Aligning 2 scopes to 1 target

[nmoushon]

If I have two scopes side by side (parallel) on the same mount and I'm wanting to image using both at the same time do they need to be just ever so slightly angled towards each other to have the target centered or does parallel work fine at this "infinity" distance that DSO are at?

[andrew s]

They should have their optic axies parallel to each other. This may or may not mean the tubes are parallel depending on there mechainics. Regards Andrew

[nmoushon]

That makes sense. So in theory the optic axis should be down the dead center of the scope with the rest of the scope(tube, focuser, etc.) in parallel to that correct? Thats if the manufacture put all the parts together correctly and have stayed that way over time. If the optical axis isn't down the dead center how would I find where exactly it is?

Ok so let me see if I can get this right: So if I take two identical scopes andhave them placed parallel (if the optical axis is directly down the center of the scope) to each other and that would produce two perfectly matching images?

[Bizibilder]

You need the optical axiis parallel not the physical tubes. The optical axis is unlikely to be precisely "down the middle" of the tube. Best way to set up would be to align one and fix it and have the other on an "adjustable" mount of some sort - even just shimmed into place would do as the alignment wont change unless you re-collimate. If the second scope is small enough then an adjustable guidescope mount would do the trick. The next job would be to get both cameras aligned. The final alignment would be taken care of by your stacking software, if you use something like DSS then it will cope with two "batches" as long as the optics are the same - if you have different sized scopes then, i believe, "Registar" (commercial software) is the thing to use (but I don't have it myself).

[nmoushon]

You need the optical axiis parallel not the physical tubes. The optical axis is unlikely to be precisely "down the middle" of the tube. Best way to set up would be to align one and fix it and have the other on an "adjustable" mount of some sort - even just shimmed into place would do as the alignment wont change unless you re-collimate. If the second scope is small enough then an adjustable guidescope mount would do the trick. The next job would be to get both cameras aligned. The final alignment would be taken care of by your stacking software, if you use something like DSS then it will cope with two "batches" as long as the optics are the same - if you have different sized scopes then, i believe, "Registar" (commercial software) is the thing to use (but I don't have it myself).

Oh well things are never as simple as you want them to be. So my options are align one then shim the other into alignment with the first one or re-collimate both scopes to have parallel optical axis?

[Bizibilder]

Don't try and collimate - you will never get the scopes optical and physical axiis perfectly aligned. Consider your two scopes as two seperate imaging sessions on different nights using one scope (if you see what I mean). You will find and align your scope to your target and will align your camera as well. On the second night the alignment will be slightly "out" as will the camera orientation. The difference is corrected during the image stacking process. Often when combining data from two or more nights you will get a final stacked image that will need the "rough edges" cropping off.

The situation with two scopes used simultaneously will be similar - near, but not perfect, alignment will be perfectly OK.

[JamesF]

Skywatcher make a mount that allows you to align the two, don't they?

James

[Bizibilder]

Yes they do - the "guidescope mount": http://www.firstligh...cope-mount.html This will easily handle scopes up to an 80mm refractor - and probably bigger.

[JamesF]

That's the beastie. I was sure they did, but I couldn't find it

James

[Gina]

if you have different sized scopes then, i believe, "Registar" (commercial software) is the thing to use (but I don't have it myself).

RegiStar certainly copes with different image sizes and rotations - perfectly IMO. I use it to combine Luminance stacks unbinned with RGB stacks binned 2x2 so totally different sized images. The results come out the size of the biggest image in terms of pixels. Superb software and something I've never regretted buying - quite the opposite - well worth the money

[nmoushon]

Thanks for the info guys. I'll have a look at Registar. If I can pull enough change out of my car I'll pick it up.

So out of just curiosity (and maybe to give me something to do on cloudy nights) how would I find the optical axis of my frac?