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Imaging with a Celestron 130


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On 17/09/2021 at 12:37, AstroMuni said:

Did you notice a big difference when you swapped mirrors? I had toyed with this idea before the pandemic hit us but wanted to understand the full potential of my scope the way its built - spherical mirror and all.

Not sure that anyone would put spherical mirror in F/5 newtonian.

Although it won't make much difference when imaging (seeing will mask any aberrations on that level) - it would seriously impact visual performance on planets and moon.

Spherical mirror won't suffer from coma - parabolic mirror will.

You should probably concentrate on collimating your scope first. Second thing to try to sort out would be focuser. Focusers on such scopes are rather poor. I've seen people 3d print replacement focuser adapters because original are not quite squared on tube.

ASI224 is too small sensor to seriously notice coma. Diffraction limited field has radius of F^3/90 (in millimeters) - where F is F/ratio of the scope - that means that diffraction limited field (as far as coma is concerned) has radius of ~1.4mm.

ASI224 has diagonal of 6mm - so for central part of sensor - coma would not be noticed even for planetary performance. DSO imaging is impacted by seeing.

Here is an example with F/6 telescope and x0.5 reducer and sensor the size of ASI224:

image.png.340e8558a872aaa4e7399ce66915ad6b.png

At F/6, diffraction limited field is 2.4mm but with x0.5 reducer that will be 1.2mm on sensor - less than 1.4mm with your setup. No coma to be seen.

 

 

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On 20/09/2021 at 10:54, vlaiv said:

Focusers on such scopes are rather poor. I've seen people 3d print replacement focuser adapters because original are not quite squared on tube.

I have noticed that and have tried to fix the wobble as best I could. Changing the focuser on this scope is beyond my skill capability :)

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