[Aavso-photometry] In defense of the ST-9 & CCD choice Considerations - CORRECTION

[Tim Crawford]

Wolfgang just sent me the following email pointing
some foo-paws I made in the original email.... his
explanation should clear up the confusion RE the fact
that I did use arsec/pixel in several places where I
should have only used pixels.

My apologies and hope I did not confuse to many
folks.... another example senior moments... ;  ).

Thanks Wofgang.... 

Ad Astra  
Tim

"Wolfgang Renz" <w_renz at onlinehome.de>

Hi Tim

Just a note.
You use arcsec/pixel sometimes instead of pixel.

> With my local seeing of 3.5-5.5 arcsec/pixel with
the
> ST-7 or ST-8 then seeing would be spread out over
5.6
> arcsec/pixel to 8.9 arcsec/pixels.  This would be
way
> outside the range of 2-3 arcsec/pixel. (Seeing
divided
> by image scale of .62 arcsec/pixel).

should read:

With my local seeing of 3.5-5.5 arcsec/pixel with the
ST-7 or ST-8 then seeing would be spread out over 5.6
pixel to 8.9 pixels.  This would be way
outside the range of 2-3 pixel. (Seeing divided
by image scale of .62 arcsec/pixel).

and:

> If I were to use a Focal Reducer and take the system
> to f/6.3 then both the ST-7 and the ST-8 would
provide
> an image scale of .98 arcsec/pixel with seeing then
> spread out over 3.6-5.6 arcsec/pixels.  There again,
> closer to the desired range of 2-3 arcsec/pixel but
> still outside that range, although not a bad
> compromise. However, in the case of the ST-8 I would
> have to spend 60 percent more money to have this
“not
> a bad compromise” match.

should read:

If I were to use a Focal Reducer and take the system
to f/6.3 then both the ST-7 and the ST-8 would provide
an image scale of .98 arcsec/pixel with seeing then
spread out over 3.6-5.6 pixels.  There again,
closer to the desired range of 2-3 pixel but
still outside that range, although not a bad
compromise. However, in the case of the ST-8 I would
have to spend 60 percent more money to have this “not
a bad compromise” match.

Clear skies
 Wolfgang

--
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO