fixed position eyepieces?

Hi,

I'm toying with the idea of doing some spectroscopy for a project. The problem is that my scope is already almost too heavy for the mount, and will not tolerate a camera, connectors, grating etc. Well it might tolerate it, but then wont track the star while I try to grab the spectra!

Anyway, apparently it is possible to modify an equatorial mount into a fixed position eyepiece. This would allow the imaging equipment to be set up in a fixed place and the light from the scope would always reach this fixed position.

This may be just theoretical since I can't find any information on how this is achieved. But I suspect that it would involve a couple of plane mirrors and a motor or two. Has anyone here come across a design for this? I'm using a newtonian type scope on an equatoial driven mount. Would it be easier to accomplish in alt-az mode if the field rotation was tollerable?

I have seen something like this being used in one of the solar observatories in Ondrejov in the Czech Republic. In this image www.laeff.esa.es/users/sma/proyectos/tra...ccion=&indice=18 The building on the left has the solar scope, and with tricks of mirrors the collected light is sent through to where the box is on the building on the right, in fact the light bounces between the two buildings I think three times, which gives a focal length to the scope of nearly 100m (I'll try and dig up more information if anyone is interested!). In this building the spectroscopic observations are carried out. This telescope was designed this way of course, and not by someone thinking of retrofiting an equatorial mount!

Cheers,
~Al

Hi,

I'm toying with the idea of doing some spectroscopy for a project. The problem is that my scope is already almost too heavy for the mount, and will not tolerate a camera, connectors, grating etc. Well it might tolerate it, but then wont track the star while I try to grab the spectra!

Anyway, apparently it is possible to modify an equatorial mount into a fixed position eyepiece. This would allow the imaging equipment to be set up in a fixed place and the light from the scope would always reach this fixed position.

This may be just theoretical since I can't find any information on how this is achieved. But I suspect that it would involve a couple of plane mirrors and a motor or two. Has anyone here come across a design for this? I'm using a newtonian type scope on an equatoial driven mount. Would it be easier to accomplish in alt-az mode if the field rotation was tollerable?

I have seen something like this being used in one of the solar observatories in Ondrejov in the Czech Republic. In this image www.laeff.esa.es/users/sma/proyectos/tra...ccion=&indice=18 The building on the left has the solar scope, and with tricks of mirrors the collected light is sent through to where the box is on the building on the right, in fact the light bounces between the two buildings I think three times, which gives a focal length to the scope of nearly 100m (I'll try and dig up more information if anyone is interested!). In this building the spectroscopic observations are carried out. This telescope was designed this way of course, and not by someone thinking of retrofiting an equatorial mount!

Cheers,
~Al

albert,
just thinking off the top of my head, i think what you are looking for is a naysmith focus. this is usually done though with an alt az mount. it would also require different optics as it has a third mirror near the end the of the tube at the sitting position. i can't remember the guys first name but i am sure if you google it you will see what i mean.
stephen.

Below is just some initial thoughts.

I had built a Nasmyth telescope some time ago. This wasn't a fixed telescope. This was a Cassegrain that could be viewed at the declination axis. The Cass secondary mirror sent the light down the tube to a focus point just above the primary mirror. It was intercepted by an elliptical flat secondary mirror and then redirected it at 90d to the observer. In fact it was a viewing position at the declination axis which considerably reduced the telescope movement and in particular much easier for the observer to view through. This telescope also had the option of replacing the Cass secondary for a conventional elliptical flat for to act as a Newtonian, this operated at f/4. The telescope could be an f/12 because the cass secondary amplified the light X3. The position of viewing was considerably reduced as compared to a newtonian. Well, this doesn't answer your question. for a 100% fixed telescope

May be the the ideal telescope is a Russel-Porter design. This a fixed telescope. It would mean designing and building from scratch.

An easier system is a "coelostat" arrangement. The only disadvantage is that once it is fixed the telescope can only view stars that are moving from east to west in a southerly mode. Your telescope tube should be placed in a horizontal mode with the optics facing north. A round optically flat mirror 20% larger that your newtonian mirror (the flat mirror needs to be around 1/15 wave to sustain the accuracy within your newtonian) is positioned within a mirror cell that is mounted and motorized in both x and y. You can use an alt az design mount that can be programmed or possibly use your existing mount but configured for the flat mirror mount cell. The flat mirror is now looking towards the south, and can be moved east-west and directing starlight to the fixed telescope. The programming is different for this arrangement as compared to a conventional equatorial drive.

This is just to give you a flavour of options. These are just some initial ideas.

Eamonn Ansbro

Continuation: Elaborating further regarding the "coelostat"

The first flat mirror is the "coelostat" and is motorized as mentioned in earlier mail. The "coelostat" directs the star light continuously on to a second flat mirror as the star passes across the sky. The second mirror is fixed in front of the newtonian mirror so that, with the first mirror in motion, the starlight is continuously directed down the telescope tube.

Eamonn Ansbro