Re: [ATM] A Null Test

[Richard <cnc@cncservo.co.uk>]

Hi Ric,

Saturday, September 9, 2006, 2:57:38 PM, you wrote:

RR> I do
RR> have one concern and that is the use of biconvex
RR> lenses.If one uses a vernier caliper to set the
RR> spacing you need large jaws to reach down to the apex
RR> of the lens and this can introduces angle error and
RR> the resulted spacing error

Optically, I found it much easier to achive a good null with a
biconvex relay lens. FYI, it can usually be very small in
diameter, maybe 0.5" diameter or so.

If you have calipers, you can use them to measure a length of
plastic bar and trim to to the right length to use as a spacer.
I use a stick micrometer to which I have added hard plastic end
caps, whose lengths you can easily calibrate out. Useful thing
to have for telescope construction and alignment too. My set
covers 5" to 20' with a 0.5 thou resolution. 5" to 10' is
probably the most common set to appear on the second hand market
or Ebay. It's not too difficult to kludge in a digital
micrometer head or dti if you want 1/20th thou resolution!.

-- 

Best regards,
  Richard in the UK

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