...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
>
> -----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
> > >
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> >
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