I need help setting the f-stop for long shutter speeds.


Farris 14 24
3 Dec 2005 7:43AM
I tried to figure this out on my own but I can't get it. I know the longer the shutter speed, the more I need to close down. Is there a formula to figure this out?
If I wanted to take a photo that has a shutter speed of say, 6 sec. how would I adjust the f-stop to get a good exposure?
Farris

Join ePHOTOzine for free and remove these adverts.

sillyconguru 15 4.4k
3 Dec 2005 7:46AM
It would depend on the available light and the ISO speed.
spaceman 15 5.3k 3 Wales
3 Dec 2005 7:49AM
It also depends on the camera - many will do it for you.
ksh 15 467
3 Dec 2005 8:00AM
Have you got a (P) program auto mode? if you have use that mode, set the shutter speed you want and evrything else will be set to match
sillyconguru 15 4.4k
3 Dec 2005 8:02AM

Quote:set the shutter speed you want and evrything else will be set to match


Not if the ambient light is too bright though.

An exposure of 6 seconds @ f22 (at ISO 100) would be EV 4.5, this would be quite dim lighting (something like a daylight lit room interior).
peter shilton 15 1.1k England
3 Dec 2005 8:07AM
Although the answer you may want is that one stop more on the shutter speed is one stop less on the aperture.

Double the shutter speed exposure and you need to go down one stop on the aperture.
barnowl 14 697
3 Dec 2005 8:09AM
For every whole stop e.g. f5.6 to f8 the shutter speed will halve. 1/125 @ f5.6 will become 1/60 @f8 and so on.

If you get to the point where the lens is at it's minimum aperture and the shutter speed is still too fast for your purpose them you could fit a ND filter which will reduce the amount of light . These are available is various grades.

Also by varying the ISO you can have a similar effect on the shutter speed. Higher ISO will give faster shutter speed.

Gary
cambirder 16 7.2k England
3 Dec 2005 9:49AM

Quote:Have you got a (P) program auto mode? if you have use that mode, set the shutter speed you want and evrything else will be set to match


P mode wont help, you need to use Tv. set the speed and the f-stop will be sorted by the camera.

For 6 seconds you may also need to use a ND filter, otherwise you may get servere over exposure.
Farris 14 24
3 Dec 2005 10:32AM
Thanks everybody. I will give some of this a try. I can't set the camera on auto though. It's for a Photography class and first day she very politely said "auto is dead to you". I'll give some of these other things a try though.
klewis 15 1.9k 1 United Kingdom
3 Dec 2005 11:48AM
even in manual mode the camera will provide an exposure value for you in the viewfinder. It's just a question of balancing the shutter and aperture values until the camera tells you the exposure is correct.

Bear in mind that the correct exposure that the camera gives you is for an 'average' scene, so if you are shooting whites that really need to be white you will need slightly more exposure. For true blacks you will need less expsoure
keith selmes 16 7.4k 1 United Kingdom
3 Dec 2005 12:08PM
Looks like you have a Canon AE1 with a maximum shutter speed of 2 seconds and TTL metering.
It would be useful to have a light meter, preferably analogue where you can see the relationship as you change settings.
As it is, if you set the shutter for 2 seconds, and adjust aperture until the light meter is happy, you can then work out the correct exposure for 6 seconds, much as described above.

For example, if at 2 seconds you have f/16, then at 4 seconds you need f/11 and at 8 seconds f/8.
I don't think you'd have half stops, and 6 seconds is in between, so in this case you could experiment with exposing slightly over or under, or adjusting the light or filter to get to a whole stop.
Hope I got that right, the brain is tired. Just in case, useful site here
Has EV scale etc.
sillyconguru 15 4.4k
3 Dec 2005 12:14PM

Quote:..if at 2 seconds you have f/16, then at 4 seconds you need f/11 and at 8 seconds f/8.


You might want to check that again Keith.
keith selmes 16 7.4k 1 United Kingdom
3 Dec 2005 12:33PM
rofl at me.

the nice meter dial says
1..11
2..16
4..22
8..32
15..45
elowes 15 2.8k United Kingdom
3 Dec 2005 1:32PM
Can I suggest, without being patronising, that you get a book about the basics of photography.

This is first level photography covered in the basic manuals and by umpteen books. You will not learn what you need by starting a thread on f stops. If you don't know this you don't know a load of other things you need to know.
spaceman 15 5.3k 3 Wales
3 Dec 2005 2:42PM
So there.

You've an eye for a good shot, the technical stuff will come with practice.

Sign In

You must be a member to leave a comment.

ePHOTOzine, the web's friendliest photography community.

Join For Free

Upload photos, chat with photographers, win prizes and much more.