PENTAX 540 High Speed Sync

[Edward Bussa]

I posted this over on another forum also, but 1) I was wondering if anyone else can confirm this behavior and 2) thought others could use the info.
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When using the PENTAX 540FGZ in P or Av mode, the program shift would go in the following sequence:

2.8 2000
3.5 180
4.0 180
4.5 180
5.6 125

Notice the shutter speed jump at 2.8 and again at 5.6!

So, eventually, I ended up locking in ISO 100 (instead of using auto mode), and the sequence went more like I'd expect, as follows:

2.8 2000
3.5 1500
4.0 1000
4.5 750
5.6 500

Now, when I noticed this, I originally the thought the ISO was floating during the sequence. Then I did the math and concluded my assumption couldn't be correct.

So, if my observations hold true with your equipment as well, you should be able to use HS sync in P and Av as you'd probably expect, you just have to FIX YOUR ISO rather than use AUTO.

I'm not sure how to explain this behavior, rather, it is what I observed.