Lens question if anybody knows

[maxim_232]

So since f-stop is the ratio of focal length to diameter, then it makes sense that in a zoom lens the f-stop would vary as you zoom. But we also have these things called "fixed aperture zoom lenses" that command an enormous price tag from the manufacturer. How is this physically accomplished? The lens diameter is fixed. Is the lens designed for the max aperture at the longest focal length, then actually stopped down as the length is shortened?

[discerning_guy]

Not sure where u got the defn of the f stop..but thats not my understanding. I haven't done pro work in 2 decades..so take it for what it's worth.

The power of the lens is the lowest aperture setting possible. The longer the lens, the more difficult it is to grind and arrange the lens combo to get a low aperture. Hence the cost differential. It get even more complicated in long zoom lens like 70-300, primarily due to the no of lens elements involved. But technological advances has made fixed aperture possible today even in a long zoom. When I was active in the 90's, I dont recall a fixed aperture nikon, but remember another (tamron or something like that) having one at 3 or 4 times the price.

As to why it matters, unless you are blowing up the picture to a half or full canvass size or doing glossy mag work, IMHO it doesnt. Then again, I only did wedding and at home kid pictures. I have never done much action work, but I heard it is must have in those situations.

[hd]

I have a couple of canon L lenses, I'm only guessing that the aperture adjusts it self to sustain the settingas you zoom in or out. As many years that I've used them I've never thought anything about your question, but it's a go one. Of course as it sounds like you know, the cheaper zooms list the f stops for the max and min zoom lengths.

You might get on your camera's brand website site and see if you could ask about it. Or as I might do, I've always dealt with Competitive Camera, next time you're in a camera (professional) store, ask one of the people.

But I'm sure we have some eccie members that should know this.

[oldbutstillgoing]

http://photo.stackexchange.com/quest...es-f-stop-mean

[phildo]

Originally Posted by maxim_232

Is the lens designed for the max aperture at the longest focal length, then actually stopped down as the length is shortened?

No. Because...

I'm no rocket scientist but in a fixed aperture zoom all of the magnifying elements are in front of the aperture, keeping it wide open relative to the
front lens.

I saved this from a while ago for a family member. It's way too deep for what I needed, but maybe you can use it.

http://www.reddit.com/r/photography/...oom_lens_work/

[slowmover]

big f stop=small opening=greater depth of field
small f stop=big opening=short depth of field

user friendly info

[DarthDVader]

+1 Photography 101 ...

Originally Posted by slowmover

big f stop=small opening=greater depth of field
small f stop=big opening=short depth of field

user friendly info

[maxim_232]

Thanks for the response phildo, interesting article, actually answered my question. I'm well beyond 101.