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Astrophotography Exposure Guide

JEFFREY R. CHARLES / VERSACORP SUGGESTED EXPOSURE TIMES FOR VARIOUS OBJECTS:

OBJECT: ISO: f/RATIO:

25: - - f/1.4 f/2.8 f/5.6 f/11 f/22 f/45

100: f/1.4 f/2.8 f/5.6 f/11 f/22 f/45 f/90

400: f/2.8 f/5.6 f/11 f/22 f/45 f/90 f/180

1600: f/5.6 f/11 f/22 f/45 f/90 f/180 f/360

SOLAR SYSTEM OBJECTS: TIME IN SECONDS (or as specified)

Sun - With Most Solar Filters 1/4000 1/1000 1/250 1/60 1/15 1/4 1

Total Solar Ecl. - Prominences - - 1/4000 1/1000 1/250 1/60 1/15 1/4

" No Filter " Inner Corona 1/2000 1/500 1/125 1/30 1/8 1/2 2

" " Outer Corona 1/125 1/30 1/8 1/2 2 8 30

Crescent Moon - Earthshine 1 4 15 1m 4m 15m - -

" " <30 Hours Old 1/125..or Underexpose Twilight Sky 1 f/Stop

" " 30-60 Hours Old 1/500..or Underexpose Twilight Sky 1 f/Stop

" " 20-35% Illum. 1/2000 1/500 1/125 1/30 1/8 1/2 2

1/2 Moon 1/4000 1/1000 1/250 1/60 1/15 1/4 1

Sunlit Earth, Full Moon - - 1/2000 1/500 1/125 1/30 1/8 1/2

Terminator of <50% Illum. Moon 1/500 1/125 1/30 1/8 1/2 2 8

Moon 4' from Terminator 1/2000 1/500 1/125 1/30 1/8 1/2 2

Partial Lunar Eclipse 0-30% Ecl. 1/4000 1/1000 1/250 1/60 1/15 1/4 1

" (+/- 1 f/stop) " 30-80% 1/1000 1/250 1/60 1/15 1/4 1 4

" (+/- 1 f/stop) " 80-95% 1/250 1/60 1/15 1/4 1 4 15

" (+/- 1 f/stop) " 95-99% 1/60 1/15 1/4 1 4 15 1m

Total Lunar Ecl. (+/- 3 f/stops) 4 15 1m 4m 15m - - - -

Mercury and Venus 1/2000 1/1000 1/500 1/250 1/60 1/15 1/4

Mars 1/250 1/125 1/60 1/30 1/8 1/2 2

Jupiter 1/60 1/30 1/15 1/8 1/2 2 8

Jupiter and 4 Moons 1/2 1 2 4 15 1m 4m

Saturn 1/8 1/4 1/2 1 4 15 1m

Uranus (or 6th Mag. Star) 4 4 4 4 15 1m 4m

Neptune (& Saturn's Moon Titan) 15 15 15 15 1m 4m 15m

Naked Eye Comet Nucleus 6m 25m 100m - - Tail = Same as M42

DEEP SKY OBJECTS: TIME IN MINUTES (or as specified)

12th Mag. Star (20 cm Aperture) 10 20 40 80 - -

Open & Globular star cluster 8 30 2h - - - -

Brighter nebulae, i.e. M42 15 60 4h - - - -

Most objects, i.e. M20, M51 22 90 - - - - - -

Very Dim, i.e. Veil Nebula 30 2h - - - - - -

* Double exposure if object is only 8-14 degrees above horizon.

* Quadruple (4x) exposure if 5-8 degrees high, or for thin clouds.

* If ISO is higher, decrease exposure time by same proportion, i.e. if

ISO is doubled (or if film is hypered) reduce exposure time by 1/2.

* Keep a record of your own exposure data, it will save film!

* Use the f/11 exposure data if you are using an f/10 SCT.

For each 100mm of focal length, the Moon's image will be about 1mm in diameter.

To calculate your f/ratio, divide the focal length by your telescope's aperture.

f/number counter; double the exposure time for each successively larger number:

Each number, or f/stop is a multiple of the square root of 2, or about 1.4142.

1 l.4 2 2.8 4 5.6 8 11 16 22 32 45 64 90 128 180 256 360 512

Copyright 3/1988 by Jeffrey R. Charles All Rights Reserved.

注:以上的曝光时间是以胶卷为准的。胶卷有一种名为“low light reciprocity failure”的特性。当拍摄低光度物体时，曝光时间会和胶卷速度不匹配，照片实际需要的曝光时间要比预计时间长，数码单反就不会有这种现象出现。据有人试验，当使用ISO 400 F2.8镜头，用胶卷拍摄需要10分钟曝光时间，而用佳能数码单反则只需2-3分钟就可以得到相同的曝光量了。

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