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12-28-2011, 11:38 AM   #1
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No TC with Sigma 70-200 OS version

I was looking at the Sigma 70-200 OS HSM lens and noticed that it says you can't use any TC with it, where as the standard none OS version says you can use one.

I have a brand new, (well maybe tried it on a lens years ago) Pentax 1.7x TC, and was wondering if any had tried it on one of the Sigma OS HSM versions of this lens.

I am thinking that the 70-200mm will meet most of my needs with the 2.8, and adding the TC would help if I needed a bit more range.
Thanks, Jeff

12-28-2011, 12:06 PM   #2
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The Pentax F converter should work as it's got its own focusing mechanism, whereas there is no sdm-compatible converter currently out there that can use the lens's native system.
12-28-2011, 12:23 PM   #3
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There was a whole discussion on the subject just yesterday...Here you go!

https://www.pentaxforums.com/forums/general-technical-troubleshooting/169696-...need-help.html
12-28-2011, 01:26 PM   #4
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I read this, but it still didn't totally answer my question as to why the one Sigma Lens (not TC) says it will work with a TC and the more expensive version with OS says it won't, or they make a point of saying it won't.

Are they just going on aftermarket TCs, or would a true Pentax 1.7x one work. I can see it making it slower, but to me it looks like it would still work, but hunt more. Just trying to find someone that had tried this with this particular lens before putting the money down for it.
Thanks, Jeff

12-28-2011, 02:55 PM   #5
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The sigma TC won't autofocus because the Sigma TC in pentax mount has screwdrive focus (driven by the camera body), not the HSM focus (which is a motor built into the lens) which your lens has. Don't bother reading up on Sigma's website, it is confusing as hell, and retailers will just list whatever marketing details they get from sigma, so they are also no help. The 1.7x Pentax TC has its' own built in focus (although it is a limited range), so it can focus with any lens you put on it (including older fully manual lenses). As outlined in the thread I linked to, the tamron PZ-AF teleconverters will focus with Sigma's HSM because it has the proper contacts to power the HSM motor.

Edit: there are no new Pentax 1.7x teleconverters - you'll be buying used whether you buy the pentax or the tamron teleconverters - the Pentax 1.7x will probably be just about double the price (over $400) of the tamron 1.4x ($200-250) on the used market. Unfortunately none of these are made new any more.
12-28-2011, 05:08 PM   #6
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The reason I was asking this is because I have a TRUE Pentax 1.7x TC that I bought years ago, and only tried it on one or two lens I had, and it worked fine on both Auto and manual lens. Never really used it, so it is basically new/used, still have all the paper work, boxes etc, and it has lived its life in a waterproof pelican case sealed up.

I know they were worth more back when I bought it, then 4 or 5 years ago they were really hard to find, and not many companies were making much more then a TC, without the focus, or drive contacts in them. Seems there are a lot today, but have not messed with any of them.

My basic question was just will that Sigma 70-200 HSM OS lens, not the bare bones HSM model work well at all with the TRUE Pentax 1.7x TC. Just wondering if any had tried the combo together.

I wasn't planning on buying any new TC, just a newer lens, and figured with something that is F2.8 that maybe I could get by with adding a good, (and from what all I remember) the true Pentax one was about as good as you could get.
12-28-2011, 05:30 PM   #7
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QuoteOriginally posted by jfischer Quote
My basic question was just will that Sigma 70-200 HSM OS lens, not the bare bones HSM model work well at all with the TRUE Pentax 1.7x TC. Just wondering if any had tried the combo together.
The Pentax 1.7x AF-A will work with any lens. It doesn't matter if it's screw-driven, SDM, HSM or manual focus. All of the auto focusing takes place inside the 1.7x AF-A itself. You will have to manually focuses in the ballpark, and then you can engage the 1.7x AF-A to take you the rest of the way and lock focus. If your target it pretty much at a constant distance away, you won't need to adjust the focus ring of the lens very much. The AF-A focuses pretty quickly, often quicker than the lens alone.

One downside (in addition to needing to pre-focus) is that the AF-A doesn't transmit focal length (then again, no Pentax TC's do as far as I know), so you won't be able to optimally use SR. You'll have to enter a focal length manually when you attached the lens, and depending on if you plan on zooming a lot or using it at lens at it's maximum focal length will dictate what focal length you enter when you attach the lens.
12-28-2011, 06:01 PM   #8
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Thanks for the fast reply.

That is why I was looking at the Sigma HSM OS, as it has the Stabilization built into the lens, with 2 different modes. That way I thought I could turn it off in the camera, and rely on the lens to be doing the stabilization of things.

I wonder what it will do with the faster motor in the lens, trying to focus on things?

Trying to look for a lens, faster then Pentax line, but still be able to get a little more out of it if I need it. Hate to carry a ton of primes around, and with what I am going to be shooting, there are times that things will be coming close to me, and a standard 200 or 300 I think would be to much, and would need to go down in size some, and why I was looking at the 70-200. I have a 70-300 Tamron now, but it is WAY to slow at any kind of focus, and wants to hunt a lot, but that is due to it being a cheaper lens, and figured with a F2.8 I could stop it down some, and still get some sharpness out of it, and if it is in the sunlight, one or two stops might not hurt.

12-28-2011, 06:12 PM   #9
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QuoteOriginally posted by jfischer Quote
Thanks for the fast reply.

That is why I was looking at the Sigma HSM OS, as it has the Stabilization built into the lens, with 2 different modes. That way I thought I could turn it off in the camera, and rely on the lens to be doing the stabilization of things.

I wonder what it will do with the faster motor in the lens, trying to focus on things?

Trying to look for a lens, faster then Pentax line, but still be able to get a little more out of it if I need it. Hate to carry a ton of primes around, and with what I am going to be shooting, there are times that things will be coming close to me, and a standard 200 or 300 I think would be to much, and would need to go down in size some, and why I was looking at the 70-200. I have a 70-300 Tamron now, but it is WAY to slow at any kind of focus, and wants to hunt a lot, but that is due to it being a cheaper lens, and figured with a F2.8 I could stop it down some, and still get some sharpness out of it, and if it is in the sunlight, one or two stops might not hurt.
A couple of things to be aware of.

1) I'm not certain how the built-in OS would work with the 1.7x AF-A in between the lens and body. Certainly the lens wouldn't be aware that there is a TC there, and I just have no idea how that might affect things. I've never used a lens with built-in OS in conjunction with the 1.7x AF-A (or on a Pentax body at all now that I think about it).

2) The faster motor (HSM) in the lens becomes irrelevant with the 1.7x AF-A attached as it won't actually function with the TC attached. Only the screw-driven focusing inside the AF-A will work.

As a side note, although they're no longer made and hard to find, the Sigma 100-300/4 is worth considering if you want a fast zoom with more reach than a 70-200/2.8.
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