Fwhm measurement and value

[Sierrase]

Hello,
Question relative to fwhm:
1. The value is given in pixel or other?
2. I have a celestron nexstar se with its original knob to focus. The camera is the zwo asi294 mcpro. Adjusting the focus on arcturus but i never obtain a value better than 6 and i Try to do the adjustment very slowly.
Is that normal or there is some tips to have better values ? Stars are not saturated When i adjust focusing.
Thanks for your replies.

[admin]

Hi,

the values are in pixels.

You can check out the field of view calculator (https://astronomy.tools/calculators/field_of_view/) for your exact setup, but an 8" SCT with a 294 camera has a pixel scale of about 0.5 arc seconds per pixel, so you are unlikely to get very small FWHM as typical 1 to 2 arc second seeing will make for wider stars. Also, with an SCT, tube currents and/or poor collimation can really affect the sharpness of the image.

cheers,

Robin

[Sierrase]

Thanks a lot. New in astrophoto but I really enjoy and also enjoy sharp cap thanks again

[yomamma]

Get an electronic focuser and learn to use it with Sharpcap autofocus you will be glad you did, especially with the se. I have an 8" SCT and it is hard to get in the 5s and stay there but auto focus configured properly and run every half hour or so will make a difference. If I just let it go my focus will degrade quickly

[Sierrase]

Get an electronic focuser and learn to use it with Sharpcap autofocus you will be glad you did, especially with the se. I have an 8" SCT and it is hard to get in the 5s and stay there but auto focus configured properly and run every half hour or so will make a difference. If I just let it go my focus will degrade quickly

Thanks a lot , it’s what I will do