Stub Mandrel

It's interesting to compare it to the eye's spectral response: This is one reason why we are so sensitive to 'green' light - we see it almost as well with our red receptors! OSC is a much closer analogue to how we 'see' than RGB imaging with 'straight edged' filters. There is nothing intrinsically wrong with using debayering, saturation and curves and other techniques to exaggerate and extract narrowband colours to simulate LRGB results. This doesn't say anything which is 'better' but Toxic's DSLR image is probably a lot closer to how we would perceive a nebula if we could see it, than the RGB one. It explains why LRGB images have much greater saturation, which no doubt, is why they are 'easier to process' as there isn't bleed across between different colour channels. ON the other hand, it also explains why the colour palette tends to be a bit 'flat'. Ha or any other narrowband 'red' light will just come out as the same 'red' with LRGB filters. With the eye or a OSC each different 'red' will generate different balance of RG & B. This isn't a problem for narrowband sources like nebulas, except you need to choose WHICH red, green or blue you will use to represent each colour. For things like stars which have a black-body spectrum, you will get a balance between RG & B with straight edge filters, but it will tend to exaggerate the saturation, which I think is why LRGB images have stars that tend towards just three shades of orange, yellow or blue. I think it would be very interesting to compare two images of a colourful 'everyday scene' such as a funfair, one taken with a mono camera using Baader type 'square' filters, and one taken using a DSLR under the same conditions. A good example might be someone wearing an orange lifejacket sitting in a red canoe. With the Baader filters I bet the canoe and lifejacket would appear virtually the same colour. Summary LRGB makes more efficient use of photons and produces more accurate luminance data. OSC collects vastly more information about actual colour, but it is debatable whether or not trhis matters for most astronomical subjects.

This might be of interest, it's certainly thought-provoking. Especially that we are woprking in eth dark(!) when debayering in ignorance of the true sensor response curves. A CGMY bayer pattern could be very good for astronomy. The CMY pixels collect twice the photons of RGB ones.

Certainly not fair to compare an unmodified 1100D on an largely ha target! OK, this is stacked and processed, but made from 60-second exposures with a modified 450D and under light-polluted skies.

Here's an interesting graph for Canon 350D, 450D appears to be close, other cameras similar: We forget that OSC bayer filters are NOT narrowband filters, instead they mimic our eyes, and with the IR cut filter removed they are even wider band. Imagine you are imaging a lager Ha nebula with an astro-modded DSLR. Its maximum red sensitivity is pretty much lines up with Ha. Green registers about 1/6 of the Ha signal and blue approaching 1/10. So sensitivity at Ha is about 1+1/6+1/6+1/10 = 1.4 times what it would be if it was just from the red pixels. If you look across the graph adding up B+2xG+R for each wavelength - you will see sensitivity is rather more than the 1/4 you would expect. Add in the recovered set from a decent debayering algorithm and I think the valid signal might be closer to the sensitivity of mono+filters than people expect.

Interesting, most people assume that because the 0.9 coma corrector makes the f-ratio smaller it makes the image brighter.

I stuck a bit of PCB on the tube to stop it winding right out.

Creditable to get ANY of the pelican with an unmodded DSLR. If you can hit the NAN (it is easy to miss!) it is much brighter.

I had to squint to see it in that one.

There's a chunk in the middle of that page telling me the best for my camera is ISO9001

Clear gap at teh left doesn't mean anything much - it only provides a space for signal values of pixels that are darker than the background sky - ok if you are after the IFN or dark nebulas.

I use 800 now, seems to give the best results.

Hmm. tried everything without luck. Then went back to the original stack, ran HLVG, a few shots of LUM/Softlight to increase the colour, two doses of make stars smaller and one of space noise reduction... Perhaps I was trying to hard?

That's the colour I keep trying for, but it just won't come :-(

I thought I had, but it seems not!

Ah thanks, that's what mine are set to. I was made nervous by @rotatux's comment giving a range from 0.5 to 1.6, and the fact that the 'adaptive' version seems to work better. I can't find a reset button, there may be one somewhere!

If you were in the nebula, you wouldn't be able to see it... The natural colour of Ha emission is deep red, but there are other colours of light from these nebulas as well so they may not be pure deep red in colour. More care in aligning histogram gave a redder colour, and then in PS I added a layer with saturation at the max so it looked psychadelic, then a colour balance layer between the original and the saturation layer. Zoom in on neutral black background and tweak colour balance so each of R-C,G-M and B-Y is at the point between where it all turns one colour or the other, then delete the saturation layer. Alternatively just use colour balance and judge it by eye. You can also selectively tweak the saturation of colours with a Hue & Saturation layer. The soft light & luminance trick also makes it look redder if it starts out a 'brick red'. I have an odd effect in the star bottom left that has a blue halo around a yellow star... Another good trick is to split you image into two images, process the first image (LUM) for best contrast and clarity, the other (RGB) for best colour, perhaps blurring it a bit to help colour up small stars, then put the LUM layer on top of RGB and set it to 'luminosity'. yet another trick is to use a Hue and Saturation layer on the luminosity layer 9assuming it has some colour in it - you might want to up it's saturation a bit first). You can then use the 'lighten' slider on different colour channels - the R and M channels will generally help brighten the densest Ha regions, reducing G and Y helps darken the background outside the Ha and helps control stars. Best to just play and see what happens.

I think that NAN looks ghastly in purple... this one looks a more natural colour to me:

Can you check what the default values are for me? I think I changed the value too high and the help documentation doesn't give any recommended values...

IMHO aligning the histograms compensates for colour changes introduced by modification and filters. This is the Sadr region with histogram alignment, slight saturation boost and an s-shaped luminance curve (with the steep bit aligned to the histo peak) in DSS. All done in DSS and NO other colour correction or processing at all, except for reducing the bit depth to 8 bits. Taken with modded camera (too much red) and a pale-cyan moon & skyglow filter. Yes, I know it's noisy!

Much of the NAN is not particularly detailed in 'broadband' but this is a surprisingly bright target - I'm surprised you haven't got a lot more faint stars at 240S exposures, it looks like something odd was going on to me as your setup is virtually identical to mine: 450D modded - same sensor as 1000D modified, 130P-DS ~= Polaris 130. That said your guiding is working, nice round stars, next step is a Ha filter and 10-minute exposures! I used 90-second subs with a moon & skyglow (poor man's UHC filter) night before last, finished processing this morning, more stars and nebula. I think we could both improve our framing though! The Pelican is much fainter, and I notice that it has barely registered in my subs despite being very clear in this image I took last year: Really hard to know what colour to aim for...

Bias frames last months, darks last a good while as well, I split mine into warm, cool and cold nights.

Do you use DSS? If you use sigma stacking the satellite trails will disappear.

Yes, although most of my 150PL shots now are planets. The Skywatcher 150 PL is the one, the Bresser is slightly shorter FL so probably not the same.

It fooled me too, you should have seen what that horrific stack looked like when I used my 130 flats instead of my 150 ones :-)

Oh Sackcloth and Ashes! I did some jupiter imaging with the 150PL last night and instead of changing to the 130P-DS I went for some smaller targets. Either I had brain fade and forgot I used the other scope or I thought this was the EQ3 DSOP Challenge thread... you decide. They are coming to take me away now...