aperture +shutter + ios

[littleblaksheep]

Hi, I apologize in advance if this has been discussed.
I can't get my settings right, I'm attempting to take photos with that perfect blur in the back round.
I noticed my aperture doesn't go under 4?
Any advice? My subjects are typically my kids.
Rebel t51

[Skirball]

Minimum aperture number will depend on the lens.  I'm assuming you're using the kit lens, perhaps the 18-55mm?  If you look around the front lens element you'll see it says something like f/3.5 - 5.6 (I think it uses the diameter symbol, not f).   That's your minimum aperture size, and it's variable depending on your focal length.  If you're at 18mm then it's 3.5, at 55mm it's 5.6.  If you can only go down to f/4 you're somewhere between that.

"Perfect blur" is something people spend a whole lot of money on.  But there are cheaper options - such as the Canon 50mm 1.8 (around $100) that will give you much more blur than the kit lens.

[littleblaksheep]

Well I have a ef-s 75-300mm lens as well...
I just didn't know of there was like maybe a guide or a general "rule "when using aperture, how much shutter and ios... Does that make sense?

[Skirball · Accepted solution]

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@littleblaksheep wrote:
Well I have a ef-s 75-300mm lens as well...
I just didn't know of there was like maybe a guide or a general "rule "when using aperture, how much shutter and ios... Does that make sense?

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Well, if your goal is to get the most bokeh (blurry background) then the general rule is to always go as wide (lowest aperture number) as you can.   If you're shooting with faster lenses (really wide apertures) then you may not go all the way open for a couple reasons, but with your lenses, open them up.

As to the other variables:

• ISO is an easy one.  Use the lowest ISO you can.  If the photo is too underexposed at your aperture and shutter speed, then you need to raise the ISO.  In general you can be at ISO 100 for outdoors in the sun.  Indoors you're going to have to go higher most the time 400 - 1600 (with a fast lens and decent light - most likely you'll need to go much higher).  Higher ISO = more noise.
• Shutter speed would be the last variable.  If you know what aperture you want (wide open), you're at ISO 100, then there's only one shutter speed that will give "proper exposure".  If you're unsure, just use Av shooting mode.  Set your Aperture wide open, ISO 100, and see if the camera chooses a shutter speed that freezes the action.  If not, boost the ISO.

Your 75-300 will actually give more bokeh than your kit lens.  You'll have to shoot outside, because you want some space.  Go to a park or something where you can have some nice trees or bushes a good 50 feet in the background.  Use the longest focal length that allows you to still shoot at f/4 - probably only 80 or 90 mm.  And get your subject as close as you can with proper framing.  It's not going to be as blurry as some of the pictures you've probably seen, but at that distance you can get nice results.

[littleblaksheep]

That lens minimum is 4 as well... Oh brother

[ebiggs1]

"That lens minimum is 4 as well... Oh brother"

Actually this is the "maximun" aperture not the other way around.  The larger the number defines the maximun amount of light that can be entered into the lens.

The specifications for a given lens typically include the maximum and minimum aperture sizes, for example, f/1.4–f/22. In this casef/1.4 is the maximum aperture (the widest opening), and f/22 is the minimum aperture (the smallest opening).

[littleblaksheep]

Sweet! Well said.. Yes I've noticed with this lens I need lots of space. Thank you so much!

[littleblaksheep]

I'm confused? My aperture doesn't get even close to 1.4? did I misunderstand you?

[littleblaksheep]

I guess that was just an example... Thanks though

[ebiggs1]

Yes, just an example.

It will be the same for your existing lens.  The smallest number (f1.4 or f3.5 or f4) is the maximum aperture and the largest number (f16, f22) is the minium.  Not the other way around.

The things to remember is to use the largest (smaller number) aperture you can.

Get as close to your subject as you can.

Have the background as far away as you can.

Those are the most important part but they are not the entire parts.  The lens itself has a great deal to do with background blur and bokeh.  Also the shape and number of aperture blades can effect this.

For instance, the recommendation of buying a EF 50mm f1.8 lens is going to make this a whole lot easier. Mostly because the working distance can be much less.  But also the fact it has a better "maximum" aperture, of f1.8 (plus f2, f2.8 and f4) is key.