hi everyone,

i noticed that my 50/1.8 lens on my 350d is always front focusing at 1.8
is it normal for this lens or is it the body?
i always use the center autofocus point.
stepping down, i do get improvements. its best at 5.6 (superb).

for those who own the same combination, are your 1.8 shots usable? or do just have a bad copy of the lens, my other lenses dont exibit this behavior.

wish i could post samples but being very new here, i still have to learn how to do it.

thanks

Hey Raul - I own a 50 mm 1.8 too ... I'm perfectly happy with it and the images are usable. Try and find a way to post your images (get the html from your flickr if you have one) so it would be better for me to see. I've taken lots of shots using my 50mm 1.8 and im very happy with it .. especially with food and portraits.

Check out this site - while its for a Nikon cam - nevertheless it outlines a bit on the AF system --- http://www.focustestchart.com/chart.html

I can post some pics on this thread - but I need to do a lot of cut and past of the html - so just check my flickr. http://www.flickr.com/photos/bluejunbeach/ (http://flickr.com/photos/bluejunbeach/)

alan,

lotsa thanks. less ignorant now about how camera focuses. ive downloaded the chart and will play with it. will try to post results if i still have a problem.

your portrait pictures at flickr are great. very natural looking, just the way i really want portraits to be - plain and simple (no fake looking "vivid colors")

the food pictures had another effect on me. the pics made me hungry. took a short break in the middle of doing this for a late breakfast. really.

Hehehe ... i enjoy shooting food and portraits. I call it food pornography ... but lens lust has gotten the better of me. Now I want to get the 100mm macro! I did adjust the images a bit but not really in a major way ... no photoshop. Just adjusted it when i converted it from raw. Enjoy your 50mm and get hold of Canon's EF LENS WORK III Book --- you can try and write your local Canon office and check if they have an extra copy ... its very handy!

hi! from what i understand the sensor of 350d is best at 2.8 center focusing. at wider apertures, the sensor tends to hunt and front focus. if you set it down to around 3.2, it'll perform better. using f1.8 is a bit tricky.

in my experience with 50F/1.8...i get sharp images starting from F/2.5 and up. F/2.0 and F/1.8 would give me soft images but not an out-of-focus problem.

alan,

lotsa thanks. less ignorant now about how camera focuses. ive downloaded the chart and will play with it. will try to post results if i still have a problem.

your portrait pictures at flickr are great. very natural looking, just the way i really want portraits to be - plain and simple (no fake looking "vivid colors")

the food pictures had another effect on me. the pics made me hungry. took a short break in the middle of doing this for a late breakfast. really.


Hi Raul, Where did you dowload the chart. I would lke to test all my lens on front & back focus. But whats back and front focus ? I am afraid I migth the same problem with my lens. Better test them all. since it is all under warranty. Anybody can guide on how to ? Thanks

See Allan's 1st post above. :)

did a quick test and i am more convinced that my 50/1.80 and 350d pair indeed is front focusing (my focus is approximately around 5mm on the test chart). and not only at 1.8 but also at my favorite 5.6 for this lens.

seems like the bigger DOF at smaller apertures led me to think that correct focus was attained but in reality it was still off.

will play some more using other lens just to check.


hi clemn,

front focus - area in front of your target focus is sharp
back focus - area behind your target focus is sharp
if this problem exist, it is more evident at large apertures such as the 1.8 on the 50/1.8

i got the chart from allan's link above

Raul Ruiz;

Thank you very much.

Cheers.

It may not be the len's fault.

On the 350D using openings of 2.8 would result in a focus confirmation but it's not very reliable based on experience. Even less reliable for 1.8 or larger openings. Even with the centerpoint focus, it makes you think you have focus when in fact you dont. With depth of field so shallow as with a 1.8, you'll easily find the lens front or back focussing simply because the camera can't focus any more accurately.

Unfortunately 350d focussing does not have double precision like those on the 20d, 30d, or the 400d. the 50mm is much more reliable and becomes a fun lens even in low light with the latter camera bodies.

It may not be the len's fault.

On the 350D using openings of 2.8 would result in a focus confirmation but it's not very reliable based on experience. Even less reliable for 1.8 or larger openings. Even with the centerpoint focus, it makes you think you have focus when in fact you dont. With depth of field so shallow as with a 1.8, you'll easily find the lens front or back focussing simply because the camera can't focus any more accurately.

Unfortunately 350d focussing does not have double precision like those on the 20d, 30d, or the 400d. the 50mm is much more reliable and becomes a fun lens even in low light with the latter camera bodies.

thanks for this info.

i did suspect somewhat that its the body thats giving me the focusing problem. guess i'll just stick to 5.6 on this lens.

i'm getting the efs60 soon which will also serve as a replacement for the 50/1.8. i hope the 350d wont give me the same problem.

Knowing your equipment and their limitations is very important.
At 1.8 there is so little depth of field especially if the subject is up close. Even the regular body sway of the subject or photographer handholding the lens would appear to make the lens front or back focus.

At that opening, you just have to take a few more extra shots and increase your odds of getting something critically sharp in the right spot.

May I add that even on an EFS 17-55 IS USM at 2.8, the 350D is still hunting and at times out of focus. I am learning how to focus manually, fast. It's a lesson i'm being forced to learn :D

It may not be the len's fault.

On the 350D using openings of 2.8 would result in a focus confirmation but it's not very reliable based on experience. Even less reliable for 1.8 or larger openings. Even with the centerpoint focus, it makes you think you have focus when in fact you dont. With depth of field so shallow as with a 1.8, you'll easily find the lens front or back focussing simply because the camera can't focus any more accurately.

Unfortunately 350d focussing does not have double precision like those on the 20d, 30d, or the 400d. the 50mm is much more reliable and becomes a fun lens even in low light with the latter camera bodies.

Great info. This is the first time I've heard of this. Question: Does this mean that b/f and f/f on a 350D can happen to any lens you pair the body with or this is isolated to the 50mm?

@ deo
My understanding is:
the 350d focuses accurately to a resonable degree (within tolerance) and it applies to all lenses. So there's a little play in the depth of field that the 350d would consider in focus while a 20d may fine tune focus just a tiny bit more.

Without the extra precision sensors activating, it's like tuning on an analog radio to the exact frequency of a station using a large knob (without the fine tuning). There's a pretty good chance you'll get the station especially with several tries. Your'e just missing out of the extra 2% accuracy. The 20d would have a tuning know and also a fine tune knob while the 350d only having a tuning knob.

In practice, it's hardly noticeable, unless in extreme depth of field situations, such as face shots of a child under 2 feet distance or macro shots at 2.8. There's more chances of camera shake, and the subject not holding still than losing focus. Basically at apertures larger than 2.8 the quality of focus is just as good as a 20d. It's when you use lenses 2.8 and larger often that you would benefit from the extra precision.

Hopefully i didn't successsfully confuse you.

This is also the case for my lens.

hi everyone,

i noticed that my 50/1.8 lens on my 350d is always front focusing at 1.8
is it normal for this lens or is it the body?
i always use the center autofocus point.
stepping down, i do get improvements. its best at 5.6 (superb).

for those who own the same combination, are your 1.8 shots usable? or do just have a bad copy of the lens, my other lenses dont exibit this behavior.

wish i could post samples but being very new here, i still have to learn how to do it.

thanks

Same thing happens to me and I have a 450d:( ... does not occur however in live mode AF

To compensate (when looking through the viewfinder) I just nudge my head less than an inch forward and i get focus everytime :( Auto Head Focus:Dum:...

still need to confirm if it's just the lens, problem is I don't have any othe lens with a wide aperture... to easily spot it.

ummm, If the body is the problem, how long does it take for calibration? :Shock:

Thanks

now I wonder how Tricia shot those 50mm1.8 shots she last posted.

now I wonder how Tricia shot those 50mm1.8 shots she last posted.

Same here...

I got more concerned about my unit, when I saw Alodia's own 50mm shots of her statuettes... and she uses xsi

(on a side note, didn't notice the date on this thread when it popped in my search hehe)

hi! from what i understand the sensor of 350d is best at 2.8 center focusing. at wider apertures, the sensor tends to hunt and front focus. if you set it down to around 3.2, it'll perform better. using f1.8 is a bit tricky.

It's 2.8 and faster lenses, so a wider lens will actually be easier. In addition, unless you're using an old manual focus lens where you can stop down the aperture, you can't "set it down to 3.2" without holding the DOF preview button as virtually all cams post 80s use an open-aperture metering and AF system where the lens will always stay at its largest opening regardless of what you camera setting may be until the moment you fully depress the shutter button.

When using large aperture lenses, especially at longer focal lengths, the chances of your AF locking at the wrong spot is increased.

The AF indicator in your viewfinder does NOT correlate with the actual area of focus as the sensors itself are much larger than the red dots/square that you see in the viewfinder.

If your subject is close to your lens' nearest focusing distance and you're shooting at large apertures, the slightest shift in camera or subject position will skew the AF accuracy.

This is very common when you're used to shooting kit lenses where you get the wider DOF of a smaller starting aperture as the mis-focusing is greatly reduced at f/3.5-5.6.

Using center AF focus-recompose may skew your AF position in addition to your subject's movements. AF errors are present in your gear, your technique, and your subject as well.

Try to get used to using your other AF points if you're trying to lock AF onto your subject's eyes if your camera is close to the subject. It makes a big difference whether your AF is locked onto the eye itself or the area between the nosetip and the eyelid.

Remember that the DOF of wide aperture lenses are really thin. I'm talking about less than half-an-inch difference from front to back... If you're certain that your subject and your cam didn't move at all and it still exhibits focus inaccuracy, then send it for calibration, but if you actually do focus-recompose or your stance/subject isn't stable, expect focus shifts with wide aperture lenses.

With even larger and longer lenses, you can't even keep the whole subject in focus, so focus-selection is even more critical (see example (http://farm4.static.flickr.com/3196/2768151830_089dde2def.jpg?)).