Re: [APML] Guiding (was M101)

["Greg Hartke" <ghartke@adelphia.net>]

Of course I meant to write 2.47 x 10**-5 radians. Sheesh. Sorry.

Greg

----- Original Message ----- 
From: "Greg Hartke" <ghartke@adelphia.net>
To: "Steve Lindsey" <stevelindsey@earthlink.net>; "Discussion of Film 
Astrophotography" <astro-photo@seds.org>
Sent: Wednesday, May 04, 2005 7:00 PM
Subject: Re: [APML] Guiding (was M101)


> Hi, Steve,
>
> I've been imaging with my 152 mm f/7 refractor so the focal length is 1064 
> mm. I think the focal length with the Mini Borg is adequate for most 
> imaging applications with the STV but I'm not so sure about the ST-4. Then 
> again, with the 60 mm and a 300 mm focal length (I think it's f/5, too), 
> that might work with the ST-4. I used to know how well the ST-4 performed 
> its centroiding computation but I lost those figures when I my old 
> computer died. (D'oh.) Let's think a second... At 300 mm focal length, the 
> image scale is (to lowest order) 0.0033 radians per millimeter. Let's 
> assume a pixel size of 7.4 microns = 0.0074 mm. This says that one pixel 
> corresponds to to an angle of 2.47 radians = 0.001413 degrees = 5 
> arcseconds at the focal plane. If the centroiding is performed to 1/5th of 
> a pixel (a reasonable and, I think, slightly pessimistic guess), then 
> you'll get something like 1 arcsecond guiding accuracy. Hmm. Might be 
> marginal. Everyone I've noticed going the compact guidescope route these 
> days has been using an STV. Has anyone here tried guiding with an ST-4 at 
> something like 300 mm focal length?
>
> Regards,
>
> Greg
>
> ----- Original Message ----- 
> From: "Steve Lindsey" <stevelindsey@earthlink.net>
> To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
> Sent: Wednesday, May 04, 2005 6:26 PM
> Subject: Re: [APML] Guiding (was M101)
>
>
>> Greg,
>>
>> I thought of getting a 60mm BORG for guiding but thought the focal length 
>> with an ST4 was getting low for imaging at 980mm with my TEC.  What fl do 
>> you image at guiding with the BORG/STV combo?
>>
>> Steve
>
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