Samyang 135mm compact and integrated

[paul]

I'm hoping to give this first light tonight. 

 

It's a Rpi 4, waveshare stepper hat running astroberry. The rings and case are 3d printed in PLA. 

 

The Rpi boots off the SSD velcroed to the side. The box includes extra power outputs to drive the camera and dew shield for the guidescope. 

 

I'm hoping the heat from the Pi will keep the primary lens clear. 

 

The ring on the focuser provides a 11 to 1 reduction. The stepper takes 1120 steps to go from closest focus to infinity. I'm hoping that is sufficient to get sharp focus. 

 

 

 

[paul]

I am now testing version 2 after first light highlighted a few over sights!  As a result, its taller than before and tapers at the base to allow clearance for the filter wheel to rotate and the saddle clamps to be tightened😏

Inside now features a timing belt tensioner. First light I will know if it has the ability to focus on infinity - hopefully tonight.

 

When I am happy with the design, I'll post the STL files.

 

Edited June 1, 2022 by paul

[Carastro]

Looks a great set up, I hope you can get focus OK as my focus is right on the end of the focusser, 1mm more and I would not be able to focus.   What camera are you using with it and is there a filterwheel? 

 

Roger (Apophis could not get focus at all with a filterwheel attached.

 

Carole 

Edited June 2, 2022 by Carastro

[paul]

Hi Carole, 

It's the ASI 1600 with Zwo 7 position EFW. If you use Zwo EOS adapter you have to remove the 10mm extender it's supplied with but on its own you can't get focus, a bhatinov mask shows I needed some negative millimeters. I had to add back in about 0. 5mm spacing to correct the back focus. I'm confident it will focus on stars now, the trees were some distance. I'll know tonight. Tbh I am having difficulty thinking of it in simple lens terms so assume multilens setup reduces the range of the focus plane to something very short (under 10mm)

Edited June 1, 2022 by paul

[paul]

Well I am now getting focus with the Bahtinov mask and ekos focus worked once for Lum. So it is possible. My star shapes are horrible so it looks like some nights of tuning ahead. 

 

Im imaging the Sadr region, badly framed as its all manual at the moment as I get to grips with Ekos. 

 

 

Rotating the camera for framing upset the system a bit. You need to find the new zero before attempting refocus. I'll mod the focus ring with timing belt glued all the way round, that should make rotation more predictable. 

Edited June 1, 2022 by paul

[Carastro]

Ah yes, that adapter is good if you don't want to attach a DSLR to the lens from time to time.

Glad it is all working.  Excellent lens I love it.

 

Carole 

[paul]

In action 😁:

[paul]

2 hours ago, Carastro said:

Ah yes, that adapter is good if you don't want to attach a DSLR to the lens from time to time.

Glad it is all working.  Excellent lens I love it.

 

Carole 

Hi Carole, it's the ZWO EF bayonet adapter:

so no problem switching back to a normal Canon camera.

[Carastro]

Pretty sure l have that adapter even though l have an Atik Camera and EFW but l am right at the limit of  focus and nothing else in the train.  
 

Carole

[paul]

I guess I'm on version 2.1.

 

The focuser ring is now double width to help fitting and keeping it square on the lens focus grip. I have stuck timing belt all around the ring and that works very well. Focusing is a lot quieter and is very consistent. There is some small backlash but I think that is the lens. I superglued the timing belt itself - I am impressed at how strong but still flexible the result is.

 

The belt tensioner can be adjusted without disassembling the rig, really pleased with how it performs - its the little things.

 

I have widened the electronics side panel to increase clearance between the RPI and add-on's such a RTC and the 12V to 5V buck converter. It was a tight squeeze before and the buck converter throws out noise reducing the WiFi range. The side panel is now symmetrically wider than the base unit by 6mm.

 

The top hat had minor tweaks to allow use of domed 5mm bolts.

 

I'm reprinting this iteration of the base for the 3rd time 🤞 hoping my printer doesn't squash layers. (I over tweaked it to remove droop! and caused printer Z-axis binding - the base ended up 3mm too short and not fitting with the side panel). 

 

I have modified the  base design to take recessed nuts instead of brass inserts. This will be more satisfactory for a build accuracy. To make the clamping of all bolts robust I've upped the infill at the top layers to 80% and have 5 layers for all top and bottom surfaces.

 

The jury is still out on astroberry and Ekos. I can crash it easily, I am not sure if I will trust it for a session. I need to get autofocus working with the limited range the focuser has and to accommodate the asymmetric backlash. I may need to modify the Waveshare driver to account for this specific scenario.

 

But the good thing is I can just swap out the RPI side panel for an Arduino one and use a windows laptop with NINA if needs be. Its also trivial to design side panels that mount alternative focusers such as a Skywatcher or ZWO EAF.

Edited June 9, 2022 by paul