Here are a couple of photos of the rig less the electronics box that controls the lens focus and captures the images.  Between the lens and the filter wheel are a "Russian Adapter" which converts the Pentax M42x1mm to T2 thread (M42x0.75MM) and a T2 extension tube to obtain the correct back focus for the lens.  The support brackets for the camera and lens attach to the jaws of a mount which not only grips the brackets but closes them onto the lens and camera, doing two jobs at the same time.

Like my other imaging rigs this will also be controlled by an Raspberry Pi 3 with INDI drivers for the camera, filter wheel and focuser - it will also control the EQ8 mount which I shall be using until I get my DIY fork mount made.  Client software will likewise be KStars/Ekos running on my Linux Mint desktop PC.

Getting this rig ready for possible imaging tonight.  Printed the gears for the lens remote focussing and ready to attach the stepper motor to its bracket.  The electronics box will be the one from the Esprit rig and temporarily attacked with elastic bands.  It's not worth making a more permanent arrangement as I'm not expecting to use this single imaging rig on the EQ8 once I have the dual rig ready.  There's no way I can get the dual rig ready for tonight as there's too much still to do to it but I expect to be working on that next.

The rain has gone and the sun is out though still plenty of clouds so still uncertain about tonight for imaging.  ATM I'm also not sure if I'm going to be ready because the rig is not working - not getting a LAN connection so I have some faultfinding to do.  I have the rig set up in the observatory and I think I shall have to bring it back indoors to sort out.  I have a digital ammeter on my observatory power supply and the rig is drawing just under an amp which seems reasonable.  The fan is running on the camera so that's getting power.  The electronics box has worked fine before so it seems something has gone wrong with it.

Here are some photos.

Have rig indoors and sorting it out.  The problem was that the fuse for the RPi and rest of the electronics had blown (goodness knows why)  replaced it with a 0.5A fuse (didn't have a 1A that was in before).  Checked all voltages and they were fine (13.5v from bench PSU, 5.1v for RPi and 3.3v).  Have the camera working and the focus moves though something is catching.

The bolts attaching the stepper motor were too long and catching on the gear quadrant - replaced with shorter one and all well now.  Testing the focussing from Ekos showed 4000 counts moved the quadrant from one end to the other - this should be fine and may even be suitable for auto-focussing.  Next to point the camera out of the window and focus on the distant horizon.

Without the rig on the mount there's nothing to hold the alignment for focussing so I've set up the rig on the EQ8 mount in the observatory and set up the focus approximately on a far tree using manual remote focus from Ekos.  I've checked the camera cooling and that's working fine.  I'll switch the mount on and check I can still control it from Ekos remotely.

Still cloud but there looks like a front almost slightly to the SW with clear sky SW of that.  If it moves NE wards the sky will clear.

The front has moved a bit in the right direction   And I have the mount on and tracking in sidereal mode so I think I'm just about ready for imaging   No dew heater but I do have the funnel shaped dew shield and maybe the heat from the camera will keep the dew off.  I can only hope

Here's the current view to the east.

Well dark enough now to see the stars and, yes, it has cleared.  Trouble is, I can't get focus.  Which is strange because I've had this lens in use with this setup before.  The only difference is that I'm now using my new ASI1600MM-Cool camera.  I think it's unlikely that the back focus could be different.  I seem to want a mm or two more spacer so I guess I'll have to bring the rig back indoors and see if I can sort out some different extension tubes.

I wanted an extra 2mm but the nearest I can get is something like 3-4mm longer so it could well be out the other way.  One plus point - I found no dew on the lens when in the observatory so if I can sort out the focus I should be good for imaging.  Unless I find another problem, of course.

I was right - now the focus is out the other way

Have you found an alternative that gets you closer?

Swapped the Russian Adapter and short extension tube for a longer T2 extension tube with the lens only part way screwed on due to the difference in thread pitch.  I now can get focus   I'm having trouble getting sharp focus though.  The auto-focus routine worked but just got me to about where I was by manual focus though auto-focus was a lot faster.

This image is with 30s exposure and gain at 540 (54dB) 3nm Ha filter and camera temperature of -30C.

Another image - 45s exposure and gain of 600 (60dB - the maximum).

That was overexposed so here is a 20s image.

Well, I think I've just about had enough for tonight and I don't think I can achieve much more ATM.  I need to sort out the focussing and I think I can do that in the daytime using a distant tree or trees. 

I guess I made reasonable use of this month's clear night but I seem to be a bit further away from being ready for imaging than I thought.  I think for the auto-focus to work properly I need finer focussing which can be obtained by a higher gear ratio and micro-stepping of the stepper motor.

Let's look at a calculation...  Back focus of M42 is 45.46mm.  Back focus of camera is 6.5mm.  We want 45.46mm plus 1mm for Astrodon filter = 46.46mm.  So distance from lens to camera faces wants to be 46.46-6.5 = 39.96mm.  ZWO EFW is 20mm so about 20mm of extension wanted.  Since the lens moves forwards for focussing extending the spacers required the extension required with EFW is 20mm+ depending on the lens focal length.  The 28mm only moves 3mm whereas the 135mm lens moves 13mm.

Using the 28mm f3.5 lens I have now sorted out the focussing.  This is the most critical with its short focal length.  Used the Baader 20-16mm adjustable extension tube plus a 5mm extension ring.  The lens will now focus on the distant horizon well within its focus range.

Have remote focus working fine and have focused on far tree.  Here's a blowup.

Now I have to find out why the mount isn't working

Quote

2017-10-05T19:50:54: Error: -> Error connecting to port /dev/ttyUSB0: Port failure Error: No such file or directory. Check if device is connected to this port.

EDIT - Fixed - mount plugged into a different USB port   Mount mow working

Observatory roof opened and rig pointed roughly towards Cygnus or Cassiopeia.

Think I've just seen the ISS pass through the FOV   Too fast for an aircraft.

Now I've seen an aircraft - quite different - three traces from the navigation lights.  The other trace was single.

I don't think the mount is tracking   Getting elongated stars.  No sign of nebulosity but I may be in the wrong area of the sky.  Haven't sorted out plate solving with this system yet.  OTOH it may be high level cloud.

This is a 120s sub with gain at 600 (maximum).  This would normally show nebulosity.

I've found Cygnus   This is a 30s exposure, gain of 600 (60dB).   Astrodon 3nm Ha filter.  28mm f3.5 lens.  Screenshot from KStars.