A budget (colour!) Planetary Camera?

[Macavity]

I have now nailed my colours to the mast as a (DSO) Video Astronomy enthusiast. 

BUT I am tempted by *Planetary* Imaging. Aside from my 8" / F4 "light bucket", I have

my trusty (Gold Coloured! MK.I) MAK 150! Now sporting a Monorail focusser too...

My Watec Camera is fine for Video Astronomy...  But has decidedly BIG (8.5 micron!)

Pixels and is firmly "Black & White". Recently I SOLD OFF my *manual* filter wheel...

I intend to buy a TS "filter tray" for specialist (DSO) filters. No hassle to change them

every 20 minutes or so... 

BUT, for the price of LRGB Filters and the necessity of "quick changes" maybe a

dedicated (budget) COLOUR (USB) Planetary Camera would suite me better? 

For a MAK150 (f=1800mm) I sense I would be better off with *eyepiece projection*

over a Plethora of Barlows? My Baader Hyperions are threaded for the former! It

is perhaps best to use longer focal length eyepieces and *project* further etc. etc.

So: Something with SMALL (colour) pixels? I guess it inevitably HALVES resolution?

But something with reasonable sensitivity? Could function at "f30, f60...? <Egads>

Looking in the sub £250 range: http://www.modernastronomy.com/camerasPlanetary.html Maybe? 

TOO MANY Questions! But maybe someone has exactly the solution I imagine? 

[Davey-T]

Have you looked at these ?

http://www.365astronomy.com/zwoptical-m-119.html?zenid=d8e5725ca461cd3f5b6a3c8e321c435d

Dave

[JamesF]

I'd suggest you really want a barlow rather than eyepiece projection.  I think you'd get a noticeably better image.

The ASI120MC works well and ideally you'd pair it with around a 2x barlow.  I don't think you'd want to go much higher than that although the Revelation 2.5x barlow might be worth a try (or the old Celestron Ultima should you still be able to get hold of one), but you could go lower depending on how much the secondary focuser adds to the effective focal length.  With a pixel size of 3.75um you probably want to be aiming for an overall f-ratio of f/20 to f/25.

The ASI034MC looks interesting though I've seen no images from it yet.  Second hand DFK21AU04 models seem to go for around the same sort of price at the moment and are fairly well proven.  With the 5.6um pixel size of these cameras you're probably after an f-ratio of f/35 to f/40, so a decent 3x barlow would probably hit the mark, although I've used the Revelation 2.5x with an extension as an alternative.  The DFK21.618 might come under budget second hand, too.  It's the same pixel size, so you'd be looking at the same target focal ratio.

(By choosing the "ideal" focal ratio here, btw, I'm trying to match the resolution of the optics to the resolution of the camera.  There's no reason you couldn't go with more focal length or less, but increasing the focal length even further is I think of questionable benefit, and using a lower focal length will mean you probably capture less detail than is possible.)

James

[Macavity]

Hi James, Thanks for going through some of the numbers - And the cam ideas.

Jupiter looks so tempting hanging there... albeit at two degrees cee outside!  

Using my interpretation of the "common wisdom", I had felt, my MAK 150 (f=1800) plus Watec pixels (8.5 micron) might need a "Barlow" of closer to 4x. I have pushed a standard 2" GSO Barlow to 3x (using the famed Hyperion EP extension tubes!) but the whole thing becomes a bit dubious and certainly unwieldy? I get the impression the total time for RGB imaging (fast rotating) Jupiter, should be kept to less than ONE minute. I doubt I can move fast enough to manually change filters and start / stop programs. lol. So I am increasingly attracted to the idea of a dedicated entry(+) level colour cam. 

I take your point re. eyepiece projection. Certainly not many people do it... and probably for good reason. I do have the "kit" for Baader Hyperions. <wink> But frankly, I was still thinking in Watec (pixel size) terms. As you point out smaller pixels bring things within range of standard Barlows with my setup. Shame I just sold a 2" 2x one! But indeed maybe 2.5x or even 3x - And in 1.25" format.

I am resigned to a slight technology change from my (remote) video astronomy i.e. USB 2.0 rather than simple coax! But intend getting a (supposedly reliable) long USB 2.0 link via one of these: http://www.amplicon.com/Data-Comms/product/USB-USB-USB-4625.cfm - Still to be PROVEN, but I have reasonable optimism. Maybe I can do all the above from indoors too!

P.S. I do wonder, when colour cam specs talk of "pixel size", do they mean 

the individual (colour) pixels or the matrix of four giving net monochrome... 

[JamesF]

I think for an 8.5um pixel size you'd be ideally aiming for a focal ratio of f/55 or slightly higher so a 5x barlow might work, but it brings a pile of other problems with it.

Colour cameras are always going to be a bit of a compromise and one has to decide how to cope with that when working out ideal optical configurations.  To do the job properly you probably have to account for how the data is recombined.  I've been doing a bit of research on that of late for my imaging application and I've found perhaps as many as twenty different algorithms for the process of interpolating the missing colours in the raw data and as a result I think it would be pretty hairy to try to approach the problem of optimal configuration that way.  Even with the relatively simple bilinear method we've already abandoned this idea of a 2x2 "superpixel" because for example to calculate the red and blue components of a pixel that has a green mask one takes the average values of the directly adjoining pixels (red will come from "above" and "below" and blue from "left" and "right", or vice-versa depending on the row in the matrix).

I prefer to assume that any resolvable feature is very likely to have a colour component from all three colours in the mask, so should be picked up even if it appears in the least appropriate colour position.  It perhaps won't end up with a perfectly correct colour composition, but that's the price you pay for using a colour camera to start with.  And in fact it may well be that if you use a drizzle transform whilst stacking it mostly comes out in the wash anyhow.  Making this assumption means that it's only necessary to match the resolution of the telescope to the resolution of a single "real" pixel on the camera, just as one would for a monochrome camera.

James

[Macavity]

Ah, very interesting - Hadn't thought much about this before. But I do see what you mean re. relative positioning of (likely multi-coloured) features and the matrix of sensory elements? Evidently interpolation / translation from the physical pixels, to the final RGB data presentation all plays a part in all this. Maybe at total cross purposes, but I liked the following animated (sadly now de-animated) gif anyway! But clearly there a many combination choices of "pixel" (sensels!) whatever... 

Past attempts at colour imaging had been a bit fraught - The (now cured!) backlash in an HEQ5 indeed didn't help at high f-numbers. My original (Mk.II) Orion "Solar System Colour Imager" had a certain notoriety re. lack of sensitivity. Certainly restricted to "brighter" planets! Worse still, mine seemed to have startup issues - First few frames looked absolutely *horrible* colour-wise and invariably had to be discarded? The (admirable!) WATEC was just the wrong tool for this job. Anyway, optimistic the current generation of colour cameras (chips) will have fixed most of these "problems".

A ZWO colour cam - indeed the ASI120MC looks genuinely exciting. And within the hoped for budget. 

<thinks> "Recover" (sold) 2x Barlow (and postpone replacing LRGB filters) - Buy one of these first!! 

Anyway, sounds like a Plan! Thanks a lot guys. 

[Macavity]

Spent some of the day wrestling with quantum efficiencies... volts / lux-sec... 

I'm trying to get a handle on how *bright* planets might look in real time.

Found about one (in very many!) references that quoted "minimum light at f1.2" as 0.1 lux for the ASI120MC camera (AR0130CS chip). Far easier to compare with my existing experience with video-type cameras? But still, one can easily miss out a factor of several, when factoring in planet surface brightness etc.

But, as luck would have it, there are a number of (presumed) live videos.

This for a (my proposed) MAK150 + 2x Barlow setup: 

http://www.youtube.com/watch?v=2EZOzLOZTb0

If right, I think I'd be happy with the ASI120MC etc. 

But is that the typical real-time preview for a (small) scope at about f25 ??????

I'd really like to confirm this... Exact answers or random speculation welcome!

[JamesF]

That's not a million miles off how Jupiter appears on-screen for me.  It does drift back and forth depending on seeing, but I'd say that's the right sort ballpark.

James

[knobby]

Same here, and I use a 150 Mak with the Asi120 mc . Not used Barlow yet though. Don't forget the image in that video can be captured brighter or dimmer by adjusting the gain / exposure time/ brightness

[Christopher Davenport]

Hello, don't know the technical stuff on the QE or Colour vs Mono.

But the QHY5L II is serving me well on planetary. Has great QE and super small pixel size.

I can ramp up my frame rates up to well over 125 FPS and can capture 35000 images over 300 sec.

The QHY5L ii has a barrel extension, which accepts filters or the Barlow lense to give you 1.5

My view of Jupiter through a 5inch Mak (1500FL) with a 2x Barlow is very similar to what you have shown.

Although that shot has got really good seeing compared to what we have had lately.

[Macavity]

Many thanks (all)! Have a while to ponder, the exact device -

The above input (and search terms) is most useful indeed. 

My only previous point of reference was the old ORION "Solar Sytem Colour Imager" (Mk.II version). I am not as unkind as some of the reviewers, but (as the Docs said) "for the Moon and *brighter* planets"! IIRC the sensitivity was of order "Several Lux" - Saturn was pretty difficult to SEE in real-time at higher f-numbers... Idem > Mag +3 stars? Not to labour the theory, but modern colour cams seem about 0.1 Lux... So 30x (approx. FOUR mags) more sensitive. Aside: Jupiter has surface brightness +5 per arc sec sq. It all does seem to tie in...  And I'll cease to torture you with this!

As a bit of entertainment, I hadn't thought of THIS either: http://www.zwoptical.com/Eng/Galleries/ASI035.asp

Interesting comparison of mono and colour versions - Combining images for LRGB, Eh? But must resist...

[Christopher Davenport]

Many thank (all)! Have a while to ponder, the exact device -

The above input (and search terms) is most useful indeed. 

My only previous point of reference was the old ORION "Solar Sytem Colour Imager" (Mk.II version). I am not as unkind as some of the reviewers, but (as the Docs said) "for the Moon and *brighter* planets"! IIRC the sensitivity was of order "Several Lux" - Saturn was pretty difficult to SEE in real-time at higher f-numbers... Idem > Mag +3 stars? Not to labour the theory, but modern colour cams seem about 0.1 Lux... So 30x (approx. FOUR mags) more sensitive. Aside: Jupiter has surface brightness +5 per arc sec sq. It all does seem to tie in...  And I'll cease to torture you with this!

As a bit of entertainment, I hadn't thought of THIS either: http://www.zwoptical.com/Eng/Galleries/ASI035.asp

Interesting comparison of mono and colour versions - Combining images for LRGB, Eh? But must resist...

One day, I will take pictures of Saturn like that

[Christopher Davenport]

Alot of that is the Scope though, look what is possible my cam and the a massive telescope.

[Macavity]

A tad better than some of my (tiny, well-sucked?) "Mint Humbug" Jupiters! 

Last season I always seemed to be struggling with my left hand on manual focus, right hand on mouse - Both at arms length - Peering (short-sightedly) at screens too far away! At that point the backlash on the mount backlash usually went "clunk" and the planet was long gone... Maybe for the rest of the session!

I believe I have my act a bit more together this time? But... 

[JamesF]

Last season I always seemed to be struggling with my left hand on manual focus, right hand on mouse - Both at arms length - Peering (short-sightedly) at screens too far away! At that point the backlash on the mount backlash usually went "clunk" and the planet was long gone... Maybe for the rest of the session!

Much easier with a motorised focuser

James