Apature

[tim11]

In Av mode and full manal mode he can: In Av mode, the photographer selects f/2.8 and the camera body is forced to use the selected aperture.
In full manual mode, the photographer selects f/2.8 as their shooting aperture, adjusting the shutter speed and ISO (if neccessary) to balance the exposure.
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You are WRONG. The photographer cannot force F/2.8 at full zoom on a Sigma 17-70 F/2.8-4.5. That's regardless of Av, M or whatever.

[Razr]

(SNIP)Are you saying that on a f2.8-4.5 that you can select f2.8 in AV or M mode and and F2.8 is available throughout the zoom range?

Yes, in Av mode.

[griptape]

He has never used an SLR, or SLR lens. That's all there is to it. That or he's a troll. Let this discussion of 30 against 1 (very undereducated person) die. Razr is wrong, everyone else has more than chicken noodle soup for a brain. End of story.

[tim11]

OK, real easy, just a yes or no answer will do. On a f2.8-4.5 (using your example on this thread, page#1, post#8) I can use the aperture of f2.8 at any focal length the lens has? Mode is set to AV or M of course.

You can.

In Av mode and full manal mode he can: In Av mode, the photographer selects f/2.8 and the camera body is forced to use the selected aperture.
In full manual mode, the photographer selects f/2.8 as their shooting aperture, adjusting the shutter speed and ISO (if neccessary) to balance the exposure.

Finally, we get a straight answer - albeit the wrong one. RAZR... You may considered yourself a pro and google and wikepidia all you like the fact is you can't use F/2.8 at 70 mm (on a 17-70 F/2.8-4.5). Regardless of Av or M modes you try to use. It's the physical limitation of the lens. And at 70 mm, F4.5 becomes the optimum aperture. Accept it mate.

[DonSchap]

I'll repeat here: only in "P" and "S" moded does the aperture setting change according to the focal setting.
IN "M" and "Av" modes, the aperture does not change until/unless the photographer sets (selects) another aperture-got it?
"Av" and "S" modes immobilze (lock-freeze) the aperture.

This statement is just NOT true. I'm sorry, I've done it on my several cameras ... without firing a single shot ... and in the Av mode ... on a zoom lens:

1) focal length to minimum ...
2) set a variable aperture lens to MAXIMUM aperture
3) telephoto to the other side of the focal range

RESULT: the aperture will creep right up and close right down.

EVERY SINGLE CAMERA BODY, my friend. They all do it ... and I've got proof!

I'd make a movie of it ... but you can just get in your car, drive down to BEST BUY and do yourself ... live-action style. Living proof. There is no "locking" ... yes, if I return to the original focal length I started at, the aperture should and does return back to the original MAXIMUM. It does not stay at the higher aperture it got to.

By the way: "OPTIMUM Aperture" does not mean "MAXIMUM Aperture", "Optimum" is the photgrapher's choice for a particular type of shot. Be it in need of bokeh or light deficiency ... the photographer chooses the aperture from the available settings at that focal length. He/She chooses the "optimum" aperture and then the camera chooses the shutter-speed to support it. That is it.

My goodness ... this is a hard case.

You simply cannot get f/4 pounds of crap into a f/2.8 bag.

Look, I placed a chart at the very beginning of this thread to demonstrate EXACTLY what happens with two different lenses ... the 18-70mm and the 18-200mm. Please stop ignoring the rather simple and duplicatable facts and just accept this as common knowledge. Thank you ... and the horse you rode in on.

[TheWengler]

Troll - One who posts a deliberately provocative message to a newsgroup or message board with the intention of causing maximum disruption and argument.

[tim11]

All this time, at the back of of my mind I'd like to believe he is in fact a troll for the reason I hate to believe anyone can be that stupid.

[griptape]

For those of you wondering, Razr has NOT been an SLR owner, and is in line to order an Olympus E-3 that hasn't been released yet.

http://www.dcresource.com/forums/showthread.php?t=34858

After being an expert on the panasonic lens debate:http://www.dcresource.com/forums/sho...098#post258098

I suggest everyone add him to your mute list, as he's a moron who is just looking for attention.

[tim11]

For those of you wondering, Razr has NOT been an SLR owner, and is in line to order an Olympus E-3 that hasn't been released yet.

http://www.dcresource.com/forums/showthread.php?t=34858

I understood the concept even before I got my D80. It's nothing to do with owning a DSLR.
If I remember right RAZR also owns an FZ20 which has aperture of F2.8 throughout the range. I wonder if that him.

[TenD]

Yes, in Av mode.

Ok I though you were maybe being a clever troll and arguing opening(aperture), but that statement is simply, utterly WRONG. If the maximum aperture of a lens gives you f/4.5 at 70mm, the maximum f stop it can give you is f/4.5, it's physically impossible to get any more light to the sensor. The lens diameter is simply not big enough to allow an opening any larger.