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11-25-2010, 06:03 AM   #1
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Long exposures, formula to judge time?

[Posted in Beginners for a reason]

There seems to be several "long exposures" topics on here, but all are very strong on showing examples, and surprising short on the theory side of the skill.

It can't be denied that for the most part exposure can be calculated, all comes down to simple math equation really, and togs everywhere proffer their wisdoms in that regard all the time, so long as it's daytime or inside lit flash work that is...

It might sound strange to you, but I've not been able to find much substance written on how to closely estimate a reliable exposure (open shutter) time for any given night scene.
Get what I mean? Pls ask if you don't.

Yet so many do it! Some regularly too and it appears most attempts are quite successful. (else everyone is not fully divulging their deletes?)
Tell me, what %age do you actually get it right or, passable results?

So what's the big secret? And no, I do not want the usual "it's all experience, just go out and try this or that..." superfluous answers.

All good experience worth listening to and learning from is bloody hard-earned gut feel and mind twisting calcs-in-head that we often flippantly call guesstimations. But we know there's 90% quantitative substance underneath!

I just want the basic constants, variables and formulas to do some sums myself, to be educated and not ignorant on the matter, that's all thanks.

Let's see who knows, and who doesn't. (atm I belong in the latter camp).

Oh, and is there mileage in buying a light-meter gadget for this? Are the good ones (I notice they're not cheap) capable of doing the whole deed for typical darkish night conditions? Or are they no better than the stuff in modern DSLRs?

.R.


Last edited by Hypocorism; 11-25-2010 at 06:12 AM.
11-25-2010, 06:59 AM   #2
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While I might expect that there may be something as analytical as you are looking for, I haven't come across anything like that. What I've typically read is to try exposures of X minutes and evaluate the results then increase/decrease the time, i.e., trial and error. I don't think that there is a one size fits all solution either. For example, I did a lot researching taking pictures of fireworks (obviously at night). My working setup for the basic starting point shooting them now is using a lens between 40-70mm, f-stop between f8-f11, daylight WB, shoot on manual mode with a cable remote, ISO 100, exposures vary between about (got that, about) 1-5sec. Even with all of that, I have to evaluate the images and adjust them based on the histogram as I'm shooting them.

Anyway, I too would be interested in an approach to something more than trial and error for nighttime photography but I think that's a lot of it. Any ideas?
11-25-2010, 07:19 AM - 2 Likes   #3
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Every scene will be different, so there's no one magic set of settings to use, but here's one way to quickly get into the ballpark figure.

Start off by framing the camera so that it's got the composition that you want (shouldn't be too hard, if you're doing long exposures, you'd probably be using a tripod anyway), put the camera into Manual mode and choose a high ISO, say ISO 3200, open your lens to its maximum aperture, say F2.8, and then choose a shutter speed, say 2 seconds (the reason why I suggest guesstimating a shutter speed, is because in the darkness, there's a chance the camera's light meter won't be much help at all). Look at the resulting image, and if it's too dark, choose a longer shutter speed. If it's too slow, choose a faster shutter speed. Don't worry if the image looks crap at this stage due to all the noise.

So, lets assume, that you've found the shutter speed that gives a good image. So at ISO 3200 and F2.8, you get a good exposure at 1 second for that certain scene. From there, you can then calculate how to get that same exposure by changing ISO and aperture to what you want.

You start with: ISO 3200, F2.8, 1s.
Because you want a clean image with less noise, you want to shoot with a lower ISO, say ISO 200. You change ISO to 200. But since ISO is 4 stops less than ISO3200 (ISO3200->ISO1600->ISO800->ISO400->ISO200), to compensate, you'll need to increase the shutter speed by 4 stops to 16 seconds. (1->2->4->8->16). Hence you can use ISO 200, F2.8, 16s.

But wait, F2.8 doesn't give you the depth of field that you want. So you change the aperture to F11. But since F11 is 4 stops less than F2.8 (F2.8->F4.0->F5.6->F8->F11), you'll need to increase the shutter speed by 4 stops to 256 seconds to compensate (16s->32s->64s-128s-256s).

And hence you end up with a final exposure of ISO 200, F11, 256 seconds for that certain scene.

Basically, all this is doing is using the relationship between the fundamental concepts of aperture, ISO and shutter speed.

Hope that helps

Last edited by pop4; 11-25-2010 at 07:30 AM.
11-25-2010, 08:04 AM   #4
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QuoteOriginally posted by blackcloudbrew Quote
While I might expect that there may be something as analytical as you are looking for, I haven't come across anything like that. What I've typically read is to try exposures of X minutes and evaluate the results then increase/decrease the time, i.e., trial and error. I don't think that there is a one size fits all solution either.

... noted - and same here btw ...

Anyway, I too would be interested in an approach to something more than trial and error for nighttime photography but I think that's a lot of it. Any ideas?
I like that you use the term "approach", and allow me to prefix the word "analytical" in front too, then it's clear that you sensed that the crux of this exercise is about seeking mostly exactly that from the collective ether-brain here;
ie. some solid, real, concrete guidelines that people can actually use and benefit from to have a more than decent chance at constructive night scene type photography for themselves, guidelines and approach 'rules' that can stand the test over the usual rough and ready t&e bandied opinion.

The great thing is that the cameras we all typical use these days can do a pretty good job out in the dark where life can still exist.
And like your fireworks example, to me anyway that's a very typical night scene that people tend to want to capture.

Attempting to describe; I mean that it obviously has d% of darkness element on the given night (such a some or much urban 'ambient' lighting, moon-phase v cloud-cover estimatable factors, perhaps many bright stars to contrast a clearer sky blackness too, etc), in contrast to n% of nearer to camera standout flare-bright explosives in action, 'fairly' predictable in light output, and possibly z% reflected light stray off that onto people, buildings, whatever... to contend and consider too.

Wait. I should not have said the fireworks would be fairly predictable there, obviously they are not. The unexpected and the huge variety differences in light output and colours range of each explosion is their appeal. So how does the cameraphile anticipate what's coming? they can't. Next Q: how does he/she judge or calc the "just right" settings without chance to experiment or take test shot in maybe 1 second so as not to blow it?

John & Jane Photog do not have said "experience" - nor do they live in caves and guess their way through life, they expect, rely on and need basic modern-science guidelines.

To blackcloudbrew: Your experience here would no doubt have described that scenario better, so pls excuse, I was just trying to define some possible constants and variables to clarify (or possibly confuse further?) the debate.

Anyway, so where does one start, considering you the hard earned f'works specialist never left your phone number that is?

How do those elements transfer into tangible manual camera settings so Joe & Jane Tog don't blow that once only chance for capturing the experience or night scene - whatever and wherever? Fish that got away tales don't really make ideal impressions when posted to Flickr or P.F!

And one chance it often is too, so T&E has to stay at home.

.R.


Last edited by Hypocorism; 11-26-2010 at 12:00 PM.
11-25-2010, 08:30 AM   #5
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Guestimate based on experience, then adjust according to reviewed image. There is no magic.
11-26-2010, 11:22 AM   #6
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I suggest you go into a used book store, check out for photographic books specifically written for available light photography. There are available a number of charts that give you a reasonable starting point for your exposures.

As for fireworks, try this for starters and adjust for your taste. It's much easier when you can look at the first few exposures while you are still at the scene as you can with a DSLR. Focal length adjusted from 28mm on film.
  • Tripod
  • ISO 400
  • f/8
  • Bulb
  • Focal length 18mm
  • Adjust so that the highest firework is in the field of view.
  • Do not have any other light sources in the field of view to avoid flare
11-26-2010, 11:56 AM   #7
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QuoteOriginally posted by Canada_Rockies Quote

I suggest you go into a used book store, check out for photographic books specifically written for available light photography. There are available a number of charts that give you a reasonable starting point for your exposures.
Good idea, thanks I'll endeavour to do that. Old books often have basic info in formats that's rare these days and not all is ever put online.

.R.
11-26-2010, 12:52 PM   #8
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It becomes a much less exact science with very low levels of ambient light, and not even a light meter would be of much practical use in this application. Previous posts are pretty much explaining my own approach, but there are some fundamental things I take into consideration.

Testing exposure of an image with high ISO shots before going the full hog with a long exposure is what I do often, but the 'calculated' shutter speed after reducing the ISO down to 100-400 is not critical - there is a significant range of time the exposure can be without blowing out the foreground unless the foreground is lit by relatively strong ambient light leaking into the scene.

For example, many of my 45 minute star trail exposures had foregrounds that were near pitch-black, but were lit intermittently by the gentle sweeping of car headlights over the scene. I figured to 'tolerate' a total of 3 sweeps of these headlights over the scene before I thought they would burn out in the exposure with the settings I had at the time (f/5.6 ISO 250), so before the 4th vehicle approached, I'd end the exposure. If these cars never were a feature of the foreground lighting, I'd have been able to tolerate a 5 hour exposure and not worry about foreground exposure problems, since stars move and don't contribute considerably to the exposure of the rest of the scene.

Fireworks can generally be captured between 5-15 seconds quite adequately. Less for fast-filling, intense fireworks and more for varied firework series that you want to fill the frame with. ISO 200-400 and f/5.6-8 is a good starting point for me, but it depends a lot on the foreground lighting and the intensity of lighting from the fireworks.

Hope this all helps rather than confuses.

11-26-2010, 03:53 PM   #9
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I am a little confused as to what it is you are looking for. On one hand it looks like you are looking for a sunny 16 rule but for night use. Then it also looks like you want to measure (as in use a light meter) so you can then decide what parameters to use.

I donít know that is would be possible to use something like a sunny 16 rule for night type photos as the range of average brightness in this kind a scene is usually greater then a day type scene.

With film you could start with some number from a light meter then use some reciprocity table for your best guess for your first shot. Then back to the table for your bracket shots. Take the film and develop it and hope you had a good one. Light meters are just not all that acute at these low light levels. To be fare to them they are not made to be used as such low levels. Then reciprocity tables have a whole plethora of variables to them.

With digital it is much easier. No reciprocity tables for one. With digital you also get one of the best light meters made for your camera. It meters the light over the entire DR of your camera and over the whole frame at the same time. It provides this in a display that can show you the parts of the frame near or below black and near or clipped white. You also get a histogram with it for free. I wish in the days of film I had such a light meter. If you had time to use some external light meter then I donít see why you would not have time to use the camera.

There also appears to be some confusion on what it is that is being calculated for exposure. With fireworks you are mainly using ISO and aperture for exposure. This is so you donít get just white streaks or no fireworks at all. How long to leave the shutter open is dependent on how many shells you get in one frame. To many and it is just a mess of light to few and it is boring. This is always changing thru out the show so it needs to be adjusted. With other night scenes it is more a typical trades you make for any day scene.

There are some sites that have charts for a best guess for when you may only get one chance. Here are 2.

Tips > Exposure > Light & Exposure Values

Things like meteors or other events you may not be able to meter.

Photographing the night sky

DAZ
11-28-2010, 12:43 PM   #10
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QuoteOriginally posted by pop4 Quote
Every scene will be different, so there's no one magic set of settings to use, but here's one way..........
Sounds simple enough. Thanks for the great advice.
11-29-2010, 04:03 PM   #11
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You need to become familiar with the concept of EV and then get yourself an EV chart. That will be the best guide. Full moonlight is around -3 to -2 EV for example. After a while, you won't need the chart and can estimate more accurately. You will still find yourself fine tuning by trial and error anyway.

Jack
12-20-2010, 06:48 AM   #12
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[A belated followup to this request I made a while ago.]

First, thanks to all who contributed constructive advice and links; esp. Daz, pop4, blackcloudbrew, Canadian Rockies, Ash, jbinpg.
All much appreciated -- although some naughty weather intruded on the best laid plans of mice & [camera]men on a recent excursion for me, opportunity coming again soon for putting it to test, I hope.

Fwiw: Perchance I just tripped over this "Cheat Sheet" Card-Guide that looks like it might be useful and am a bit tempted to order one, is available from eBay or its Home site for about same price:
Day & Night Photography Exposure Guide -- by FotoSharp
GUIDE~Pentax K20D K100D K200D K2000 K-m K-7 K-x K-5 K-r (eBay item 110625403812 end time 23-Dec-10 18:28:58 AEDST) : Cameras Photo

Anyone have experience or comments on this company's Products? Like, IYO does it seem worth the twenty bucks + del., ...

They seem to offer quite a range of ready-printed out "field reference" cards too that might prove handy thing™ to stoke the neurons when out & about, durable laminated too.
(realistically I can't see the bother of trying to gather the info, format, print and laminate for the price asked.)

.R.

Last edited by Hypocorism; 12-20-2010 at 07:15 AM.
12-20-2010, 09:34 AM   #13
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I'm not familiar with this company's products. I think anything that might "stoke the neurons" is not a bad idea. You can soon find out how to interpret the suggestions of exposure. If you have the $$ go for it.
12-20-2010, 10:39 AM   #14
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QuoteOriginally posted by Hypocorism Quote
...Anyone have experience or comments on this company's Products? Like, IYO does it seem worth the twenty bucks + del., ...

They seem to offer quite a range of ready-printed out "field reference" cards too that might prove handy thingô to stoke the neurons when out & about, durable laminated too.
(realistically I can't see the bother of trying to gather the info, format, print and laminate for the price asked.)

.R.
I used to have a Pentax Spotmeter V, sometimes useful for long exposures. Older spotmeters like that had a meter calibrated in Ev, then a set of wheels on the side to give you actual camera settings. I found the wheels on the side nearly as useful as the whole spotmeter, and this chart is the equivalent of them. Most of the time I wanted to know the lighting conditions after taking a shot, trying to figure out how I could have done better.

I think trial and error, tempered by experience, is always going to be an element of long exposures. The camera's meter is only rated down to Ev 0 or Ev 1 depending on model, and lighting is often very uneven across a scene in small bright spots. A good image often requires part of the frame to be blown out and part completely dark, and the photographer has to decide those things. A meter or a chart might give you a good starting point and a chance to be ready quicker, but be ready to make changes yourself.
12-20-2010, 06:11 PM   #15
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Just start with a very high ISO and a moderate aperture and do test shots, adjust a bit up or down until you hit it. You can usually get it in two or three shots; use the histogram to help. After that it is very simple in-your-head math to adjust the shutter speed for the ISO and aperture you want to shoot at. Just remember that the longer the times get the less need there is for precision on the timing. After you've done it a couple of times you'll wonder why you ever imagined there could be anything difficult about it.
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