Posted by Scott Borger on June 29, 2006 at 4:49 PM
I've seen a few interesting shots lately using long exposures...3 minutes and longer. Obviously, a tripod, remote, small aperture, flash bulb mode and low ISO are necessary. However, I'm not sure I understand how people accurately meter beyond 30 seconds (the limit of the camera's internal metering). Educated guess? External metering device? Other?
On Film I regularly get >1minute exposures on 4x5 B/W? My exposures are usually Bulb and watching the secondhand on my watch.
I meter the stuff with my Pentax ZoneVI Spotmeter. Just take an average EV reading and place it on Zone V. It may sound confusing but it isnt that bad.
Anybody - Is there reciprocity to deal with in Digital?
RichieV
Posted by Scott Borger on June 29, 2006 at 5:13 PM
Richie, I'm using Digital. More specificly- Canon 5D.
Posted by Brent Murphy on June 29, 2006 at 5:48 PM
What I would do is change your ISO so it meters within the 30-second range, then calculate back to figure out the shutter speed for the ISO you really want to shoot.
For example, you want to shoot at ISO 100, but the exposure is longer than 30 seconds, so you can't properly read the internal meter. So, you change the ISO to 800, and you determine that at ISO 800, you need an exposure of 15 seconds. So, change back to ISO 100 (3 stops from ISO 800), and shoot for 2 minutes (3 stops from 15 seconds) on the Bulb setting.
Also, if you plan to do a lot of this type of low-light shooting, there are charts you can find online that list approximate shutter speeds for different situations (moonlight landscapes, star trails), that should get the exposure close enough that you won't have to calculate it all the time.
[Note: As Rich pointed out, I'm not sure if there is any sort of reciprocity failure that needs to be accounted for when shooting digital, but obviously, you'd need to include that in your calculations, if applicable.]
I've never shot digital, so forgive me if i sound a little naive. You really dont need to meter beyond 30 seconds. Just crank your ISO up and or meter wide open, and then compensate your exposure time by how much you decrease to your shooting aperature or shooting iso. I.E.- Lets say you cant get a meter reading using ISO 50 at f/22, try metering using ISO 800 at f/22. Say your meter gives you 15 seconds, that means then at ISO 50, the equivalent would be 4 stops longer than 15 seconds, which is 4 minutes.
Wow, nevermind, Brent cleared that up as i was entering my response, great minds think alike!!
Posted by Scott Borger on June 29, 2006 at 6:06 PM
Brent,(and Adam),thanks for your help. This makes perfect sense- I guess I was just looking for the "easy" way. If you find a good chart, let me know. Otherwise, it would be simple to build a model in Excel.
Posted by Scott Borger on June 29, 2006 at 6:40 PM
Here's a simple math model I thought of using the reasoning of Brent and Adam. I imagine that this is the calculation used for making a chart.
CONSTANT: Aperture
GIVEN: Metered ISO # at X seconds (found by metering with high ISO)
Metered ISO # / Desired ISO # = Y
XY= Needed exposure in seconds
XY/60 = Needed exposure in minutes
Scott, you can use the above mentioned method to get in the ballpark then use the histogram function on your camera's LCD screen to fine tune exposure. If you could find a copy of the old Kodak DataGuide there is a really spiffy exposure calculator for "unusual" lighting conditions. As far as reciprocity, that is a function of the particular film emulsion's characteristics and each film is different so my best guess is there is no reciprocity effect on digital capture. Of course the only supporting data I have for that conclusion is my own arcane thought process which is most always suspect.
Scott-
It sounds to me like the issue is being over-complicated.
But what do you mean by "I've seen a few interesting shots lately using long exposures...3 minutes and longer."
Are these night-time or daylight shots? Shots in low light? Moving subjects or stationary? Star trails? Blurry flowers?
Please give some examples, as this clearly falls into the realm of creative photography and is less governed by rules and formulas and more by chance.
Re: looking at the histogram - by that point, you might not get another chance at "the shot".
With regard to digital, the longer the sensor is activated the more noise will be evident in the image.
Reciprocity with digital is roughly equivalent to modern films.
The real question is "what will I gain with a longer exposure?"
Keep in mind that the longer the exposure, the more time an element needs to remain in the frame to register.
Try this - in a very dimly lit room, expose a shot for whatever the camera tells you it should be; say, 15 seconds. While the exposure is going, step into the frame for a couple of seconds, then step out. Your image won't even show in the final image. Factor this into your planning for long exposures.
Posted by Scott Borger on June 29, 2006 at 10:50 PM
I also have a EOS 5D and you can get decent long-exposure shots with noise reduction turned on. But I still use my old film camera for most long exposures, as the noise gets worse and worse with digital the longer you expose a shot. For star trails w/out a moon, just open your aperture up as wide as it will go and shoot for as long as you want. With the moon, you can start to overblow the image if you expose for too long with aperture all the way open...it's mostly trial and error. If it's not completely dark, then the advice above is good.
Discussion
11 repliesThanks for your comments in advance,
Scott
On Film I regularly get >1minute exposures on 4x5 B/W? My exposures are usually Bulb and watching the secondhand on my watch.
I meter the stuff with my Pentax ZoneVI Spotmeter. Just take an average EV reading and place it on Zone V. It may sound confusing but it isnt that bad.
Anybody - Is there reciprocity to deal with in Digital?
RichieV
For example, you want to shoot at ISO 100, but the exposure is longer than 30 seconds, so you can't properly read the internal meter. So, you change the ISO to 800, and you determine that at ISO 800, you need an exposure of 15 seconds. So, change back to ISO 100 (3 stops from ISO 800), and shoot for 2 minutes (3 stops from 15 seconds) on the Bulb setting.
Also, if you plan to do a lot of this type of low-light shooting, there are charts you can find online that list approximate shutter speeds for different situations (moonlight landscapes, star trails), that should get the exposure close enough that you won't have to calculate it all the time.
[Note: As Rich pointed out, I'm not sure if there is any sort of reciprocity failure that needs to be accounted for when shooting digital, but obviously, you'd need to include that in your calculations, if applicable.]
CONSTANT: Aperture
GIVEN: Metered ISO # at X seconds (found by metering with high ISO)
Metered ISO # / Desired ISO # = Y
XY= Needed exposure in seconds
XY/60 = Needed exposure in minutes
It sounds to me like the issue is being over-complicated.
But what do you mean by "I've seen a few interesting shots lately using long exposures...3 minutes and longer."
Are these night-time or daylight shots? Shots in low light? Moving subjects or stationary? Star trails? Blurry flowers?
Please give some examples, as this clearly falls into the realm of creative photography and is less governed by rules and formulas and more by chance.
Re: looking at the histogram - by that point, you might not get another chance at "the shot".
With regard to digital, the longer the sensor is activated the more noise will be evident in the image.
Reciprocity with digital is roughly equivalent to modern films.
The real question is "what will I gain with a longer exposure?"
Keep in mind that the longer the exposure, the more time an element needs to remain in the frame to register.
Try this - in a very dimly lit room, expose a shot for whatever the camera tells you it should be; say, 15 seconds. While the exposure is going, step into the frame for a couple of seconds, then step out. Your image won't even show in the final image. Factor this into your planning for long exposures.
I also have a EOS 5D and you can get decent long-exposure shots with noise reduction turned on. But I still use my old film camera for most long exposures, as the noise gets worse and worse with digital the longer you expose a shot. For star trails w/out a moon, just open your aperture up as wide as it will go and shoot for as long as you want. With the moon, you can start to overblow the image if you expose for too long with aperture all the way open...it's mostly trial and error. If it's not completely dark, then the advice above is good.