Gina

Although the present mounting on cameras only with a shim gets pretty close to alignment, I really feel that this is not quite up to par. I like to do the best I can on any project and I enjoy building things so I'm looking into both the longer base support system and providing adjustment for alignment. The guider picks up plenty of stars so that doesn't need any pointing adjustment. For imaging it's only the relative alignment that matters because the Ha imager will be pointed to target with plate solving so we just need to align the two imagers horizontally and vertically. This may be achieved with either both adjustments on one imager or one on each. The longer base is already designed based on the C type support system so this just leaves the adjustment. Two decisions need to be taken for this :- Moving lens or camera. There's more room for adjusting the lens but this is what takes virtually all the weight so I think I'll adjust the camera. Two adjustments on one camera or one on each.

Polaris.

No, it's a screw fitting. Pentax type.

I'm not sure what you mean - AFAIK the lenses are not made like that.

DRAT!!! Print failed!! At 80%!!!

I couldn't persuade it to move sideways (X axis) but I have plenty of tolerance in that direction. If by any chance the sky is clear tonight I might put the rig on the mount and see how it does. Only manual focussing so far but the focus on a distant comms mast seems pretty good so it might be adequate for nebulae.

While waiting for the 3D printer I thought I'd have another play with the shim. This is with a piece of aluminium foil.

Between camera body and mounting. I used a very thin piece of metal.

To recap, this is the C mounting in this photo.

There isn't a problem, Chris. I'm now 3D printing the base part of the camera and lens mounting. I am going to try a fixed setup to start with and see if that is accurate enough. If it isn't I can go on to design adjusters but if I can get away without adjustment it will save a lot of work. A small amount of misalignment of Ha and OIII images can be accommodated in the Star Alignment process but too much loses image data round the borders. Here is a screenshot of the model. This will be mounted on a Losmandy style dovetail bar. The main weight is taken by the right hand side in this pic (lenses). The extra depth is to accommodate the filter wheel (ZWO EFWmini).

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.

Yes I do!!

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

Some other targets...

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

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.

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

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.

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.

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.

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

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.

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.

I have the same problem with the ZWO full size wheel but not with the EFWmini. I think all filter wheels should be light sealed and be suitable for taking darks and flat-darks in daylight with a metal cap on the scope or lens. (Plastic caps let light through, even black ones!!)

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.