Focus Advice

[siulcr]

Hey guys! I just want general recommendations or advice with getting the proper focus, I've training with my manual professional mode for a while now and I'm getting brilliant exposures, so I guess this is not a problem anymore. However, I still have to remove some pretty good shots due to lack of sharpness, most of the time I use auto single point focus, but I'm not sure how to get this technique into perfection.

Any advice for getting the proper focus for a sharp image?

Best,
Luis.

 

[PhotographTalk]

Could you post a few of them that you seem to think did not work out as it would be a lot easer to see where you may be going wrong

 

[Derrel]

At times, using MULTI-point autofocus can help tremendously, such as when the lighting is low in contrast, or the subject has fairly low contrast. If the light level is lowish, such as toward the evening time, multi-point AF, such as Nikon's 9-point,k or 11-poinmt, or even 21-point AF modes, can help in getting FAST, accurate, consistent autofocus, especially on subjects that are moving a little bit.

This Sunday, I shot a session from 4:30 until 8 PM, in the fading light, and 2/3 ofd the way through, I switched from single-point to 11-point AF, and then finished in 51-point AF, as focusing became exceedingly difficult due to low-contrast clothing, overcast lighting conditions, open shade, and lower and lower light levels. ANd the lenses were pretty fast ones, and telephotos, the 80-200mm Nikon f/2.8 AF-S and the Nikon 105mm f/2.0 AF-D Defocus Control, both of which are "good focusers".

 

[siulcr]

Sure! Thanks! I will post something soon.

 

[siulcr]

At times, using MULTI-point autofocus can help tremendously, such as when the lighting is low in contrast, or the subject has fairly low contrast. If the light level is lowish, such as toward the evening time, multi-point AF, such as Nikon's 9-point,k or 11-poinmt, or even 21-point AF modes, can help in getting FAST, accurate, consistent autofocus, especially on subjects that are moving a little bit.

This Sunday, I shot a session from 4:30 until 8 PM, in the fading light, and 2/3 ofd the way through, I switched from single-point to 11-point AF, and then finished in 51-point AF, as focusing became exceedingly difficult due to low-contrast clothing, overcast lighting conditions, open shade, and lower and lower light levels. ANd the lenses were pretty fast ones, and telephotos, the 80-200mm Nikon f/2.8 AF-S and the Nikon 105mm f/2.0 AF-D Defocus Control, both of which are "good focusers".

Great! This is just great! what can you tell me about landscapes, it's so hard to get the proper focus.

 

[TCampbell]

Landscapes are more often shot with a high focal ratio (e.g. f/22, f/16, or maybe f/11). We all want our "subject" in focus... but for a landscape the "subject" is often the entire scene. By using a high focal ratio (often on a wide angle lens) you get tremendous depth of field.

You may want to learn about "hyper-focal distance". The hyper-focal distance is the distance (for a given lens and f-stop combination) which achieves the maximum possible depth of field.

When you focus to a specific distance, the depth of field allows objects both nearer and farther to also be in acceptable focus (depending on your depth of field.) You might think you could just set a high depth of field, focus to infinity, and take the shot. But it turns out that while doing this would provide focus to some range in-front of your focus distance, you also get some range "behind" the focused distance -- and as you've focused to "infinity" there is nothing "behind" infinity. So the hyper-focal distance is a way to find the optimal focus distance by pulling the whole focus range closer to take advantage of the wasted focus "behind infinity".

Here's how we used to do it.

The first image shows the camera focused to infinity using f/22. If you look at the depth of field marks left and right of the focus indicator line, everything between the two "22" marks should be in focus. But since this lens is focused to infinity, we gain nothing from that end. Meanwhile the "22" mark on the left indicates everything from ... let's call that 12 feet ... to infinity will be in acceptable focus.



This next image shows the lens focused for "hyper-focal" distance. Since we are using f/22, rather than focusing to "infinity" as the focused distance... we rotate the focus ring so that "infinity" is aligned with the "22" depth of field mark on the far end of the range. This pulls our "near" end of the range down to about 6'.



This is a 50mm lens (on a 35mm film body). For landscapes, you may find you prefer shorter focal length (wide) lenses. If you need to "look around" to take in the image, chances are that a wide angle lens would do better. A side-effect of shorter focal length lenses is that the depth of field naturally gets even larger (assuming the focus distance and f-stop are the same).

As I mentioned above, the hyper-focal distance is the distance that achieves the maximum possible depth of field for a given camera, focal-length, and f-stop combination. So with this "full frame" (really 35mm film) camera, using a 50mm lens set to f/22, the "hyper focal distance" is 12'... (that's where the focused distance is set on the lens even though we did this by adjust the "infinity" mark to the "22" on the far end of the range.)

So that's the idea... but modern "zoom" lenses usually don't include depth of field marks anymore and prime lenses may have them... but they aren't as usable (modern lenses usually move the focus element faster with less physical rotation of the focus ring. That puts the depth of field marks so tightly together that they're harder to use.)

You can look up the depth of field and find the hyper focal distance of a camera/lens/f-stop combination using a website such as dofmaster.com

There are also apps you can download to a smartphone so you can look up the info while in the field and not connected to the internet. But I suspect you'll find you usually don't need to look it up very often. This is because the hyper-focal distance is associated with a lens & f-stop combination. Remember... assuming the same camera sensor size (e.g. suppose it's an APS-C crop-sensor camera), lens focal length (how many lenses do you own??) and f-stop combination (and you'll probably tend to shoot these using a consistent f-stop such as f/16 or f/22) there is ONE "hyper-focal" distance for that combination. Suppose you shoot landscapes with a 24mm lens at f/22... you'd need to know the one hyper-focal distance for that lens (which wouldn't be hard to remember). That's why I say you probably won't need to be looking this stuff up all the time (but it's nice to know how you figure out what the number is the first time you need it.)

Landscapes often look better when there is something of foreground interest in the shot... knowing how to get the foreground sharp and still having a sharp impressive background is key.

 

[cynicaster]

Hey guys! I just want general recommendations or advice with getting the proper focus, I've training with my manual professional mode for a while now and I'm getting brilliant exposures, so I guess this is not a problem anymore. However, I still have to remove some pretty good shots due to lack of sharpness, most of the time I use auto single point focus, but I'm not sure how to get this technique into perfection.

Any advice for getting the proper focus for a sharp image?

Best,
Luis.

Without example photos we can only speculate, but I can almost guarantee your sharpness issue is being caused by:

a) getting too giddy with the "blurred background" look, and in the process depriving yourself of the DoF required to capture your subject(s) sharply

b) manually setting shutter speeds that are not appropriate (i.e. not fast enough) for the conditions

... or some combination thereof.

For (a), I'd suggest you fire up a DoF calculator and run some example scenarios. You'll probably be shocked to see how thin DoF can get under certain conditions.

For (b), I'd suggest you acquaint yourself with the 1 / (focal length) guideline. Oh, and don't fear the ISO.

 

[DannyZphotos]

I had a question on this same subject, and using center focus, lets say you're photgraphing a family of four. If you're using center focus would you just focus in the center of the 4 then recompose, or would multi-point focus be better?

 

[KmH]

There can only be 1 plane of focus in the photo.
Unless a lens has significant 'field curvature' that 1 plane of focus is parallel to the plane of the image sensor in the camera.
So even if you use a multi-point AF mode the camera ultimately has to choose just one of the multiple points to use to focus the camera.

To get subject matter at different distances from the plane of the image sensor we control the 'depth of field' (DoF) so the DoF is deep enough to have subject matter in front of and behind the plane of focus inside the DoF.

Many online DoF calculators say how far in front of and behind that plane of focus acceptably sharp focus is.

So you focus at that distance that is about the middle of the near/far distance of your subjects from the camera.
Note that the near/far distribution of the DoF can vary from 50/50% to as much as 70/30% depending on lens focal length, lens aperture used, image sensor size and point of focus distance.
Understanding Depth of Field in Photography