Okay, to look into this issue, which is actually not really so mysterious and arguable as it should be, the simple solution is to do measurbation. Once enough measurbations have been carried out and adequate results and data are obtained and compared, we can know about the true answer. Well, now it is when measurbators show their true value for existence this time!
In fact, the answers have already been there! So, further arguments are actually meaningless. Since quite some times ago, the Imaging Resource has routinely measured various shutter and system time lag figures in their Digital SLR test reviews, for 3 or 4 different timings under different usage conditions, namely, "Full Autofocus", "Prefocused", "Continous AF" and "Manual Focus", as called by them.
To know and understand the background for why they have been conducting the tests and how accurate are their test results, here is a quote of the introductory remark in the beginning of the timing test data page of their earlier DSLR test reviews:-
"When you press the shutter release on a camera, there's usually a lag time or delay before the shutter actually fires. This time allows the autofocus and autoexposure mechanisms time to do their work and can amount to a fairly long delay in some situations. Since this important number is rarely reported on (and even more rarely reported accurately), I routinely measure it, using a custom-built test setup. (Crystal-controlled, with a resolution of 0.001 second.)"
Okay, now let's read the performance data page of the latest Imaging Resource Pentax K10D review, we can first have a look at the measured figures and also the corresponding explanations which illustrates the true meanings of those, at the right side column in the table.
Nonetheless, do note that the explanations and remarks in the above K10D review page are, however, not entirely clear and exact. To know exactly, one need to look at some earlier test reviews which the Imaging Resource explains in more details for what they are actually doing. I think they just have assumed that their readers have already understood all those and thus have trimmed down the remarks (but then they might have forgot about there are new readers!).
Well, to make the case clearer, I shall explain once more in my own words and quote the words in certain previous Imaging Resource test reports, wherever appropriate, for the four measured timings of the (can be different) system time lags of a DSLR, as follows:-
1. "Full Autofocus":- The camera is put in the Single AF mode but the target is pre-focused beforehand but the shutter release button is released first. And then the timing is measured "from scratch" by re-pressing the shutter release button for measuring the time required till the exposure finally happens. The following is quoted from (the timing results page of) their earlier Canon EOS 30D review, here it is: "This is basically a measure of how quickly the camera can determine focus, with the lens elements already set to the focal distance of the subject."
The true meaning of this timing figure is to look into the responsiveness of the AF system under the Single AF mode, plus, the *remaining* system time lag of the DSLR. Since the Single AF is focus priority, full AF system operations, from measure the focus, move the AF motor (if any required) and then checking the focus again, are carried out before the shutter can be released. The travelling time of the lens is ignored and it's wise to ignore it as it varies with different lenses and different travelling distances for different objects and etc., as it is also mentioned very clearly about this by Imaging Resource in (the timing results page of) their Canon EOS 5D review, "AF time will vary greatly, depending on the lens in use, the brightness and contrast level of the subject, and the amount of travel required of the lens optics to move to the new focus position. The number at left is essentially a best-case figure with the Canon 100mm f/2.8 macro lens already in-focus on a target.";
2. "Prefocused": - The camera is put into Single AF mode again but the focusing is achieved beforehand with focus held and locked by keeping half-pressed for the shutter release button before the measurement. The true meaning of this measurement is an attempt to ignore about the delay incurred by the AF system and check the *net* system lag time;
3. "Continous AF":- Since in Continuous AF mode, it is not (correct) focus priority, which means that no correct focus will be re-confirmed and re-assured and the shutter release will not be withheld and it can be released at any time. So, whilst the AF are still in operation and continuously, the total system lag time can yet be shorter but it should be longer or just equal to the prefocused one as the AF system is still in operation which might affect the overall system responsiveness;
4. "Manual Focus":- It's self explanatory, the camera is put into MF mode and the system lag time is measured. Still, do note that the focusing system of the camera is not totally inactive as measurement of the in-focus point is being carried out continuously for the provision of focus indication to assist the user to do the MF.
Okay, now that we can go forward to check and compare the measured figures for different DSLRs, for the data results obtained in various Imaging Resource reviews. For the sake of easy reading and quick comparison, I summarise the results in the following table:-
| Camera | "Full AF" (Single AF, Prefocused but Released first) | "Prefocused" (Single AF, Prefocused and Held) | "Continuous AF" | "Manual Focus" | Source Page Link for the Timing Results |
| Pentax K10D | 0.254 s | 0.107 s | 0.183 s | 0.181 s | Click |
| Pentax K100D | 0.182 s | 0.149 s | 0.148 s | 0.150 s | Click |
| Pentax *ist D | 0.23 s | 0.13 s | - | 0.18 s | Click |
| Canon 30D | 0.245 s | 0.068 s | 0.105 s | 0.154 s | Click |
| Canon 400D | 0.20 s | 0.105 s | 0.12 s | 0.13 s | Click |
| Canon 5D | 0.149 s | 0.078 s | - | 0.133 s | Click |
| Canon 1Ds MkII | 0.18 s (?) | 0.070 s | 0.057 s (!) | 0.052 s (!) | Click |
| Nikon D80 | 0.250 s | 0.083 s | 0.095 s | 0.083 s | Click |
| Nikon D40 | 0.26 s | 0.098 s | 0.20 s | 0.19 s | Click |
| Nikon D200 | 0.21 s | 0.057 s (!) | 0.057 s (!) | 0.057 s (!) | Click |
| Nikon D2Xs | 0.045 s (!!!) | 0.045 s (!!) | 0.045 s (!!) | 0.045 s (!!) | Click |
| Olympus E-500 | 0.37 / 0.38 (??) | 0.095 s | 0.43 (??) | 0.32 (??) | Click |
| Sony A100 | 0.31 (??) | 0.116 s | - | 0.301 (??) | Click |
| Camera | Full AF | Prefocused | Continuous AF | Manual Focus | Source Page URL |
So, now that you can compare and judge yourself and I won't comment particularly on anything further. Just for a final remark, for people who are always trying to defend for anything and argue about human reaction time is the slowest thing on Earth, I indeed regard this "point" is indeed rather groundless and actually pointless. It is because in fact the machines are made differently as we can all see from the above. There are obviously great to certain degree of differences under the above four shooting conditions. The true fact is that cameras (of different grade) are engineered and built differently, as all camera makers are well known about this fact. BTW, who will really want to add even more time lag on the top of the somehow already slow human reaction time? Nevertheless, the human reaction time is not really that slow as some would believe, especially if the photographer has stood by to take some photos. If still unconvinced, just use a single-button stop-watch, press to start and try your best to press again to stop, then note the time difference, one can then see the (stood-by) human reaction time can still be quite fast (mine is about 0.12 s).
