Sharpness issues with Canon 50mm f/1.8 and Canon Rebel XTi

Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.

http://www.flickr.com/photos/10974317@N07/1012760583/

All of these crops except the 3 marked "center" are from the corners
of the photos.

1. I get good corner sharpness only if I stop down the lens to f/11.
Is that usual with this camera/lens combination?
2. Are these crops of acceptable sharpness?
3. Sharpness at widest aperture is unbearably soft. Is that usual with
a Canon 50mm f1.8?

Thanks in advance,
Shaji.

"shaji" wrote in message
ps.com...
Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.

http://www.flickr.com/photos/10974317@N07/1012760583/

All of these crops except the 3 marked "center" are from the corners
of the photos.

1. I get good corner sharpness only if I stop down the lens to f/11.
Is that usual with this camera/lens combination?
2. Are these crops of acceptable sharpness?
3. Sharpness at widest aperture is unbearably soft. Is that usual with
a Canon 50mm f1.8?

Thanks in advance,
Shaji.


I'm not familiar with the lens, but a prime should be pretty sharp once it's
stopped down one stop or so, say f2.8 with a f1.8 lens. Looks out of focus
to me, with the smaller apertures hiding it with a large depth of field.
You need to do a back/front focus test to see if it's focusing in front or
behind the intended focus point. There's plenty of info around, like this
page for the D70 with a focus chart you can print.
http://focustestchart.com/chart.html

"Steve B" wrote in message
...

"shaji" wrote in message
ps.com...
Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.

http://www.flickr.com/photos/10974317@N07/1012760583/

All of these crops except the 3 marked "center" are from the corners
of the photos.

1. I get good corner sharpness only if I stop down the lens to f/11.
Is that usual with this camera/lens combination?
2. Are these crops of acceptable sharpness?
3. Sharpness at widest aperture is unbearably soft. Is that usual with
a Canon 50mm f1.8?

Thanks in advance,
Shaji.


I'm not familiar with the lens, but a prime should be pretty sharp once
it's stopped down one stop or so, say f2.8 with a f1.8 lens. Looks out of
focus to me, with the smaller apertures hiding it with a large depth of
field. You need to do a back/front focus test to see if it's focusing in
front or behind the intended focus point. There's plenty of info around,
like this page for the D70 with a focus chart you can print.
http://focustestchart.com/chart.html

I just used this test chart to test two new lenses and if you follow the
instructions it will only take a few minutes to conplete. Do make sure you
use a tripod though. My FA50mm F1.4 and 90mm F2.8 macro were perfect now all
I need is some decent weather to get outside and get some decent shots.

Cheers.

Pete

"shaji" wrote in message
ps.com...
Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.

http://www.flickr.com/photos/10974317@N07/1012760583/

All of these crops except the 3 marked "center" are from the corners
of the photos.

1. I get good corner sharpness only if I stop down the lens to f/11.
Is that usual with this camera/lens combination?
2. Are these crops of acceptable sharpness?
3. Sharpness at widest aperture is unbearably soft. Is that usual with
a Canon 50mm f1.8?

Thanks in advance,
Shaji.

Hello Shaji.

I assume this is the digital SLR known as the 400D here in the UK. What
settings for sharpness are you using? You could try taking the test shots in
RAW mode.
It is also possible that the lens is faulty so can you try the shots with
another lens?

I am trying to look at your photos but I'd recommend that you print the
photos and look at them on paper rather than on a screen.

Regards, Ian.

Hi Steve,
Thanks for this valuable info. I shall try out the test. But, just out
of curiosity; Could this be a problem with the camera body in any way?
Need I check that too? If so, how can I check the camera for these
sort of issues?
Thanks,
Shaji.

"shaji" wrote in message
oups.com...
Hi Steve,
Thanks for this valuable info. I shall try out the test. But, just out
of curiosity; Could this be a problem with the camera body in any way?
Need I check that too? If so, how can I check the camera for these
sort of issues?
Thanks,
Shaji.

There is always a possiblility that it could be the camera body, but this
would be noticeable with other lenses and would not be very likely anyway.
The 50mm f/1.8 is sharp by f/2.8 and critically sharp in the f/4 - f/8
range. Corners should be excellent at this range as well.

Your crops look out of focus to me rather than lens aberration caused.
John

Fred Anonymous wrote:
"shaji" wrote in message
ps.com...
Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.


With that lens and my 30D it is extremely sharp over the whole field
at f/4, and even f/2.8. However, the autofocus is not always
right. Try manual focus and a tripod.

Doug McDonald

"shaji" wrote in message
ps.com...
Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.

http://www.flickr.com/photos/10974317@N07/1012760583/

All of these crops except the 3 marked "center" are from the corners
of the photos.

1. I get good corner sharpness only if I stop down the lens to f/11.
Is that usual with this camera/lens combination?
2. Are these crops of acceptable sharpness?
3. Sharpness at widest aperture is unbearably soft. Is that usual with
a Canon 50mm f1.8?

Thanks in advance,
Shaji.


As others have said, it looks as if your shots are basically out of focus.
They look sharper at higher f-numbers, where accurate focus is less
critical. How close were you to the targets? This lens will not focus
sharply closer than 0.45 m (18 inches), so it would be unable to get a sharp
image of anything closer, and you would get a warning signal in the
viewfinder. Have you tried other subjects than test targets, such as houses
across the street?

Maybe a silly question, but is the switch on the lens (near the red dot) set
to AF (auto focus), not M (manual)? If so, does the lens try to focus? -
the front rotates when it does - and you should see the image snap quickly
into good focus in the viewfinder when you partly press the shutter button.
If the lens is set to AF and does not try to focus when you press the
shutter release, or focuses wrongly, there is a fault with either the lens
or the camera body. Note that you can choose various points in the frame
for the autofocus to aim at - the centre is best for testing.

If none of the above applies, your dealer should be able to try the body
with another lens, and try the lens on any Canon autofocus SLR (film or
digital).

Hope this helps.

TrevM

On Sat, 04 Aug 2007 23:48:08 -0700, shaji wrote:
: Hi all,
: I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
: II just a few days back. I feel the pictures I get are not as sharp as
: I expect them to be. An image with 100% crops from pictures taken at
: various apertures can be seen at the following link.
:
: http://www.flickr.com/photos/10974317@N07/1012760583/
:
: All of these crops except the 3 marked "center" are from the corners
: of the photos.
:
: 1. I get good corner sharpness only if I stop down the lens to f/11.
: Is that usual with this camera/lens combination?
: 2. Are these crops of acceptable sharpness?
: 3. Sharpness at widest aperture is unbearably soft. Is that usual with
: a Canon 50mm f1.8?

Because of its multiple focus points, the XTi can be tricky to handle at
first. It's easy for it to lock onto a focus point other than the one you
intended. Until you get more experience with it, try setting it to use only
the center point. This won't constrain your placement of the subject in the
picture, because you can reposition it after it has focussed, as long as you
keep the shutter button halfway down. (Obviously, you can't change the
*distance* to the subject without allowing it to refocus.)

Bob

On Aug 5, 2:48 am, shaji wrote:
Hi all,
I'm a newbie to SLRs. I bought my Canon Rebel XTi and Canon 50mm f/1.8
II just a few days back. I feel the pictures I get are not as sharp as
I expect them to be. An image with 100% crops from pictures taken at
various apertures can be seen at the following link.

http://www.flickr.com/photos/10974317@N07/1012760583/

All of these crops except the 3 marked "center" are from the corners
of the photos.

1. I get good corner sharpness only if I stop down the lens to f/11.
Is that usual with this camera/lens combination?
2. Are these crops of acceptable sharpness?
3. Sharpness at widest aperture is unbearably soft. Is that usual with
a Canon 50mm f1.8?

Thanks in advance,
Shaji.

A f1/8 lens at short distance has an incredibly shallow depth of
field. At 2 feet (approx 60cm), your DOF is maybe an inch (2 to 3
cm). Therefore, you are well below the tolerance that you can
"eyeball" whether your camera is square to the image you are copying,
or not. When you stop down to f11, the DOF increases to about 3
inches.

My first thought would be that your camera is not precisely square to
the image you are copying. Therefore, while the center of the paper
is in focus, the corners are out of focus because they are outside
your DOF.

Visualize it this way. Say you have your image square to the camera
and everything is in focus. Now someone walks by and hits your
copyboard and it pivits along the center of the image. The center
remains exactly the same distance to your camera and remains in
focus. But one side is now closer to your camera and the other size
if farther -- thus they are out of focus.

At f 1.8, it doesn't take much to be off. That's why they use really
bright lights for copy-work -- so they can stop down the lens.