Long Exposures
 

Hello

I want to take a long-exposure photo during the day. Here's the question: how do I get an exposure of, say, 20 seconds at 100ISO without having a ridiculously overexposed photograph? Narrow aperture like f/22 is a good idea, anything else needed? Any general tips on long exposures?

As usual I'll be using film, I have heard about this thing called reciprocity failure, if anyone could explain it I'd be very grateful.

All help much appreciated

Alex

I reckon using a ND filter would be your best bet - depening on the strength these will cost you ~2-10 stops - http://www.warehouseexpress.com/cate...spx?cat03=3072

Basically reciprocity failure is when the film stops responding to increased exposures in the normal way resulting in the wrong exposure so you end up under exposing so you have to compensate by giving a longer exposure than you think. A very rough rule of thumb is to double the exposure time for exposures much over 1 second but the effect gets more pronounced the more over one second you go (ie not constant) and also varies from film to film. Bracket fairly widely is the answer and for really long exposures you may well get a colour cast as well. I have not looked but you may well be able to find more detail on what sort of correction you might need for your Velvia on line, there used to be tables of time versus estimated correction for each film.

I'll be using Ektar for this shoot, and research tells me it has very little reciprocity failure. I won't be going longer than 2s so it won't be a problem. I will need an ND filter though.

Don't shoot on a very bright day at noon would be a tip I'd add.

Colour negative film like Ektar has more exposure latitude than slide film so as you say you should not have to much trouble with 2 seconds. In your original post you did mention 20 seconds though so that would make a difference.

Sorry, revised what I want - 20 seconds is an unfeasibly long time, and I think the motion blur with 1 or 2 seconds would be quite sufficient. I'll take some average light readings someday and see what the camera thinks the correct settings are.

Interesting reading... it happened to me also to have this problem when I wanted to take a shot of a fountain during the day and have the water not frozen but silky.... hard to do... also with dslr need not to have a bright day first... iso100 f22 and luck if more then 1 or 2 sec.

The camera currently meters 1/30th or 1/15th of a second under daylight conditions, f/22 and 100 ISO. I want about 1/2 or 1 second exposure time, so I'm about 3 f stops short. I'll have a look in Jessops to see what they have.

Alex,
If you have a polariser that will cut 2 stops so you are nearly there.

Don

Suggest you try 1/15th and see what it comes out like. Moving water will still have quite a lot of blur at this speed.

Wait until it gets darker, dawn or dusk, you'll get much slower speeds then. 1 or 2 seconds will be easily achievable in darker conditions.

... but if you have two polarisers you have complete control and the ability to shut it down to almost complete darkness.

Here's how it works:
Light travels in waves like ~~~~ A polarising filter works like a grid and only lets waves through that are the right way round like = or ||. So, if you have two turned at 90 degree angles you stop light no matter which way round it is.

This means you have variable control in all light conditions, just turn one of the polarisers to get from a minimum of 4 stops to pitch black.

Polarisers have other effects as well which you may or may not want, especially when shooting water. Their effect is not uniform across the frame either which especially shows up with wide angles. Best to use the correct tools for the job.

Yes this is true, polarisers are often used for removing unwanted reflections and glare from glass or water so it will have an effect on the image (good or bad is subjective) but the versatility of it is incredible so a handy technique to know.

The other downside to this of course is cost, a decent circular polariser for a 77mm lens is around £150 so not the cheapest option either - then again each ND is £70-£80 for comparable quality.

I've been doing some tests and it turns out that 1/15th or 1/8th give me the perfect amount of blurring, so I guess I don't need a polariser or ND filter, just a tripod =)

Excellent, look forward to seeing some shots then. :)

The event was last Sunday - went down with my OM-1 and tripod and got some good frames at 1/8 and 1/4 of a second. Weather was typical British cloudiness which worked in my favour. I don't know when the roll will be finished and developed but once it is I'll get it onto the forum!

As promised the best photo is now in the gallery http://www.worldphotographyforum.com...hp?photo=49437

Alex

Looks like you got what you wanted exposure wise. The 'still group' a bit small in the frame to make the contrast between them and the moving people stand out? Nit picking I know as you would have had limited or no real control.