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01-22-2011, 04:08 PM   #1
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Sigma lens aperture help

I am borrowing a Sigma 28-80 1:3.5-5.6 Macro lens to play with on my KX.

The question I have is about the aperture settings. The aperture ring on the lens ranges from 3.5 - 22 and has an A setting.

I'm fairly confused, as when I set it to A I am only able to set it to 4.5 in camera, not 3.5, and it will go all the way to f40 the other way. Why is this?

Also, when I try to set the aperture manually (physically turn the ring) the EXIf data only ever reads it as f4.5, the aperture is definitely changing, but the camera doesn't seem to record this

I have set the camera to allow the shutter to release when the aperture ring is not set to A.

Also, looking on the forum lens reviews the closest I could find to this lens is this one. It looks exactly the same, except that the numbers on the rings seem to be going in the opposite direction. I'm pretty sure it's the same lens, but I'm not sure, which leaves me uncertain of the quality.

Which leads me to my next question.... do I need this lens?

I have the kit 18-55, and the kit 50-200, both of this lenses cover the range of the SIGMA, I'm not sure if the fact that these lesnes are 4.5 and the sigma is 3.5 will make any difference?

Perhaps as a walk around the slightly longer zoom and slightly less wide angle makes it a bit more versatile.

Thanks for any help/suggestions.

edit: one more question, what do the markings in the middle mean? 22 R | 8 22 22'|'22 W T


Last edited by paul cliff; 01-22-2011 at 04:14 PM.
01-22-2011, 04:20 PM   #2
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To use the aperture ring you need to set custom menu 22 Using Aperture Ring to Permitted. As for the reported aperture being wrong, it's probably a dirty contact.

I have the "Identical Twin Cousin" the Quantaray 28-90 f3.5-5.6. Not as good a lens as the kit.

If you like the focal range the FA 28-80 f/3.5-5.6 is arguably a better lens.

SMC Pentax-FA 28-80mm F3.5-5.6 AL Lens Reviews - Pentax Lens Reviews & Pentax Lens Database

The markings are the DOF scale.
Lens DOF scale
01-23-2011, 04:44 PM   #3
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thanks for the info, I think there is a contact issue, sometimes I'm able to set it to f4.5-40, and sometimes its will be 3.5-22.

The connections all look clean so I don't know why this might be.

When I get a chance I'll go for a walk with it and give it a proper try out.
01-23-2011, 06:19 PM   #4
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QuoteOriginally posted by paul cliff Quote
thanks for the info, I think there is a contact issue, sometimes I'm able to set it to f4.5-40, and sometimes its will be 3.5-22.

The connections all look clean so I don't know why this might be.

When I get a chance I'll go for a walk with it and give it a proper try out.
This happens with your kit lens too. Zoom to 18mm, and you can set it to f3.5. Turn the zoom ring a little while the display is still active and it changes to f4. At the 55mm end you can only set f5.6. If your Sigma is an autofocus lens, that's the most likely explanation. With Sigma, there's also a random element of incompatibility, since they reverse-engineer the mount, not license it from Pentax.

01-24-2011, 10:54 AM   #5
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QuoteOriginally posted by Just1MoreDave Quote
This happens with your kit lens too. Zoom to 18mm, and you can set it to f3.5. Turn the zoom ring a little while the display is still active and it changes to f4. At the 55mm end you can only set f5.6. If your Sigma is an autofocus lens, that's the most likely explanation. With Sigma, there's also a random element of incompatibility, since they reverse-engineer the mount, not license it from Pentax.
Thanks for the info, so does that go for all AF lenses then? the lowest f stop will only be available when it's at its widest angle?
01-24-2011, 01:02 PM   #6
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QuoteOriginally posted by paul cliff Quote
Thanks for the info, so does that go for all AF lenses then? the lowest f stop will only be available when it's at its widest angle?
Only for variable aperture lenses. Consumer zoom lenses are usually variable aperture to keep the cost down. For example the DA 18-55 f/3.5-5.6. Higher quality zooms with a non-variable aperture cost a bit more.

For example the DA 16-45 f/4.

SMC Pentax-DA 16-45mm F4 Lens Reviews - Pentax Lens Reviews & Pentax Lens Database
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