math question: test shooting SLR for Super 8

[grainy]

I hear you -- I'm not really trying to create still versions of super 8 images, I just want to be able to eyeball the light situation.
thanks again for your help!
G

[carllooper]

Also, your camera most definitely is a XL camera meaning it has a 220 degree shutter and therefore has a shutter speed of only 1/30 of a second. Only very old super 8 cameras with slow lenses (f1.8 or worse) are going to have a 1/40th or so shutter speed.

Hi super8man - yes, it's a sankyo XL 420 sound.
So with a 1/30 shutter speed for the super 8, that puts me at an even slower speed on the SLR. Currently I'm at "1/11", which on my camera I rounded down to 1/8. But knowing this am I really looking at more like a 1/4?

G

Just for completion - reruning computations for 1/30th sec on S8

log(1/30) / log(2) = -4.90689

We now add that 1.7 stops (the difference in lenses)

-4.90689 + 1.7 = -3.20689

And convert back to exposure interval:

2^-3.20689 = 0.1083 secs ~= 1/9 secs

Answer is: 1/9 secs

Or nearest SLR setting.

But if the real reason for the question is to use the SLR as a light meter, then no film required. And the difference in lenses is irrelevant because the light meter will be telling you what to set the aperture at anyway. Set the SLR shutter to 1/30th sec. Set the ISO on the SLR to 200. Fine adjustment is just the difference between 200 and 160 which is:

log(200)/log(2) - log(160)/log(2) = 0.322 stops

So whatever your SLR says for an aperture, open the S8 aperture by the SLR aperture plus 1/3 stop.

If you set the SLR ASA/ISO to 400, then open the S8 aperture by a further 1 + 1/3 stop.

For 800, open S8 aperture by a further 2 + 1/3 stops.

[S8 Booster]

Set the SLR to the appropriate film & shutter speed to match the "8", point both at a "grey scale" like background and the true deviation between the 2 will be apparent and the deviation will be constant all over the range of technically possible exposure.

youll be surprised........


shoot....

[grainy]

Answer is: 1/9 secs
Or nearest SLR setting.

But if the real reason for the question is to use the SLR as a light meter, then no film required...
So whatever your SLR says for an aperture, open the S8 aperture by the SLR aperture plus 1/3 stop. If you set the SLR ASA/ISO to 400, then open the S8 aperture by a further 1 + 1/3 stop. For 800, open S8 aperture by a further 2 + 1/3 stops.

Thanks Carl! I'm gonna use film to print because that's the way I think, so it looks like 1/8 actually is my setting after all.

[grainy]

Set the SLR to the appropriate film & shutter speed to match the "8", point both at a "grey scale" like background and the true deviation between the 2 will be apparent and the deviation will be constant all over the range of technically possible exposure.

youll be surprised........


shoot....

Thanks S8Booster -- I'll be curious to see how close this ends up being to the 1/8 determined via math. I suck at numbers so my main hope here is to find a setting and leave it, we'll see how it pans out. Now all I gotta do is steal some time and get out at night to shoot! ;)
G

[carllooper]

Set the SLR to the appropriate film & shutter speed to match the "8", point both at a "grey scale" like background and the true deviation between the 2 will be apparent and the deviation will be constant all over the range of technically possible exposure.

youll be surprised........

shoot....

The "the true deviation" between the two systems is not really given by the above measurements.

For example, if you discover a mismatch between the math and the measurements then one must be false: the math or the measurement?

The math can be checked for correctness, but how do you check the measurements for correctness? Without the math (which is correctable) you can't.

What can make the measurement false? Well simply the light meters. One or both of the light meters can be incorrect - which the correct math will tell you*

Note that if both meters are indeed correct then using the SLR as a light meter becomes redundant - because one can just use the S8 light meter.

Carl

* although there is a remote possibility that both light meters happen to be incorrect by the same amount - which is all the more reason to factor out the light meters altogether (ignore measurements) and just use the math.

[retoxproductions]

Wow!! I was about to do the same thing with both my Bauer S 715 XL Microcomputer-ngenieux Macro 1,4 / 6 - 90 mm-Shutter degree: 200 at 18 frames and my Elmo 1012 S-XL shutter 220 1,2 / 7,5 - 75 mm. If I'm shooting Tri-x and 200 ASA 200 TUNGSTEN. what should I set my canon 60d to with a manual 50mm 1.4 lens

[carllooper]

Wow!! I was about to do the same thing with both my Bauer S 715 XL Microcomputer-ngenieux Macro 1,4 / 6 - 90 mm-Shutter degree: 200 at 18 frames and my Elmo 1012 S-XL shutter 220 1,2 / 7,5 - 75 mm. If I'm shooting Tri-x and 200 ASA 200 TUNGSTEN. what should I set my canon 60d to with a manual 50mm 1.4 lens

Rather than me carrying out the computation here are the formulas I was using. Dig out your calculator and feel the power of using that Log button.

To calculate the difference between two aperture settings, in terms of stops (eg. when using different apertures) then use the following formula:

Code: Select all

DIFFERENCE = log(FSTOP1^2)/log(2) - log(FSTOP2^2)/log(2)

where FSTOP^2 means the squared FSTOP, ie. FSTOP x FSTOP

Example, the difference in stops between f4 and f8 should be 2 stops:

DIFFERENCE
= log(8^2)/log(2) - log(4^2)/log(2)
= log(8*8)/log(2) - log(4*4)/log(2)
= 6 - 4
= 2

To calculate the difference between ASA, in terms of stops, use the following formula (no squaring). This same formula can also be used for Shutter Time.

Code: Select all

DIFFERENCE = log(VALUE1)/log(2) - log(VALUE2)/log(2)

Example.

What's the difference, in stops, between 100ASA and 200ASA?
Here's the button sequence when using the calculator application on Windows. Put on your Scientific hat.

Select: View > Scientific
Press the following buttons:

200
log
/
2
log
-
100
log
/
2
log
=


Now it's my turn. What's the difference, in stops, (all else being equal) between the following shutter times:

5.7 secs
1/200 secs

Carl