Sagittarius Mosaic

[avandonk]

Two panels. Same exposures for both.

Details
Canon 5DH, Canon 300mm F2.8L at f3.5 with external aperture and lens hood extension. ISO 1600. Hutech LPR filter. Fridge at -11.0C.
Exposures 20x(15s, 30s, 60s and 120s). Usual HDR method. No enhancement.

Small Image 5.5MB. FoV 11.2 X 4.6 degrees

http://d1355990.i49.quadrahosting.com.au/2010_04/LTmosS.jpg


Dust has come up well. The lens hood extension is really helping here.

Bert

[alan meehan]

Top shot Bert ,so many stars and a lovely area of sky .

[strongmanmike]

This looks great Bert, the dark lanes show up well and I like the long panorama look too.

Mike

[gregbradley]

Fantastic image Bert. I love it. So many stars it looks like sandstone.

Greg.

[bojan]

Bert, your work became a trade mark of IIS :thumbsup:

[avandonk]

Alan, Mike, Greg and Bojan if you liked the image here is a larger high resolution version. It takes a lot longer to upload it than download it. The 128kbits/sec upload speed limitation is a constant annoyance.

19MB

http://d1355990.i49.quadrahosting.com.au/2010_04/LTmosL.jpg


Bojan I spent forty years using my technical expertise to make my bosses famous. I am quoting them. My group leader was once asked by a TV crew (that was interviewing him) what Bert's job was in the lab and he said ' it is Bert's job to use his skills to make us famous!' His tongue was firmly in his cheek.

Now in retirement I can maybe do a bit more for myself as well as passing on any new methods.

This very difficult hobby of astrophotography keeps me as sane as I was last week. I will get bored with it when I cannot further improve. Fortunately this will not happen as there is constant exchange of ideas and stimulation on forums like this that stops us from going stale.

Bert

[bojan]

Thanks Bert,
this image will be my very valuable reference in the future, like a super star chart :-)
Who knows what you managed to captured on it..

[duncan]

Imagine having two of these images and doing a blink comparison.
WOW!!!!!!!!!!!
Cheers,
Duncan

[Phil Hart]

you've got some equipment working well together there bert.. very impressive.

i'm interested in why your stars have a cyan-ish colour balance. i tend to get magenta casts in my images from star halos, although I'm mainly using a 50mm lens. i use star size/halo reduction in ImagesPlus, and set it stronger for red/blue than green channel which helps.

phil

[avandonk]

Phil there are a few things happening here. Top quality lenses are not designed with HA wavelengths in mind when minimising CA. So in the case of the 300mm F2.8L it is a matter of compromise when focusing as to what end of the spectrum is slightly out of focus. The Canon 300mm F2.8L has one lens element made from a single crystal of Fluorite and two ED elements in main front lens groups. Even then it is not perfect.

The CA near the corners are slight aberrations due to the fact no lens at f/3.5 can be perfect. It can be minimised by using f/5 but then signal goes down and thermal noise rears it ugly head due to the longer exposures needed.

In the case of your 50mm lens CA and aberrations are worse due to the wide field of view. That is why even at 'perfect' focus both red and blue are slightly out of focus.

You are quite correct that careful star reduction at the red or blue or both end of the spectrum can help.


The large images of the mosaic are actually upsized by a factor of 1.6 from native pixel size of 4368X2912 to 7014X4668. This with dithering the mount between exposures when collecting really helps with star profiles as at 300mm FL the stars are undersampled. This only works if the lens has more resolution than the sensor.

Here is the image with adequate star reduction of the blue channel, slight Richardson Lucy enhancement and a boost in saturation and reduced to native pixel size.

Large Image 12MB

http://d1355990.i49.quadrahosting.com.au/2010_04/ltsatL.jpg


If I simply processed at native pixel size the stars all end up as lovely squares!

Dithering and upsizing before stacking would really help widefields at 50mm to 100mm even more as long as the lens is of high enough quality.

Bert

[multiweb]

Awesome. Are you going to keep on mosaicing towards M16/17 ? At this rate you should do a whole Milkyway High-res mosaic and print it on A0 :)

[mswhin63]

Looks great so many stars. Showed my wife, very visual person saw a Hippo yawning in the Nebula.

See if you can find it.