Lens question from SLR rookie

[Bendixen]

I'm new in the SLR world, and I can tell there's a huge difference in lens prices. Could any one explain to me the following:
- Why does some lenses have a aperture range and other a fixed aperture (assure that what it is when some lenses say f/2,8-3,5 others just f/2,8?
- Which is better a large range or a fixed, small or large values?

Thanks,

[cmM]

zooms, most of the cheaper ones have an aperture range (they have one aperture at certain focal lengths and beyond that, when zoomed out the barrel is not big enough to allow the same amount of light in as when zoomed out, which is way the max aperture goes down a stop of so, usually.

As for the price differences, it's not the fixed vs. variable aperture that determines the price, but rather the aperture value itself. Lenses with larger apertures (smaller numbers) are more expensive because they're bigger, bigger/more elements, etc...

[Andy_T]

Bendixen,

welcome to the forum!

In addition to what CMM said ... some basic info on f/stop (aperture)

The number stated is the LARGEST aperture. You can always 'stop down' the lens (e.g. use a 24-70/2.8 lens at f/5.6), but the opposite is not possible.

The aperture basically measures how much light can enter the lens and hit the sensor. A large aperture (e.g. 2.0) lets a lot of light into the camera, a small one (e.g. 8.0) only a fraction.

Full F-stops are 1.0 - 1.4 - 2.0 - 2.8 - 4.0 - 5.6 - 8.0 (multiply the previous full f-stop with 1.4). A difference in one full f-stop means that twice as much light hits the sensor in a given time. If you have enough light to take a photo with a 200/4.0 lens at 1/125 second, then a 200/2.8 lens will allow you a shutter speed of 1/250 second. Of course, you could also double the ISO sensitivity (e.g. 800 instead of 400) for the same effect, but this increases noise and is only possible up to ISO 3200.

Also, aperture has something to do with sharpness.

First, at a smaller aperture, a larger area of the picture will be in focus. If you use a large aperture at a long focal length (e.g. f/1.8 at 85 mm), only your subject will be in the focus, whereas the rest of the pictures (the parts in front or behind the subject) will be blurred, drawing the viewer's attention to the subject.

Second, most lenses are sharper when they are stopped down than when they are used wide open. If you have a 135/2.8 and a 135/5.6 lens, the 135/2.8 lens will be certainly sharper when you stop it down to f/5.6 than the other lens.

Last, bear in mind that it is a lot more difficult to build a good zoom lens than a good prime lens, because you need fewer elements. The fastest lenses are prime lenses, like the formidable 70$ 50/1.8. If you stop down this lens to f/4.5 and compare it to a standard zoom lens at the same aperture, it will be a lot sharper. Still, it will also give you the flexibility to creatively blur the background or get the picture when there is not enough light available.

Hope this helps a bit ...

Best regards,
Andy

[robertwgross]

The number stated is the LARGEST aperture. You can always 'stop down' the lens (e.g. use a 24-70/2.8 lens at f/5.6), but the opposite is not possible.


What Andy stated is true for most decent lenses. However, there are some cheap mirror lenses that have one fixed aperture (generally not too good) and they cannot be stopped down.

I will plead guilty to having owned one of those many years ago when I did not know any better, but I would not put up with one now.

---Bob Gross---

[Citizensmith]

- Why does some lenses have a aperture range and other a fixed aperture (assure that what it is when some lenses say f/2,8-3,5 others just f/2,8?
- Which is better a large range or a fixed, small or large values?


To answer specifically.
Ranges are quoted when for a zoom the maximum available appeture varies dependant on focal length.

For a given lens there is no benefit to having a fixed maximum apperture vs a variable. For instance the canon 70-210 f/3.5-4.5 was a great lens, while the 70-210 f/4 sucked. Often though fixed maximums show up in the higher quality lenses.

Smaller numbers are better than large (as better described in previous posts) as they let in more light.

[PJ Saine]

Smaller numbers are better than large (as better described in previous posts) as they let in more light.

Wanted to lend a little more accuracy to the concept of aperture:

The f/stop of a camera lens is a ratio between the focal length of the lens and the diameter of the aperture. Since the aperture can be considered circular, its area is proportional to the square of the diameter. (Hint: Every other aperture doubles in number.) Apertures on modern cameras are 'relative apertures': that is, an f8 on one lens will let in the same amount of light as the f8 on another lens. When considering a lens purchase:

- With a larger the maximum are, more light is available, allowing a faster shutter speed. Will your future shooting conditions be in low light or fast action situations where faster shutter speeds are required?

- The larger the maximum f/stop, the larger (and heavier) the lens. Will the weight and size of the lens be affecting your lens choice?

The flip side:

- Lenses with larger maximum apertures are generally more expensive and often manufactured to higher tolerances. Are you willing to pay the premium to get & use the 'best'?

- The maximum aperture is never the sharpest aperture. If you are interested in the sharpest image - stop down by 2 or 3 stops for greatest sharpness.

Other possible questions you might have:
How close does the lens focus - and does that matter? Will your filters from your other lens fit this one? What is the minimum aperture? Does the focusing ring take a long or short throw to move from close to far?Does the lens/camera combo balance well in your hand?

No lens is perfect - just as no hammer is perfect. Every lens is a tool which gets the creative job you have defined done. While any one lens is not always 'better' than another, any one lens is almost always 'different' than another. If you get a chance, try to put each of the lenses on your camera and shoot a picture or two (even if it is just of the parking lot outside of the camera store.) You'll get a feel for which lens 'feels' right, how easy it is to zoom & focus, how sharp the image looks, and how good (or bad) the rest of the picture looks.

Hope this helps you think about your decision!

PJ
www.pjsaine.com

[Bendixen]

Thanks for all the great answars. Very helpfull!

Downside to my knew "knowledge" is that I will probably need 2 lenses to fit my needs:
- I wish to take quality pictures of my family, landscape etc. No zoom needed.
- I'm a golf fanatic, and would like to take pictures of golfswings, i.e. lots of zoom required.
Any recommendations?

[tim]

- I'm a golf fanatic, and would like to take pictures of golfswings, i.e. lots of zoom required. Any recommendations?

Get a video camera?

[Bendixen]

Tim, I'm more into still pictures. I haven't found the quality of video cameras to be very good.

[Jesper]

Thanks for all the great answars. Very helpfull!

Downside to my knew "knowledge" is that I will probably need 2 lenses to fit my needs:
- I wish to take quality pictures of my family, landscape etc. No zoom needed.
- I'm a golf fanatic, and would like to take pictures of golfswings, i.e. lots of zoom required.
Any recommendations?Are you sure you are not mixing up the terms "zoom" and "telephoto"?

"Zoom" means you can change the focal length of the lens, for example from 28 to 135mm, to "zoom in". The opposite of a zoom lens is called a prime lens - it has only one focal length. To make the subject larger or smaller, you have to get closer or stand back.

"Telephoto" means you can make a photo of a small subject from far away - it enlarges things, just like binoculars.

You have prime wide angle lenses, zoom wide angle lenses, prime telephoto lenses and zoom telephoto lenses.

[Bendixen]

Jesper, you got me a bit confused :-)

when you "zoom in" on a subject, you enlarge this image, right?
Is a lens that have a range from 28-135mm, a telephoto lens?

[Andy_T]

Bendixen,

in general, you don't 'zoom in' to enlarge the image.
You use a telephoto lens.

A telephoto lens CAN be a zoom lens, but it does not have to be. A telephoto lens basically is a lens with a long focal range.

Some examples:
- a 'light' tele is something longer than 80 mm
- a 'medium tele' might have 200 mm focal length
- a 'long tele' lens could be 300 mm or 500 mm... and so on

Some other examples for lenses that are NOT telephoto lenses:
- a 28 mm lens would be a 'wide angle' lens
- a 50 mm lens would be a 'normal' lens.

A ''zoom lens' is a lens that does not have a fixed focal length, but rather can be 'zoomed' between two focal lengths, e.g. from 28 mm focal length to 135 mm focal length.
This would be a 'wide angle to medium tele' zoom lens.
It allows you to take photos at any focal length between 28 mm and 135 mm.

There are also 'wide angle zoom lenses' e.g. from 17-40 mm focal length. Although this is a zoom lens, it is by no means a tele lens.

If you want to get the image close, you need a telephoto lens.
This could either be
- a 'prime' lens (e.g. 200/2.8 or 300/4.0 or 400/5.6 and so on) or
- a 'zoom' lens (e.g. 70-200/4.0 or 100-400 ...)

Does this clear it up a bit?
If not, you might really profit from reading a basic book on photography to get more familiar with the foundations ;)

Best regards,
Andy

[Bendixen]

Andy,

Very helpfull. Can I skip the photo for dummies book now :-)
But any recommendations on litteratur to get started? I generally feel I have a "good eye" for photografy, but when upgrading from compak to SLR camara, I would like to be able to take full advantage of all opportunities.