Re: [APML] Petzval hot spot?

["Philipp Salzgeber" <philipp@salzgeber.at>]

Hi Mike,

I read Mr. Christen´s reply, but my question, if Vixen´s DED 108 has a similar "problem" still remains. The layout´s
look quite similar. Televues NP101 is also a Petzval type refractor - how did Uncle Al solve the problem?

center filters for battling vignetting are also commonly used for wide-angle large format lenses (Schneider
Super-Angulon, etc.) even the 30mm for the Hasselblad XPan has one.


with best regards

Philipp Salzgeber

----- Original Message -----
From: <mschex@verizon.net>
To: <astro-photo@seds.org>
Sent: Wednesday, September 18, 2002 5:33 PM
Subject: Re: [APML] Petzval hot spot?


> Please see the earlier message from Roland Christen.  This issue has been discussed before on this list -- you can
search for FSQ in the AMPL archives.  The Petzval design has uneven illumination at the edge of the field -- this is the
compromise made for the flat field.  As Roland said, it would be silly and expensive to put a 127mm objective on a 106mm
refractor just to get a fully illuminated 90mm image circle.  The problem can be corrected for in software quite easily
because there is exactly the same amount of exposure falloff every time.
>
> The FSQ is an excellent telescope with a *very* flat field, this "hotspot" issue just keeps coming up because people
are unfamiliar with the Petzval design.  For 35mm or CCD work you never even see the problem becaue you never use the
edge of the field.  The famous old Kodak Aero-Ektar lenses have a similar issue. ( Roland -- do you know if they used a
Petzval configuration? )  They solved the problem by placing a radial gradient filter on the front of the objective.
>
> Mike Schexnaydre
>
> >
> > From: "TEIVA LEROI" <leroiteiva@minitel.net>
> > Date: 2002/09/18 Wed AM 10:45:58 EDT
> > To: <astro-photo@seds.org>
> > Subject: Re: [APML] Petzval hot spot?
> >
> > Hello Philipp,
> > what do you mean by "Hot spot"??
> > teiva
> > http://www.astrosurf.com/leroi
> >
> >
> >
> > >The FSQ-106 and Vixen´s DED 108 have a very similar design:
> > >http://www.vixenamerica.com/images/In_Database/
> > DED108SS_schematic_w530px.gif
> > >http://www.optique-unterlinden.com/sch_fsq.gif
> > >
> > >Has the DED a similar hot spot? If not, it would seems to be more of an
> >  engineering problem, not a design problem...
> > >
> > >with best regards
> > >
> > >Philipp Salzgeber
> > >
> > >
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