Focusing tips for Canon 50mm 1.8 with shallow DOF

PistolPete · 29 Sep 2010 at 21:47

OK,

So I go my 50mm and I've been playing around with it....and virtually all the shots I've taken with a shallow DOF seem to be out of focus for where I'm trying to hit.

I've tried auto and manual focus but I seem to keep missing.

Any tips?

Pete

mrthingyx · 29 Sep 2010 at 21:58

As somebody who initially struggled with a Sigma 50mm f1.4 (and assuming the lens AF is calibrated correctly)...

Try using AI Servo to track the subject, as well as different focussing points.

Also, if you're trying to photograph something that's moving, AI Servo will help again.

Bottom line, however, is practice. Lots of practice.

PistolPete · 29 Sep 2010 at 22:01

I've only being trying to photo still-ish things so far (the cat and various inanimate object) so I've been on AI Focus.

I've also set the focusing points to just the centre as the whole focusing points thing confuses me atm!

EGuitarStar · 29 Sep 2010 at 22:07

Pete, I have had trouble with this lens too, just a note that in poor light it really does struggle to focus correctly. You really got to just try anything and everything with this lens to master it. I am still learning.

p0ss3s3d · 29 Sep 2010 at 22:11

AI servo (not AI focus), single AF point (any of the 9/11/19/45 etc. should track pretty well, but the cross type clusters around the middle are often the best). Keep the AF running and fire. Simples.

PistolPete · 29 Sep 2010 at 22:35

I'll try it again tomorrow in AI Servo, and I have already got a single AF point set.

Light wasn't an issue - it was plenty bright enough.

mcc49 · 29 Sep 2010 at 23:52

When shooting still object like you said you should be using one shot AF not AI servo. Use the center AF point as its the most sensitive and aim the focus node over something with some contrast (aka not something that is plain in colour) on the same plane of focus to achieve AF lock then recompose with shutter still half pressed and shoot.

p0ss3s3d · 30 Sep 2010 at 10:20

mcc49 said:
When shooting still object like you said you should be using one shot AF not AI servo.

Narp, I'd use AI servo to keep the subject in focus rather than focus on it once and then let you sway just slightly and get an OOF result.

mcc49 said:
Use the center AF point as its the most sensitive

For many cameras yes, but it also means you can't compose your shot aswell, therefore you either need to select an outer point an live with it, or get a camera where the outer points are as good as the inner points (7D/1D for example)

mcc49 said:
and aim the focus node over something with some contrast

Good advice - if it's linear note the contrast must run in the correct direction.

mcc49 said:
to achieve AF lock then recompose with shutter still half pressed and shoot.

Recomposing would be a big no, no. If you only have 2-3 cm of DOF, moving could easily sway this.

Therefore, I'd say servo (even on a static subject - only downside is the battery life), use the correct point for the desired composition (linear or crosspoint) fire whilst the AF is engaged (static subject or not.)

blastman · 30 Sep 2010 at 10:48

can you post some examples??

What shutter speed, f-stop and iso are you using??

A slow shutter speed will give you that kind of result.

PistolPete · 30 Sep 2010 at 12:55

I deleted them.... but from memory I was a couple stops or so from wide open (as the lens is apparently a little soft @1.8), ISO100 and shutter was easily 1/250 as it was bright - the pics were all outside.

bloodiedathame · 30 Sep 2010 at 13:57

Tried faster shutter speeds? Tripod? Also what camera are you using? Might just be that the focus is soft when looking at 100%, an unsharp mask treatment in PS could sort out the problem.

33L · 30 Sep 2010 at 14:56

what sort of distances are you trying to shoot. if its anywhere the near the minimum focus distance then the DOF is so shallow that even your breathing could make you miss your mark!

@0.5m DOF is 1cm @f/1.8
@5m DOF is 68cm @f/1.8

EGuitarStar · 30 Sep 2010 at 21:13

Pete, I think you may find this useful, it sure helped me out a great deal.

I read through that and gave it a try in Leicester Square and got 90% good shots with no blur on them.

Essentially, it does come down to a experience and plenty of practise practise and more practise. I was starting to get really fustrated with this 50mm and looking for stablised lenses as a solution, how wrong I was.