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Astrophotography Exposure Tables

One-Step Photo Exposure Tables - "canned" objects

These tables are in the experimental stage. For the viewing objects listed, they will generally give calculated results that agree, within one stop, with the Appendix A measured value tables published in Astrophotography for the Amateur, 2d edition, by Michael A. Covington. For more detailed calculations, use our multiple-step Custom Exposures page.

To use the tables, pre-select the object you will be photographing from the popup field choices currently offered below. Given the ISO setting of the film or camera you will be using (across), and the total system focal ratio (down), the table outputs calculated shutter speeds (seconds). Please see detailed notes for more information on using these values for astrophotography.

Object for photographing:
telescope f-ratio1 (optional):


You can use the tables that this program outputs to determine shutter speed, for a given film speed and f-stop, for photographing over 20 built-in solar system objects. This works for a plain tripod-mounted or "piggyback" camera, capable of manual exposures, as well as for a telescope with a camera back attached.

1Use the telescope f-ratio field to select the f-stop that will be used with a camera-only setup. Some popular telescope models are listed for convenience, but only the f-ratio value is needed.

If the optional f-ratio in the popup is selected, the program will highlight the appropriate row in the table. We have supplied values for a built-in table range of f-ratios the amateur astronomer might encounter, and labeled them for a couple of telescopes we're familiar with.

For photography calculations for filters, eyepiece projection, afocal coupling, or for custom scenarios and settings, use our multiple-step Custom Exposures page.

  • The Covington tables (for those lucky enough to own the book) list measured exposure values. Since no formula calculation will be more "accurate" than data taken from field measurements, use the book tables when you have access to them.

Basic Exposure Calculation

These tables are calculated using the Appendix A formula

    t (seconds) = f2/SB

    where f is the f-ratio, S is the ISO value or film speed, and B is the brightness of the object being measured, in candelas per square foot. "In practice B is somewhat arbitrary as the subject spans a range of brightnesses."

    we take the B value from the published table, since it is available. We'll supply a way to calculate this (later) if you do not know it.

    total system f-ratio must be calculated using published f-ratio of telescope, and focal length of eyepiece (if doing eyepiece projection photography), and focal length of camera lens.

    for focal plane photography (camera back, no lens) f-ratio is just telescope's f-ratio.

    for piggyback and field tripod photography (no telescope), f-ratio is just f-ratio of camera lens.

common telescopes:

  • Meade LX-90: 8", 2000mm focal length, f/10
  • Orion StarView Pro 127 (Mak): 5", 1540mm focal length, f/12
  • Meade ETX125 5", 1900mm focal length, f/15 (Mak)
  • Please send us other models you'd like included


  • for film cameras, speeds greater than 1 second need to be corrected for "reciprocity failure". This correction is NOT needed for CCD cameras, and the one-step tables do not adjust for film reciprocity failure. We build that correction factor into the custom tables.
  • Tables are generated on the fly in Perl. Print or save them off for field trips and photo sessions.
  • Accuracy is generally within one stop or shutter speed of published observational values, well within a range where you would not notice a difference from using a published value.
  • A table entry of "<<" indicates the result (speed) is too fast for most cameras. Use a slower film or lower the digital camera ISO setting. Cutoff is 1/8000.
  • A table entry of ">>" indicates the result (speed) is too slow for reliable calculation. Use a faster film, or higher digital camera ISO setting. Cutoff is 1800 seconds (1/2 hour). Longer exposures are certainly stock in trade for deep-sky photographers, but here a range of exposures is a more appropriate result in such cases.


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