Re: [APML]: Coma correctors

[sdilling@ford.com (Stephen Dillinger)]

> It's a simple design that has one major problem; it intruduces spherical
> aberration which blotes the images slightly. However it is not too serious
> and it provides uniform spot sizes over the 35mm format. One might see the
> difference on tech pan in good seeing.

In other words, it would be adequate for color film but show it's flaws with
tech pan or a CCD with small pixels.

> I have no knowledge of the Lumicon unit but the TeleVue model uses two
> doublets, probably of high index glass, to keep spherical corretion in check
> but still correct the coma.

So the Televue model at least would be good for any use, including visual if I
recall their advertisement claims correctly...

> The problem with all of these units is their size. I suspect, please correct
> me if I'm wrong, they would introduce more vignetting, especially with an
> f/4 beam.

Unfortunately, I also suspect this.  The Lumicon unit claims a clear aperature
of 48mm, so perhaps it wouldn't be too bad in that respect...  I've seen a
Celestron coma corrector and it didn't look anywhere near that large, though
maybe my recollection is imperfect.

Thanks for the info, you've given me food for thought.

Steve