Re: [APML] Petzval hot spot?

[mschex@verizon.net]

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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