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04-29-2009, 12:13 PM   #1
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problem with my 540

The zoom feature on my Pentax AF540 stops when I get to 58mm and won't go higher. Have I unintentionally pushed some setting that limits it? Or used some mode that limits it? Or is my flash malfunctioning?

I thought I was in leading-shutter mode.

Any help appreciated.

04-29-2009, 12:31 PM   #2
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What lens do you have attached? Is it in auto/manual zoom mode?

My zoom function wouldn't work at all so I had to get it fixed cost £70 is yours under warranty?
04-29-2009, 12:34 PM   #3
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Are you displaying the zoom position in APS-C format? 58mm is "equivalent" to 85mm in 35mm format.

85mm in 35mm format is the max position of the 540. It can't go any "more tele."
05-06-2009, 01:30 PM   #4
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Similar issue with my 360FGZ

I posted earlier today a similar Issue with my 360FGZ... will not zoom past 58mm. Contacted pentax and they said there was an issue with the flash. Perhaps you can check one other thing with your flash that I noticed with mine... Once the Distance meter stops displaying (don't half press the shutter for a little while) the flash actually displays the correct focal length.

One last thing.. previous poster.. Please correct me if I am wrong (and I recognize I'm probably wrong), but if the flash is "interpreting" the focal distance for APS-C it should zoom to 75mm for a 50mm lens. The multiplier is 1.5

That is what I understand... but I really could be wrong. Perhaps you too will need to contact Pentax to get some answer

05-06-2009, 04:49 PM   #5
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QuoteOriginally posted by Wildfire_ja Quote
One last thing.. previous poster.. Please correct me if I am wrong (and I recognize I'm probably wrong), but if the flash is "interpreting" the focal distance for APS-C it should zoom to 75mm for a 50mm lens. The multiplier is 1.5

That is what I understand... but I really could be wrong. Perhaps you too will need to contact Pentax to get some answer
You're thinking about it backwards. The flash doesn't really have a focal length like a lens. It just has a reflector which focuses the light at different possible angles. By industry convention (for whatever reason!), there are standard flash zoom stops at positions that cover approximately 74°, 65°, 54°, 40°, 29°, and 24°. (Give or take.) These angles of coverage happen to correspond on 35mm full-frame to 24mm, 28mm, 35mm, 50mm, 70mm, and 85mm. On a 1.5×-sensor dSLR, the same field of view is covered by a 1.5× shorter lens — so the flash displays numbers 1.5× smaller.

When you put that 50mm lens on there, it should display 48mm — that's the 29° zoom point in 1.5× crop terms, which is the narrowest point which still covers the focal length of the lens. (Makes sense — just a few mm wider than the actual focal length.) The surprise comes when you put a 70mm lens on there — turns out, 58mm is as narrow as the flash can go — it's the 24° point.

Does that make sense?
05-06-2009, 08:28 PM   #6
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Wow... thanks much... I wanna tell you that I totally understand... but truth is ... I am daft. I do understand the crop factor.. and I will admit that I was expecting the flash to behave like my old 500FTZ. I understood how that one worked. With my 50mm attached the the equivalent focal distance in film is 70mm and the flash displayed 70mm. The same applied for other focal lengths. That flash would step through and display the effective 35mm distance. If I am understanding you right.. what the 360FGZ does is to attempt to do is to present the focal lenght as close to actual 35 focal lenght as possible. Therefore my 50mm lens will show as 48 (the closest angle it can get to the actual 50) and 58 for my 100.

K... I sorta understand.

I do hope you're right. I'm not relishing the idea of sending my flash back... I even went to your guide today to research a new one.

Thanks much.. the help is really appreciated...
05-07-2009, 04:49 AM   #7
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QuoteOriginally posted by Wildfire_ja Quote
If I am understanding you right.. what the 360FGZ does is to attempt to do is to present the focal lenght as close to actual 35 focal lenght as possible. Therefore my 50mm lens will show as 48 (the closest angle it can get to the actual 50) and 58 for my 100.
As close to the actual, actual focal length as possible.

The flash will also convert the display for Pentax's 645 medium-format cameras. The flash will still display the zoom setting that's closest to the actual focal length of the lens. Since a lens with a given focal length will give a much wider field of view in that format, but the actual reflector of the flash can't actually do anything different, the possibilities go from 45mm to 150mm instead of from 24mm to 85mm on film or 16mm to 58mm on dSLRS.

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