Thoughts on which imaging rigs to concentrate on

[Gina]

Yes indeed, I have read that.

I think there are advantages of having two separate RPi control units, even if using one RPi for 2 imaging cameras, 2 focusers and a guide camera is possible.  I think all that traffic could be a problem on just the one RPi.  Having separate systems means you don't lose both if one goes down (as mentioned in the INDI forum).  Finally, I think the extra complexity would be difficult to get working - a lot of work for a relatively small gain.

In fact, my aim is a number of RPis controlled from indoors.  Dual imaging rig (2 RPis), all sky camera (imaging and dew heater), roof control (open/close roof, show state, detect rain, check for faults) and finally a weather station with multiple sensors.

[stash_old]

2 hours ago, Gina said:

I think all that traffic could be a problem on just the one RPi.  Having separate systems means you don't lose both if one goes down

Totally 100% agree - should be great when its finished 🙂 Will follow with interest and benefit for my future project. 

[Gina]

Got the ASI 120MC-S apart and managed to prise the PCB out.  Changing the USB3 connector looks a bit tricky.  Big soldering iron for the case prongs and little one for the 9 signal connections.  I know what the 4 in a square do but not the 5 in a row.  USB2 only uses 4 wires so I'm wondering whether to just connect a USB2 cable and take it out through a hole drilled in the casing.

[Gina]

Found the information on high speed (or superspeed) USB3 connectors on Wikipedia.  Hadn't realised there were these extra connections. 

The RPi doesn't do superspeed USB3 - only USB2 which only uses 4 connections.

Edited February 5, 2020 by Gina

[Gina]

Connection diagram.

[JamesF]

Hmmm.  Unsoldering that doesn't look like the simplest job, though I'd have thought it ought to be possible.  Using just the four USB2 data pins and running a cable out through the side might be a viable short-term workaround though.  It's not like you're going to need huge data rates for guiding.

James

[Gina]

I could probably swap connectors at a pinch but I think a USB2 cable would be a lot less effort.

The only way I might want USB3 in that camera would be if I went over to RPI4 and used it for planetary imaging.

Edited February 5, 2020 by Gina

[Gina]

Connected a USB2 cable onto the Gnd and 4 USB2 connections.  Couldn't find a suitable place to drill a hole in the casing so removed the ST4 connector and ran the cable in that way, going up through one of the ST4 connector fixing holes.  Not tested it yet.

[Len1257]

Always used to Dremel or otherwise destroy the socket first then remove each pin individually when I did this sort of thing for a living.

 

[Gina]

Checked the ASI 120MC-S by using the RPi I have set up for my ASC and it works. 😀

[Gina]

Been sorting out the firmware for the RPi and I think I'm about ready again for imaging.

Although I have been able to overcome the problem, there is a lot of backlash in the 3D printed gears that drive the focus sleeve from the 28BYJ-48 stepper motor.  I'm going to try timing pulley and belt instead of spur gears and see if the sideways pressure on the focus sleeve due to the tension in the timing belt, affects the image at all.

[Gina]

After a rest, I decided to service my 3D printer and now trying a print of a bracket for the second camera.  If that works and also the second bracket, I plan to swap to a smaller nozzle and try printing better focus gears.  I've done this in the past.

[Mick H]

The Girl is up and running.

Hats off to ya Gina

[Gina]

Decided to go for a larger quadrant gear for focussing.  The current remote focussing covers a lot bigger focus range than needed.  I only need to accommodate the variations due to the lenses not being fully apochromatic - I can set the position approximately in daytime by focussing on distant trees then tighten the clamp on the focus sleeve.

Edited February 16, 2020 by Gina

[Gina]

With the current (smaller) quadrant gear on the working rig I needed to move the focus about 10mm so with the longer arm is should be around 20mm.  The rack is 60mm long so should give plenty of range.

[Gina]

I'm finding I often want to go out and turn the camera for better framing.  Currently using 0° and 90°.  Makes me wonder if I can arrange remote control to rotate the camera(s).  Both want to be at the same angle so one stepper motor such as a NEMA17 could do the rotating.

Two problems come to mind - connecting the stepper motor to the cameras and ensuring that the cameras point in the same direction and don't move relatively as the mount rotates.

[Davey-T]

I should think that unless you resort to precision engineering with bearings you'll introduce flop into the imaging train.

Dave

[Gina]

I rotate the entire imaging train - camera, filter wheel, lens and remote focuser system.  All optical components are solidly screwed together.

[Gina]

ATM I have a filter wheel on each camera but I don't have enough filters to need two filter wheels.  With camera lenses I can only do narrow band as they are not apochromatic down into the deep red.  For LRGB eg. for galaxies I need an APO telescope.  So I only need Ha, OIII and SII.  This means a single filter for one camera and two in a filter wheel for the other.  I shall have to decide on which filter goes where. 

Since OIII and SII need more imaging time than Ha and also both seem to need the moon out of the way I think I need both available at the same time.  That just leaves the Ha.  I think that will go on the same camera as the SII since some DSO have negligible SII and thus it makes sense to be able to image Ha and OIII at the same time.  This also means less focus change as Ha and SII are both in the deep red.

Edited February 28, 2020 by Gina

[Gina]

The camera without a filter wheel will have a 1.25" filter mounted in an adapter right on the camera.  All these parts are supplied with the camera.  Next to the camera, 7, is a ring with internal T2  (M42) thread.  Inside that goes an adapter, 6, from M42 to the 1.25" filter thread and inside that a standard 1.25" filter, 5.  In this case an Astrodon 3nm OIII filter.  The filter couldn't be any closer to the camera so vignetting will be minimal (even better than with the ZWO EFWmini on the other camera).

[Gina]

A couple of photos of the part completed rig.  Needs focus mechanism for LH lens and dew shield also the extra electronics for the 2nd camera & focuser.  Then I need to add dew heaters to both dew shields.

[Gina]

Now printing the focuser parts for the second lens.

[Gina]

First imaging run with this rig last night, processed today in PixInsight.  Only Ha due to very bright moon. 

Monoceros widefield 13° x 10°.  Ha.  146m (just under 2½ hours) integration time.  HistogramTransformation.

[wimvb]

On 28/02/2020 at 16:59, Gina said:

A couple of photos of the part completed rig.  Needs focus mechanism for LH lens and dew shield also the extra electronics for the 2nd camera & focuser.  Then I need to add dew heaters to both dew shields.

 

Doesn't the dew shield of the RH lens get in the way of the guide lens?

[Gina]

No, because the FoV of the guide lens is quite narrow (relatively).