[ATM] 20" f/4 - f/23 spherical Mangin Cassegrain

[Jean Fejes <JsFejes@Swva.net>]

Anthony Stillman wrote:

>Jean,
>
>Assuming it has a chance to fully equilibrate, what
>happens to the correction when you change the
>temperature five or ten degrees C ?
>
>Anthony 
>  
>
  Hi, that's a good question. I'm not sure about the answer,  but as far 
as I can tell the image quality changes very little due to a small 
temperature change.

  Here is a design using Quartz for both lenses, the images are similar 
to the BK7 design, but the curves are a little steeper. High quality 
Quartz is available for lenses in this 4 inch size and should have no 
problems caused by temperature changes.

  The spacing between primary mirror and secondary lens/mirror assembly 
will change because of temperature changes, but the image quality is 
changed little by even 50 degrees Fahrenheit. A telescope made of steel 
has half the thermal expansion of aluminum.

         radius   thickness  aperture   type

SRF 1    -4000     -1650      250        reflect

SRF 2     410        -10       45        Quartz

SRF 3     784.52      -1       45        air

SRF 4    -410        -12       45        Quartz

SRF 5    -799.7        0       45        reflect

SRF 6    -799.7       12       45        Quartz

SRF 7    -410          1       45        air

SRF 8     784.52      10       45        Quartz

SRF 9     410       1899.523   45        air

Steve
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