Long exposures and fogging

[John Curran]

I plan to shoot some star trail shots in Death Valley later this week and have had little success in researching exposure details. I plan to do long exposures (1hr or more) and can find little technical info on issues of fogging.

I've read that because of the relatively slow lenses on LF cameras that fast films (400 ISO or more) are recommended. However is it not true that faster films fog sooner, I've also seen recommendations for using a medium speed film (200 or 100 ISO) but this was for a 35mm situation.

Does anyone have technical advice/experience with fogging and long expos? Has anyone had experience with say 6hr exposures re: fogging? Are smaller apertures (f5.6 or f8) a better idea on such long expos to reduce fogging, and does using a smaller aperture increase the time that one can expose w/o fogging?

Thanks in advance

John

[Ron Marshall]

For very low light situations you are best to use a film with good reciprocity characteristics, such as Fuji Astia.

If you are shooting mostly sky you may be able to use a wide aperture.

[Ben Chase]

In the past when I have done this, I've used Provia. I have yet to ever encounter problems with 2-4 hour exposures. I've never used anything other than an ISO 100 film for this.

With 35mm cameras, I normally used an aperture of f/8 or so.

Cheers,

Ben C

[Jim Jones]

Much depends on how dark the sky is. Here in rural Missouri, away from city lights, I've done 10 hours star trails on T-Max 100 at f/11 with just enough skylight recorded to silhouette the foreground. With Tech Pan an aperture of f/6.8 worked even better.

[walter23]

I've heard people swear by tungsten-balanced film (e.g. Fuji 64T) for long exposure star trails because of the deep blue colour it turns. I've done a couple of crappy star trails on velvia 50, decent ones on 35mm kodak gold 100, and some very nice ones with digital. I'm not sure that fogging would really be a problem with any setup or film choice unless you had light leaks in your camera or sources of flare, but I've never done this with LF. Of course, light pollution (which I'd consider a separate issue from film fogging) is going to be a problem whether you have fast film or slow film.

[GPS]

Google Robert Reeves astrophotography.

[Kirk Keyes]

I've read that because of the relatively slow lenses on LF cameras that fast films (400 ISO or more) are recommended.

Are smaller apertures (f5.6 or f8) a better idea on such long expos to reduce fogging, and does using a smaller aperture increase the time that one can expose w/o fogging?

John

When shooting point sources, i.e. stars, large format lenses actually have some benefits. Exposure of point sources is dependant on the effective aperature of the lens. Think about telescopes - the larger diameter the telescope the fainter the stars it can see. Same with lenses - you want lenses that have large effective diameters.

An everyday run-of-the-mill 150mm f/5.6 normal lens for a 4x5 has an effective aperature of 26.8mm. (150mm divided by 5.6 = 26.8.)

If you have a 50mm f/2.0 lens, has an effective aperature of 25.0mm. The 4x5 lens actually has more light-gathering area than the 35mm lens!

For 8x10 people, a 300mm f/5.6 lens has an effective diameter of 53.6mm - a lot more than even the 4x5 lens.

Slow lenses are a factor, but because you are using large format you can get away with what would normally be considered a "slow" lens, since is it actually a fast lens with point source subjects. Don't be afraid to stop down a bit to f/8 or f/11 if you need to controll the brightness of the sky.

I usually try to include some forground in my star trail shots, so faster film does help here. I either double expose at dust to record outlines of the forground and then do the second exposure later when most of the light from the sunset has faded and continue until I get bored out of my mind, or I try to balance moonlight with the star-trails - which can be especially difficult as conditions are highly variable due to atmospheric clarity...

See this great site for more inspiration and a lot of information:
http://home.earthlink.net/~kitathome...lery/index.htm
(the shot on this page was done with 4x5)

[Kirk Keyes]

Shoot Fuji Provia 100 - it has very good long exposure properties. Push it a stop if you need more speed for foregrounds. Use Fuji Acros 100 for B&W for the same reason. See the discussion on Kit's page that I linked above.

[John Curran]

Thanks for the advice and technical info. Unfortunately there was way too much air traffic in and out of Las Vegas to try any long exposures. This suprised me as the skies just west of the park are restricted airspace. Instead i tried some shots of zodiacal light in the west just after sunset on provia. Images are still in the mail.

Thanks again

John