Spent some time carefully collimating the TAL200K last night with the help of many mozzies. Thought I would do a quick HDR of the Jewel Box as a test early this morning just before beginning of twilight.
Details
Tal200K FL 1800mm f/9, no filter. Canon 5DH.
All at an ISO of 500. 8s, 15s, 30s, 1m, 2m, 4m. Converted from RAW to TIFF and corrected for flats with images plus. Aligned with Registar and generated an LDR from this data with EasyHDR.
As you can see the HDR process tends to preserve star colours. The EQ6 also seems to be tracking fine at 1800mm as I really did not have to use Registar to align as there was virtually no drift over the full set of exposures except for the last 4m image. At 1800mm focal length the image scale for the 5DH is 0.94 seconds of arc per pixel.
The second image is a 100% crop. The third is a full frame defocused image that gives some idea of the state of collimation and star colours. I actually collimate by viewing a defocused bright star centrally through the camera viewfinder, adjust and then take a defocused image. Repeat until the image is nice and symmetrical for the central star.
Beautiful result and nice colors Bert...!
I have always enjoyed this little cluster as its one of the first I ever looked at through a scope many years ago!
cheers Gary
Here is an image produced from only the 4min data. I tried to get it as similar to the 100% cropped HDR picture as possible. It is obvious which is visually more pleasing.
Not sure Bert. I think the single 4min shot has potential. Its stretched too hard, which makes the stars look bloated and washed. All of the HDR images are clipped in the blue channel hence we're not seeing any traces of the subtle blue hue in Kappa Crucis.
Try a minor r curve to manage the star intensities (see below). I typically use 3 to 4 points in the curve. The benefit of such a curve is you're managing the top end intensity so the star core doesn't bloat or wash, but still raising the surrounding star edges. If desired then follow up with a minimum filter and saturation adjustments - both should really bring some nice star colour back into perspective.
You and others may find this link of interest. It details stellar profiles for different star spectra. http://www.vendian.org/mncharity/dir3/starcolor/
Note: Alpha Cent A is a G2V star that can be used to determine colour balance, though I would recommend choosing another G2V star considering its close companion proximity. You want to get the cleanest reading possible.
You are correct Jase. If I do as you say I get all the lovely light pollution from the Mercury blue line from all the street lights around here and all the way to Melbourne! These lights are far from subtle. I won't even mention those abominations called high pressure Sodium street lamps. If only these lights put their energy where it is wanted, on the ground not into the sky.
This was only a quick test and the image was just an afterthought.
Could always make a compromise Bert. Far from optimal however...
Duplicate the layer. With the new duplicated layer selected, enter Saturation (control+u), select the colorize check box. Change the hue slider to 230 (blue), then boost saturation to around 30. Click ok. Change the duplicated layer to lighten. Select the original background layer and raise the red channel black point with levels (control+l) by a few points to get rid of the red background. Season to taste.
Quick tip in Photoshop. If you make a mistake perform adjustments in one of Photoshops adjustment dialog boxes - curves, level, saturation etc etc. simply hold down the Alt key and the cancel button will turn into a reset button. When selected the settings will revert back to defaults. Saves you having to click cancel and go back in to the dialog again. I use CS2, not sure about the other versions.
It does sound like a variation of the old joke "my mother made me a homosexual. Reply. If I gave her the wool would she make me one too!"
What I really mean by that Jase if I send you the TIFF images by snail mail on CD or DVD would you have a go at using your vast experience to tweak them. Not necessarily this image but one in the future. Purely at your leisure of course and something that is worthwhile.
Can do as you mention. Would prefer if the data is already calibrated/reduced (darks/flats), though can do this via MaximDL/CCD/DSLR software I have. The only thing I ask is to collect plenty of data on the chosen target so we aren't severely limited in how far the data can be stretched.
!
Nice one Bert.
