Amateur Question on Long Exposures

Discussion in 'Accessories' started by joshcouts, Oct 24, 2006.

  1. 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.
     
  2. 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?
     
  3. 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...
     
  4. 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.
     
  5. 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.
     
  6. 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.
     
  7. 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...
     
  8. 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)
     
  9. "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.
     
  10. 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!
     
  11. From what I've heard, another problem with digital SLRs and ultra-lengthy exposures involves the sensor getting overly hot (for say, 45 minute exposures).
     
  12. 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....
     
  13. 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.
     
  14. 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
     
  15. 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
     
  16. 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.
     
  17. I would suggest you get an old fashioned locking cable release and either make your own adaptor for it:

    http://www.eosdoc.com/manuals/?q=CableRelease

    or look for a similar commercial version e.g.:

    http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=109447&is=REG&addedTroughType=categoryNavigation
     
  18. 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
     
  19. ISO 1600 and 800 were used only as a example how to count long exposure with camera light meter :) What for should I use ISO 1600 with tripod? :)
     
  20. Thank you for your answers, I'll try to make some shots just like Frank said. That seems to be a good idea. By the way - I'm not using digital camera so I don't have to worry about noise etc :)

    Thank you, Michael.
     
  21. "I've never been taught much of how EV and the few other bits and pieces of exposure factor in"

    try this out - a bit dry but well worth pushing throught

    http://www.fredparker.com/ultexp1.htm
     
  22. 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.
     
  23. 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.
     
  24. Oh shoot! this is for digital?
    I was using film only, sorry.
     
  25. 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.
     
  26. I would add just a few observations:
    The purpose of the long exposure times is to allow the earth to rotate enough to make a nice star trail. Pointing the camera toward the North Star will make concentric circles, and directly overhead & somewhat to the South will get straight lines across the sky. (I'm in the Northern Hemisphere.)

    Expose the film for the stars not the sky. Reciprocity adjustment is intended to adjust low light scenes to make them brighter to read better on film. The advice given above to use trial and error starting with about a 5.6 f-stop is probably more helpful. This is actually the opposite of reciprocity adjustment. The intent is to keep the sky black in the picture even after a long exposure that would otherwise make it too light. The theory is that you really can't underexpose the black night sky.

    Bulb setting originated when photographers used air hoses and rubber bulbs to trip their shutters. Squeezing the bulb caused the shutter to open and releasing it allowed the shutter to close again. Timed setting requires you to press the cable release to open the shutter and again to close it. Timed is probably more useful for the night sky. Set the camera on a good sturdy tripod and make sure that it is standing on a good footing. Adjust the camera for the part of the sky you want. Focus on infinity. There is really no DOF so there's no need to sight anything. Do everything possible not to touch your setup again until the photograph is finished once you open the shutter. Bumps and jiggles will show up in the light trails you get.

    Timing to the second is not so critical with exposures that are many minutes long. If you don't mind having to lug something else along, an ordinary kitchen timer will probably do the job. You'll need some kind of small flashlight anyway.

    To get stars over mountains, I think I would set the camera with the mountains at the bottom of the frame around sunset so I could still see clearly enough to get the composition right. I would wait until the twilight sky makes them look right and take my first picture. Then I would adjust the exposure for the night sky without moving or jarring the camera and wait for the stars to rise. Then I would take my starry pictures. I think I would put two pictures together for the finished image. The point of keeping the camera still is to get the pictures as perfectly registered as possible.

    The whole thing would be a lot of fun. Have a great time.

    BTW: Film SLRs usually will not take double exposures because the film advance lever cocks the shutter as it move the next exposure into position. There is no way to cock the shutter independently on the SLR cameras I've seen. I don't know about making double exposures with DSLRs. I think I would prefer separate exposures to try together later so that I would be able to select the combination I like the best without fear of ruining the whole project.
     
  27. Film SLRs usually will not take double exposures because the film advance lever cocks the shutter as it move the next exposure into position. There is no way to cock the shutter independently on the SLR cameras I've seen. I don't know about making double exposures with DSLRs. I think I would prefer separate exposures to try together later so that I would be able to select the combination I like the best without fear of ruining the whole project.
    Albert, almost every film SLR I can ever remember handling has a little button on the bottom plate which would temporarily disconnect the film winding mechanism from the winding lever. You press and hold the little button while winding, and the shutter will reset but the film won't move. Some of the more modern film SLRs have other mechanisms requiring you to go through the electronics; the Nikon F100 is one example.
    Some digital SLRs will do double-exposures in-camera (the D200 is one of them), but it seems to make more sense to do it in post if you have the luxury of time.
     
  28. Oops! Thanks Mark. I only ever used the button to release the mechanism to rewind the film. I hadn't occurred to me to use it to make double exposures!
     
  29. Heh, it's been so long that I forgot that the button was also for rewinding the film!
     
  30. It's been a long time since I used my old 35mm, too. I forgot that once you press the rewind button there is no way to engage the mechanism again except to open the back of the camera. This would double exposures such a nuisance I would use another camera altogether.

    Incidentally, amateur astronomy magazines and books should have a lot of material and examples to help set up and make celestial photographs.
     

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