Dual Imaging Scope Alignment Mechanism

[Gina]

Taking the base of 200mm, 40 arcminutes becomes about 2.5mm so a slot in a plate giving that much movement might be a way to do it. This need not necessarily be on the same scope as the alignment adjustment.

[Gina]

I believe I now have a design for a combined alignment and matrix shift mechanism.

I propose to the move the objective ends of the scopes nearer or further apart by using a turn buckle across the top. The difference in top dimention will be halved with the bottoms fixed providing finer adjustment.

The adjustment orthogonal to this (up/down if the mount was horizontal) will be obtained by moving the objective end ring bottom mounting up and down. A bolt screwed into the M6 hole in the ring will be turned to provide the adjustment. To stop the bolt moving relative to the mounting plate it will be mounted in a ball bearing and secured with a nut. In turn the ball bearing will sit in a recess in the mounting plate and be held in by a large washer bolted onto the main mounting plate. To provide the turning motion I propose to attach a timing pulley to the bolt underneath the mounting plate and drive this with a timing belt form a stepper motor. Much like focussing, the stepper can be turned in very small steps to achieve alignment. Matrix shift can then be obtained by stepping an appropriate fixed number of steps.

Here are a couple of screenshots of a SketchUp model I have constructed showing a part exploded wiew of the up/down mechanism. I may produce a cross-sectional diagram to make tis clearer.

[Gina]

Here is the sectional view.

[Gina]

I have done a test with the two ED80s and 314L+ cameras using my original mounting - no adjustment. There is a slight misalignment parallel to the mounting plate probably caused by my screw holes not being in exactly the right place. There is negligible misalignment in the other direction. The "horizontal" misalignment could easily be corrected using an elongated mounting hole.

Here are images taken by running two instances of Artemis Capture and saving a few images from each camera and labelling them red and gold. The third image is a result of using RegiStar to align the images and combining the result using "union". The black margin shows the error in alignment. This would be quite acceptable IMO though could easily be reduced as I said above.

[Gina]

So... nothing complicated to get alignment quite adequate so I just want to work out a simple and easy to operate "matrix shift".

A rocking plate may be easiest. The offset being given by the height of the pivot. I have a piece of 5mm thick ali plate about 290mm x 75mm. OTOH the rotating screw driven by stepper motor idea would provide remote control.

[Auntystatic]

I see your trying to match field of views, but have you thought of pixel size? overlaying a 1.4mp image on to a 6mp image will reduce the resolution of the 6mp image, effectively blurring the image slightly, great excuse to buy a second 460, just a thought

[nmoushon]

Been following this one. Very interesting thoughts from everyone. Hope it goes well for you Gina.

Would someone mind posting a link to the Cassady plate? I can't seem to find it for the life of me.

[Gina]

I see your trying to match field of views, but have you thought of pixel size? overlaying a 1.4mp image on to a 6mp image will reduce the resolution of the 6mp image, effectively blurring the image slightly, great excuse to buy a second 460, just a thought

There is no problem with combining images with different pixel sizes. I feed image files through RegiStar to align and rescale them. This results in all images upscaled to the highest resolution image. Yes, there is a lower real resolution from the lower res original but, like binning, this can be arranged not to reduce the overall apparent resolution. eg. higher resolution luminance can be combined with lower res or binned RGB. Similarly I have used hi res Ha combined with lower res OIII and SII in NB Hubble pallette images. Most nebulae are very rich in Ha but need a lot more exposure in OIII and SII.

[Gina]

Been following this one. Very interesting thoughts from everyone. Hope it goes well for you Gina.

Thank you

Would someone mind posting a link to the Cassady plate? I can't seem to find it for the life of me.

I gather the Cassady plate is not longer being produced.

[Gina]

To put exact figures into my 460EX frame compared with 2 x 314L+ mosaic panels...

Calculating the 314L+ image size :- Width - 1392 x 6.45 = 8978.4 microns Height - 1040 x 6.45 = 6708 microns

460EX image size is quoted as 12.49 x 9.99 mm

With the sensors at right angles the width of the 314L+ corresponds to the height of the 460EX ie. 8.98 cf 9.99 which differs by 10%. Just under twice the height of the 314L+ (allowing for a small overlap) corresponds to the width of the 460EX ie. 2 x 6.7 = 13.4 mm - less 5% = 12.7 mm ie. 12.7 cf 12.5 which gives a nice match.

Conclusion :- 10% difference means no problem with alignment and the shift required for a 2 panel matrix can be adjusted to give close coverage while allowing for a small overlap in the panels. This seems a very good result to me

[Auntystatic]

Well I can not wait to see your results, I haven't taken an image since last November, and currently don't have any astro darkness, it won't return until the last week in July, I start an astronomy course in Oct with the open university so I better use this down time to check and maintain the gear, the 190mn is sat at the bottom of the stairs all covered up so it doesn't get dusty, as always good luck with your project

[Gina]

Well I can not wait to see your results, I haven't taken an image since last November, and currently don't have any astro darkness, it won't return until the last week in July, I start an astronomy course in Oct with the open university so I better use this down time to check and maintain the gear, the 190mn is sat at the bottom of the stairs all covered up so it doesn't get dusty, as always good luck with your project

Thank you Danielle We get a couple of hours dark enough for imaging a night but very few clear ones recently. However, we are forecast a week of so of summer complete with clear night skies so I'm hoping for some imaging time

Good luck with you OU course - sounds interesting And good luck with your imaging

[Gina]

I've thought some more about the matrix shift mechanism and decided on the threaded bolt in the tube ring mounting hole with stepper motor drive but with a redesign to suit what I have available. I was intending to use a trepanning tool (tank cutter) to cut the recess for the ball bearing but it doesn't go small enough. So I'm avoiding the recess by mounting the bearing on the surface of the mounting plate and using another small plate to locate the bearing.

[Gina]

Here are some photos of the design put into practice.

[russellhq]

What about a second mount? Might make things easier.

[Gina]

What about a second mount? Might make things easier.

I thought of the possibility of a second mount for my widefield rig. Something like an HEQ5. Of course, if I were to upgrade to an EQ8 the NEQ6 could be used for widefield

[Gina]

I've now added a stepper motor to drive the matrix shift screw.

[russellhq]

Of course you have :-D

[Gina]

Yep!

This will be controlled by a multipurpose Arduino control box. This will be powered by an Arduino Mega 2560 as I need more pins than the standard Uno or Nano. I plan to move this control box bewteen imaging rigs of which I shall have three :-

1. Single imaging with the MN190 - focuser and dew heater to control
   
2. Dual imaging rig with two ED80s - 2 focusers plus matrix shift steppers and 2 dew heaters
   
3. Widefield triple imaging rig with 3 imaging cameras and guide camera fitted with lenses with focusers on each = 4 focusers plus 4 dew heaters
   

So the control box will cover the widefield rig but can be used with the others. I have a shield with 16 char x 2 line LCD display and 5 push button switches labelled RST SELECT LEFT UP DOWN RIGHT just the job for controlling a menu system. Focusers have course, fine and single step. The telescope alignment shift stepper will have Top/Bottom panel plus fine control of alignment. In addition to local control, these functions will be available from a control box in the warm room and later by computer control. I already have a twin focuser system I used with the previous dual imaging widefield rig.

I shall put the details in another thread - there's already a thread on remote focussing and dew heater control.

[Gina]

I have now cut and fitted the top bracing plates which with stepper motors for the second scope height and both focusers, completes the hardware side. The objective end top plate is fixed with thumb screws so the spacing can be adjusted if needed though I'm pretty sure it won't be.