- professional lighting solutions available from the Imatest store, and
- how to build a low-cost test lab that is well-suited to Imatest Studio users: individual photographers who want to test the quality of their cameras and lenses. It is relatively portable and also useful for photographing artwork.
Companies and organizations who use Imatest Master/IS may need a more professional test lab setup. Imatest partners with companies who offer professional lab setup services.
Substitutions can be made for most of the parts listed below.
|Aputure HR672c LED lights are moderately-priced lights for illuminating reflective test charts. Color temperature can be varied between 3200K (near incandescent) and 5500K (near daylight) using 2 sets of LEDs. Dimmable over a 10:1 range without flicker, wireless remote control, high color quality: CRI (Color Rendering Index) = 95.
They are no longer recommended because we prefer a longer aspect ratio (at least 25x80mm— Strapping pairs together on each side to evenly light large charts is a real kludge), a larger dimming range (at least 100:1), and computer control (DMX or similar).
A light box is needed for transmissive charts, which are generally smaller than reflective charts and can be particularly useful in manufacturing environments. Transmissive film charts have much higher resolution than inkjet charts.The GLX-16 fluorescent light box is shown on the right with an SFRplus chart.See our range of lightbox options in the Equipment Section of the Imatest Store.
|Our best available lightbox is the ITI LED Lightbox (shown on the right with the Imatest 36-patch High Dynamic Range chart, which has a tonal range of over 6 density units (20 f-stops)), available from the Imatest store. It has several advantages over other lightboxes.
Low cost DIY lighting
To obtain reasonably even illumination for test charts up to 40x60 inches (100×150 cm) and highly uniform illumination in smaller areas (comparable in size to popular color/grayscale charts like the X-Rite Colochecker), we selected a track lighting system that takes the outstanding SoLux 4700K (near daylight) 12V MR16 halogen lamps, which use long-lasting built-in dichroic filters.
Fixture. MR16 track lights were formerly available at local hardware outlets such as Home Depot, but most have been discontinued in favor of less expensive products. A promising mail-order track system is the Pro Track® 150 Watt 3-Light Low Voltage Track Kit from Lamps Plus, which should be purchased along with the Pro Track® Track Lighting Black Outlet Extension Cord (24324).
Light & stand
Lamps. We use 6 SoLux 50W 4700K/36 degree MR16 bulbs, along with 6 Plano Convex diffusers, which are necessary for even light. The diffusers are mounted in front of the lamps (rightmost image), in place of the clear glass supplied with the track lighting kit. “T” braces with self-adhesive felt pads were added to the sides of the lamp fixtures to block stray light from reaching the lens (rightmost image).
SoLux halogen bulbs are inexpensive and produce extremely high quality near-daylight 4700K illumination, with a CRI (Color Rendering Index) of 98 out of 100. They were featured in an article in Inkjetart.com.
SoLux also sells track lighting components.
Stand. The Radio Shack 33-335 folding microphone stand is simple, lightweight, sturdy, and cheap.
Assembly. The track is attached to the stand with an 8-32 bolt. Here is the procedure.
Drill holes large enough for an 8-32 bolt about 1.25 inches (3.5 cm) below the top of the upper shaft of the microphone stand and about 10 inches (25cm) below the top of the track (the end without the cord). The head of a 1.25 or 1.5 inch 8-32 bolt is placed inside the track, then attached with two nuts on the back of the track to provide a little spacing with the stand. A wing nut (optional) is used to secure the bolt to the stand. [Parts sequence: 8-32 bolt (head), track, 2 8-32 nuts, upper shaft of microphone stand, 8-32 wing nut.] (CAUTION: do not do this unless you know how to work with electrical wiring safely. DO NOT do this when the track is plugged in! )
Attach the track to the stand using materials from your local hardware or camping store, such as nylon webbing with tension buckles, double-sided Velcro tape, or sticky-back Velcro tape that allow the stand to be raised and lowered. The lights are mounted near the top, middle, and bottom of the 40 inch high targets.
The Mabef M-10 easel was chosen because it was sturdy, could be adjusted vertically (checked with a small level), had just the right features, and was on display at a local art supply store. A self-adhesive felt pad on the bottom of the upper clamp helps secure targets.
The BK Precision 615 Light meter (Lux meter) is an excellent low-cost instrument (about $100 USD) for measuring incident light (illuminance). It has a flat diffuser and photopic response (similar to the human eye in bright light). It is particularly useful for measuring evenness of illumination. We purchased ours from Action Electronics, which offers several alternative choices. The BK was chosen over similar Easyview meters because it has a flat (rather than hemispheric) diffuser that better represents the geometry of the flat targets. Readings can be somewhat slow, with settling times around 3-5 seconds.
Several additional items can come in handy: a small level, a flashlight (LED models are cool), rulers, a few clamps, etc. A bubble level mounted on a camera’s accessory shoe can be particularly helpful. Irwin Quick-Grip Handi-Clamps work well for attaching targets to the easel.
|A laser distance measurer is very convenient for measuring precise distances— much more accurate than the measuring tape shown on the right. You can find them for under $100 USD at home improvement chains like Home Depot in the US.|
The tripod should be sturdy, easy to adjust, and easy to move. Any good tripod with a pan/tilt head should work; geared heads are much better. Ball heads are not recommended. We illustrate a few Manfrotto components, which offer good value for the price. These represent typical choices; many more are available to meet special needs.
Manfrotto 475B tripod legs with geared center column – supports 26.5 lbs. Height 16.6 – 74 in. A geared center column can be convenient in a tripod dedicated to a test lab. The built-in spirit level is valuable for leveling the tripod: If the base (where the head is mounted) is level, fine adjustments are much easier to make because head movements (swivel, etc.) don’t interact.
Manfrotto 3275 / 410 compact geared head with quick release – supports 11.1 lbs. Especially nice for making precise adjustments; more expensive than comparable pan-tilt heads, but worth every penny. Uses the 3271 quick release mounting plate. Get several of these.
Manfrotto 3137 variable leg spread portable dolly. Useful for keeping legs in place while moving the tripod. (We’ve replaced this with a rolling video dolly, below.)
3275/410 geared head
Manfrotto 3137 dolly
475B tripod legs
|Solidtrax Video Tripod Dolly|
Solidtrax Video Tripod Dolly (shown above) is helpful when you have to move the tripod to various distances from the chart.
Glide Gear Aluminum Track for use with the above dolly. Track for the dolly can also be built using 1-inch Schedule 40 PVC plastic pipe.
regular quick-release tripod mount is appropriate for most cameras, a sturdy clamping system is needed for testing camera phones, webcams, and tablets. We put two of them together after rummaging through the aisles of Home Depot. They consist of Irwin Quick-Grip Mini or Micro bar clamps mounted on Manfrotto quick release plates. The images below give a good idea of how they’re constructed. A hole had to be drilled in the larger clamp (above) and enlarged in the lower clamp (below) to accommodate the 1/4 inch bolt.
|Larger (Mini) clamp (above) recommended||Smaller (Micro) clamp (below)|
|1.5″ long 1/4″ bolt, 1/4″ coupling nut||3/4″ long 1/4″ bolt, 1/4″ washer|
|Irwin Quick Grip Mini bar clamp||Irwin Quick Grip Micro bar clamp|
|1/4″ coupling nut, “T”-brace||large 1/4″ washer, 1/4″ coupling nut, “T”-brace|
|Quick release plate||Quick release plate|
The larger clamp (the Mini) is sturdier, and has proven to be more useful.
Recently (since we build these clamps) clamping devices have become available, for example, the Manfrotto TwistGrip Tripod Adapter Clamp for Smartphones B&H # MAUTACSP MFR # MTWISTGRIP .
Putting it together
The image below summarizes how the lights should be positioned. The goal is even, glare-free illumination. The lamps represent the stacks of three SoLux track lamps, described above. This may involve a tradeoff, especially with wide-angle lenses. Lighting angles between 35 and 45 degrees work well for normal and long lenses. Avoid lighting behind the camera, which can cause glare. Ambient light should be kept subdued. Check carefully for glare and lighting uniformity before you expose, especially with wide angle lenses, where glare can be difficult to avoid: you may have to move the lights further than normal from the target— or allow glare in portions of the target, taking care that it doesn’t affect critical areas.
Use the meter to check for the evenness of lighting. ±20% over the entire target is sufficient for SFR and Distortion measurements, where small portions of the target are analyzed and exposure is not critical. ±5% or better should be the goal for tonal and color measurements (Stepchart, Colorcheck, and Multicharts). This should be easy to achieve because illumination only needs to be even on the relatively small charts themselves, not on the entire target. The widest (the Kodak Q-14) is 14 inches (35 cm) wide; most are under 11 inches (28 cm). Lighting uniformity is strongly affected by the distance and orientation of the lamps. Our lamps are roughly 50 inches (125 cm) from the center of the target.
Charts are mounted on 40x60 inch (100x150 cm) or 30x40 inch (75x100 cm) 1/2 inch (1.25 cm) thick foam board, which is lightweight, rigid (unlikely to warp), and easy to find at art supply shops. In some cases, the charts are mounted on neutral, middle gray (~18% reflectance) mat board, which is attached to foam board, to ensure correct exposure in camera phones and webcams with autoexposure.
Charts are mounted using permanent double-sided tape or spray adhesive, available from hardware and art supply stores. We have used 3M 45 and 3M Photo Mount sprays, both of which are “Photo safe.” 3M Super 77™ is not labeled “Photo safe,” (and can’t be sold in California), but it should be OK for attaching gray mat board to foam board.
The Adorama Double Bubble Level” (sounds like chewing gum) costs about $29; identical levels from Cullmann, Hasselblad, or Manfrotto, all of which fit in the accessory shoe, cost about $33 at B&H. (They’re probably all made in the same factory in China.)
Rope trick (for horizontal positioning)
(Since we installed our Dolly & Track system we haven’t needed this trick.)
This trick uses rope and mirrors, as well as the red dots • that mark the horizontal center of the target (or whatever marker you choose). This is as close to smoke and mirrors as Imatest gets.
The cord should be about 1 meter long and have a small weight on one end. A heavy nut— the type that mates with a bolt, not the type that grows on trees— serves well.
Hold the cord in front of the camera (between the camera and mirror), and align your eye and the cord so the so the cord passes in front of the horizontal center markers (red dots • in the images), and so the reflection of the cord passes directly behind the cord. The camera is positioned properly if the center of the lens is aligned with the cord. If it isn’t, shift the camera horizontally until it is.
To complete the horizontal adjustment, rotate (pan) the tripod pan/tilt head so the chart is centered in the image frame.
At this point you should be close enough to correct alignments so the final, fine adjustments should proceed quickly.
Glare in the outer patches can ruin measurements. With semigloss charts i’s hard to avoid, even with careful lighting placement. You can reduce it by decreasing the angle between the lights and the chart, but this may make the illumination less even. For this reason matte charts are often recommended when wide angle lenses are being tested (this includes most camera phones).
SFRplus chart on easel (left), Kodak/Tiffen Q-14 Step chart and X-Rite™ ColorChecker® (right)
The charts on the right can be analyzed with Imatest Stepchart, Colorcheck, Multicharts, or Multitest. They are mounted on neutral middle gray (~18% reflectance) mat board, which is mounted on foam board for rigidity.