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#1
20-03-2012, 07:35 AM
 cybereye (Mario) Mozzies love me! Join Date: Aug 2009 Location: Brisbane Posts: 1,277
A question on eyepiece projection & resolution

Good morning!

I have a question on just how much resolution I can expect from my current planetary imaging setup. To set up the question, I'll firstly go through how I understand some of the basics.

I have an 8" reflector with a focal length of 1200mm. As I understand it, the maximum useful magnification I will get from my scope is 400x. Now using a 10mm eyepiece I have a magnification of 120x and if I add my 2x Barlow into the mix my magnification is now 240x which is still well below the theoretical 400x that I spoke about before.

However when I take an image using eyepiece projection onto the chip of my QHY5V, I calculate from my plate scale that I'm working my scope as though it has a focal length of about 6400mm. So my question is:

Does that mean my magnification is 640x and I've gone way past my theoretical limit of magnification for my scope? Or am I OK and I can use a 3x Barlow to give me more detail (this being 360x magnification)?

Obviously I haven't taken seeing into consideration but I'll keep that out of the equations for the time-being!!

Thanks in advance for any help people might be able to give me on this,

Cheers,
Mario
#2
20-03-2012, 10:45 AM
 bojan amateur Join Date: Jul 2006 Location: Mt Waverley, VIC Posts: 5,700
Magnification is meaningful only when you observe something visually.
Than the magnification (this is a number without dimension) indicates how larger the viewing angle is - for example, Moon has apparent diameter of 0.5° on the sky .
If your telescope has magnification 100x, the Moon will be seen through the eyepiece with apparent diameter of 50°.

When taking photographs, we are dealing with the scale: arcsec/pixel for example.
Your estimate of FL (6400mm) and you pixel size will give you the scale of your camera system.
Assuming pixel size is 5.7u, you have 0.36 arcsec/pixel

Last edited by bojan; 20-03-2012 at 11:34 AM.

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