Best solution for studio lighting

Q. Often the only time I can paint is at night, but my studio lighting creates a glare on my oil paintings to the point that I don’t want to paint at all. I have a daylight easel lamp above my painting and an incandescent ceiling light behind me. I’ve tried turning off one or the other, but neither adjustment helps. What kind of lighting would you suggest?

Krista Wargo, Yucca Valley, CA

A. One of the problems with an easel lamp is that it can create uneven lighting. With the lamp at the top of the easel, most of the light is concentrated on the upper area of the painting while the lower area remains dimly lit. Also, the easel lamp’s small bulb is a point light source that can cause glare or a reflection. An incandescent ceiling lamp, another point source, can create the same problem.

The best solution is diffuse light. Banks of fluorescent tubes give more evenly distributed lighting, especially if they’re equipped with diffusers. Suspended from the ceiling, these lights won’t create a hot spot on your painting. Even with fluorescent lighting, however, you may need to angle your painting or change the height of your seat to remove the glare.

Professional painters and lighting manufacturers often recommend fluorescent bulbs with a temperature of 5000 degrees Kelvin (K) and a color rendering index (CRI) of 90 or better. (For comparison purposes, consider that sunlight is described as 5000 K with a CRI of 100.) Many artists, however, prefer a mix of warm and cool bulbs. I’d suggest that half the bulbs be somewhat warmer, perhaps in the 3200-3400 K range, which is closer to standard photo flood lighting. I would use two fixtures, one with warmer bulbs and the other with cooler bulbs. This will allow you to selectively turn on only the cool light or the warm light or both at once, so you’ll be able to see your work under a variety of different lighting conditions (See Bridge of Dreams, above). Additionally, I would put in a rack of spot halogen or LED lights with a dimmer switch, which will allow you to simulate gallery lighting.

BEST EASEL FOR SUPER-SIZED PAINTINGS

Q. I’d like your recommendation for a wooden studio easel that can accommodate canvases in the neighborhood of 8×14 feet.

Scott Glaser, Westport, CT

A. Although several studio easels can handle large-scale paintings, they won’t necessarily handle them well. For example, a single-masted easel that can hold a narrow 8-foot tall canvas may be unstable with a canvas of the same height but with greater width. A double-masted easel, which gives more points of contact for the canvas, improves stability, but even a double-masted easel may not be wide enough. Sure, you could use two or even three H-frame easels to support a single canvas, but adjusting the canvas would be a nightmare. You could simply attach the canvas to a wall, but you’d have to use a step stool to reach the upper areas.

That brings up another consideration–adjustments. Painters have what I call an “optimum painting point,” where the hand and arm can be held easily for long periods without tiring. (For me, this is just below shoulder height.) If the canvas can be slid up or down, you won’t have to move your arm to an uncomfortable position to paint the upper or lower portions of the surface. Some painters also work seated, so being able to slide a canvas horizontally without having to move a stool is a benefit. Additionally, tilting your head down as you work is more comfortable than tilting it up, so being able to angle the canvas is helpful. Having all the elements–bottom shelf, top bracket and canvas–move as a unit is better than having to loosen and tighten various knobs. Some easels use counterweights, which enable the painter to move the painting with the touch of a finger; other easels use hand winches.

Although several easels, such as the Richeson Best Classic Santa Fe II (www.richesonart.com), can handle an 8-foot tall canvas, only one that I know of will properly handle the width you require. The Hughes 6000 (www.hugheseasels.com), which is used by the Smithsonian Institution for restoration work, is the biggest easel commercially available. This triple-masted unit has all the recommended features I’ve mentioned, including the ability to move the canvas horizontally, as well as counterweights that can be changed to accommodate lighter or heavier paintings.

BEST PASTEL STUDIO FLOORING

Q. What’s the best flooring material for a pastel studio?

Name withheld

A. I can tell you what’s the worst flooring material for a pastel studio–carpet! Carpet is almost impossible to clean, and the dust will get ground into it, remaining a problem for years. Best is a surface that’s easy to damp mop. I say “damp mop” because you don’t want to sweep pastel dust and cause it to become airborne. Any smooth surface that will stand up to mop and water will work: linoleum, tile, laminate and wood are good choices. (When cleaning laminate, make sure you follow the manufacturer’s instructions. Also, avoid surfaces with a pronounced texture.) If you’re concerned about tracking the dust throughout the house, you can place “sticky mats”–the kind used in surgical wards–at your studio entrance to trap dust from your shoes. These mats are readily found on the Internet.

By the way, if you vacuum, make sure your vacuum cleaner is properly sealed and isn’t blowing out dust. Pastel creates a very fine dust, and some vacuums, especially shop vacs, may not trap it and may actually shoot it into the air and redistribute it throughout the studio. A vacuum with a high-efficiency particulate air (HEPA) filter will do thebest job of capturing dust.

Dust tends to get other places besides the floor. Countertops, tables, windowsills and easels are subject to dust collection. Don’t ignore them when you’re cleaning your studio, and make sure you attack them with a damp rag. Wear latex or nitrile gloves to keep the dampened dust away from your skin. When I’m painting in pastel for a few weeks, I like to give my studio floor a quick damp mop daily and everything else a more thorough cleaning once a week.

You may find it more convenient to trap dust at the source. You can attach a “gutter” along the bottom of your easel shelf–a wallpaper tray works well–to trap the dust, and then empty the tray periodically. I also like to attach along the bottom of my painting a piece of wide masking tape, hinged so the sticky side juts out like a shelf. The tape acts like flypaper, trapping the dust. A more high-tech option is an Artist’s Air (www.artistsair.com) air cleaning system, which consists of a gutter with a HEPA vacuum cleaner attached.

Tips for creating a professional head shot

Years ago a writer sat for a head shot if she was lucky enough to need a photo to adorn the back of her book. Today, with the surge of social media, all writers should have a professional-looking photo, lest they find themselves transformed into an ominous outline with a question-mark face.

Don’t answer the need by quickly cropping your face out of a recent group photo taken at Aunt Gilda’s birthday party. Whether your head shot will be at the top of your high-visibility print column or will accompany your digital conversations, the photo should represent you at your best. That said, don’t stray too far from your everyday look.

Lori Ann Robinson, an image and fashion consultant in Los Angeles, says you should choose clothing that’s simple but flattering. “Patterns can be distracting,” she advises. “Wear your best colors if the head shot is in color. Also, make sure your neckline is flattering and frames your face, and keep to simple jewelry.” Women may benefit from getting hair or makeup done by a professional, Robinson suggests.

It’s up to you whether or not you wear your eyeglasses. “It’s easy to light the studio to avoid glare in the glass, and so that the subject’s eyes are visible,” says Joanne Smith, of Headshots Photography in New Hampshire and Massachusetts.

Remember that you may count on this photograph for multiple years, so avoid trendy items or jewelry that may soon look dated.

It’s OK to have your photographer touch up your photo to minimize signs of age, but don’t go overboard, Robinson warns. “If you [end up] doing a book signing, you don’t want to look too [different] from your picture. People may not recognize you,” she says.

Those writers with the opposite problem–fear that their photo broadcasts their fresh-out-of-school status–should not try to age themselves. “Look well groomed and professional, not older,” Robinson advises.

Your photo doesn’t have to capture the perfect smile. Sometimes a different expression–thoughtful, laughing, friendly–can work for you. The key is not to look contrived. Tell your photographer what you’d like to capture, and he or she should be able to help you achieve a natural outcome.

Creative by nature, many writers bypass the traditional bust shot for something with a bit more flair. Tread carefully, though, when going for the unique. This picture may be the only image many people will associate with you. You don’t want to be forever remembered as the writer in the hammock, or the one chewing a quill pen. “It’s fun to be creative, although there is a fine line between creative and cheesy,” Smith says. So shoot some creative shots and some traditional images, and then decide which works better for you.

Creative shots will include more props and background, so consider the final size of the photo, Smith adds. “Often it becomes a thumbnail-sized image in a magazine or blog. Your readers want to see your face, so, if it’s too small in the frame, you lose the impact of a tight head shot,” she says.

When done well, a creative shot can enhance your image, Smith says: “For example, we shot an [environmental] writer outside with trees and plants in the background, which suited her column. If you’re a romance writer, a head shot taken at sunset on the beach may work well.”

Photography costs vary by region, so shop around to find the going rate in your area. Seek someone who will provide a variety of shots and is flexible. Most important, choose someone that makes you feel relaxed and comfortable.

To cut costs, look into photography schools, or round up some fellow freelancers and try to negotiate a group rate.

You may hesitate to pay a photographer or other professionals to help you put together your head shot, but a small investment may be worth it to have a photo you’re proud of.

Some tips on getting to grips with the vagaries of exposure, white balance and ISO settings

Modern cameras have a range of programmed exposure modes; indeed, some have nothing else: they automatically set the shutter speed and aperture depending on the exposure reading made by the camera’s built-in light meter. There’s an automatic mode for portraits, another for landscapes, one for sport and action, another for close-ups, and several options for shooting at night, with or without flash–there seems to be a different exposure mode for every eventuality. For each mode, the chosen exposure is determined using different combinations of aperture and shutter speed.

Such point-and-shoot automation brings ease of use to the photographer, but placing this much trust in the camera to define the ‘correct’ exposure and set the right combinations of shutter speed and aperture every time is to forsake control. In many situations, it’s far better to implement some manual control over the choice of shutter speed and aperture for your desired result.

But what is meant by ‘correct’ exposure? Although the product of changing ratios between shutter speeds and apertures controlling the amount of light reaching the film plane or image sensor, a correct exposure is as much an aesthetic value as it is a mathematical one. For many photographers, it’s where the resulting photograph renders a level of detail in both the highlight and shadow areas that is acceptable to the eye of the photographer.

Many camera meters are fooled by scenes of high contrast or extreme brightness, such as high direct sunlight reflecting off sand or snow. In such scenes, a built-in meter reading, if left alone, will inevitably lead to underexposure, so the photographer needs to override the metered reading to achieve the ‘correct’ exposure. However, camera technology can help in this quest thanks to built-in spot meters that allow the photographer to make individual readings from different parts of the scene to check exposure variance within the frame, thereby helping you to decide which reading to use to best render the contrast range within the frame. Even then, an average reading of all these different levels won’t always provide the ‘correct’ reading.

Camera meters are calibrated to reproduce a scene as an 18 per cent shade of grey. As a result, an all-white scene such as a snow-covered field will be recorded grey when exposed at the camera’s metered reading. In these situations, additional exposure is needed, and this can be supplied via the camera’s exposure-compensation facility. Most cameras allow you to compensate exposure in third- or half-stop increments. How much exposure compensation you give depends on the amount of white or highlights in the frame. For example, beach sand beneath a bright sun reflects a lot of light and will fool your camera meter into underexposing, so keying in exposure compensation of +2 stops might well be necessary.

A less extreme and more common exam pie is the summer landscape with a clear blue sky occupying the top half or third of the frame. Here, the meter is likely to give a reading bias towards a perfectly exposed sky, resulting in the foreground subject matter being too dark. Exposure compensation will also be required but only around a half or two thirds of a stop. For a balanced exposure that reproduces highlights and colours accurately and reveals shadow detail, a single compensated exposure may not always give the best possible result. So, given that ‘correct’ exposure–like beauty–is in the eye of the beholder, a productive course of action is to take a bracketed sequence of images.

Bracketing is the practice of taking two or more additional shots either side of the ‘correct’ reading, at values above and below the metered exposure. Whether you bracket by a third of a stop, half stop, one stop or more around the metered light reading depends upon your personal taste and experience. Like so much of photography, it boils down to trial and error based upon myriad situations.

As well as shutter speed and aperture selection, there’s another camera setting that helps determine the exposure value of the scene you’re composing in the viewfinder. This is the ISO rating, which is a measure of the light sensitivity of the recording media used by the camera. In the case of film, the higher the ISO rating, the more sensitive it is to light. For example, an ISO 200 film is twice as sensitive as an ISO 100 film, the same is also true of ISO ratings on a digital camera. Consequently, 1/500sec at f/8 with ISO 200 will deliver the same exposure value as 1/250sec at f/8 with ISO 100 and 1/125sec at f/8 with ISO 50.

Whether using digital or film, a characteristic of higher ISO numbers is a coarser image and deterioration in colour saturation. Grain becomes more visible on the finished photograph made on film, while increased noise is the comparable trait of digital images made using higher ISO settings. The prime advantage of using ISO settings on a digital camera is that you can select a different ISO value for every photograph; with film, you need to stick to the same ISO value for the whole roll.

White balance is a feature you won’t find on film cameras, but it has an influence on the quality of light recorded with a digital camera. There are three primary colours existing in varying proportions in a light source, depending on its colour temperature. These are red, green and blue, usually abbreviated as RGB. When the colour temperature is high, there is more blue light visible; when it’s low, there is more red light. As the colour temperature increases from low to high, the colour casts rendered change in the following sequence: red, orange, yellow, white and blue/white.

While the human eye can adjust automatically to variations in light quality brought about by changing colour temperature or mixed light sources, our cameras aren’t quite so adaptable. When we all used film, the emulsion was daylight-balanced, but special film types were available for different light sources, such as infrared to record those otherwise invisible wavelengths of the spectrum, or tungsten-balanced film for shooting indoor scenes lit only by household lamps. Cameras have improved in this digital age, as they have a plethora of programmed white-balance settings to match the type of light illuminating your subject. Typical white balance settings include auto, sunlight, cloudy, fluorescent, tungsten and incandescent.

Unsurprisingly, the automatic white balance setting is the most popular among photographers, but unless there is an actual area of white, such as a cloud, in your scene for the auto setting to refer to, then your resulting image will appear flat and lacking in true colours. The reality is that most light sources aren’t 100 per cent pure white: they have a range of colour temperatures that produce different colour casts (see The colour temperature scale), but this in itself isn’t an obstacle. Instead, it reminds us that light is the source of all colour and how we depict that colour is in itself another key factor in the overall impact of photography.

Equipment selections

Accessory option: handheld light meter

Contrary to popular opinion, sophisticated in-camera light meters haven’t made the separate handheld instrument redundant. Many professionals still swear by the finer accuracy of the light readings achieved by modern meters such as the Sekonic L758D Digital Master. This meter was made purely for digital photography and can be calibrated to match the sensitivity of a digital camera’s sensor at all ISO settings.

Cleverly, it includes and exposure-latitude warning that flashes on the analogue scale if a measured highlight or shadow exceeds the dynamic range of your camera.

Compact option: Sigma DP1

The recently launched DP1 is more than just another digital compact camera: it’s the first to use an APS-C-sized image sensor, normally found on SLR cameras. More than this, the DP1 uses a 14-megapixel full-colour sensor made by Foveon, with the array of pixels arranged in three separate layers–red, green and blue–for the three primary colours found in every light source. Initial tests have produced superb image quality and it’s expected that quite a number of professionals will add this little camera to their kit.

Camera option: Nikon D300

A pro-specification SLR, the D300 is only eclipsed by the D3 in Nikon’s stable of award-winning digital cameras, but shares most of the flagship model’s features. Number one is Nikon’s revered 3D matrix metering system, using a 1,005-pixel RGB sensor with readings linked to the camera’s 51-point AF system. With a 100 per cent field of view in both the viewfinder and the LCD monitor and exposure compensation of +/- five stops in either 1/3- or 1/2-stop increments, the D300 is one of the most accurate and versatile digital SLRs on the market when it comes to focusing and metering.

DOS AND DON’TS OF EXPOSURE

DO

* Take spot readings of the brightest and darkest areas of the frame in order to measure the exposure variance (contrast) in the scene

* Bracket your exposures. Check the results on the LCD monitor and vary the amount of over- and underexposure between frames to find the result that pleases you best

* Meter off the main focal point of your composition: as the point that draws your eye into the picture, this area should be both sharply focused and correctly exposed

DON’T

* Use the automatic white balance setting if there is no area of white in the scene for your camera to refer to

* Rely on your camera’s automatic metering in scenes dominated by bright skies or reflective surfaces such as water, snow or wet sand. Instead, overexpose the meter reading by up to two stops

* Use high ISO settings in low light unless there is no alternative. Image noise and colour degradation become visible on most cameras at settings of ISO 400 or above

Recommended reading

* Understanding Exposure by Bryan Petersen, Amphoto, pb, pp160.

* Understanding Raw Photography by Andy Rouse, Photographer’s Institute Press, hb, pp144,

* Exposure and Lighting for Digital Photographers by Michael Meadhra and Charlotte K Lowrie, John Wiley & Sons, pb, pp368,

Capturing star trails with a digital camera

Today’s digital SLR cameras and image-processing software are breathing new life into an old film-based technique.

Like many amateur astrophotographers who grew up using photographic film, I’ve been a bit reluctant to embrace the virtues of CCD imaging as a complete replacement for film. Sure, thermoelectrically cooled CCD cameras on telescopes play an important role at all levels of astronomy, but I’ve stubbornly (perhaps even a bit irrationally) held to the belief that some images can be obtained only by using good old-fashioned photographic emulsions.

One realm where I thought film would always reign supreme is in capturing star trails. One might ask why anyone would even consider taking something as simple and straightforward as star trails and adding the cost and complexity of digital photography to the mix. As I have recently discovered, however, it’s definitely worth the effort. The results presented in this article demonstrate the advantages of recording star trails digitally and show how this new realm of possibilities can breathe new life and creativity into your tired old star-trail photos.

Although I have to admit that working for Gemini Observatory with telescopes on Mauna Kea in Hawaii and Cerro Pachon in Chile gives me regular access to nearly perfect skies as backdrops, the technique described here can be adapted to urban sites as well. In fact, the improvements are even more dramatic in situations where light pollution or bright moonlight would prohibit shooting long-exposure star trails with film.

A Serendipitous Discovery

It all began one chilly night in early 2003 at the Gemini North Telescope, where two other astrophotographers and I were enjoying an evening of digital imaging. Our main purpose was to set up our Nikon D1x digital SLR (single-lens reflex) camera and to experiment with the possibility of creating a time-lapse movie of stars passing over Gemini’s dome from a sequence of 1-minute stills. Armed with an electronic timer, a portable power supply, cold-weather gear, and lots of hot chocolate, we began shooting images.

As often seems to happen when one experiments with new ideas and equipment, serendipity provided us with an opportunity to learn something new. In this case, the microdrive card that we were using could hold only 1 gigabyte of data. (A microdrive card is a miniature hard-disk drive that fits into the camera’s memory-card slot.) Every hour or so we bundled up and left the comfort of the observatory’s warm control room to stumble around in the darkness to replace the card. With time on our hands between downloading the cards’ contents, we experimented with the images we had obtained.

First we opened the individual images with Adobe Photoshop software and created an automated routine to subtract (remove) the electronic noise generated by the camera’s CCD detector using a dark frame. (A dark frame is an image of the same exposure duration and camera settings as the desired image, only with the camera lens covered.) This is done with Photoshop’s Difference blending mode, with the dark frame in one layer and the desired image in another. Each of these processed images was then flattened (combined) and saved and archived as a separate file on a CD.

After verifying that our image sequence would make a nice time-lapse movie, we began experimenting with a “stack” of images in Photoshop to see what other interesting things we could do. Inspiration struck one of our team members, Kevin Jones, when he began playing with the different blending-mode options used to combine the image layers. It turns out that the Lighten mode takes the selected image layer (the foreground) and compares its pixel values (in each color channel) with the underlying layer. If the foreground’s pixel values are the same as (or less than) the underlying layer, it leaves the resulting pixels unchanged. However, if the foreground’s values are higher (brighter), the Lighten mode uses the higher value of the two pixels in the composite. On the surface, this might not sound very profound, but the effect is that the sky brightness never increases beyond that present in the brightest single image. Meanwhile, the star images themselves continue to build up as the stars drift across the camera’s field.

The more images you add to the stack, the longer the resulting star trails. Since the sky brightness stays at a constant low level, the visual depth and contrast of a digital star-trail shot is more dramatic compared to a traditional long-exposure film photograph. (In the latter, the sky brightness accumulates during the entire exposure, reducing contrast between the stars and the background sky;)

Another advantage of the digital technique is that any foreground object that is illuminated will not become overexposed, as it would in a long-duration film exposure. This is especially important when you are attempting star trails with well lit foregrounds or under bright moonlight. Light pollution is also suppressed, allowing for dramatic star trails in relatively well lit areas that would otherwise quickly saturate film.

Tips and Pointers

For those wishing to try this technique, it is very helpful to use some sort of inter-valometer or timing circuit to automate the exposure times and intervals so you can leave the camera and not have to attend to each exposure.

It’s also important to keep pauses between exposures to a minimum (pauses will mean gaps in your star trails). With the Nikon D1x fitted with a 14-millimeter f/2.8 Nikkor lens, we were able to start the next exposure within about 1 to 2 seconds of the previous image–any longer than this and we would see a noticeable gap between exposures, even with such a short-focus lens. Most of our experiments were done centered on the equatorial region of the sky; the exposure gaps, however, were minimized when we shot circumpolar star fields.

Digital cameras differ in their ability to take long exposures, but detector noise is an issue with all digital cameras once exposures go beyond a second or two. To overcome this, some cameras have an automatic “noise-reduction” option, which might help, but could be unreliable depending upon the exposure time. For star-trail exposures I suggest disabling any of the camera’s built-in noise-reduction features and taking a dark frame. It’s a good idea to take a dark frame at the start and end of each session since the noise characteristics of a CCD or CMOS chip can change with temperature.

Use flash-memory or microdrive cards with the largest capacity that you can afford. Some cameras will allow you to switch cards while an exposure is being taken (but not while it is saving an image, of course) so you can keep a sequence going without missing a frame to change cards.

Experiment with different exposure times, white-balance and ISO settings, lens f/stops, and so forth. Each camera’s silicon detector is different, so plan on doing some preliminary tests first to find the best combination.

When you’re taking images, it’s always best to capture them in a noncompressed format such as TIFF. Make sure that the dark frames used have the same image format.

If you have a portable power supply, use it. Digital cameras require a lot of power when you’re using the bulb (time-exposure) setting, and, as the ambient temperature drops, the camera battery’s performance will also suffer.

Autofocus digital SLRs might have trouble focusing at infinity, so set the focus manually. If you use a manual-focus camera, notice where its infinity setting is located, as it’s often just inside the lens’s focus stop. Do some tests first to find the best focus.

With our setup, we obtained optimal results with 45- to 60-second exposures, but we also obtained good results with exposures up to 2 minutes long. Our 60-second shots recorded stars down to about 7th magnitude.

Image Processing

Once you have obtained all your exposures, transfer them to a computer with image-processing software. I use Photoshop 7.0 on a Macintosh G4 running under OS X, but I suspect other programs would work. The following instructions will be for Photoshop users:

1. Open the first image of your sequence and save it under a new name that you want to use for the final star-trail image.

2. Open the next image in your sequence. Use the Select > All command and copy this image (Edit > Copy).

3. Paste the copied image onto the first image–this is the beginning of the “stacking” process. You can now close the image that was copied to avoid confusion since you’re now done with that image.

4. Open the Layers palette (Window > Show Layers) and select the new layer created in the previous step.

5. Click on the Blend Mode menu in the Layers palette and select the Lighten mode. You should now see both images merged together as one.

6. Repeat steps 2 to 5 until you’re done with all images. You will probably want to flatten (under the Layer menu bar) your star-trail images periodically to save on disk space and memory in your computer. When you flatten an image all of your existing layers are merged into one and the file size becomes much smaller.

7. Once you’ve stacked and flattened all your images into a single one, you need to subtract the dark frame. To do this simply open the dark-frame image, click on Select > All, then copy the dark frame and paste it onto the star-trail image. At this point the image will go dark, so make sure that the new dark-frame layer is selected. Go to the Blend Mode menu again in the Layers palette and select the Difference mode. Now most of the noise on your image should be minimized, and you can flatten the image again and make final adjustments to it. Save the final image and you’re done!

Steps 2 to 6 can be tedious if you have a lot of images to stack. Photoshop has a very nice automation feature that can make processes like these much easier and quicker, so check your manual for detailed instructions on how to use it.

Exposure Gaps

Depending on your camera’s resolution, lens, and sky location, if you look closely you might notice small gaps between your stacked images. The reason for this is that at the end of each exposure, the pixels that are being exposed are not (on average) getting the full duration of exposure. Then, when the next exposure begins, these same pixels are still not getting the full exposure. Since the Lighten blending mode is not additive, when you stack the images the brightest single pixel is selected in the stack and, on average, at each gap it’s only 50 percent as bright as the adjacent area.

Shooting at less than full resolution (by binning, or combining, the pixels) will often cause the gaps to close up. Also, if you shoot the polar regions (or use a very short lens), the problem is not as evident since the overlap is so great.

If you find the gaps unacceptable, there are several Photoshop techniques that you can use to correct them. The technique I’ve found to be most effective is to simply duplicate the completed star-trail image, copy and paste it onto the original with Lighten mode, and shift and/or rotate it slightly to fill in the gaps. However, for viewing on a computer screen and for making small to medium prints, these tiny gaps should not be objectionable or, in most cases, even noticeable.

I’d be interested to hear from readers who might come up with a more clever (and more elegant) solution on how to minimize exposure gaps.

I also discovered in my tests that if you take the images (and the dark frame) without using the camera’s “sharpening” feature, the dark frame subtracts out much cleaner. If you use sharpening you will notice an annoying black ring around bright pixels that goes away when you turn off sharpening. However, if you don’t use internal sharpening in the camera, you might find it necessary to do it with Photoshop (under Filter) once the final image is stacked and flattened.

Our experiments were all done with a fairly high-end Nikon digital SLR camera, but I suspect that most other professional digital SLRs could be made to work as well. Overall, I’ve been impressed with the power of digital photography, achieving results that I had previously thought were possible only with film. While our technique does require fairly good equipment and significantly more effort in the processing stage, the results are nothing short of spectacular, and I look forward to seeing what others can accomplish using this technique.