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Coma reducing


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Hi

You don't need a coma corrector if you choose a camera with a small sensor. It is also possible to correct coma with modern software should you wish to use a larger sensor. 

Even so, if you're beginning, I think it best to correct coma in hardware.

HTH

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10 hours ago, Anthony1979 said:

a nikon d3500

It's doable in software, but I'd still recommend a coma corrector for that size of sensor. Astro imaging with a telsecope isn't going to come cheaply I'm afraid but there are loadsa other ways to take good sky images. 

If you want to try, to achieve focus, you'll have to bring the primary mirror closer to the secondary. Replace the three bolts holding the main mirror with 4cm m5. Get some extra nuts and washers to go with the new bolts.  

Cheers and HTH.

Edited by alacant
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Moving the mirror up will only shift the focal point further out on your focuser. I understand what you are suggesting but if you move the mirror and leave the camera in the same spot, you wont be focused and will have to move the camera out the same distance as the mirror. So the coma will still be present.

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30 minutes ago, Anthony1979 said:

So theres no reason to touch the collimation just leave it like it is 

The centre circles doesnt seem to be centre tho

There is always some offset in a correctly collimated Newtonian. 

Regards Andrew 

Edited by andrew s
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19 hours ago, Anthony1979 said:

The centre circles doesnt seem to be centre

Correct. A well collimated f5 Newtonian reflector will show an offset. Yours looks perfectly offset to my eye.

My f3.9 is even further offset. My f8, dead centre.

Don't forget to have a go at coma correction in software. No need to wait until you have saved for the cc. e.g. StarTools does an excellent job if it. I'm sure most other astro software will do it too 

HTH

Edited by alacant
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