My Ideal Telescope

© Brooke Clarke, 2005

Use

This is a scope for remote only use although some provision needs to be made for local alignment and testing.  It is intended for use with remote computer control and imaging my means of a Silicon based imager, uncooled TV camera, cooled TV camera, uncooled astronomical camera or cooled astronomical camera.

Design Features

Wavelength Range

The human eye can see light in the 400 to 700 nm range with peak sensitivity in the greens,, maybe 550 nm).  Silicon based imaging chips have a sensitivity curve that covers 400 nm to 1100 nm with a peak around 700 nm.  Most telescopes have been designed for eyepiece viewing and so have an optical system that works in the 400 to 700 nm range.  The more expensive scopes do a better job of this than the lower cost scopes.

If the 700 nm and longer wavelengths are filtered out then an optical system using one or more lens elements will be able to focus, but a lot of photons have been taken away decreasing the sensivity of the socpe.  Also a multi spectral analysis will be lacking in the near IR range.

To make a lens that will focus light in the 400 to 1100 nm range all in one plane is extremely difficult both in terms of design and manufacture (very expensive).  But mirrors with the proper coatings will reflect light over this range without a problem, so a scope design that uses all reflecting elements will cover the wavelength range.  Common scope optical systems that are made this way are the Newtonian and Cassegrain.

f Number & Image Size

When using an imaging chip it's important that the image size of a star is about the same size as a pixel where the seeing is as good as it's going to get.  If a star image is spread across more than one pixel then the sensitivity is reduced.  If a pixel is much smaller than a star image then resolution suffers.  For poorer seeing conditions caused by the atmosphere the camera should have the ability to do binning like 2x2 or 3x3 etc. 

Since the primary focus image size is about the same as the f number the scope should have a small f number without adding a focal reducer (that has a lens).

Mount

Az-El or RA-Dec

To support satellite tracking and terrestrial use (Az-El) or astronomy (RA-Dec) the mount should be convertible by means of installing a wedge.  The scope should not have to be "flipped" like a German Equatorial.

Fixed Scope Position

When a digital camera is added to the scope there are a lot of wires and cables that get tangled as the scope moves.  To avoid this problem and also to avoid optical problems caused by the changing scope orientation, like mirror flop, the scope should be held in a fixed position.  Where in the sky it's looking should be controlled by computer controlled mirrors.  For example if the scope was pointing straight up a flat mirror at 45 degrees would allow the scope to look at any azimuth in a level plane and the rotation could be on a continuous basis, i.e. like turning clockwise without any stops.  If now a second mirror at 45 degrees is added turning on a horizontal axis this mirror would allow viewing in a continuous vertical circle. 

If the above scope was put on a wedge so that the main scope was pointing at the North Celestial pole then the movements would correspond to RA and Dec.

Weather Proof

This mount - scope combination could be made weather proof thus allowing the scope to be on a permanent pier that's outside all the time.

Self Contained Dome

The purpose of a dome is to shield the scope from the radiant heat loss to a black sky.  This heat loss causes the scope to cool below the dew point and then there's a dew problem.  The scope could have shields built in that would act like a dome.

Sun Filter

The mount should have a way to know if the scope is aimed at or near the Sun and when it is insert a filter in the light path.

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