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Re: PE Estimating


Mar 14, 2003

 


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#14410 Mar 14, 2003

I am writing up a "first light" report on my new G-11 and want to

include an estimate of the PE. Using my 12mm illuminating double

crosshair ep at approximately 1800mm fl it takes a star 2.5 seconds

to cross the guiding box once I turn off the power to the mount.

Assuming a star is moving at 15 arc sec/sec, is it correct to

calculate the box at 37.5 arc sec square?

Steve



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#14411 Mar 14, 2003

Yes, it's 37.5 arcsec on each side. Using a 2x or 3x barlow with a

12mm eyepiece may give you a more precise PE estimate.



Looking forward to your report,



-Paul



--- In Losmandy_users@yahoogroups.com, "steve220us" steves@e...>

wrote: > I am writing up a "first light" report on my new G-11 and want to

> include an estimate of the PE. Using my 12mm illuminating double

> crosshair ep at approximately 1800mm fl it takes a star 2.5 seconds

> to cross the guiding box once I turn off the power to the mount.

> Assuming a star is moving at 15 arc sec/sec, is it correct to

> calculate the box at 37.5 arc sec square?

> Steve



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#14413 Mar 14, 2003

steve220us wrote: >

> I am writing up a "first light" report on my new G-11 and want to

> include an estimate of the PE. Using my 12mm illuminating double

> crosshair ep at approximately 1800mm fl it takes a star 2.5 seconds

> to cross the guiding box once I turn off the power to the mount.

> Assuming a star is moving at 15 arc sec/sec, is it correct to

> calculate the box at 37.5 arc sec square?



Hi Steve,



The center box on *most* (caveat emptor) dual reticle EP's have a

crosshair spacing of .2mm



A=41,250/F



Where A is the guidebox size in arc-seconds

Where F is the guidescope focal length in mm



IIRC estimating the size based upon travel of a star through the EP you

have to select a star on the celestial equator. For your set-up my best

guess is this:



22.91 arc sec = 41,250/1800



This sounds much more reasonable to me.



Hope this helps .....



Best Regards



Bill



--

William R. Mattil.| Fred Astaire wasn't so great.

wrmattil@....| Ginger had to do it all backwards

(972) 399-4106..| and... in high heels.



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#14440 Mar 14, 2003

Another way to determine this accurately is with double star

spacing. I did my 9mm meade one this way to determine the spacing

between multiple sets of lines and circles in its pattern. Worked

real well to allow me to determine my G11 was getting 7.4" peak to

peak which I understand is quite good.



Kevin



--- In Losmandy_users@yahoogroups.com, "William R. Mattil"

wrmattil@i...> wrote: > steve220us wrote:

> >

> > I am writing up a "first light" report on my new G-11 and want to

> > include an estimate of the PE. Using my 12mm illuminating double

> > crosshair ep at approximately 1800mm fl it takes a star 2.5

seconds > > to cross the guiding box once I turn off the power to the mount.

> > Assuming a star is moving at 15 arc sec/sec, is it correct to

> > calculate the box at 37.5 arc sec square?

>

> Hi Steve,

>

> The center box on *most* (caveat emptor) dual reticle EP's have a

> crosshair spacing of .2mm

>

> A=41,250/F

>

> Where A is the guidebox size in arc-seconds

> Where F is the guidescope focal length in mm

>

> IIRC estimating the size based upon travel of a star through the

EP you > have to select a star on the celestial equator. For your set-up my

best > guess is this:

>

> 22.91 arc sec = 41,250/1800

>

> This sounds much more reasonable to me.

>

> Hope this helps .....

>

> Best Regards

>

> Bill

>

> --

> William R. Mattil.| Fred Astaire wasn't so great.

> wrmattil@i....| Ginger had to do it all backwards

> (972) 399-4106..| and... in high heels.



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