Re: ATM 3" 75mm or 4" 100mm eyepieces

[Chris Westland <westland@uxmail.ust.hk>]

I'm not sure exactly why you would want that long a focal length.  But the
design objectives for a scope are different than for an eyepiece ... in
short, scopes are designed with a long focal length and good correction over
a FOV of a fraction of a degree;  eyepieces are the converse ... short focal
length and good correction over a wide field of view. You might start by
looking at copier lenses that require a wide flat field of view ... Joe
Sunseri had some of Zeiss mnfr at Riverside this year that were 80mm (I
bought one ... great optics).  

-c


At 07:45 PM 8/19/96 -0400, you wrote:
> 
>At 01:02 PM 13/8/96 -0400, you wrote:
>
>>>Hi!
>>>
>>>I am looking for a commercial, military or even home made 75mm 3" eyepiece
>>>and a 100mm 4" unit. The diameters  of  3" and 4" respectively must be the
>>>minimum, though the 75mm and 100mm specs can vary somewhat.
>
>>>Otherwise...Does anyone know of a source of these or way to build them? 
>
>
>> Hmmm. This almost sounds like you are describing a large 35mm camera lens.
>>I wonder if using one would be better than scaling up a Plossl design (using
>>a couple of 3 or 4 inch achromats as elements)?
>
>
>Hi Mike,
>
>Thanks for the idea.
>
>I'm not really versed in "lens techniques"... Just exactly how would I take
>say a cheap 3" Meade refractor and use it? How do you get the required 75mm
>or 100 mm out of say an F10  3" or 4" refractor lens system?
>
>Anyone else lend a suggession? I really need to build up an 75mm  3" and
>100mm 4" eyepiece....I'm stuck with an F8.5 system here.
>
>
>Tom Cathey
>
>
>