doublers

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astraman1

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328
Name
nick
Edit My Images
Yes
ive a pentax k100d super and im starting to get into the wildlife photography abit my biggest lens is a sigma apo 70 - 300 and im sometimes finding i could do with abit more ive found a doubler on ebay..
http://www.ebay.co.uk/itm/X2-2X-AF-...02862760?pt=Camera_Lenses&hash=item1e688988a8

this should turn it into a 140 - 600 lens if im correct are these anygood to use or do you lose quality in the picture or anything i should be aware of

any help much appreciated
 
Hi Nick.

Tele converters can work very well as long as you use a decent lens.

First off make sure that your Sigma can take a converter as not all can. You can find out via the Sigma website.

Secondly, remember that a 2x converter will raise the lens aperture by 4 stops which can make them really slow.

Hope this helps.

Andy
 
Keebsuk said:
Secondly, remember that a 2x converter will raise the lens aperture by 4 stops which can make them really slow.
Click to expand...
A 1.4x converter slows the lens 1 stop, a 2x converter slows it 2 stops (not 4).
 
Keebsuk said:
Ops my bad. Thanks for that!
Click to expand...
No probs. It's easy when you think about the physics. Take a 400mm f4 lens, wide open. Then its aperture will be 100mm (400/4 = 100). Now put a 2x converter on it and it becomes an 800mm lens (2x converter) but the aperture still stays the same (100mm). So now it is an f8 lens (800mm focal, 100mm aperture). Can be used with any TC...
 
With Canon camera's they will auto focus with a maximum slowest lens of f/5.6. Meaning if I have a f2.8 lens I can use a 2x converter and still retain AF, and an f4 will take a 1.4x converter and retain AF. I don't know what the limit is with Pentax but you really should find out before you get a converter. However I recently bought a Kenko DGX 1.4x converter and even with the 100-400 f4-5.6 L IS it still retains AF even though the converter takes it to f8, although I don't think Kenko converters will fit the Pentax mount.
 
I would only use a 2x converter on a f2.8 lens and a 1.4x on f4 or faster (obviously there are a couple of exceptions). The 70-300mm Sigma is basically a consumer grade zoom .. yes you will get 600mm but the quality will be disappointing at best.

Just my opinion but having been through exactly the same thing when I first started you quickly find out that there is rarely a cheap fix where image quality is the main goal.
 
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