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
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Fabio Fiorellato
Sent: 14 July 2006 09:33
To: olympus@xxxxxxxxxx
Subject: [OM] Re: Tamron 350/5.6 cat
Just a little additions and a few pondered thoughts:
Concerning the DOF, for a 300mm lens on a 35mm frame, it turns out that you
have to focus on a subject set at least at 10m before getting 1m of DOF at
f/16.
If you look at the donut highlights in the background you can see that they
progressively get less 'blurred' as you stop down the lens. Their size, and
the size of the black center circle, however, doesn't change with the
f/stop.
This leads me to think that the lens should have a diaphragm or the like of
it.
Other opinons are welcome
Ciao!
Fabio
On 7/14/06, Fabio Fiorellato <flowerside@xxxxxxxxx> wrote:
>
> I had the same feelings.
>
> It's undoubtable that the donut-shaped bokeh is a real cr*p.
>
> Anyhow - if my eyes aren't fooling me - I can see small DOF
> differences in the test shots. Maybe the not-so-prononuced DOF
> differences are a consequence of the tester being very near to the focused
subject?
>
> After all we're talking about a 300mm lens which is supposed not to
> have a huge DOF especially at short distances.
>
> Of course, these are just my humble suppositions: I too was wondering
> about how could it be possible to build a variable-aperture CAT...
>
> Ciao!
>
> Fabio
>
> On 7/14/06, Moose <olymoose@xxxxxxxxx> wrote:
>
> > Fabio Fiorellato wrote:
> > > What about this CAT?
> > >
> > > [ http://homepage3.nifty.com/3rdpartylens-om/ohnar300.htm ]
> > >
> > > and
> > >
> > > [
> > http://homepage3.nifty.com/3rdpartylens-om/Lens%20Test/ohnar300test.
> > htm]
> > >
> > > So far, it's the only one I know with variable aperture!
> > Doesn't look like it's really variable aperture. Looks more like it
> > may have built in neutral density filters, convenient, but not at
> > all the same thing. The reason I say that is that the DOF doesn't
> > change from
> > f5.6 to f16. With a true aperture change, the DOF would change a
> > great deal over that range.
> >
> > We've had discussions about whether, and how, variable aperture with
> > a mirror lens might be possible. Looks like nobody has yet figured
> > it out. :-)
> >
> > Still has that donut bokeh, particularly awful in the demo shots.
> >
> > Moose
> >
> > ==============================================
> > List usage info: http://www.zuikoholic.com
> > List nannies: olympusadmin@xxxxxxxxxx
> > ==============================================
> >
>
>
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