Lenses - explain.

stokecity_m

stokecity_m

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Chris
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Can someone please explain all the different number etc that lenses have and what they refer to?

Thanks.

For example Sigma DC 18-200mm 3.5-6.3

what the chuff does all that mean?

:)
 
18mm-200mm is the focal length.

3.5-6.3 is the aperture of the lens. 3.5 being the largest @ 18mm, then the largest @200mm is 6.3

Between 18-200mm you will have other apertures f4, f4.5, f5.6 etc.
 
JustinB said:
18mm-200mm is the focal length.

3.5-6.3 is the aperture of the lens. 3.5 being the widest @ 18mm, then 6.3 @200mm

Between 18-200mm you will have other apertures f4, f4.5, f5.6 etc.
Click to expand...


right - can someone now explain the above then :)
 
With the particular lens you have picked, the DC means it is designed for digital cameras with cropped sensors. The 18-200mm refers to the focal length of the zoom lens. The link below will give examples. The 3.5-6.3 is the maximum aperture opening at the minimum and maximum focal lengths, i.e. at 18mm the maximum aperture is f3.5 and at 200mm it is f6.3.

http://lens-reviews.com/Technical-Talk/Technical-Talk/Lens-Field-of-View-Visualisation-Tool.html

Hope that helps a bit.
 
i'm getting there :)

will have a look at the links provided and be back

cheers so far :)
 
Focal length will determine your field of view. A low number is a wider angle (ie. very zoomed out), a high number is a narrower angle (ie. very zoomed in, for taking pictures of things far away).

Your aperture is the hole that lets the light in to the lens. A smaller number is a wider aperture. Rather than me trying to explain, check out this camera simulator: http://www.dryreading.com/camera/index.html
 
Most people have used an old 35mm point and shoot camera with film, take that as a reference. The lower number 18mm gives you a wider shot meaning you can see more at either end of the photo. The higher number 200mm brings the subject closer to you, a zoom.

The 3.5-6.3 is the light that the lens can use, the lower the number the better, this one will be at 18mm the lens can use an aperture of 3.5 and at 200mm an aperture of 6.3
 
thanks alot guys :)

now i just need to work out the best lens i can afford that will be good for me :)
 
18-200mm 3.5-6.3

so is 3.5-6.3 fairly poor - making a cheapish lens?
 
stokecity_m said:
18-200mm 3.5-6.3

so is 3.5-6.3 fairly poor - making a cheapish lens?
Click to expand...

Not necessarily cheap (although fairly cheap in this case)! The larger the focal range (difference in focal lengths), the greater the convenience, and the greater the compromise. As 18-200 is a biiiiiig range, you'll get a smaller aperture at the long end.

f/6.3 is fairly slow, so you'll need good light to use it. However, it's a very convenient lens as you can avoid having to keep switching lenses, due to covering everything. Personally I wouldn't really want much less than f/5.6, but if you're in a situation where you only want to or can possibly carry one lens, it could be a very useful tool.

Chris
 
so with a 50mm - 300mm lens the lower the Fstop number the better?

i'd guess it's not worth going lower then 50mm as the lens i will get with the camera is 18mm - 55mm?
 
stokecity_m said:
18-200mm 3.5-6.3

so is 3.5-6.3 fairly poor - making a cheapish lens?
Click to expand...

I guess it depends on your point of reference. :)

A lower number is better as it gives you more options...

A lower number means you can open up the lens to let more light in and thus get faster shutter speeds -- but this will be at the expense of depth of field (how much front to back is in sharp focus).

A lower number makes it easier to blur our backgrounds.

Your camera will likely autofocus with the lens wide open so it will have faster focus in lower light using a lens with a lower f number such as 2.8.

Yes, you will pay more for a lens with smaller f numbers.

Having said that, you'll often use an f/2.8 lens at f/8 or more so...
 
Depends on what you shoot mate. Your style and long term goals come into play when choosing a lens.

If you're just whatever, and going with the flow, the standard kit won't do any harm. If you're finding 55mm to be unfulfilling, get a standard zoom lens to try out first.
 
stokecity_m said:
i'd guess it's not worth going lower then 50mm as the lens i will get with the camera is 18mm - 55mm?
Click to expand...

Don't worry about leaving gaps in coverage, say between 55 and 70 or 75mm -- you'll hardly notice.

An 18-200 lens is very convenient but you pay a price for that convenience as the manufacturers have to make compromises in the design to keep size and cost down.

Don't be afraid of getting the 18-55 and say a 75-300 lens, or pair the 18-55 with a 55-200 if you're trying to keep the cost down for now.
 
stokecity_m said:
so with a 50mm - 300mm lens the lower the Fstop number the better?
Click to expand...

In short, yes. But because the aperture is bigger to let more light in, the size of the lens barrel needs to be larger. This means more glass needs to be used, and that means more money. LOTS more money! For example, to get:

  • f/5.6 at 300mm, you can get a £100 lens.
  • f/4 at 300mm, you'll need to spend about a grand
  • f/2.8 at 300mm, it'll set you back 3-4 grand.

It's a fairly extreme example, but you get the idea (all based on canon lenses)


stokecity_m said:
i'd guess it's not worth going lower then 50mm as the lens i will get with the camera is 18mm - 55mm?
Click to expand...

It depends. I've got the Tamron 17-50 f/2.8, I was perfectly happy with the kit lens until I needed to use it in low light, when it just wasn't fast enough.

Chris
 
right guys cheers for all the info - one thing that does confuse me is the zooming.

how many times zoom would a 70-300 lens be capable of?
 
stokecity_m said:
how many times zoom would a 70-300 lens be capable of?
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"Times zoom" is more a concept of cameras with non-interchangeable lenses. If you really want to know, just do the big number divided by the little number, but it's sort of irrelavent with SLRs.

For example, a 300mm prime lens doesn't zoom at all, it's fixed, but it would give you a very 'zoomed in' view if that makes sense? You can't zoom in and out, it's fixed at 'zoomed in'. I know that's not very clear, sorry!
 
acs said:
Far more than you need to worry about :)

Some lenses do slacken off but that is rarely a problem and it is really just an inconvenience.
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Right so it's just a case of getting a nice stable camera and the other settings (iso, shutter speed etc) right?

Also with a standard 18mm-55mm lens how close could i get to items?
As i really like some of the close ups on show.
 
stokecity_m said:
right guys cheers for all the info - one thing that does confuse me is the zooming.

how many times zoom would a 70-300 lens be capable of?
Click to expand...

It's about a 4.3 x
 
stokecity_m said:
Right so it's just a case of getting a nice stable camera and the other settings (iso, shutter speed etc) right?

Also with a standard 18mm-55mm lens how close could i get to items?
As i really like some of the close ups on show.
Click to expand...

Don't worry, the cameras will do most of the work for you if you want them to. Most even have Point and Shoot do everything for you modes these days.

The best way to start is probably to put the camera in Aperture (A or Av) mode, you set the aperture you want and the camera will set the other values to get a good picture, or warn you if you're chosen an aperture that simply isn't going to work in the available light.

If you're shooting something fast moving you can put the camera in Shutter (S or Tv) mode, set the speed you need to capture the motion and the camera will again do the rest.

You'll need to see the lens specifications to check how close you can focus on something, though there are 'tricks' to get closer if you need to.
 
stokecity_m said:
right guys cheers for all the info - one thing that does confuse me is the zooming.

how many times zoom would a 70-300 lens be capable of?
Click to expand...

Ok this 'x's zoom is very misleading. A 50-300mm lens would be 6x zoom, a 200-500mm lens will be a 2.5x zoom.

Best to stick with mm than x zoom for chosing a lens.
 
Stokecity_m, with my D50 camera I had an 18-55 lens and a 70-300mm lens. Both lenses were good but there was a real pain that I was invariable having to swap lenses because of the gap in the focal length. With my new D90 I got a 18-105 lens and I have found that it is extremely versatile.

In terms of how close you can go all lenses have minimum focus points. If you want to get closer then you need to get a macro lens.
 
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