M8,HaRGB-RGB comparison on a 40D

[Bassnut]

Hi Guys

This was interesting.
I processed 2 pics, one straight RGB and a second HaRGB (Ha as lumanance).

Taken on an LX200R OTA, G11 and EOS40D DSLR camera, with INCR (no other dark processing, or flats)

http://fredsastro.googlepages.com/temp2

Ha (clip in 15nm) is some 50 mins, 10 off 5 min subs, and RGB 80 mins 16 off 5 min subs.

Im of two minds on which is more pleasing, the RGB is smoother, but the Ha as Lum has more detail and more noise. Stars are bigger in the RGB, as excpected.

I found RGB easy to process, and am suprised at the result (its been a while since I used a DSLR, my ST10 is crook and away for fixing), but the Ha needed lots of stretching and noise reduction, I suspect more data is required.

Useing the 40D was a pleasure with live focus, but I didnt use focus max with it (been wondering if that is possible, cant see why not, must try that).

Ha results are problematic, as expected with a DSLR, but with lots of exposure time I think its well worth the investment.

The higher res of the 40D at long FLs over the ST10 is not so obvious though, although the extra FOV is handy (the pics were croped).

DSLRs have come a long way, makes the transition from a DSLR to CCD less urgent methinks after this little trial (for bight objects at least).

[peter_4059]

Fred,

That's a great comparison. I really like the HaRGB image. It's interesting how fewer stars show in the HaRGB.

Peter

[Bassnut]

Peter

Yes, Ha ditches dim stars, and some outer neb. Cleaner, but a subjective improvement.

[CoolhandJo]

Fred, it seems to me that no matter what camera you were using the images would be pretty good. This is one example (I like the first image best)

[h0ughy]

that's really interesting, i thought the combination would have been a lot better?

[multiweb]

I like the HaRGB better coz it's got way more details and contrast in the neb. Have you thought about blending the two finals in PS? Maybe use the HaRGB as greyscale Highpass, see what happend to the RGB if you keep it as base. Maybe you get the best of both worlds with a bit of masking?

I played with the two layers and attached the result. RGB as base, HaRGB as 26% opacity highpass 60px and one more HaRGB on top as Lum Opacity 70% with a star mask from the RGB layer.

[telecasterguru]

Fred,
I also like the Ha but only because of the greater detail. The RGB is very smooth.
I think that the comparison of DSLRs and CCD imagers is a very informative as well.
It has made me think about my next imager as I currently use a 1000D but want to move to a more specialised camera.
Not sure that about the outlay as compared to the results.
I would like to see a few more comparisons between DSLR and CCD cameras.
Thanks for the fabulous images.

Frank

[strongmanmike]

What's this?... a Lagoon Nebula with stars?? :shrug: and kinda normal colours :eyepop:....nearly didn't recognise it :whistle:

Mike

[gregbradley]

I like the top one better, tighter stars, more detail.

Good job. A good ad for DSLRs.

Greg.

[dugnsuz]

Very nice comparison Fred - nebular detail and tight stars on the HaRGB image is marked in comparison with the RGB pic. Very heartening as this is an imaging path I'm embarking on!!
How did you find the processing? So far I've found simply using the Ha data as a Lum layer pretty easy - and I've achieved better results with this simple combination over the more complicated Ha/Red channel blend + Ha Lum channel blend.
What say you!!??
Thanks for this
Doug

[Bassnut]

Thanks Dr Paul, the 40D allowed the nice pic, no more difficult than a CCD in this case.



So did I David, was more obvious with the CCD, its possible though that it was just the Ha was not as good as it could have been. BTW, since I thought the RGB was initially Ha (I forgot to put the filter in), it was taken with moon up, and yet it was of good quality, without flats. And there was more RGB data than Ha, arse about.



Excellent work there Marc, I lined them all up side by side and your blend is the go. I didnt attempt that to show the difference, but will now. Ive never done that with the CCD, didnt need to, the Ha was OK, but Gregs recent blend has shown some advantages too so I will try that. I didnt bother with muliple layer masking this time, thinking it was all just a quick poke, probably did myself a disfavour.



Thanks Frank. If you mean by specialised an Astro CCD, for bright objects on a wide field scope, a modified DSLR gives near CCD performance with very high res for MUCH less dollars. For narrowfield and or dim objects, CCDs really kill it, QE is then important and res less so. Very large CCDs are expensive and the QE isnt that flash, id say for bight widefield, youd have to be pretty keen to go CCD. Less expensive small chip CCDs undersample with refractors, not a good match.



Boring he :), thats why I juiced it up a bit as a comparison rather than just a pic post. Im running out of different ways to image M8, ive done it too often :P.



Thanks Doug. Well, I found the Ha processing hard, but as I said previously, the Ha data wasnt good, it needs a lot more exposure time relative to RGB than a CCD, but then again they were only 5 min subs, and half the imaging time was taken with ICNR, im trying a seperate dark stack next on M16.

Not sure what you mean by Ha/red + Ha/Lum, ....altogether?. Red in the mono Ha (as Lum) would boost red saturation lost by useing just Ha as Lum, but would make colour balance tricky. Just boosting red in the RGB layers usually does the same thing. The red channel on its own then can look awefull, but RGB image quality in an Ha/lumRGB is less important than with straight RGB. Lum in Ha (as the Lum channel) can boost brightness and reduce nosie, but works best with a layer mask and some selective painting (on the mask) so detail is not lost on bright features. Marcs tweak is a good example, and Greg also does this to good effect.

As you say, this is more complicated. I found (so far) just Ha as lum with lots (I mean mega hrs) of data, and perhaps layer masks to selectively sharpen highlights and blur dim bits gives the sharpest detail, but it takes time (both in exposure time and in PS).

[Bassnut]

Thanks Greg, an add?, you think :P, wish someone would pay me then :thumbsup:

[AlexN]

Looks like a good test Fred.. I must say I prefer the HaRGB shot.. Detail is what I look for in an image, the HaRGB oozes detail, and despite missing some of the outer nebulosity and the dim stars, its still my favourite of the two... (as a matter of fact, I much prefer less stars or heavily reduced stars produced by NB filters..)

I had to have a double take when I read DSLR next to your name in a deep sky imaging thread! :)

[Bassnut]

Thanks Alex. Yeah well, its the only cam I have right now, and I must say its been fun. I have just a sneaking suspicition that with far too much more Ha, id get embarissingly close, or equal to the M8 APOD I took with the SBIG ST10, and Peter Ward would just hate that :lol::lol::whistle:.

[AlexN]

Only cam you've got? Wheres the ST10XME?? getting upgrades?

I have to agree, with PLENTY more Ha data that image could quite easily look much like the APOD image... I think for both Peter and Strongman Mike, it would be worth going for it... Try to score an APOD with a DSLR... That will show everyone it can be done with any equipment!!

[strongmanmike]

:rofl:

[Bassnut]

Well, another APOD is pretty unlikely, let alone with a DSLR :P:P, but I get what you mean. At a long FL, that would be a killer (with a DSLR):lol:.

The ST10s crook (horizontal banding), is being fixed.

[gregbradley]

The main barrier a DSLR user has to overcome in my opinion is the lack of colour in stars and that is one main area CCD images tend to win.

I am not sure if that is from the well depth of the sensor pixels or if it
has something to do with the 14 bit versus 16 bit.

There are examples of DSLR images with colourful stars but not very often.

Perhaps also many DSLRs are used in a suburban environment and they tend to show up light pollution more easily than a CCD exactly why I am not sure but perhaps because the gain used on the sensor (ISO) is way pumped up compared to a CCD which is usually a fixed gain set by the camera manufacturer.

Perhaps an ideal DSLR image is the main image taken with lots of subexposures then a series a shorter ones only for the stars so they don't oversaturate into all white.

Then layer in the stars separately using Photoshop star separation techniques.

Anyone want to test the theory?

Greg.

[dugnsuz]

Probably phrased badly! What I meant was the method where the Ha data is combined with the RGB red channel data then this combination is used as the Red channel. Then the saved new Red channel is used as a Lum layer.
The "Rob Gendler Method"!!
http://www.robgendlerastropics.com/HARGB.html

:thumbsup: