The Digital Photo Guy

Tag: flash

Monday Morning Tip – 6/15/09

by on Jun.14, 2009, under Monday Morning Tips

(Added Photoshoot info at the bottom)

Monday Morning Tip

OK, I know you’re probably sick and tired of ACR (Adobe Camera Raw) so this is the last one for a while. We’ve really only begun to scratch the surface but there’s a limit to how much time I can spend playing with and writing about ACR and I’m sure there’s a limit to how much you want to read.

Today, we cover the Histogram in ACR and, in passing, mention the Exif data and RGB values below the Histogram. BTW, per Japan Electronic Industry Development Association (JEIDA), the keeper of Exif standards, the proper terminology is Exif with a capital “E” and the rest in lower case and it is an ancronym for Exchangeable image file format.

As always, the full MMT is in the Tips & News section and requires a password that is e-mailed to you upon registeration. Registration is simply a means of preserving the value of the MMTs for readers. Without registration, there would bots slurping down all the MMTs and who knows where they would end up.

Quick Tip

When using an external flash, did you know that there is a modeling light feature? A modeling light puts out a low power, pulsed light so you see what the scene will look like when the flash fires. It’s great for detecting where the light and shadow will fall. In the old days, photographers often used Polaroids to get a sense of the lighting and pose but a modeling light is more convenient. Like a Polaroid, it won’t give you a completely accurate view of the final image but it gets you in the ballpark.

To activate the Canon modeling light, press the Depth of Field Preview button on your Canon camera. On current Nikon flashes, only the SB800 and SB900 have modeling lights. They are triggered by a separate Modeling Light button on the back of the flashhead. Check your manual for specific details.

A cool use for modeling lights on strobes is Light Painting. By pressing and holding the button, the flash can be moved around an object to “paint” it with light. This handy when you want a photo of a small object with absolutely no shadows. With Canon flashes, I use the High Speed Sync function to do the same thing but it’s a bit more effort to set up. You can do the same with a Nikon but the modeling light is quicker to set up.

Photoshoot

On Sunday, June 21 (yeah, I know it’s Father’s Day), I’ll be at the Torrey Pines Glider Port with the San Diego Photography Meetup Group. The group is meeting at 10AM but I’ll be there in my RV by about 8AM. If there’s nothing happening that early, you can have a fresh cup of coffee from my RV. I’ve lived in San Diego for nearly half my life and have never been there so it’s about time. You don’t have to join the Group, just show up.

If you’re using Canon, you’re welcome to try my 300/2.8 or 100-400 to see if a long lens is in your future.

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Focal Plane Shutter and High Speed Sync

by on Jun.09, 2009, under Articles

There seems to be some confusion about the definition of a focal plane shutter so, hopefully, this will shed some light on the subject (pun definitely intended). A shutter is simply the camera mechanism that controls the length of time the medium (film or sensor) is exposed to light. A focal plane shutter is a design that places the shutter directly in front of the medium. This is the predominant shutter design in modern digital SLRs.

There are several variations of FP shutter designs but almost all incorporate 2 curtains to block the medium. The photo below shows a modern FP shutter in a Casio P&S circa 1999. As the shutter is released, the metal blades fall down, exposing the sensor. At the precise moment, a second set of blades falls down to block the sensor. At faster shutter speeds, the second set of blades (curtain) closely trails the first such that, in effect, a slit of light moves across the sensor.
Modern Metal Vertical Focal Plane Shutter

Modern Metal Vertical Focal Plane Shutter

This helps explain why digital SLRs have a maximum flash sync speed of about 1/250 second or less. At faster shutter speeds, the blades block off the sensor before the flash is able to fully expose the sensor. In other words, the first curtain opens, fully exposing the sensor. Just before the second curtain descends, the flash must fire while the entire sensor is exposed. Otherwise, a portion of the sensor is covered and produces a dark band across the image.

Older SLRs typically had horizontal curtains made of a rubberized fabric that moved from side to side but the concept was the same. The first curtain moved out of the way to expose the film and, after a predetermined time, the second curtain blocked the film.

Why is all this important today? Most modern flash units have a mode called High Speed Sync (FP Flash) that allows shutter speeds faster than the camera’s top sync speed of 1/125 to 1/250. It works by pulsing the flash to emit a series of flashes as the small slit travels across the sensor. Less expensive flashes like the Canon 420EX have a set pulse rate while more expensive units like the 580EX can be set to specific pulse rates.

When is this important? In a “typical” flash situation where the entire scene is dark, a slower shutter speed is fine. In fact, it is often desired because the shutter needs to stay open longer to capture the background ambient light. What if you want to take an outdoor portrait using a shallow depth of field. Setting your aperture to f/2.8 and ISO to 100, your shutter speed jumps up to 1/2000 second, way too fast for the flash. You could stop down the aperture to f/11 but that increases your DoF and you lose that nice creamy bokeh in the background. This is where FP Flash comes in handy. Set your flash to High Speed Sync (FP Flash) and blast away at 1/2000 second.
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