Dual Imaging Rigs - my thoughts and ideas

[Gina]

perhaps this would work https://www.teleskop...pe-bis-7kg.html looks good and baader kit is normally very well made i know there is kit made by robin casady but that is very expensive and maybe overkill for an 80mm frac

Thank you I've seen that one and I don't think it's up to taking an ED80 without flexure. We need a really rigid connection between the two scopes as only one can have OAG guiding. This is why I use a connection between the scopes at the top as well as bottom.

[ollypenrice]

So far I'm not winning with my experiments.

lly

[Gina]

So far I'm not winning with my experiments.

lly

Oh dear What seems to be the problem? I have an engineering background and might be able to help.

[jnc71106]

What do do you think of the ADM Max Guider Gina ?

[Gina]

What do do you think of the ADM Max Guider Gina ?

It's certainly a lot better but I still think there would be too much flexure.

[ollypenrice]

Oh dear What seems to be the problem? I have an engineering background and might be able to help.

Can't get the scopes aligned, Gina. I put a track rod between them at the front and that worked but I haven't found a way to align in Dec. I tried shims but got fairly random movements. The Cassady tilt-pan is the answer and Yves has one here but we don't have a mount to carry its mass. It is gargantuan. The FSQs are also more akin to 6 inch refractos in weight, very heavy indeed.

We'll use two mounts for the moment.

Olly

[Gina]

Can't get the scopes aligned, Gina. I put a track rod between them at the front and that worked but I haven't found a way to align in Dec. I tried shims but got fairly random movements. The Cassady tilt-pan is the answer and Yves has one here but we don't have a mount to carry its mass. It is gargantuan. The FSQs are also more akin to 6 inch refractos in weight, very heavy indeed.

We'll use two mounts for the moment.

Olly

I see. I've heard the FSQs are very heavy - much heavier than my ED80s. I haven't got to aligning them as yet but when I do I'll see what engineering solutions I can find. Sorry I'm not much help ATM. If you have two mounts available, that seems a good solution in the meantime.

[Gina]

I'm now looking at using my Atik 460EX CCD camera with the lenses in the widefield rig. Being only 60mm diameter rather than 110mm it will fit in much easier than another 314L+ and the present mounting plate will take it quite easily. With the higher resolution of the 460 I think I shall put it in the number 2 position rather than number 3. The number 1 position on the EFW2 is not suitable for the 460 as that would mean the two bigger 314L+ cameras one above the other, losing the advantage of the thinner 460.

To use a third camera and lens I need to cut another hole in the mounting panel, make a filter wheel or other method of holding a filter or two and make up and fit a third focussing motor/gearbox unit (plus 3rd control output on the Arduino control box). Meanwhile, I'm still working on the 36mm filter wheel for the 2nd ED80 for dual imaging. All this can be going on while I use the 460 on the MN190 whenever the weather permits.

Here are screenshots from a quick and inaccurate SketchUp model of the triple imaging system.

[Gina]

I'm thinking that I might separate the widefield rig from the ED80s - the combined assembly is getting a bit weighty at around 14-15KG depending on which lenses I use. I doubt I shall want to do imaging with ED80s + WF but if I did I could put the WF rig back on top of the ED80 and not have 3 quite heavy lenses on it. TBH I think trying to image with 3 cameras at the same time with widely differing fields of view would do my head in

If I were to do this I would no longer have the guiding from one of the ED80s (as I have for WF ATM) so I would need either OAG on one of the lenses or another lens with the Lodestar on it directly. Or with a lens I could use the QHY5 and leave it on permanently.

Apart from less loading on the mount this might mean I could manually attach the rig to the mount instead of having to use the hoist.

[Gina]

I've been taking the wider view (as it were) - considering the ED80 alignment problem as well as the weight. Separating WF from ED80s would give more options for the alignment mechanism as I wouldn't have the WF rig on top of the ED80s to contend with. I think in view of all this it would be best to separate ED80s and WF rig. I could still link the tops of the rings on the ED80s for less flexure between the two.

[Gina]

I guess the triple imaging widefield rig has gone off-topic a bit - if I had realised I would go to triple imaging I would have made the title "Multi Imaging Rigs..."

Going from dual to triple imaging with the WF rig has changed the requirements. There is now little need for remote controlled filter wheels - I will most likely stick with the same filter for each camera/lens combo for unattended operation in the early hours. What it needs instead is an easy way to change filters manually. Removing the rather large EFW2 from this setup would ease the design considerably.

[Gina]

I've just had a horrible thought!

The 460EX has a bigger sensor than the 314L+ which means it covers more sky (OK so this is obvious ) but whereas different pixel size, like binning can be covered by RegiStar, differing sky coverage means that there will be a border covered only by the larger sensor. The only way round this would be to change the optics so that the coverage is equalised. I can do this with the widefield rig as I have a range of focal length lenses but not with the ED80s. With a 314L+ on one covering 60 x 45 arcmins there would be no point in then having a 460EX covering say 100 x 80 arcmins as only 60 x 45 would be usable. There would be slightly higher resolution due to the smaller pixels but I doubt the difference would be significant. I shall have to calculate the coverages for the 460 like I did for the 314 and see how to mix and match the lenses.

Actually, having thought more about this and from looking at the coverage chart, there is one way I could ameliorate the different camera coverage with the ED80s and that's to use one with the focal reducer and the other without. And I've almost finished making an electronic filter wheel to match the FR assuming FRs on both scopes! Oh well... Think I'll go and lie down

[Gina]

Here's a new chart with both 314L+ and 460EX data. I've also added the 135mm lens as the difference in coverage between the two cameras is about 1.4x (1.4x in width and 1.5x in height)

The 460 on the 200mm lens and the 314s on the 135mm lenses would be quite a good match. The 460 on a 135mm and 314s on 105mm lenses slightly less so but reasonable. one 200mm and 2 105mm lenses are Asahi Takumar but the 135s are lesser quality.

[Gina]

Some of those figures in the cahsr above are patently wrong So I'll have to check it all again.

[Gina]

OK Let's see if I can get my old brain round this different sensor size question... The larger sensor wants a longer focal length to make the image bigger to fit the bigger sensor - yes that's right

So for lenses 200mm with the 460EX and 135mm with 314L+. Or 55mm with 460 and 35mm with 314. (As I thought )

And for ED80s, 600mm for the 460 and 510 for the 314 ie. 460 without FR and 314 with FR. My DIY FW goes on the FR so a 314 goes on that. Hmmm... that's the wrong way round for LRGB. I wanted the 460 for L with the CLS CCD filter and the 314 on the EFW2 running RGB in sequence with the lower resolution. Drat! That means I'll have to fit a T2 adapter to the DIY FW so I can use it without FR. Not impossible but a it of a nuisance, oh well...

For NB on the ED80s I would have the 3nm OIII filter in the EFW2 and Ha and SII Baader filters in my DIY FW. Now that works out right for the natural pallette with Ha mapped to red and OIII mapped to green and blue. But for Hubble pallette Ha maps to green and with generally more Ha it would be best to use the best camera for this, I would think.

Having different size camera sensors makes thing difficult! OK so I don't HAVE to use the 460 I could do what I was going to do before I bought the 460. OH NOOOOO that would be too much of a waste!!! "My bwain hurts Bwian"

NO NO NO - I can't afford to buy another 460EX!

[NickK]

I wouldn't worry about different pixel sizes. The image registration packages, like PI, will find the centre of stars against a grid 10x or higher precision than the original image. The image would then be interpolated as required.

If you upscale 2x2 then register & stack before downscaling, I'd have though the images would be decent enough

Just admit it to your bank manager.. you'd like a bank of 8 cameras with 8 separate filters with 8 lenses

[Gina]

No, different size pixels are no problem, RegiStar can handle that it's the field of view covered by the sensors. If you use the same focal length optics on both cameras a margin of the larger sensor will have nothing to match up with and cannot be used. So the 460 sensor becomes effectively the same size as the 314. Mind you it does mean the alignment doesn't need to be as accurate.

[Davey-T]

No, different size pixels are no problem, RegiStar can handle that it's the field of view covered by the sensors. If you use the same focal length optics on both cameras a margin of the larger sensor will have nothing to match up with and cannot be used. So the 460 sensor becomes effectively the same size as the 314. Mind you it does mean the alignment doesn't need to be as accurate.

See Gina, told you you'd need two 460's

Dave

[swag72]

Just put your credit card details on here - The good folks of SGL will get you exactly what you need!!

[ncjunk]

I wish i had your camera problems!

Sent from my GT-I9003 using Tapatalk 2

[Gina]

See Gina, told you you'd need two 460's

Dave

Yes, I know that

[Gina]

Following on from my thoughts about alignment adjustment of the ED80s, I've been thinking more about how to equalise the FOV for my two different cameras. I was thinking of changing the focal length of the ED80 with the focal reducer ie. FR with the 314L+ and not with the 460EX but this doesn't really produce enough difference and I don't like using an ED80 at f7.5 - so slooooooowwww!

Using FRs on both scopes, if the 314L+ were orientated at right angles to the 460EX I could get a better match by using a 2 panel mosaic with the 314L+ and the single 460EX image. The adjustment system for alignment of the scopes could be used to shift the FOV of the smaller sensor to make the mosaic. The scope would want moving a little under 45 arcmins - say 40 am. That would produce a FOV of 85 x 60 am for the 314L+ and 83 x 67 for the 460EX (If my calculations are correct).

How easy or difficult that will be remains to be seen. It would be easiest if the movement were in just one direction, of course.

[melsky]

Simpler option Gina is to sell both 314L+'s and get another 460, you only live once

Mel

[Gina]

Simpler option Gina is to sell both 314L+'s and get another 460, you only live once

Mel

With my seemingly virtually non-existant ability to sell anything I think that might not be as simple as you think Anyway, I'd need to sell three 314L+ cameras to buy one 460EX - they just don't come up second hand

[Gina]

Here are ED80/314L+ images prior to alignment. The cameras are orientated with long axis parallel to the mounting plate. This is trees on the horizon looking roughly east.

This shows that the vertical alignment is pretty much spot on. The horizontal accuracy depends on my ability to drill holes in the right place