Running two cameras.

[don4l]

I've never checked my setup for cone error.  My guide scope is on it's own alt-az mini mount which is mounted on a crossbar.  I just get it pointing in the same general direction and it seems to work OK.  So, I've definitely got loads of cone error on my guide scope.

I can see that if you are not platesolving then meridian flips would be greatly speeded up without cone error.  It doesn't seem to be an issue for me at 2000mm focal length and 10m subs.  When I do a meridian flip, my target is always way off, but a quick platesolve and mount sync sorts things out in less than a minute.

Of course, without platesolving, finding the target after a flip can take ages.

[alan potts]

I tried a meridian flip last nigh on the back of all this talk about the subject and mine was a small distance off, my PA is only about 1.5 arc minutes so even that may account for it, it's no big deal to me as i don't normal image both sides as we tend to get runs of clear nights, unlike the UK.

Alan

[carastro]

Quote

I’m still not sure this is cone error playing a role here. If scope 1 is adjusted to be pointing to the same place after the flip then scope 2 must be still pointing to the same place it was before. Unless it’s moving separately from scope 1. 

I was assuming with the 2nd scope being mounted further from the Axis of the mount that the cone error would be even more exaggerated than the one closer to the axis of the mount. 

Carole 

[tooth_dr]

50 minutes ago, carastro said:

I was assuming with the 2nd scope being mounted further from the Axis of the mount that the cone error would be even more exaggerated than the one closer to the axis of the mount. 

Carole 

I’m not an expert Carole! but the cameras are aligned relative to each other, so where one points the other must also point irrespective of whether it’s on one side of the meridian or the other or anywhere on the sky.  This isn’t cone error as I understand it.  This is movement between scopes 

[gorann]

38 minutes ago, tooth_dr said:

I’m not an expert Carole! but the cameras are aligned relative to each other, so where one points the other must also point irrespective of whether it’s on one side of the meridian or the other or anywhere on the sky.  This isn’t cone error as I understand it.  This is movement between scopes 

I agree, this cannot be cone error. The two scopes sitting maybe 30 cm apart are initially pointing at the same star, many light years away, so their optical paths must be absolutely parallell. If they after a flip do not point exactly the same way, one or both must have sagged a bit after the flip. Maybe the saddles or maybe the image train have shifted, but it is not cone error, it is gravitation.

PS. As I understand it the term cone error means that a scope is not being exactly in plane with the polar axis, which is something different.

Edited November 17, 2019 by gorann

[carastro]

Thanks Guys, well it's so little I am not going to scratch my head trying to fix it, I will just live with it.

Carole 

[gorann]

4 minutes ago, carastro said:

Thanks Guys, well it's so little I am not going to scratch my head trying to fix it, I will just live with it.

Carole 

Or maybe try to tighten your clamps and screws a bit more Carole😉

[alan potts]

All this talk of cone error make me feel the need to have a spanner in hand. The cradle of the M/N 190mm actually has small screw like adjusters to deal with this but as far as I see the Vixen rails on all my APO's is basically not adjustable and I imagine would require shims of some kind. Even though the mounting bars are pressed tight against the mount I do wonder if the scope it ever true to the PA of the mount, close yes, exact I doubt. I do see an improvement in pointing over he AZ EQ 6 though. Feel these CEM mount are decent quality for the money.

Alan

[ollypenrice]

Going back a few steps in the conversation I keep things simple by capturing onto two PCs. I know I'd tie myself in knots if I tried to run both cameras on one PC and I have more screen space which is good.

How precise your second scope alignment needs to be depends of the relative FOVs of the two rigs. The original dual rig had identical kit on both sides so it had to be close to perfect. The solution came, at staggering expense, in the form of a second hand Cassady T-GAD alignment system but FLO now do a good alternative. If one FOV is much larger than the other you might get away without anything. (The T-GAD has no difficulty holding two TEC140s still at a highest resolution of 0.9"PP.)

I don't dither but I do take a lot of data and the noise patterns of the two cameras are not the same, which I think helps. (One guy on the French forum insisted that 4 + 4 hours from two cameras gave the noise of a 4 hour capture while 8 hours in a single camera gave the square root of that amount of noise. I don't think he's correct.)

Is a two mount solution easier? Sara automates her capture while I don't. In her case I can see that it might be easier but in my case the dual rig works like a charm.

Olly

Edited November 18, 2019 by ollypenrice

[alan potts]

3 hours ago, ollypenrice said:

Going back a few steps in the conversation I keep things simple by capturing onto two PCs. I know I'd tie myself in knots if I tried to run both cameras on one PC and I have more screen space which is good.

How precise your second scope alignment needs to be depends of the relative FOVs of the two rigs. The original dual rig had identical kit on both sides so it had to be close to perfect. The solution came, at staggering expense, in the form of a second hand Cassady T-GAD alignment system but FLO now do a good alternative. If one FOV is much larger than the other you might get away without anything. (The T-GAD has no difficulty holding two TEC140s still at a highest resolution of 0.9"PP.)

I don't dither but I do take a lot of data and the noise patterns of the two cameras are not the same, which I think helps. (One guy on the French forum insisted that 4 + 4 hours from two cameras gave the noise of a 4 hour capture while 8 hours in a single camera gave the square root of that amount of noise. I don't think he's correct.)

Is a two mount solution easier? Sara automates her capture while I don't. In her case I can see that it might be easier but in my case the dual rig works like a charm.

Olly

I was only really interested in running two scopes so I wouldn't have to chop and change so much, I wasn't interested in mixing the data, though I know you do. I could do it with two laptops as I have a few of them all the same and decent machines, albeit a few years old now.

Raining at the minute but that won't last long, for the ultra keen clear sky will be about 10.30, but I dare say like where you are with tomorrow being decent, I personally will not bother, especially not long after my operation.

Alan