The Manfrotto 521PFI problem

bengiles said:
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.
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Good work, I'll be interested to hear how that works out. Piher makes a variety of potentiometers, as seen here:

http://www.tawelectronics.com/piher_potentiometer.htm

If you know the Piher model number, we can find out how its precision is rated. Most potentiometers' max resistance is rated at +/- 10-20% of their nomimal specs. In addition, the sensitivity of each AF100's remote control circuit can vary over a similar range. The max resistance of my 521PFI unit measures 20.8K ohms, which is 4% higher than its nominal 20K specification. This particular unit works properly on my AF100 with all supported MFT lenses I've tried. If the precision of the 25K Piher pots is no worse than 10%, they should all have at least 22.5K resistance.
 
lpowell said:
Good work, I'll be interested to hear how that works out. Piher makes a variety of potentiometers, as seen here:

http://www.tawelectronics.com/piher_potentiometer.htm

If you know the Piher model number, we can find out how its precision is rated. Most potentiometers' max resistance is rated at +/- 10-20% of their nomimal specs. In addition, the sensitivity of each AF100's remote control circuit can vary over a similar range. The max resistance of my 521PFI unit measures 20.8K ohms, which is 4% higher than its nominal 20K specification. This particular unit works properly on my AF100 with all supported MFT lenses I've tried. If the precision of the 25K Piher pots is no worse than 10%, they should all have at least 22.5K resistance.
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The model coming to me is PT15NV18-253A2020. Here's the data sheet:

http://www.piher-nacesa.com/pdf/14-PT15v03.pdf

Quoted tolerance is +/- 20%. Interesting that you say you have a 20K pot. Mine has a 22k pot inside it. Based on the additional 2.1k that was working for me, I was ideally after a 24K (sadly not available in that impedance) - but I figured a small amount of additional headroom should be OK, without changing the linearity from closed to open.

It's not a very scientific approach, but it seems to be working so far...

Ben.
 
bengiles said:
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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im going that way too, I don't think I will ever want to lay $25K for lenses that I can rent at the clients expenses, for my own work stuff and small corporate/film projects I think the native lenses are just fine. I have the 45mm 1.8 on its way.

back on subject, thanks again for figuring this out, I nearly grabbed one hen I had 4/3rd lenses. Might be sending cash your way or a cable or following your how too.

by the way, I have a jib crane and external recorder for pro res 422hq and three 650 Fresnel if you ever need such things London way ;0)
 
Update - it works.

The new pots arrived from Texas today. They're not an absolute match physically, but they're all Mouser had in stock - would have meant ordering hundreds from Piher otherwise. You can see the differences here:

Modified 521PFI 001.jpg

The original is on the left. However, it's nothing too dramatic and you can snip the third leg from the original and solder it on the new 25K pot (see notes below.) The result is here:

Modified 521PFI 002.jpg

You can see I've had to bend the legs slightly. The original pot is custom made by Piher for Manfrotto, but the new pot went in with a bit of manipulation to the legs and sits nice and securely.

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I can confirm that, with this hack/mod, the Manfrotto 521PFI now works perfectly through the entire range with the 25mm/1.4, 45mm/2.8, 12-35/2.8 and 100-300/4.0-5.6 lenses.

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If you feel like doing it yourself, I've got 8 spare pots which I can send at cost (£2.00 each plus postage.)

A few tips:

1) Make sure you have a good clean area with light, a fine-tipped soldering iron, desoldering pump, small snips and fine plyers. Allow 30 mins of time.

2) The grease on the focus pot shaft is very sticky - more like glue, so take your time and avoid touching the grease - you'll need white spirit or similar solvent to remove it and it will attract dirt easily and make you cry.

3) You'll need to carefully snip the third leg off your old pot and solder it on to the new one (or perhaps better still, fabricate a small third leg from wire - once you've tinned it, it should be strong enough to support the pot securely.) I cheated by snipping one of the legs off a spare pot and bending/soldering that. You'll also need to bend/snip the additional legs on the sides - I just snipped mine and they help to secure the pot against the board.

4) Don't be a numpty like me and solder the pot onto the wrong side of the board... it'll just take you longer and wind you up...

I think that's about it. If you don't want to mod the internals of your 521 PFI, my patch cable idea in the Vimeo link is still valid and works fine - just make sure you secure cables adequately, as these 3.5mm 4 pole jacks aren't the most robust termination for professional work.

Have fun.

Ben.
 
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I had a 521PFI but wanted a combined focus, start/stop, zoom and iris remote, so I bought the Studio 1 Productions "ProZoom" $99 remote.

I did a detailed review of this remote somewhere in one of these forums. Pretty fantastic, especially on smooth zooms in/out.

I found the focus on the 521PFI to be too sensitive. The ProZoom is also sensitive and I cannot recall whether there is any difference. At the end of the day unless you have a multi-turn helix pot the diameter of the dial is what determines the sensitivity. Problem is the only one that might seem to work costs $150 i.e. 1.5 times the cost of the entire remote. So, it's back to the drawing board. I tried to put a 2.5 inch dial on the remote but it got in the way.

What I would like in a remote is to have the ability to dial in and set three (3) separate focus settings that I could then switch to. I cover a lot of stage presentations where, sometimes, you want front stage, mid stage and back of stage. It's very annoying to be at 48 feet on focus and when you try to go to 52, it goes to 55, then to 46, then 54 before finally going to 52. Then, when you finally get it set to where you want it and you inadvertently brush up against the dial, it goes off, this is even more annoying.

I don't find on my camera that red lining works all that well. Many times there is nothing that will highlight. And, if you are able to see highlighting, it seems to stay on for too wide a range.

I used to string out a 100 foot surveyor's tape but switched a few months ago to a permanently-mounted laser distance meter. The disadvantage of this is you have make your measurements before a theatre has any people in it, otherwise it could be dangerous. The laser meter, of course, does not work out of doors in broad daylight.

Any suggestions ?
 
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