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jbren3160 Feb 6, 2005 9:52 AM

I know this is a silly question that I should have asked years ago, but I have started to purchase some lenses and am curious about the different types and qualities? I have a Nikon D70 and am wondering whether Sigma lenses are of high quality, or do I need to stick with Nikon lenses? Also there is quite some differences in price for some lens. Why? What does the F number on the lens signify? Or is there a good book that explains all this? Thanks, John

JohnG Feb 6, 2005 8:24 PM

Sigma does, indeed, make some good lenses - not all of them are good, but they do make some very excellent alternatives to the Nikon or Canon lenses. Typically a lense will have the f-stop range the lense supports imprinted on the barrel of the lense. For instance, a lense with just 2.8 should signify the lense has a constant maximum aperture of 2.8 across the entire zoom range. A lense that has 2.8:5.6 would have a max aperture of 2.8 at it's shortest zoom, but only 5.6 at it's maximum aperture. If you provide some information on the type of lense you are looking at purchasing there are plenty of people here who can suggest both Nikon and off-brand alternatives - but you are likely to have the most luck in the Nikon D70or Nikonlense forums.

As for difference in prices can you be more specific? Difference between two similar sounding lenses from two different manufacturers? There are all sorts of things that go into the quality of a lense - many people coming from a point-and-shoot background immediately look for a lense with the longest zoom only to find out later that the lense is poorly made, has slow auto-focus or has a very narrow aperture (say >5.6).

jbren3160 Feb 7, 2005 8:21 AM

John- Thanks for the info. I don't have any particular lens in mind, but that is a good point. When I get to that point I will have to use your 'collective knowledge' as to the best lens. In yours or anybody else's opinion,for that matter, should I stick with a lens with a constant aperture? If that is the case, what aperture do I want, or does that depend on the focal length of the lens?

JohnG Feb 7, 2005 9:27 AM


should I stick with a lens with a constant aperture? If that is the case, what aperture do I want, or does that depend on the focal length of the lens?
Not sure if there is still some confusion - remember this is a constant MAXIMUM aperture - just because a lense has a constant max of 2.8 you can still go to f12 or whatever with it. To answer your question above: constant aperture lenses are usually of higher quality but they are also heavier (the components need to be in order to maintain that constant aperture at full zoom) and are often much pricier. So, you get the 'depends' answer: If money is not an object and you don't care about the added weight then yes these are the better choice. But that isn't always the case. Now, as to whether or not you NEED the constant aperture that depends on what type of photography you like to do.

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