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Messages - marekc

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Gallery / Re: Sadr Region Widefield Ha+RGB
« on: 2015 August 25 12:35:56 »
I really like that image, Jose.  :)

When I clicked on the link to the image, it immediately struck me that "this is what I like". If someone asked me what I like in a wide-field astro-image, this is a good example. I like the colors in the RGB stars, and they're nice and sharp and small. (If only I had a scope that could make such small stars!  :o)  I like the color of the nebulosity, in both the Butterfly and the Crescent. The tonal range in your image also suits my taste very well, too. The regions of dark nebulosity are quite dark, as my aesthetic sense says they "should" be, but you haven't pushed the rest of the background to a very dark level. The amount of contrast in this image suits my taste quite well!

I was tempted to write a reply that said "That's it! That's how all images of nebulosity in the Milky Way *should* look!" Then I thought about it a little more and realized "Hmmm, it may be that not everyone has the same aesthetic sense about astro-images that I do. Instead, maybe I should thank Jose for making an image that suits my taste so well!"

Someday, if I can improve my autoguiding near the zenith, maybe I will be able to shoot a decent Sadr image! Thanks for the inspiration  :)


Ditto to what Josh just said.

(That's a USA English expression for "I'm thinking the same thing Josh is".)

- Marek

This is a really neat thread!

First, Colin, great job making that H-R diagram. That's totally neat! It brings back a lot of memories, since I made an M67 H-R diagram when I was working on my Swinburne degree.

(I didn't have my own images, though. I was an even less advanced imager than I am now, if that's possible.  :tongue:  I used some images that had been shot at McDonald Observatory in Texas. Hmm, how I did I automate the photometry?... IIRC, I think I used some non-PI software and some star coordinates from a recent paper whose authors had done high-precision astrometry on M67.)

I've been wishing I had the time to try and use the PI photometry script to re-do this project, just for fun. It would be big fun to do it in PI!

(Plus, if I could simplify the whole affair as much as possible, maybe I could use something like this as a lab exercise in my astronomy lab class. That would be fun, to get students making H-R diagrams from images. Might give me ammunition to try and find the money to purchase PI for the lab computers, hmm..)

Thanks for reminding me of this dream, good job on your diagram, and thanks to Vicent for reminding us of the PI photometry script.

- Marek

General / Re: How do I cut and paste stars?
« on: 2014 December 31 14:20:07 »
Hi Earl,

I think you did a great job of getting the stars out in the first place! (Heck, stars can be so difficult to deal with that I find myself admiring your `nebula-only' image purely for it's own sake!)

I'd love to see how you did removed the stars - or did you follow a tutorial that's already been published?

- Marek

Thanks, Morten!

That's a nice-looking image  ^-^  It's got a lot of resolved stars, plus HII regions and the faint outer portions of the galaxy. Good `ol M33!

- Marek

I have to admit, I'm really quite amazed by this approach to imaging! The results that MortenBalling has posted look really good to me.

When I looked at the M31 image, I checked the credits to see if my image was in there... it wasn't, IIRC. That's neither here nor there, but it made me think about something: Images like these may have a bit of a `Google Earth effect' for some viewers. When people first use Google Earth, they immediately try to go find their house. When people go up in an airplane, they say "I can see my house from here!" When a crowd-sourced image gets posted, people who've posted their own individual images will probably check the credits, to see if their work is in there. Interesting!

This has also made me think about licenses and copyright more than I had before. I'll have to go check the default CC license setting on my (exceedingly modest) little imaging blog. Maybe I didn't allow people to modify the images, or something like that. I never thought much about that until I saw this thread.

What a neat technique! I don't know if there enough M33 images out there to make a good M33, but I'd love to see that. It's a personal favorite of mine.

It also occurs to me that crowd-sourced images are kind of like mineral deposits or oil fields. All of the easy stuff will be gone through fairly quickly. The supergene deposits and big surface anticlines were all discovered long ago. In some cases, those mining districts and oil fields still yield commodities today. That's kind of like if someone decided to apply really advanced PI processing to the crowd-sourced M31 data, to try and squeeze a slightly better result out of it. The rarer deep-sky objects will be like the more recently-discovered resources. Yes, they're there, and we can find them and extract them, but it's much harder to do so. Like trying to make a crowd-sourced image of some obscure Sharpless object that has very few publicly posted images. It could, technically, be done, but it would be very hard to do. In the case of minerals and oil, sufficient demand/scarcity/high price can make a `tough' deposit worth going after - there's a profit motive, at least at certain times. But with crowd-sourced imaging, the lack of a profit motive might, I'd guess, provide a fairly strong dis-incentive against trying to do the tough stuff via publicly-posted images. At a certain point, it's easier to just buy one's own gear, go on a road trip to a dark site, and shoot that sucker oneself.

It's like a little economics lesson! What a fascinating thing - I'm glad someone did this!

- Marek

Gallery / Re: Galactic Center Mosaic
« on: 2014 July 01 15:50:16 »
That's a very nice image! I liked the south-up orientation; it made for a fun time identifying objects like M8, M24, M16/17, etc, compared to the usual `north-up' view that we have here in the northern hemisphere!

- Marek

General / Re: General Question on Drizzle
« on: 2014 June 26 16:39:18 »
I've got a followup question, concerning how we measure seeing:

What is meant by a phrase like "the seeing is 3 arcseconds"? Am I correct in assuming it means something like the following?...

1) If there were no atmospheric turbulence at all, a star would show up as a diffraction pattern with a central Airy disk surrounded by bright rings that get progressively dimmer outward.

2) Due to seeing, that pattern is almost never what we really get. In real life, we mostly get a "diffraction + seeing" point-spread function that looks roughly like a Gaussian peak. (A Gaussian may not be the ideal approximation of this peak, but it's basically a single mountain-like hump for each star.)

3) If we had a very well-sampled image of one of these star PSFs, we could measure its full width at half maximum. That FWHM is what we mean by the "size of the seeing".

Is that roughly correct? I hear people say things like "I've got two-arcsecond seeing", and I am never quite sure what they mean. The FWHM of a PSF `hump'? The half-flux radius (HFR) of that hump? The tightest double star that could be visually resolved if we replaced the CCD camera with an eyepiece? I'm guessing it's the FWHM of a star image.

- Marek

Announcements / Re: PixInsight Resources
« on: 2014 April 08 09:36:12 »
I couldn't see the videos before, but now I can. What a great instructional resource! Thanks very much for creating this!

- Marek

Gallery / Re: M42 to Horse Head in Bi Color
« on: 2013 December 31 20:03:19 »
I'm rather a fan of bicolor, I have to say. First, I find that I like the colors of the nebulae that result from the bicolor process. Sure, I guess I'm *supposed* to want emission nebulosity to be "H-alpha red", and that color *is* indeed very nice. But I like the orange nebulae, too. I also think there's something elegant about being able to assemble a color image from just two filters, rather than three. It's kind of like a visual expression of the concept of `color index', which is determined using two filtered exposures.

I've probably mentioned this before, but I'd love to figure out a PI way of reverse-engineering Davide deMartin's bicolor processing of DSS data. He really gets those colors to pop!

This image has nice colors, too! I particularly like the emission nebulosity behind the Horsehead.

- Marek

General / Re: Success!!!
« on: 2013 December 28 22:21:18 »
I'll second the recommendation for the "deconv deringing wrecks images?" thread. (Happily, Juan shows that it doesn't, at least not if one can find the right settings.)

When you do dive into the wonderful world of deconvolution, I think you'll find that getting the right PSF (Point Spread Function) is a big deal. I have often struggled with this. I'm quite embarrassed to say that I haven't been able to post a new image to my blog in nearly a year, but the last thing I posted talked about this subject:

Basically, one of the PI videos from Warren Keller and Rogelio had some tips about the PSF, and those tips *really* helped me! Made it all quite worth the money, IMO.

I haven't done deconvolution in PI 1.8 yet, but if it hasn't changed too much from 1.7, then those tips will probably still be good. (Heck, Warren and Rogelio might have even made the video in 1.8, I can't recall.)

- Marek

Gallery / Re: Helix nebula in bi-colour NB with RGB stars
« on: 2013 December 18 15:09:27 »
Another nice example of narrowband nebulosity with good-looking RGB stars!

There have been a lot of nice images of this type on the PI Forum lately, and it's a lot of fun to send people kudos! I think this is another very good example of putting RGB stars into the image, and the deep nebulosity is really impressive.

- Marek

Gallery / Re: NGC7000 Wide Angle in HST
« on: 2013 November 20 12:23:27 »
That's a really nice image. I like the colors, I like the background level, and I think you did a great job with the stars. It's very enjoyable to look at!

- Marek

General / Re: Overriding pre processing script behaviour with flats
« on: 2013 November 18 18:43:58 »
Hi Steve,

I would be curious to know your reason for wanting to apply the blue flats to all of the color channels. Are you shooting through separate R, G, and B (+/- narrowband) filters?

The reason I ask is because I've often heard that one should shoot a separate set of flats for each filter. A flat-field frame compensates for uneven illumination, including dust on the filter. Therefore (it is often argued), one should shoot a set of flats for each filter, since each filter could have a different set of dust particles on it, producing different shadows on the sensor.

I shoot a separate set of flats for each color filter in my filter wheel. I've been pleased with the results. I must admit, though, that the pattern of dust spots looks pretty much the same from filter to filter, so I suspect I'm really mostly seeing dust on the CCD sensor window. But, just in case there are some dust spots from the filters that I'm not noticing when visually inspecting my raw lights, I shoot flats for each filter.

- Marek

Gallery / Re: Bubble Narrowband
« on: 2013 November 07 15:28:14 »
Hi Marc,

That's a great Bubble image! That really has a lot of `wow' factor. I can't think of another Bubble image I've seen like that. Interesting composition, interesting orientation, nice and sharp, lots of IFN... that image has a lot of great qualities.

I like the color palette, too, in much the same way that I like Davide De Martin's color palette in his DSS-based images. That's a cool orange!

- Marek

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