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Pentax A*300mm (1 Viewer)


Well-known member
I've just aquired the "almost" legendary A*300mm f4 weighing in at just 850grams and only 132mm long this is one awfully compact lens given its focal length.

This lens could be anything from 22-27 years old but aside from the lack of AF it works a treat, took it down to Fairburn Ings today to try it out on our feathered friends and I have to say I am quite impressed, now all I need to do is learn how to focus manually again|:d|

Sample shot, this is a crop of roughly 1/4 the original frame size.


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Well-known member
A delightful shot. That A* is the lightest 300mm and a wonderful piece of lens. Try 'catch-in focus'- it sure is likely to make life simpler. there are a no. of 'catch in focus' or 'focus trap' threads on pentaxforums and dpreview.


Well-known member
I have been using Catch in focus but so far have not got it mastered, I prefer to manual focus where I know something will land then rely on the DoF to make up for discrepancies, obviously I need days with good light in order to stop down to f11 or even f16

This lens has a very long throw on the focus ring and you seem to be turning it forever, by the time you've reached focus and the shutter has fired the critters have flown off, I will persevere with it though.


Well-known member
Here's A*300/4 with a couple of vivitar 2x TC's that I removed the glass from
to use as extension tubes from about 7 meters.About maximum focus with
that much extension.Contacts for lens info on one TC is a gummed up,
need to tear it down and clean it. This spring,my hummingbird rig will be
"old faithul"(A*300/4) and 50mm to 75mm of extension. Deadly!
BTW... Canon L glass and pentax * glass are from same slugs.


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Well-known member
Lovely shot Spider ! Great piece of glass. Very sharp though the bokeh is a little busy in that one. Personally I don't think CIF works too well when birding because the shutter drops whenever anything comes into focus (branches, twigs, leaves etc.), of course even with AF you are often better off manual focusing so I don't think you are going to lose out much to an AF lens, as you first foray has shown !

BB - sharp indeed. Can you explain what you mean by Canon L and PEntax come from the same 'slugs' ? Thanks !


Well-known member
Essentially same raw silica component.Production methods,coatings, etc then defining
proprietary characteristics of piece. Both are absolute marvels of optical technology.

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