

[cinecymru]

Mine also has the sundial exposure indicator which I suppose was calibrated for the old 25 asa stock.


Thanks for your re-assurance on picture steadiness.

I'll keep you posted on my results after the first roll is back from processing.

Regards,
Harley