Mountings and Controls For Widefield Imaging Rig

[Gina]

This thread is a fork from my "Thoughts on which imaging rigs to concentrate on" thread to cover just the DIY aspects of my imaging rig.  The other thread has moved to the Imaging - Discussion forum and will be confined to the imaging aspects only which it has mainly become.

Here I will be posting about 3D printed parts that allow for different lenses to be mounted on my EQ8 and also maybe electronics to control more than just focus such as zoom on zoom lenses.  I would also like to arrange some sort of mechanical motor driven system to remotely control rotation of the camera so that I can frame the object not only in X, Y coordinates but also rotate the frame to fit the DSO(s) being captured.

[Gina]

Adding extra controls to the imaging rig has repercussions apart from just the actual mechanics of it and the drive electronics, I would like to go over to Linux rather than using Windows which would mean either adapting the current INDI drivers or writing my own.  If I were to stay with Windows I would need to adapt my focuser app to include the other functions.  One possibility in Linux/INDI would be the indiduino driver which controls an Arduino from INDI.

I have plenty of experience of writing Arduino software/firmware so that part would be easy enough.

ATM the idea of additional controls is just that - an idea - food for thought.

[Gina]

When the adapter to use EOS lenses on the ZWO EFW filter wheel arrives I shall be able to use the Canon lenses in addition to the M42 screw mount lenses, the first thought being the standard zoom lens supplied with the EOS cameras of which I have several.  These lenses seem to work well enough for terrestrial photography so I see no reason why they shouldn't be fine for astro use.  The ability to change focal length remotely has considerable appeal

Of course, it does remain to be seen just how well these lenses perform for astro imaging and until I've tried one I won't be providing remote zoom control.  Same applies to the Vivitar zoom lens with M42 screw mount though I can try that as soon as I've designed and printed a mounting bracket and focus gear for it.

[D4N]

Being able to remotely rotate the camera and adjust the focal length to perfectly frame targets sounds great, it also sounds like it will be quite hard to implement!

Are you thinking to rotate the camera and lens together?  I guess this would be optimal if you are using flats.

[Gina]

Yes, I think it will be best to rotate the lot, which is what I do manually now.  The difficulty will be providing a rotating assembly that won't move as the mount rotates in RA.  Ball bearings may be sufficient at the focal lengths I'm using otherwise maybe some kind of spring loading.  At least the EQ8 won't be bothered by the extra weight involved.  Fortunately, the ZWO EFW mini filter wheel is both light and small.  I wouldn't like to rotate an Atik EFW2   I think this will be an interesting project

[Alien 13]

Look forward to this thread, I have been using my DSLR for remote shooting with control and liveview over wi fi via EOS utils but one thing it cant control is lens zoom. I eventually want to get a complete robotic set up.

Alan

[Gina]

Controlling the zoom should be much the same as controlling the focus, both are knurled sleeves on the lens and I would use the same sort of control except that the zoom would need a wider segment gear.

Here are a couple of photos of my current rig with ASI1600MM-Cool camera, ZWO EFW mini filter wheel, T2 spacer, M42/1 to T2 adapter and 135mm f2.5 lens with home made dew shield.  The mounting brackets were 3D printed with a gap in the base such that tightening the mount clamps tightened the brackets and clamping the camera and lens.  The lens bracket also holds the stepper motor for focussing.  The 3D printed (pink) focus gear segment is clamped onto the focus sleeve with lugs and M4 screw.

The third pic is a screenshot from SketchUp showing the focus gears.

[Gina]

Just looked at the zoom lenses - the Canon looks like about 45 degrees range on the zoom and the Vivitar is about 90 degrees.

[Gina]

As for the camera rotation, 180 degrees will cover the amount needed to give any orientation as the image can be turned 180 in the processing.  Not sure if those tiny stepper motors would be strong enough to rotate what almost amounts to a turret - would depend on the gearing and that depends on how long I would be prepared to wait for it to turn to the new orientation. 

I'm thinking that the turret gear would be around 100mm diameter and the stepper motor (with built-in 64:1 gearbox) rotates at 10s per revolution at full speed.  I think I could put up with maybe a minute to turn 180 degrees = 12x the time for the motor to turn 180 degrees and a 12:1 gear ratio.  That makes the motor pinion 8mm diameter.  Alternatively, a 16mm pinion would give about 6:1 and half a minute maximum rotation time.  That's better - think that would work

[Gina]

The Atik EFW2 filter wheel has the facility for rotating the camera, though best done manually and the clamping screws tightened before imaging.  The ZWO has no such facility but I think it would be very difficult to keep the optical axis exactly in line whilst allowing rotation.  Anyway, the Atik isn't an option as it's broken and I can't get a spare part.  OTOH having the whole optical train solidly screwed together makes for a sound system.

Avoiding movement between optical rig and mount is important but not as critical as the lens to camera sensor.  As long as it doesn't move during an exposure, any longer period movement will be corrected by image registration.  This already corrects for imperfect PA without guiding and with exposures under a few minutes there is no problem.

So for changing the orientation of the FOV the whole optical train will rotate together with the servos motors that drive the focus and zoom (if applicable) plus the USB cable from camera hub to FW.  And we might as well include the Arduino Nano as that connects to the USB hub in the camera too and connects to the stepper motors for focus and zoom.  In fact the stepper motor for camera rotation could also rotate with the rest and use a fixed gear ring.

[Gina]

Here's a couple of photos of the imaging rig with Vivitar 35mm to 105mm zoom lens.  The mechanics of this lens are rather loose so I might have to provide extra support.

[Gina]

Zoom lenses would be very nice from the operational point of view but I've been put off by the considered opinion that zoom lenses are not good for astro use due to all the extra glass to air surfaces that can cause reflections etc.

I think what I'll do to test this is to produce mountings for the Vivitar lens similar to previous ones for my prime lenses and use remote focus only.  I would adjust the zoom manually for testing.

[Gina]

The ZWO EOS lens adapter came today so I shall be able to make the bracket and focus gear for the 45mm medium format lens.  Plus I shall be able to try Canon lenses such as the standard 18-55mm zoom and the 75-300mm zoom lens that I also have.  Those together with the M42 35-105mm zoom cover  full range of 18-300mm focal length if I find zoom lenses usable.  The prime lenses are still preferable where the FOV fits, having wider aperture.

[Alien 13]

I am thinking of control of my zoom lenses over bluetooth using the microbit, it looks do able but am wondering how I could control the end stops and if the system could be calibrated so that it could step to fixed zoom lengths between min and max.

Alan

[Horwig]

Don't forget that you can still use your Pentax screw lenses via adaptors like this:

http://www.ebay.co.uk/itm/Carl-Zeiss-Pentax-Zenit-M42-screw-mount-lens-to-Canon-EOS-EF-mount-adapter-5D-II-/262147333294?hash=item3d0932dcae:m:m-1Sf-OLAe1syQ6Cln4XBkg

And eos to Pentax 67 adaptors are not that much more:

http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=pentax+67+to+eos&_sop=15

But beware these, the ones I've played with are not that rigid, with the heavy glass up front the pentax bayonet has play, but fine if the lens is supported.

Huw

[Gina]

4 hours ago, Alien 13 said:

I am thinking of control of my zoom lenses over bluetooth using the microbit, it looks do able but am wondering how I could control the end stops and if the system could be calibrated so that it could step to fixed zoom lengths between min and max.

Alan

Yes, the zoom will want the remote control to go from end to end but not over-run.  The range can be calculated in terms of number of steps of the stepper motor given the gear ratio.  The system would need setting up with the initial position at one extreme of the zoom, then the other end would be reached with the calculated number of steps.  To allow for powering down without turning the zoom to the reference end, the current position would need saving to EEPROM.  I know how to do this with the Arduino but I know nothing about the microbit.

Intermediate zoom positions could be calculated in the same way as the full range and these position could be incorporated into the control software or the microprocessor firmware.

As an alternative to setting the reference position to one end of the zoom range you could perhaps arrange a mechanical endstop microswitch or Hall switch and let the firmware find the reference point in the same way as 3D printers are homed to a fixed position.

[Gina]

For my own setup, I have found an Arduino Nano stepper motor control board I made up for one of my triple imaging rigs.  This would drive 3 little 28BYJ-48 stepper motors for focus, zoom and camera rotation.   My zoom control would use the system I described first in my post above.

[Gina]

4 hours ago, Horwig said:

Don't forget that you can still use your Pentax screw lenses via adaptors like this:

http://www.ebay.co.uk/itm/Carl-Zeiss-Pentax-Zenit-M42-screw-mount-lens-to-Canon-EOS-EF-mount-adapter-5D-II-/262147333294?hash=item3d0932dcae:m:m-1Sf-OLAe1syQ6Cln4XBkg

And eos to Pentax 67 adaptors are not that much more:

http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=pentax+67+to+eos&_sop=15

But beware these, the ones I've played with are not that rigid, with the heavy glass up front the pentax bayonet has play, but fine if the lens is supported.

Huw

I'm using an M42/1 to T2 adapter for my Pentax screw lenses which makes for a very rigid connection - better than any bayonet mount.  Unfortunately, I have to use bayonet mounts for my 45mm MF lens.  But I will be supporting the lens as well as the camera so it should be alright.

[Gina]

Here is a SketchUp model of my thoughts for a framework to carry the camera, filter wheel and focus motor allowing for rotating the whole rig by 180 degrees.  Imaging rig will be supported within this frame with the filter wheel and focus motor sticking out the side.  Camera will go in the left hand end as shown here, with the lens looking out the right hand side.  

Not sure yet about the motor drive for remote rotation but most likely a gear on the camera end with a stepper motor and pinion on the fixed part.

Fixed part is shown in green, rotating cage/frame in yellow and supporting wheels in red.

[Gina]

Been thinking about the best way of placing the imaging rig within the framework.  Originally I was thinking of having the camera and optical axis in the centre ie. optical axis in line with rotation axis, but now I'm wondering whether it would be better offset in view of the filter wheel.  This would mean that camera and lens supports would be offset but I don't think that would be particularly difficult and should mean I can get away with a smaller cage/framework.

[Gina]

Here's a screenshot of camera and FW model and another with a minimal sized tube/framework.  It will be a frame rather than a solid tube.  May need to be bigger depending on the lens.  The tube in the model is 120mm ID and 130mm OD and well within the capabilities  of my "GinaRep Pilot" 3D printer.

[Gina]

This model shows the camera support ring and the place where it will go.  I have yet to work out clamping arrangements.

[Gina]

Models of 135mm lens support ring with stepper motor mounting and focus gears (segment spur gear and motor pinion).

[Gina]

45mm medium format lens support ring and segment gear models.

[Gina]

I think the lens support rings will need to be split so that they can be fitted to the lens as well as allowing for clamping the lens.  Then to secure both the lens ring and camera ring the cage/tube/frame would be split with lugs for screws to clamp up like the focus segment gear.  The cage/tube/frame (or whatever we call it) is getting ever more complicated   Never mind, almost anything is possible with 3D printing

The general idea is that any of the various lenses can be fitted to the filter wheel and held in place with a custom support ring and focus segment gear in the frame.  The same cage/tube/frame and drive system being common to all rigs of different FOV.