Shutter speeds compared with Lens Aperture?

This maybe be a dumb question but here it goes. Lets say I have two set ups:

Set Up 1
Camera - 50D
Lens - 85mm f/1.8

Set Up 2
Camera - 50D
Lens - 85mm f/1.2

Now take both setups and take a picture of a static object with all the same environment settings and camera settings. If both were taken @ f/1.8 would I have a faster shutter speed with the faster lens? I would guess it would have twice the shutter speed? Anybody could shed some light I would appreciate it...Jeff

No. Aperture is aperture. If both lenses are set to 1.8 , the shutter speed will be the same.

If you had the same lighting conditions and both cameras were shot at f/1.8, then you would have the same shutterspeed. The f/1.2 lens would be able to get a higher ss if you opened up the aperture to f/1.2 but the f/1.8 lens cannot as it is maxed out.

nope, they should have the same shutter speed.
If you saw different results, that's probably because the lighting changed (more/less light entering lens)

Aperture size is not relative to the size of the lens. So a lens size of 82mm with an aperture of f/1.8 should have the same exact aperture size of a 58mm f/1.8

Just because the faster lens has the ability to shoot faster doesn't mean it will shoot faster under the same settings and conditions or another lens. I guess there's marginal difference in the quality of the glass and how clear it is to let light in, but it shouldn't affect the shutter speed.

It's like saying you have a Prius and a Ferrari and saying if they both go down the street at 45 mph, which one would be faster. The Ferrari has the ability to smoke the Prius, but if they are going at the same speed, they will be arrive at their destination at the same time.

What msowsun said is theoretically correct. In real life you may find a 1/3rd stop difference in shutter speed in certain conditions. I'm not sure why that happens but I think it has to do with lens construction.

right, if you were trying to attain the exact same exposure with both setups, you'd wind up with a faster shutter speed on the f/1.2 setup (faster shutter speed decreases the amount of time the camera is taking in light, but this is offset by the larger aperture allowing more light in).

dipps wrote in post #7861741
right, if you were trying to attain the exact same exposure with both setups, you'd wind up with a faster shutter speed on the f/1.2 setup (faster shutter speed decreases the amount of time the camera is taking in light, but this is offset by the larger aperture allowing more light in).

I do believe you failed to read that the OP was asking about using both lenses set to f/1.8.

SkipD wrote in post #7861786
I do believe you failed to read that the OP was asking about using both lenses set to f/1.8.

oops, sorry, yes i missed that. apologies.

Well said!

Thanks for the explanations everybody, it help cleared the confusion....Jeff

I think you might have worded this wrong. Aperture size in terms of how much light gets to the film plane (I guess sensor now) is the same. f1.8 at 50mm and f1.8 at 35mm are going to have the same exposure and let in the same amount of light (all other things being equal).

However the physical size of the aperture opening can and on prime lens most likely are different sizes.

Originally the f-stop was a ratio of lenght of the lens to opening of the aperture. So at that time a 50mm f1.0 would have a 50mm aperture opening and a 200 mm f2.8 would have a 71 mm aperture opening. Modern lens design can change this, but it isn't fixed so that f1.8 always equals an aperture opening of x number of mm.

Sorry, my confusion. On re-reading this I believe you are talking about filter size. In that case you are correct. different filter sizes on the same focal lenght lenses will not have different aperture sizes (or if they do because of design differences they let in the same amount of light.