Looking for a step up from DSLR for Planetary

[Xiga]

Hi fellow Gazers!

So then, at present my only camera is a Canon 60D (unmodded). I am using it for both planetary and DSO, and the in-built 640x480 60fps movie crop mode works surprisingly well for planetary (I've also been using Jerry Lodriguss' excellent CD-Rom book which deals with such methods). I've attached my best Jupiter attempt to date below.

However, I'd like to upgrade to a dedicated planetary camera to achieve better results. My other equipment should all be in my sig, but for clarity I'm using a C8 SCT, HEQ5 Pro, x2 Barlow, a Crayford focuser (no auto-focuser yet, one day!), Eqmod and APT, and an ancient Samsung N220 netbook (USB 2.0 only). Oh, cost is important too, I'm only looking to spend around £200 (£300 absolute max), bearing in mind the best results I'm ever likely to achieve given the aperture I have to work with.

Ok so the obvious question is, Mono Vs Colour. I know the advantages to Mono, but given the added expense with filters, filter wheel, etc plus the added complexity of taking 4 sets of images and hoping the focus and seeing conditions are all similar, I'm thinking OSC will be the more practical choice for me (also I'm in the UK, so seeing conditions are generally pretty crap!).

What I'd ideally like to do, is use an IR Pass filter (e.g something like the Astronomik ProPlanet 742) to capture the Luminence, therein by-passing a lot of the bad seeing conditions for the all-important L part of the image. The colour is not as important, so the plan would then be to remove the IR-Pass filter and replace it with a general UV/IR Cut filter to capture the colour data. Obviously most OSC camera's already ship with a UV/IR filter in place, so for this to work I'd have to remove it or, better still, have it permanently replaced with a clear AR window.

The thing I'm not sure about is, when using an IR Pass filter on an OSC camera, will all of the pixels in the Bayer Matrix capture the IR light, or only the red pixels (i.e only 1 out of every 4)? I'm a but confused about the NIR/IR spectrum and how it gets recorded in an OSC camera. If there is indeed a way (even through software?) for all of the pixels to record the IR light, then this plan should work out ok shouldn't it? Or am I missing some other piece of the puzzle?

Assuming the above is correct, and I can record all of the IR light in an OSC camera, the next question is what OSC camera to get, given my budget. The ZWO cam's look very tempting, especially the low low price of the 120MC. Given my netbook doesn't have USB 3 I think a USB 2.0 one will suffice, so what's the big difference between say the 120MC and the 224MC? They both have the same size pixels (3.75um), so why is the 224 over twice the price of the 120? The 120 can already do over 100fps, are there other things that make the 224 easier to use (or give better results)?

Sorry for the long post guys, and clear skies!

[iwols]

thats a very good image was it heavily cropped,im in the same boat as you confused

[vlaiv]

Go for 224.

Price difference comes down to usb3.0 - even 120 in usb 3.0 is more expensive than usb2.0 version (something you will need to consider in order to get high fps), also 120 is less sensitive, has higher read noise, and has built in UV/IR cut filter.

224 on the other hand is better suited for idea of using IR for lum - sensitive past 700nm, only AR coated window and there is region where all three components of bayer matrix have same response curve so if you shoot in that range you will not have to debayer, and can have full resolution (although less resolution due to size of airy disk being dependent on wavelength)

And yes, both will suit you fine for C8 with barlow x2 as max res for these cams is in range of F/18-F/20 due to pixel size of 3.75um

[Xiga]

Thanks vlaiv, sounds like the 224 is the way to go then. 

My only concern, is the ancient Samsung N220 netbook. It only has USB 2.0, a 5400rpm HDD and a single core Atom N450 processor. Obviously i'd have the option using a lower ROI (such as 640x480) for the likes of Jupiter, but if i'm not able to get upwards of 100fps at that res it would be a huge turn off, as i'd effectively be wasting a lot of the camera's potential. Unfortunately, a new laptop is out of the question at this stage, i'm stuck with the netbook for now. I'd be curious if any others out there are using similar equipment? 

ps - out of curiosity how did you get to your figure of F18-F20? I know Jerry Lodriguss says to multiply the size of the pixel side (in um) by 5 (for average seeing) and by 7 (for excellent seeing, which is rare) to get to the optimal F ratio but this is for DSLR's, i'm not sure what the rule is for other camera's, and whether you use the diagonal or not? Using this rule i've been aiming for F20 for Jupiter. 

@ iwols, iirc the original video was shot at 640x480, then it was put through PIPP (which i think then cropped it down to about 448x448) then it went through WinJupos which again cropped it down to about 318x318, then finally in Photoshop i upscaled it by about 150% to get to around 477x477. 

[vlaiv]

First thing to note about fps is your exposure length, I imaged planets with 8" aperture and I don't think I went below 10ms - for any exposure length higher or equal to 10ms you will not exceed 100fps - there is simply no time to do so as 10ms x 100 = 1s. For optimal resolution for planet imaging I went by the rule of x3 of max resolution of scope (airy size based) and used following formulae page: http://www.wilmslowastro.com/software/formulae.htm#CCD_Sampling

(I've read somewhere that Nyquist criteria for 2d sampling is actually x3.3 but x3 is close enough).

Since Airy disk size is wavelength dependent I usually look at the blue light for resolution (green and red will be oversampled in this case, but that should not be the problem). It turns out that since Airy disk size in micrometers is dependent on aperture and focal length (Airy size in arcsec is dependent only on aperture - but if we look at physical size at focal plane it depends on focal length as well), and resolution of camera in arcsec/pixel is dependent on focal length and pixel size - it turns out that critical sampling resolution for camera with certain pixel size is just function of focal ratio (does not depend on aperture). So if someone is recommending F/such and such for planetary work it is worth checking for which camera is that recommendation (what pixel size).

[Owmuchonomy]

The only reason I moved from my 60 D to a planetary camera is to go to mono particularly for Solar. Don't underestimate the true movie crop mode of the 60 D. For planetary images in colour it works very very well indeed.  Make sure you can take full advantage of your planned change before you go ahead.

[nightvision]

Check this out:  

 

 

[Xiga]

I know what you mean Chris. The true movie crop mode of the 60D is indeed very good. It was a big part of the reason why i picked one up 2nd hand. The data is unfortunately compressed, but according to the pros you apparently don't actually need any more than 8bit data for planetary anyway. I'll admit that part of me really wants to capture higher bit data (10, 12, or even 14 if i can have a go at using Magic Lantern), but if it truly doesn't matter then i suppose that's another tick for the 60D. It also does 60fps and the pixels aren't too big at 4.3um, so when you boil it right down, i can't really see what specific feature (other than a higher fps) something like the 120MC has that puts it ahead of the 60D on paper? But it really does produce better images, so does going from 60 to over 100fps really matter that much? (i've seen some truly astounding images taken at really low fps like 30). 

But anyhoo, back to the 224MC. For an 8 inch scope, what IR pass filter would you recommend? ZWO do an 850nm filter, but Astronomik only suggest using their own 807nm filter for scopes of 10 inches and up. Is an 850nm filter asking too much for an 8 inch scope? I've attached the QE graph for the 224MC below. As you can see, at 742nm the response for R, G, and B is really different, whereas at 850nm they are nice and tight. However, the red response looks ~50% higher at 742 vs 850, so i'm not sure which would work out better for my needs, so any advice would be much appreciated.