Dual rig speed calculation - meanigful or not???

[ollypenrice]

54 minutes ago, gorann said:

This is probably besides the point, but my thought is that if I ever get a dual rig (assuming it means having two identical scopes side by side, and not a refractor and a telephoto lens side by side as I now have) I would equip one with a mono and one with a colour camera with the same chip (like ASI1600MM and MC) and then collect RGB with one and Lum and possibly Ha with the other. That would save having a filter wheel on one of them and it just seems a bit dull to me to let the two scopes do the same thing.

I've thought about this as well. However, we don't normally do the same thing in both scopes though we might sometimes do so if we had two Astrodon 3nm Ha filters during the moonlight. (Buying one was bad enough: two isn't going to happen!!!)

Because our dual rig is widefield we are often shooting emission nebulae so we can do LRGB on one and Ha on the other, or L and Ha on one and RGB on the other, etc. One camera is older and has more defects than the other so we tend to use that for colour.

The arrival of the 36 meg QHY CMOS OSC does have me wondering, though. If it were available in mono I'd have jumped by now! I still think 2 x mono is the most productive. (Eg Ha in one, OIII in the other.)

Oh, another possibility on a dodgy night is RGB on one and BGR on the other. Maximise yur chances.

Olly

[gorann]

2 hours ago, ollypenrice said:

I've thought about this as well. However, we don't normally do the same thing in both scopes though we might sometimes do so if we had two Astrodon 3nm Ha filters during the moonlight. (Buying one was bad enough: two isn't going to happen!!!)

Because our dual rig is widefield we are often shooting emission nebulae so we can do LRGB on one and Ha on the other, or L and Ha on one and RGB on the other, etc. One camera is older and has more defects than the other so we tend to use that for colour.

The arrival of the 36 meg QHY CMOS OSC does have me wondering, though. If it were available in mono I'd have jumped by now! I still think 2 x mono is the most productive. (Eg Ha in one, OIII in the other.)

Oh, another possibility on a dodgy night is RGB on one and BGR on the other. Maximise yur chances.

Olly

Whatever you go for Olly, if CMOS becomes a viable alternative then having those scopes with the capacity to fill up real estate it will cost you...

For once the sky is clear here so I am off to the obsy!

[ollypenrice]

1 minute ago, gorann said:

Whatever you go for Olly, if CMOS becomes a viable alternative then having those scopes with the capacity to fill up real estate it will cost you...

For once the sky is clear here so I am off to the obsy!

It always costs!

You'll struggle with the moon tonight unless you're using narrowband! 

lly

[gorann]

1 hour ago, ollypenrice said:

It always costs!

You'll struggle with the moon tonight unless you're using narrowband! 

lly

What did Oddball say in Kelly's Heroes? I think it was something like "Don't hit me with them negative waves". It is now 21.45 and the moon just went behind the forest and soon the horizon, so I got some hope, as always

[andrew s]

Other possible complication is that a dual rig will have correlated events. A plane or satellite will be in both images. For small scopes they could be looking through the same turbulence cell. Miss tracking, wind gusts etc. will impact two subs

However to first order I would say it doubles the effective captures to within a few percent, say 5%.

Regards Andrew 

[andrew s]

Slightly off topic but I recall a paper some years ago that showed that the most cost effective way to get better signal to noise was to reduce read noise v aperture or quantum efficence. So maybe a new camera rather than a dual rig?

(Or for Olly both)

Regards Andrew 

[ollypenrice]

3 minutes ago, andrew s said:

Slightly off topic but I recall a paper some years ago that showed that the most cost effective way to get better signal to noise was to reduce read noise v aperture or quantum efficence. So maybe a new camera rather than a dual rig?

(Or for Olly both)

Regards Andrew 

Hmmm, I'm just about to process some data sets from a QHY 36 meg CMOS... (Not mine, I stress!) 

Olly

[vlaiv]

You know what is even better than dual rig?

Quad rig!

Just imagine:

4x RC 10" with focal reducers 0.67 and x4 ASI1600, arranged so that you can either have all 4 point at the same place, or each pointing to a slightly different location in sky (some sort of tangential assembly holding each).

So you can have either:

20" aperture shooting at 1.17"/pixel with field of view: ~ 45' x ~34' and read noise of: 3.4e

Or

10" aperture shooting at 1.17"/pixel with field of view: ~1.5 x 1.1 degrees with same "low" (well compared to most CCDs) read noise of 3.4e

Or many other combinations, depending how you decide to bin / mosaic image from 4 rigs (all in same place, 4 panel mosaic, 2 scopes x2 panels either vertical or horizontal mosaics) / shoot different filters at the same time.

Versatility is the key here

It even isn't that far fetched. Total weight of such system would be around ~75kg so proper mount should be able to carry it, cost is not prohibitive either (well, probably for most people it is, but for a dedicated amateur astronomer with decent funds it is not), <20K euro for all gear needed (x4 scope, x4 camera, x4 reducer, not sure how many computers would be needed but I think at least 2-3), provided that proper mount is already owned, but even if not, it would not add much to overall figure (less than 50%).

It would probably be a bit awkward to operate, but aren't most imaging rigs when you first start using them?

[wimvb]

8 hours ago, ollypenrice said:

Hmmm, I'm just about to process some data sets from a QHY 36 meg CMOS... (Not mine, I stress!) 

Olly

If you have access to the camera, you should evaluate the dark current. Imo, you might think twice before getting a cmos. Many cmos cameras (not all, mind you) have a substantially higher dark current than ccd. You might be swapping your pristine dark skies for not-so-pristine dark current, if you go the cmos route.

8 hours ago, vlaiv said:

You know what is even better than dual rig?

Quad rig!

Hmm, this reminds me of the dragonfly project going on at the University of Toronto (discussed on this forum some time ago)

http://www.dunlap.utoronto.ca/instrumentation/dragonfly/

[ollypenrice]

14 minutes ago, wimvb said:

If you have access to the camera, you should evaluate the dark current. Imo, you might think twice before getting a cmos. Many cmos cameras (not all, mind you) have a substantially higher dark current than ccd. You might be swapping your pristine dark skies for not-so-pristine dark current, if you go the cmos route.

 

The camera lives here in our robotic shed so at least the sky is a constant. 

Olly