Mewlon 250 First Light

[Atmos]

Decided I really should start jumping into the longer focal length imaging and later last week I got some adapters to allow me to attach a camera to my older Mewlon 250 with CRS installed.

Collimation so far is what I could do with a Tak Collimation Scope a few months back on my kitchen table. I had hoped on checking the collimation a bit last night but the seeing wasn't crash hot.

It's showing some lateral chromatic aberration, not sure if that's a consequence of the CRS, the ZWO UV/IR filter OR imaging at 45-50º above the horizon on a not great night.

As I haven't taken any calibration frames I did attempt to create some synthetic flats but they didn't turn out so well. Helped remove a few of the numerous dust donuts but the corners weren't great so I've just cropped them out. Stars are very good out to the corners but I think I need to square the sensor off a bit more.

Higher Res Astrobin Link (https://www.astrobin.com/full/412791/0/)

I'm thinking I need to play with the settings in my mount software in the future. When creating the pointing models it was really struggling at times to plate solve the images. It doesn't help imaging in skies so bright that most of the stars in a 10s exposure are barely detected (unless reasonably bright). There were a number of 10s exposures that didn't appear to show a single star!

It was a learning experience and one that has me contemplating adding an OAG into the mix. Imaging unguided at 0.4"/pixel with a 20kg telescope definitely isn't as easy as imaging at 1.16"pixel with a 10kg one :P

EDIT: Oh and that weird mottling towards the top of the frame... That's some frost on the sensor that dissipated after the first 40 minutes or so. Cooled the camera to -15ºC a little too fast with the high air humidity.

[Slawomir]

After reading the long intro listing numerous issues I certainly was nicely surprised when I looked at the image - I think it is a great close up on one of our favourites Colin :thumbsup:

Curious - what causes hexagonal halos around brighter stars?

[Atmos]

Waiting for a night of better seeing to be able to check collimation, the Tak scope does well to get pretty close but there is usually small tweaks that need to be done especially for those astute planetary observers :)

Four spider veins give four diffraction spikes, three veins give 6 weaker spikes. The older Mewlon have 3 veins where as the new M250CRS has four.

[Slawomir]

Thanks Colin - I think you have a very nice scope that with a bit of fine-tuning will give you wonderful high resolution data.

[multiweb]

Looks good Colin. Much flatter fov than my Mewlon 210. Does the 250 have a corrector in the imaging train?

[Atmos]

I’m hoping to install fans as well in the coming weeks which will help with cooldown. Need a night of good seeing to see whether collimation is correct. It’s certainly close but I’m not sure if it needs tweaking yet.
I have an OAG and ASI120MM-S so I can go back to guiding and might do that especially I want to do 1200s exposures at 0.4”/pixel.



The stars in the corners are virtually the same as on-axis, maybe better seeing will change that as the stars get smaller however. A few months back in installed the corrector baffle tube (replaces the original baffle tube that screws into the primary) into this older Mewlon 250 which reduces it from F/12 to F/10.

[traveller]

Very good for first light Colin and beautiful star colours too!
Bo

[beren]

:thumbsup: Great work, be keen to see what you do further with the corrected Mewlon

[Andy01]

Only seeing this on my mobile but looks impressive! :thumbsup:
Wacky star diffraction spikes, haven’t seen those before :question:
Lovely colours, nicely done :)