questionable focusing with 50mm f1.4 in low light conditions

[olas]

i am having a problem with focusing my canon 50mm/f1.4 lens (on D10) in low light conditions. the autofocus servo seems to be experiencing alot of flutter... and i am unable to gain focus lock when i attempt to change the focal length by focusing on a far object after focusing on nearer one.
much of the time if i switch to manual focus and get it close, then the auto focus can finish the job and obtain focus lock.

selection of AF point or aperature does not seem to make a difference.
i am not convinced that it is a problem with the camera since my tamron 28-75 works just fine....

i have this problem even in room lighted conditions... i.e. incandescent or flourescent light. anyone?

[Hatem Eldoronki]

I experienced the same, then just gave up the idea of having the aperture set at f1.4. From what my friends here advised, I increased the shutter speed to 1/125, and that's where I started seeing a better output. Don't forget that the f1.4 will yield a shallow depth of field, so try f2.0-f2.8, higher ISO, and/or increased lighting..to get the sharpest image.

[olas]

ok... so what is the advantage of the f1.4 over the f1.8... or an even slower lens?

[Hatem Eldoronki]

It's still able to capture more light of course, than the f1.8..
Even at f1.4, remember that you don't have to use flash, or higher ISO. I didn't try putting the camera on a tripod at speeds slower than 1/125 f1.4, but it is definitely worth trying.
I am no expert in photography, and wish that someone would explain the advantage of the 50mm f1.4 if I miss some point or another, but I can tell you that since I bought this lens, and I almost haven't taken it off of my camera! I like the color it renders, and the 'lighting' it captures. I always use it in the 'M' mode, while my finger is on the wheel adjusting the speed constantly!
I love it, but don't really fully understand why!!

[Tom W]

I have the 50/1.4 and don't have any real focus problems with it. Yes, its not a true ring-type USM focus motor, so it isn't as fast or as quiet as my 28-105, but it does focus reliably for me. Focus Hunting is rare, though it occasionally will do so in the right conditions.

Just out of curiousity, are you trying to focus on a smooth, low contrast surface such as a wall? If so, point your AF point over something with a little contrast - most autofocus schemes require something with a little contrast to acheive focus. This could be the edge of a doorway, a picture frame, lampshade, or facial features - but there has to be something other than a flat surface in order for the focus system to "see" the object.

The shallow DOF at f/1.4 is an advantage, but it requires very pricise focusing. Plus, if your subject has too much depth, you may find that it exceeds the shallow DOF offered at f/1.4. Best to stop down a bit.

Do note that the f/1.4 lens is known to be very sharp from f/2.8 up, and is supposed to be slightly sharper than the f/1.8 lens at the wider aperture settings, at least from f/1.8 through f/4.0. After that, they are quite similar. So it does have that advantage in low-light situations or when you want more substantial blurring effect.

[olas]

i have tried on and off the tripod... but the problem i am encountering is not with the final image... it is with gaining focus lock period... the focus will completely blur the frame on the closest setting and i have to manually focus it out...

even when i choose the center AF point and a high contrast subject.

to give you an idea of the lighting conditions... f1.4 / shutter speed = 1/6 sec... i was under the impression that this lens should have no problem gaining focus in this situation.

[Tom W]

For the purpose of gaining focus, the shutter speed should not matter. In fact, even the f-stop setting won't matter when focusing is occuring - the camera doesn't actually close down the aperture until either you take the shot or press the depth-of-field preview button.

How does it focus in brighter conditions? It must be pretty doggone dark if you're getting f/1.4 and 1/6 second exposure. What's your ISO set at?

[olas]

it seems to focus fine in brighter conditions... but gets "confused" when i take it from dark to light in that it remains in the shortest focus and i have to manually adjust the focus back out... then it will work fine in auto.

i am using iso 100 to avoid grain.

[Tom W]

it seems to focus fine in brighter conditions... but gets "confused" when i take it from dark to light in that it remains in the shortest focus and i have to manually adjust the focus back out... then it will work fine in auto.

i am using iso 100 to avoid grain.

I take back the ''pretty dark" comment - if you had those shutter/aperture readings at ISO 400 or 800, you'd be in a very dark environment, and I wouldn't expect autofocus to work very well. But since you have them at ISO 100, it would seem to me that there is enough light to focus.

In fact, I just put the 50 on my 10D and went into the bedroom to check. I adjusted the blinds to give me similar settings (1/4-1/6 sec at f/1.4, ISO 100) and it focused every time I pushed the button.

In my opinion, what you're experiencing shouldn't happen. Since your other lens(es) work fine under the same conditions it would seem to me that you have a defective lens. Is it new? If so, I'd try and exchange it for another copy.

[olas]

that is the conclusion i am coming to... but still a bit in denial since it is a two week old lens... i suspect there is something wrong with the servo... it feels like it gets 'stuck' then releases... then stuck... its just confused in general... maybe it needs some "counseling". :lol:

thanks for your responses.

[NILOLIGIST]

I have this lens and it works fine for me. In fact, it has really been outstanding. I shoot dancers and most have very low light and movement, this lens performed everytime. I have a few images but they are very small.

It does sound like there is a problem with the lens you have. I haven't had any issue with my 50 1.4 and it is fast and light enough for me to carry around. When you get a good copy you will find this lens is great.

This photos was taken in COMPLETE darkness with an ultraviolet light as the only light source.
http://frederiqueporter.com/portfolio/thearts/537_3777.jpg
This was taken in very low light too.
http://frederiqueporter.com/portfolio/thearts/526_2657.jpg
This was taken with a little more light but not much.
http://frederiqueporter.com/portfolio/thearts/508_0877.jpg

NiL,

[Tom W]

that is the conclusion i am coming to... but still a bit in denial since it is a two week old lens... i suspect there is something wrong with the servo... it feels like it gets 'stuck' then releases... then stuck... its just confused in general... maybe it needs some "counseling". :lol:

thanks for your responses.

One other thing and its a shot in the dark (no pun intended) - make sure that the auto/manual focus switch is firmly in the auto position. Operate it back and forth a couple of times to wipe the electrical contacts. Also, check your lens electrical contacts where it connects to the camera - they may need cleaning. There's a lot of data interaction between the lens and the camera that takes place there.

I'd hate to have to send a lens back before expiring all of the possibilities first.

[Tom W]

PS - nice shots, NiL.

[NILOLIGIST]

Thanks Tom. They will get better that was the first time using the lens under those conditions so there were more tricks I could have tried and played with. I really love this lens, it takes great sharp images.

NiL,

[MediaMagic]

Do note that the f/1.4 lens is known to be very sharp from f/2.8 up, and is supposed to be slightly sharper than the f/1.8 lens at the wider aperture settings, at least from f/1.8 through f/4.0. After that, they are quite similar. So it does have that advantage in low-light situations or when you want more substantial blurring effect.

Speaking of blurring effect... The other thing I'd add to this accurate sharpness comparison, is that the 1.4 has a little prettier bokeh. It uses 8 blades wheras the 1.8 uses 5.

I agree with Tom on this one, try to swap out that lens for another copy.

[nosquare2003]

Do you have the external flash such as 420EX, 550EX? These external flash will emit a red beam to help autofocus even in complete darkness. There shall be a custom function in 10D so that the flash will not fire -- but to emit the focus assist beam only. By the way, this red beam may be annoying in some situations.