Not for the faint of heart - DIY 350D backfocus fix

Started Dec 1, 2007 | Discussions
RobertoAvanzi Senior Member • Posts: 1,003
Not for the faint of heart - DIY 350D backfocus fix

Shortly after buying the 70-200 L IS f4 I noticed that the focus was not spot on, and that the lens had a bit of backfocus. I was not really noticing it on the 17-85 IS - the lens is not that sharp anyway, I though, and at those focal lengths and such slow aperture the subject was always almost completely in the focus range. I attributed the problems with the SIGMA 30mm f1.4 at apertures below 2.8 to its famous erratical behaviour. And I still had enough keepers.

But recently, things got worse (AF drift?) and the 70-200 was able to pinpoint the symptoms of the illness.

Printed some focus charts, all lenses were backfocussing by more or less the same amount. Went to the shop (not the one where I bought the camera, but the one where I bought the 70-200), tried my lenses on a 40D body, also not perfectly calibrated it seems, it was front focussing by at most 1 mm, nothing to bother about, in fact, except perhaps for some macro work (that I do not do). But, the 350D was systematically backfocussing 20 mm with the Sigma at 30 mm, about 16 mm at 70 mm with the 17-85 AND with the 70-200, and still around 12 mm at 200.

Canon in Willich was treating me in an arrogant way on the phone (no we do not have a price list for fixing AF problems on cameras and lenses), the shop where I bought the camera refused to help me (that's one reason more to stay with the new one), and then I remembered this

http://www.astrosurf.com/buil/autofocus/adjust.htm

Since I already decided to buy a 400D for the imminent travel, and later to have the 350D fixed and then ebayed, I decided to try it.

Finding two allen keys for 1/20" in germany is not easy, here is all metric, but I was lucky.

Not for the faint of heart. Waving an allen key in front of the sensor is not what you always wanted to do. Touch it and you are boned. And you have to exert some force while turning, and you hear some clicks.

The result? Now the camera is focussing MUCH better. A bit of front focus (but the other closest setting had a slightly bigger back focus), but something like one mm at the fastest setting on the 30mm sigma, and a couple of mm at 200 mm on the L zoom, nothing noticeable on the 17-85 IS.

Now, I am exhausted. Tomorrow is (weather permitting) another shooting day! The purchase of a new camera is delayed. I hope I can wait for the 40D successor and devote next year's budget to glass. A wide angle (The canon 10-22 or the new fast tokina 11-16) is due!

Roberto

 RobertoAvanzi's gear list:RobertoAvanzi's gear list
Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Tokina AT-X Pro 11-16mm f/2.8 DX Sigma 30mm F1.4 EX DC HSM Canon EF 70-200mm f/4L IS USM +2 more
RicksAstro
RicksAstro Veteran Member • Posts: 3,737
Re: Not for the faint of heart - DIY 350D backfocus fix

I've done this to ultra fine tune a 350,400,30D and 5D, all with fantastic results. It makes a huge difference in sharpness to have the camera focus tweaked.

Some say it's dangerous, or isn't really adjusting the correct thing, and it will be out of alignment. My experience has been that every camera has come out of the procedure a much better camera...never have any of the focus points been mis-aligned. Once tweaked, all lenses worked very well!

The 40D no longer has this option. It took me 3 40D's to find one that was a great focuser out of the box like my other cameras were able to be after tweaking.

Rick

ZeroTX Contributing Member • Posts: 518
Re: Not for the faint of heart - DIY 350D backfocus fix

Perhaps the 40D does this completely electronically, hence the lack of this manual adjustment?..... now if Canon would just put that in a menu setting, liike Nikon on the D300.

-Michael
--
Canon Rebel XTi
http://duran.smugmug.com

michaeldixon
michaeldixon Forum Member • Posts: 88
but it's in french!!

looks like an interesting website for those who like fiddling...but my french isn't that good. Any chance of a summary of the method? (like which way to you turn the screw?)
--
mike@michaeljdixon.co.uk

RicksAstro
RicksAstro Veteran Member • Posts: 3,737
Re: but it's in french!!

Push the allen wrench down towards the bottom of the camera to push focus back (correct front focus). Push wrench up towards top of the camera to pull focus forward (correct back focus).

Just move the slightest amounts possible...

Rick

michaeldixon wrote:

looks like an interesting website for those who like fiddling...but
my french isn't that good. Any chance of a summary of the method?
(like which way to you turn the screw?)
--
mike@michaeljdixon.co.uk

EricDP Regular Member • Posts: 456
Re: but it's in french!!

michaeldixon wrote:

looks like an interesting website for those who like fiddling...but
my french isn't that good.

Try google translation... it's a little rough, but good enough to understand the key points.

http://translate.google.com/translate?u=http%3A%2F%2Fwww.astrosurf.com%2Fbuil%2Fautofocus%2Fadjust.htm&langpair=fr%7Cen&hl=en&ie=UTF-8

michaeldixon
michaeldixon Forum Member • Posts: 88
merci bien, monsieur!!

I'll grind off a key and try it
--
mike@michaeljdixon.co.uk

Delphidb96 Contributing Member • Posts: 775
Re: but it's in french!!

I ran it through both Babelfish and Google translations and Google was the best.

Derek

EricDP wrote:

michaeldixon wrote:

looks like an interesting website for those who like fiddling...but
my french isn't that good.

Try google translation... it's a little rough, but good enough to
understand the key points.

http://translate.google.com/translate?u=http%3A%2F%2Fwww.astrosurf.com%2Fbuil%2Fautofocus%2Fadjust.htm&langpair=fr%7Cen&hl=en&ie=UTF-8

-- hide signature --

Derek Benner

-----

Proud owner of an XTi, 18-55, 28-105 Asph, 70-300, 100-400 and a DF400MZ flash. Loving it!!!

OP RobertoAvanzi Senior Member • Posts: 1,003
Re: merci bien, monsieur!!

michaeldixon wrote:

I'll grind off a key and try it

Just be VERY, VERY careful not to touch the sensor, and use only full, good batteries. Keep in mind that the key can enter several millimeters in the hole, so removing can be a bit tricky, but when it is inside it will be more difficult for the key to slip out.

Roberto

 RobertoAvanzi's gear list:RobertoAvanzi's gear list
Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Tokina AT-X Pro 11-16mm f/2.8 DX Sigma 30mm F1.4 EX DC HSM Canon EF 70-200mm f/4L IS USM +2 more
EricDP Regular Member • Posts: 456
Anybody try this on a 300D?

My 300D has always focussed slightly beyond the subject, but not much. Actually, I would say it more like the subject is on the very inner edge of the depth of field: it's usually in focus, but just barely, while things slightly behind are also in focus, but things in front are not. e.g. on a face, focus on the eyes and the eyelashes will be out but the ears will be in. I'm not sure if it's worth messing with it to achieve a perfect balance with the focus landing in the middle of the depth of field. Especially since this is only noticeable in the shallowest depth of field situations. Has anybody else tried this on a 300D? Worth the risk of a slip and scratch?

Paul De Bra
Paul De Bra Forum Pro • Posts: 12,499
do *not* try this in sensor-clean mode

The typical suggestion is to put the camera in sensor-clean mode so that the mirror flips up.

Much better is to manually (very gently) lift the mirror up and work with the camera simply powered down. The shutter remains closed and there is no risk of scratching the sensor (or actually the AA filter).

RobertoAvanzi wrote:

Shortly after buying the 70-200 L IS f4 I noticed that the focus was
not spot on, and that the lens had a bit of backfocus. I was not
really noticing it on the 17-85 IS - the lens is not that sharp
anyway, I though, and at those focal lengths and such slow aperture
the subject was always almost completely in the focus range. I
attributed the problems with the SIGMA 30mm f1.4 at apertures below
2.8 to its famous erratical behaviour. And I still had enough
keepers.

But recently, things got worse (AF drift?) and the 70-200 was able to
pinpoint the symptoms of the illness.

Printed some focus charts, all lenses were backfocussing by more or
less the same amount. Went to the shop (not the one where I bought
the camera, but the one where I bought the 70-200), tried my lenses
on a 40D body, also not perfectly calibrated it seems, it was front
focussing by at most 1 mm, nothing to bother about, in fact, except
perhaps for some macro work (that I do not do). But, the 350D was
systematically backfocussing 20 mm with the Sigma at 30 mm, about 16
mm at 70 mm with the 17-85 AND with the 70-200, and still around 12
mm at 200.

Canon in Willich was treating me in an arrogant way on the phone (no
we do not have a price list for fixing AF problems on cameras and
lenses), the shop where I bought the camera refused to help me
(that's one reason more to stay with the new one), and then I
remembered this

http://www.astrosurf.com/buil/autofocus/adjust.htm

Since I already decided to buy a 400D for the imminent travel, and
later to have the 350D fixed and then ebayed, I decided to try it.

Finding two allen keys for 1/20" in germany is not easy, here is all
metric, but I was lucky.

Not for the faint of heart. Waving an allen key in front of the
sensor is not what you always wanted to do. Touch it and you are
boned. And you have to exert some force while turning, and you hear
some clicks.

The result? Now the camera is focussing MUCH better. A bit of front
focus (but the other closest setting had a slightly bigger back
focus), but something like one mm at the fastest setting on the 30mm
sigma, and a couple of mm at 200 mm on the L zoom, nothing noticeable
on the 17-85 IS.

Now, I am exhausted. Tomorrow is (weather permitting) another
shooting day! The purchase of a new camera is delayed. I hope I can
wait for the 40D successor and devote next year's budget to glass. A
wide angle (The canon 10-22 or the new fast tokina 11-16) is due!

Roberto

-- hide signature --

Slowly learning to use the DRebel (only around 30.000 shots) and now also the Fuji E900.
Public pictures at http://debra.zenfolio.com/ .

 Paul De Bra's gear list:Paul De Bra's gear list
Fujifilm FinePix F200EXR Olympus OM-D E-M5 Olympus E-M5 II Panasonic Lumix G 20mm F1.7 ASPH Olympus M.Zuiko Digital 45mm F1.8 +3 more
Paul De Bra
Paul De Bra Forum Pro • Posts: 12,499
Try the "scotch tape" trick instead.

On the 300D the hole is actually square, and when I tried it the adjustment screw didn't budge at all.

As an alternative you can put a tiny strip of scotch tape on the back side of the mirror, all the way over to the side where the mirror normall rests on the screw. The piece needs to be small enough to not block the secondary or submirror from moving independently. The scotch tape pushes the mirror a bit forward, which moves the focus a bit forward. Works fine for me, and it would work for you but you can only fix backfocus with this trick, not frontfocus.

(My camera initially had a bit of frontfocus. I sent it in for service and it came back with backfocus, twice. I gave up on Canon service and just used the scotch tape trick.)

EricDP wrote:

My 300D has always focussed slightly beyond the subject, but not
much. Actually, I would say it more like the subject is on the very
inner edge of the depth of field: it's usually in focus, but just
barely, while things slightly behind are also in focus, but things in
front are not. e.g. on a face, focus on the eyes and the eyelashes
will be out but the ears will be in. I'm not sure if it's worth
messing with it to achieve a perfect balance with the focus landing
in the middle of the depth of field. Especially since this is only
noticeable in the shallowest depth of field situations. Has anybody
else tried this on a 300D? Worth the risk of a slip and scratch?

-- hide signature --

Slowly learning to use the DRebel (only around 30.000 shots) and now also the Fuji E900.
Public pictures at http://debra.zenfolio.com/ .

 Paul De Bra's gear list:Paul De Bra's gear list
Fujifilm FinePix F200EXR Olympus OM-D E-M5 Olympus E-M5 II Panasonic Lumix G 20mm F1.7 ASPH Olympus M.Zuiko Digital 45mm F1.8 +3 more
RicksAstro
RicksAstro Veteran Member • Posts: 3,737
disagree...Re: do *not* try this in sensor-clean mode

Actually, the shutter is FAR more delicate than the sensor cover is, and is closer to the adjustment screw. But, yes, the shutter is cheaper to fix.

Moving the mirror by hand also increases the risk of damaging the mirror, and requires both hands to be used for the adjustment.

Either would work, but I'd stick with sensor clean mode. As always, YMMV.

Singh Regular Member • Posts: 471
Canon why not install a little motor for fine adjustment?

It's a shame this can't be done electronically.

Instead of a small cap screw, a little motor could be fitted to make the fine adjustment. If a motor was installed Canon can set-up the camera as normal (factory default), and 'If' the camera is out of calibration the end user can then make the adjustment as required.

This would benefit Canon as there would be fewer cameras sent back to service due to being out of calibration. It would help the end user because they will not have the hassle of returning their camera becuase of a focusing problem.

Everyones a winner!!

 Singh's gear list:Singh's gear list
Canon PowerShot S110 Canon EOS 6D Canon EF 50mm f/1.4 USM Canon EF 135mm F2L USM Canon EF 70-200mm f/4.0L USM +4 more
EricDP Regular Member • Posts: 456
Re: Try the

Paul De Bra wrote:

On the 300D the hole is actually square

Since an allen wrench is hexagonal, it wouldn't grip very well in a square hole. What kind of wrench did you use? What size?

I think I would prefer a very slight front focus to a very slight back focus. With faces, most of the important features are in front of the eyes...

Colin Peart Regular Member • Posts: 193
Re: disagree...Re: do *not* try this in sensor-clean mode

If you don't want to manually hold the mirror up, you could use the custom function mirror lockup mode -- that way the camera holds the mirror out of the way, but the sensor is protected by the shutter.

Is there a similar screw to adjust the optical path through the viewfinder? My autofocus is dead on, but I appear to have backfocus issues if I rely on my eyes (aka manual focus). Mind you, despite my testing with a focus chart, I still can't decide if the problem is the camera, or my own eyes. At first I thought it was the camera, but as I ran more tests, I got better at focusing it manually, and I started to hit some right on... I plan on getting someone with better eyes than me to check it out before I consider talking to canon about it.. from what I can tell here, sending it for service is a little hit-or-miss.

-- hide signature --

Colin Peart

RicksAstro
RicksAstro Veteran Member • Posts: 3,737
Re: disagree...Re: do *not* try this in sensor-clean mode

EEEK! No, do NOT use mirror lock-up...it times out after a short while, and the mirror will slam back down.

I stand by using cleaning mode with fresh batteries...all the time in the world!

Rick

Colin Peart wrote:

If you don't want to manually hold the mirror up, you could use the
custom function mirror lockup mode -- that way the camera holds the
mirror out of the way, but the sensor is protected by the shutter.

Is there a similar screw to adjust the optical path through the
viewfinder? My autofocus is dead on, but I appear to have backfocus
issues if I rely on my eyes (aka manual focus). Mind you, despite my
testing with a focus chart, I still can't decide if the problem is
the camera, or my own eyes. At first I thought it was the camera,
but as I ran more tests, I got better at focusing it manually, and I
started to hit some right on... I plan on getting someone with
better eyes than me to check it out before I consider talking to
canon about it.. from what I can tell here, sending it for service is
a little hit-or-miss.

-- hide signature --

Colin Peart

OP RobertoAvanzi Senior Member • Posts: 1,003
Re: disagree...Re: do *not* try this in sensor-clean mode

RicksAstro wrote:

EEEK! No, do NOT use mirror lock-up...it times out after a short
while, and the mirror will slam back down.

I can imagine the panic. My allen key fits quite tightly in the hexagonal hole, so I had to exert a tiny bit of force to remove it (being very careful not to let it slip out too quickly when it is finally free and, for instance, hit the sensor... ouch). Using MLU is most definitely NOT what you want while doing that operation.

best
Roberto

 RobertoAvanzi's gear list:RobertoAvanzi's gear list
Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Tokina AT-X Pro 11-16mm f/2.8 DX Sigma 30mm F1.4 EX DC HSM Canon EF 70-200mm f/4L IS USM +2 more
Colin Peart Regular Member • Posts: 193
Re: disagree...Re: do *not* try this in sensor-clean mode

Good to know! I haven't tried to mess with it in any case.

I suspect that it may be tight because the factory may have used Lock-tite or a similar substance to hold the screw in place once they calibrated it.

thanos Regular Member • Posts: 300
Great! Can it be done on the lens too?

Well, I don't have the nerve to try this any time soon now, but it's good to now it can be done without any proprietary calibration machines.

But does anyone know if there is some similar way to adjust a lens like the Tamron 50-135/2.8?

Thanks.

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