Imaging Array - What are you getting?

[Christopher Davenport]

Living in the UK, tests the most hardened astro imagers will power.

I noticed that some people are setting up arrays to get data quicker. This comes at some considerable cost though.

Dual scope, dual CCD, steady mount.

Triple, even more so.

But just what are you really getting with more sub's?

So a dual 80ed f6 = 96ed f5

Am I not better off just getting a 100ed at f5.

Does double the data stacked equal a drop in exposure by one f stop?

Or put another way does 3 x 8inch f4 quattro reflectors = 1 x f2 16inch

I feel like I am missing something?

[nmoushon]

It not really the same thing as a true telescope array. So it doesnt effect the f/ratio in any way. Now if it was a binocular setup, like the Large Binocular Telescope, then it would. But the LBT is focusing two beams of light from two telescopes onto one camera chip. The setup you are talking about is just multi imaging rig. Its no different than gather data from 10 people all around the world and stacking all their data into 1 image. All 10 people image on the same night for 8 hrs you get a total of 800 hrs worth of data in one night versus you spending 10 nights of 8 hrs each. It doesnt speed up your camera or scope. What it does does is allow you to gather as much data as possible in your given amount of time. It goes back to my example of 10 people sharing their data. Except its 2 or 3 or how ever many telescopes your budget can purchase. And its all your data and not sharing with other people. Not that sharing is bad  . It also lets your data be taken shorter number of nights so less data is effected my the seeing and sky conditions of imaging on different nights. 

[ollypenrice]

Don't set about this by looking at pure numbers. The dual/miltiple rig has some practical advantages not evident in the theoretical numbers. You would have to be very optimistic to imagine that  a multiple Quattro rig would deliver regularly. Each component would need fine tuning and collimating, the tilts tuning out, etc etc. Your guider couldn't correct for independent mirror movement.  The point (the real point) about the multiple rig, for me, is that you use multiple easy scopes instead of one difficult fast astrograph. Multiple difficult fast astrographs, well, no, not for me. I do this a lot and know what it's like!

So our dual rig is 2x old Tak FSQ106N fluorite quadruplets. This is twice as fast as one, and slightly more than that, in a way, because the defects of particular cameras can be neutralized and we think the noise reduction of combined cameras is greater than double the data of one. The two old Taks cost a little less than one new one. There's honestly nothing wrong with them. We are about to present a rather large image, over a gig, taken with this rig. At no point in this marathon did any aspect of the rig present any difficulty whatever. Aim, focus, shoot. 2 x easy = easy. 2 x diffiult = 4x dfficult...

The numbers are well and good but fast F ratios ae not user friendly if you want real quality.

Olly

[steppenwolf]

What Olly said!

However, I use my dual imaging rig slightly differently because I'm not as wealthy as Olly :grin:  - (just joshing with ya) - I use two disparate imaging systems, a one shot colour CCD camera mounted on a WO FLT 98 and a mono CCD camera and filters mounted on a WO Megrez 72. The aim is not so much to double my data collection like Olly but to collect two different types of data at the same time for combining in post processing. Why such disparate systems? I'm just running with what I've got!

[Davey-T]

Any particular reason you've got the OSC on WO FLT 98 and the CCD on the WO Meg 72 and not the other way round Steve.

Dave

[NickK]

So our dual rig is 2x old Tak FSQ106N fluorite quadruplets. This is twice as fast as one, ...

Olly

Grr.. trying to find another Pentax 105SDP is even worse than trying to find two 106 fluorites!

However this place has seven.. a set of 125s and a 150.. http://telescopemuseum.sakura.ne.jp/wphome/?page_id=1207

The main issue with multiple scopes is really getting something like that you want to get the same scope, same cameras etc.. the problem comes over time if you want another and they're discontinued or you want a new scope!

[steppenwolf]

Any particular reason you've got the OSC on WO FLT 98 and the CCD on the WO Meg 72 and not the other way round Steve.

Two reasons really:-

1. The FLT 98 is an excellent triplet so CA is extremely low making it ideal for OSC whereas the Megrez72 is good but not as good as the FLT 98 but it is great for capturing narrowband data with the mono camera

2. The FLT 98 has the longer focal length (494mm v 346mm with reducer/flatteners installed) and the OSC CCD camera has the larger sensor (28.12mm diagonal v 22.48mm) and this pair of combinations gives the closest FOV match (162.7 arc.sec wide v 178.6 arc.secs wide)

I like to blend narrowband with OSC RGB.

[lensman57]

Any particular reason you've got the OSC on WO FLT 98 and the CCD on the WO Meg 72 and not the other way round Steve.

Dave

You use the OSC with a scope with better colour correction and the Mono CCD, usually with an ha filter, with a scope that may not be as well colour corrected. The FLT 98 also has a longer FL coupled to a larger CCD so you try and bring the scales closer together between the two scopes. Well that was what I had planned to use this winter on a couple of difficult targets but no luck as yet. You may also use a twin matched set up to do a Bi colour in the same time that you'd use to pick up either Ha or Oiii or even LRGB.

A.G

[Christopher Davenport]

Reason I asked was due to the latest article on the wasp project in astronomy now mag. Looks really interesting.

I agree if a array is setup you want as little complexity as possible.

Understand what Olly is saying two cameras same setup means stacking will even out differences, similarities to a dither, which increases quality of SNR. Speed of a lesser importance, clear skies in the mountains.

Steve it is just about halving how long it takes to gather the different kinds of data needed ... Lum or Ha at same time as RGB.

Thing is, the article made out like two scopes is like double the signal or a change in Fstop.

I guess it is a more fundamental question about stacking. Is 2hrs of data the same as 1hr at a reduced fstop?

[Davey-T]

So apologies to the OP not trying to hijack your thread, but If I have  WO 110FLT, a WO Star 71, an Atik 314L+ and an Atik 4000 OSC what should I put on which ?

Can't afford Tak 106 and a Tak 85

Dave 

[steppenwolf]

I have  WO 110FLT, a WO Star 71, an Atik 314L+ and an Atik 4000 OSC what should I put on which ?

I'd put the 314L+ with the WO Star71 (FOV 88.1 x 65.9arcminutes) and the Atik 4000 with the WO 110 (FOV 74.4 x 71.7arcminutes) although the WO 110 could really do with a field flattener for imaging.

[Davey-T]

I'd put the 314L+ with the WO Star71 (FOV 88.1 x 65.9arcminutes) and the Atik 4000 with the WO 110 (FOV 74.4 x 71.7arcminutes) although the WO 110 could really do with a field flattener for imaging.

I've got the WO flattener IV so that's ok.

Dave

[laser_jock99]

Or put another way does 3 x 8inch f4 quattro reflectors = 1 x f2 16inch

Sounds like an engineering challenge!

Think I'll just stick to OSC at F2.9 with a large area CCD's !

[Christopher Davenport]

Sounds like an engineering challenge!

Think I'll just stick to OSC at F2.9 with a large area CCD's !

Well yes, I have seen what this setup is capable of in short exposure times although your asa reducer costs the same as a second scope, not the second CCD though.

I'm guessing it is not worth it, doing these types of arrays as the gain in speed is not worth the capital outlay and the complexity inherent in getting it to work.

Seems like two scopes is the sweep spot with refractors. The guy at new forest observatory has a tripple refractor rig.

Hmmm much to think about when I undertake journey.