PERFECTING THE PANORAMIC

It’s getting easier to make panoramics with today’s cameras. Some will actually do the stitching together for you without the need for software. But unless you take control of the process, you may be selling yourself short on results.

Here is a checklist you can follow in preparation for shooting your panoramic. It may look a little daunting, but it will become old hat with a little practice:



• Arrive Early   In order to get through this checklist, you’ll need the extra setup time before the light changes!
• Use a Tripod   A panoramic is comprised of a series of adjacent photographs stitched together in software to form a single wide-angle image. In the stitching process, the software does its best to match adjacent images seamlessly, but there is usually a bit of twisting required to match them perfectly. This requires cropping the final panoramic. Unless the individual images are shot with the camera absolutely level, the twisting and subsequent cropping may get to the point where much of the scene is lost.
• Level the Tripod and Camera  I have a bubble level on the base of my tripod which I use to get the legs levelled up first. I also use a bubble level that slips onto the camera’s hot shoe, which I use to do fine levelling adjustments. The reason for using both is that uneven legs may give me the impression that I have a level camera at one position, using the hot shoe level. But as I pan, I would likely see the level drift off centre. Once you have tweaked both the legs and the pan/tilt head, try panning through the intended range of your panoramic to ensure you have optimized both.
• Set the Camera to Manual (M) mode   Imagine you’re shooting a panoramic made up of photos that have dramatically different light content. In any mode but Manual, each photo would be exposed differently because the light metering system built into your camera tries to set the exposure automatically to an average 18% grey level. In this scenario, the panoramic wouldn’t look right because the inherently darker scenes would be forced to look lighter compared to the others, resulting in a patchy-looking result. Sure, you could try matching the exposures in software before stitching, but it’s easier to get it right in the camera. I pan the entire scene first, using the digital meter to set a shutter speed/aperture combination that averages a normal exposure. As a result, some shots will be over-exposed slightly, others under. As long as the histograms for all photos don’t show any clipping at the black or white points, you’re OK.

  

  The camera's digital light meter. Zero is optimal exposure.

  

 

 

 

 

 

 

•  Set the Camera ISO setting to a fixed value  Some cameras have Auto ISO setting. Per the last point about exposure, ensure you choose a fixed value (eg. 200) rather than Auto.
• Set the Camera to manual focus  Most SLR lenses have a switch allowing you to disengage the motor that automatically focuses your lens before you take a shot. For panoramics, set it to manual focus (MF). The reason for this is that as you pan to take each of the shots, the camera may refocus on something close in or far away, especially if there’s an object in one of the shots that is prominent. That could result in uneven focus across the panoramic. Pick one focus setting that works for the whole panoramic and leave it there.
• Take the Camera out of Auto White Balance  Similar to the argument in the last two points above, you don’t want the camera to change the colour balance as you pan because of changing content. Choose one of the presets instead of Auto. For instance, if shooting on an overcast day, use the Cloudy Bright setting. If shooting an indoor scene under fluorescent lights, use the Fluorescent setting. If you have access to a photo editing program that allows white balance adjustment, don’t worry about what preset you choose, because you can correct all the shots by the same amount if the preset you chose results in wonky colour.
• Overlap the Photos  Panoramic software uses artificial intelligence to look for similarities between adjacent shots then join those features seamlessly. In order to provide those reference points, you need to provide overlap in content between adjacent shots. I typically overlap by 25%. If I start my panoramic on the left end then take subsequent shots by panning left to right, this means that my second photo contains the rightmost 25% of the first photo. I’ve made marks on my tripod head that tell me how far to pan before taking the next shot while allowing 25% overlap. I have marks for both landscape format and portrait formats. But, of course, those marks only work for one focal length, which brings me to the next point….
• Use a “Normal” focal length  For a consumer digital SLR with an APS-C sensor, normal focal length is about 33mm. Anything shorter is considered wide angle. The wider you go, the more barrel or pincushion distortion will be introduced. This may make it harder for the stitching software to match the photos without twisting the photos to counter this effect. The more twisting, the more cropping of the final panoramic you’re likely to have to do. Of course, you could use a longer focal length without this concern, but remember that depth of field reduces with focal length.  I use a 35mm prime lens for panoramics, adapted from an old film camera.
• Choose the Right Content  I like shooting sky panoramics. I found out the hard way that sometimes the stitching software will not work properly with some content – particularly soft images with few hard edges. Some sunset clouds fit that description. Sometimes, it helps to include some hard edge detail (like treetops) to assist in the stitching. You can always crop it out later.

• Choose the Right Software  I find that the ‘premier’ photo editing package gives too many choices when creating panoramics. You have to try them all to find out which one works best, but my experience is that I generally don’t like any of the results. On the other hand, a cheap and cheerful package sometimes works better and with less fuss. I particularly like ArcSoft’s Panorama Maker, which came bundled free with my point-and-shoot camera.

 

 

3 overlapping images stitched together, before cropping. Note how the software has to distort the images to make them match up.



As you can see, the process of shooting panoramics like a pro is very manual. If you’re shooting a scene with moving clouds, set up marks on your tripod so you can rapidly make all your shots before the clouds change position and shape. And finally, resist the temptation to use more than 3 or 4 shots in a panoramic, because you’ll end up with a long, skinny picture sitting in the middle of your print that will look silly.

MAGIC HOUR

Here’s the typical professional travel/landscape/fashion photographer’s day:

1. Get up well before dawn and drive to a location scouted the day before.
2. Shoot as the sun comes up.
3. Go back to the hotel by about 8 or 9 am for breakfast.
4. Do some personal tours in town.
5. Have a late lunch.
6. Go back to the hotel for a long siesta.
7. Start out late afternoon and scout locations for tomorrow.
8. Find a place to have dinner.
9. Get to next location for the evening’s shoot well before sunset.
10. Go to bed early, rinse and repeat.

Huh? What happened to partying until dawn? There’s always the afternoon for taking pictures, isn’t there?

Well, no. The reason that pros avoid mid-day sun is that it provides the coldest light and the worst shadows imaginable. With the sun directly overhead, the colour temperature is at its highest (counter-intuitively, perhaps), resulting in a very bluish light. As a result, colours look washed out and take on a cold cast.

Alternatively, shooting in the magic hour around dawn or dusk provides a warm (low colour temperature) orange-red light that increases colour saturation and contrast. The reason is that when the sun is low in the sky, it is filtered through more of the earth’s atmosphere because of the low ‘grazing’ angle. Shadows are also longer, resulting in more drama. Particularly at the evening magic hour, a clear sky also takes on a deep inky blue hue when you shoot facing away from the sunset. Is there any wonder that commercials, particularly for automobiles, are shot around magic hour?

 Now, sometimes logistics dictates that a shoot has to be done in the middle of the day. Cinematographers often get around this by using warming filters and light modifiers. These modifiers may be elaborate tents to diffuse the harsh overhead sun and eliminate hard shadows, or they may be coloured reflectors aimed at the subject to modify the apparent colour temperature. If you’re faced with this situation and you need to get the shot before the bus leaves for the next tourist trap, consider taking filters (polarizing, warming and graduated, for example) and maybe a photographer’s umbrella or reflector to help mitigate the lousy light.

 Best advice: consider a car rental to allow you to scout freely and return to a location when the light is at its best. And, you’ll get to discover more about your host country as you take the back roads to your next shoot.

 

Have a look at these shots, taken during Magic Hour, and see if you can spot why it's the best time for photography.

 

Meter this.

We’ve all seen the portrait photographer holding a white-domed object next to the subject’s face to take a light reading. So why is that being done? Why not just let the camera do its automatic exposure thing and take the picture?



 

It’s a good question in this digital age, where we can instantly review our shots to see if we need to re-shoot with a little exposure compensation. After all, the histogram in the camera tells us just about everything we need to know about the exposure in the shot – is it under- or over-exposed and is the exposure evenly distributed over the entire tonal range?

The short answer is that the handheld meter is mostly used to measure the light falling on the subject from studio strobes or flashes mounted off-camera.  In this scenario, the camera doesn’t typically have the ability to control the flash output, as it does in ETTL mode when the flash is mounted on the camera’s hot shoe.  Hence, studio photographers usually work with the camera in manual exposure mode, where they manually set the shutter speed to a value that will synchronize with the flash and the aperture to a value that gives the correct exposure. Alternatively, they can use the  meter reading to set the brightness of each flash in a multi-light setup to give a particular effect while ensuring a proper exposure.

Here, I’ve used the words ‘light falling on the subject’, meaning incident light. Hence, the incident light handheld meter measures the ambient light and ignores how much light the subject is likely to reflect.  The metering system in our camera, on the other hand, does rely on the light reflected from the subject to determine exposure.

Which is more accurate? The incident meter is, because it is calibrated so that it will give camera settings to make an 18% grey card look like 18% grey (middle mark on the histogram) when photographed.  The reflected meter, however, relies on the subject's tone averaging out to 18% grey in order for the exposure to be accurate. If the subject is overly dark or bright (such as a snow scene), the reflected meter gets fooled because it tells the camera to expose as if the subject is mid-grey. The incident meter would read the light falling on the snow rather than the light reflected from it, thereby resulting in the snow looking like bright white snow rather than grey slush.

I started out stating that the incident meter is used in the studio to measure the light from strobes or flashes, but obviously it has a function in outdoor ambient (continuous) light photography as well. Some photographers work in manual exposure mode all the time and therefore rely on an incident meter for camera settings.

So why bother? Part of the answer may be a throwback to the film days, where you never knew until it was developed whether you got the exposure right or not. An incident meter (and a little exposure  bracketing) gave you the confidence that you got the shot. That way of working may still influence the photographer who has made the transition to digital, partly because it’s good practice.

The bottom line, though, is that anyone seriously considering turning pro using studio lighting setups should consider working with a combination flash/continuous incident meter, if for no other reason than to save time. The alternative is to shoot, tweak, shoot and then tweak some more.

Combination meters can be a bit of an investment, so they’re not for everyone.  If you’ve got the spare change, though, a meter can help you understand the exposure mystery a little better and hit the bullseye every time.

Lenses for the DSLR: Crop Factor and Image Circles

(Not to be confused with crop circles)

 

A few months ago, I wrote about how sensor size affects the way different cameras capture an image when using the same lens. To refine the topic a bit further, I’m going to introduce two terms: crop factor and image circles.

Why bother with this techno-babble? Well, as stated in the earlier article, if you now own a consumer DSLR with an APS-C sized sensor, chances are that when you want to replace it down the road, your next camera will have a full frame sensor. This means that the lenses you have now are going to behave differently on your future camera, or, worst case, will force you to buy at least one new lens.

Now for my definitions:

Crop Factor – The ratio of apparent magnification provided by the same lens when switching between two different-sized camera sensors.

For example, a lens on an APS-C sized sensor will produce an image that appears magnified by a factor of 1.6 times over the image captured by that same lens on a full frame sensor. The actual image projected by the lens is the same in both cases (note that the focal length of the lens is assumed to be fixed), but the smaller APS-C sensor sees fractionally less of the projected image than the full frame sensor. In effect, the APS-C sensor is ‘cropping’ the image, thereby giving the impression that it is magnifying part of the image.

Image Circle – The diameter of a circular image projected by a lens when focused on a surface. It is usually expressed in millimetres.

In this context, the lens is projecting the image from a scene in front of the camera onto the back of the camera. At the back of the camera is the sensor. In order for the image to fully cover the sensor, the image circle must be at least as large as the diagonal measurement of the sensor. Otherwise, we would see a darkening in the corners of the resulting image where the projected image didn’t fully cover the sensor. This is called vignetting.

One important fact to note is that lens manufacturers make two different types of lenses for DSLRs: full frame and digital-only. For example, Canon full frame lenses are designated EF and digital-only are designated EF-S. They may have exactly the same focal length, but the difference is that the full frame version projects a bigger image circle, more than sufficient to cover the full frame sensor. The full frame version works fine on both full frame and APS-C cameras, whereas the digital-only version would cause vignetting on the full frame camera. Note: while the mounts look the same on the EF and EF-S lenses, there is a protruding 'shoulder' on the EF-S lenses that prevents you from mounting them on full frame cameras.

Now, you would be tempted to think that using a full frame lens on an APS-C sensor when compared with the digital-only lens would result in apparent magnification, just like the crop factor, because the smaller sensor is only capturing part of the full frame lens image circle. An important difference, however, is that if you looked at the projected images from the full frame and digital-only lenses (with the same focal length) under the exact same conditions, an object in the scene would be projected at exactly the same size. Why? - because the full frame lens actually captures a wider field of view. In other words, putting the full frame lens on an APS-C camera will project peripheral information outside of the sensor, while the digital-only lens will not project that peripheral information but will adequately cover the sensor.

If that didn’t do it for you, here’s a scenario that might explain the difference between crop factor and image circle. Hopefully, the accompanying graphics will help:

1.  I have an APS-C sensor DSLR in front of me. I also have two lenses – both are 50 mm focal length, but one is designed for full frame and one is designed for digital-only. I have the camera set up on a tripod aimed at an object (X) which sits in the middle of the viewfinder. I try each of the lenses in turn and focus on the X. I notice that the X appears to be the same size in each case, and fills the frame from top to bottom. As long as the focal length on both lenses is the same, there is no change to the size of the image or the apparent angle of view in the captured image. The only difference is that the full frame lens is projecting a bigger image circle with more peripheral information (the dots) that the sensor doesn’t see anyway.

 

2.  I now take the full frame 50 mm lens and put it on a full frame sensor DSLR. The angle of view now appears wider than it did on the APS-C camera and the X is smaller (doesn’t fill the frame from top to bottom) by a factor of 1/1.6 (62.5%) because of crop factor in reverse. Saying it another way, the full frame lens now just covers the full frame sensor as opposed to the APS-C sensor which cropped the full frame lens image circle and caused apparent magnification. Again, focal length remained the same, but sensor size changed. Note that the full frame sensor captures some of the peripheral image (dots) that the APS-C sensor didn't.

 

3.  If I put the digital-only 50mm lens on the full frame camera (not generally possible as explained above), the object size is the same as in 2., but I see severe vignetting in the corners. This is because the image circle of the digital-only lens is too small for the full frame sensor.

To tie this discussion up with a nice ribbon, we can summarize where crop factor and image circle come into play as follows:

 

• Crop factor is a consideration when using the same lens on two different cameras with different sensor sizes.
• Image circle is a consideration when using two different lenses with the same focal length but different image circle sizes on the same camera.

Taking this one step further, what if you had a full frame DSLR, but you wanted to use a lens of the same focal length (ie. 50 mm) but with a bigger image circle than the full frame lens provided? Those of us geezers who used to use medium format film know that the lenses for those old cameras projected an even bigger image circle than full frame DSLR lenses because medium format film sizes were larger than a full frame sensor. So, as long as you were comfortable shooting in manual mode, you can adapt your medium format film lenses to your DSLR for reasonable cost. Why would you need a bigger image circle if the full frame lens covered your sensor? Well, with a bigger image circle, you can (with the right adapter) use tilt and shift functions over a wider range than you could with a full frame lens.

But tilting and shifting is another subject for another blog post….



Fill Flash: Balancing Ambient Background and Subject

I've often ranted in my courses about how horrible mid-day light is for photography. Apart from the colour temperature concerns - an overly bluish, cold tinge to the light - harsh shadows cast from overhead are unflattering, particularly on human subjects.

The flash, either the built-in pop-up variety or the accessory hot shoe type, can assist if you are forced to shoot in the daytime outdoors. Weddings fit this scenario. Turning on your flash to shoot outdoors may seem absurd, but pros use it all the time as 'fill flash'. The word fill refers to the fact that the flash illuminates the face to fill in shadows in the eye sockets and under the nose and chin. Photographic Botox®, as it were.

The modern digital SLR does its best to balance the ambient outdoor light and the fill flash through ETTL (evaluative through-the-lens) metering. ETTL uses a number of different points on the image to determine what the correct exposure setting (ie. aperture and shutter speed) should be, and controls the output from the flash to properly illuminate the subject.

As brilliant as the microcomputer in the camera is at doing this, results can sometimes be other than expected. Let's say the background looks properly exposed but the subject looks a little dark. If you have a strong backlight, this may mean re-positioning your subject. If that's not possible, you can adjust the flash output, independently from the camera's exposure setting, by using flash exposure compensation.

Accessory Flash Exposure Compensation

There are two ways you can change flash output. The accessory hot shoe flash will allow you to adjust output using either the buttons on the flash itself OR through the flash exposure compensation setting in the camera. Depending on the camera, either the camera's flash exposure compensation will be used or the setting dialled into the accessory flash will be used: they cannot be used in combination. For the built-in pop-up flash, you can (obviously) only use the camera's flash exposure compensation setting. So, for the underexposed subject, set the compensation for, say, +2/3 stop and try again. The subject should brighten and balance with the background. 

Exposure Compensation button on camera

For the opposite scenario - the subject is properly lit by the flash but the background is too dark, you can use exposure compensation to control the background exposure. This is different from flash exposure compensation in that it controls the choice of aperture and/or shutter speed but not flash output. For a dark background, dial in a positive number, and for an overly bright background, dial in a negative number. You may have to tweak the flash exposure combination again to get the best result.



Negative Exposure Compensation plus
positive Flash Exposure Compensation

So, by setting flash exposure compensation and exposure compensation independently, you can achieve a balanced image.

Let's leave the mid-day scenario and think about doing a portrait just after sunset ('magic hour'). Using aperture priority or shutter priority modes, the camera's metering system will try to expose the twilight sky properly before lighting your subject with the flash. If the subject looks overly bright and unnatural against the sky, you can balance them by using negative flash exposure compensation or a bit of positive exposure compensation, or both.

The results from doing so will amaze you. After all, the pros adjust their light sources to balance them against the ambient light.

A Little Off-Topic

Although this is a photography blog, I feel it is important to mention something a little more pressing in this post.

A neighbour became quite ill during 2012, and is now unable to work. Apart from the stress of waiting for an organ transplant as his health declines, finances are becoming a concern.

As a stopgap to remove the money worries, I have started a campaign on Indiegogo to raise some funds to help cover living expenses for the next 6 months. While it has only been going a few days, it is a disappointment that more people who have been notified of the campaign have not made even a small donation. Perhaps if a lot of people make even a small donation (ie. $1 to $5), momentum will be created.

Please take a moment to read the listing at http://www.indiegogo.com/ivorohan

Many thanks!