Re: [guide-user] Setting the position of the guide chip

JoeMize Apr 10, 2018

Eric, since you are using the STL11000M CCDs.nam entry, here is my STL11K + MMOAG entry which Bill setup for me, to help you get started. HTH...joe
1) I requested my 2nd Guide Chip be rotated 90deg for better coverage and placed opposite the STL on-board guider chip.
2) The 2nd Guider Chip is a ST-237H just like STL on-board chips.

SBIG Research 11000XM KAF-11000M 9 9 4008 2672 917 0,.6231,.1313,.1477,640,480 0,-1.08117,.098470,.196939,480,640

Bill’s eMail to me fellows this:

OK, it should work about like this :
The main chip is a KAF-11000, with 4008 x 2672 pixels, each nine
microns square. That makes it 36.072 x 24.048 millimeters.

The guiding chips are both TC327s, with 640 x 480 pixels, 7.4
millimeters square. So they're 4.736 x 3.552 millimeters.

The built-in guider chip is 4.736 / 36.072 = 0.13129 times the width
of the main chip, and 3.552 / 24.048 = 0.14770 times the height. That
leaves us with the separation between the chips to figure out... which,
fortunately, SBIG documents :

(which could have spared me even the very modest amount of arithmetic
done above). The center-to-center distance is 15.39 millimeters, which
is 15.39 / 24.048 = 0.63997 times the height of the main chip. Which
is why the guider chip specification for the SBIG-11000 is


...first the separation horizontally (zero, in this case; the chips
are one over the other), then the vertical separation (0.6231 times the
height of the main chip, not quite what we got... looks as if I used the
height from the above URL, which probably contains some non-imaging rows).
Next, we have the ratios in width and height between guider and main chip.
Finally, we specify that the guiding chip has 640x480 pixels.

Your extra guiding chip, being tilted 90 degrees, would have width
ratio 3.552/36.072 = 0.098470 and height ratio 4.736/24.048 = 0.196939.
If it's 26 millimeters, center to center, from the main chip, that would
be 26/24.048 = 1.081171 main chip height units. Except we'll make it
negative, to put it on the opposite side from the built-in guiding chip.

Tacking all that on to the existing guiding chip specifier, we get

0,.6231,.1313,.1477,640,480 0,-1.08117,.098470,.196939,480,640

Edit your 'ccds.nam', look for the SBIG 11000 line, and add that
second bit, and the guiding chip will show up. (Unfortunately, without
a second set of guiding rings...)

As a side note: in hindsight, this was a really dumb design
decision. At the time I wrote this part of Guide, I assumed there
would only be a few guiding chips, and I'd add them in as I learned of
them. So I didn't invest a lot of time making it user friendly. But
even given that, it would have been about as easy for me to make
the format for the above line look like this :

0,15.39,9,9,640,480 0,-26,9,9,480,640

...i.e., offsets in millimeters, followed by guider chip sizes in
microns, then guider size in pixels. Had I done so, it would have
saved a lot of trouble, both for Guide users trying to add their own
guiding chips (or making mosaics), and for me in terms of providing
tech support for them. Dunno what I was thinking when I made it the
way I did, but it's definitely not my finest hour.

-- Bill

"May He Go Among the Imperishable Stars"
Joe Mize, StarFields Observatory,
Chiefland Astronomy Village

Sent: Tuesday, April 10, 2018 12:29 PM
Subject: [guide-user] Setting the position of the guide chip

I have asked this question before but nevere’s mer really figured out how to correctly position the guide chip on my SBIG 16200 and filter wheel with built in guide camera.

Here is what I already know. First the size of the imaging chip and size and position of the guide chip is held in the ccds file. I have that file open in Notepad now. I see the line with the camera selection. I am still selecting the SBIG STXL 11002 camera, even though the parameters for that selection are for the KAF-16200 chip.

Here is the text for that selection.

SBIG STXL 11002 KAF-16200 6 6 4500 3600 961 0,.92,.24,.28,640,480

I can interpret the pixel size, chip dimensions and guide chip dimensions. What is a mystery is what parameters control the distance from the main chip to the guide chip. I am assuming it is those other numbers in the string, but don't know exactly how to change them to move the guide chip position out to its proper location. I think now it is still set for the 11002 camera.

Any instructions would be appreciated.

Thanks in advance.


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