Rho Ophiuchi Mosaic

[Paul Haese]

Well two panels down.

This I must say is an interesting exercise, dynamic range is hard to balance as well as the colour of the individual objects within the image.

This is two panels of LRGB all up comprising 320+180+140+200=840 minutes of data or 14 hours.

Click here for larger resolution image

[multiweb (Marc)]

I reckon your black point may be too high. There is a lot nebulosity in the area and it's not that faint. Do you need that much integration time? Stars on clusters tend to saturate quickly. The FSQ is a very fast scope.

[Paul Haese]

Originally Posted by multiweb

I reckon your black point may be too high. There is a lot nebulosity in the area and it's not that faint. Do you need that much integration time? Stars on clusters tend to saturate quickly. The FSQ is a very fast scope.

Thanks for your comments Marc. Black point looks fine to me. See attached. You cannot really show an image with a tiny section of the same detail and compare them mate. The dynamic range of both is like chalk and cheese.

As to integration time, I found that long and more subs suits my imaging. I won't be going back to short subs excepting for areas with very high dynamic range. I tried that years ago with the TSA and QSI combo and it resulted in very noisy images even after doing lots of integration time. I don't need to stretch very much using my current methodology. These are only 9 frames per lum at 20 minutes and a max of 5 frames in the colour at 20 minutes. That gives a smooth background without the need for any noise control.

Yes the FSQ is a fast scope but it is not a light bucket.

[multiweb (Marc)]

If you look at the very bright stars and the cluster at 10 o'clock you'll notice the stellar profiles are gone. This is because when you balance the dynamic range to blend the panels, the one with antares and the yellow neb is very different from the one with the cluster. Once you blend them in, one has to give. In this case the cluster got black clipped. There are two things you can do to avoid this. Do a pixel maths prior to join them or save scaled data and cheat a little in the stretching. The final histogram in PS doesn't reflect individual panels clipping. Once you join them the histogram will show the whole picture

[Paul Haese]

Originally Posted by multiweb

If you look at the very bright stars and the cluster at 10 o'clock you'll notice the stellar profiles are gone. This is because when you balance the dynamic range to blend the panels, the one with antares and the yellow neb is very different from the one with the cluster. Once you blend them in, one has to give. In this case the cluster got black clipped. There are two things you can do to avoid this. Do a pixel maths prior to join them or save scaled data and cheat a little in the stretching. The final histogram in PS doesn't reflect individual panels clipping. Once you join them the histogram will show the whole picture

Actually that has been brought about by my doing. The base data has some high cloud issues and as a result the whole of M4 has a very definite magenta cast to it. You can see the blue stragglers and the orange giants but the white stars are the ones with the magenta. This is why I want to collect another couple of frames. It has upset the balance right from the start. I will have to deal with it better once I do the next two panels down. I don't doubt that one has to give way over the other. Doing a mosaic in this area is not going to be easy and I am sure in the end it will be a compromise as it is now.

[IanP]

Geezzz Paul and Marc, your technical discussions are beyond my level, anyhow, the data is “uber” impressive .. and I’m patiently waiting for the “red” part …

[Rex]

Really nice detail Paul. Can't wait to see the rest of it.

[DJScotty (Scott)]

Very impressive Paul. I second Rex's sentiments. Looking forward to seeing the rest of it.

[jase (Jason)]

I'm liking it Paul. The resolution from the combined two panels is starting to show. The colours contrast well. All in all with a couple of more panels it will be a splendid result. I don't see the black point issue. It's certainly on the edge. I've always left the black point low to provide greater flexibility in seam stitching panels, then toward the end raise it. You can always use the burn and dodge tools to get a near perfect match. I'm looking forward to the final result.

[Paul Haese]

Thanks Rex and Scott for you comments.

Ian, it might have to be next month now for the next panel. There is a tiny hint of the red in the left hand corner, just as a teaser.

Originally Posted by jase

I'm liking it Paul. The resolution from the combined two panels is starting to show. The colours contrast well. All in all with a couple of more panels it will be a splendid result. I don't see the black point issue. It's certainly on the edge. I've always left the black point low to provide greater flexibility in seam stitching panels, then toward the end raise it. You can always use the burn and dodge tools to get a near perfect match. I'm looking forward to the final result.

Thanks Jase. I sort of often keep my black point there for every image I produce. It will be interesting when I get the next two panels down and see what the dynamic range will be like for the mosaic then.