Multiple Exposure Question:

[IanBarber]

Can someone confirm I have this correct please.

I have metered a scene to be 2 seconds @ f/32. Forget reciprocity as I am using Acros 100

I want to use 1/8th of a second shutter speed and nothing else.

To get to my final destination of 2 seconds, how many times would I need to open the shutter speed?.

My calculation tells me, 5

Have I got this right or wrong.

[xkaes]

Just double the number of exposures for each decrease in shutter speed:

1 exposure -- 2 seconds
2 exposures -- 1 second each (1+1=2 seconds)
4 exposures -- 1/2 second each (.5+.5+.5+.5=2 seconds)
8 exposures -- 1/4 second each (.25+.25+.25+.25+.25+.25+.25+.25=2 seconds)
16 exposures -- 1/8 second each (.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125=2 seconds)

[John Olsen]

Or f8 for 1/8th second. I'm curious, what's your reason for wanting 1/8th of a second?

[Vaughn]

And any inaccuracy in the shutter speed (plus or minus) will be magnified 16 times, but test negatives will show this and corrections can be easily made.

[tgtaylor]

Easily solved using one of the crown jewels of education - elementary algebra:

Let X be the number of shutter openings needed. Then,

X*(1/8)=2. Given.
Multiplying both sides by 8 gives
X=16.
Proof: 16*(1/8)=16/8=2.

Thomas

[pjd]

5 1/8 exposures adds up to 5/8ths of a second.

8/8ths = 1 second. So you need 16 exposures at 1/8th for 2 seconds in total. Don't think algebra need come into it, just a cup of tea or coffee and a fresh look at it ;)

[Andrew O'Neill]

What Peter said. With a cup of tea for sure.

[IanBarber]

Thanks everyone for putting me straight on this, I was way off but now I know for next time :-)

[Drew Bedo]

Just double the number of exposures for each decrease in shutter speed:

1 exposure -- 2 seconds
2 exposures -- 1 second each (1+1=2 seconds)
4 exposures -- 1/2 second each (.5+.5+.5+.5=2 seconds)
8 exposures -- 1/4 second each (.25+.25+.25+.25+.25+.25+.25+.25=2 seconds)
16 exposures -- 1/8 second each (.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125+.125=2 seconds)


This sort of relationship holds true for multiple "pops" of strobe units for fractional exposures. If reciprocity is not an issue, the exposures are cumulative.

[xkaes]

This sort of relationship holds true for multiple "pops" of strobe units for fractional exposures. If reciprocity is not an issue, the exposures are cumulative.

With film, when using any meter, with very long exposures, the calculated or recommended exposure(s) might not result in the expected result, and some amount of adjustment or compensation must be made. Similarly, with very short exposures, the calculated or recommended exposure(s) might not result in the expected result, and some amount of adjustment or compensation must be made.

Unfortunately. But, at least with film, I can make them -- corrected or not.