Spot focusing help... what did I do wrong here?

[nola.ron]

Today was a huge let down! I ordered my 50mm 1.8G this week and today I received a 35mm 1.8G instead. I still took it out for some test shots and wow, what a difference with a fast lense! Impressed with low light performance compared to my kit lenses! But I noticed that my focus seems to be off. I have not done much up close photography of animals/people, so I guess this is my first chance at noticing something wrong.

On all of these images I used spot focusing on the eye closest to me. I compose the image, then move the focus point as close to the closest eye I can and then recompose to get it spot on the eye. I have included 2 different shots.. both are processed but 1 of each is sharpened and the other is not sharpened. I notice that the focus looks fine after sharpening, but not before? Is this correct?

In the unsharpened images it looks like the focus point was actually on her nose or snout rather than the eye. What am I doing wrong here? You may have to view full size and zoom in on the face to see what I am talking about. I can't see it here but could see it during processing.

These images were literally ONLY FOR TESTING of low light performance on this lense!

1: No sharpening

Focus 1 unsharpened by nola-ron, on Flickr

1: Sharpened

Focus1 by nola-ron, on Flickr

2: No sharpening

Focus2 by nola-ron, on Flickr

2: Sharpened

Focus2 Sharpened by nola-ron, on Flickr

 

[Tee]

Just clarify what you're saying is when you press the shutter the focus point is directly on the eye? Or are you recomposing after you place the focus point on the eye? Lastly, does your camera have 3-D tracking focus mode?

 

[nola.ron]

Just clarify what you're saying is when you press the shutter the focus point is directly on the eye? Or are you recomposing after you place the focus point on the eye? Lastly, does your camera have 3-D tracking focus mode?

Yes, I am pressing the shutter after the focus point is right on the eye. When I compose I can't always get the focus point spot on the eye because my D3000 doesn't have a lot of focus points. So, what I have to do is get it close, then slightly recompose to get it spot on, then focus and release shutter.

It does have 3d tracking focus mode but I thought that was only for moving subjects? My dog was dead still for both of these shots (super tired pup, did not want to cooperate with me at all! lol). My focus mode is set to AF-S and the area mode is set to Single Point. Maybe I just need a real explanation of the different focus modes and area modes and which ones i should be using? IDK. I thought I had this figured out but apparently I don't.

 

[Overread]

A few thoughts as to the potential problem:

1) It is not uncommon for some lenses to have back or forward focusing issues, where the lens focuses slightly forward or back of the point its supposed to focus upon. This is repeatable and normally at a fixed value and so you can do tests to check to see if you have the problem. Focusing charts are easily found online to print off and focus upon to test focusing errors (its also something that shows up a lot more when using very wide apertures because the thin depth of field shows up any minor calibration errors much more readily).

2) Single point isn't always just a single point, often it will have support AF sensors around the AF point selected which also contribute to the focusing. This can mean that the focusing spot is larger than you expect. If this is the case then normally your camera manual will detail this and often the camera will also offer up a full single spot AF mode (where it only uses the single point). The small area effect helps generally with moving or with more difficult to focus upon scenes.

3) Contrast - the nose has a more contrasting texture and lighting than the rather shaded and dark eye. As a result even though the focus is upon the eye itself (in the first shot eye and nose look to be in the same focal plane) the nose appears more in focus because it holds a greater amount of contrast (we see sharp differences in contrast as "sharp" parts of a photo). As a result after sharpening this difference is reduced and for a scene like this you would not be unwise to consider selective area sharpening/contrast adjustments to bring out the eye a little more whilst not oversharpening the nose areas.



Personally without seeing some focus tests done to confirm that its not slight back/forward focusing errors I would suspect that the contrast element is the likely culprit based upon what you have shown. I would consider doing further focusing test to ensure this - however since I'm unsure if you're keeping the lens or not it might be a waste of time (even if the lens shows up the error focusing calibration can be a very fickle thing and is also dependant upon your cameras calibration - as a result it might show up fine on a different camera body - unless it were showing very extreme focus problems, which it is clearly not).

 

[cgipson1]

Shooting at f1.8 at this distance, your DOF is paper thin. Any "recomposing" and you will be off!

Your were what, 3 feet or so from the subject? Or were you even closer with that 35?


.07 ft or a little over 3/4" of DOF for 50mm

.15 ft or about 1.5" of DOF with a 35mm.

So if when recomposing, you move the camera even a 1/2" forward or back.. boom.. different focal point.

Online Depth of Field Calculator

 

[Overread]

I wasn't 100% sure about the description of the focusing method - my impression was that the OP was:

Framing the shot
Shifting the AF point to the one nearest to the point of focusing with the frame (not actually using the AF point though)
Reframing the shot so that the nearest AF point is now right upon the point of focusing
Focusing the photo using AF on that specific point and then taking the photo.


I do agree 100% that if the OP was focusing the photo, recomposing the frame and then taking the photo without re-focusing (either auto or manually) then yes the refocusing element will shift the plane of focus and thus, esp at very wide apertures, will have the potential to very easily (even with very slight adjustment) shift the plane of focus off the intended point.

 

[Tee]

In the unsharpened images it looks like the focus point was actually on her nose or snout rather than the eye. What am I doing wrong here? You may have to view full size and zoom in on the face to see what I am talking about. I can't see it here but could see it during processing.

I took a look at the original sized non-sharpened images (3872X2592) on your Flickr and the focus appears to be where you wanted it- on the eyes. The snout only looks like it was sharper due to the texture and contrast involved but there is some blur to the nose. I wanted to add the reason I asked if you were in 3D mode is because while it's a great mode, on static subjects sometimes the focal point will shift at the very last minute as your pressing the shutter. From my point of view, I think what we're dealing with here is a narrow depth of field but not as much dramatic blur to really define that focal plane. You have a good subject to practice on. I did some DoF playing around today and all I had was a candle. :thumbdown:

 

[joshua_]

New guy here with more of a question than anything....

Does this, in any way, look like it could be related to the lighting?

I ask because in some of my practice I found a similar problem a few times and felt like I fixed the problem with light. I see that in some ways it looks related to focus, but when I had a local friend help me we recreated it and solved the issue I had with light. Mine would also clean up some in lightroom, but I was looking to correct the initial issue if possible.

Anyway, not sure if that is relative or not and was just hoping for a little clarity.

Thanks

 

[Overread]

joshua_ - the lighting argument can be part of it and can factor in on two potential fronts:

1) Focusing requires light, in low light conditions the cameras AF is put under greater strain to detect contrast differences in the scene to focus upon. This can be exacerbated if you're using edge AF points which might not be cross type or as sensitive as middle points (higher end cameras also generally have better AF points and features of course).
You can use focusing aids (eg some speedlite flash units like the 580EX2 have a built in focusing aid which patterns the surface with a red light) to help in low light conditions and if the scene itself is fairly static even a torch can be used to shine on the subject to help get focus.

2) The contrast arguments listed above - in flat lighting the difference in contrast over a scene might be very muted and textures won't stand out very well. As a result very flat lighting can make photos appear "soft" even though they are actually sharp and in focus. Editing and boosting the contrast as well as sharpening can, of course, help to counter this effect - as can adding lighting so that the light falls with a direction across the scene and thus helps to create contrast differences and highlight textures.

 

[joshua_]

Overread, thanks for that.

Also, I just learned how to use the 'like' button by accident when I hovered over that area. Apparently I'm somewhat slow. :meh:

 

[nola.ron]

Shooting at f1.8 at this distance, your DOF is paper thin. Any "recomposing" and you will be off!

Your were what, 3 feet or so from the subject? Or were you even closer with that 35?

.07 ft or a little over 3/4" of DOF for 50mm

.15 ft or about 1.5" of DOF with a 35mm.

So if when recomposing, you move the camera even a 1/2" forward or back.. boom.. different focal point.

Online Depth of Field Calculator

Yes, about 2-4 feet. I was moving back and forth during my testing but was within this range the whole time. I definitely understand what you are saying about focusing and moving front/back after focusing. I don't do that. BUT...I think after all of this maybe I don't understand DOF as much as I thought.

I know that DoF is front and back area of "in focus", but is it spherical from the focus point or is it kind of like a line horizontally that gets wider or is it something that grows out spherically from the focus point? I've seen pictures of books where it looks like 1 line of the book is in focus while the rest is out at like 1.4, but in my own test shots here it seems otherwise. I can see that part of the bed directly under her face is in focus and then fades out, while her body fades out just behind her face.

I do agree 100% that if the OP was focusing the photo, recomposing the frame and then taking the photo without re-focusing (either auto or manually) then yes the refocusing element will shift the plane of focus and thus, esp at very wide apertures, will have the potential to very easily (even with very slight adjustment) shift the plane of focus off the intended point.

Sorry for the confusion! I see how you could think that. I didn't explain well. I definitely focus during shutter release. I was just trying to explain my method for getting the focus point spot during composing.

 

[bratkinson]

Hopefully, a Nikon guy can straighten this out...But the OP indicated he was using AF-S auto focus mode. If the non-Canon part of my memory serves me, that's single shot focusing. Ie, once you press the shutter button 1/2 down to get focus, that's where it focuses...eg, 2.12345 feet in front of the camera. Then you move out or back a bit, but the focus point relative to the front of the camera moves with you. So if you moved back an inch or so, now the focus point is on the nose. The solution is (non-Canon memory again) shooting in AF-C, or continuous focusing mode. That way, as you move, the focus point will move too. Also, as your dog (or any living subject) is moving, albeit slowly, the exact point of focus will move with him (her?) as well.

As has already been mentioned, there's a very small depth of field due to the wide open shutter that was used on the first one. I checked another and it showed f2.2. Still, a very small depth of field.

Also...a the shots were taken at 1/50th and 1/40th, that I looked at. With the short focal length lens, this is probably OK to prevent subject/photographer motion blur. But I like shooting faster exposures anyway...just to be safe.

 

[greybeard]

I have that lens and at f/1.8 that is about as good as it will do. I usually use it at f/2.2 or higher and at those apertures it is razor sharp. At the distance you are shooting her I would use something like f/4 or f/5.6 so as to get more of her in focus.

 

[vtf]

I have that lens and at f/1.8 that is about as good as it will do. I usually use it at f/2.2 or higher and at those apertures it is razor sharp. At the distance you are shooting her I would use something like f/4 or f/5.6 so as to get more of her in focus.

Ditto with the 50mm if you chose to send then 35mm back.

 

[Joves]

joshua_ - the lighting argument can be part of it and can factor in on two potential fronts:

1) Focusing requires light, in low light conditions the cameras AF is put under greater strain to detect contrast differences in the scene to focus upon. This can be exacerbated if you're using edge AF points which might not be cross type or as sensitive as middle points (higher end cameras also generally have better AF points and features of course).
You can use focusing aids (eg some speedlite flash units like the 580EX2 have a built in focusing aid which patterns the surface with a red light) to help in low light conditions and if the scene itself is fairly static even a torch can be used to shine on the subject to help get focus.

2) The contrast arguments listed above - in flat lighting the difference in contrast over a scene might be very muted and textures won't stand out very well. As a result very flat lighting can make photos appear "soft" even though they are actually sharp and in focus. Editing and boosting the contrast as well as sharpening can, of course, help to counter this effect - as can adding lighting so that the light falls with a direction across the scene and thus helps to create contrast differences and highlight textures.

Also AF can easily get confused when there is no real clear definition of the subject, i.e the eye are is too uniform in color so as to disguise the area. This is where you have to either a) choose and area that is better defined on about the same focal plane, or b) manually focus using either Live View or a dedicated focusing screen with a split prism. Also if using Live View you can check you DoF using the stop down button if you are not shooting wide open.