I am currently putting together a table so i can easily convert exposures taken on a digital camera to exposures taken completely manually on a pinhole film camera (in preparation for actually buying one) with an aperture of f/192.

It's all about the maths - if you take a photo at f/5.6 and the exposure is say 0.5" to get it properly exposed, then for the equivalent film/ISO speed at f/192 you just multiply the shutter speed by 1024 - so 512 seconds...

So in the whole 1 f-stop shift = double or half (depending on which way you go) of the value you started at for shutter speed, i decided to extrapolate from the standard 1second exposure.  I then decided to write down what my camera told me (as 1/15th exposure is displayed differently that 15 seconds) so i could quickly convert what exposure i would need on the film camera using a printed table.

Anyway - the lie came when i realised that my camera told me it takes a 30" exposure when my maths told me it should be 32"... so out came the stopwatch and i took a "30 second" exposure.  Guess what - it was 32 seconds long... damned liar!

ROFLMAO!!! How rude :-)

he he thanks for sharing my friend.

:::sigh:::

if you can't trust your own camera.....  

:unsure:

CPUs in cameras must use algorithims to determine these things and display them in fractions that are meaningful to people, hence the 32 seconds shifted to 30 seconds. When you get into time exposures though, a 2 second difference in a 30 second exposure is of little consequence.

Still, these stupid fractions coming from digital cameras these days are unfamiliar to everyone, for example, 1/640 s, as my camera displays. What is that? Why not go into normal engineering notation and present it as 1.56 ms (milliseconds) and start people down the path of learning about units? But then they would probably round it to 1.5 ms and we'd be right back where we began, almost.

Wayne

Attached Link: http://www.mrpinhole.com/exposure.php

Then you will need to make a new chart for each film you use, that factor in that individual film’s reciprocity failure.

If you are going to use B&W film, use Ifords HP5 as it needs very little adjustment for reciprocity failure, whereas TriX needs a lot (a 15min exposure turns into 1 hour).

I use to do a lot of pinhole photography with a bunch of homebuilt cameras (120, 4x5 and 8x10).

Here is the only one I kept after going digital ….my Pin-o-Flex (hey don’t laugh, it has a viewfinder).

Chuck

Swamp, nice camera.   Got any shots to share?    Rich, you seem to make it all over the world somehow..enjoy the extra 2 seconds. : )

Your camera can't be trusted. My advise is to kill it with fire!

Actually, the odd numbers for exposures and f-stops are simply coming from mathematics.  I had time to kill last week and ran out of reading material and decided to leaf through my flashmeter userguide.  In there, they had a table for equivalent EV values. Now, since I always used my flashmeter in aperture priority, I never bothered figuring out wath the EV mode did, but simply put, the flashmeter can read the light intensity and return an integer EV value. Where EV = AV + TV.  Both AV and TV are integer values.

The relation between AV and your f-stop number is:  f-stop = 2 ^ ( AV / 2 )... So:
     for AV = 0, you get an f-stop of 1,
     for AV = 1, you get an f-stop of 1.414 (square root of 2), shortened by 1.4 on cameras
     for AV = 2, you get an f-stop of 2,
     for AV = 3, you get an f-stop of 2.828 (2.8 on cameras)
and so on and so forth.... recognize the numbers ? 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, etc.

The relation between TV and your exposure time is: exposure time = (1 / 2) ^ TV
     for TV = 0, you get an exposure time of 1 second,
     for TV = 1, you get an exposure time of 1/2 second,
     for TV = 2, you get an exposure time of 1/4 second,
     for TV = 3, you get an exposure time of 1/8 second,
and so on and so forth.... so you get 32, 16, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, etc.

As whaleman suggested earlier, why camera makers write 30 seconds instead of 32 is probably due to the fact that humans prefer nice round numbers. The same applies to the factions, it is easier to remember 1/8 and 1/16 to 0.125 and 0.063.

But the rule of thumb is that from one stop to the next, you always double the amount of light so the exposure time scale has to work the same increments.

But in the examples above, where did the 3.2 and 3.5 f-stop go ?  They are respectively 1/3 and 2/3 stop increments between f/2 and f/4.

I know, I'm a geek.

Biquet, you have explained it very well and geeks are great! Without geeks and nerds which, to most people are pejorative terms, we would not have DSLRs, cell phones, microwave ovens and television sets, to name a few. Oh, we probably would not have the internet either, nor this conversation!

Wayne (from nerdville)