Ad Astra Observatory

Dear Mr. Harris,

we are sorry but it is very unlikely that our MPCC will work for your telescope.

At first it is not calculated for f3.3, maybe it is possible to modify the main mirror but a much better approach is to calculate a individual coma corrector and field flattener for this telescope.
Second the free diameter is 38mm, this is enough for f4.5 but not for f3.3. With 35mm film or full frame CCD you will have severe vignetting. You will need around 68mm free diameter for the necessary 55mm between the outer lens and the focal plane.
There are special correctors for very fast Newtons on the market, they are built with the necessary geometrical and optical sizes. Maybe a Wynne type is that what you need.
Please excuse, but our product line doesn’t include such correctors.

Best regards,

Martin Rietze
BAADER PLANETARIUM

——– Original Message ——–
Subject: MPCC hyperbolic mirror overcorrection factor (21-Apr-2006 6:02)
From: jimbo@jimbo.net
To: service@baader-planetarium.de

> Hello,
>
> I am an amateur astronomer and amateur telescope maker and wish to design

> my primary mirror around your company’s coma corrector. I am currently
> grinding a 150mm mirror which I intend to turn into a 500mm focal length
> f/3.3 Newtonian astrograph.
>
> I intend to use the lens primarily with a DSLR, but might also use it for
> some 35mm film photos (I will not use it for medium format).

>
> Such a fast mirror will have a severe amount of off-axis coma, and I have
> decided to use the Baader MPCC to correct it. I understand that the MPCC is
>
> not tuned for such a fast f/ratio (is it correct that it is best tuned for
> f/4.5?). Also, I understand that changing the distances between the focal
> plane and MPCC and between the MPCC and the mirror can help the MPCC to

> work to best effectiveness. However, from my understanding of how coma
> correctors work, it is my belief that I should also overcorrect my mirror
> to be somewhat hyperbolic in order for the MPCC to have the most positive
> effect.
>
> My question is this. By how much should I overcorrect my mirror? An answer
> in units of either Schwarzchild constant, eccentricity, or wavelengths of

> 550nm light would be most appreciated.
>
> I thank you in advance for your help.
>
> Sincerely,
> Jimbo S. Harris
> Newark, CA, USA

> 37� 31′ 44” N
> 122� 00′ 42” W
> http://www.jimbo.net/astro/

>