Constant vs variable aperture lenses

[tim]

I've noticed that generally, fixed aperture lenses are better quality than variable aperture lenses. Does anyone have an explaination for why that is that's not too complex?

[AJSJones]

Do they not also generally cost more? Better design and/or build quality costs more.
Not sure about the physics, though :-)

[mblanton]

From my understanding which is not the greatest, I think it comes down to better optics. When I bought my camera I splurged and bought one L series lens, the 17-40 f/4 L. The quality is awesome. It's not my most often used lens, but that is because of its focal length. I think if you over shoot it you loose the appeal of wide angle.

Mike

[CyberDyneSystems]

The two do not have to go hand in hand.. (constant aperture and high quality)

...but they pretty much allways do simply because to build a constant aperture zoom,.. is more expensive.

In addition,.. there is no point in doing so if the lens is going to have a slow constant aperture... and faster (larger aperture) again costs more. Now we have two apsects of the les that are going to cost more money than not including these aspects. Why would such high dollar aspects be included in an otherwise run of the mill lens?

FYI,. just to throw a monkey wrench into the works,.

Constant aperture zooms maintain a "fixed" wide open f/stop when zooming because the aperture, or iris changes.

non-constant aperture zooms change there wide open f/stop value when zooming because the aperture/iris does NOT change when zooming. ;)

[tim]

I assumed that constant aperture zooms had a variable sized iris, thought that'd have been common sense! Good point re price, usually variable aperture zooms are cheaper, and non-constant aperture sounds easier to make.

[Jon]

Actually what changes is the "Entry Pupil", the apparent diameter of the aperture as seen from the front of the lens. What you're seeing is the various elements in front of the aperture changing how much they "magnify" the aperture as they move during the zooming process.

[Lord_Malone]

In the case of the 28-80 f2.8-4L, image quality is exceptional.

[tim]

Excellent revival or a 2.5 year old thread LM :p

[Lord_Malone]

heh heh... but the question is still relevant. ;)

[Moppie]

Excellent revival or a 2.5 year old thread LM :p


It shows how far you have come Tim.
Altough your current sig does look a little odd under that particular question :p

[tim]

It's so old I only noticed I started the thread when you mentioned it Moppie!

[Lord_Malone]

Moppie, you haven't shown any love to the Transformers thread in a while. I'm hurt.

[Moppie]

Moppie, you haven't shown any love to the Transformers thread in a while. I'm hurt.


I've been trying, but Starscream won't let me get close enough.....

[amfoto1]

Constant aperture zooms maintain a "fixed" wide open f/stop when zooming because the aperture, or iris changes.

non-constant aperture zooms change there wide open f/stop value when zooming because the aperture/iris does NOT change when zooming. ;)

And we drive our cars on a "parkway"... But park them in a "driveway". :)