Collimating the big mak

With the constant bad weather, it was propbably a good idea to collimate the 180mm F/15 Maksutov properly.

This involved a quit afternoon, a long inside raneg in the house free of obstacles, and a Geoptik artificial star (fixed brightness).

(Image credit: Teleskop Optics)

The collimation took place in bright daylight, however in the house, with the curtains closed. I positioned the star on a photo tripod, and the Maksutov on a HEQ5, allowing good positioning, and also re-positioning of the scope after tweaking the mirror.

The first image that came out looked as follows:

Initial image maksutov collimation

It may look like the collimation is already ver good. However, on closer inspection (using Sharpcap and a ASI2600MC camera) with a bullseye ring overlay, it was clear that the Poisson point (the little dot in the center) was not dead center in the middle of the diffraction rings.

A closer look at the defocused image, revealing the upwards leaning poisson point

Quality assesment of the diffraction pattern: smooth mirror surface, no ponched or deformed optics.

The de-centering is also visible in the in-focus diffraction pattern. It’s obvious that the rings on top of the star are closer together then the rings on the lower side. The upper side almost touches, where there is a clear gap on the lower side!

in-focus image (bahtinov mask focused) reveals a decentered diffraction pattern.

So the next step was to tackle this de-centering by using the push/pull bolts on the OTA backside. I used visually with a 4mm (675x) and 7mm (385x) eyepiece the in-focus pattern to slightly move the point towards the center. Ofcourse, everytime I touched the bolts, the star would move out of the field, so there it came in handy that I used the HEQ5 which allowed me to correct electronically using the mounts stepper motors.

In-center star diffraction pattern with pinched optics

A new processing of M109

My previous processing of M109 – 360x60s – did not turn out well. Serious issues with noise, most likely calibration files that were not ok.

So I did a complete re-build of the calibration files darks and bias.

The resulting stack and processed image is noticeably better:

M109, 360x60s Gain 0 Esprit120 F7 ASI2600MC Darks, Bias

Using the F/15 Maksutov as an astrograph

The F/15, 2700mm focal length 18cm aperture Maksutov is never intended to capture deep-sky images. Instead it excell’s at planets and the Moon.

However, with this focal length, it makes sense to give it a try at small objects like galaxies.

This is what came out of it, as a test, stacking 40 subs of 300s at gain 0. That’s 3 hours and 20 minutes. The detail is ok, what I noticed are triangular stars so I need to take a look at the collimation, seems to tight.

M66, Maksutov 180mm F/15 43x300s ASI2600MC

Compared to what my C11 did with an ASI183mm RGB last year:

M66, C11 F10 46x120s at G111 ASI183mm RGB