Finding The North and South Celestial Pole

27 02 2008

I’m sure all of you have seen those cool star trails photos of the stars spinning around a circle. Well that circle is either the North or South Celestial pole.

Now I don’t know about you, but my astronomy is not that flash, and when I was out doing some photography the other night, I couldn’t work out the axis that the stars rotated around so I could frame my shots.

I decided to do a bit of research to work out how to locate them, and here’s the answer.


Night Shoot Number 3 – The Old Blast Furnace

24 02 2008

Last Saturday my Old Man and I threw our swags into the 4WD and headed up to the mountains for a planned evening of night photography. It was a full moon so we figured the old Blast Furnace at Lithgow would be a great location for some long exposure work.

Got some interesting images.

Architecture Under The Stars

This first one was a 12 minute exposure… my longest yet. I jumped down into the basement of the old gas works and camped out there in the dark to get this image.

We were lucky in the fact that a bunch of clouds finally came overhead to create some drama to this image of the ruins.

The clouds Did Come After All

Starting to feel like I am getting the night photography sussed out… I’ve got a routine going to calculate exposures and to compose my shots and I seem to be making the captures correctly (hardly any noise and the amp glow hasn’t posed a major problem).

I love the pace of night photography… lots of time to think and plan while the shutter is open. My new torch seems to work well, so I’ll have to start doing more painting with light.


How Do You Calculate Night Exposures?

21 02 2008

One of the most frustrating aspects of jumping into night photography was the exposure metering. Forget your handy-dandy in-camera meters, mine will only meter to 30sec and I expect thats pretty much standard.

So how do you work out your exposures? Hand held light meter? I don’t think so…

Most hand-held light meters are only sensitive to about -2ev, so thats not going to help you work out your exposures.

Trial and Error – Yup, that works… but here’s a way to get close to the right exposure out of the gate.

I came across an interesting article by Fred Parker called “The Ultimate Exposure Computer”. If you haven’t seen this, it’s worth a read. Fred has published some exposure tables that allows you to calculate exposures under any lighting conditions, using any combination of shutter speed, ISO and Aperture.

What I have done is to distill the relevant information into a handy pocket card that allows you to get a pretty good starting point for your exposures. This is what it looks like.

You will see that it “hard-coded” to 200 ISO (because thats what the speed that I’m going to shoot all my night work) and the aperture ranges from f4 to f16 (because I’m unlikely to shoot outside that range).

So just look at what sort of moon you have, and then read off how many minutes you need to expose for at the various f-stops.

If anybody wants this chart in PDF format, just drop me an email, otherwise you can just print this article and cut it out.



Now I’m getting ready for a serious shoot

20 02 2008

OK, I’ve done two weekends of test shoots at Turrimetta and learned some useful techniques. I feel I’m ready for a more serious night shoot.

I just bought a neat little torch from Surefire, these things are very cool. Very small, very bright, rechargable and have a 5000 degree colour temperature, so I shouldn’t get any colour casts when I do some light painting.

This weekend The Old Man and I are headed up to an interesting location, we are going to up to the Old Blast Furnace in Lithgow. I went there about a year ago and took some shots like this one.

Old Blast Furnace 4

The conditions look good. Full moon rising 30min after dusk, fine weather (I hope we get some clouds).

Going to shoot sunset, then dusk, then night, then sunrise.

Hopefully I will have some half-decent images to post next week.

More findings on noise and night shooting.

17 02 2008

Went out last night for my second night of night photography. The moon was mostly hidden behind heavy overcast which was frustrating, however I got this shot from the rocks looking back under the moonlight.
Turrimetta Rocks At Night

So a couple of important learnings from my second night out.
Moonlight helps big-time
It looks like I may have been just a tad quick off the mark about the lack of noise reduction. The Long Exposure noise reduction doesn’t seem to impact the noise levels in the picture per-se, but Toby and Tim nailed with their comments. It seems the Long Exposure noise reduction doesn’t significantly help with overall noise levels, but what it looks like it helps with is “Amp glow”.

Check out this shot (you may need to click on it to view it large).

Check out the purple amp glow in the bottom right (very bad) and also in the bottom left.

This shot was a 10min exposure. I went back and looked at my earlier shots to see where it seemed to kick in, and it looks like it kicks in around the 5-6 min mark. Anything under that and I couldn’t really notice it, but definitely on the 6 min exposures and 8 min exposures I could see it.

Very Cool Sun & Moon calculator

13 02 2008

Now that I’m a night photography “Newbie” I have to assemble some new tools to properly research when and where I am going to shoot. A new dimension that doesn’t exist in day photography is the moon.

  • What time does it rise?
  • Which direction will it be in?
  • What altitude will it be?
  • What phase will it be (crescent, half, full etc.)

I’m sure that the moon will dramatically impact the quality of my night shots. I have come across a pretty cool calculator for both sun and moon. Check out Jeff Conrad’s Sun and Moon calculator.

Now Jeff is obviously a minimilast judging by the user interface in his web page, but his calculator rocks!!! It’s not the most inuitive interface, but read the tutorial and you’ll quickly get the hang of it.

My favorite feature…. I love the way I can dial in a set of conditions and it will show me the dates and times that these conditions exist. For example I can say to the calculator “Show me all dates and times in the next 3 months where a crescent moon will be between 30 degrees and 40 degrees high in the East 1 hour after sunset.” Like magic, if those conditions are possible, the dates and times will be listed.

In my book… thats a very handy and very cool calculator. Thanks Jeff Conrad.

My Geeky Analysis of Noise and Night Photography

12 02 2008

OK, If you are the creative type looking for some creative tips… skip this blog entry. If you like the technical aspects of photography, then you might find this interesting.
Warning.. this is pretty nerdy stuff.

After my first outing of night photography I was pretty happy with the results but concerned about the noise levels I was seeing in my captures. So I wanted to get a clear understanding of how noise impacts night photography. The specific questions I wanted to answer were…

  • Does noise increase with exposure time?
  • Is there a point where it increases dramatically?
  • Does the Long Exposure Noise Reduction help a lot here?
  • How bad is the noise really?

At first I was going to do a subjective evaluation of some test shots, and then as I started hunting around for a suitable test chart to shoot, I came across an ISO Standard test chart for evaluating noise (for the geeks it’s called ISO15739).

I thought this looked promising, and then I came across a free plug-in for Photoshop that automatically performed the noise measurements from the standard test chart.

Click on any of the images to see the full-size image

Well that was pretty cool… all of a sudden my qualitative measurements could now become quantitative. Now if there are any ISO standards people out there who are going to have a go at me for my lack of controls blah blah blah.. for the record… I don’t give a rats! It’s good enough for me so don’t waste your breath.

Doing a first pass to get used to it – The impact of ISO on Noise.
I thought I would start with something simple to get the hang of the process, so I shot a series of test shots of the chart at different ISO ratings. From 100 – 3200 with my D200. Here’s the results of that test.

Nothing overly surprising to me… Just so you understand the chart, across the bottom (x-axis), it shows you the different luminance levels (there were 12 patches on the chart), so you can see the shadows on the left and the highlights on the right. The Y axis is the average noise that was read by the tool (I averaged the horizontal noise readings and the vertical noise readings to create one AVERAGE noise reading for each patch). It was interesting to see how the noise really goes out of control over ISO 400, and how @ ISO100 and ISO200 the noise is for all intensive purposes the same.

Test2 – Impact of Exposure time on Noise
Next test was to understand two things… the impact of exposure time on noise and also whether the Long Exposure Noise Reduction does much (except piss me off when I’m taking the photos and waiting for it to process). I took 2 exposures at 15sec, 30sec, 1min, 2min, 4min & 8min. One exposure with NR on, and one exposure with NR off. Now this wasn’t a totally controlled environment (the sun was setting and light was changing, but I tried to get the histograms roughtly the same for each set. Here’s the results.

I didn’t graph all the results because the graph would be too confusing. The pink & yellow lines are the 15sec exposures, and the cyan and purple are the 8 min exposures. OK… so you are probably thinking “What gives” How come the 15sec exposures have more noise than the 8 min ones…. Basically that is because I exposed the 8min exposures with +1.5ev and the 15sec exposures were + 1ev…. So the 8 min exposures were “exposed to the right” of the histogram more and required less exposure boost in the RAW conversion to get the patch densities to the correct level. So two key takeouts here from this graph.
1) Exposure time doesn’t appear to impact noise levels (at least up to 8min duration)
2) Long Exposure noise reduction does bugger all (it did stop a couple of red pixels, but thats it).

Test 3 – Impact of Under and Over Exposure on Noise
So I did one final test. I wanted to understand the impact of exposing to the right on noise. I shot 4 exposures at the same shutter speed – The first @ -1ev, then 0ev, then +1 ev, and finally +1.5ev. Note: Even at +1.5ev the histogram was not clipping, so this was definitely “exposing to the right” without clipping. Here’s the results.

So my key learnings from two days of Geeky stuff.

  1. Super long exposures don’t create noise in my D200
  2. Long Exposure Noise Reduction is not worth it (at least for exposures up to 8 min)
  3. Under exposing (even slightly will give you the biggest noise hit)

Some of you experienced guys are probably reading that thinking “No shit sherlock”! Yeah I know I know… but at least I fully understand the dynamics of noise now on my camera.