From: Milton Aupperle <milton@outcastsoft.com>

Date: March 21, 2006 9:53:29 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] adapter question

Hi Tim;

I doubt if 1.25" will adversely affect anything. The only concern would be how much travel your scopes focuser has and that likely won't be an issue in this case.

Also if you use a Barlow with your scope, the further the distance between the Barlow and the CCD, the more magnification you get. I use a set of extender rings (an extra 6" back) with my 2x Barlow and actually 3.6x out of it. However as your increase the magnification, you get the inverse square of the light on the CCD.

So:

Prime Focus 1x = 100% light  = exposure time 1x

Barlow 2x = 25% light = exposure time 4x

Barlow 3x = 11% light = exposure time 9x

Barlow 4x = 6.25% light = exposure time 16x

And the same thing applies to a Focal Reducer too in revers, as the further the distance between the Reducer and the CCD the less magnification you get.

HTH..

Milton J. Aupperle

President

ASC - Aupperle Services and Contracting

Mac Software (Drivers, Components and Application) Specialist

#1005 - 815 14th Avenue. S.W.

Calgary Alberta Canada T2R0N5

1-(403)-229-9456

milton@outcastsoft.com

www.outcastsoft.com

On 21-Mar-06, at 9:36 AM, centurion40tim wrote:

No wonder I was having trouble! Not only had I not taken the lens off my webcam, I

was shooting through an eyepiece! Milton set me straight but I have another question.

With a unibrain webcam, about how far should the webcam be from the top of the star

diagonal sleeve? Presently, I am using the distance from the top of the eyepiece sleeve

to the front of the webcam case. But I could just as easily measure from the plane of

the CCD chip.

Since I crafted my adapter to slide over my 17mm plossl (geez - lol) that is the

present distance, about and inch and a quarter. I'm thinking it will be fine but wanted

to check.

thx Tim H