dyximan wrote:
I Realize These are very general question and depends a great deal on what your shooting. I have a few questions all related to flashes. I see flashes that are rectangular which are photos are, and I see flashes that are round which are lenses are, What are the advantages a Disadvantages to each and is there a particular scenario when you would choose one over the other. I would use them for some portraits and/or outdoor shots when I needed I guess it's called fill Flash when the Sun is behind my subjects. And other times I would like to use it for long exposures to set off the final image to identify it at the end and/or beginning of say a light trail of a cable car etc. I want to thank you in advance for your kind answers please refrain from the snarky ones if you can't come up with a nice one.
I Realize These are very general question and depe... (
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There is not much difference between round and rectangular flashes.
Generally speaking, the round ones are more powerful. They are sort of like small, portable studio strobes. The round part you are seeing is basically just a diffuser. The flash tube behind it might be any shape... wound, half moon, straight. Some of the round flashes are designed to work with powerful external battery packs, to give a lot more shots than is possible with AA. Some of the more advanced and powerful "standard" flash have means of using an external power source, too. External, supplementary power sources also can make for faster flash recycling.
A more "standard" rectangular flash simply doesn't have a diffusion panel installed in front of the tube. You can use it that way, or... in many cases... you can add some sort of light shaping and diffusing device to the front of it, if you wish. These can give your images somewhat different "looks". If buying this type of flash and planning to use a modifier on it, be sure to check what's available. For some popular brands and models there are a lot of accessories being made. But for more obscure brands, it might be difficult to find good fitting accessories or require you to do some adapting to make something generic work. Heck, I've been known to use some white gauze bandage held on with a rubber band to diffuse a flash's output. Works great. Add layers to reduce output, such as when using a standard flash for close-up work where it would otherwise be too powerful.
Some "standard" flash have a built in "zoom" feature, that probably won't be found on any of the round ones. Essentially, this is a small Fresnel lens that sits in front of the flash tube, that's repositioned closer to or farther from the light source to widen or narrow the light output from the flash, so that it's coverage best matches the angle of view of the lens that's being used. There have been manual implementations of this (Vivitar 285 is one example that comes to mind).... and there are more advanced automatic versions (Canon 550EX and 580EX II flashes I use). Typically this allows adjustment for lens in the 24mm or 28mm focal length to 100mm or 105mm range. My Canon flash also have a little built-in panel that can be manually installed to make the flash work with even wide lenses in the 16mm to 17mm range (in all these cases, I'm referring to focal lengths on "full frame"... so make allowances if using on cameras with smaller or larger format sensors where the angle of view of any particular focal length will differ).
I sometimes use an accessory Flash Extender, which is basically just a more extreme version of the built in "zoom" lens on some flash. This mounts a larger Fresnel about 8 or 10 inches in front of the flash, to further narrow the light beam and give the flash more reach. I use it for wildlife and occasionally for sports, when shooting more distant subjects with a telephoto lens. In fact, the shortest lens that can be used with it is 300mm (or around 200mm on APS-C cameras).
There may be similar accessories for the "round" type of flash. I haven't really looked into it. Any flash with a diffuser would need for that to be removable, for these othoer sorts of accessories to be substituted.
Either type of flash should work fine for your purposes. The round type are popular with event photography pros, i.e. for portraiture.
For the night photography use you mention, you need to be able to set the flash to 2nd curtain sync. Be sure to check that your camera and the flash are both able to do this. Below is an example where I used 2nd curtain fill flash with a fairly slow shutter speed while panning with the subject (i.e. "dragging the shutter)...
Notice the "ghosting" that suggests forward (right to left) movement in this image. If I hadn't used 2nd curtain sync, if I'd used standard 1st curtain sync, that ghosting would be on the opposite side and would have made the subjects appear to be moving backward! Standard 1st curtain sync means the flash fires when the shutter first opens. 2nd curtain sync delays the firing until just before the shutter closes. It doesn't matter when subjects aren't moving.... but makes a difference when they're moving and you're using a slower shutter speed (if I recall correctly, 1/30 in the above example).
The round flash also tend to be more expensive, I've noticed. For example, the Quantum Q-Flash and Profoto A1X flash are each around $1200, though that includes a large, rechargeable power supply. In comparison, large flash such as top-of-the-line Canon 600EX-RT costs $450 or Nikon SB-5000 sell for $600. There are similar from third party manufacturers for $200 or less.
BTW, I think I was wrong when I wrote above that the round flash are more powerful! I just compared the Q-Flash with it's Guide Number of 105 feet to the Nikon SB-5000 with a GN of 118 feet (with both flashes at approx. 35mm lens setting and ISO 100). I couldn't find the GN of the Profoto A1X and Canon only lists the 600EX GN at the max telephoto setting (197 feet). No doubt it would be a lot less when set for 35mm lens coverage... probably pretty similar to the Nikon (because that has a 180 foot GN at the same telephoto setting as the Canon flash). It's worth noting, though, that the Q-Flash's GN is probably derived with the diffuser in place (don't know if it's removable). Neither the Canon or the Nikon have a diffuser and no doubt would have lower GN if an accessory diffuser were installed.
Also, all three... the Q-Flash, Canon 600EX and Nikon SB-5000... are able to give 2nd curtain sync. It doesn't appear the Profoto can.
With any of these, for those portraits I highly recommend putting the flash on some sort of flash bracket, off to the side and higher up. This reduces chance of redeye and also usually causes shadows from the flash to be less obvious. You'll need an off-camera shoe cord when using a flash bracket. Note: redeye in people or "eye shine" with animals... which can be different colors... is more of a problem with longer telephotos and flash. I use an extra tall flash bracket when using with anything longer than 200mm (full frame equiv.) There is a wide range of flash brackets available. The smaller, primary one I use is a generic cheapie and it works fine. My extra tall one is a Manfrotto (height adjustable) that cost 2X or 3X as much. But there are others that cost 2X or 3X the price of the Manfrotto.