I recently acquired an EvoGuide to use as a guiding scope on my old C8 SCT. While in the city apartment though, I have been experimenting with the Evoguide as an imaging scope, and this is one of my first efforts.

I have modified an old Meade ETX90 mount to be used with the Evoguide scope and with OnStep for tracking and slewing. It has been quite a journey as I have not yet found a Meade ETX90 mod to stepper motors yet. I stripped all electronics and motors and left only the RA and DEC worm gears. To those, I attaced GT2 gears and timing belts with NEMA17 stepper motors. I drive the stepper motors with OnStep on R32 CNCv3 and it works like a charm. I removed the ETX90 scope and made a custom base out of some wooden pieces for the Evoguide scope to connect it to the fork mount. The system works beautifully, I control it with NINA, platesolve works and I have even left it to take images overnight unattended. There are two problems that I have struggled to fix: (1) the RA worm gear shaft is not 100% cylindrical but very slightly conical, which leads to the GT2 gear not being exactly perpendicular to the axis of the worm and thus there is a small wobble over the 24minute period of the RA axis , (2) there is significant backlash, especially in DEC, about half degree, and I have struggled to get PHD2 to work. Thus, I am limited to unguided 10second exposures in order to keep my stars round and I end up having to throw away about 20% of the exposures where the stars are streaking.

The M8 nebula photo consists of about 900 10 second exposures, of which I kept 580. The rest I had to bin either due to high altitude clouds, or streaking stars, or off-centre image. I also took 50 bias, 50 darks, 50 flats (tshirt method) and 50 darkflats. I am wondering about the applicability of flats as I am not tracking and thus each sub is wobbling quite a bit between each frame.

My location is Athens, Greece. The image is taken without any filters with heavy light polution as I am imaging over a city of 4million population. Sagitarius stars are hardly visible at all to the naked eye.

I used:

Modified Meade ETX90 mount with custom tracking based on OnStep and custom base for Evoguide scope.

Evoguide 50 as imaging scope.

Bahtinov mask for focusing.

ZWO ASI 385 Color (not cooled) for imaging, at gain 100.

Onstep controller (R32 CNCv3) for tracking and slewing.

NINA for Camera control, Telescope control, Sequence, Plate Solving.

My processing skills are still very basic (simple stretches/curves), just using Gimp or Photoshop.