Arp 316 at 2500 mm

[Nocturnal]

Hi,

I just processed another image. It's a bit deficient with a large dust mote in the center and a substantial lens donut but the galaxies look OK so here it is anyway.

http://www.carpephoton.com/index.php?option=com_content&view=article&id=38

I have had several people try to fix the dust mote with various PS tricks. Now of course I need to give that a try with PI

CS,

     Sander

[Alejandro Tombolini]

Hi Sander, may be this can help: http://pixinsight.com/examples/NGC6914-CAHA/en.html but I've never tried.

Nice picture, congrats.

Saludos. Alejandro.

[Nocturnal]

Thanks Alejandro, that looks worth a try!

[Andres.Pozo]

I like the images like this with small and unusual galaxies.

I have used the full resolution version for testing my plate-solving script. The results are these:

Code: [Select]

Image plate-solve v0.2:
------------------------
Referentiation Matrix (Gnomonic = Matrix * Coords[x,y]):
    -0.000030271057438856858 -0.00015602718165551058 0.18584126961503783
    0.00015600470120715948 -0.000030033834661093352 -0.16038955127886845
    0 0 1
Resolution..... 0.5721 arcsec/pix
Rotation....... 100.934287 deg
Focal.......... 2019.20 mm
Image center... RA: +10 18 00.414  Dec:+21 50 17.576
Image bounds:
  TopLeft...... RA: +10 17 12.356 Dec: +21 59 53.998
  TopRight..... RA: +10 17 31.410 Dec: +21 37 14.047
  BottomLeft... RA: +10 18 29.506 Dec: +22 03 20.786
  BottomRight.. RA: +10 18 48.364 Dec: +21 40 40.286


[Nocturnal]

Hi Andre,

the pixel size for the camera is 7.8 um square. Does that bring the focal length closer to 2500 mm?

[alejandromeira]

very nice job!! great color at the galaxies and stars.

[Andres.Pozo]

the pixel size for the camera is 7.8 um square. Does that bring the focal length closer to 2500 mm?

Hi Sander,

using 7.8um pixels the focal is 2810mm. This is normal if the camera is located very far from the back of the telescope.

Code: [Select]

Image plate-solve v0.2:
------------------------
Referentiation Matrix (Gnomonic = Matrix * Coords[x,y]):
    -0.000030287092111367392 -0.00015612575996351387 0.1858942439983827
    0.0001561303266751038 -0.000030362582601555993 -0.16015712658938203
    0 0 1
Resolution..... 0.5726 arcsec/pix
Rotation....... 100.993518 deg
Focal.......... 2809.93 mm
Image center... RA: +10 18 00.451  Dec:+21 50 17.266
Image bounds:
  TopLeft...... RA: +10 17 12.364 Dec: +21 59 53.105
  TopRight..... RA: +10 17 31.428 Dec: +21 37 12.060
  BottomLeft... RA: +10 18 29.563 Dec: +22 03 22.154
  BottomRight.. RA: +10 18 48.431 Dec: +21 40 40.558


[Giorgio]

Sander, Excellent image,
I see a little green background, but maybe it's my new LCD monitor.
Giorgio

[Nocturnal]

Hi Andres,

I was wrong with my estimate, it should be about 2800 mm of course (11 x 254). Luckily your measurement showed the same number!

Hi Giorgio,

it's possible there's a little green but I did an SCNR green removal and BN after that. I think it's about as neutral as I can get it now. Thanks for commenting though!

[kwiechen]

Hi,

very nice group of galaxies!

Best,

Kai

[Lex]

Sander,

Nice image, is there no way to get rid of the rest noise? DBE more restrictively with a nice lightness mask?

I do see an artefact in your image, wich i also had with my C11: there is a ghost print of the main mirror decentered of the brightest star? Why is this often decentered even if the optic is well collimated?

[Nocturnal]

hi Lex,

DBE does not remove noise so I'm not sure what you're talking about. I could be more aggressive with noise reduction but I don't like the effect that gives. The background looks like it's drawn with a pastel brush. I'd rather have this appearance. I think gradients are pretty well under control but maybe you see differently?

I think the reflection is off-center because the light source (star) is not in the center either. I suppose if we really wanted to know we could do some ray tracing but in short the light hits the reflective surface at a slight angle, hits a second reflective surface (again at an angle) and finally hits the CCD. It's not hard to see that way that it would be slightly offset. Only the long focal length (steep angle) kept it this close.

[Lex]

Hi Sander,

Lol, i was thinking about ACDNR but have written DBE because I mainly remarked the noise in the background area 
I do really like your image, I never managed to obtain a quality like yours, my CGEM doesn't track precisely enough with long FL's even guided and PEC activated, hypertuned and cycled through PEM pro 


Thanks for the explication of this mirror ghost, so if I correctly understand, it only appears at longer FL's?

[Nocturnal]

Hi Lex,

please always feel free to comment. I do too and this is how we learn. My exposure length wasn't very long so that's why the image is relatively noisy. I could push it down further but I don't like the result in that case.

How do you guide your CGE? I use an OAG. Without that I'd be lost too. A good mount can't compensate for a large and flexible mirror like the one in my HD 1100

I think mirror ghost can appear at any focal length. You were asking why it's not centered around the star and this is my best attempt at understanding it. With shorter FL the ghost may miss the sensor if you're far enough from the center.

[Lex]

Sander,

I used to guide with a guide scope, for now i try to use an OAG but i must honestly say that it is much more tricky and guidestars are not really often available...
I use the 9mm OAG from Teleskop-Express in GER, it is a nice piece of equipment but it demands very much precious time to find GS...