Constant Aperture vs. Sliding Aperture vs. Fixed Aperture: Judging from reading other Topic Posts of late, I'm not the only one who confuses Constant Aperture and Fixed Aperture. The...

Chris T Loc: from England across the pond to New England

Judging from reading other Topic Posts of late, I'm not the only one who confuses Constant Aperture and Fixed Aperture. The latter, of course, refers to Reflex Mirror Lenses, and the like. The former - Constant Aperture - just refers to the fact the fastest aperture (f2.8 for instance) doesn't slide up to be f5.6 or f6.3 or something. Many lenses (primarily, zooms) do not stay at f2.8 or f3.5, even - but stop down to a slower maximum aperture as you zoom in. Judging from reading other posts, some are of the opinion the Constant Aperture of f2.8 - means the lens will maintain that aperture, regardless of the focal length of the lens in use. Now, clarified ....

Tomcat5133 Loc: Gladwyne PA

One thought is as I shoot a lot of video now. Constant aperture is great
because as you move the camera or zoom in the lighting reacts and stays put.

GoofyNewfie Loc: Kansas City

Tom Daniels wrote:

One thought is as I shoot a lot of video now. Constant aperture is great
because as you move the camera or zoom in the lighting reacts and stays put.

With all my variable (maximum) aperture lenses, if you use nothing faster than the smallest maximum aperture, it stays there.
As with a 3.5 ~5.6 lens; if you use 5.6, it will stay there throughout the whole zoom range.

Chris T Loc: from England across the pond to New England

Tom Daniels wrote:

One thought is as I shoot a lot of video now. Constant aperture is great
because as you move the camera or zoom in the lighting reacts and stays put.

That IS a thought, Tom ... that helps, huh?

Chris T Loc: from England across the pond to New England

GoofyNewfie wrote:

With all my variable (maximum) aperture lenses, if you use nothing faster than the smallest maximum aperture, it stays there.
As with a 3.5 ~5.6 lens; if you use 5.6, it will stay there throughout the whole zoom range.

Jim ... that's what I meant ... variable = sliding ....

I chose to use the term "sliding" in order to differentiate it further from "constant" and "fixed" ....

Now, your terms are a little suspect, here ... "smallest maximum aperture" ....?

The most maximum aperture is the largest .... (f1.2, for example) ... smallest apertures are ones with highest numbers = f32, f45, etc.

So you have a lens which will stay at f5.6 - no matter what, do you, Jim? .... which one is this?

jerryc41 Loc: Catskill Mts of NY

Chris T wrote:

Judging from reading other Topic Posts of late, I'... (show quote)

Yes, "constant aperture" can be confusing. We've had quite a few questions about how that works. The fact is that the aperture is not actually constant. It can be very small, but it can also remain at f/2.8 throughout the zoom range.

Fotomacher Loc: Toronto

Aperture designations can be confusing in that f/4 is LARGER than f/8. Think of fractions when discussing apertures - 1/4 is larger than 1/8 and you’ll never make a mistake.

Chris T Loc: from England across the pond to New England

jerryc41 wrote:

Yes, "constant aperture" can be confusing. We've had quite a few questions about how that works. The fact is that the aperture is not actually constant. It can be very small, but it can also remain at f/2.8 throughout the zoom range.

Jerry ... think you're straddling the fence, a little on this one ... "the aperture's not really constant" ... "but it can remain at f2.8 throughout the zoom range" .... ?

Chris T Loc: from England across the pond to New England

Fotomacher wrote:

Aperture designations can be confusing in that f/4 is LARGER than f/8. Think of fractions when discussing apertures - 1/4 is larger than 1/8 and you’ll never make a mistake.

Oh, thanks, FM ....

tayho

Back to basics:
Some zoom lens’s have a constant Maximum aperture. I have a Nikon AF-S 70-200 F/2.8G IF-ED VR, the aperture stays the same throughout zoom range. If you choose F/2.8 (or any other f/stop)it will remain constant from 70-200.

Some zoom lenses Maximum aperture changes as the zoom magnification changes. I also have a Nikon AF/S DX 16-80 F/2.8-4E ED VR, the aperture changes automatically from F/2.8 at 16mm up to F/4 at 80mm. It can not be set to F/2.8 at 80mm.

If you want to have your aperture the same throughout the zoom range, you would need to use F/4 with the 16-80 lens, but you could use F/2.8 with the 70-200 lens.

An interesting tidbit I learned along the way is that the minimum aperture can change through the zoom range as well.
The Nikon AF/S DX 55-200 F/4-5.6G ED VR has a minimum aperture of F/22-32.

I hope this helps

Chris T Loc: from England across the pond to New England

tayho wrote:

Back to basics: br Some zoom lens’s have a constan... (show quote)

Thanks, there, Tayho ... some interesting additional insight, there ....

So, for YOU, at least - Constant Aperture - means it will not change on its own. But, it doesn't mean - when you choose wide open at f2.8 - it will stay there to 200
... or does it? .... No, that's exactly what you DO mean, huh, Tayho? .... a) that'd make for a pretty heavy lens ... f2.8 at 200mm ... plus b) very expensive ... yes?

tayho

Chris T wrote:

Judging from reading other Topic Posts of late, I'... (show quote)

I agree! You do seem confused on this issue. You ARE good at missinterpreting people trying to clarify it for you. Pretty simple concept.

Chris T Loc: from England across the pond to New England

tayho wrote:

I agree! You do seem confused on this issue. You ARE good at missinterpreting people trying to clarify it for you. Pretty simple concept.

What did I get wrong, in the final assessment, then, Tayho?

Los-Angeles-Shooter Loc: Los Angeles

GoofyNewfie wrote:

With all my variable (maximum) aperture lenses, if you use nothing faster than the smallest maximum aperture, it stays there.
As with a 3.5 ~5.6 lens; if you use 5.6, it will stay there throughout the whole zoom range.

WRONG. As you can readily observe and prove for yourself w/ camera's meter; test photos; histogram

RichardTaylor Loc: Sydney, Australia

GoofyNewfie wrote:

With all my variable (maximum) aperture lenses, if you use nothing faster than the smallest maximum aperture, it stays there.
As with a 3.5 ~5.6 lens; if you use 5.6, it will stay there throughout the whole zoom range.

This statement is correct for manual exposure mode and for aperure priority mode where the photographer, not the camera, controls the aperture.