[Clem Nichols]

I've been taking some sample shots with a recently purchases Sigma 17-70 lens. I've noticed that I'm unable to obtain a wider aperature than 3.5 despite the fact that the lens is supposed to open up to 2.8. Any suggestions other than sending the lens back to the seller or to Sigma? Thanks.

[pschlute]

Apologies if you know this already, but i think you will find that f2.8 is only possible at 17mm zoom. As you zoom in the minimum aperture will get slower.

[egordon99]

That's why it's called the "Sigma 17-70mm f/2.8-4.5", note the "f/2.8-4.5" part At 17mm, you can open up to f/2.8, but at 70mm, the maximum aperture is f/4.5

If you want f/2.8 throughout the entire zoom range, you need to buy the Sigma 18-50mm f/2.8 and/or the Sigma/Tamron 24/28-70/75mm f/2.8...

[Clem Nichols]

I'm aware of the fact that I'm only supposed to get 2.8 at 17mm. The problem is that the camera will only show a maximum aperature of 3.5 at 17 mm. (At 70mm I get 4.5 just as I'm supposed to.) I don't have any faster lenses to put on my K10D, so I'm wondering if the problem is with the lens or with the aperature indicator on my camera???

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Last edited by Clem Nichols; 05-11-2007 at 11:43 AM. Reason: Additional info

[kskjon]

Sounds like a problem with your lens.

[calicojack]

Make sure you're not in the MTF mode. I just checked my 17-70 which I have set in P & MTF and the max aperture shows as F4.0. I can turn the dial to get 2.8, or if I put it back in straight P mode it goes to 2.8 fine.
Brian

[Clem Nichols]

No luck! Nothing seems to work. There seems to be nothing mechanically wrong with the aperature blades in the lens, as they open fully to 4.5 at f70. It's too bad there's no one close with another Pentax camera I could check the lens on or a faster lens I could check on my camera. That should certainly tell me if the problem is with the lens or the aperature indicator on my K10D.

[KennJ]

If there is a camera store near you that deals in Pentax cameras you may be able to check your camera with another lens they carry in stock or try your lens on a store camera.
I hope you get the problem figured out soon.Best of luck .
Kenn

[slip]

this sounds to simple and you might have already tried it but take the lens off and put it back on. my camera was acting weird with my sigma flash one day and I did this and it seemed to clear up the problem.

randy

[Clem Nichols]

Already tried removing and replacing the lens to no avail. Thanks anyway.