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/.

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21 Comments

  1. Pingback: Milky Way Exposure Calculator – Lonely Speck

  2. very interesting, thanks a lot.
    But I ask you please to add the calculation sheet also for crop 2; you stopped at 1.6
    That’s good also for us poor Olympus OM-D eM1&5 owners
    Regards

  3. Hi Thomas!

    Making night sky photos I have the same problem: how to calculate exposition properly.

    I’m wondering why you have different shutter speed for vertical and horizontal.

    Then I discovered your method of calculation. You calculate Pixel to Angle Radio for all sensor dimensions, but it is not right, because sensor is plain. Star tracks are longer on a side of image cause of lens distortion. Wider lens makes more distortion and you calculations show this.

    So I made own calculations based on pixel size.
    We need to know how long a dot of light will travel through a pixel.
    In terms of JavaScript:

    var speed = 360 / 24 / 60 / 60;

    pixelSize = sensorHorizontalSize / sensorHorizontalResolution; //same for all directions
    pixelAngleOfView = 2 * Math.atan(pixelSize / 2 / focusLength) * 180 / Math.PI;

    pixelSpeed = pixelAngleOfView / speed;

    Then just multiply pixelSpeed by given Pixel Tolerance.
    This method is more accurate and give the same speed for any direction excluding lens distortion mistake.

    Best Regards,
    Alexey

  4. Excellent work , I was there was an Android App

  5. Very nice calculator 🙂 forgive a stupid question though…
    Shutter speed vertical is that the shutter speed if you have your camera mounted in portrait? If so i guess horizontal is if you have your camera “flat” in landscape so to speak? Again sorry for the stupid question

  6. I thought the Vertical, Horizontal, and Diagonal was based on camera orientation on how the stars move across the sensor. So if the starts mu straight up and down and you have your camera in Portrait mode, then the stars are MOVING ACROSS the LONGEST part of the SENSOR. That would be the Horizontal exposure??

  7. Hey thanks for this, I wonder however,
    how come this calculator doesn’t have the option to fill in the f number?

    • hey thanks for the comment.
      The F number is really important for night photography but it does not influence this directly. A higher F number will force you to increase the shutter speed, but as long you have a good ISO performance of your camera and a relatively low F number (< 2.8) than you will not need this for calculations. Best, thomas

  8. Hmm, the app is a very practical tool as long as you use Canon or Nikon. SONY must be included if you are serious about this.

  9. Thanks Thomas, I’m using Night Fox, but I don´t understand what about ISO, why it’s not considered. Regards.

    • Hi Carlos,

      ISO and aperture will influence the time you need to expose the images to get a well lit image. But both parameters do not influence the time you can let the shutter open until the stars streak on the image.

      Best,
      Thomas

  10. Any chance of updating the calculator for 1″ sensors (crop factor of 2.7272)?

  11. Mike Nicholson

    Any chance Pentax dslrs will be added?

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