Sharpness and contrast

[Phillyo]

I'm curious about how some of the 'better' imagers around manage to get such high contrast and details in their images? For example Sara's narrowband imaging just blows me away with the amount of detail you can see in the dust lanes and how the nebulosity just leaps out of the image away from the background. I could almost fall into some of them, but how is that achieved?

Is it having a good scope? (Tak85...?) Is it the camera? Processing? Mount? Filters? Or is it a combination of them all? How much difference do dark skies make especially when narrowband imaging?

The images I see on this forum, and others, are amazing and inspiring but some of them just stand out above the rest and obviously I'd be interested in knowing how to do that

Thanks

Phil

[Kropster]

I suspect it is all the things you mention plus getting plenty of exposure time.... giving plenty of data to work with.

[johnrt]

I think you have answered your own question to a large degree.

A quality OTA like a Tak will produce a great flat field with sharp stars to the corners and a quality camera like a mono Atik or QSI (other imaging solutions are available) will hoover up the photons with it's superb quantum efficiency. A quality narrowband Ha filter was also used by the imager you mention above, the Astrodon 3nm filters boost the contrast and minute detail in the gas structures. A quality mount to put it all on, DSO imaging needs loooooooooong exposure times to capture that elusive wisp of Ha, or that outer shell of OIII.

Once you have the gear, spend some series exposure time of the target in question, multiple hours or even nights in each filter. You won't find many world class DSO images coming in at under 10 hours of exposure time.

The capture of the raw files to process is, despite all this, a mechanical process, but what sets apart images from Sara or Olly (other world class imagers are also available on this forum) is the skill in processing the data. The eye to extract the detail and present the colours in a way that screams out detail and contrast without looking over processed is where the difference lies. "Good" imagers will tell you that they spend as long processing their images as they did capturing them, if not longer.

[Phillyo]

Thank you both, I thought that's what it might have been but it's good to know. Sara mentioned I needed to start saving for some nice 3nm Astrodon filters and I guess she was right. There's always something better to spend your hard earned cash on isn't there?

I'll stick to what I have for now and learn how to capture and process whilst saving my pennies I guess!!

Thank you,

Phil.

[swag72]

I think that it's a combination of many things.

I just started writing a response and it was pretty much the same as John - So I've deleted that now!

The only thing I would add to what he's written is focus - You need to get that bang on the money, it will make or break an image. I don't think there's a 'that'll do' attitude to focus either, it's either yes or no. If you have to hesitate about whether it's good enough, then it won't be.

Dark skies are I guess good to have. I hope that Olly comes into this as I know that he has dark skies and swears by them! I don't have them and have never imaged in a dark sky - Would my images be better from a dark sky? I have no idea.

Processing  ............ hours and hours. For me, some images can take 10 hours alone to process, the more complicated ones anyway. I think that sometimes people under estimate the amount of time taken to process. 

Good quality kit makes life easier, it doesn't necessarily make it better  

[Phillyo]

Hi Sara,

Thank you for the input. Dark skies aren't really an option from where I live, though I could travel a little distance if I really wanted them and they made a huge difference. With regards to focus, how do you achieve accurate focus? Do you use a specific method? Specific hardware/software? Manual or automatic?

Processing is a massive learning curve! I'm still mostly using photoshop but I have dabbled a little bit with PI and think it's a very powerful tool.

The most important thing is clear skies...not had those for a while!! ha.

Thanks

Phil.

[swag72]

Sadly I'm in the same boat as you with regards to clear skies - Just not getting them at the moment sadly.

With regards to software in processing - Many folks use PS and to good effect, it's not dead in the water yet! Yes I flip between PI for a couple of things, but the majority of my processing (perhaps over 90% is in PS)

For focus, I use a Bahtinov mask, Bahtinov grabber (good piece of free software) and my own fingers!!! There's no automatic focusing here!!!

[johnrt]

I'll second the advice on focus, you need to nail it. No room for error there.

Dark skies? I'm sure that would make a huge difference, but us mortals who have to live under urban skies certainly have options. The 3nm Astrodon filters certainly help. But like Sara, I've never imaged from anywhere remotely close to the skies Olly is blessed with so can only wonder what I might be able to manage with dark, dark skies.

[Phillyo]

I've looked at those Bahtinov Masks but i've just been using the FWHM(?) method in APT and going for the smallest number possible.

Phil

[swag72]

Some folks use the FHWM method with great success. I can use either the mask or FHWM, but do prefer the former. If your way of focus works for you, then that's good, no need to change!

[ollypenrice]

Nice thread.

For narrowband you really don't need pristine skies and they won't make a huge difference. They'll help, but I doubt Sara would find much difference between her site and mine with her very tight Astrodon filters. She will get more benefit from her Astrodons than I get from ours because they exclude LP better. For us the main bonus is reduced star size in the Astrodons.

You will always get far more sharpness and contrast in narrowband than in the essentially broadband (natural colour) imaging that is what I mostly do. So natural colour imagers like to blend Ha and O111 narrowband into their natural colour images in order to pump up the sharpness and contrast. This means a mono camera with filters will beat a one shot colour which can only shoot NB slowly and at compromized resolution.

For LRGB (natural colour) imaging a dark sky is an enormous boon. You can take much longer exposures and working in long subs does generally beat working in short ones. The dark site helps contrast because that which is dark stays dark on the image while that which is bright is... bright! (You amaze me, Holmes!) The key thing is that the dark and faint stuff are not drowned in LP and can be distinguished from each other and the background.

Optics? The glorious FSQs and other premium scopes usually have three advantages apart from reliability and sex appeal. 1) Speed. 2) Large flat field. 3) Excellent colour correction.

1 (speed) is always an advantage.

2 (big flat field) is only an advantage if you have a big chip which needs it.

3 (colour correction) is of little importance in narrowband but is game-changing in natural colour because it prevents blue bloat and gives much smaller, tighter stars.

So if I'm right on this Sara's FSQ does not explain the quality of her images. She is really only exploiting its speed but not its colour correction or flat field in her NB work. It ain't the scope, it's the Sara! Conversely I do get a huge Tak bonus from our FSQs because we use natural colour filters and huge chips. It ain't the Olly, it's the FSQ! (Gotta be honest!)

You have to track well and you have to be in focus. Both vital and already covered in the thread.

You have to take a vast amount of data. Why? Because when you process you stretch and when you stretch you increase noise, so the less of it you have the harder you can stretch. When you run sharpening algortithms you sharpen the noise as well as the object so, again, less noise means more sharpening.

Processing skills. These are many and varied but have a big effect on sharpness and contrast. My keynotes would be, amongst other things,

Don't shaprpen stars.

Don't sharpen faint regions.

Don't black clip data. (The last operation should be one final clip off the black point, maybe.)

Don't stretch anything to saturation.

Work on zones within an image to maintain high local contrasts.

Don't go mad!!! Too little is better than too much.

Olly