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Pixel Size of CCD

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HlafordCrux

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<p>I was using CloudyNights and here was my question.</p><p><br /><font class="post">What size would I need for a 20 inch f/5 newtonian? </font><br /><br />Here was my answer</p><p>I suppose you said "pixel size" of the CCD.<br />In my opinion it's the more important parameter for imaging.<br /><br />At F5 you work with 2500 mm of focal.<br /><br />According the turbulence, the best sampling is between 2 and 3 arc/" <br /><br /> /> /> I think a minimum size of 18&micro; would be correct.<br />So you can work in bin 2 with 1603ME, for example.<br /><br />Or better, the KAF 1001E (24&micro;)<br /><br /><br />Now if you said "field", you have to work with a large CCD, a 3200ME it's a minimum.<br /><br />But a long focal = large pixel size CCD, to avoid the oversampling.</p><p>&nbsp;</p><p>WHAT DOES THIS MEAN???</p> <div class="Discussion_UserSignature"> <p> </p><p>-Hlaford Crux Observatory</p><p>Devoted to spreading God's word through research in astronomy.</p> </div>
 
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Saiph

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<p>First, I'm not sure what cloudynights is...so are you asking about what size of a CCD camera you are needing?&nbsp; If so, then the answer provided is the appropriate one, even if it assumes you understand the principles.</p><p>Second, I'm going to go with the values provided in your answer, and assume they are correct (no time to check the work just now... and I'm lazy :) The Equations for the resolution and "field" of your scope are readily available however, and pretty easy.&nbsp;</p><p>The first thing to understand is that any telescope has a theoretical maximum resolution.&nbsp; It's the "smallest" seperatoin between objects (in arc seconds) that your telescope can detect (resolve, image, display).&nbsp; So if two objects in the sky are closer together than 2-3 arcseconds, it'll appear as a single image.&nbsp; It's also the smallest possible size of a single object (like a star) that your telescope will produce.&nbsp; Anything smaller gets blurred out into a 2-3" blob.</p><p>This is why things appear a bit blurred in smaller telescopes, but clearer and in more detail in larger ones.&nbsp; The larger scopes are able to resolve the smaller, finer details.&nbsp; As a side note, the best a ground based telescope can do (without adaptive optics of, say, Keck) is ~1 arcsecond due to atmospheric turbulance. </p><p>So, what does this mean for CCD selection?&nbsp; Well, this resolution means that the images your telescope projects onto the camera (instead of your eye) have a certain finite size...which the response you provided states is 18 micrometers (the funny u).&nbsp; If your CCD camera has pixels larger than this value, it could actually have 2 or more closely spaced stars on a single pixel, instead of on two seperate pixels.&nbsp; Essentially your resolution would no longer be limited by the size of you telescope, but by the camera.&nbsp; </p><p>
So you can work in bin 2 with 1603ME, for example.<br /><br />Or better, the KAF 1001E (24&micro;)
Beats me :) </p> <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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HlafordCrux

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<p align="center"><font face="Times New Roman" size="4"><strong>Typical Specifications</strong></font></p><div align="center"><table border="1" cellspacing="0" width="400" height="194"><tbody><tr><th colspan="2" width="284" height="19" align="left"><p align="center"><font face="Arial" size="2" color="#ffffff">CCD</font></p></th></tr><tr><th width="139" height="24" align="right"><font face="Arial" size="2">CCD </font></th><td width="145" height="24" align="left" bgcolor="#ffffc4"><font face="Arial" size="2">Kodak KAF-0402ME</font>
 
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Saiph

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<p>Here's a good resource, from a leading astronomical CCD manufacturer on this topic:</p><p>http://www.ccd.com/ccd113.html</p><p>Using your numbers for the telescope, and the equations on the page I linked to, you'd want a telescope with pixels of approximately 12um for the f5 to 24um for the f10.&nbsp; This is assuming you obtain ~2 arcsecond seeing conditions.</p><p>The CCD you listed easily achieves that (it lists a 9um pixel size).&nbsp; There is a draw back to having pixels smaller than the <em>required </em>size for adequate sampling:&nbsp; You'll have to use longer exposure times for any given image to obtain the same "brightness" on the pixels.&nbsp; In amateur photography this isn't a huge drawback, and it can provide with better detailed images.&nbsp; Of course, the CCD offers the ability to "bin" your pixels, which will treat a group of pixels (say a 2x2 arrangement, so 4 pixels) as a single pixel.&nbsp; If you find exposure times required to be to long to obtain sufficient brightness in the image, try this option.&nbsp; It essentially increases the pixel size. </p><p>Out of curiosity, is this setup for still photography, or live video feed?</p><p>If it's still photography, do you know how to use flats, darks, and bias pictures to best process the CCD images you'll be taking?&nbsp; If it's live video feed...I'm not familiar with the software, and you may want to know about these anyway.</p> <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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HlafordCrux

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<p>The program won't open it says something about not having an installation log. What can I do?</p> <div class="Discussion_UserSignature"> <p> </p><p>-Hlaford Crux Observatory</p><p>Devoted to spreading God's word through research in astronomy.</p> </div>
 
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