Advice Required: Long Exposure Moving Clouds

[DurExplorer]

Hi All,

First off, if I have the wrong area please feel free to move/delete this post.

I'm experimenting with different types of photography and i'm particuarly keen to try and capture some long exposure shots to blur the clouds moving.

I'm familiar with the requirements (Tripod, ND Filters, Manual mode etc) but I just can't capture a half decent image.

Even with a ND filter attached, Aperature set at F22 and a shutter speed of 10s I end up with a completely blown out image.

I'm looking for some advice on what I may have overlooked. I went out today to have an experiment and took a lot of shots, altering the exposure compensation to see what effect it may have but the results were very poor.

Thank-you.

[jdepould]

Make sure you're at base ISO, and shoot manual mode. You want your EV compensation at 0.

You may need to stack your NDs to get enough for a good daytime exposure with that long of a shutter speed.

I'd actually try to back off the aperture a little (f/16 maybe), because you're going to be running into diffraction at f/22.

What strength NDs are you using? I think 10 stops on the filter would probably get you where you need to be for shutter speed (this is assuming you've got about 1/250 @ f/8 for your "normal" exposure).

[DurExplorer]

Hi,

Many thanks for the reply.

I have tired stacking ND filters today and still the results were blown out images. I stacked a ND8, ND4 & ND2 I also tried mixing them together in different combinations.

I will definitely try increasing the aperature, well worth a shot.

I think the biggest problem appears to be too much light getting in as the images are really badly blown.

I must admit im very new to photography so I don't fully understand your comment (this is assuming you've got about 1/250 @ f/8 for your "normal" exposure). Would you be able to explain it?

Thank-you

[RichardTaylor]

Re exposure.
This tute, on this site, may help with the basics..

Exposure (1) A balancing act

If you are starting at 1/250 @ F8 without any filters that would equate to 1/60 @ F16 without any ND filters.

A ND2 only would take that to 1/30 @ F16
A ND4 only would take that to 1/15 @ F16
A ND8 only would take that to 1/8 @ F16

A ND2 + ND4 would take that to 1/8 @ F16
A ND2 + ND4 + ND8 would take that to 1second @ F16

If you were shooting @ 10 seconds you would be 3+ stops over exposed (with all 3D filters).

[OsmosisStudios]

ND8 = 3 stops
ND4 = 2 stops
ND2 = 1 stop

That's 6 stops. Assuming a "standard" exposure of iso100, 1/250th and f/8 (not unreasonable on a bright sunny day), then:

f/8 -> f/11 -> f/16 (2 stops)
Add filters (6 stops)
Now -8EV
So, 1/250 becomes:

250 -> 125 -> 60 -> 30 -> 15 -> 8 -> 4 -> 2 (or 1/2 second).

10s is 3 1/3 stops OVER.

When I was shooting in a bright sunny day (like the example above), I was using 13 stops of ND (3stop+10stop) and even then only managed to get 20s or so at f/22 (which was causing more issues than I expected).

(Damn, RichardTaylor beat me to it! Must have been typing at the same time!)

[RichardTaylor]

Sorry about that.
+ smile

This thread may help also.

Long Exposure - 10 stop filters

[jdepould]

Originally Posted by DurExplorer

Hi,

Many thanks for the reply.

I have tired stacking ND filters today and still the results were blown out images. I stacked a ND8, ND4 & ND2 I also tried mixing them together in different combinations.

I will definitely try increasing the aperature, well worth a shot.

I think the biggest problem appears to be too much light getting in as the images are really badly blown.

I must admit im very new to photography so I don't fully understand your comment (this is assuming you've got about 1/250 @ f/8 for your "normal" exposure). Would you be able to explain it?

Thank-you

What ISO have you been using? Do you know how to read your exposure meter?

When I said "normal" exposure, I meant your exposure without any ND filters on the lens.

[DurExplorer]

All your advice is excellent I really appreciate the effor and time you have given.

I don't think I gave enough consideration to the balance that needs to be struck, I assumed that if I had a small aperature that I would be safe to increase the shutter speed, clearly not.

I'm hoping that the weather today will be such that I can get out again and experiment some more (my holiday ends on Sunday so hopefully the weekend will be kind).

I think I should try and write down some of this info so I can carry it with me next time I go out. Does anyone know of a good grid/chart that shows the relationship that I could perhaps take with me?

[OsmosisStudios]

Learn the stops. You should be able to do this on your fingers.

[inkista]

Stops are how we equate aperture to shutter speed to iso. To break down what OS said above a little more:

Each stop is a doubling of a light. So, exposure-wise (only)

Doubling your ISO from 100->200 is the same as:
Opening up your aperture from f/22 -> f/16 or
Slowing your shutter speed from 1/200s -> 1/100s.

So, if say, you'll get a good exposure without filters at

iso 200, f/16, 1/100s

And you want to use a shutter speed of >1 second, then you'll need:

1/100 -> 1/50 -> 1/25 -> 1/12 -> 1/6 -> 1/3 -> 2/3 -> 1.3"

7 stops in ND filters on the front of your lens to achieve that with iso 200 and f/16.

You can halve your iso to 100 or stop down to f/22 and make it 6 stops, or do both and only need 5 stops.

ND filters also have different names of describing how much darkening they add, but for quite a few, the number on them is the darkening factor, not the number of stops. That's why an ND8, which makes the scene 8 times darker, is only a three-stop filter because stops are how many times you double (2³ = 8).

But, as OS said, just keep doubling/halving, and you can count the stops you'll need on your fingers and you don't really need a chart. You will, however, probably need to learn the full-stop f-number scale.