few camera and lens questions

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Joined: 03/16/15
Posts: 53852
few camera and lens questions

Ive been looking at reviews trying to figure out what I want to start saving towards...

I dont understand what the difference is between all the lens. My questions might be silly/obvious but I just want to know if I understand this all

These two for instance:
sigma 170-500 4.0/5.6
sigma 17-70 dc macro

What do the numbers mean? Are the first two numbers the focal length? And the second something to do with aperture? When it only has one number at the front is that maximum or minimum? Or something else?

Do certain bodys have certain aperture settings allowable or is that specific to lens?

Im sort of looking at the Canon XTI as a step up from my Powershot but Im hesitant to get that and end up wanting something more.. (Its still many months off but Im wanting to start looking and saving now) If I go with the XTI what lens would you guys recommend?

totally lost on these. Any help is appreciated.

faeriecurls's picture
Joined: 06/04/08
Posts: 790

The first two sets of numbers are focal lengths - 170mm-500mm is a telephoto zoom lens. The 17-70mm is also a zoom (zoom=more than one focal length in the same lens. The other choice is a prime lens which just has one focal length) but with a more standard range of focal lengths. The 17mm is pretty wide angle focal length but you would get a pretty good range with that one.

The other numbers are the aperture values for the lens. Since the first one has 2 numbers, that means it has a variable aperture setting. The first number would be the aperture you can get @170mm and then it gets a bit smaller as you go up in focal length (the larger the aperture or f/stop number, the smaller the opening - sort of confusing initially). Some zoom lens have fixed apertures for the entire range of focal lengths but those are usually more expensive.

You would get much more use out of the 17-70 lens when you do get a new camera, IMO. I don't know what you like to shoot though.

I can't answer anything about the Canon, since I have Nikons. You do have to check which lenses are compatible with your camera though, they have different mounts. Also - if your camera isn't a full frame sensor camera the focal lengths of the lenses you buy will change slightly (it's called sensor crop and the focal lengths will be slightly longer - doesn't mean you can't use it though - you just need to figure out what your camera's crop factor is (it will be a number like 1.5 (that's for my D200 - I think Canon's might be 1.6) and you just multiply that number by the focal length. So a 50mm lens on a camera with a 1.5 crop factor would be more like a 75mm lens.

I would save $ for the camera first because the camera you buy will dictate what lenses you will get.

I hope I answered your questions and I didn't confuse you more.

Joined: 03/16/15
Posts: 53852

Thanks. I did end up searching more and finding a bit more information but was still confused on some things. Im still not sure what camera to get. Those lenses were just used here as an example.

I do want a camera/lens that will allow me a larger aperture and Im a little confused on the aperture part of the numbers still.. I understand that smaller number means more light/larger opening and larger number means smaller opening/less light.. But when it comes to lens that was a little confusing. But I think I understand it now.. Please correct me if Im wrong.

The aperture number that goes with the lens numbers would be the lowest aperture (biggest opening) possible.. right? As the focal length changes (or the lens is zoomed) then the ap changes with that?

With my current P&S I can shoot full manual but Im limited with the settings. My ap only goes from 2.8 to 8.0. Id like something to go higher (at least 16). I will probably end up needing 1-2 lens to shoot what I want.. Im not really into macro but would love to get a macro lens as well.. Im just wanting to figure everything out before I do save and end up purchasing a lens that isnt what I need.

Thanks for taking the time to answer those questions.

Joined: 10/20/07
Posts: 480

I went from years on my powershot to a Canon 50D with a 50mm 1.8 lens at Christmas. Many people will say that it is the best "basic" lens and it is usually around $100. It is still my only lens, but it works in most situations and I LOVE it.

I will be purchasing a zoom lens soon, but am leaning towards one with a fixed aperture since they tend to get better reviews and feedback from the pro community.