Re: Question about Dithering and Offset Guiding


Dec 20, 2004

 


----------------------------

#15340 Dec 20, 2004

While I'm driving you all crazy, here's another beginner question(s).



Dithering. I know what it is but I'm unclear about is using the SBIG

internal guider. As we all know, when the shutter is closed, the

guider can't image. So, during downloads, the guider is off-line.

This is explained in the Maxim manual. There is a delay parameter

that allows the guider to re-sync with the star following any

inadverent drift or dithering move. This is also mentioned in the

manual.



What I'm not clear on is this. When the shutter opens and the guider

is resynchronizing, the main CCD is being exposed. Naturally the

guider will move the mount a bit to get resynchronized so that

portion of the exposure is trash.



How is this eliminated? Does Maxim close the shutter, reset the main

CCD, reopen the shutter and start again? I suppose this would work

fine, it probably doesn't take much time.



I'm just curious about this.



Also, is anyone using the Offset Guiding? I plan to try this on

Maccholz. My question is how do you determine the parameters to

enter for the x/y offsets?



This would vary according to the camera orientation as well as the

motion of the comet. Getting an accurate set of values could be

tough. But maybe there's an easy way that I'm overlooking....



Thanks!



Steve...



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#15342 Dec 20, 2004

k4ikm wrote:

> What I'm not clear on is this. When the shutter opens and the guider

> is resynchronizing, the main CCD is being exposed. Naturally the

> guider will move the mount a bit to get resynchronized so that

> portion of the exposure is trash.



No, it's not exposing. The main CCD chip is in flush mode; the

photonelectrons are all being shuffled out to the readout register and

dumped.

> Also, is anyone using the Offset Guiding? I plan to try this on

> Maccholz. My question is how do you determine the parameters to

> enter for the x/y offsets?



At www.cyanogen.com/products/maxim_extras.htm you will find a

useful utility for generating an offset file (MaxTrack.zip), contributed

by John Farrell.



Doug



---------------



Doug George

dgeorge@...



Diffraction Limited

Makers of Cyanogen Imaging Products

www.cyanogen.com



25 Conover Street

Ottawa, Ontario,

Canada, K2G 4C3



Phone: (613) 225-2732

Fax: (613) 225-9688



---------------



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#15345 Dec 20, 2004

Doug,



Two followup questions on the Offset Guiding.



What happens when Maxim hits the end of the file? Will it continue

using the last offset values? Or does it stop offsetting?



Does Maxim restart at the top of the file each time a new exposure

begins? (by this I mean a "Slot", not the guider's exposure).



Thanks!



Steve...





--- In MaxImDL@yahoogroups.com, "Douglas B. George" dgeorge@c...>

wrote: > k4ikm wrote:

>

> > What I'm not clear on is this. When the shutter opens and the

guider > > is resynchronizing, the main CCD is being exposed. Naturally the

> > guider will move the mount a bit to get resynchronized so that

> > portion of the exposure is trash.

>

> No, it's not exposing. The main CCD chip is in flush mode; the

> photonelectrons are all being shuffled out to the readout register

and > dumped.

>

> > Also, is anyone using the Offset Guiding? I plan to try this on

> > Maccholz. My question is how do you determine the parameters to

> > enter for the x/y offsets?

>

> At www.cyanogen.com/products/maxim_extras.htm you will find

a > useful utility for generating an offset file (MaxTrack.zip),

contributed > by John Farrell.

>

> Doug

>

---------------

>

> Doug George

> dgeorge@c...

>

> Diffraction Limited

> Makers of Cyanogen Imaging Products

> www.cyanogen.com

>

> 25 Conover Street

> Ottawa, Ontario,

> Canada, K2G 4C3

>

> Phone: (613) 225-2732

> Fax: (613) 225-9688

>

---------------



----------------------------

#15346 Dec 20, 2004

k4ikm wrote:

> What happens when Maxim hits the end of the file? Will it continue

> using the last offset values? Or does it stop offsetting?



It stays at the last offset values.

> Does Maxim restart at the top of the file each time a new exposure

> begins? (by this I mean a "Slot", not the guider's exposure).



No. It starts at the top whenever you start guiding.



Doug



---------------



Doug George

dgeorge@...



Diffraction Limited

Makers of Cyanogen Imaging Products

www.cyanogen.com



25 Conover Street

Ottawa, Ontario,

Canada, K2G 4C3



Phone: (613) 225-2732

Fax: (613) 225-9688



---------------







----------------------------

#15352 Dec 20, 2004

Doug,



Thanks, this is very good news I think.



Sky6 gives the motion of Machholz in arcseconds per second for RA

and DEC. This is easy to convert to fractions of a pixel per guiding

frame based on the calibration Maxim does to compute arcseconds per

pixel and camera angle. A very simple Excel spreadsheet does this

calculation. Then just pop the seconds per guiding frame, the x and

y offset in pixels per frame into a file and off you go. This single

value will be applied by Maxim until you change it. That should be

adequate for tracking over a moderate period.



This seems very simple, it also includes camera angle which seemed

to be missing from the application you pointed me to.



Thanks again! Both for the answer and your patience.



Steve...



--- In MaxImDL@yahoogroups.com, "Douglas B. George" dgeorge@c...>

wrote: > k4ikm wrote:

>

> > What happens when Maxim hits the end of the file? Will it

continue > > using the last offset values? Or does it stop offsetting?

>

> It stays at the last offset values.

>

> > Does Maxim restart at the top of the file each time a new

exposure > > begins? (by this I mean a "Slot", not the guider's exposure).

>

> No. It starts at the top whenever you start guiding.

>

> Doug

>

---------------

>

> Doug George

> dgeorge@c...

>

> Diffraction Limited

> Makers of Cyanogen Imaging Products

> www.cyanogen.com

>

> 25 Conover Street

> Ottawa, Ontario,

> Canada, K2G 4C3

>

> Phone: (613) 225-2732

> Fax: (613) 225-9688

>

---------------



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