[LVAS] FW: Cone Nebula

[roger ivester]

David,

 

I know now why I have to draw everything with a pencil and a piece of paper. You  APer's have to be brilliant. Hope this explains what Frank did on his image. David I "kinda" got lost on the first two sentences, became dizzy and stopped reading. 

 

If you have any further questions please send Frank an e-mail direct. Frank is one of the nicest guys you could ever hope to meet.

 

Roger 

 

 

 

 

 

> Date: Sun, 28 Feb 2010 10:39:01 -0500
> Subject: Re: Cone Nebula
> From: frankb at celestialwonders.com
> To: drivester at hotmail.com
> 
> Roger,
> 
> No big secret on the field of view. I used the 10" LX200R which has a native focal length of about
> 2500mm. But with any catadioptric design where the primary is moved for
> focus, the focal length changes as the mirror is moved. I use an SBIG
> STL-11000M and a Moonlite focuser; so with those hanging off the back of
> the OTA I have nearly 5" of backfocus. That requires me to "push up" the
> mirror to achieve focus. I use PinPoint to plate solve and it reveals to
> me that my effective focal length is about 2800mm with this configuration.
> 2800/250 gives the f-ratio of f/11. OK so far?
> Now, to get at the field of view we need to know two more things. The
> pixel size of the camera (9 microns) and the pixel count (4008 by 2672). 
> We can first calculate imageScale = 206.265*pixelSize/focal_length. For
> me that is about 0.66 arcsec per pixel. Then FOV = imageScale *
> pixelCount. So if you haven't gotten an anerism by now, that works out to
> a field that is 44.3 arcmin by 29.5 arcmin. I can just about image the
> full moon in one frame. The "secret" is that 35mm format CCD!
> 
> Trust me Roger, you are amazing in your own way. I would never be able to
> do what you do. As funny as it may sound, I just don't have that kind of
> patience (but I will fiddle with an autoguider for hours to get it
> right...go figure).
> 
> Frank
> http://celestialwonders.com
> 
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> > The moon and stars to govern the night..... Psalm 136:9
> >
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> > _________________________________________________________________
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> 
> 

 		 	   		  
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