Aperture auto-adjust while zooming?

[leslie_e_olmedo]

I sold a Canon EF 35-80 mm 4/5.6 III Auto Focus Aspherical Ultracompact Lens on eBay and it was returned to me

because the lens was "defective".

 

The buyer says that when he "zooms", the aperture auto adjusts, which seems to be a malfunction. In manual mode

on his Canon 60D, aperture should be manual regardless of zooming or not. He tested it out on his friends 5d Mark

II and it did the same thing.

 

I tested the lens with a Canon Rebel film camera and it works fine. The aperture or speed does not change while

the autofocus is zooming.

 

Now, I don't know if he's refering to focal lenght zoom or the auto focus mechanism. The aperture cannot change

while the lens is focusing, right?

[brian_wallace5]

<p>Absolutely it changes - and it should. Any variable aperture lens will change the aperture as it zooms if the previous setting is too low for a given focal length. For example:<br>

On this lens if its zoomed to 35mm you can set the aperture to 4.0. As you zoom out though the camera will automatically change the aperture to 4.5, 5.0, and finally 5.6 as you zoom to 80mm. <br>

In short, there's nothing wrong with the lens if this is the behavior the buyer experienced. Now, if it's set to 5.6 it should not change at all. </p>

[Robin Smith]

<p>Oh dear. It's f4 at the wide end and f5.6 at the long end. There is no way to get around this. Your buyer has no idea what he is talking about. As one zooms in, the max aperture will <em>of course</em> decrease from f4 to f5.6. That is how the lens is designed.</p>

<p>This is one of the many reasons why I steer clear of selling anything on ebay - purchasers who are profoundly ignorant.</p>

[Marcus Ian]

<p>The camera also remembers if (in Av) your 'chosen' aperture is wider than the max available 'now' (at the new point in zoom), so if you have aperture set to f4 zoomed out, zooming it in results in f5.6. Zooming it back out should result in f4 again.<br>

If, OTOH, while zoomed you change the f to say f7.1, then, even if you zoom back out, the f stop will remain the same.</p>

[PuppyDigs]

<p>Leslie, your lens is working perfectly and exactly as posters described. However, your buyer is defective! Now he'll need to spend the big bucks for a constant aperture zoom like the EF 24-70 2.8L USM (they only come in L flavors!). I suffer from that very same problem and the only cure is a large credit limit. Perhaps next time you'll need to write it up as a variable aperture zoom and detail how the max aperture works as you zoom.</p>