Getting a starting point for a night sky exposure

[hoffy]

Howdy,

I want to have a bit of a play around with a long night time exposure and I am trying to get a starting point.

The scene is to involve shooting towards a horizon that is what I would describe as light polluted (the majority of the lights are around 10 KM's away). The scene is also going to involve a person sitting (to create a silhouette, so I want to keep exposures within a reasonable sitting time (I get that there is going to be a bit of movement). With this in mind, I was thinking of shooting HP5+ (6x6) either at box speed or pushed up to ISO800.

I have had a look at the following website to get some information - http://www.fredparker.com/ultexp1.htm and think that I am looking at around an EV value of -1 to 0 @ EI 100 (I tried to meter it tonight and my Minolta IV wouldn't take a reading). For how I described the scene, does this sound about right? If I am, I would expect a base exposure of around 2 minutes @ F11, converting the EV value up to EI 800.

How would I take reciprocity failure into account? According to the chart I have, @ box speed, HP5 + metered to 120 seconds should be exposed for 285 seconds. Would I use the same figures if I metered at EI 800 for 120 seconds? OR am I missing something?

Cheers

 

[JDP]

Ok I'll have a go at this. At 800ASA try a 30 second exposure at f8. that is usually enough to show a light-polluted sky but it does of course depend on induvidual circumstance such as brightness of the lighting and the amount of cloud. The picture will come out dark. If you want brighter results you will need to expose for much longer. I reckon a moonlit night and a two minute exposure at f8 gives something looking like daytime. Regarding correcting for reciprocity failure I use the very general rule of allowing an extra stop, which works ok for exposures of a few seconds.

 

[mcgrattan]

You might find using a slow film is faster. Acros doesn't have much reciprocity failure. A 2 minute measured exposure will be a 2 minute exposure, no compensation needed.

 

[hoffy]

OK, I never thought of using Acros – but that may prove to be a bit of a double edged sword. I would like a bit of grain, hence why HP5 was on my list and why I also wanted to push it a bit. I had also considered a fast film such as delta 3200…but I’ll see.

It looks like I need to do a bit of experimenting to see how it will all work and not be afraid to reshoot if needed.

 

[Steinberg2010]

To increase grain you could use a grain-increasing developer and a more aggressive agitation routine.

S