izofotoblog

For long time now, i always hated, how this lense misfocus (ff in most cases) target at open apertures. If i recall right, i read somewhere, that most of these lenses came with ff out of factory, but that’s just guessing imo. I was aware that there is a possibility to do diy calibration, so i try it.

Before any action: i recommend this only to those, who are handy and have proper tools etc!

First, some info:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=21351476
http://f20c.com/stuff/canon/partslist/EF%2050%201.8%20II.PDF
http://photography-on-the.net/forum/showthread.php?t=118806&highlight=ron+chappel
In the last link, you must be signed in to view the pictures, which are very important (i know, i should take some pics, while i was doing this, but just forgot, sorry).
For the calibration, there is no need to dissemble lens group, you only need access to electronic circuit, where contacts for calibration are located (red ring on the picture below).

So, here is inside of the lens. Like i said, we’re interested only in that 5 contacts, which are soldered together from factory, i think. First thing to do is remove the zinc, so all contacts are free and ready for testing.

From all 5 contacts, 2 are in circle shape, positioned far most left and far right and 3 squares in between. In the link, mentioned before, author says that in his case for good focus he need to soldier far most dot on the left in square next to it. Anyway, calibration is done by choosing two contacts to each other. Moving pair to left you move focus more to back (so, this would be in most cases for this lens, i guess), and moving to right you get focus more to front. In my case, even if i moved pair far to the left, i still did get some front focusing, but when i leaved all contacts unsolder (clean), focus was on the spot.

If the font focus is not that big, you should try to move the pair more to right etc. Best thing to do is just test the lens and redo the procedure if necessary.

So, if u have the guts, you can try this and see how it goes. Of coarse, i don’t take any responsibility for any damage that you could face with toying with your lense.
This are results after the calibration:

100& crop from pic above.

At last, lense is focusing like it should from the start. All photos above are taken @ f/1.8 and they are usable, for what i thought is not possible with this lense, sharpness is also nice, imo.

So, i’m happy wide open again..

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