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Oct. 11, 2008

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Digital Camera Home > Digital Camera Reviews > Pentax Digital Cameras > Pentax Optio750Z

"Picky Details" for the Pentax Optio 750Z digital camera
(Timing, Power, and Storage Info)

Timing

When you press the shutter release on a camera, there's usually a lag time or delay before the shutter actually fires. This corresponds to the time required for the autofocus and autoexposure mechanisms time to do their work, and can amount to a fairly long delay in some situations. Since this number is rarely reported on (and even more rarely reported accurately), and can significantly affect the picture taking experience, I routinely measure both shutter delay and shot to shot cycle times for all cameras I test, using a test system I designed and built for the purpose. (Crystal-controlled, with a resolution of 0.001 second.) Here are the numbers I collected for the Pentax Optio 750Z:

Pentax Optio 750Z Timings
Operation	Time (secs)	Notes
Power On -> First shot	4.0	LCD turns on and lens extends forward. A little slow.
Shutdown	2.9 - 42	First time is time to retract lens, second time is worst-case buffer-clearing time. First time is average, second time is very slow, but corresponds to emptying the buffer of more than 100 small/basic images in continuous mode.
Play to Record, first shot	1.8	Time until first shot is captured. About average.
Record to play	6.3 / 2.1	First time is that required to display a large/fine file immediately after capture, second time is that needed to display a large/fine file that has already been processed and stored on the memory card. Rather slow.
Shutter lag, full autofocus	0.844 / 0.931	First time is at full wide-angle, second is full telephoto. About average. (Average is a range of 0.8 - 1.0 second.)
Shutter lag, prefocus	0.217	Time to capture, after half-pressing shutter button. Quick enough to catch fast-breaking action, but slower than average for prefocused operation.)
Cycle Time, TIFF, max resolution	13.1	Times are averages. No buffer memory, all shots take this long. Slow, but actually not bad for 7-megapixel TIFF images.
Cycle Time, max/min resolution	3.11 / 3.06	First number is for large/fine files, second number is time for "TV" size images. Times are averages. Shoots 5 large/fine images at this rate, then slows to an irregular rate of about 4.7 seconds apart. In TV mode, shoots continuously at this speed. Buffer clears in 9 seconds for large/fine images, about 2 seconds for lowest resolution. Rather slow.
Cycle Time, continuous mode, max/min resolution	1.4 / 1.16 (0.71 / 0.86 fps)	First number is for large/fine files, second number is time for "TV" size images. Times are averages. Shoots 5 large/fine images at this rate, then slows to an irregular rate of about 3.3 seconds apart. In TV mode, shoots continuously at this speed. Buffer clears in 9 seconds for large/fine images, about 1 second for lowest resolution. Not very fast for a continuous mode.

Average shutter response, slower than average cycle times. With full-autofocus shutter lag ranging from 0.84 - 0.93 second, it's solidly in the middle of the average range of shutter response. Its shutter response when "prefocused" (by half-pressing and holding down the shutter button prior to the shot itself) is fast enough to capture fleeting action, but at 0.22 second, is slower than average these days. Shot to shot cycle times are slower than average, a bit over 3 seconds between shots in single-shot mode, and fully 1.4 seconds for large/fine JPEG images in continuous mode.

Power

The Pentax Optio 750Z uses a custom rechargeable LiIon battery for power. Here are the power drain numbers I measured in various operating modes, along with projected run times based on the stated capacity of its battery pack.

Operating Mode	Power (@4.5 volts on the external power terminal)	Est. Minutes (1800 mA LiIon cell)
Capture Mode, w/LCD	576 mA	154
Capture Mode, no LCD	410 mA	216
Half-pressed shutter w/LCD	567 mA	157
Half-pressed w/o LCD	418 mA	121
Memory Write (transient)	604 mA	n/a
Flash Recharge (transient)	1365 mA	n/a
Image Playback	286 mA	310

With a worst-case run time of 154 minutes in capture mode with the rear-panel LCD enabled, and 216 minutes in capture mode with the LCD turned off, the Pentax Optio 750's battery life is well above average. In playback mode, the camera should be able to run for over 5 hours on a freshly charged battery. While I always recommend purchasing an extra battery right along with your digital camera, the Pentax 750z's battery life is good enough that most users will probably be able to get by with just the battery pack that's included with the camera.

Storage Capacity

The Pentax 750z stores its photos on Compact Flash memory cards, and a 32 MB card is included with the camera. (I strongly recommend buying at least a 128 MB card, preferably a 256 MB one, to give yourself extra space for extended outings.) The chart below shows how many images can be stored on the included 32 MB card at each size/quality setting.

Image Capacity vs Resolution/Quality 32 MB Memory Card		Fine	Normal	Basic	TIFF
3056 x 2296	Images (Avg size)	7 4.1 MB	15 2.0 MB	23 1.3 MB	1 22.2 MB
3056 x 2296	Approx. Compression	5:1	10:1	16:1	-
2592 x 1944	Images (Avg size)	10 2.9 MB	21 1.5 MB	33 945 KB	2 15.5 MB
2592 x 1944	Approx. Compression	5:1	10:1	16:1	-
2048 x 1536	Images (Avg size)	17 1.8 MB	33 945 KB	50 629 KB	-
2048 x 1536	Approx. Compression	5:1	10:1	15:1	-
1600 x 1200	Images (Avg size)	28 1.1 MB	55 579 KB	74 430 KB	-
1600 x 1200	Approx. Compression	5:1	10:1	14:1	-
1024 x 768	Images (Avg size)	60 607 KB	107 344 KB	148 197 KB	-
1024 x 768	Approx. Compression	5:1	8:1	11:1	-
640 x 480	Images (Avg size)	128 278 KB	175 180 KB	241 115 KB	-
640 x 480	Approx. Compression	4:1	5:1	7:1	-

Download Speed

The Pentax Optio 750z connects to a host computer via a USB interface. Downloading files to my Sony desktop running Windows XP (Pentium IV, 2.4 GHz), I clocked it at 805 KBytes/second, a very respectable rate. (Cameras with slow USB interfaces run as low as 300 KB/s, cameras with fast v1.1 interfaces run as high as 600 KB/s. Cameras with USB v2.0 interfaces run as fast as several megabytes/second.)