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06-30-2018, 01:01 PM - 6 Likes   #1
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Astrophotography tips - a short tutorial

Someone PMed me with questions about an astrophoto I posted in a different thread. Rather than just reply to them, I figured I'd make it a little bit of a tutorial here. I use Lightroom but the concepts apply to other software.

The attached image shows before and after processing a photo of the Sagittarius region of the Milky Way.

Equipment:
  • K-1 using astrotracer. These concepts apply with any camera, even my comparatively limiter micro four-thirds camera.
  • Lens: DFA 100 WR macro. Macro lenses tend to be evenly sharp across the frame, making them good for stars.
  • Tripod
Settings:
  • ISO 1600. If I redid this shot, I probably would use ISO 800 based on how I've seen my K-1 work. Lower ISO looks darker in camera but offers further processing leeway.
  • Shutter speed 60 seconds. I usually stay with conservative exposure lengths with the astrotracer, using less than the maximum the camera says because calibration and tracking can be hit-and-miss.
  • Aperture f3.5. The DFA 100 can show a purple halo around bright stars, especially when dim parts of a photo are brightened during processing. Stopping down a little reduces the fringing.
  • Single exposure, no stacking used.
  • Raw DNG. That offers more processing headroom than JPG.
  • Take a few photos, in case one or more are ruined by aircraft lights or other issues.
Processing:
  1. All processing for this photo done in Lightroom. Photoshop was not needed. It looks like a lot of steps below, but it only takes 10 minutes, then I step away and come back later for a fresh look.
  2. The first step is to assess whether the photo has potential. Check the overall photo for composition. Zoom in 100% to make sure focus is reasonably good, check that I didn't accidentally kick a tripod leg, and make sure wind didn't shake the camera. There's no sense wasting further procesing on a fundamentally bad photo.
  3. Basic panel - to get exposure and colors correct
    1. The first processing settings are lowering the black point slider and raising the white point slider. Hold the Alt key (on Windows, I think different on Mac) as you move the sliders to see if any area are getting too black or too white. The sky background should retain a little gray in it. It's okay if the center point of stars hit 100% white.
    2. I then test the other bright/dark sliders in the basic panel: highlights, shadows, contrast. Exposure slider usually stays at 0 because I already used the white point slider. Sometimes I'll add clarity instead of contrast - using both usually looks overprocessed to me. In hindsight I'm surprised to see I went as high as +88 contrast.
    3. Get an overall pleasing color. I compare White Balance as shot to around 4000K. I prefer a gray rather than too-blue background. Saturation usually gets boosted a little bit.
  4. Detail panel - for sharpness and noise reduction
    1. Boosting brightness like we just did makes noise more visible. I usually use little or no sharpening. If you do sharpen make sure to use the masking slider, to avoid false sharpening of noise in bare areas.
    2. I'll add some luminance noise reduction (this photo was at 27) and color noise reduction (29).
    3. When using micro four-thirds, I get too much color noise to fix without blurring details, so I just convert the entire photo to B&W.
  5. Lens Corrections panel - varies by lens
    1. I enable profile corrections by default to reduce vignetting. It's more important with my K-1 than prior K-5.
    2. That purple fringing I mentioned earlier ... fix it in the Manual panel. Zoom in on a bright star that has a purple halo, click the eyedropper, click on the halo. Tweak sliders as needed.
  6. You might be done! Take a break. Come back later.
  7. Take a fresh look.
    1. Beginners often process too much. Return to earlier panels and back off some sliders if needed.
    2. Visit additional panels to do further tweaks. When I used the K-5, the IR cut filter blocked more red than happens with the K-1, so I would go into the HSL panel to bring back some red.
    3. Are there any dust spots or other issues? In this photo, I caught a short trail from a satellite. You can see it in the before image upper-right from center. It's small, but I wanted to fix it. The Lightroom Heal brush was able to do a satisfactory job. usually, planes and satellites leave longer trails that require Photoshop context aware erase.
Note that this is how *I* do it. Others get great results using different techniques. For example, you can use the Tone Curve panel and spend less time in the Basic sliders. You can work exclusively in Photoshop or other software.

Astrophotography can be an exercise in fun plus frustration. Some nights I get good results. Other nights nothing works out well because of human error, subtle equipment glitches, extra humidity in the air, and other factors. Be patient and persistent.

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06-30-2018, 01:20 PM   #2
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Very interesting, thanks for posting.
I don't have the astrotracer, so I need to stack to get good results, but your processing tutorial can still be applied
06-30-2018, 06:25 PM   #3
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Thanks for being so helpful, DeadJohn. Best wishes.
07-03-2018, 10:58 AM   #4
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That's wonderful, thanks for taking the time to explain!

Your processing techniques are not too far from mine, however I don't seem to get such good results. Maybe there's too much light pollution where I usually shoot...?

07-03-2018, 11:11 AM   #5
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Great with a step by step tutorial, join the Astrophotography group to see more: Astrophotography - PentaxForums.com
07-03-2018, 01:04 PM   #6
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QuoteOriginally posted by bdery Quote
That's wonderful, thanks for taking the time to explain!

Your processing techniques are not too far from mine, however I don't seem to get such good results. Maybe there's too much light pollution where I usually shoot...?
How much light pollution? My linked photo was taken from the outer edge of NYC suburbs, Southold NY.

My example photo was done with 100mm. It's a relatively small slice of the sky so background light pollution is even across the frame, allowing me to hide it with the black point slider. As you go wider angle the gradients become more visible - horizon is bright, zenith is darker.
07-04-2018, 04:55 AM   #7
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QuoteOriginally posted by DeadJohn Quote
How much light pollution? My linked photo was taken from the outer edge of NYC suburbs, Southold NY.

My example photo was done with 100mm. It's a relatively small slice of the sky so background light pollution is even across the frame, allowing me to hide it with the black point slider. As you go wider angle the gradients become more visible - horizon is bright, zenith is darker.
Quebec city's suburbs are probably not worse than NYC suburbs... It's probably because I usually shoot the sky at wider angles indeed. I'll try your technique soon.

Regarding aim, how do you determine if the camera points your target?
07-04-2018, 12:14 PM   #8
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QuoteOriginally posted by bdery Quote
Quebec city's suburbs are probably not worse than NYC suburbs... It's probably because I usually shoot the sky at wider angles indeed. I'll try your technique soon.

Regarding aim, how do you determine if the camera points your target?
Usually, I do a rough aim, take a test photo, look at the LCD to see if I have something interesting on the back. Re-aim if needed. If photographing a dim object you can crank up the ISO to shorten exposure time on the test, then return to a more moderate ISO with longer exposure for the actual photos.

Wide angle makes it easy to find targets. Look for the band of the Milky Way during summer and you are good. The Milky Way changes orientation each season and sometimes hugs the horizon, so be wary of that.

You are further north than me. Good for aurora, bad for Milky Way. The brighter portions of the Milky Way near the constellation Sagittarius will be low on your southern horizon during summer. That's a target-rich area with 50mm or 100mm. Try scanning the Milky Way working your way up from there. The Cygnus area has some interesting dust lane detail.

With a 200mm or 300mm lens and astrotracer, you can try the Andromeda Galaxy. You might be able to see it naked eye from a dark site to aim, otherwise learn how to "star hop" to find it. The Orion nebula is a winter object very east to find near visible stars in the "sword" of Orion.

TLDR; it pays to learn some astronomy.

07-05-2018, 05:26 AM   #9
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QuoteOriginally posted by DeadJohn Quote
it pays to learn some astronomy.
Thanks for all the advice. As a physicist, my astronomy basics are decent, though I'm more specialized in optics (and to some extent materials). For some reason astrophotography is the only field in photography where I feel like I struggle. Night scapes are ok, but astro? Not there yet
07-28-2018, 10:25 PM   #10
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Solid write-up, thanks for taking the time.
07-29-2018, 02:43 AM   #11
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QuoteOriginally posted by DeadJohn Quote
How much light pollution? My linked photo was taken from the outer edge of NYC suburbs, Southold NY.
That's an astounding end result from an outer-surban sky! I'd normally suggest for any single exposure shot to head out somewhere decently rural.

Excellent advice on equipment too - I have found the DFA 100 macro to be an excellent performer for astrophotography, and the astrotracer sweet-spot is 50-100mm, wider runs the risk of field rotation, longer becomes more and more restricted by the quality of your calibration.

QuoteOriginally posted by bdery Quote
Night scapes are ok, but astro? Not there yet
The secret to getting serious in astrophotography is to have deep pockets

Really though, you can have a lot of fun at night with regular lenses, going astro-landscapes and super-wide field (which in astrophotography is around 200mm and wider). Your lenses will also double up as useful when the sun is up - sadly my 8-inch telescope doesn't make for a very usable telephoto!
07-29-2018, 05:13 PM   #12
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I heartily agree with GPM here, just learning the techniques of astrophoto imaging and processing is enough for plenty of hours of fun. Some of it with cuss words.

Stacking has become so simple these days that IMHO there's hardly a reason not to do it. I still stack a lot of my deep-sky stuff taken through my telescope in bog-standard Photoshop -- no special software or complicated techniques needed.

Also agree that this is Quite The Image, especially for one shot taken in high light pollution! I've found that by getting lots of integration time I can get around LP, but it's SO MUCH EASIER if you can get away from it!
07-29-2018, 05:25 PM   #13
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Nice. I'm going to be at the Dixon Bioblitz this weekend, putting my FA100 and DA300 through their paces. That's as dark as I'm gong to get this summer, I think.
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