Although the aperture may be marked f8, f11, and f16 the reality is that the
diameter of the lens opening is significantly larger since the center
obstruction limits how small the diameter can be. Hadn't thought about this
before. Probably the CAT lenses have less DOF than a conventional lens
having the same claimed f-stop.
There was a very fast fairly long Sigma cat that used the lens cap to stop
down the aperture. I've only seen one offered for sale. It was at Adorama
several years ago and had a price tag of very roughly $1000.
-jeff
----Original Message Follows----
From: "Fabio Fiorellato" <flowerside@xxxxxxxxx>
...and what a diaphragm, indeed! :)
The strange thing is that the donut shapes doesn't seem to change (while
they were supposed to) and their resolution seems to improve by reducing the
aperture...
Anyhow I'm still of the opinion that there still is a (rather unperceptible,
I do admit) impact on the DOF by stopping down the lens, judging by the test
images. Maybe the 300mm focal length and the mirror design don't help at
getting a more pronounced effect, who knows.
At least it seems that someone has found a way to build variable aperture
mirror lenses (and we all have seen with what results! :)
Thanks for the additions!
Ciao
Fabio
On 7/14/06, Piers Hemy <piers@xxxxxxxx> wrote:
>
>
> Machine Translation of the page and clicking the link at the bottom of
the
> page will help here, Fabio. The link is to a further image which indeed
> does show a diaphragm mechanism which would change the physical siz of
the
> lens aperture, and thus change the characteristics of the
bokeh-doughnuts.
> But interpreting a machine translation of the page (you can get one by
> navigating to the site homepgae, then clicking the English buttom
> top-right
> - sorry, no Italian) reveals that the author did not find any impact on
> DoF
> from changing the aperture, it's just like having a variable ND filter.
>
> Thanks for the original link!
>
> --
> Piers
>
==============================================
List usage info: http://www.zuikoholic.com
List nannies: olympusadmin@xxxxxxxxxx
==============================================
|