50 1.8 II do it yourself calibration

Started Dec 20, 2006 | Discussions thread
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Paul G5 Regular Member • Posts: 256
50 1.8 II do it yourself calibration

Hi everyone,

Just wanted to pass along some info that might help the mechanically inclined people that have a front focusing 50 1.8 II. I bought this lens about a year ago off ebay for $50. The purpose was to take indoor pics of the kids in low light situations without a flash. I realized I was only getting usable pictures at f/4 and up. At 1.8, it was completely useless. So, I downloaded one of the charts and sure enough, the lens had front focus of about 10mm. Before I messed with the lens, I used my kit lens on the chart and it looked like it had front focus as well but only by about 2mm. So, I took out the .050" allen wrench and made the a slight adjustment on my XT to the focus and after a couple of back and forth's between the lens and the adjustment, my kit lens is now dead on. By the way, that adjustment is not one you want to do after a cup of coffee. Before doing anything else, I went and borrowed my dad's L lens and it was dead on as well on the chart. So, knowing that my XT was pretty much where it needed to be, I tried the 50 1.8 on the chart again and sure enough, it was at about 8mm front focus.

After doing lots of reading last night, I see that many people have a front focus problem with this lens. So, being that mine is out of warranty I did some research on how to take the lens apart and where and if adjustments can be made. Sure enough, I found the info on taking it apart and even where adjustments can be made for that particular lens. What I couldn't find is how to actually make the adjustments.

To make adjustments on this lens, one needs to be able to solder. As far as solders go, these are failry large and easy but I wouldn't recommend it to a first time solderer. Basically, once the lens is apart, there is a printed circuit board with chips on it and a place where the focus adjustment is. It is essentially 5 dots of solder in a row with the two outside dots being the biggest. To make adjustments, you connect the dots with solder. I had no idea where to start. So, I started from the right and connected the 2 furthest right dots, quickly put it back together and tried the chart. Sure enough, it was now at about 14 mm front focus so I knew then I started on the wrong side. I removed the solder I had just put on and then connected the two furthest left dots. Did my test again and sure enough, I am now at about just 1mm front focus at 1.8. I tried various other dot combos, but none brought it closer than that so I can't get it 100%, but at least now it's much more usuable for the purpose I bought it for.

I can post the link I found most of the info on if anyone wants it. I will have to go back in my history to see where it was. I figured if I messed up the lens I was only out $50 so it was worth the shot. It only takes about 10 minutes total to take the lens apart, solder and put it back together. It actually took longer for my soldering iron to heat up than it did to do the adjustment. If your lens is still under warranty, by all means send it back to Canon and let them do it. If it's just sitting on your shelve because it is frustrating you when you use it, you may want to try and make the adjustment yourself (if it's out of warranty).

Good luck,

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