Tomcat:
I have read this entire thread. From your opening post, I think you are confused as to what 50mm, 300mm, 500mm actually represents. You seem to be under the impression that these numbers represent the diameter of the front lens element. They do not.

These mm numbers represent the focal LENGTH of the lens. Or how much magnification of the view before you. A 50mm lens will generally show you what the eye sees. A 10mm lens is often used for recording broad landscapes, the interior of buildings, or large groups of people. A 300mm or 500mm lens is used to bring far away things close, like using binoculars. A 10-18mm zoom will be quite short. A 300-500mm zoom will be quite long (and heavy). A 35mm or 50mm prime will be very short and light weight. A 10mm lens will let you take photos of the entire basketball court and half the crowd. A 500mm lens will only let you get head shots close to you, and maybe waist shots from the other end of the court, if you can get things in focus that quick.

Your numbers indicate to me that you are shooting Canon equipment. I shoot Canon and recognize the numbers.

Now. If you compare a 24-70mm f4 lens to a 24-70 f2.8 lens, you will find that the diameter of the front of the f2.8 lens is larger than than the f4 lens. This is necessary to get more light into the camera. You will also find that the f2.8 lens is heaver, and will cost more (quite a bit more). You will also find a diameter symbol (a circle with a diagonal line through it) followed by 88mm for the f2.8 lens or 77mm for the f4 lens. These numbers indicate the diameter of the thread for screw on filters and lens hoods.

I might suggest a series of books written by Al Judge and available through Amazon either as paper books, or downloadable E-books. He explains the very basics of photography, especially digital, it's terminology, and post processing. I've been taking photos since the mid 60's and took classes in college. I bought his whole series and learned new things and better understand things I thought I had a handle on. I highly suggest his books. They are inexpensive, direct and to the point.

I hope I interpreted your opening post correctly, and I hope this helps. If I mis- interpreted, let me know.

Tomcat:
You seem to have answered your basic question yourself. You stated that the photos from the 50mm f/1.4 are a lot brighter. This allows you to either shoot at a lower ISO (less noise) or at a faster shutter speed (less blur and sharper images).

Again you are right, that 300mm f/4 lens is much better suited to outdoor work where you have the brightness of the sun, than indoor work. That 300mm lens is also going to be a pain to focus, and will induce a lot of shake at the rate things happen on a basketball court or even a gymnastics court.

If you shoot mostly indoors, I would suggest you stay with as fast a lens that you can afford. The f/1.4 lenses are generally quite expensive. The f/2.8 lenses can usually cost quite a bit less.

I would also suggest that you take your 70-200mm zooom lens to a practice to concentrate on what focal length would best suit what you prefer. Shoot a bunch at 70mm. Then shoot a bunch at 200mm. Then at 100mm and finally a bunch at 150mm. While reviewing your photos, disregard if they are too dark, just concentrate on the field of view you got close up and far away. Once you have decided on a focal length now it's time to decide on a zoom or prime lens. A fast zoom (f/4) is probably going to cost more than a faster (f/2.8 or 1.4) prime. And now it's time to decide which is more important, the ability to zoom, or the extra light of the faster lens. If the places you shoot are not well lit, I'm betting you will opt for the faster prime lens as this seems to be your target.

Sorry this took two posts. This approaching weather front has me all me all achey and running in grandma gear.

Huh? This makes little sense!

Distance has very little do with exposure! It is the brightness of the subject and how you're trying to render an image of the subject that determine what exposure factors you need to use. And, unless you are shooting in near darkness, with way too small aperture and way too fast shutter speed, there's no reason you should be "forced" to use such a high ISO.

When you say the "lens is noisy", I assume you mean you are finding yourself using very high ISOs and you are seeing digital "noise" in images.

BUT... there is no reason why focusing on something "more than 50' away" should force you to use high ISOs.

The three exposure factors are: ISO, shutter speed and lens aperture.

ISO is the sensitivity to light of the medium (in this case a digital image sensor).

Shutter speed is the amount of time that light is allowed to reach the medium.

Aperture is the size of opening that's allowing the light to pass through.

It's a combination of these three factors you need to use to make a "correct" exposure. The choices are determined by the brightness of the subject being photographed.... regardless of distance, for the large part.... and how you're trying to photograph it.

Think of it as a bucket full of water with a drain in the bottom. You can change the size of the drain and control how long it remains open. You can use a small opening that's held open for a long time OR a large opening for a short time.... and drain the same amount of water from the bucket either way.

With photography, you generally want to use shutter speed and aperture that allow you to use as low an ISO as possible, in order to minimize "noise" in images (this was true with film, too, BTW.... higher ISO films got "grainy").

But you need a shutter speed that's fast enough to be held steady to prevent "camera shake blur", unless you're using a tripod or other type of support. Aside from that, with stationary subjects most any shutter speed can work. But with moving subjects you either need a fast enough shutter speed to freeze the movement or a slow enough one to allow deliberate subject movement blur effects in your images.

And you need to choose an aperture that renders the depth of field you want to see in your images. A larger aperture renders shallower DoF effects, while a smaller one increases DoF. Maybe you want a shallow DoF in order to make a background blur down so that the subject stands out against it. Or, maybe you want things to be sharp from your toes to the horizon. Achieving different DoF effects varies depending upon lens focal length and distances. A wide angle lens (short focal length) gives greater apparent DoF than a telephoto (long focal length).

A very close subject at macro magnifications can make for very shallow DoF, too. A very distant background behind a subject may be more easily blurred down, too.

Over time and with practice you will learn how different focal lengths perform and how to control DoF and subject movement effects. There's a limit to how much you can do, of course. But there are "work arounds". For example, I wanted to make a macro shot of a flower with some other flowers recognizable in the background. If I used a typical macro lens to photograph the flower, the ones in the background became too strongly blurred and unrecognizable. So instead I used a 20mm wide angle lens with a short macro extension tube to make it able to focus closer, which I knew from experience that the shorter focal length in addition to a smaller lens aperture would reduce the strength of the background blur so that the more distance flowers wouldn't be blurred down to unrecognizable blobs of color. I had to use a slower shutter speed to achieve this at a fairly low ISO. Here's the the result:



Other times I wanted to do the exact opposite. For the following, 15 or 20 feet behind the flower was a fence that I didn't want to see in the image, so I used a 500mm lens and a fairly large aperture (for that lens), on a tripod for stability at a reasonable shutter speed. As you can see, doing this completely obliterated the background to help the subject stand out:



You can do similar things with shutter speeds and moving subjects. Of course you need to use a shutter speed fast enough for you to hand-hold without camera shake blur problems, unless you're using a tripod or similar to support it. If you want to freeze a subject's movement in the image, use a faster shutter speed, as I did for the following shot:



Or perhaps you'd like to let some of the subject's movement blur.... or pan with the subject to cause the background to show motion blur.... or a bit of both... and need to use a slower shutter speed:



It sounds to me as if you are really struggling to grasp how the three exposure factors work and you can use them in various ways to achieve a "correct" exposure. It's a lot to try to cover properly in forum posts... you're likely to get only fragments of info and coming from people with wildly different levels of experience, responses that try to help but may be right or wrong, or are described in a way that's easy to understand or not.

There have been whole books written on the subject. It sounds as if you have some fairly serious investment in camera gear, so I'd recommend you spend another $18 over at Amazon and order a copy of Bryan Peterson's "Understanding Exposure". Many people find that book very helpful. It will certainly be better than the snippets of knowledge you'll get from a discussion forum or Youtube videos. Alternatively, enroll in a local photography class.

Hope this helps!

Yep, it really is. I got it for two reasons: it is an Art lens pedigree and Nikon did not have one (theirs is a 105 mm micro). I also have the Sigma Art 50 mm f/1.4 lens and believe it or not, I have often used it as a "telephoto". Because it is soooo sharp, I can zoom way in on the image, crop it, and still have a sharp result.

By the way, if you ever have a focusing issue with it, send it back to Sigma for an AF adjustment. I have done that with both of the Art lenses and it makes a tremendous difference. I don't mess with that camera fine-tuning because it's marginal at best and is distance and camera specific and a waste of my time. I'd rather let Sigma do the adjusting--they are better than me.

What you say is true at a given distance that does not change. I might not have been too clear on the subject distances. When the gymnasts are close to me at 25 ft away, the f/2.8 lens (70-200 mm) is fine and gives good exposures. But when they are 75 feet away, there is a loss of light that gets transmitted to the lens and the exposures at f/2.8 are a lot noisier and run a higher ISO value. I don't know if it's because the light levels are less in the back walls or it's an actual loss of light (inverse squares) from them moving further away from the good light, but there is definitely a drop in the exposures for the shots farther away. It's a reverse principle where the light source stays constant (maybe), but the subject is moving instead of the other way around like in a studio where you move your lights in and out and the subject is stationary.