The 24" Idea

Kyklopas 24" f/4.1

To dimensioning and making of the mechanical components

Last update: 21. Jun. 2001
To mirror making
Last update 03. Apr. 2001

Article as published in the German Magazine "Sterne und Weltraum" Jan. 2003 [.pdf]
Deep Sky Observing with the 24" Telescope (German)
Pictures from ITT 2020

The 24" Idea and the Minimalist Spirit

Image courtesy Friedl Lamprecht with Canon 20 D

"Be honest. You want to observe trough the biggest telescope you can get your hands on" this wise statement from David Kriege applies to me in a slightly altered form: "...the biggest telescope you can carry with your own hands"
I didn't really need a new telescope, my existing ultra-light Dobsonians were made to fulfill my personal needs in an ideal way. It's the ATM- spirit, to capture 0.7 magnitudes more than with Aristarchos onto the retina. After a Dobson session in summer 2000 high in the Austrian Alps with 20 and 30 inch telescopes Aperture Fever caught me again (see German article). After the trip I ran like mad through the house with a folding rule in my hand, measuring widths of doors, diameters of racing bicycle wheels and nothing but glass, teflon and carbon fiber in my brain. How lightweight and compact can I make it without compromising optical and mechanical performance?

More than 7 years I managed to keep my two basic rules: Never build a Dobson, that is heavier than yourself, and never never grind again a mirror larger than 16 inches! Then the Dollar rate went up trough the roof and obviously no company wanted to guarantee good quality at 4 cm thickness. On top of this, the lead times were intolerable long. So why break with tradition and buy a mirror, after having made all others myself? How good can I make such a big, thin and high focal ratio one?

Then I found several other minimalist Dobsonian designs in the internet and contacted people, who succeeded in large thin mirror making. So I decided to start eating carbo grains again. Overnight the name was found: Cyclops was big and one eyed, ... and I think, he was a Greek as well!

I want to thank all folks from the ATM mailing list and other friends and telescope makers, who supported me in critical questions and helped, to make this thing happen.

Requirements

1. Blank thickness: No more than 4 cm (1 5/8"). There is no other way for me to handle a 24 inch piece of glass. The professionals don't like "the thin ones", other ATM's warned me of mirror flex and astigmatism. But some people showed, that it's manageable, provided you follow some rules when making and supporting the mirror.

2. Low eyepiece height: Tall ladders are no good place to stay on at night. A high focal ratio is more difficult to parabolize though. It requires a low profile mirror cell and a low rocker box as well.

3. Sharp mirror: This is in direct conflict with points 1 and 2 and asks for an even more ambitious "ATM- spirit"

4. Lightweight: Minimum material spending and high stability leads to large cross sections and sandwich construction. I have to be able to carry the mirror box as the heaviest single component myself over short distances.

5. Compact design: The instrument has to fit into even small cars. This asks for a low mirror box, a low secondary cage and removable altitude bearings.

6. Open structure: Enables rapid cooling of the mirror and helps against local seeing. A draw back is, that the own body heat gets into the light path, but I didn't see this to be a serious problem so far.

7. Small wind resistance area: I hate light shrouds, that become wet and shake the telescope in the wind. However, the open secondary cage might require a resistance heater to prevent dew formation on the secondary.

8. Quick set up: As few hand grips as possible, no loose parts, no tools.

9. Tools: All parts have to be fabricated with hand tools, a drilling machine on a stand and a router, no parts that require a lathe or a milling machine.

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1. Blank thickness:	No more than 4 cm (1 5/8"). There is no other way for me to handle a 24 inch piece of glass. The professionals don't like "the thin ones", other ATM's warned me of mirror flex and astigmatism. But some people showed, that it's manageable, provided you follow some rules when making and supporting the mirror.
2. Low eyepiece height:	Tall ladders are no good place to stay on at night. A high focal ratio is more difficult to parabolize though. It requires a low profile mirror cell and a low rocker box as well.
3. Sharp mirror:	This is in direct conflict with points 1 and 2 and asks for an even more ambitious "ATM- spirit"
4. Lightweight:	Minimum material spending and high stability leads to large cross sections and sandwich construction. I have to be able to carry the mirror box as the heaviest single component myself over short distances.
5. Compact design:	The instrument has to fit into even small cars. This asks for a low mirror box, a low secondary cage and removable altitude bearings.
6. Open structure:	Enables rapid cooling of the mirror and helps against local seeing. A draw back is, that the own body heat gets into the light path, but I didn't see this to be a serious problem so far.
*7. Small wind resistance area:*	I hate light shrouds, that become wet and shake the telescope in the wind. However, the open secondary cage might require a resistance heater to prevent dew formation on the secondary.
8. Quick set up:	As few hand grips as possible, no loose parts, no tools.
9. Tools:	All parts have to be fabricated with hand tools, a drilling machine on a stand and a router, no parts that require a lathe or a milling machine.