A new treatment of the same shot, going back to the linear file and removing the stars (which is amazing in itself) and processing them and the nebulosity with different stretches (allowing the bright stars not to be completely blown out by the stretching needed for the underlying faint tonal details), then recombining. I doubt I’ll ever do another astro capture without using this very easy technique.
The photographer is looking for generalized feedback about the aesthetic and technical qualities of their image.
Description
We finally had the first clear skies in darkness near the new moon in many moons (as the saying goes). And I finally got what I hope are the last wrinkles ironed out with the new tracker and astro camera and scope, and with the processing software, PixInsight. This object is one of the low-hanging fruits on my conquest list. I had shot it with an older tracker and DSLR equipment 6 years ago with much less pleasing results. It is a star cluster about 450 light-years away – practically a next-door neighbor. You can see it in the southern skies for the next few months, being chased by Orion.
Specific Feedback
All comments welcome!
Technical Details
Askar FRA400 astrograph (refracting telescope), ASI2600 cooled color camera, SkyWatcher EQM 35 tracker, ASIAIR controller. Four hours of 30-second subframes (longer blows out stars and bright nebulosity with the fast scope), dark, flat and bias calibration frames, processed in PixInsight. Churning through calibrating and registering the subframes took 5.5 hours on a fast computer that was otherwise unoccupied. I didn’t count the electrons used. Pixinsight was used to do processing stuff that is mind-boggling, but made easy by recent advancements.
Nice image, Diane. That is a hard object because of the brightness of the stars. I see you picked up the red pretty well indeed. I don’t use PI much but once mastered it is quite a program
Hi Diane,
wow, that looks fantastic. I only tried Deep Sky two times (Orion and the Pleiades) with my 70-200 and a small star tracker. But my results look embarrassing compared to your masterpiece.
Really great details!!!
I was curious about what your setup looked like and researched your listed equipment… not bad.
I can’t wait to see your next results.
Thanks, @Dean_Salman and @Jens_Ober! PI used to be extremely difficult but in the last couple of years it has been changing almost monthly and has gotten so much easier with new modules and scripts that basically automate some tedious and difficult tasks.
Deep sky objects are very dim and it takes the equivalent of hours of exposures to capture the tonal detail, and there is a huge dynamic range between the dimmest and brightest details. The exposures need to be in smaller increments and a large number of them are “stacked” to greatly reduce noise, and then the almost-black histogram is stretched, similar to us brightening exposure but hugely more. That brings up any noise that is left and wants to blow out stars, but there are methods to deal with that.
The most difficult problem now is that new stretching methods have so much tonal adjustment capability that it is hard to know when to quit pulling out detail. If you look at pictures of deep sky objects you will see a lot of variation, even among very high-end treatments.
The optics of telescopes far exceeds that of camera lenses, and the sensors of astro cooled cameras exceed even the best DSLR or mirrorless camera. I run my cooled camera at -10 degrees C. I could go to -20 but the difference in noise is negligible.
Here is a recent shot of my fairly modest equipment and its normal mode of transport.
but this year it wasn’t dry so we settled for a nearby old emergency field. But the Pleiades was shot from a more convenient location – behind our garage.
That is great info, @Diane_Miller. I am so jealous that you can just fly there and setup. I never got a pilot license so missing my calling. I built a simulator as a work around. Your post processing is fantasic
Thanks again, @Dean_Salman! I owe a lot to Adam Block, whom you probably know from his time at Kitt Peak. His tutorials on Pixinsight are graduate-level textbooks.
It’s a special astro camera – really just a sensor attached to the back of the telescope. It looks like a soup can. Cooling the sensor lowers noise. I can’t figure out how they do it – from the outside you just hear a tiny fan running, but it’s cooled to a precise value you can set.
