It's not impossible to put a diaphragm in there, just mechanically
difficult.
Chuck Norcutt
Fabio Fiorellato wrote:
> 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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