20D Canon focus advice

Hi all,

I have a nagging suspicion that the focus on my new 20D isn't all that it
should be. Do any of you have any suggestions on the best way to test this?
I was thinking of photographing a sheet of A4 "Math - graph" type paper.

If the camera's focus is out, will it be out consistently when focusing on
close and distant objects? Should I have the lens wide open or stopped down
for the test. Is it possible for an image to be in focus through the
viewfinder, and yet be out of focus at the CMOS sensor? Any other thoughts
(I only have the one kit lens at this time, so I can't do any lens
comparisons).

Thanks for your input.

Cheers,

CC

Cockpit Colin wrote:
Hi all,

I have a nagging suspicion that the focus on my new 20D isn't all
that it should be. Do any of you have any suggestions on the best way
to test this? I was thinking of photographing a sheet of A4 "Math -
graph" type paper.

Try printing this:

http://www.photo.net/learn/focustest/scale45.jpg

Place it at 45 degrees and focus on the line in the middle.

Should I have the lens wide
open or stopped down for the test.

A large aperture will show the results more clearly.

Is it possible for an image to be in focus through the viewfinder,
and yet be out of focus at the CMOS sensor?

Yes, but IMO that would mean a major physical problem
which I would expect to show up as other symptoms as well.

-Mike

Hi all,

I have a nagging suspicion that the focus on my new 20D isn't all that it
should be.


Hi Colin...

Not sure what you mean about the focus...whether you are talking about
through the lens or the actual results.

Don't mean to be condescending here...but if you are talking about the focus
through the lens, have you checked the diopter adjustment on the viewfinder.
The only reason I ask is that I had a friend with the same complaint and the
diopter just got knocked a fraction.

Cheers
Steve

"Cockpit Colin" wrote in message
...
Hi all,

I have a nagging suspicion that the focus on my new 20D isn't all that it
should be. Do any of you have any suggestions on the best way to test
this?
I was thinking of photographing a sheet of A4 "Math - graph" type paper.

If the camera's focus is out, will it be out consistently when focusing on
close and distant objects? Should I have the lens wide open or stopped
down
for the test. Is it possible for an image to be in focus through the
viewfinder, and yet be out of focus at the CMOS sensor? Any other thoughts
(I only have the one kit lens at this time, so I can't do any lens
comparisons).

Thanks for your input.

Cheers,

CC



I'm probably teaching old dogs new tricks but always ensure you know which
AF point the camera is focusing on, I always lock it to the center one, and
remember the AF sensors maybe bigger than the markings in the viewfinder.

take a look at http://www.knighttrain.freeserve.co.uk/400.htm where you can
see 10D AF markings and sensor sizes.

This is based on 10D info but probably holds true for the 20D.

In article , says...

I'm probably teaching old dogs new tricks but always ensure you know which
AF point the camera is focusing on, I always lock it to the center one, and
remember the AF sensors maybe bigger than the markings in the viewfinder.

take a look at http://www.knighttrain.freeserve.co.uk/400.htm where you can
see 10D AF markings and sensor sizes.

This is based on 10D info but probably holds true for the 20D.

Also, try the test with different lenses and versus your own manual
focusing ability.

I thought my camera was poor on focus, then I tried beating it with my
own eye. The AF wasn't perfect, but I wasn't anywhere close!

If you still have problems, send the camera with your lenses to a Canon
repair facility. People have reported success after the techs re-
calibrated their body and lenses.
--
http://www.pbase.com/bcbaird

Cockpit Colin wrote:
Hi all,

I have a nagging suspicion that the focus on my new 20D isn't all that it
should be. Do any of you have any suggestions on the best way to test this?
I was thinking of photographing a sheet of A4 "Math - graph" type paper.

If the camera's focus is out, will it be out consistently when focusing on
close and distant objects? Should I have the lens wide open or stopped down
for the test. Is it possible for an image to be in focus through the
viewfinder, and yet be out of focus at the CMOS sensor? Any other thoughts
(I only have the one kit lens at this time, so I can't do any lens
comparisons).

Thanks for your input.

Cheers,

CC


Using an angled scale is not the best way to test your focus. 20D's have
a really tight tolerance to distance from the rear element to the film
plane (sensor). They are much less tolerant to errors than a 35mm camera
is due to the closeness of these 2 points.

According to Canon: correct focus is anywhere within the depth of field
of the lens. If you bought a camera with a "Kit lens", the focus point
could be anywhere within a inch of the centre at about 2 feet and still
be within acceptable factory tolerances. Pretty poor stuff when you
decide to shoot some flowers or small animals!

The most common focus error on 20Ds is called "back focus" which is
independent of lenses. All three of my 20Ds had back focus errors which
only became evident when I used a 50mm f1.4 lens at close range. Canon
fix it by plugging in a computer and making a few adjustments, no lens
attached. Try to get the software yourself and see how friendly and
cooperative Canon are not!

You can get an *IDEA* of the error by using the chart Mike Warren posted
a link to but the process of using a chart at an angle becomes imprecise
when you use a wide angle lens or a wide aperture lens designed for full
frame cameras (like a 50, f1.4 or 1.8). Sort of self defeating unless
the error is substantial.

All canon (non macro)lenses exhibit barrel distortion or a pincushion
effect at close quarters so your results might *indicate* a back focus
error but they cannot quantify it.

Canon will take very little time in fixing the problem. You might
discover a relapse of the problem if you have to remove the camera's
"stay alive" battery when it dies on a lens change or from connecting
your Speedlight when it's switched on, but inside 12 month, they'll do
it free as many times as you need it.

Just make sure the error is consistent between lenses or you need to
take all the lenses in as well! In all the years I used Nikon cameras, I
never saw one instance of faults or reliability relating to quality
control during manufacture at any of the newspapers I worked on.

Since buying Canon gear I've seen many photographers with 20D problems
and experienced some severe problems with my own gear which should not
have happened. People seem to think quality is related to price. Canon
have disproved that with their 20D. Those who don't get the faults,
don't push their cameras.

--
Douglas,
You never really make it on the 'net
until you get your own personal Troll.
Mine's called Chrlz. Don't feed him, he bites!

In article ,
says...
Those who don't get the faults,
don't push their cameras.

Translation:

Measurebators will always find faults with their cameras.
--
http://www.pbase.com/bcbaird

David Littlewood wrote:



Unfortunately, current AF bodies (except top-of-range models like
Canon's 1-series) are stuck with screen almost totally unhelpful for
manual focussing. This is, BTW, a major problem with using DSLRs for
photomicrography, one of my main interests.

I agree and this was one of my "shopping criteria" when buying a dSLR,
something the review sites NEVER even mention. Most dSLR's assume you will
ALWAYS use AF, have no idea how to focus a camera yourself so they design
the focus screen to be as bright as possible (to brighten the view with the
slow kit lens?) at the expence of manual focusing ability. And not all
camera makers screens are like this. Some models get "blasted" by the
reviewers for having a dimmer focus screen when the fact is, they designed
the screen so you can actually see the focus plane for manual focusing.

Just another thing people should check out when camera shopping. If you
can't focus the camera well, it really doesn't matter how great the other
features are.

--

Stacey

Brian Baird wrote:

In article ,
says...
Those who don't get the faults,
don't push their cameras.

Translation:

Measurebators will always find faults with their cameras.


Actually you're the one who said you can't even manually focus your camera
so how would you know?
--

Stacey

In article , says...
Measurebators will always find faults with their cameras.

Actually you're the one who said you can't even manually focus your camera
so how would you know?

Can't you go two seconds without trying to stir **** up, Stacey?
--
http://www.pbase.com/bcbaird