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Blurred shots wide open with Canon 50mm


Geraint 14 715 34 Wales
3 Sep 2006 3:41PM
Hi. I'm fairly new to photography. I recently bought the highly recommended Canon 50mm 1.8 lens for my 350D, as I find the kit lens (18-55) a little disappointing. I've taken a few shots wide open (at 1.8) of people mainly, and the problem that I have is that some are sharp but others are not. I was on aperture priority; the shutter speeds were around the 1/2000 mark, and there was plenty of light. The subjects ranged from a couple of feet away to about 15 feet away. Could it be that I'm simply shooting too wide and need to use a smaller aperture? Sorry if this is a stupid question!
doczoc 18 773
3 Sep 2006 3:46PM
In those conditions I would have thought it would be hard not to get sharp results! Is everything blurred? Or has the lens focused on areas you didn't want it too?
Carabosse 18 41.6k 270 England
3 Sep 2006 3:47PM
Possibly lack of depth of field plus misfocusing.
Geraint 14 715 34 Wales
3 Sep 2006 3:56PM
Thanks for the quick replies. Perhaps the lens focused on unwanted areas like you suggested. I used the middle autofocus point in every shot though. Almost everything in the shots is soft. Maybe by using such a wide aperture only a tiny part of the picture is actually in focus, and the subsequent lack of depth of field makes it difficult to see it! I'll try different aperture settings to see what I can come up with! Thanks again
JohnHawthorne 15 1.7k 5 Scotland
3 Sep 2006 4:00PM
You say you are quite new to photography - how much do you know about depth of field (DOF)? Apologies if you already know this, but DOF is how much of the image, from front to back, is in focus. At a large aperture of f/1.8 the DOF will be very small so you will notice any slight mistake in focussing, especially when you are focussing quite close (a few feet). Smaller apertures increase the DOF so slight inaccuracies in the focussing won't be noticed.


Quote:Could it be that I'm simply shooting too wide and need to use a smaller aperture?

Don't worry, it's certainly not a stupid question. The answer depends on what kind of image you wanted. Do you want most or all of it sharp, or just a little bit of it? I would guess you wanted most of the image sharp, so in that case, yes, you need to use a small aperture. Try an aperture around f/8 and you will find that most if not all of your images are sharp.

(EDIT: you posted too quick for me!)

Hope that helps a bit though,
John.
conrad 17 10.9k 116
3 Sep 2006 4:04PM
According to several reviews I read, the 1.8 50 mm is ideally used with an aperture of at least 2.8, and just to be sure I usually keep it on at least 3.5. That still blurs the background while giving the sharpest pictures.

Conrad
LAF 18 1.7k
3 Sep 2006 5:25PM

Quote:the problem that I have is that some are sharp but others are not


Well, that means the lens isn't to blame. The optics don't vary between shots. So, as shutter speed isn't the issue, there's two things that might be going on. Either f1.8 isn't giving you as much DoF as you were expecting (it really is narrow at f1.8!) or your focusing is a smidge out - again this can be REALLY exacerbated by the minimal DoF at that aperture. If you shoot a head and shoulders style portrait of someone at f1.8 you'll find that if you focus on the eyes, then just a tiny bit of forward/backward movement will move the point of focus elsewhere. Indeed, at f1.8 I wouldn't expect the tip of the nose to be at all sharp if I were focussing on the eyes. F4 and above would be needed to get all the facial features looking crisp, assuming you get your initial focus point right. Bare in mind, too, that this lens is at it's sharpest from f2.5 onwards.

Try shooting the same shot repeatedly at different focal points and different apertures, then comparing the shots afterwards to see what kind of an effect it's having. Remember that stuff that looks olay in the viewfinder and on the LCD can fall apart at high res on a comupter screen. I'm pretty sure that it's just a bit of practice and familiarisation that you'll need to get the results you want with consistency.

Lee.
Paul Morgan 20 19.5k 6 England
4 Sep 2006 12:33AM
Have a look at this, a great learning tool. A depth of field Calculator.

www.dudak.baka.com/dofcalc.html

Paul
Geraint 14 715 34 Wales
4 Sep 2006 7:06PM
Hi, I'd just like to say thanks to everyone who replied to my post. I was indeed shooting too wide! Cheers,

Geraint
LAF 18 1.7k
5 Sep 2006 10:48PM
Glad we were some help Geraint! Makes a pleasant change ;o) Best of times with your camera!

Lee.
ade_mcfade 17 15.2k 216 England
6 Sep 2006 9:03AM
gets very sharp at F8 and smaller
mattmatic 17 598
6 Sep 2006 12:59PM
You normally stop the lens down to around f8 to get the "sweetspot" where the lens passes the highest detail through. This is also known as the "MTF" - (modulation transfer function).

However, it sounds like mis-focussing when shooting at f1.8.
I use an f1.4 lens and the focus is absolutely critical at f1.4 or f1.7. Like you I use the centre focus only, but always focus this on the eyes before reframing - making sure not to move at all (photographer or subject). Even a millimeter or two of movement will get the shot mis-focused. A head-only portrait will get just the eyes and eye-brows in focus - their nose is slightly soft, and their ears are definitely out of focus.

The wider you go, the shallower the depth of field.

It's worth practising though, because I find I can get cracking portraits at f1.7 or f2 Wink

The DOFMaster link is worth checking out - look at the "total depth of field" to see how the DoF changes with subject distance and aperture.

Matt
fauxtography 16 6.6k 36
6 Sep 2006 1:17PM
Good advice from matt though I have to say that i've found with reframing at f1.8 it can mean the wrong area is in focus after you've reframed. (this could be to me shifting slightly)
Carabosse 18 41.6k 270 England
6 Sep 2006 1:32PM
I use the 50mm/f1.4. Shooting wide open, or even at f1.6/f2, your DoF is very limited and even a slight focusing error will show up all too readily.
plooto 15 12 England
10 Sep 2006 2:34PM
So glad it's not just me. I have the same lens and had exectly the same problem. Did some portrait stuff but went in at 1.8 and found lots of noses in focus but net much else. We live and learn but it is nice to know we do not do so alone!.

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