The Manfrotto 521PFI problem

B

bengiles

Well-known member
So I've still got this 521 PFI while I wait for the dealer to talk with the Manfrotto rep. I pulled out a multimeter tonight and had a play...

The problem I'm trying to resolve is the iris not fully opening - always a third stop out. The interesting thing I've discovered is that zero impedance on the dial equates to minimum aperture and max impedance is max aperture. Interesting because this suggests that adding a resistor in line might solve the problem. It's a 22k pot on there.

Anyone got any intell on what additional impedance the camera might want to see to persuade the lenses to open fully - without making the whole thing too sensitive across the range?

Ben.

www.matobo.co.uk
www.bengiles.co.uk
 
After a morning of playing around with various resistor values, I think I've cracked the 521PFI. The answer is 2.1 K ohm. I've now got a fully functioning and smooth electronic follow-focus which focuses right through the full range of all of my active MFT lenses and, with this small hack, now fully opens and closes the iris on all of them.

And you don't need to touch the 521 itself - I've made a temporary pad cable with the resistors in-line between a 4 pole 3.5mm jack and socket. Just about to order the parts to do something neater and more robust.

Nice.

Ben.
 
If there's a demand for them, i'm happy to look into getting a batch made up.

Let me know if you're interested.

Otherwise, I'll knock up a quick "how to" video very soon.

Ben.
 
I'm interested - happy enough to buy off you as you've put the time in for R&D.
Just as happy to make my own if you are going to post the secret recipe.
 
bengiles said:
After a morning of playing around with various resistor values, I think I've cracked the 521PFI. The answer is 2.1 K ohm. I've now got a fully functioning and smooth electronic follow-focus which focuses right through the full range of all of my active MFT lenses and, with this small hack, now fully opens and closes the iris on all of them.
Click to expand...
Great work, bengiles, I'm very interested to test your findings on my AF100 and 521PFI, which has been working properly on all Micro 4/3 (and many legacy Four Thirds) lenses I've tested it on. One question that comes to mind is how precise the 2.1K resistance will need to be to produce reliable results? As you may know, standard 5% precision resistors are commonly available in 2.0K and 2.2K values, but not at 2.1K. Likewise, I'd expect the nominal 22K value of the potentiometer in the 521PFI may vary by as much as 10% across different units.
 
lpowell said:
One question that comes to mind is how precise the 2.1K resistance will need to be to produce reliable results?
Click to expand...

Good question. I went and bought some regular 2K and 2.2K resistors after posting yesterday and tested them on a multimeter. I used one of the 2K resistors, which measured at 2.05K and made up a new cable which seems to be working fine. I think the ideal scenario would be to replace the pot inside the 521, but this looks like an effective workaround for the time being. I used increments of 470ohm resistors to find the correct value (235 when 2 are used in parallel) and, anecdotally, it looks like you've got around 200 ohms flexibility in terms of the "window" between giving it enough resistance to achieve a fully open iris and too much that it then starts to restrict full closure of the iris.

Will post a video later today.

Ben.
 
Hi Tom.

No, I didn't. I understood it had focus issues. Which lenses are you using it with successfully through the entire focal range?

Ben.
 
Hi Ben,

I've used the Lumix 14-140, 7-14, 100-300 and also the Olympus 14-35 f2. I understand some people find that it focuses past infinity which may be true; I didn't notice any focus issues personally, though I have to admit I didn't really check for that whilst I was using mine.
 
Thanks Tom.

It would be kind of useful to know definitively. There's so much misinformation out there. A guy calling himself HD Warrior announced that he'd sorted it last year by tweaking the pots on the Foxi, only to then (I think) update that to say the pots adjusted only the iris and that the Foxi continued to have full-range focus issues.

T'would be useful to have the facts!

Cheers,

Ben.
 
As far as i remember, the lens update that came after Philip Johnston's article sorted the issue. You sound like the man to give us the definitive answer though, you should buy one and test it definitively! I hear there's one going on BB List ;)
 
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Happy to test it for you, Tom, but - no - I still don't want to buy your Bebob, despite constant emails from the archaic BB List telling me off for not being a good chap... :happy: By the way, I hadn't reaiised it was you selling it until now.

Joking apart, I've seen several comments saying the Foxi works, only for them to be then retracted or admitting that they haven't actually tested it properly. I can't see the point in that.

And that's the simple reason I wasn't interested in going ahead with a Bebob Foxi - things like:

"Works fine on my lenses, as i suspect you know!" - followed by - "though I have to admit I didn't really check for that whilst I was using mine."

I'm sure you'll sell it, Tom, but maybe you should put some legwork in first and prove that the thing actually works! :happy:

Bebob would probably be very grateful - they still don't officially support the AF100/101:

http://www.bebob.de/Remote-controls/FOXI-DVX-HD.html

Ben.
 
Sorry Ben, don't mean to sound at all combative, but I'm not an engineer as you clearly are. All I've said is that it works for me. I haven't tested it for focussing past infinity because I just get the shot in focus and press record. I'd appreciate it if you didn't quote me as a form of attack - i was trying to be helpful. I'll leave pedants corner now.
 
Hi Tom.

I really hadn't intended to offend you - I guess my sore head got the better of me this morning and the added smilies didn't offset the tone. Sorry.

For the record, I really wouldn't claim to be an engineer - I'm not bright enough for that. Thankfully, this 521 stuff is pretty simple.

As an update for anyone who has the 521 and would still like to make it work fully without adding a pad cable, I've found a supplier of the Piher pot that lives inside the unit and controls the iris. They're going to send me a 25K version (24 not available) and I think that should do the trick - it means that you'll get a true 0 ohms at the botom end and a bit more than you need to fully open at the top end.

Will update once I've got it in there.

Ben.
 
Hi Ben, Tony here from XSVpro, I did a little work with you in London with my AF and your GH2?, was looking into this setup myself and recognised the logo on the Matte Box in your video. Hope all is well and thanks for the tip!
 
Hi Tony.

Good to hear from you. Was reading your thread about lenses. I've gambled and decided to go with MFT native lenses - I think it's a format that will only get more popular. Ordered a 12-35 a few days ago - should be arriving tomorrow. Have got a 14mm and 20mm selling on ebay at the mo.

Re the Manfrotto, I've got 10 new pots on their way from Texas. If that works, I'll have 9 going spare and up for grabs. Due to arrive on Weds/Thurs.

Cheers,

Ben.
 
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