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Amateur Question on Long Exposures


joshcouts

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Ok, so this is a question springing from not only being an amateur, but also

not being able to afford an SLR of any sort until recent months...

 

The question I have is how are photographers executing exposures of longer

length (ie, 5 minute exposure...45 minute exposure of star trails, etc.), when

the cameras they are using only show the ability to execute an exposure with a

maximum shutter speed time of say, 30 seconds (ie, Canon 5D, 30D)? I am sure

it's something ridiculously basic and elementary, I've just never seen anything

documented on it.

 

I had read something once about someone needing a remote shutter release to do

this? Is it a custom setting of some sort that wouldn't be documented in the

camera specs?

 

While I'll likely be purchasing a Canon 30D or even possibly a 5D within the

next year, I currently only have a Canon Rebel K2 as my SLR. Whatever the

answer is to my question, is my current SLR capable of multiple minute

exposures of this sort?

 

Thanks.

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Using "B" on most shutter speed dials, and pressing the shutter release, opens the shutter until you release it. Usually a release cable is used, and one with a locking mechanism for very long exposures. "T" (not as common anymore) will open the shutter and it will stay open until you press the release again. Is that what you're looking for?
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What you're looking for is "bulb" mode, and may only be available in the 'M' (Manual) mode. Try this experiment: put your camera in manual mode, and keep increasing the shutter time. After the 30 seconds setting, does one more click show the work 'bulb' (at the bottom of the viewfinder)? If so, then in bulb mode, the shutter stays open as long as you have the shutter button depressed. (This is why a remote control may be better - you can use it to keep the shutter "button" depressed w/o having to stand with the camera.)

 

Hope this helps, and hope others correct any errors I made...

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Ok. That makes sense as to why a remote shutter release would be used...if holding down the button, one would probably be prone to camera shake as well if pressing directly on the camera for 5 minutes, rather than remotely. That's probably where that tidbit of info came from.

 

I'll have to look at my SLR today and see if it gives me the bulb option.

Thanks.

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But how do you know what kind of aperture and exposure lenght should you use if light meter works only to 30 seconds? How do you count it? How do you know that the shutter must be opened 45 minutes and not 35?

 

 

Do you need to use second light meter 'not in a camera'? I'm usually not doing long exposure shots but I'm just curious how do you know what exposure to set - without light meter.

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I wasn't completely clear - many times the remote release has a bulb feature which allows one to hit the remote button once and keep the shutter open, even when you let go of the remote button. For example, there may be a little plastic "shelf" which slides over the remote button and keeps it depressed....

 

I didn't mean to imply that one had to stand by the remote with the finger on the button.

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Michael,

 

Generally one uses a light meter - but exposure times for various types of long exposures are well known, and you can look them up (e.g., google for "star trails".) But there is an issue with film (I'm ignorant about digital), called "reciprocity failure" - which means that for a given film, once the METERED shutter time exceeds a certain amount, you have to add additional time - usually based on a table available from the film manufacturer's website. (For those still using film, Fuji Acros 100 B&W film and Fuju Provia E6 film have good reciprocity - you can have shutter times up to one minute, I believe, before you have to start compensating.)

 

Again, hope this helps, and feel free to correct any errors...

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So when I want to take a picture of mountains in a dark moon-light I just have to use a light meter (this one which is not in a camera)?

 

Of course there are some ready exposure times but they are very general and they doesn't always give good effect on a developed picture.

 

Can I somehow recount it using camera light meter? If on ISO 1600 I would have to set the time on 30 seconds then on ISO 800 I would have to set 1 minute... am I right or it won't work? :) (of course considering the fact that I'll have to use a little bit longer times to avoid underexposure)

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"if holding down the button, one would probably be prone to camera shake as well if pressing directly on the camera for 5 minutes"

 

this is definately true in B mode, when there would be ongoing camera shake, but not T mode where the shake at the beginning and end of the exposure would have negligable effect as it would be such a small percentage of total exposure. The cynic in me believes the loss of T mode might be to allow Canon (and Nikon) to sell very expensive brand specific electronic cable releases.

 

I believe in digital "reciprocity failure" is not a concern in long exposures, but "battery failure" is a serious concern, and some of the astrophotography guys set up external power sources. the other option would go second hand for under $100, which leaves room for a lot of film!

 

IMHO it may be worth looking carefully at old manual film cameras with manual cable releases (reciprocity failure is easy to deal with), as these go for a song - the cost of a new digital body + electronic cable release + external power source could really build up.

 

Using an external light meter to work out your exposure is an expensive option. I am not aware of any meters (in or out of camera) that work well on really low light subjects (I would be interested to hear of any). Also for some long exposures such as firework and lightning photography the lighting is varying so quickly that using pre-selected apertures (based on values found on the web or photo books) is much easier. the general values for stars/fireworks/lightning etc work really well.

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woops - accidently moved some text last post should have read:

 

I believe in digital "reciprocity failure" is not a concern in long exposures, but "battery failure" is a serious concern, and some of the astrophotography guys set up external power sources.

 

IMHO it may be worth looking carefully at old manual film cameras with manual cable releases (reciprocity failure is easy to deal with), as these go for a song - the cost of a new digital body + electronic cable release + external power source could really build up. The other option would go second hand for under $100, which leaves room for a lot of film!

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Brent is quite right to mention the problem of powering digital cameras over long

exposures.

If you google for "star trails" some of the sites talk about how to address this.

 

Michael, using an off-camera light meter doesn't solve all your problems, and sometimes

you need to conduct experiments. The good news with digital is that this is much

cheaper than conducting the experiments with film. I was trying to say that some people

have posted the results of their experiments and that will provide a starting point for

you....

 

I use an off camera light meter with a pinhole camera (ZeroImage), the aperture is the

equivalent of f/256, and there is a handy circular dial on the back for taking the meter

reading and adjusting it for that tiny aperture. Once you get the resulting shutter speed,

sometimes you need to refer (I'm talking film) to the reciprocity failure tables, etc, as

explained above.

 

Michael, there is a huge difference between long of exposures of, say, one minute and 8

hours. In my advice I was probably biased towards toward the former. There are many

situations where an off-camera light meter is only the beginning of the exposure

calculation....

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My answer is similisr to Brent's with one addition,unless I missed it, Bracket and bracket. Doing something like this there is no cut and dried formula, just keep track of what you're doing and keep adjusting til you get what you want. Or maybe you'll find something totally different that you like better.
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Yes Michael, you're right--that's exactly how you do it. Keep setting your ISO higher and higher until you can actually get a reading, and then calculate the equivalent exposure at whatever ISO and aperture you plan on using. If you metered 30 seconds at ISO 1600 but plan on shooting at ISO 100, you'd have to adjust your shutter speed by 4 stops. So 4 stops would be 30 secs to 60 secs, 60 secs to 120 secs, 120 secs to 240 secs, and 240 secs to 480 secs (which is to say 8 minutes).

 

The second step, if your original metering was done at f/2.8, but you intend on shooting at f/8 for example, you'll have to continue calculating. So your 8 minutes would then turn into roughly 64 minutes (8 to 16, 16 to 32, and 32 to 64) since there's 3 stops difference between f/2.8 and f/8.

 

So your initial (in camera) meter reading of 30 seconds at f/2.8 and ISO 1600 turned into 64 minutes at f/8 and ISO 100. No need to spend money on an external meter.

 

When doing that, I try to get a reading at the aperture I'm going to shoot at at the lowest ISO setting that will give me a reading just because it makes it easier to calculate the final exposure at my chosen ISO and you can eliminate the second round of calculations

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Your Rebel K2 uses battery power to keep the mirror up and the shutter open, so be sure that you have fairly fresh batteries installed before using it for very lengthy exposures. I doubt that the camera meter will be able to help you a great deal if the light level is very low. Its specifications claim that it will meter down to EV 1 at 100 ISO with an f/1.4 lens (i.e. 1 second at f/1.4 and ISO 100).

 

You may find the following is a useful guide to starting points for exposure, but don't forget to allow for reciprocity failure of your film:

 

http://www.fredparker.com/ultexp1.htm

 

The best techniques for very long exposure with digital photography are somewhat different. You don't have reciprocity failure to deal with, but because noise and sensor heat build up become intrusive with long exposures, it's best to divide your exposure up into several shorter ones taken one after the other, and to shoot a dark frame of the same length with the lens cap on. You then use software, first to subtract the dark frame from each of the other shots, and then to add the noise reduced shots together to create the final image.

 

http://www.tawbaware.com/imgstack.htm

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I doubt I'll be doing much of the 45 minute star exposure type of thing, so battery power won't be all that much of a worry for me.

 

I'm primarily interested in doing the 1-2 minute exposures just after dusk, sort of thing. I will definitely need to do some calculations though on exposure settings for durations past 30 seconds...while I'm familiar with the relationship between aperture and shutter speed, as well as the way that ISO affects that relationship, I've never been taught much of how EV and the few other bits and pieces of exposure factor in.

 

My main curiosity is whether or not my K2 model supports remote shutter release, because from what I've read, the only model of K2 that does support the wireless release (or any sort of release) is the date-version model, which I'm not completely sure I have, as it was a gift purchased for me by someone else.

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Michael, if you are considering the moonlit mountain and the dark background, or whatever

other setting, I would try to avoid the high ISO settings for two reasons (you mention ISO 800

and ISO 1600 in one of your comments)

 

1) the first times you experiment you can go for longer exposure times and therefore longer

star trails before you overexpose the mountain

 

2) in general, you'll have less noise at a small ISO setting, what might preserve details in

some of the dimly lit areas you are interested in

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Michael, if you're shooting film then you should also pay attention to the answers above that talked about reciprocity failure. I don't know if you're shooting slides or negs, but I used to shoot negs, and sometimes I'd add 10%-20% to my exposure time because of that. (Not scientific I know, but it wasn't critical for me to get the colours exactly right either. How much extra I'd add would be whatever "felt right"). Negs could handle the extra exposure easily, and hopefully it would counteract the effects of reciprocity failure as well. Though it can be adjusted in post processing after a scan as well.
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I used to do this alot a while back and it took a great deal of trial and error. It was a balancing act of many factors: ASA of film, exposure time, and lens opening, to get the effect you are looking for. So many other things show up in no time at all such as light-haze in the night sky.

I would suggest using black and white film starting out so you dont have the color sensitivity to deal with, however if you do go color use a light-polution filter to control ambient light from street lights or a nearby city.

Start with say a 15-minute exposure at f-8, take notes. Then do another 15 minute exposure at f-5.6 gradually opening the lens more.

After you get the film back and look at your notes, you can see where you attain the balance you are looking for: where you see the amount of star trails and color, but you also have contrast and good blacks. After a couple rolls of film you can make a chart, where the balance is good along the y axis lens opening and x axis exposure time for each film speed. After many nights experimenting, that is the most direct approach I've found. Sorry I don't have my chart anymore. Have fun, you will see some amazing discoveries.

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Look into a manual focus, battery independent SLR. The normal advantages a K2 has (autofocus, autoexposure, autoadvance) are of little value under the low light levels encountered when making time exposures. I use a Nikon FM (shutter inoperative above 1/30) to make many of my star trail photos with.
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