KB Loc: Tennessee

Which of these lenses would yield the fastest shutter speed using the same F Stop, Iso and lighting conditions? A 58mm f 2.0 or a 77mm f 2.8? The 'mm' references the lense diameter not a focal length.
Both lenses are by the same manufacturer.

MT Shooter Loc: Montana

Wide open, obviously the f2.0. However, at say F16, the lens with the 77mm object lens should yield a faster shutter speed as the larger lens is letting in more light. That is, IF you are talking PRIME lenses at equal focal length. Zooms are a whole different story.

KB Loc: Tennessee

The 58mm is fixed, the 77mm is a zoom (24-70). I thought perhaps the 77mm would gather more light because of the larger diameter.

MT Shooter Loc: Montana

It will gather more light, but that light is reduced by the number of lens elements between the object lens and the sensor, many more elements in a zoom than in a prime.

KB Loc: Tennessee

I'm shooting in low light ( son's basketball game ), and trying to determine the best lens I have for the job.

MT Shooter Loc: Montana

I use a 28-70mm F2.6 for basketball, works good at ISO 1600

KB Loc: Tennessee

Thanks for your help MT Shooter.

MT Shooter Loc: Montana

Anytime, here to help when I can.

dirtpusher Loc: tulsa oklahoma

sure dont want a sigma 70 300 apo dg with no is or os have to be real patient. it is a light hog. but it's fun to play with

Flash Falasca Loc: Beverly Hills, Florida

Using the same F stop they would be the same !

WAL

The F stop indicates the amount of light reaching the sensor. I doesn’t make a difference what the focal length is. Just consider an F stop w/o reference to focal length. The formula for F stops balances it out.

With modern coating there is little light loss in lenses based on the number of elements. Keep in mind with most cameras today the exposure is set by the camera which compensates for any light loss from any thing in or on the lens.

The longer the lens is the more difficult it is to hold steady. The usual formula for holding it steady is to use the focal length to equal t the shutter speed. For example a 200 mm lens would require a shutter speed of 1/200. That assume a fixed object is being photographed.

If the lens is stabilized you can probably use a shutter speed of ¼ of what this formula calls for.

From what you describe the 24 70 zoom would be the lens to use. The variable focal length would be a great advantage.

Be sure to set the ISO high, try 1600. Modern digital SLR’s give incredible results with high ISO settings.

You may want to set the camera to a fixed shutter speed if you are shooting sports, etc. There are others that would have a better idea what the shutter speed should be. My uneducated guess would be 800 or more.

With a 24 to 70 lens you have a very capable lens. On APS SLR’s that translates to 36mm to105mm.

steve_stoneblossom Loc: Rhode Island, USA

First, let me say that I understand that the OP is using lens DIAMETERS, and not lens LENGTH, when giving measurements to compare in his post.

That being said, my question is this: Since the f stop is a function of the lens length, and given two lenses of unequal lengths, wouldn't the shorter lens allow more light at the same fstop than the longer and, consequently, allow for faster shutter speeds?

Roger Hicks Loc: Aquitaine

It's called RELATIVE aperture for a good reason: it's RELATIVE to the focal length. Yes, the same f/stop on the longer lens is a bigger hole, but it's further from the sensor or film.

Consider a 50mm lens with an effective 25mm hole: f/2. Now consider a 100mm lens with an effective 25mm hole: f/4. In order to be a 100/2 it would need a 50mm hole. As WAL points out, the number of elements is a minor concern in a modern multi-coated lens.

There's a lot about aperture and focal length in http://www.rogerandfrances.com/subscription/ps%20basics%20lens%20design.html

Cheers,

R.

dirtpusher Loc: tulsa oklahoma

something with big glass

steve_stoneblossom Loc: Rhode Island, USA

Understood. So then at any point does the maximum aperture of any particular lens become restricted by the physical opening in the camera where the lens is mounted, or is the camera opening irrelevant?