Pentax Optio 750Z Test Images and Analysis
|I've begun including links in our reviews to a Thumbnail index page for the test shots. The data on this page includes a host of information on the images, including shutter speed, ISO setting, compression setting, etc. Rather than clutter the page below with all that detail, we're posting the thumbnail index so only those interested in the information need wade through it!|
The extreme tonal range of this image makes it a tough shot for many digicams, which is precisely why I set it up this way, and why I shoot it with no fill flash or reflector to open the shadows. The object is to hold both highlight and shadow detail without producing a "flat" picture with muddy colors, and the Pentax Optio 750z had a little trouble with it.
The shot at right was taken with a +1.3 EV exposure compensation adjustment and with the camera's contrast adjustment at its lowest value, but the image is still a bit underexposed and detail is still lost in the strong highlights. The midtones do show fairly good detail, however. I didn't shoot any versions of this with more than +1.3 EV of exposure boost, because that level results in completely blown out exposures with the vast majority of cameras I test, and generally just run off a wide bracket of exposures while shooting, going back to evaluate them after the fact. Here, while I'd be interested in seeing a shot at +1.7EV (but not interested enough to drop everything and go back to reshoot it), I really don't think there'd be much point to it, given how badly the highlights are blown out in the +1.3EV version. Any more exposure, and the highlights on Marti's face would completely blow out, and even more of her shirt would be lost as well.
The Pentax 750Z's Auto white balance setting produced the most accurate results here, despite a very slight warm cast. The Daylight option resulted in a stronger warm cast, and the Manual setting had a slight reddish cast.
Overall color is a bit dark-looking from the underexposed midtones, but Marti's skin tones look pretty good. The blue flowers in the bouquet are quite dark, but without the strong purple tints produced by many cameras. (Many digicams have trouble with this blue, but the 750Z gets the hue just about right.) The strong reds, greens, and yellows look pretty good as well, though they too are fairly dark. Resolution is very high, and a lot of fine detail is visible in Marti's face and in the flower bouquet, with a lot of detail also present in the fabric background. The 750's anti-noise processing seems pretty subdued here, as there's very little loss of subtle detail in the low-contrast areas of Marti's hair. Shadow detail is moderate, and image noise is moderately high (but with a relatively fine grain pattern).
To view the entire exposure series from zero to +1.3 EV, see files O75OUTAP0.HTM
through O75OUTAP4.HTM on the thumbnail index page.
Excellent resolution and detail, but once again high contrast.
As with the wider shot above, the overall exposure here is slightly dim, though the highlights are actually quite bright. The shot at right was taken with a +0.7 EV exposure compensation adjustment (a bit more than the average required for this shot) and the camera's contrast adjustment at its lowest setting, resulting in reasonable midtones, but bright highlights and dark shadows. Still, detail is fairly good at both extremes of the tone curve. The Pentax Optio 750Z's 5x zoom lens helps prevent geometric distortion in Marti's features, and picks up crisp details in her face and hair. Resolution and detail are much stronger in this close-up shot, with strong definition in the strands of Marti's hair as well as in the details of her face.
To view the entire exposure series from zero to +1.3 EV, see files O75OUTFACAP0.HTM
through O75OUTFACAP4.HTM on the thumbnail index
Indoor Portrait, Flash:
Underexposure at the default settings with the flash in the normal and Slow-Sync modes, with a cool color balance as well.
The Pentax Optio 750Z's built-in flash illuminated the subject fairly well with a +1.3 EV exposure compensation adjustment, but the default exposure proved very dark. Even with so much exposure adjustment, the shot is still slightly dim overall. (This shot generally requires between +0.7 and +1.0 of exposure compensation, so the +1.3 required by the 750Z is a bit higher than average.) The color balance is a little cool, lending a blue tint to Marti's skin tone, but the flower bouquet and white shirt look pretty good. The camera's Slow-Sync flash setting also underexposed quite a bit, even with a +1.3 EV exposure compensation adjustment. Overall color is again quite cool, with very strong blue tints on Marti's features, though the background incandescent lighting does result in a slight orange cast.
To view the entire exposure series from zero to +1.3 EV in the normal flash mode, see files O75INFP0.HTM through O75INFP4.HTM on the thumbnail index page.
To view the same exposure series in the Slow-Sync flash mode, see files
O75INFSP0.HTM through O75INFSP4.HTM on the thumbnail
Indoor Portrait, No Flash:
Good to very good color with all three white balance settings, but higher than average exposure compensation required.
This shot is always a very tough test of a camera's white balance capability, given the strong, yellowish color cast of the household incandescent bulbs used for the lighting, but the Pentax 750Z handled it pretty well with all three white balance settings I tried. The camera's Incandescent white balance setting produced the best results here, with the most natural overall color and skin tones. The Auto setting resulted in a warmer cast and the Manual setting resulted in a slightly greenish image. Marti's skin tone looks very good, and the flower bouquet looks about right as well, though the blue flowers are a little dark and purplish. The main shot was taken with a +1.3 EV exposure compensation adjustment, which is a little higher than the +1.0 that's average for this test.
To view the entire exposure series from zero to +1.3 EV, see files O75INTP0.HTM
through O75INTP4.HTM on the thumbnail index page.
Very high resolution and a lot of fine detail, with good color.
Though just a little cool overall, the Pentax 750Z's Manual
white balance setting produced the most accurate overall color and white
value here. The Daylight setting resulted
in a warm cast, and the Auto setting had
a reddish tint. Resolution is excellent, and a lot of fine detail is visible
in the tree limbs and front shrubbery, as well as in the house front.
Details are slightly soft, but maintain the same level of sharpness throughout
Very high resolution and strong detail, with pretty good color. Underexposure at the default setting, with high contrast.
This image is shot at infinity to test far-field lens performance. NOTE that this image cannot be directly compared to the other "house" shot, which is a poster, shot in the studio. The rendering of detail in the poster will be very different than in this shot, and color values (and even the presence or absence of leaves on the trees!) will vary in this subject as the seasons progress. In general though, you can evaluate detail in the bricks, shingles and window detail, and in the tree branches against the sky. Compression artifacts are most likely to show in the trim along the edge of the roof, in the bricks, or in the relatively "flat" areas in the windows.
This is my ultimate "resolution shot,"
given the infinite range of detail in a natural scene like this, and the
Pentax Optio 750Z does indeed capture a lot of fine detail. The leaf patterns
and branches in the front shrubbery and in the tree limbs above the roof
show a lot of fine detail, as does the brick pattern on the house. Details
are well-defined and reasonably sharp, from corner to corner. The 750
underexposed this shot somewhat, apparently trying to hold onto detail
in the strong highlight of the paint around the bay window. Despite that
though, it loses essentially all detail there, and detail in the deep
shadows around the front door is only so-so as well, with high noise.
Here is a sample image with the camera's Vivid
color setting, which brightens the color overall, and really helps the
sky color quite a bit. The table below shows a standard resolution and
quality series, followed by ISO, sharpness, contrast, and saturation series.
Lens Zoom Range
A good 5x zoom range.
I routinely shoot this series of images to show the field of view for
each camera, with the lens at full wide angle, at maximum telephoto (5x,
in this case), and at full telephoto with the digital zoom enabled. The
Pentax Optio 750Z's lens is equivalent to
a 37.5-187.5mm zoom on a 35mm camera. That corresponds to a moderate wide
angle to a pretty substantial telephoto. Following are the results at
each zoom setting.
Moderate color casts with each white balance setting, but great resolution and detail.
This shot is often a tough test for digicams, as the abundance of blue
in the composition frequently tricks white balance systems into producing
a warm color balance. The Pentax Optio 750Z's
white balance system had a little trouble here, and either produced too
cool of an image or one that was too warm. I chose the Daylight
setting for the main shot, though overall results are reddish. The Manual
setting was much too cool for my taste, and the Auto
setting really too warm. (You could likely do a little color correction
on a computer to get better results here.) The red cast creates purplish
tints in the blue background and robe, and turns the white values pink.
However, resolution is very high, and the embroidered bird wings on the
blue robe show a lot of fine detail. (The original data file for this
poster was only 20MB though, so cameras like the seven-megapixel Pentax
750Z are capable of showing more detail than the poster has in
A very small macro area with great detail. Underexposure with the flash, but good detail still visible.
The Pentax Optio 750Z performed very well
in the macro category, capturing a minimum area of only 1.61 x 1.21 inches
(41 x 31 millimeters). Resolution is very high, and a lot of fine detail
is present in the dollar bill. Details are soft on the coins and brooch
due to the shallow depth of field from the very short subject distance.
A moderately high level of image noise interferes with detail definition
slightly, but results are still pretty good. Details soften quite a bit
toward the corners of the frame, but are fairly sharp on the dollar bill.
(Most digicams produce images with soft corners when shooting in their
Macro modes.) The Pentax 750Z's flash
throttled down a little too well for the macro area, producing a dark
exposure. Still, results aren't too bad, considering most digicams' flash
performance at such close range. (I'd still say to plan on using external
lighting for your closest macro shots.)
"Davebox" Test Target
Slightly dark exposure and color, but nearly accurate color with the Manual white balance.
Though just tiniest bit magenta, the Pentax Optio
750Z's Manual white balance setting produced
the most neutral white value here, as the Auto
and Daylight settings were both warm. Exposure
looks pretty good, though maybe a little dark, and the Optio 750Z distinguishes
the subtle tonal variations of the Q60 target well. The large color blocks
look about right, though there are some minor hue shifts, and the blues
are oversaturated more than with most cameras I test. (Other colors are
less saturated, closer to their correct values than I usually find.) The
shadow area of the charcoal briquettes shows a fair amount of detail,
with moderate noise. (Here's a sample image shot with the camera's Vivid
Pretty good low-light performance, although a slightly reddish color balance. Pretty good low-light focusing, very good with AF-assist light enabled.
The Pentax Optio 750Z produced clear, bright, usable images down to the 1/8 foot-candle (1.3 lux) light level at the 200 and 400 ISO settings (though you could arguably use the image captured at the 1/16 foot-candle, 0.67 lux, limit of the test at ISO 400). At ISO 80 and 100, images were bright down to the 1/4 foot-candle (2.7 lux) light level, though the target is visible at some of the lower light levels. Color balance is reddish with the Auto white balance setting, and the red cast increases as the exposure darkens. Noise is fairly low in most shots, and even at ISO 400, image noise is lower than I expected. The 750z focused down to between 1/2 and 1/4 foot-candle with its autofocus-assist light turned off, and in more or less complete darkness (on nearby objects, anyway) when the AF light was enabled. The table below shows the best exposure I was able to obtain for each of a range of illumination levels. Images in this table (like all sample photos) are untouched, exactly as they came from the camera.
(Note: If you'd like to use a light meter to
check light levels for subjects you might be interested in shooting, a
light level of one foot-candle corresponds to a normal exposure of two
seconds at f/2.8 and ISO 100. One foot-candle is also the light level
that roughly corresponds to typical city street lighting at night.)
Flash Range Test
A fairly weak flash, dim at eight feet, with falloff from nine feet on.
In my testing, the Pentax Optio 750Z's flash just barely illuminated the test target at 14 feet, showing significant decreases in intensity from the nine-foot distance on. Below is the flash range series, with distances from eight to 14 feet from the target.
High resolution, 1,450 - 1,500 lines of "strong detail." Lower than average barrel distortion at wide angle, higher than average pincushion at telephoto. Low chromatic aberration, very good corner to corner sharpness.
The Pentax Optio 750Z performed well on the "laboratory" resolution test chart for its seven-megapixel class. It started showing artifacts in the test patterns at resolutions as low as 1,200-1,250 lines per picture height vertically and horizontally. I found "strong detail" out to at least 1,450 lines horizontally (corresponding to the vertically-oriented target elements) and 1,500 lines vertically. "Extinction" of the target patterns didn't occur until about 1,800 lines.
Geometric distortion on the Pentax 750Z
is lower than average at the wide-angle end, where I measured approximately
0.6 percent barrel distortion. The telephoto end fared about the same,
as I measured approximately 0.6 percent pincushion distortion there. (While
the barrel distortion at wide angle is lower than average, 0.6% pincushion
is quite a bit more distortion than average at telephoto focal lengths.)
Chromatic aberration is very, as I only about one pixel of faint coloration.
(This distortion is visible as a very slight colored fringe around the
objects at the edges of the field of view on the resolution target.) Sharpness
is also much better than average in the corners of the frame.
Resolution Series, medium focal length
Resolution Test, Zoom Series
Viewfinder Accuracy/Flash Uniformity
A tight optical viewfinder, but very accurate LCD monitor.
The Pentax Optio 750Z's optical viewfinder
is very tight, showing only 82 percent of the final image area at both
wide angle and telephoto zoom settings. The LCD monitor actually proved
very slightly loose, showing just a bit more than what made it into
the final frame, though results were near 100 percent accuracy. Given
that I like LCD monitors to be as close to 100 percent accuracy as possible,
the Pentax 750Z's LCD monitor performed
well here, but its optical viewfinder has room for improvement. Flash
distribution is uneven at wide angle, with some falloff at the corners
and edges of the frame. At telephoto, flash distribution is more uniform,
O750Z Test Images
O750Z "Picky Details"
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