technique

full-frame vs crop-sensor comparison :  depth-of-field & perspective

When the differences between full-frame and crop-sensor cameras are discussed, there is an inevitable question about whether the crop sensor multiplies the focal length. Whether a 50mm lens on a crop-sensor acts like a 75mm lens (on a 1.5x crop sensor) or 80mm lens (on a 1.6x crop sensor).

The answers given on the photography forums are confusing – yes, the focal length effectively increases. No, it doesn’t. Two polar opposite answers. The discussion (which tend to devolve into arguments) are convincingly made for both sides. The reason is because the topic is a complex one … and therefore the answer is (kinda) complex too.

One argument goes along the lines that the crop sensor is just that, a crop. An enlargement. That nothing changes – you just get less of the scene. And that there is no “equivalent focal length” when you go to a crop sensor camera. But what really happens is more complex than that.

With this article, I want to help analyze what happens when you change lenses between a full-frame camera and a crop-sensor camera. And we’ll analyze whether there is actually an equivalency between certain focal lengths, when using a crop-sensor camera. In other words, whether your 50mm lens becomes “equivalent to” a 75mm or 80mm lens when used on a crop-sensor camera.

Since this article ended up being a long meandering discussion, I thought it best that we start with the final summary. Just to save the impatient people some work.

Summary:

Yes, a 50mm lens does indeed behave like an equivalent focal length of a 75mm lens (on a 1.5x crop sensor), or an 80mm lens (on a 1.6x crop sensor) … however, the depth-of-field increases by about a stop.

Yes, a 100mm lens on a crop-sensor camera will give you the same perspective as a 150mm / 160mm lens (on a full-frame camera), if you don’t change position … however, the DoF increases. (i.e., less shallow DoF)

But let’s discuss this with some images:

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using the Profoto B1 portable flash at a wedding

With wedding photography, there are nearly inevitably time-constraints. It is therefore imperative that you, as the wedding photographer, are able to keep everything running as smoothly as possible on your side. Which implies that it is important that you (and your equipment) are adaptable. And it is also hugely important that your gear is easy to set up, and very reliable.

Karissa and Rory’s wedding was the first where I pulled out the Profoto B1 battery powered flash (vendor). I’m even more impressed with it now, than I was when I first tested it for my review: Profoto B1 500 AirTTL battery powered flash.  (And if you’d like to buy my previous AcuteB 600R kit, let me know.)

When using additional lighting, you ideally need a few things from your lights:
power! 
– and yet, a delicateness to the light when necessary.
speed of use is essential.

At 500Ws, the Profoto B1 dumps sunlight-levels of light, but you can pull it down 8 stops, to where the light can be used in subtle ways.

With off-camera flash, I’m mostly working with a specific distance, and then manual flash makes sense. The  Profoto B1 (vendor) offers TTL as well, and this might seem superfluous to some. But it really makes it easier and faster to get to correct exposure. You can do an initial exposure via the TTL mode, and then switch to Manual if your exposure is correct. This gives you the speed of TTL flash, and the consistency of Manual flash.

Here are more images from this wedding, with examples shot with the Profoto B1, as well as other images using various types of light ….

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various scenarios: balancing flash with ambient light

Adding flash to ambient light – its’s a topic that can appear to be confusing. With advic that ranges from under-exposing the ambient light by a stop or two … or dialing FEC down for fill-flash, or advice that you should be metering for the background … it all appears confusing and contradictory.

What we do, and the thought-process we step through, depends on the (lighting) situation we find ourselves in. There isn’t one blanket do-all method. No single piece of instruction that will fit every occasion.

So let’s try to work through various general scenarios, to see how we’d approach each one:

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finding interesting available light & white balance options

It’s always a feel-good moment to discover interesting available light while out on a photo shoot. Something unusual to add a new flavor to a different sequence of images.

While photographing a model with Tilo Gockel and Mike Silberreis (both from Germany on a visit to NYC), we started off with off-camera flash to help with the strong sunlight. (You might remember Tilo from a recent guest article on product photography on a budget.)

Then, while positioning Olena, I saw part of her dress had a patch of bright light on it. Turning around to see where this came from – I expected sun flare from nearby building window – I saw that it was actually the sun reflecting off a traffic sign right next to us. The light that was reflecting off this traffic sign was pretty hard, but had an interesting specularity, yet appeared flattering. So we shot an entire long sequence here, ditching the off-camera flash.

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using tele-converters: extra lens compression for tighter portraits

One of the techniques to have your subject really stand out from the background, is to use the longest focal length on your 70-200mm telephoto zoom. One of the first things I do, is to zoom to maximum focal length, and then step backwards to find the composition … and then only zoom wider if necessary.  Doing it this way, forces you to use the longest focal length. This compression focuses attention on your subject by creating separation from the background.

To extend the range of my 70-200mm f/2.8 lens, I always keep a 1.4x teleconverter in my bag. This extra 1.4x boost in focal length gives me reach, or as in this case, that extra compression to help with my photograph’s composition:

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Light Blaster: image projection effects for creative backgrounds in the studio

Working with an idea in mind – a moody B&W portrait with a stylized cityscape as background. Using the Light-Blaster again in the studio, this final image was a progression of that idea. I knew I wanted to use the cityscape background of one of the metal gobos that came with the Light-Blaster kit.

Because I wanted the final photo to be black and white, I set my camera to Monochrome so that I’d have a good idea during the shoot what the final image would look like. Since I shoot in RAW, the image would pull up in color the moment I start my post-processing. Then I reverted it to B&W again, and edited it for contrast and for the vignette you see in the final image at the top.

The first step of the shoot was to set up the Light Blaster, then get the exposure, and then figure out the lighting on our model, Priscilla.

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flash freezing the action at slow shutter speeds  (model: Oktavia)

Does flash freeze action when shooting with slow shutter speeds (in low light)?
The answer is … maybe. Perhaps. It depends.

It is difficult giving a definitive answer because it depends on the scenario. In short – if your subject isn’t lit by much available light (with ambient light 4 stops or less than your flash exposure), then flash will freeze the action … if there is no bright background. Probably. But it depends on the type of movement, and how critical you are about image sharpness.

See? We just can’t quite get away from those qualifiers – perhaps / depends / probably. But let’s jump into this and see when flash will freeze the action, and when you’re likely to be succeed.

The photo above, of Oktavia dancing, was shot at  1/10 @ f/2.8 @ 1600 ISO
At 1/10th of a second, the flash did freeze her movement.

You can see the background lights streak as I moved my hand-held camera to try and keep up with her movements. I was trying to hide the flash behind her, but I liked the effect here. You can also see the city lights streak through her arm as she moved.

Let’s quickly look at the pull-back shot to see how the flashes were set up, and then we continue the discussion on whether flash freezes action …

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Using your lens’ bokeh as a design element

In previous articles we could see how a fast 85mm can be used for shallow depth-of-field to shoot nearly anywhere by melting away the background. There’s another aspect to this – the bokeh of the lens. The bokeh is a reference to how the quality of the background blur is rendered by a lens. It can be smooth, or have “jittery” patterns to the edges of objects, and the highlights.

Do note though that bokeh and shallow depth-of-field are not quite the same thing. While the DoF / choice of aperture does affect the appearance of the bokeh of a lens, the shallow depth-of-field look isn’t “bokeh”. Similarly, you can’t do something like “add more bokeh”. Bokeh is the quality of that background blur. It’s mostly an aspect of the lens design.

Now, very often, when a fast prime lens is used wide open, there’s a kind of swirly feel to the background blur – and if you’re aware of this, and find an appropriate background, it can really accentuate the portrait.

The image at the top of Jen & Corby, was shot at f/1.4 and you can see how the background behind them has a distinctive circular swirl to the out of focus high-lights.

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creating foreground bokeh effects in-camera

The closer you move to a foreground object, the more it’s shape and color and opacity will affect the image … in unpredictable ways. It’s a well-established technique then to create unusual color splashes and shapes in the image by creating flare highlights. It is often called “foreground bokeh effect”.

Ulorin Vex is an unusually photogenic model that I have photographed on a few occasions. When Ulorin visited the East Coast again recently, I jumped at the opportunity to meet up with her again and play in the studio. Her striking looks and colorful latex dresses would work perfectly with this technique – the random kaleidoscope patterns and colors wouldn’t be incongruous.

With a standard lighting setup in the studio, using a beauty dish, I also added an extra light to throw light directly towards the camera. I then held up various colored objects right in front of the lens – a colorful translucent plastic flower with colorful petals and leaves worked best. Shooting through an opening between the petals and leaves of the decorative plastic flower, all kinds of interesting random patterns appeared. It was unpredictable, and that is what made the effect interesting in part – you wouldn’t quite know what you’re going to get.

If this effect appeals to you, it would make sense to collect all kinds of objects to try out – glass elements and prisms work well too. Anything that will create a pleasant visual surprise.

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boudoir photography and the 50mm lens

With shooting space often times so tight for boudoir photo sessions, there is the temptation to use a 50mm lens for tighter headshots on a full-frame D-SLR. Instead of stepping back a bit and using an 85mm lens or longer, a bit of visual laziness comes into play, and we rely on the 50mm lens too much. It really is too short a focal length for a tight portrait. I think many photographers are even too in love with their 50mm lenses, and use it without thought of how this would distort someone’s face when used too close to their subjects.

I totally understand the need for compromise. Quite often the angle we need to shoot from, dictates a shorter-than-ideal focal length – whether because of the shape of the room, or the direction of the light. This still doesn’t make the 50mm a good lens to shoot tight portraits with. A longer focal length would still give you more flattering results.

The example photographs in this article are by Petra Herrmann, Kansas City boudoir photographer. Petra also maintains the Business of Boudoir, website which has a lot of useful info for boudoir photographers.

She used a 50mm lens for these images, but kept to half-length as the closest distance to photograph her subject. The 50mm really is more of an environmental portrait type lens, rather than a tight portrait lens.

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