Ball park time for a night exposure

[Rain Dance]

Let's say I want to take a long exposure at night near the beach here. The film would probably be Acros 100 and the largest aperture I can use is f4. How long should I open the shutter to get star trails (those that look like spinning white lights)?

[Light Guru]

http://www.weatherscapes.com/techniq...age=startrails

Keep in mind you will have to do some big exposure adjustments for reciprocity.

[E. von Hoegh]

Let's say I want to take a long exposure at night near the beach here. The film would probably be Acros 100 and the largest aperture I can use is f4. How long should I open the shutter to get star trails (those that look like spinning white lights)?

The stars will move fifteen degrees per hour, and Polaris will remain a point. So foigure out how long you want the trails, and time your exposure accordingly. The aperture you use will depend on the ambient light and the speed of your film.

[Rain Dance]

Thanks for the link. Looks like I'm gonna be staying there for quite a while to get what I want. Any recommendations for a Color Negative film to use in this kind of situation?

[al olson]

I use Kodak Portra 160. If I start the exposure about 45-50 minutes after sunset, I can get some deep blue left in the sky. I use an aperture midway between f/8 and f/11.

[Rain Dance]

Looks like I gotta get some of the 160, all I have is the 400 and Ektar. How long do you usually time your exposures?

[Daniel Stone]

Looks like I gotta get some of the 160, all I have is the 400 and Ektar. How long do you usually time your exposures?

my wrist watch I wear daily, and set an alarm for the time i will need to wake up to close the shutter.

[ki6mf]

f22 with bracketed timed exposures in 5 10 20 40 80 minutes. Compensating developer of choice. A notebook to make notes and remember what the ambient light was like. use a similar time when ambient light is similar. Bracket all exposures. Bring a folding beach chair to sit in. Dress warmly. Read The Nocturnes web site. http://www.thenocturnes.com/

[al olson]

Looks like I gotta get some of the 160, all I have is the 400 and Ektar. How long do you usually time your exposures?

There is no right duration for twilight or night exposures. For example, if you are in total darkness photographing star trails, then you would leave your lens open for as long as you intend for the star trails to register. If you are in nautical twilight, then you would use a shorter exposure. If you are photographing in an urban setting with ambient light sources, then you would expose differently yet again. It also depends on how you want to emphasize detail in the shadows of terrestrial features.

Assuming that you are not photographing in total darkness, a good starting point (presuming there is some twilight) is to take a spot meter reading on the brightest part of the sky. If you are in civil twilight, this might be sufficient for a good exposure of features on the ground. If you are in nautical twilight, I increase the exposure by at least one EV. Then I account for reciprocity failure. If the exposure is 30 seconds, I double the exposure. If it is around 1 minute I quadruple it.

I have worked out a procedure that seems consistent in creating the desired results. I usually begin exposing midway through nautical twilight (the period after civil twilight where you can still see details on the ground, but it is difficult to perform sports or other activities). Since most sources (GPS, Naval Observatory, etc.) do not provide a time for the end of Nautical twilight, I estimate it to be the same length of civil twilight which is provided by a number of sources.

As mentioned above, I prefer to begin exposing halfway through nautical twilight. A good estimate of this time is adding an additional 41-44 minutes to the official time of sunset (assuming it has been a sunny day). This usually results in a deep blue color of the sky.

My procedure was developed initially from etering the bright area of the sky. Assume that I begin exposing around 41 minutes after sunset. Bear in mind that for a long exposure there is less light than when you made the meter reading. The first exposure is for two minutes to account for reciprocity failure. The second exposure (after time to change the slide and cock the shutter) is for four minutes to account for fading light and reciprocity failure. Likewise, the third exposure is for ten minutes. Often all three exposures are acceptable.

By this time it is nearly 60 minutes after sunset and the sky is dark to the eye although there may be some color still registering on the film. Usually, each of the exposures will be usable, just with different emphasis from the lighting. This is done, as mentioned in my post above, with Portra 160 and the aperture set halfway between f/8 and f/11. When in doubt it is better to overexpose than underexpose.

For photographing in the urban setting, these rules of thumb are still applicable. If there are point light sources they will blow out, but seldom is there any noticeable bloom and small specular highlights are acceptable. Direct lighting out of windows should not exceed five seconds, porch lights should be exposed for around three seconds. Spill light out of side windows I usually ignore unless the exposure is a longer than, say, four minutes.

There are a number of books and charts giving exposure recommendations for available light photo of fireworks, nighttime sporting events, interiors, etc. A list of WEB site sources (not necessarily current) as well as a bibliography are available in my now out-of-date guide for Existing Light Photography. Go to www.Photo-Artiste.com, select "Guides" at the top of the home page, and then select "Existing-Light Photography from the list of guides. Scroll to the bottom of the page to find the bibliography and WEB sites.

Cheers,