Mak's primary mirror

[tom33pr]

Any Mak experts around here?

I've been googling a bit on Maks and tried to find any useful diagrams that would show the primary mirror in a Maksutov (specifically Nexstar)... but couldn't really find anything detailed enough.

I'm just wondering how exactly the primary mirror is built in Maksutov scopes. Any input appreciated...

[damnut]

Hi there,

In general the primary mirror sits at the rear of the scope in its own 'cell' there is a hole in the middle to allow the light through to reach the eyepiece. This hole is commonly a tube that is baffled to keep out stray light.

The whole of the cell is usually moved to achieve focus, the focus spindle moves the primary cell forwards and backwards. In general there is no need to recollimate as the secondary mirror is silvered (aluminised) onto the rear of the meniscus lens at the front of the tube. This makes them great grab & go scopes as the collimation is reliable.

See link for plenty of images :--- https://www.google.co.uk/search?q=maksutov+telescope+design&hl=en&tbm=isch&tbo=u&source=univ&sa=X&ei=fN5dUbvXC-mw0QWng4DQAQ&ved=0CEIQsAQ&biw=1077&bih=536

Hope this helps.

[tom33pr]

Great Damian, thanks. I was wondering how the primary is attached... is there a spring(s) behind it? What gives it this smooth movement?

Thanks.

[JamesF]

The mirror has, as has been said, a hole through the middle. A metal carriage passes through the hole and there's a retaining nut to hold the mirror against the backplate of the carriage. To focus the entire carriage and mirror assembly slides back and forth on the baffle tube, changing the distance between the primary and the other optical surfaces.

The focusing movement is achieved by means of a plate that is fixed to the carriage and on a threaded rod on the inside of the focusing knob. Turning the knob pushes and pulls the plate back and forth which moves the carriage back and forth. The plate itself isn't actually threaded, but fixed to the end of the rod. There's also a threaded collar on the rod that is fixed in place on the backplate of the OTA when assembled, so turning the focuser knob actually moves the threaded rod in and out of that, achieving the required motion of the plate.

There's a photo of a disassembled Skywatcher 127 Mak here that might help visualise things:

http://www.tanstaafl.co.uk/2012/02/127-mak-collimation/

James

[tom33pr]

Thanks James. Geat answer!