PHYSICS HELP - cameras, shutter speeds, aperture, etc.?

Question

PLEASE VAGUELY EXPLAIN!

A camera is equipped with:
Speed: 15, 30, 60, 125, 250, 500, 1000
Frequency: 2.8, 4.0, 5.6, 8.0, 11, 16

a) Which aperture setting permits 8x more light to enter camera than f/8?

b) Which permits 4x less light to enter camera than f/5.6?

c) Which shutter speed permits twice as much light to enter camera as 250?

d) Which permits 1/4 as much light to enter camera as 125?

e) The camera is loaded with ASA 1000 film & a perfect exposure is taken at 500 & f/8. State 2 other combos of settings equivalent to this.

f) Which setting combo in part "e)" would give the greatest depth of field?

g) The photographer changes film to ASA 120. State one combo of camera settings that could be used to take a perfect exposure., assuming there is no change in the available light from the situation in part "e)".

Answer 1

Okay, first you have to understand that the amount of exposure depends on both the shutter speed and the aperture. Each 'click' of either control lets in twice the amount or half the amount of light. Both are logarithmic, like decibels.

Given a particular setting of shutter and aperture, you can open the aperture one stop, speed up the shutter one setting, and have the same exposure. In other words one step on either one is the same size.

F isn't frequency, it is the focal length. An aperture of F:4 or F/4 (and there's usually a colon there, or a /) means that the diameter of the aperture is 1/4 of the focal length.

So (a) F/5.6 is twice as much light as F/8. F/4 is four times as much. F/2.8 is 8 times as much.

(b) F/11 is 4x less light than f/5.6 (but it is more correct to say '1 fourth as much' than 'four times less').

(c) 125 is twice as much light as 250. That is, if the shutter is open for 1/125 of a second, that's twice as long as 1/250 of a second.

(d) 500 at f/8 is the same as 1000 at f/5.6, 250 at f/11, 125 at f/16. (for problems like this it's nice to have a camera right there. You set the f-stop and shutter speed, then click each one one click at a time. I do this all the time when taking a picture!)

(e) The greatest depth of field is gotten at the smallest f-stop. This camera can go down to f/16 so 125 at f/16 would give you the best depth of field.

(g) 120 is roughly 3 stops less sensitive than 1000, so you need to slow the shutter or open the aperture three steps, or some combination of both that is three steps. So instead of 125 at f/16, you could use 125 at f/5.6.

In re-reading the question I see you asked me to explain 'vaguely'. I hope that's vague enough. 8^)

Answer 2

If we do your homework, do we get credit?

All your questions could be answered by simply reading any photography text book.