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Author Topic: So Sigma, f2.8 or not?  (Read 1171 times)

Justinr

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So Sigma, f2.8 or not?
« on: September 05, 2010, 08:04:45 am »

A used Pentax mount Sigma 24-135 f2.8 - 4.5 recently came into my hands which I thought might be worth hanging on to as a quick lens for interior work.

Having tried it out this morning I am somewhat puzzled by its performance and operation. Besides the normal zoom and focussing rings there is a third aperture ring with the stop settings marked upon it from 2.8 - 32 and then A which I assume means auto, allowing the body to decide aperture setting.

The problem I have is that when on auto the camera only stops down to f4 and if I switch to manual and stop it down to an f2.8 on the ring the camera does not display any setting (either during shooting or during playback) nor does the resultant image look any different from the f4 auto shot, the histograms being more or less identical. So does this lens open up to f2.8 or not? I don't think that it does but it may well be me doing something wrong and not using it correctly. I have no manual or instructions with it and it appears that there are no downloads on Sigma's site. I am using a Pentax K10 and lens was set to shortest focal length.

Am I missing something obvious? Probably, so if anyone can put me out of my misery it would be appreciated.


Edit. I've been playing with it some more and it appears to have AF focussing issues as well so I think it will be going back whence it came.
« Last Edit: September 06, 2010, 05:29:53 am by Justinr »
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kpmedia

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Re: So Sigma, f2.8 or not?
« Reply #1 on: September 06, 2010, 08:17:48 am »

It's only 2.8 at 24mm. It's 4.5 by the time it hits the 135mm mark.
I don't know enough about the modern Pentax mount to give any further information.

I can put my camera in auto mode, and it never chooses low apertures. So that's not telling you much.
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Long time Nikon user. Currently using D200 + D3s for sports photography.

Justinr

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Re: So Sigma, f2.8 or not?
« Reply #2 on: September 06, 2010, 11:37:59 am »

Sadly it doesn't appear to be f2.8 anywhere at all and it won't AF at maximum zoom either, it 'hunts' rather than settles but this is easily overcome by backing off ever so slightly.
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