Night Fox – Night Sky Photography Shutter Speed Calculator Android App

Due to the overall great response and the high number of mails from users of my Shutter Speed Calculator i’m glad to announce here: Night Fox – Shutter Speed Calculator for Android!

The App features a simple interface to input your camera, your focal length and the tolerance in pixels. After that you can simply hit the calculate button and read the suggested speeds.

If you cannot find your camera in the list, simply write me an email or leave a comment. I can add cameras live and you just have to hit the “Download Camera File” Button to load the newest definition data. If you enjoy the app, please leave a comment and help me improve the interface and the user experience!

You can get the app for free from here:
Get it on Google Play

 

If you want to learn more about how it works, check out my two other posts:
https://www.tl-photography.at/stars/shutter-speed-calculator-for-night-sky-photographing/
https://www.tl-photography.at/stars/night-sky-photography-shutter-speed-calculator/

Night Sky Photography Shutter Speed Calculator

UPDATE: I’m glad to announce that I finally found the time to release the Night Fox Android App for my Shutter Speed Calculator!

Get it on Google Play

This is the shutter speed calculator for night sky photographing. Basically you just insert the data of crop factor, the megapixel you want to archive or your camera has, the focal length and the tolerance of pixels you can accept. The description of all these different factors is below. The description of the whole process can be found here.























Crop Factor
The crop factor is depending on your camera. It is influencing the field of view (FOV) of your camera, like the focal length also does. This calculator includes the factors 1 (3:2), 1.5 (3:2), 1.6 (3:2) and now also 2.0 (4:3). (Thx to Livio for the comment)
See also http://en.wikipedia.org/wiki/Crop_factor and http://en.wikipedia.org/wiki/Aspect_ratio_(image).

Megapixel
This is the amount of megapixels you want to achieve. It can be the maximum of your camera or also a lower Value. I included this value, because somebody may what to have the pictures not in full resolution, but a maximum of exposure time. With a smaller resolution I’m recommending to reduce the pixel tolerance as well.

Focal Length
The focal length is very important for the field of view and therefore how fast the stars are moving. The rule of thumb is “the lower the better”. But be aware of the speed of your lens. This influences the needed exposure time as well.

Pixel Tolerance
Depending on what you can live with, you can adjust this value. Basically it describes the tolerance of how many pixels a star can “move”. In some cases 20 pixels are OK, but for having really sharp stars, I recommend 10 pixel.

The Milky Way Exposure Calculator can be found here and as well as the other articles of http://www.lonelyspeck.com/.

Shutter Speed Calculating for Night Sky Photographing

Night Sky at the Alois Günther Haus

Night Sky at the Alois Günther Haus

Recently I wanted to improve my skills in night sky photographing. So I opened the PC and asked Google a lot of questions. I was reading a lot about shutter speed, focal length and exposure adjustment. A very good site I found was How to Photograph the Milky Way of the site www.lonelyspeck.com. They created a very good tutorial and answered many of my questions. They also created the Milky Way Exposure Calculator, witch lets you calculate how a lens may perform on your camera. For ranking the lenses they calculate a score, basically from the physical parameters of the lens. I agreed with the majority of the parameters, but I was wondering if the slowest possible shutter speed is maybe a bit inaccurate.

In night sky photography the shutter speed is mostly longer than 5-10 s or even more. Without a tracking device the stars will move over the sky and produce, depending on the shutter speed, streaks on the picture. But we want actually a clean image of the stars. So what we need is a lens with a short focal length and an aperture which should have less than f/2 to gather a lot of light. The basics can be checked in the links above. Anyway, the rule of thump for the shutter speed, 500/focal length, seems a bit inaccurate and, as stated there, also not completely usable for APS-C cameras. So I started to think, how can this be solved better…? I was drawing some sketches and made some calculations and concluded: there might be a better and more accurate way: I started to research about what information are available for all lenses and cameras. I concluded that the sensor size and the focal length is available in any case. The angle of view was not all the time available or I just couldn’t find it. Anyway, with the sensor size and the focal length we can calculate the angle of view with the following equation:

alpha = 2 * \arctan {\dfrac{d}{2 * f}}

In this equation, d is the diameter of the sensor and f is the effective focal length. Since f is depending on the focus, the focal length F of a 50 mm lens is only 50 mm when set to Infinity. Since in astro photography we use only the infinity setting we can assume f = F. So we can also calculate the horizontal and vertical angle of view for a lens. In this case I will just use the stock Canon EF-S 18-55mm 1:3.5-5.6 IS II on a EOS 600D with 18 MP as example. Why we need the horizontal and the vertical angle of view, will be pointed out later. With the pixel count on the camera we can now calculate the angle to pixel ratio. The 600D has 18 MP with a 3:2 ratio. This leads to a pixel count of 5.184 px by 3.456 px. The pixel to angle ratio is calculated by α / Σnpixel. The diagonal pixel count is just calculated by Pythagorean theorem.

  • Vertical AOV: αv = 27°; Pixel to Angle Radio = 0,0185°/px
  • Horizontal AOV αh = 37.4°; Pixel to Angle Radio = 0,0164°/px
  • Diagonal AOV αd = 46.8°; Pixel to Angle Radio = 0,0153°/px
The night sky can be seen as  a cylinder rotating around the camera.

The night sky can be seen as a cylinder rotating around the camera.

The next assumption we make is that the sky is rotating around the world. I know that some people will now say “NO! Galileo was very clear with that!”. Yes its not true but since we focus anyway on infinity and the sky is more more less a flat area for the lens, this is ok. This lead so my next assumption. The sky is not a sphere, its like a cylinder. The picture demonstrates this assumption. The cylinder rotates with the angular speed of 360° per 24h or 0.00417 °/s. Depending on the pixel to angle ratio we can now calculate the minimum shutter speed. In case of my 18 mm focal length the numbers are very small and and seem not right.

  • Vertical max. Shutter Speed: 4.4 s
  • Horizontal max. Shutter Speed: 3.9 s
  • Diagonal max. Shutter Speed: 3.6 s

But this is only the half truth. Since the stars are not only one pixel big, we can use a threshold. For example a threshold of five pixels will give us five times the shutter speed. In my test, five pixel threshold was mostly ok and not really visible. Somebody who wants to have more clear pictures can reduce the threshold.

  • Vertical max. Shutter Speed: 22 s
  • Horizontal max. Shutter Speed: 20 s
  • Diagonal max. Shutter Speed: 18 s

I’ll program a calculator using javascript in the near future and upload it to this website. Stay tuned!

Light Pollution

Some people ask me, where to find a good spot to have a great view to the stars. For Austria, this is a good link to follow. There are also a lot of other sites, just search for light pollution. There are also overlays for Google Maps here.

Light Pollution, taken from http://www.nightsky.at/

The second thing to remember is, that you need a clear sky and no clouds. Above 2000 m, the light pollution is at the most places acceptable and the air is thinner and also the lights of the stars brighter.

Third, you need a long dark time span. In winter you will find the perfect conditions. Also to mention: if you hear in the news, that a weather inversion takes place, get your car and find a hill. The air near the surface will be colder than in the highs and all clouds will follow the cold air.

Fourth: As i said before, find the highest place you can get! The air gets thinner, the stars become brighter. So simple, so good.

 UPDATE:

Stephan Paukner from paukner.cc has also found some information and made a nice Google Maps overlay.

Dark Spots in Austria, taken from paukner.cc

 

aloisguentherhaus V2 pictures

At the first day in 2014, I decided not to stay at home and to cure my hangover. The first idea i came up with: what’s about a timelapse with stars? So I loaded my camera and went on the hunt for some food and warm clothes. I had an idea for the Location: the Alois-Günther-Haus. Unfortunately, I was a bit late, so there was a climb to the summit is no longer in question. But, “no problem” I think to myself, i’ve a car! Once at the road to the house I realized the road was unfortunately completely covered in snow and I had no snow chains. After several failed attempts I decided to try the way backwards.

8 Kilometers and three breaks later (the car starts to overheat quickly, because of no cooling from the front), I arrived at a nice spot and started immediately build up my equipment. For the shots, I choose my standard Canon 18-55mm IS II. The 50mm 1.4 Sigma is for sure brigther but at my APS-C (and the resulting ~80mm) the stars will be streaks with a exposure longer than 20s.

After some test shootings i had my settings. I used ISO 1600 and an 25 seconds exposure. I also set the aperture to the highest value, that my lens allows: 3.5 at 18 mm. This is what i got:

Thereafter, I started a timelapse and sat in my car, waiting. Luckily i bought delicious ham and cheese for dinner. 🙂 Maybe I should buy a camping boiler.
After 1 1/2 hour I canceled my adventure, because -8 C and 80 km/h wind are no fun… But i think the result is quite impressive. I will upload this in the TIMELAPSE section later. So I took my stuff, drove to the house, get a coffee and hit the road straight to vienna.