Re: ATM which one first

[Robert Duvall <rduvall@jlc.net>]

At 8:14 AM -0700 6/12/98, Gary Seronik wrote:
>At 09:48 PM 6/11/1998 -0400, David McCarter wrote:
>>The helical takes forever to change focus if your eyepieces are not
>>strictly parfocal. I thought I would like them too, but discovered I had
>>not enough patience.
>
>Hi Dave:
>
>You know, I hear this a lot as a knock against helical focusers and
>frankly, I just don't get it.  I mean, am I the only one with reasonably
>parfocal eyepieces?  Seriously, I've got quite a mixed bag, and I think the
>biggest difference between eyepieces is about 1/4" of focus travel.  This
>is pretty easy to deal with, you just slide the eyepiece in until it's
>close to focus and use the helical for fine-tuning.
>

I don't get it either. I think the problem is the helical is too easy and
too simple. I have a r&p, a helical, and a crayford. Nothing can touch the
helical for fine tuning focus on a fast system.

Just add an o-ring or several winds of tape or a plastic ring on the ep's
to make them closer if they are not parfocal. Some may not like seeing dirt
on the ep rotate when focusing, but there's an easy fix for that...

>On the other hand, one of the big advantages helicals have is the precision
>with which focus can be achieved.  For f/6 and under they're a must.  At
>f/4.5, accurate focus with a r&p is almost a matter of luck.
>
>One helical of guy's opinion...

I'll ditto that.


Robert Duvall
Force5 Telescope Making Resources

Software Engineer, Amateur Astronomer (TN),
and General Scientist (according to my son)
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