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07-16-2011, 01:00 AM   #1
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Please explain telephoto 'power' aps vs ff lens

Ok hope someone can help me with become a bit smarter here. At the moment I want to upgrade from my kit lens, and buy a fast zoom for sports picks of the kids.

So I look around and decide I need something in the 70-200mm range, I am looking at the Sigma 70-200mm f2.8 APO EX DG... now when I look at the pentax range I dont see anything similar, but if I look at the FOV spec it seems the D* 50-135mm f2.8 has about the same FOV ,give or take, as the Sigma... Am I right to believe that in terms of telephoto 'power' these lenses on my K-r are much the same as there FOV is much the same, ie I can 'zoom in' just as close (all else being equal) with either lens?

Now I'm only new to all this so be gentle if I have this all wrong... but is that right??

07-16-2011, 01:19 AM   #2
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The 50-135 is not going to give you the same pulling power as the 70-200, despite the angles of view mentioned in the specifications.
The Sigma is a full frame lens, and the angle of view is given for a full-size sensor. When used in a APS-C camera like Pentax, you will only be using some 2/3 of the given angle of view. In case of the Pentax the angle of view given is for a APS-C size sensor.
Therefore with a similar sensor the Sigma will have a smaller angle of view at the long end.
They could have stated this more clearly in the specifications though...

Last edited by PePe; 07-16-2011 at 01:39 AM.
07-16-2011, 10:24 AM   #3
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In other words, if you will use the DA*50-135 on K-r and the Sigma on Pentax film SLR or CaNiSon FF cameras then you'll have the same FOV. But if you put the Sigma on K-r the you'll see the same as with 100-300 on film/FF camera...
07-16-2011, 11:02 AM   #4
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You may find this recent thread of use.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/151339-why-han...rry-overs.html

H2

07-16-2011, 11:33 AM   #5
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QuoteOriginally posted by Robboa Quote
Ok hope someone can help me with become a bit smarter here. At the moment I want to upgrade from my kit lens, and buy a fast zoom for sports picks of the kids.

So I look around and decide I need something in the 70-200mm range, I am looking at the Sigma 70-200mm f2.8 APO EX DG... now when I look at the pentax range I dont see anything similar, but if I look at the FOV spec it seems the D* 50-135mm f2.8 has about the same FOV ,give or take, as the Sigma... Am I right to believe that in terms of telephoto 'power' these lenses on my K-r are much the same as there FOV is much the same, ie I can 'zoom in' just as close (all else being equal) with either lens?

Now I'm only new to all this so be gentle if I have this all wrong... but is that right??
The answers already posted are spot-on, but I'll make it real simple: whatever the focal lengths of the lens, that's it. Don't worry about "crop factor" or anything like that. They are all the same for your camera.

As far as a 70-200ish lens... Pentax has the 60-250 f/4, which is a stop slower but has more range. And, of course, folks get outstanding outdoor sports pics with the plain ol' Pentax 55-300, or even the Tamron & Sigma 70-300's. In many cases, skill>lens.
07-16-2011, 10:12 PM   #6
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Thanks folks... yep I think I've got it now...

Your right luftfluss the FL is the only variable so effects the FOV on my camera and is all I should worry about. The confusing bit is when I looked at the manufacturer specs, and saw the same FOV's reported... but of course for the Pentax that is for an APS-C and the Sigma for a FF, hence as PePe says at the long end of the Sigma on my camera its actually a narrower FOV than is shown the specs... got it!

Means, they are NOT equal and I need to decide if I want the extra pulling power of Sigma... thx
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