Aperture and shutter speeds?

Question

I'm confused about a question in physics, it's about cameras so if anyone is familiar with this unit or about cameras I would appreciate it if you could look this over.

A camera is equipped with the following settings:
SHUTTER SPEED 15 30 60 125 250 500 1000
f/ 2.8 4.0 5.6 8.0 11 16

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

I know that when the aperture decreases in number, the amount of light that can enter are multiples of 2 so from 8.0 to 5.6 would be 2x more. But the question is asking 8x more, and the last number is 2.8 which is only 6x more than 8.0. There should be one more number on the left? Is there something I am missing, or is this just a trick question?

Also...
f) The camera is loaded with ASA 1000 film and a perfect exposure is taken at 500 and f/8. Which camera setting would give the greatest depth of field?

From what I understood, depth of field is greater if there is less to focus on, or if there is a smaller space to focus through. I don't know if that's right, so I'm not sure how to answer this question?
I put 2.8 as aperture and I'm really not sure for shutter speed?

Thanks so much for reading this & for your help!!

Answer 1

a) the f numbers are called f-stops. each increment (increasing number) lets in 1/2 the amount of light as the next lower number. So if you want tl let in 8X more light than at f8 you must lower your setting to 2.8 (3 'stops' = 2*2*2=8)



f)In a camera, the largest number f stop will have the greatest depth of field. You would go for f16 and compensate by decreasing shutter speed. going from f8 to f16 is two stops (2*2=4 times less light) so you must decrease your shutter speed to 1/4 your starting point. 1/4*500=125



Notice that decreasing shutter speed and decreasing f number increase the amount of light getting in the camera. The shutter speed settings shown on cameras are the inverse of the actual shutter speed. ie 500 on the camera = shutter speed of 1/500 sec.

Answer 2

Shutter speed means for how many fractions of a second will the shutter opens (and permits the light in).

Apertures are measured in f/ stops. In the above, f/2.8 means max aperture and f/16 means minimum aperture. As you also say that the light increases in multiple of 2, therefore at 5.6 it will double,(2X), at 4.0 it will be 4X and at 2.8 it will be 8X.

Highest f/stop will give the best depth. So in this case it will be f/16. but you will have to decrease the shutter speed to 125 to permit the same light.

However, be careful that the objects are stationary and camera is on a tripod otherwise slow speed blurs the picture. So you have to make a choice between the depth and speed.

Answer 3

I think UR mistaken about "depth of field" or what I call "depth of focus".

The smaller the aperture the greater the depth of focus, AND the smallest

aperture with the settings listed is at f 16 not f 2.8 which is the largest lens opening.



U actually said it right (smallest space to focus thru) but indicated the wrong end of scale.



{as to the first part WHY can't a shutter speed adjustment be used in conjunction WITH a lens opening adjustment to get 8 X more light? ie 4 X by lens & 4 X by shutter speed}