Shooting in daylight with a 2 (ish) second exposure...

Kryptix

Kryptix

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I've bought a car rig and I want to shoot cars in the day with a 2 second exposure but it's pure white where it's completely over exposed. I expected that so I've now just bought a Hoya ND8 filter to add 3-stops on but I'm not sure if this is going to be enough.

I got a shoot on the weekend so I can't really wait and find out. Will this be enough or will I need to stack another? I have a Hoya CPL filter I can stack onto it to make it a little big darker, I think?

I was shooting at ISO 100 and f/29.

That's my other question... Is there anything negative about shooting at such a small aperture? I heard something that the ideal aperture to shoot at is like 3 from the biggest or 3 from the smallest, but never right at the end as you loose quality? Is that true or not?

Does it matter what aperture you shoot in for quality loss? I understand the depth of focus and letting in more light, but is it as simple as that?

Thanks!
 
Aperture will effect the sharpness of the image hugely. My Sigma 120-400 lens is pretty soft wide open (f5.6) at 400mm. Stop it down to f7 or f8 and sharpness improves markedly. I believe shooting at tiny apertures such as f29 causes similar problems, although perhaps not quite as pronounced.
 
Going that small there will be loads of diffraction of the light around the aperture blades - do a Google on "youngs double slit experiment" to see why.

You could stack the ND filters though.
 
I'd be more worried about camera shake softening the pictue on a two second exposure.

Is there a reason you need two seconds?
 
Is the 2 seconds just for the amount of blur you want in the background? If so, just drive / push faster... that's probably a bit obvious though.

Easy to work out what effect the filter will have. What settings did you get without it? If you could get correct exposure at 1/4 of a second without, then with the filter you'll get 2 seconds.
 
Cheap option - wait until it gets darker.
 
2 seconds seems very long for a car rig, I was under the impression you needed less than a second to produce a good background blur
 
Do some maths:

A fairly bright day, ISO 100 and f16 would want a 1/60 exposure.

+1 stop = 1/30, +2 stops = 1/15, etc, etc, +5 stops = 1/2, +6 stops = 1s, +7 stops = 2s

So at those settings on a fairly bright day, you will need a -7 stop ND filter.


try your -3 stop filter with the polarise which will subtract another two stops to give -5 this will give a suggested starting point of f16 for 1/2 second or f22 for 1 second.



Steve.
 
Cranky said:
2 seconds seems very long for a car rig, I was under the impression you needed less than a second to produce a good background blur
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I've never tried this sort of thing, but reasoning from first principles i'd have to say I agree.

At 30mph, you'll cover 88 feet in 2 seconds. At 20mph, you'll cover 59 feet in two seconds. Do you really need that much blur? It seems pretty extreme to me.
 
StewartR said:
I've never tried this sort of thing, but reasoning from first principles i'd have to say I agree.

At 30mph, you'll cover 88 feet in 2 seconds. At 20mph, you'll cover 59 feet in two seconds. Do you really need that much blur? It seems pretty extreme to me.
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Quite....

With this amount of blur the background will be unrecognisable, so why not just do a 1/2 sec shot and PP a blurred background in :shrug:
 
StewartR said:
I've never tried this sort of thing, but reasoning from first principles i'd have to say I agree.

At 30mph, you'll cover 88 feet in 2 seconds. At 20mph, you'll cover 59 feet in two seconds. Do you really need that much blur? It seems pretty extreme to me.
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I push the car at 1-2mph... Ask that question again. :lol:
 
StewartR said:
I've never tried this sort of thing, but reasoning from first principles i'd have to say I agree.

At 30mph, you'll cover 88 feet in 2 seconds. At 20mph, you'll cover 59 feet in two seconds. Do you really need that much blur? It seems pretty extreme to me.
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A lot of car rig shots are done at no more than walking pace with the engine off.
 
Most of my shots in the car park have been a 1 second exposure to a 1.6 second exposure. I can easily see this not being enough, and I think I'd like a faster 'effect' hence wanting to be able to do a 2 second exposure.
 
You might want to go more than 2 seconds as well, Look into one of the 6 stop ND filters available - alternatively shoot near dusk :)
 
StewartR said:
Wow. I had no idea. Thanks for explaining. Is there any particular reason why it's done like this?
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Safety. Ease of setting up the shot, what's going to be in the background, etc. Ease of repeatability. Legalities possibly, for public roads at least.

And vibrations. Your camera's not going to be too steady with 30mph or whatever wind rushing past it as the car bounces down the road.
 
Get a mate to help push the car faster ;)

At 1-2mph you're going to need a stronger ND I think Kryptix, but shooting at f/29 will not be pretty, I'd try not to go anything over about f/13 as you start to lose quality due to lens diffraction but that way you'll lose about 3 f-stops so would use all of the effect of the filter without extending your shutter speed.
 
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