>"Robert P. VanNatta" wrote:
>>
>> I've lately acquired a 300 mm F2.8 A* big glass
>
> If I read the materials correctly 300mm
>> is sort of the breaking point between whether you should use an "S" or "L"
>> converter. Someone know which works best with this lens/focal length?
>
The Pentax XL convertors have a long snout which extends into the lens
it's connected to. So they won't physically fit every Pentax lens,
because the snout contacts the rear element of many lenses.
The XL teleconverters fit 300/2.8 and longer lenses, at least from the
A series and later. The XL convertors won't fit, for example, any of
the 300/4.5 models. Also, one cannot connect a 1.4 XL and a 2.0 XL
together without putting a thin extension tube between the two.
I believe the main advantage of XL teleconverters is a reduction in
light fall-off in the corners compared to teleconverters without the
long snout. The secondary advantage of XL teleconverters is optimized
image quality for their compatible lenses.
--
Happy Trails,
Texdance
http://members.fortunecity.com/texdance
http://members1.clubphoto.com/john8202
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