Two Important Custom Functions for Proper Metering

There are two Custom functions (CFs) in all Pentax DSLRs which many new users (or even more experienced old ones) are asking about frequently. They are the CFs of "Link AF Point and AE" and "Lock AE with AF locked". I shall explain more below what these two functions are about and what proper setting should be selected for each of the CFs.

1. "Link AF Point and AE":-

I think to be more exact for better understanding, some words should be added for the description, just say if it is called "Link AF Points to the Evaluative Metering", I bet it would be better.

Now, let's look what exactly this CF means. Normally and by default, the 16-Segment Multi-Pattern Evaluative Metering does not take information from the AF system for determining the exposure value. However, if this CF is enabled. The Evaluative Metering will take into account which AF point(s) is/are in focus and which "corresponding" (see more below) metering segment(s) at these point(s) will be given more weight.

So, would enabling this CF help to improve metering accuracy and reliability? Putting aside the in-born deficiency of the Pentax DSLR metering system (which metering levels are much dependent on lens, metering mode, colour temperature and etc., even for the same objects), there are two reasons why this "feature" will not work well:-

(i) Object(s) that is/are in focus is/are not necessary the point(s) of interest, nor, each individual's reflectance it known;

(ii) The AF points of the SAFOX VIII system are not exactly aligned at the centrals of the metering segments. See the illustration below:-



Almost all Pentax DSLRs made since 2003 are having the same architecture as above, except the *ist DL/DL2 and K-m which some of the 11 AF points omitted. As you can see, only the dead centre metering segment has its AF points aligned exactly, whilst for all the remaining 9 surrounding metering segments, the "corresponding" AF points are not aligned, and some are even at the dead corner of the metering segment. And, there are still 6 remaining metering segments which do not have any AF point to cover.

Furthermore, the issue gets more complicated when the user selects an AF point manually or just let the camera decide for it. Just say if the user (as many users are) selects only the central single AF point most of the time, weight will only be given to the centre metering segment, but anyway it is *just* the basic assumption made by the Evaluative Metering, regardles of what AF point(s) the user/camera chooses. Afterall, the evalutive meter always assume the subject is in the centre of the frame, unless the CF "link AF point to AE" is enabled. If this is the case, and if the camera is let to select the AF point(s) (depending on the model, one or more AF points will be selected (e.g., the *ist D would select only one AF point whilst the *ist DS selects more than one point, as indicated), then those selected points will be given top priorit(ies) in the Evaluative Metering calculations.

After all the above explanations, I think the only case which the above Pentax CF should be enabled is only WHEN the Pentax DSLR is put into Auto AF point selection mode and the user does NOT recompose. This is the only scenario that the Evaluative Metering will do its job correctly as only under this scenario all the *preliminary* assumptions made by Pentax are valid. But do remember that the *assumption* of a subject is in-focus should be given more weight in metering does NOT usually hold - just imagine about taking landscapes, e.g., everything in the frame are at infinity and thus they should be all in-focus, so?

2. "AE-L with AF locked":-

As continued from the last part, the issue gets even more complicated when the user uses the AF lock and re-compose. If this CF is enabled, just say with a single AF point in Single-AF mode, the measured AE value will automatically be locked once the AF is completed. On the other hand, if this CF is disabled, once upon recomposition, the calculated Evaluative Metering value once again could be wrong, as the measured exposure value is Not Locked (but then this is by default), since the central metering segment of the evaluative metering is now pointing to another subject other than the interested object. If the user selects the Multiple Auto AF point mode and recompose, again, everything would be meaningless *just because* the AE is not locked and he/she recomposes, again! (but default it is!)

In fact, all the old days Minolta AFSLRs with multiple AF sensors (since the Dynax 7000i), some Pentax Z model AFSLRs, and every Canon and Nikon DSLRs will have AE locked by default or compulsorily when their cameras are put in Evaluative Metering mode. For many of them there is not even a CF to disable this for the Evaluative Metering. This leaves alone Pentax who just overlooked the problem and thus many Pentax DSLR users have been receiving more errors in the photos they took just because of this "simple" oversight.

Fortunately, the description of this CF is somehow clearer than the above one and at least it is more easily understood by most. As I have just said, I think this CF should be enabled by default, especially with Evaluative Metering, no matter which AF point or what AF point selection mode is selected. To de-link the AE lock from the AF system (after AF is to be locked) is just an *unique* oversight by Pentax indeed, which opens up this option is almost meaningless, for most users and will just create more troubles with even more exposure errors, which holds 100% true for the Evaluative Metering, at least.

If Centre-Weighted Average Metering is chosen and when the Single AF point at Central is used, enabling this CF could give more convenience for avoiding pushing the AE-L button all the time before recomposing. Well, this time it can be well assumed that the subject which is focused is just the point of interest, in this case! As for Spot Metering, since precise "circling" of an areat and careful selection of mid-grey objects is required, enabling this option may not be as practical, though.

Since Evaluative Metering is the default metering mode which is designed and aimed to be fool-proof. I highly urge Pentax to change their default CF setting, so as to be truly fool-proof, for the only reason, merely.

Least but not least, I must mention about the poor and unclear documentation which is also the culprit of creating the troubles, in addition to the inappropriate default setting. All the Pentax DSLR user's / operating manuals are simply poorly written IMHO, which the users could by no means know more about the actual practical meanings (not even to talk about more in-depth) technical knowledge) about many features and functions of their cameras - and of course, better appropriate modes and settings could not be selected by many novice (or even some more experienced) users, as a result. Afterall, all the confusions and inaccuracies show how unthoughtful Pentax really are. In contrast, my Canon 5D has far more thoughtful default settings which are more logically put as well as better documentation, which the difference is clear and has been shown. If anyone who is unconvinced, just go to the Pentax and Canon official websites to download some of the user manuals to compare!