Long exposure -- how to avoid "over-exposure"?

[mikael212340]

I'm reading that some people use > 1 minute exposure and I wonder how they do it without over-exposing the photo (a ND filter gives +8 stops which doesn't seem adequte for 2 minutes exposure, even if it's pitch black?).

Also, a very long exposure push the aperture to minimum... and I read that beyond f16 is not recommended. But you need a really small aperture with long exposure...

What am I missing?

Also, if someone has a link that covers "long exposure techniques" I'd be happy to read it :>

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Canon RB owner

 

[Eric217138]

Also, a very long exposure push the aperture to minimum... and I
read that beyond f16 is not recommended. But you need a really
small aperture with long exposure...

Not necessarily, I don't think.

If you're in an area that's truly pitch black, then a 10 minute exposure shouldn't really show anything. If I'm away from city light pollution and take a 30 second exposure of the night sky, I see some stars, but the black part of the sky is still black on the exposure. Even at wide apertures.

 

[Julianne Bonner]

When I tried to take shots of the moon I was advised to use F5.6 or F8 and expose for 1/125 or so. The shot came out totally dark. When I made it a few seconds it was totally white! I was in an area where there were no lights other than the moon. I managed to get a shot but the moon had a weird orange tint and still didn't pick up much detail, even with a 300mm lens.

I'd be very interested to know how people manage to get good shots of the moon, also of startrails where the shutter is open for ages.

 

[Jan Moren]

Well, it needs to be dark, that's the basic trick really. We don't really notice it (our vision system is wired to ignore it), but it's an enormous difference in light intensity between sort-of dark dusk and real night. There's also a huge difference with just a small light source nearby. If you can't take long-exposure pictures, you need to get out of the light.

Here's a couple of recent ones for me.

The first one is pretty crappy as pictures go (composition didn't work out the way I wanted). EXIF says 61 seconds; its actually a composite of two images with the upper, lighter part at 61 seconds, and the lower at 240 seconds (give or take). ISO 100, aperture f9.

It was night, and no lights were close by; still you can see that the lighted tree is almost blown out.



The second one is ISO400, 30 seconds and f5.6. I chose to go fast in part because there's some buildings just behind that mound and the light from them risked blocking out the sky. Also, it was late and I wanted to go home I'd like to try to redo the shot again later at night, though, with longer exposure to bring out stars better.



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http://lucs.lu.se/people/jan.moren/log/current.html

 

[Jan Moren]

When I tried to take shots of the moon I was advised to use F5.6 or
F8 and expose for 1/125 or so. The shot came out totally dark.
When I made it a few seconds it was totally white! I was in an
area where there were no lights other than the moon. I managed to
get a shot but the moon had a weird orange tint and still didn't
pick up much detail, even with a 300mm lens.

My guess is, it was not straight overhead.

The exposure rule to treat it as lit by the sun works only when it's a full moon, straight up, in a cloudless sky. As the moon sinks toward the horizon, it gets dimmer, redder and fuzzier.

I'd be very interested to know how people manage to get good shots
of the moon, also of startrails where the shutter is open for ages.

Just point it straight up and wait. I tried it a few nights ago, and at ISO 100, 4 minutes was not enough to get a clear image of the stars. I'll try it again someday, and probably use upwards of 10 minutes and maybe open up a bit more too.

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http://lucs.lu.se/people/jan.moren/log/current.html

 

[mikael212340]

Ok,

Going to buy a tripod then and try out for myself :>

This is what my vendor recommended:

Manfrotto 190D Black (tripod)
Manfrotto 484 (head)

Using Canon 350 with 50mm 1.8

Will add 17-85 in 6 months time.

Please comment tripod if you know of something better around same price :>

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Canon RB owner

 

[Time2Play]

I posted this a few days back in another thread, but here it is again anyways..
This is a 23 min. exposure. iso200, f/5, with a polarizing filter only.

I was at a cottege, with a bit of light pollution, and a street light reflecting at the bottom of the frame. Taken at 10.40pm, not the darkest time of night
A tripod was used of course, while I sat back and nursed a couple of beers..

I could have left the shutter open for longer, but was getting impatient to see the results..
Anyhow, they say with a fresh battery, you can expose for up to 2 1/2 hrs.



--
Save your memories in case you go senile
Dave
CATS Member #83 > ^..^
My meager gallery : http://www.pbase.com/time2play

 

[mikael212340]

Well, that's what I don't get...

How can you expose for 23 minutes at f5 without the picture getting overexposed?

I mean, 23 minutes is a LONG time... not to mention 2 hours?

I thought "optimal exposure" was a simple equation of "aperture" and "light collection". Change one variable and you have to change the other as well... So, given aperture at "5" I can't see how you can vary length of exposure without having the picture being overblown??

I posted this a few days back in another thread, but here it is
again anyways..
This is a 23 min. exposure. iso200, f/5, with a polarizing filter
only.
I was at a cottege, with a bit of light pollution, and a street
light reflecting at the bottom of the frame. Taken at 10.40pm, not
the darkest time of night
A tripod was used of course, while I sat back and nursed a couple
of beers..
I could have left the shutter open for longer, but was getting
impatient to see the results..
Anyhow, they say with a fresh battery, you can expose for up to 2
1/2 hrs.



--
Save your memories in case you go senile
Dave
CATS Member #83 > ^..^
My meager gallery : http://www.pbase.com/time2play

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Canon RB owner

 

[Julianne Bonner]

You're right, the moon was in front of me. It was above a mountain and I thought I'd get a lovely atmospheric shot with the moon bringing the mountain out of the gloom. Oh well, it was a nice idea...

 

[Jason Hutchinson]

How can you expose for 23 minutes at f5 without the picture getting
overexposed?

Because it was DARK . Really dark!

I thought "optimal exposure" was a simple equation of "aperture"
and "light collection". Change one variable and you have to change
the other as well... So, given aperture at "5" I can't see how you
can vary length of exposure without having the picture being
overblown??

It is a simple equation of course.

The picture will not be overblown if the conditions are dark. You threw out the term "pitch black" before. Do you realize a 1 year exposure under pitch black conditions (you'd have to use film) would be underexposed? Light is light, there is no magic here. Unless you live in a very light polluted area you should be able to find a dark spot. Heck your profile says Sweden but you'd think you lived in Times Square???

Try this, lock yourself in a closet and take a 5 minute self-portrait. It will be underexposed. If its not plug the holes in your door.

Jason

 

[jtsmith25]

The camera will not increase the amount of light it takes in infinitely. It will reach a certain point and then level off. Leaving the shutter open will not produce a totally white picture if you left it open forever.

 

[Jason Hutchinson]

The camera will not increase the amount of light it takes in
infinitely.

Yes it will. If you're talking about the reciprocity curve of film, this is a film specific effect that really has no relevance to the original posters questions.

It will reach a certain point and then level off.
Leaving the shutter open will not produce a totally white picture
if you left it open forever.

I've done it (well not forever) and the photo is entirely white except a few dead pixels.

Jason

 

[Alex Morse]

Did you focus on the north star? Just wondering, is that how you got the trails to revolve around it.
--
Alex Morse

 

[Jason Hutchinson]

Did you focus on the north star? Just wondering, is that how you
got the trails to revolve around it.

The stars always revolve around that point (which is merely very close to Polaris) anywhere on earth. No work required.

Jason

 

[mikael212340]

Heck your profile says Sweden but you'd think

you lived in Times Square???

Not sure what you mean by that? If I accidently claimed that I lived in the US I take it back. If you are implying that Times Square is the most lit up place in the world (at least compared to Sweden) I have to tell you that we have a few places in our small cities that come with lamp posts :>

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Canon RB owner

 

[Jason Hutchinson]

Not sure what you mean by that? If I accidently claimed that I
lived in the US I take it back. If you are implying that Times
Square is the most lit up place in the world (at least compared to
Sweden) I have to tell you that we have a few places in our small
cities that come with lamp posts :>

I am implying to ask the question you did, you must have never been in a dark situation taking a photo. Have you ever seen stars in the sky? Because you really don't in Times Square unless there is power outage. If you lived near Times Square I could understand your confusion but surely there have to be plenty of areas in Sweden where it can get dark?

Here's a 12 minute exposure under dark conditions. The trees are still WAY underexposed, and it even got darker than night.

 

[jrynash]

Did you focus on the north star? Just wondering, is that how you
got the trails to revolve around it.

The stars always revolve around that point (which is merely very
close to Polaris) anywhere on earth. No work required.

Jason

OK...I couldn't resist: Of course the stars aren't revolving around anything, the earth is spinning on its axis of course...so your camera is turning. But we all realize that I think. As far as anywhere on earth...not really...anywhere in the Northern Hemisphere?

 

[Jason Hutchinson]

OK...I couldn't resist: Of course the stars aren't revolving
around anything, the earth is spinning on its axis of course...so
your camera is turning. But we all realize that I think. As far
as anywhere on earth...not really...anywhere in the Northern
Hemisphere?

Yes you're right it is really the camera rotating not the stars, and those folks in the southern hemisphere look at the south celestial pole which doens't have a nice bright star like Polaris.

Jason

 

[Jan Moren]

You're right, the moon was in front of me. It was above a mountain
and I thought I'd get a lovely atmospheric shot with the moon
bringing the mountain out of the gloom. Oh well, it was a nice
idea...

You can get such a shot, but you'll have to wait for the right weather. You'll also have to composite two shots, probably.

The redness and fuzziness comes from atmospheric distortion. So, wait for dry weather (less water vapor to disperse), after a rain or snowfall (no dust), in cool or cold weather (less heat blurriness). Then take one picture exposed right for the moon, and another exposed for the mountain and so on. You can tweak the moon color a bit in PP, of course.

When you succeed, post the picture - I haven't yet

--
http://lucs.lu.se/people/jan.moren/log/current.html

 

[Eric217138]

I've done it (well not forever) and the photo is entirely white
except a few dead pixels.

What were you taking a photo of?

Exposing the night sky for 4 hours will yield a photo with plenty of dark area, right? The sensor doesn't sense light unless light hits it, right?

• Eric