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Basic lens information.
I am getting my self confused. I have a 18-200 lens with the variable aperature which I think I understand. However, I was thinking of purchasing the 17-55mm l2.8 lens. Now I think this means that the lens can be at 2.8 over it's whole range. But what would the minimum aperture be on this lens? The description does not mean it's a fixed aperature lens does it? I have been trying to read up on the subject but the brain cells don't seem to be working tonight...

Comments (6)

On the variable aperture lens, the widest the aperture will go is the first number (probably 3.5) at 18mm, and the widest it will go at 200mm is the second number (probably 5.6 or 6.3)..

On the 17-55, you can go as wide as F2.8 at 17mm, at 55mm and everywhere in between. The smallest aperture would probably be F22, at all ranges, but you would have to check the official specs..

Hal17 wrote:.

I am getting my self confused. I have a 18-200 lens with the variableaperature which I think I understand. However, I was thinking ofpurchasing the 17-55mm l2.8 lens. Now I think this means that thelens can be at 2.8 over it's whole range. But what would the minimumaperture be on this lens? The description does not mean it's a fixedaperature lens does it? I have been trying to read up on the subjectbut the brain cells don't seem to be working tonight..

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Comment #1

Thank you for your reply. I do appreciate that. I was getting confused as the spec on the Nikon 17-55 lens only showed F2.8 and then I read an article on fixed aperature and then I lost the plot...

Comment #2

Using the terminology correctly helps with this..

*Fixed* aperture means literally that - a single, fixed aperture. Very, very few lenses have a fixed aperture, the most notable example being mirror lenses..

The 17-55 f/2.8 has a *constant* aperture. This means that f/2.8 is always ('constantly') available, throughout the zoom range - something you get only with better lenses. It says nothing about the minimum aperture, but this information is readily available on the manufacturers' web sites...

Comment #3

I'm still a beginner too, so I understand your frustration and confusion, there are still lots of things I don't understand, mostly terminology. As has already been explained the 2.8 lenses are a constant aperture. The thing I found confusing is that the number of the aperture is inverse to it's actual opening. Meaning that the smaller the number the larger the opening in the iris in the lens, therefore letting more light in, the opposite is also true, the larger the number, the smaller the opening in the iris, less light gets through. So a constant 2.8 gives you the ability to open the aperture all the way up to 2.8 at any zoom range, giving you the ability to gather more light, faster, than a comperable zoom with only a 3.5 or a 5.7, etc. That is also the largest (based on size of iris opening) aperture that lens is able to support.

Now if I could only afford them . Along the same lines, a lens with a 1.4 aperture (usually in high-end non zoom "primes") would be able to open the iris further yet, allowing a capture of a picture faster yet under the same circumstances. Hope this helps. It was a lot of reading for me to get this part figured out.Jeremy.

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Comment #4

Thanks again everyone, especially Jeremy for taking the time to type a reply. I fully understand now and is how I thought the lens should work. Once the "constant" aperature was mentioned the penny dropped. Funny how you can get a wrong thought from reading something inappropriate i.e. "fixed" aperature and then you get confused. Thanks again everyone...

Comment #5

Anytime... the only reason I was able to type that in the first place is because of the kind helpful people on this forum that have endured my questions time and again. I read other (non photography)forums and I wish the people were half as helpful in them.Jeremy.

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Comment #6

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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