Coma reducing

[Anthony1979]

Just wondering if i adjusted my primary mirror up or down would this reducing the comas in my images 

[andrew s]

No it will not assuming it a Newtonian telescope. Could you tell us what you have?

Regards Andrew 

[Anthony1979]

Skywatcher explorer 150p

[andrew s]

To reduce coma you need a coma corrector designed for a Newtonian telescope. 

Regards Andrew 

[Anthony1979]

Thanks 

[Anthony1979]

Expensive 133 pounds.. Wow

[alacant]

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

[Anthony1979]

I use a nikon d3500...... What hardware 

[alacant]

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 April 13, 2020 by alacant

[david_taurus83]

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.

[Anthony1979]

What it is is that i collimated my scope because one of the kids knocked it and before the comas wernt really noticable but after collimating they are more noticable... Thats what i dont understand 

[alacant]

5 minutes ago, Anthony1979 said:

after collimating they are more noticable

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

[Anthony1979]

24 minutes ago, alacant said:

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

My collimation looks spot on though

Edited April 13, 2020 by Anthony1979

[Anthony1979]

Is this good or bad

Skywatcher 150p f/5

[alacant]

29 minutes ago, Anthony1979 said:

good or bad

Good:)

[Anthony1979]

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

The centre circles doesnt seem to be centre tho

Edited April 13, 2020 by Anthony1979

[alacant]

I'd leave it and decide whether to get a coma corrector...

 

[andrew s]

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 April 13, 2020 by andrew s

[Anthony1979]

Thank you everyone.... Looks like a coma corrected purchase some time in the future

[alacant]

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 April 14, 2020 by alacant