Whats the difference between these aperture's?

Question

for example, Ill see a telephoto lens with a aperture that reads 4.5 - 4.6 , then I will see another lens with a aperture of 1.8 .... why does this only have 1 setting, does this make it a better lens? i thought being able to change aperture settings (like the first one ) can do more effects

Answer 1

The first lens, with the f/4.5 to 5.6 (I'm sure you typed it in wrong) is what is known as a "variable aperture" zoom.  At the widest lens setting, the maximum aperture is f/4.5.  At the telephoto setting on the lens, the maximum aperture becomes f/5.6.   The number only measures the *maximum* aperture.

By comparison, the other lens with an aperture of f/1.8 keeps that aperture as a maximum.  If it were a zoom lens, if you were to zoom from wide angle to telephoto, the maximum aperture would remain constant.  Typically for pro lenses, you'll see something like a 70-200mm f/2.8 zoom for example, which means at 70mm the maximum aperture is f/2.8 and at 200mm, the aperture is also f2.8.  As you could see, this is good, because the aperture stays constant and thus, so will your exposure.  This is generally a more expensive lens design.

Both of these types of lenses can adjust their apertures; the difference is that one has a variable maximum aperture that changes as you zoom while the other has a constant maximum aperture.

In addition, you need to understand that fixed focal length lenses do not zoom.  Thus a 50mm f/1.8 lens always has the same view, while an 18-55mm f/3.5-5.6 lens does zoom (change focal lengths) and has a maximum aperture that changes as you zoom (f/3.5 at 18mm and f/5.6 at 55mm).

Once again:  the range of f-numbers on a lens name on refers to the *maximum* aperture.  

And the range of focal lengths will indicate a zoom lens or only 1 focal length number (in mm) will show a fixed focal length lens.

Answer 2

Larger number (i.e. 1.8) = larger hole to allow light to enter = faster (meaning, better in low light). Telephotos, with the exception of high-dollar pro gear, normally have higher aperture numbers (the 4.5 of which you speak). Normal SLR fixed-focal length lenses, the 50mm and such, are normally 1.8. My 18-200mmG VR is 3.5-5.6 (3.5 at the 18mm end, and 5.6 zoomed out to 200mm).

Changing aperture settings controls depth of field. Your 1.8 probably goes up to f16 or so.the higher the aperture, the more depth of field (the greater range of focus).

Answer 3

Well, aperture means how wide the lens can open to take in light. A wider aperture means more light and thus faster shutter speeds -- very useful in low light. This means less shots will come out blurry. It also means a shorter depth of field (which can be useful sometimes for artistic purposes, but so can lots of depth). So, this is mostly opinion, but I would go for the lens with the lower aperture so that I could use the faster shutter speed.

Now if you are seeing these numbers right next to the title of a lens, that probably means that it is the minimum aperture of that lens. You don't see too many fixed aperture lenses, because they're not as flexible. The reason that those telephoto lenses have two f-numbers by them is because that at the minimum length (let's say 28mm), the minimum f-stop might be 4.5. However, it is very difficult (and expensive) to make a lens that can stay the same large width for the whole time, so the minimum aperture at the maximum length might be 5.8.

Hope that that helps!