Jones-CHiefspiegler

This is a new Catadioptric Herschellian design that uses lenses to correct for the aberrations introduced by tilting the mirror.  I dubbed the name CHiefspiegler as a play on words.  Previous Herschellian designs have been limited to about f/10 with poorer off-axis images.

    Schiefspiegler comes from German meaning tilted mirror which this scope has.  Most Schiefspieglers have two or mirror mirrors and  very long f ratios which are good for high power on the planets but not so good for other observing.  This design can be as fast as f/6 (even f/5.5 in an 8 inch size) using only one mirror if you don’t count the diagonal.   (This is not the design in the Jan. 1971 Sky & Telescope by the way which used a spherical mirror).  It uses simple lenses that in some F ratios designs can be bought off-the-shelf.

Advantages of a CHiefspiegler?

Another way to make an unobstructed scope would be to use an off-axis segment made from a large mirror (off-axis Newtonian) and these are commercially available.  However the off-axis aberrations are largely dominated by the coma of the original mirror which is rather huge and limits the f number to about f/10.  The off-axis image is much better in the CHiefspiegler because it’s mirror is a figure of revolution.  Comparing the spot diagrams this design at f/7 is equal or better than to the off-axis Newtonian  at f/10.

    Another advantage is tube length.  F/7 is a much shorter and portable tube than an f/10 only a diameter longer than a common f/6 Newtonian. Also the diagonal also can fold the light closer to the primary than a Newtonian giving a long focusable distance that can be used for a camera, diagonal etc.

    The diagonal can be baffled better than a Newtonian since it is out of the way.

1. Unobstructed refractor like images

The advantages of not having a secondary obstruction is well known to improve the contrast of planetary images and with no spider there are no diffraction spikes. The image is refractor-like but without the color fringes of most refractors or the center field darkening at low power that Newtonians have.

2. Reflector color correction (no purple fringes)

You get a diffraction-limited image with no secondary refractor color. See spot      diagram.     

3. Fast 

Most  schiefspieglers have a large F number resulting in very high power but also a very narrow field of view. A few schief designs are f/10 or less but requiring many mirrors or torroidal  surfaces. This is the fastest, simplest, best performing schiefspiegler and can be as fast as f/5.5 in an 8 inch scope!

4. Wide well corrected field

The Maksutov Herschellian has a lot of astigmatism in the field but this design has nearly the same off axis performance as an equivalent Newtonian. The correctors contribute very little to the off-axis aberrations. This design has off-axis images comparable to a much slower off-axis Newtonian at f/10.

5. Field tilt

Field tilt is less than 2 degrees and is better than many other schiefspieglers.

6. Only two mirrors

The Kutter Schiefspiegler also has two mirrors but many schiefspieglers have three or more mirrors or a non-reversed image.  Three or more mirrors lose a lot of light with a 90% reflectivity. 

7. Short tube

Compared to an off-axis Newtonian at f/10 the overall length is significantly shorter             at f/7. In fact with a 45 degree fold back the distance from the bottom of the tube to focus is about like an f/6 Newtonian.

8. Better baffling

Believe it or not the light cone is better baffled than a Newtonian and better protected from dew than a Newtonian.

9. More focal distance

Newtonians are cramped for focal distance to keep the secondary size small.  This is not a problem with this design as there is 6.5 inches from the last surface to the focal plane, plenty of focus room. I use either a diagonal or an extension tube

Performance

Features

Wyorock Crayford style focuser

Maple wood frame

Beam construction for better ventilation

Excellent baffling

Quoting Dick Suiter “If ever a simple-to-make TCT could be designed with good field of view and good central correction, I would say they finally have something.” 

I say “This is the scope of the future”.

     8 inch F/7 Chiefspiegler with a 90 degree fold

Please contact me at solarview@isoc.net