How to blur a backgruond with flash

[david_mcgillivray]

<p>Hi All<br>

I uses a canon 20D and have a metz 48 Mecablitz flash . What settings do I use and how do I blur the background I generally use a canon 50mm f1.4<br>

Any help most appreciated<br>

Regards</p>

<p>David</p>

[kendrawise]

<p>David, </p>

<p>I can't help you with the flash, as I'm learning on that myself, but one way to get a blurred background is to use a shallow depth of field, which equates to a large aperture. So, if you set your camera to aperture priority, and then open your lens up to f/1.4, f/2, f/5.6, etc. you can blur the background to various degrees. </p>

<p>I took my camera out to the harbor and shot the same picture about 10 times using different apertures just to get a feeling the blurry background produced at different apertures. It really helped me understand how my camera performed under that set of conditions. </p>

<p>Hope that helps. I'm sure wiser heads will be along shortly to talk about the flash. Good luck!</p>

[Alan Johnson]

<p>Look up yor camera's maximum sync speed and open up the aperture till it is just not exceeded. This is the widest aperture can be used with the flash and gives the most background blur.You can get wider aperture still and more blur if your flash is powerful enough by using a neutral density filter, I have an 8x (3stop) ND.</p>

[david_mcgillivray]

<p> I want to know what settings to put my canon 20D on for a kids indoor party (fstop, speed, ISO etc)<br>

regards<br>

David</p>

<p> </p>

[jpo3136b]

<p>With flash, some of the correct settings have to do with distance to subject. As your subject gets closer to the flash (often mounted on the camera), then either the flash power out will need to drop, or the f/stop will need to be closed.</p>

<p>Generally speaking, wider apertures will tend toward a shallower depth of field (some caveats, but generally). So, the flash photos with the f/stop opened up a lot will be more likely to have a blurry background when the subject is within 10'. Yet, those same settings will permit a great deal of light to enter the shutter chamber. So, you would need to safeguard against over-exposing your subject by reducing the power out on the flash.</p>

<p>One of the things you could do would be to set the camera for 100ISO, a modestly wide f/stop (like f/4 or smaller), the camera at about synch speed (say, 1/125). In the area where the kids are going to be, keep the settings like that, and figure up how much flash power you are going to need to expose the subject at a common distance (like, 10 feet).</p>

<p>As long as the flash can kick out enough power to make the exposure okay at that distance, then you know your settings are good. Idea next would be to adjust the power out on the flash based on how close they get to you.</p>

<p>In a fast moving situation, this method can be kind of "iffy" and require a little experience to guess what the correct power out would be on the flash. I would recommend that you try some practice photos at various distances a couple of days before the party starts, so that you don't have to wait until the critical moment to try this out.</p>

<p>This is similar to calculating flash exposure based on guide numbers. </p>

 

[picturesque]

<p>Settings will vary with the environment. Generally, indoors, I'd use ISO 400 (ISO 800 is a bit iffy on a 20D), an aperture of about f4 (generally), and shutter speed of 1/125th. I like to bounce the flash backward off the corner between the ceiling and walls. If the ceiling and walls are white or light colored, you're good. If they are colored, you will need to either gel your flash or correct it in processing (assumes you shoot RAW). Or, get yourself a modifier like a white card (A Better Bounce Card, which you can make) or a Demb Diffuser/Flip It. These are more set and forget, and don't come with white balance problems, but they are not as soft with the light.</p>

<p>The Metz should be on ETTL and you should know how to compensate it and when.</p>

<p>I can't see shooting a kid's birthday party entirely with a 50mm. As for blurring the background, that is a function of selecting the right DOF. The wider the f stop, the narrower the DOF, although other factors, such as subject distance and focal length also make a difference. With the 50mm, you can probably blur backgrounds just fine at f4. Remember that f1.4 gives very narrow DOF, which will be hard to focus accurately. The flash has nothing to do with DOF.</p>

[bueh]

<p><a href="../photo/10912087"><img src="http://d6d2h4gfvy8t8.cloudfront.net/10912087-sm.jpg" border="2" alt="" hspace="20" align="right" /></a> To shoot with a large aperture (=small depth-of-field) and high shutter speeds activate High-Speed Sync on your flash unit. The Metz mecablitz 48 AF-1 is an E-TTL-II system flash and sync speed of your camera is irrelevant. HSS allows flash sync at all shutter speeds. Then it is just same as with taking pictures without flash.</p>

<p>See my example right for more tech. details.</p>

[frank_skomial]

<p>Once you decide what kind of background blur you want, you can use advices already given, as appropriate.</p>

<p>You can have blur caused by fast motion of objects moving in far background where the flash contribution gets diminished and ambient light is used, or blur cused by lens out of focus for those far objects Also, you can fast pan camera, and cause motion blur of static objects in the far background.</p>

<p>So, you can have perhaps 3 types of blur effect with flash in your picture? You decide which one you want or combination of all, with emphases of one perhaps? Blur caused by out of focus lens setting is the easiest to achieve.</p>

<p> </p>

[david_mcgillivray]

Thank you all very much for your help

cheers

 

David