Originally posted by Zafar Iqbal Aren't the kit lenses for K-r the same as for K-x? Mine interchange perfectly fine. Just tried it
Yes you're correct in saying that both cameras use the same kit lenses, and that both being 52mm filter head the hoods will interchange (I presume), but it's the 2 lenses under discussion here that are significantly different to each other.
Problem is if they do interchange, then it's a potential trap for the (unsuspecting) user. Pentax really should design so that they won't fit on another lens that is unsuitable to the hood's size and shape.
Please read the prior post by
jolepp, and I suggest that you interpret the word "longest" in his first paragraph to be "shortest", or "widest".
The crux of the issue is called vignetting.
Ref:
Vignetting - Wikipedia, the free encyclopedia
In this instance, the 18-55 is a wide-to-normal view zoom lens therefore it requires extra view clearance unobstructed by a lens hood, to cater for its wider field of view capability. Zoomed down to 18mm that is 76° wide, v's a much narrower 29° when zoomed right up to 55mm.
Therefore it uses a petal shaped hood (PH-RB
A type) so the cutouts don't interfere.
Conversely, the 50-200 is a normal-to-telephoto range lens which at its widest only has 31.5° minimum width of view at 50mm (down to 8.1° at its max 200mm), so it can get away with a hood that shrouds the front glass elements a lot more.
With that fairly narrow 31.5° at its widest zoom point of 50mm, the hood for it doesn't need cutouts. And the PH-RB
B type can be designed to give that bit more shielding against unwanted stray light. But if you put that same RBB hood on the 18-55 it would surely vignette the wide[r] view.
Hope that makes sense.
.R. -- Vignette, the black hole in reverse.
Last edited by Hypocorism; 03-28-2011 at 04:14 AM.