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07-20-2010, 01:25 AM   #1
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canon 55mm F1.2

Hi everyone,i happen to found this lens on market place and was told that i need a adaptor to use on pentax dslr and he was saying that there is a glass element for correction of infinity focus, the IQ will be degraded a little. Without the glass element, there is no degradation, but there is no infinity focus.what does he mean by no infinity focus?should i just find a pentax lens 50mm f1.2 instead?need some advice and opinion..thank

07-20-2010, 01:29 AM   #2
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Have a look at here I don't think such adapter exists

get a Pentax 50/1.2 if you really want one f/1.2 lens.
07-20-2010, 06:34 AM   #3
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Infinity focus means that a lens on a camera can focus all the way to infinity. Every lens has a certain working distance, called the register -- this is the distance from the front of the lens, to the sensor or film plane. A long-register lens (like a Pentax or Nikon) placed on a shorter-register camera mount (like a Canon or Leica) can use bare extension tubes to be able to focus to infinity. A short-register lens placed on a longer-register camera mount needs an adapter with an optical element, basically a teleconverter, to change its focus point.

Canon-to-Pentax optical adapters exist, starting at about US$30 on eBay. I have not used such an adapter, although I might buy one just to see. I have read that the optics will degrade a lens' images, but I don't know how badly. Such adapters force totally manual operation -- automatic aperture and focus will not work. I suspect that using such an adapter with a 'special' lens will interfere with the very qualities that make that lens 'special'. Still, if a f/1.2 Canon lens costs US$200 less than a f/1.2 Pentax lens (because there is no demand for old Canon lenses) then an adapter might be practical.
07-20-2010, 09:11 AM   #4
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For the purposes of photography, infinity might mean anything further than 50-100 feet or so (depends on the lens & aperture). An adapter that doens't allow infinity focus means you can only focus on things close than that. In other words, you'll have wasted a lot of money. In general, no, don't go buying Canon lenses and hope to use them on a Pentax.

07-20-2010, 09:25 AM   #5
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Also keep in mind that with the adapter it will no longer be a f/1.2 lens. The adapter works like a 1.42x multiplier and adds at least 1.5 stops.
07-22-2010, 05:02 AM   #6
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QuoteOriginally posted by edd1388 Quote
Without the glass element, there is no degradation, but there is no infinity focus.what does he mean by no infinity focus?should i just find a pentax lens 50mm f1.2 instead?need some advice and opinion..thank[/I]
I say you'd only be able to focus maybe 1 meter or less, because without the glass elements you just add extra space between the lens and the sensor.

I'm not by any means recommending you to do this, but I have modified this lens and use it with my K20D. I removed the FL mount and glued a M42 flange adapter instead. This way I think I've reduced the distance to the sensor for 1 or 1.5 millimeter (FL mount is slightly thicker than the M42 adapter), but this is still not enough to get infinity focus. I can only focus up to 3 meter away. Since you're adding more distance with the hollow adapter, that means even closer max focus distance. 1 meter is just my guess. And 1 meter is not enough for portrait IMO.

So my point is, I don't think using it with glass-less adapter is very useful. Just get an actual Pentax 1.2 or Chinon 1.2

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