Shallow Depth of Field 'Bokeh'

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nickl360

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This weekend I will be looking after my girlfriends niece and nephew and I wouldn't mind getting a few portraits of them in the park and then surprise them with a birthday gift later in the year.

I'm planning on using my Canon 30D with my newly acquired Canon 50mm f1.8.

However... I'm quite confused, in order to get a shallow depth of field I need to have a wide aperture (i.e. f1.8) but in good light this will give me a fast shutter speed which isn't really necessary - is it?

Can someone clear this up for me please?
 
nickl360 said:
This weekend I will be looking after my girlfriends niece and nephew and I wouldn't mind getting a few portraits of them in the park and then surprise them with a birthday gift later in the year.

I'm planning on using my Canon 30D with my newly acquired Canon 50mm f1.8.

However... I'm quite confused, in order to get a shallow depth of field I need to have a wide aperture (i.e. f1.8) but in good light this will give me a fast shutter speed which isn't really necessary - is it?

Can someone clear this up for me please?
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the fast shutter spped is needed (in this case) to get the correct exposure. It won't cause you any issues unless you want to get some movement into your shots though
 
You will want a fast shutter speed to get correct exposure as the wide aperture f1.8 lets in lots of light.

If you really needed f1.8 for shallow dof combined with capturing movement then using a ND filter will reduce the amount of light enabling correct exposure with a slower shutter speed.

ISO 50 is also an option on some cameras.
 
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The only other thing I would say is watch your DOF, F1.8 is quite capable of getting less of your subject in focus than you might realise especially if you're up close and they are not facing you square.
 
OK, so it's fine to use an unbelievably quick shutter speed for the cameras correct exposure?

So if I think of it the other way around, I'd of thought 1/125 would of been enough to capture a nice portrait, but this wouldn't give me the shallow depth of field? Correct?
 
SparkUK said:
The only other thing I would say is watch your DOF, F1.8 is quite capable of getting less of your subject in focus than you might realise especially if you're up close and they are not facing you square.
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Good point, well made! I hadn't thought of that, I could have the nose in focus and the eyes blurred!

Would you float around f2.8 then?
 
You can not look at either dof, iso or shutter speed in isolation, they are all linked.

1/125 will give you a fast enough speed to capture a portrait, but in order to get the correct exposure you will need to alter either the dof or the iso. If you were in bright sunlight for example 1/125 will mean you will have very different dof / iso than if you were shooting at the same speed in a more darkened area.
 
nickl360 said:
Good point, well made! I hadn't thought of that, I could have the nose in focus and the eyes blurred!

Would you float around f2.8 then?
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That all depends how close you are, there are a few DOF scales online you can play with to get some idea of how much of your subject will be in acceptable focus.
 
OK thanks guys, I'll have a play about. I want to get one of them holding a daisy and focus on that and have them blurred. I'll see how I get on.
 
You need decide what's important in your shot, and it sounds like the DOF.... so you'll need to pick your aperture to suit the look you want, then a shutter speed to control your exposure, I'm not including ISO here as you'd be best off keeping that as low as you can which should be no issue in bright sunlight. The easiest way would be to shoot in A mode and let the camera control the shutter speed.
 
I normally shoot in Ap and change the ISO or aperture as and when needed.

I'm still very much a beginner and I've not done any portraits before and found it obscene to use such a high shutter speed.
 
Not sure what the issue is with using a high shutter speed? It's not going to have any affect on the aperture/DOF. I've shot a good few portraits at f/1.8 outside in very bright sunlight with no issues. Just pop the camera into Aperture Priority and let it do the work. I can show an example if you wish?
 
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nickl360 said:
So if I think of it the other way around, I'd of thought 1/125 would of been enough to capture a nice portrait, but this wouldn't give me the shallow depth of field? Correct?
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Depth of field depends entirely upon your aperture. You set your aperture to get the depth of field you want, then you set your shutter speed to get the exposure you want.

If that means you have to shoot at 1/8000th, then so be it. :)

The only reason you'd *NEED* to shoot slower speed at wider apertures is if you're either working in very low light, or you need to work within flash sync speeds (but I'm assuming you're not using flash in this case), or you want to catch some movement in your image. In the case of the latter, ND filters as others have suggested will work just fine.
 
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SparkUK said:
That all depends how close you are, there are a few DOF scales online you can play with to get some idea of how much of your subject will be in acceptable focus.
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I use iDof Calc on my iPhone for doing this as needed in the field. Should work on iPad and iPod touch too.
 
Kaouthia said:
Depth of field depends entirely upon your aperture...

<snip>
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I think John knows that's not the only thing that affects depth of field, but the image size also has a very big impact. The image size is varied by the focal length and also the subject distance.

Since your lens will be fixed at 50mm, the distance at which you shoot will make a huge difference, and the closer you go, the less depth of field you will get. Check it out with this on-line DoF calculator www.dofmaster.com
 
Kaouthia said:
I use iDof Calc on my iPhone for doing this as needed in the field. Should work on iPad and iPod touch too.
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That looks quite useful, won't work on my Sony phone though. Even just having a play with the link Hoppy just posted might give the OP a better understanding of it though. Even if it's a just an understanding of how your DOF is affected.
 
SparkUK said:
That looks quite useful, won't work on my Sony phone though. Even just having a play with the link Hoppy just posted might give the OP a better understanding of it though. Even if it's a just an understanding of how your DOF is affected.
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DoFmaster is excellent for this stuff :thumbs:

There are only two factors affecting DoF - f/number and image size (magnification). Image size is obviously controlled by a combination of both focal length and shooting distance and using everything at your disposal you can get DoF from right in front of your nose to the horizon, or reduced to just a few mms at macro distances.

So while image size has the biggest affect on DoF, since that is generally fixed by the faming and what you want in the picture, you're left with the f/number.

Simple rule of thumb is that when you're close-ish, say within a few feet like a portrait, then that's the time when a) you need to be careful, and b) you usually have a decent amount of control with the f/number.
 
HoppyUK said:
I think John knows that's not the only thing that affects depth of field, but the image size also has a very big impact. The image size is varied by the focal length and also the subject distance.
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Of course, I meant in the aperture vs. shutter speed argument. :)
 
HoppyUK said:
DoFmaster is excellent for this stuff :thumbs:
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If you have an iPhone though, don't bother wasting money on the DoFmaster application. Just make a shortcut link to their website. It's the exact same identical interface, but it doesn't cost anything. :)
 
The 50mm f/1.8 is a bit soft wide open as well. If you want piccies that are tack sharp, it's best stopped down to about f/4.
 
If your camera has a DoF button it might be useful when playing with the aperture size to see how it affects the shot...

Andrew.
 
Just set your camera to Aperature Priority and select the widest you can cope with. The camera will adjust the shutter speed for you to get the correct exposure. Adjust ISO if available light is limited and shutter speed is too slow (camera shake/subject movement issues) - though I'm sure this wont be an issue.
 
nickl360 said:
Good point, well made! I hadn't thought of that, I could have the nose in focus and the eyes blurred!

Would you float around f2.8 then?
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Jim.R said:
The 50mm f/1.8 is a bit soft wide open as well. If you want piccies that are tack sharp, it's best stopped down to about f/4.
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I've found that lens works best between F2.8 and F4 for portraits.
Don't forget your camera had a depth of field preview button, press it and you will see the effect your aperture will have on the shot
 
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