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 How to calculate long exposures? 
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Post How to calculate long exposures?
I was out doing some early am photography this morning, and this dilemma popped into my head again. I shot this picture below with my sigma 10-20 lens (the photo is cropped) at f4.5, iso 320, 30 seconds. I usually don't run into these lighting situations where such long exposures are needed. I'm thinking the lights would look a lot better at f22, so how would I go about figuring the exposure time for that? I try not to shoot above iso 400. Is there a formula or conversion factor that's handy?

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Sun Feb 08, 2009 7:00 am
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Post Re: How to calculate long exposures?
Yes - when you double the f-number you need four times the exposure time. Or more generally, if you increase the f-number by a factor x, you need x^2 (x squared) times the exposure time. So in this case, to get the same exposure at f22 as you did with 30 seconds at f4.5 you'd need:
30 sec*(22/4.5)^2 = 717 sec = 11 min 57 sec
That's a shot that would require some patience - or higher ISO. And still some patience. :-)
Another way to remember it is that the camera adjusts aperture in 1/3 stops, so for every three increments on the camera you need to double the exposure time.

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Sun Feb 08, 2009 7:56 am
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Post Re: How to calculate long exposures?
But high f values allso makes the dirt on the sensor more visible...

Btw, Andrew, does the automatic metering not work? Because I have realised that forlow light levels (or if one uses a ND filter), my camera has terrible problems to compute the right exposure time, it is always underexposed!

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Sun Feb 08, 2009 10:01 am
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Post Re: How to calculate long exposures?
tmophoto wrote:
another benefit of shooting at really high fstops at night is all the lights have a nice star pattern on them, kinda like the cheezy star filters that you can get.


Yeah, this is what I'd be looking for in shooting at f22.

Michael wrote:
Btw, Andrew, does the automatic metering not work? Because I have realised that forlow light levels (or if one uses a ND filter), my camera has terrible problems to compute the right exposure time, it is always underexposed!


No my D80 can't handle metering properly in this light, if I recall the in-camera meter was showing off the chart overexposure, meaning if I went by the meter it would have been way underexposed like you said. I just go by trial and error until it looks good on screen. As you can see the photo probably could have done with a little more exposure time. Isn't that what the histogram is for? I still haven't figured out how to use it.

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Sun Feb 08, 2009 11:46 am
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Post Re: How to calculate long exposures?
I don't know what you think about it, but I would try to avoid very long exposures (let's say more than 5 minutes) not to get too much long exposure noise (or heat noise)... It can really ruin a shot.


Sun Feb 08, 2009 9:02 pm
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Post Re: How to calculate long exposures?
I don't mean to make this into a film/digital war by my comment, but I would seriously consider buying a cheap manual film camera if you decide to do a lot of long exposures. You never have to worry about your battery going out and you can leave the shutter open forever to get some neat effects. I use a Nikon FM and it's perfect for this application. And you can also play with low ISO films to really get some long exposure times! I really want to try a star exposure with Velvia 50!

There is a website I once stumbled upon where the guy has done considerable research with aperture values and extended exposure times. I wish I could find it again but I can't seem to at the moment. Perhaps someone here knows the site. He was calculating values for 2, and 3 hour exposures from what I remember. Good stuff! I know you're doing times that are much shorter than that, but some of what he writes about may be of help if I can ever find the link! :-)

I just came across this link. It's not at all what I was looking for, but may offer some assistance to you: http://www.cambridgeincolour.com/tutori ... graphy.htm

Take care,
-Andy


Wed Feb 11, 2009 7:16 pm
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Post Re: How to calculate long exposures?
aorr@mac.com wrote:
I don't mean to make this into a film/digital war by my comment, but I would seriously consider buying a cheap manual film camera if you decide to do a lot of long exposures. You never have to worry about your battery going out and you can leave the shutter open forever to get some neat effects. I use a Nikon FM and it's perfect for this application. And you can also play with low ISO films to really get some long exposure times! I really want to try a star exposure with Velvia 50!

There is a website I once stumbled upon where the guy has done considerable research with aperture values and extended exposure times. I wish I could find it again but I can't seem to at the moment. Perhaps someone here knows the site. He was calculating values for 2, and 3 hour exposures from what I remember. Good stuff! I know you're doing times that are much shorter than that, but some of what he writes about may be of help if I can ever find the link! :-)

I just came across this link. It's not at all what I was looking for, but may offer some assistance to you: http://www.cambridgeincolour.com/tutori ... graphy.htm

Take care,
-Andy


I am not sure about this. Sure, there is no sensor - so no noise as far as the digital noise is concerned. However, with reciprocity failure, I think you would have more to worry about.

Tying in with the original post, I usually set the camera to ISO 25,600 and a wide open aperture, and then work my way back down to a low ISO by working your way down the scale. I have a nice Sekonik light meter, but in the middle of the night, that thing doesn't even give me a reading -- too dark. A film camera wouldn't help here. But I would like to try some night scenes with it.


Wed Apr 08, 2009 11:24 am
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Post Re: How to calculate long exposures?
I generally start with a fast lens... usually my 16-35 2.8 II, and high ISO, to figure out where the dark point is, and how much light is available. Then I just reduce the ISO to 100 and start doubling my exposure times. Sometimes it can be a bit of a guessing game, but it doesn't take too long to dial it in.

It's a lot easier with a full moon, so I always try and shoot around that, if I can.

Here's a shot I did last weekend during the full moon:

Image


Fri Jun 12, 2009 6:48 am
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Post Re: How to calculate long exposures?
Todd Lambert wrote:
I generally start with a fast lens... usually my 16-35 2.8 II, and high ISO, to figure out where the dark point is, and how much light is available. Then I just reduce the ISO to 100 and start doubling my exposure times. Sometimes it can be a bit of a guessing game, but it doesn't take too long to dial it in.

It's a lot easier with a full moon, so I always try and shoot around that, if I can.

Here's a shot I did last weekend during the full moon:

Image


Very nice picture :D Could actually by nice framed on the wall :)


Tue Jun 16, 2009 1:09 am
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Post Re: How to calculate long exposures?
Thanks, I appreciate the kind words! :)


Thu Jun 18, 2009 4:38 pm
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Post Re: How to calculate long exposures?
Has anyone heard of a spot ND filter?
There are times I have wanted to knock back the intensity of a single light source or the moon or the sun in the frame...

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Fri Jun 19, 2009 3:18 am
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Post Re: How to calculate long exposures?
Todd Lambert wrote:
I generally start with a fast lens... usually my 16-35 2.8 II, and high ISO, to figure out where the dark point is, and how much light is available. Then I just reduce the ISO to 100 and start doubling my exposure times. Sometimes it can be a bit of a guessing game, but it doesn't take too long to dial it in.

It's a lot easier with a full moon, so I always try and shoot around that, if I can.

Here's a shot I did last weekend during the full moon:

Image


Amazing shot. Can you give us the details of this shot? Lens? Body? Exposure time, etc?


Mon Jun 29, 2009 9:52 pm
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Post Re: How to calculate long exposures?
I accidently came across the above snap .. and something just didn't look right. The moon looks liked it's superimposed.

It has been shot with a full moon alright, but I think the actual moon is out of frame, to the RHS.
Below is a reference shot of a full moon with a water reflection trail (heck I know - I've shot too many of them :? )




I guess you can put it down to the photographer's 'artistic license' and me hanging around the studio with too much time on my hands :roll:


Mon Dec 07, 2009 11:40 pm
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Post Re: How to calculate long exposures?
Matt, just coming back to this, I think the geometry works when the foreground water is calm. Here's a shot I did recently that has no stairway to the moon, only a direct incident reflection off the smooth water.
Attachment:
Lake-Indoon-Moonrise.jpg
Lake-Indoon-Moonrise.jpg [ 89.42 KiB | Viewed 10664 times ]

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Fri Dec 18, 2009 1:24 am
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Post Re: How to calculate long exposures?
I stand corrected.
I also just noticed a very, very slight 'white foam' water brightness around behind the red light on the channel marker and also on the shore break hidden in the photographers logo bottom LHS that lines up with the moon. ( But I still can't figure why the 'white foam effect' doesn't carry across the sandbar as does the red channel marker ripple? ... must be extremely still water ?)
Me bad.


Fri Dec 18, 2009 2:35 am
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Post Re: How to calculate long exposures?
Hey, sorry... totally lost track of this thread.

Yes, I can assure you, that shot is, as it was when I took it. No artistic license was taken at all. It's a single shot on full moon with a whole bunch of different lighting (moon, ambient from passing traffic, a neon sign, my own light painting, etc..)

The exif info is intact on the shot, but in a nutshell:

5D2
16-35L II
98 seconds
ƒ9
ISO 100

A little background on the shot.. this was one of numerous attempts I did in order to get these conditions. I shot this location for 3 months, on the full moons, in order to get a completely still, night with no clouds etc. I had to wait until past 3am in order to get the moon on the right side of the composition. This was the 3rd month attempt and I got absolutely perfect conditions.

Not long after this was shot, the ship was removed and sunk off the coast, becoming an artificial reef. The ship was actually a ghost ship (broke loose during Katrina) that floated around in the Biloxi Sound for several weeks before finally making ground near the Biloxi Harbor. To this date, I am the only one who has a shot of this ship taken at night. (I sure wish I was into Time-lapse back then - dammit!)

Anyways, thanks for the kind words. 8-)


Mon Nov 14, 2011 8:00 pm
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Post Re: How to calculate long exposures?
jamesgott wrote:
I am not sure about this. Sure, there is no sensor - so no noise as far as the digital noise is concerned. However, with reciprocity failure, I think you would have more to worry about.


Reciprocity failure is not as big a deal as some people make it out to be. All that is required to compensate for this is to increase your exposure time - I recommend bracketing your exposures. You may get a colour shift but this can lead to some cool and interesting colours in your final image. And I'd prefer funky colours to digital noise.


Fri Dec 07, 2012 5:36 pm
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