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Taken from a thread here, http://dpnow.com/forum2/showthread.php?t=6138 regarding critique on a Macro photograph of a flower, long term forum member Ash replied with a useful insight to focal length, apertures etc in a nice easy to understand way.
As such, I agree with Ash and think it would be useful for others to have look at, especially newcomers to photography.
Firstly if your out in the field, tripods are not always convenient.
But for this exercise lets just say that it is convenient.
By using a tripod this will mean:
you can close the aperture blades within the lens smaller (higher f number) which will give you more depth of field ( more things in focus).
But by doing this you are reducing the light entering the lens so you need a longer shutter speed to let the required amount of light into the lens to expose your image. Hence the need for a tripod because you cannot hold the camera steady for a long shutter speed.
Ok now your saying well whats a long shutter speed, well without going on all night, if I was shooting at 28mm thats like as wide as a normal lens will go, I would not go below 1/30 sec without vr or image stabilisation. As a guide match you shutter speed for your focal length 'at least' and you will not go far wrong.
Using a high iso number will mean you can attain a faster shutter speed but at the expense of noise or grain on the final image.
Just think of, APERTURE as light entering the lens.
SHUTTER SPEED as how long it will expose the image for.
and ISO as how sensitive you want to make the image to light, but at the expense of noise.
Its taken me 5 years to get my head around what Ive said above and be able to use all three aspects comfortably together in manual exposure mode on a camera. If you understand what they do then you have cracked it, then there's all the other stuff like white balance, flash etc.
Ive tried to make it clear for any novices on the forum, which I once was, I no how confusing it is, Ill share what ive learnt, just ask.
For an example, this was taken at 150mm f2.8 @ 1/125sec iso 100 handheld.
Because i am already at 150mm, ive instantly decreased the depth of field to a very small amount, and because I am so close to the caterpillar this has reduced this even more, even if Ide have had the light to close the apperture to f22 the whole of this image would still not be in focus.
This is the problem you have with long focal macro lenses, but they have there uses.
I would purchase a macro lens between 50 & 70mm if you are just getting your first macro lens. And you dont have to spend alot to get exceptional results.
As such, I agree with Ash and think it would be useful for others to have look at, especially newcomers to photography.
Originally posted by ash
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Firstly if your out in the field, tripods are not always convenient.
But for this exercise lets just say that it is convenient.
By using a tripod this will mean:
you can close the aperture blades within the lens smaller (higher f number) which will give you more depth of field ( more things in focus).
But by doing this you are reducing the light entering the lens so you need a longer shutter speed to let the required amount of light into the lens to expose your image. Hence the need for a tripod because you cannot hold the camera steady for a long shutter speed.
Ok now your saying well whats a long shutter speed, well without going on all night, if I was shooting at 28mm thats like as wide as a normal lens will go, I would not go below 1/30 sec without vr or image stabilisation. As a guide match you shutter speed for your focal length 'at least' and you will not go far wrong.
Using a high iso number will mean you can attain a faster shutter speed but at the expense of noise or grain on the final image.
Just think of, APERTURE as light entering the lens.
SHUTTER SPEED as how long it will expose the image for.
and ISO as how sensitive you want to make the image to light, but at the expense of noise.
Its taken me 5 years to get my head around what Ive said above and be able to use all three aspects comfortably together in manual exposure mode on a camera. If you understand what they do then you have cracked it, then there's all the other stuff like white balance, flash etc.
Ive tried to make it clear for any novices on the forum, which I once was, I no how confusing it is, Ill share what ive learnt, just ask.
For an example, this was taken at 150mm f2.8 @ 1/125sec iso 100 handheld.
Because i am already at 150mm, ive instantly decreased the depth of field to a very small amount, and because I am so close to the caterpillar this has reduced this even more, even if Ide have had the light to close the apperture to f22 the whole of this image would still not be in focus.
This is the problem you have with long focal macro lenses, but they have there uses.
I would purchase a macro lens between 50 & 70mm if you are just getting your first macro lens. And you dont have to spend alot to get exceptional results.
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