Long (night) exposures

Simmotino

Simmotino

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OK, so I get the whole principle behind calculating for long exposures (using ND filters of varying strengths) to make sure you expose the scene correctly when you can take a 'conventional' reading without a filter (ie when it's light), but how do you know the reference exposure when it's dark?

Do you just guess? Trial and error? Always expose the same scene?

:shrug:
 
I don't quite understand what you're saying, but the way to do it is to take a normal reading, and then adjust your shutter speed by the appropriate number of stops, according to the filter factor. If it's a strong ND filter like 10 stops, then your 1/1000sec exposure becomes 1sec.

That will get you pretty close, then fine tune according to the histogram.

If you have a light ND filter, like 3 stops, then just metering with the filter in place will probably sort it.

And cover the eyepiece during exposure as light can creep in around the mirror and cause streaking.
 
HoppyUK said:
I don't quite understand what you're saying, but the way to do it is to take a normal reading, and then adjust your shutter speed by the appropriate number of stops, according to the filter factor. If it's a strong ND filter like 10 stops, then your 1/1000sec exposure becomes 1sec.

That will get you pretty close, then fine tune according to the histogram.

If you have a light ND filter, like 3 stops, then just metering with the filter in place will probably sort it.

And cover the eyepiece during exposure as light can creep in around the mirror and cause streaking.
Click to expand...

Yep, fully understand that concept. How do you do that when it's dark though? Even without a filter you'd be looking at a bulb exposure, so what do you use as the 'reference' exposure to calculate from when you then add in a filter?
 
Simmotino said:
Yep, fully understand that concept. How do you do that when it's dark though? Even without a filter you'd be looking at a bulb exposure, so what do you use as the 'reference' exposure to calculate from when you then add in a filter?
Click to expand...

Ah, sorry! Got it now. So your question is basically how do you take a night exposure reading.

Well, if it's beyond the camera's metering, with difficulty. But you may be surprised how sensitive the meter is, and if you maybe use spot to pick out a lighter tone from the darkness it may well give you some kind of starting point. Depends on subject and how dark it is of course.

You will just have to experiment, and see what comes up on the LCD and histogram. However, night scenes seem to be very tolerant of big exposure variations, or more correctly, a wide range of exposures often yields a quite acceptable result.

If you do a few test shots under various conditions, you will soon get a good idea for a decent starting point. Take it from there.
 
HoppyUK said:
Ah, sorry! Got it now. So your question is basically how do you take a night exposure reading.

Well, if it's beyond the camera's metering, with difficulty. But you may be surprised how sensitive the meter is, and if you maybe use spot to pick out a lighter tone from the darkness it may well give you some kind of starting point. Depends on subject and how dark it is of course.

You will just have to experiment, and see what comes up on the LCD and histogram. However, night scenes seem to be very tolerant of big exposure variations, or more correctly, a wide range of exposures often yields a quite acceptable result.

If you do a few test shots under various conditions, you will soon get a good idea for a decent starting point. Take it from there.
Click to expand...

So basically, guess :lol:

Thanks Hoppy, muchos helpful.
 
Yep, you could always try taking a reference exposure, but that'll just be guesswork/trial and error as well! Although it'll take less time as the exposures will be shorter, so if you're in a hurry you could give it a go!
 
you can also use the ISO adjustment to get an extra couple of stops worth of metering - what may be a bulb exposure at 100 might just be a 15 second at your camera's highest ISO.
 
TheBigYin said:
you can also use the ISO adjustment to get an extra couple of stops worth of metering - what may be a bulb exposure at 100 might just be a 15 second at your camera's highest ISO.
Click to expand...

Good thinking.

So set it to it's highest ISO. Caluclate form there to get the 'correct' exposure at 100, and then use that exposure to caluclate up for the filter.

Who said photography was difficult eh? :D
 
Simmotino said:
Good thinking.

So set it to it's highest ISO. Caluclate form there to get the 'correct' exposure at 100, and then use that exposure to caluclate up for the filter.

Who said photography was difficult eh? :D
Click to expand...

It doesn't work like that. The meter's sensitivity is not altered by ISO. Only the light level does that.
 
Simmotino said:
Good thinking.

So set it to it's highest ISO. Caluclate form there to get the 'correct' exposure at 100, and then use that exposure to caluclate up for the filter.

Who said photography was difficult eh? :D
Click to expand...

On manual mode, set it at highest ISO and widest f-stop, compose and meter, and see what shutter speed you get. Then adjust for reduced iso - eg 1600 to 100 = 5 stops. Then adjust for change in f-stop between wide open and whatever you've decided on for your pictures composition eg. f4.5 -> f13 = 3 stops. So - if wide open f4.5 at 1600 iso was a 1/4 second exposure f13 @ 100 iso is 32 seconds on bulb as a starting point. Don't forget though - if you're doing long exposures at or around sunset, it's generally getting darker all the time, so you may have to give it a bit longer. This is even more pronounced if you're doing 5 minute exposures with in-camera noise reduction switched on - you can lose a lot of light in 10 minutes!
 
TheBigYin said:
On manual mode, set it at highest ISO and widest f-stop, compose and meter, and see what shutter speed you get. Then adjust for reduced iso - eg 1600 to 100 = 5 stops. Then adjust for change in f-stop between wide open and whatever you've decided on for your pictures composition eg. f4.5 -> f13 = 3 stops. So - if wide open f4.5 at 1600 iso was a 1/4 second exposure f13 @ 100 iso is 32 seconds on bulb as a starting point. Don't forget though - if you're doing long exposures at or around sunset, it's generally getting darker all the time, so you may have to give it a bit longer. This is even more pronounced if you're doing 5 minute exposures with in-camera noise reduction switched on - you can lose a lot of light in 10 minutes!
Click to expand...

Thanks TBY, very helpful :thumbs:
 
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