[Class A]

There's a lot more to a full featured dedicated system flash than P-TTL mode.

I finally had a chance to read through pages 14-19 of your guide you pointed me to regarding my question as to what you were referencing with your statement I quoted above.

The only features I found that are not also found with other manual solutions are:

1. Automatic control of flash head zoom setting.
2. Flash to subject distance indication.
3. Flash-ready indication in the viewfinder.

Features 1. & 2. only make sense for an on-camera flash, pointing directly at the subject (i.e., not bouncing it from a reflective surface). The P-TTL flashes I've seen all disable at least 2. once you take the flash head off the "direct forward" position, which makes sense as in any other usage scenario, the distance indication would not be reliable anymore.

Disabling feature 1. would also make sense in such a scenario because when bouncing flash the ideal setting for the flash head is determined by the distances between camera - surface - subject. You don't want that setting to be automatically changed whenever changing the zoom setting of the lens.

Speaking of zoom lenses, feature 1. only makes a noteworthy difference when using a zoom lens. With a fixed focal length, one can just set the flash head zoom accordingly, sometimes deviating from what the nominal focal length would suggest. As you state yourself elsewhere in the guide, this is often useful.

IMO, this reduces the applicability of 1. & 2. to subtle fill flash since a key light from an on-camera flash will give a typically rather undesirable look. Do you agree?

Feature 3. (flash-ready indicator in the viewfinder) is nice. Many flashes support a "ready beep" as a substitute, but I personally turn it off because I find it distracting for subjects. A silent visual feedback in the viewfinder is much preferred.

Does it work for off-camera flashes as well, or is the indication for the on-camera mounted flash only?

Modern flashes recycle rather quickly though, so I don't find a ready signal to be super essential anymore, but surely it can be nice to have.

Did I miss anything?

On the negative side, in comparison to a good manual system, we seem to have:

1. No manual control for off-camera flash units from the camera position.
2. No individual turning on and off of flashes from the camera position.
3. No influence on the off-camera flash power level ratios or flash compensation from the camera position.
4. Off-camera flash heads cannot be zoomed from the camera position.
5. All the issues with optical triggering such as limited distance, less flexibility regarding placement, reliability in less then ideal situations, introduction of shutter lag, and sometimes the issue of making sure that control flash is not seen in the image (it can sometimes be seen in reflective areas, even when the on-camera flash is set to "control" mode.).

After going through your guide, admittedly speed-reading at times, I gained the following impression regarding P-TTL power level control:

• Power ratios can be set for a maximum of two off-camera flashes.
• The only available ratios are 50%, 33%, or 66%. Different ratios or finer control are unavailable.
• The on-camera flash reduces to a heavy, bulky optical trigger for those off-camera flashes. If it doesn't, i.e., if it can still contribute itself in the presence of two off-camera flashes, how does its own lighting ratio control setting influence the overall mix?
• None of the off-camera ratios or flash compensation levels can be changed from the camera position.

Please correct me if any of the above is not applicable.

I also wonder what happens if both off-camera flashes are set to "1/3" lighting ratio control. Does that work out to a 50:50 contribution again?

P.S.: I noticed a couple of inaccuracies in your guide:

You wrote that radio triggers support a range of "20-30m". I cannot think of many triggers that do not easily support 100m range or more outdoors. Some radio triggers rather have the inverse problem in that they require a minimum distance to work (say 25cm or so). This can lead to challenges when doing macro work, for instance. That's why the Cactus V6 has a "short range" option that removes this minimal distance requirement at the expense of extreme (100m+) reach. It will still support ~30m in that mode.

You state that HSS bursts "only lasts for as long as, or shorter than the time value set (1/500s / 1/1000s etc.).". That's not true. HSS bursts always have to last as long as it takes the second curtain to reach the end of its travel. That's 1/180s in the case of Pentax. So you cannot save power by increasing the shutter speed in HSS mode. On the contrary, higher shutter speeds cut down on the light received from a flash so if you want to maintain the same flash exposure, the flash needs to work harder accordingly.

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Last edited by Class A; 11-21-2015 at 07:34 AM.

[mcgregni]

I have replied in to the above detailed post from ClassA over on my Guide Support thread, in order to avoid cluttering this thread with more general P-TTL talk .....

https://www.pentaxforums.com/forums/125-flashes-lighting-studio/306843-its-time-upgrade.html