Dual Widefield Imaging Rig

[Gina]

This was an attempt using the Losmandy style dual mounting bar but it doesn't actually make any difference when eyeballing the line-of-sight of the imagers.  However, a smaller rig on the top end of the dovetail bar would.

[Gina]

Single camera bracket for Ha only rig.

Edited April 18, 2020 by Gina

[Gina]

Thinking about a dual imaging rig using the Asahi SMC Takumar 200mm f4 lenses which will give a suitable FoV for IC1396 alone and the Cygnus Loop.  Problem is the weight of these lenses and that the objective end moves with the focussing.  I'm using a similar one for guiding but with that I can focus it and then clamp the objective end since focussing is less important for guiding.   I was originally thinking of using the same approach for mounting the imaging lenses as the guider but I can't clamp the object end since focussing will be needed when in the observatory.  I suppose the objective end could be mounted in three ball bearings but this is getting too complicated.

Now I'm thinking I may go for unsupported objectives and relying on clamping the camera end of the lens and the back of the cameras - similar to the arrangement for the smaller/lighter lenses but with one clamp on the lens and one on the camera.

[Gina]

This is the current imaging rig with the 200mm lenses attached.  No remote focussing yet or dew shields.  There is a lot of overhang with these lenses and they are heavy.  I think I need to arrange support where the arrow is pointing. IOW supported at the arrow and back of the cameras.

[Gina]

Here are several possibilities for the lens support.  The rear support would be on the cameras anyway.  As shown, A is the current front support position.  I thought of B but I'm not sure that would be of much benefit since the diameter is smaller.  Position C is twice the separation of A and should be significantly better.  Only disadvantage is that the reference for the focussing would be fixed with reference to the dovetail and mean the imager system could not be rotated.

[MarkAR]

How about an open u shape support right at the front of the lens. All it has to do is take little strain off the rear attachment to the cams, doesn't have to be clamped around the lens.

[Gina]

Yes, I thought of that but I don't think it would hold it well enough.  OTOH I am testing various arrangements.

[Gina]

Here is a test with the current clamping on the cameras.  Focused by hand on the distant trees.  The alignment is not good!  Particularly in the vertical direction.

Edited May 17, 2020 by Gina

[Gina]

Here it is colour combined HOO > RGB.  Horizontal alignment isn't too bad, vertical is not acceptable and rotation isn't bad but is easily corrected by turning one of the cameras.  The vertical misalignment is a problem.  Looks like I might have to make that adjustable.

Edited May 17, 2020 by Gina

[Gina]

Vertical misalignment is about 10% or 350px out of 3520.  Vertical FoV is 5° so error is 0.5°.  This much error is marginal for the Cygnus Loop.

[DaveL59]

looks to be about as much fun as trying to collimate a pair of binos that don't have adjustment screws or eccentric rings Gina. Does look like you need a form of clamping that will allow micrometer adjustments up/down and left/right. As you say, rotational you can always tweak the camera to align.

[Gina]

Yes, here is the rotation tweaked.  A bit - needs a bit more ideally.

Edited May 17, 2020 by Gina

[DaveL59]

supporting at C in your pic might be best, since B still leaves the weight of the lens hanging on what should effectively be the SLR camera body plate. Not sure what your adaptors are made of but perhaps from what you've written they may not be able to provide it with the required rigidity.

Edited May 17, 2020 by DaveL59

[Gina]

The adapters are aluminium - standard astro adapters.  I agree that C would be best.  Looking at what I might image I don't think I shall want to rotate the FoV.  These are Cygnus Loop, IC1396 and Sh2-129+OU4.

[Gina]

Here's the camera rotation alignment as good as I can get it.

[DaveL59]

looks pretty good, just needs a little X-Y adjustment and should be spot on  

[Gina]

Some other targets...

[DaveL59]

ambitious stuff Gina, looking forward to your results  

I had a play with that makeshift shroud and improved it a bit, should be able to run the lens down to maybe 100/135mm zoom and the velcro should hold it secured behind the OEM lens hood in a more tapered shape now. Won't get anything like your images, but heck its a bit of fun to try. Pushing a 12YO bridge camera to its limits for sure, a DSLR would do better but I'm limited on options unless I ditch the old Minolta gear which I'd rather not and the full-frame Sony Alpha's are real pricey  

[Gina]

Had a play with thin shims.  Reduced vertical misalignment but increased horizontal.  We're only talking of tenths of mm.

[DaveL59]

you've a lot of patience there Gina!

left a bit... no no right a bit... up a bit... remember the golden shot?  

[Gina]

Yes I do!!

[Gina]

Been designing the C version mounting base.  Did a quick check on printing time and it said 8 hours plus!!  My printer will be busy tomorrow.  That's just the base - there are the clamps as well.  I'll see how accurate the basic bracket turns out and only look into micro adjustments if really needed.

Edited May 17, 2020 by Gina

[MarkAR]

I was going to suggest shimming with bits of paper. You've nearly cracked it.

Depending on where you've shimmed it might just need moving slightly.

[Chriske]

On 05/04/2020 at 10:54, Dr_Ju_ju said:

Looking good.... 

I think we need a new Sub-Section of "DIY Astronomer" called "3D files" of ALL types, for all the various bits we design, but don't publish, that others can comment on, refine and even generally use.... 

In the near future I was planning to start a site on the net to do just that.
Making a subsection here on SGL would be a good/better idea indeed.
To make the files more 'user-friendly' it would be interesting posting the source files together with the stl file. When someone want to change the part or project a little bit he needs a work-able file.
The most interesting file would be a STP or STEP file. Nearly all software can import/open  these files.

Sorry about the hijack Gina...😟

[Chriske]

Did not read the thread, sorry, but I've read something about shims to adjust things.
Well, I'd go for a completely other approach. I would give each separate unit it's own adjustment 'unit'. Each unit needs two screws to control a direction.
If I'm not mistaken, you do have a printer, you can draw(very good imho), so what is the problem...?...😁