Please explain why I need the lens to be faster...

I've got the Nikon D50, Nikon 18-55, and a Tamron 70-300mm macro, AND I'm on the hunt for another lens that will allow me to get closer to birds, as well as any other subject. But, I'm not sure why I'd need it to be "faster", as some seem to say about one lens or another. For instance, I read in a thread where the poster said that the Sigma 50-500mm lens was much faster than the 170-500mm Sigma lens. I'm a complete rookie, so don't laugh. Is it just that the lens Auto Focuses faster, or what? I'm buying a lens to get me closer, that I know, but what will the lens do IF it is one of these "faster" lenses ALSO.

My kids are active, so might use this lens to shoot some sporting action type photos as well, if that helps!

Thanks again for the schooling...

Kevin

Faster can mean a couple of things. AF speed is one of them. The other deals with the maximum aperture of the lens. For example, the larger the maximum aperture (smaller f/ number) the faster the lens is. What this means is that the diaphram inside the lens will open up further, and let in more light. The more light you let in, the faster shutter speed you can use. The wider opening also helps the AF. A wider aperture is also very nice for low light situations.

Most zoom lens are veriable aperture lenses. For example, the Sigma 170-500mm lens is and f/5-6.3 lens. What that means is that at the shortest focal lenght (170mm), the max aperture you can use is f/5. At the longest focal length(500mm) your max aperture is now f/6.3. So your your lens is letting in less light, at the long end. This means that you will have to use a slower shutter speed, to get the same exposure that you would if you shot wide open at 170mm.

The 50-500mm Sigma is an f/4-6.3 lens. So at the long end, your max aperture is the same as the 170-500mm lens so I'm assuming that when the other poster said that the 50-500mm lens is much faster, they were refering to AF speed.

Another benifit of a larger aperture, is more control over depth of field.

I hope I didn't make things more confusing for you... I'll see if I can find another tread that talks about this.

Check out this thread for a much simpler explanation.

http://forums.photographyreview.com/...ead.php?t=3071

Thanks Mike. It helps.

Still don't know what lens I'm getting, but I understand more now. And, that is atleast getting me somewhere.

Kevin

Hi, Kevin. Perhaps you are rushing a bit? Your system is what, not even 48 hours old and your already upgrading? If I may suggest, use what you got and really take time to learn what it is that you do and do not like about it. What you think you want now may be completely different from what you will need later.

Example - return/replace the 70-300 with:

2 zooms, a 70-200 and a 170-500
1 zoom like a 100-400
1 zoom and 1 prime like a 70-200 and a 400 prime
1 zoom and 1 teleconverter like a 70-200 and 2xTC (I use this combo)
3 primes like a 100mm, 200mm, and 400mm

A lot of possibilities and you could end up wasting a lot of money and having a bunch of lenses that you don't really like if you rush into it. Now would be great time to work on good techniques and thoroughly learn that new DSLR or yours.

Just my opinion.

Quote:

---

Originally Posted by Kevin2

I've got the Nikon D50, Nikon 18-55, and a Tamron 70-300mm macro, AND I'm on the hunt for another lens that will allow me to get closer to birds, as well as any other subject. But, I'm not sure why I'd need it to be "faster", as some seem to say about one lens or another. For instance, I read in a thread where the poster said that the Sigma 50-500mm lens was much faster than the 170-500mm Sigma lens. I'm a complete rookie, so don't laugh. Is it just that the lens Auto Focuses faster, or what? I'm buying a lens to get me closer, that I know, but what will the lens do IF it is one of these "faster" lenses ALSO.

My kids are active, so might use this lens to shoot some sporting action type photos as well, if that helps!

Thanks again for the schooling...

Kevin

---

One thing that nobody has mentioned - the autofocus on Nikon DSLR's including the D50 is only supposed to work on lenses with a maximum aperture of f5.6 or larger (f2.8, f4, etc).

What actually happens as you zoom out to 500mm on some of the lenses you mention is that the amount of light getting through the lens decreases as the maximum aperture decreases to f6.3 (viewing and focussing is always done at maximum aperture). You're going to have a hard time seeing what you're shooting and the autofocus is going to have a hard time finding focus and may even stop working.

Charles

Yep, I'm in a bit of a rush, but I'd rather have something close to what I "really" want and need while on my month long vacation VS wishing that I had something to do the job.

Can't learn "good" technique on something that is still sitting in the store!

My present 70-300 Tamron is 4-5.6, and it seems to focus pretty well, atleast most of the time. I don't mind manually focusing sometimes anyways, or atleast I'll continue to tell myself that to remain blissful...

I'll say this, after reading the manual a few times, one would have to spend plenty of time referencing the many terms, models, abbreviations, modes and buttons to ever say that they had a handle on this camera!

I've got 24 hours to make up my mind! Any additional info will be gladly accepted with a smile on this end...

Kevin

You can learn good technique with what you have and I think that is what Loupey was trying to tell you. Just because you have a shiny new lens isn't going to make you a better photographer. Some of the best photos that I have seen were done on on a 50mm prime. If you don't like the 70-300 then sell it and take that money and add to the lens fund, but learn everything that your camera can do and what it can't.

Z

Faster generally refers to the maximum aperture of the lens. AF speed is hard to quantify - the same lens will vary with different cameras and also in different light conditions.

Like Charles said, f5.6 is kind of the magic number with autofocus systems. F6.3 might work with AF but it'll be slow and possibly not accurate even in bright sun. The thing to remember with teleconverters (TC's) is that they multiply the focal length but they also cost you a certain amount of light (lens speed). A 2x TC will turn a 300mm lens into a 600mm lens, but you'll lose two stops of light. If your 300mm lens is already at f5.6, then you'll be at f11 with your 2x TC. AF won't work and the viewfinder will be very dim. A 1.4x TC will make that same lens into a 420mm lens at f8 which again won't work with AF.

Well, I'm not one to wait on anything I really want, so I bought the Sigma 170-500mm DG lens today! I got back into photography to photo birds, with my son, in and around my back yard. Furthermore, we are leaving on a family vacation for 4 weeks, and then another 3 weeks in late July early Auguest. I may not have another summer of fun like this for some time, so I'm living it up!

And, with the other 2 lenses I just couldn't get to them on my 2 main trees. I enjoy the 70-300 Macro Tamron, so I see no reason to sell it now. Might I get another "better" macro in the future? If it exists, then I figure to get it!

Well, here's to spending money! That it what it is for...

Kevin