Focus/Recompose Rule Of Thumb

[Derrel]

Derrel on one side, A. Molitor on the other side.

 

[amolitor]

But how many thumbs apart are we, man? I feel like.. I feel like we're growing apart. I feel a dozen thumbs away, man

 

[usayit]

If you stick to a single thumb-width, the change in target distance is something like 6/100ths of a percent, which is probably a lot less than the focusing error of whatever system you're using.

The trouble with "leaning back" is that the amount you have to lean back depends on the target distance. On the other hand, at greater target distances it matters less. I expect you can get used to it, and kind of feel the right amount, especially if you have a good viewfinder.

* As the subject distance increases, it matters less. DOF increases.
* As the focal length increases, angle (t) becomes significantly less. Focus Error "E" decreases.
* As the focal length decreases, DOF also increases.
* As you stop down, it matters less very quickly. DOF increases quickly.

My point is, other than at very fast apertures at close focus distances with normal focal lengths, recomposition error becomes almost a non issue when calculated against DOF and FOV calculators. In most cases, the recomposition error falls within the DOF.

DOF calculator:
Online Depth of Field Calculator

FOV calculator:
Field of View Calculator - Rectilinear and Fisheye lenses - Bob Atkins Photography

I practiced with a 50mm f/1 at the lens's 1 meter close focus range which covers the worst case scenario. Once subject distance is about 8-10 feet away, the error falls within DOF. Do the calculations and see for yourself. Don't forget that most spreadsheets assume angles are in randians not degrees.

Again... this is just my experience based on calculations and practice with the 50mm f/1 with putting things into perspective. My conclusion was that I was obsessing over a perceived larger margin of error that really didn't exist. If the "thumb" method works better.. all the more power to you.

 

[Joves]

I am in the F&R sucks crowd. I had to do it for too many years when all you had was the prism in the middle days. Now I only do it when I am using a manual focus lens, but I use the moving focus point to confirm I am still where I want to be with the Green Dot method. Got to love the technology.

 

[StandingBear1983]

I would gladly give up F&R...but i have a D5100 so its a bit tricky to count on the relatively small viewfinder and 11 focus points to nail exact focus...and i like the best to shoot portraits at 1.8 so its quite hard to nail focus. also the center focus point has vertical and horizontal focus which the other focus points around it don't have (or something groovy like that, from what i understood).

The bigger the viewfinder and the more focus points you have to be able not to recompose and choose which focus point to pick does all the difference. also i have glasses so its hard for me sometimes to view exact focus (and yes i adjusted the diopter), i guess personally i have a reason to buy a better body now...

 

[kchoi]

I think this is too complicated for me.
What I do is to put the focus point on where I'd like to focus. I normally do not care about if it is cross type of what. They just work fine in most cases.
If the focus point cannot reach the place where I want to focus, I will step back a little bit and put the subject on the focus point. Then go home and crop.

 

[o hey tyler]

For everyone that's under the impression that focus and recompose doesn't work is apparently doing it wrong. I've used it for the past five years and have had zero issues.

 

[robbins.photo]

I am of course pretty confident that I have the math right. Presumably someone will check my work shortly, and then you can all be that much more confident.

My right thumb is 1 inch wide (wow - didn't think it would be that big!), at arms length, it is 27.5 inches from my eye.

You said it should be about 2°... At 27.5", 2° would cover 0.95975" of my field of view - that's pretty much dead on.

I was bored.

But, hey! At least now I have a handy way of measuring angles! My thumb at arms length covers 2°, almost exactly.

My rule of thumb is, stop putting it in front of the lens. It's distracting and I've got enough photos of my thumb already. Other than that I use the focus points on the camera and just pick the one that I need. Haven't done a lot of high end math or division, no in depth research on the topic. Just noticed my camera had the feature and figured, oh, that's what that does. So far so good.

 

[amolitor]

I am fascinated by these systems that apparently have a focus point every place you'd want to focus. Maybe it's just me, but while mine always has a focus point that is "pretty close" it's almost never exactly on it.

 

[usayit]

For everyone that's under the impression that focus and recompose doesn't work is apparently doing it wrong. I've used it for the past five years and have had zero issues.

Yup! This is exactly my impression. I simply did the math to see how much "error" is involved. I then realized people are getting all worked up over a relatively small error within a small corner case situation.

I think this is too complicated for me.
What I do is to put the focus point on where I'd like to focus. I normally do not care about if it is cross type of what. They just work fine in most cases.
If the focus point cannot reach the place where I want to focus, I will step back a little bit and put the subject on the focus point. Then go home and crop.

Yup… whatever works for you. Modern cameras are great that the focus can be assigned. I personally found that futzing with the focus points can slow me down at times but my most recent camera is neat that it has a touch screen. I can simply touch where I want the point to be. So quick and no more multiple button pushes.

 

[Blasthoff]

Just think, back in the "old days" street and press photographers all used a moderate wide angle, stopped the lens down, set the hyperfocal to that f-stop distance scale and just shot everything beyond the minimum distance or within wide zones without having to think or fuss, that WAS focusing. Just point and shoot and it never failed. I remember trying to teach that to newbe's back in the day of manual focus slr's, I'd make it easy using a wider 28mm at f11 where everything just beyond arms length would be in focus, Invariably, they just couldn't ignore the focus screen and just had to fidget with the focus ring. My point being, it helps to gain a "sense" of what the depth of field zone is in any particular situation as to gauge how much latitude there is to work with.

 

[Rick58]

Yep, Simpler times for sure!

 

[FocusTester]

If in doubt (or close to wide open), put the subject on a focus point and crop later. It doesn't even have to be a rectangular crop, if you are using a decent image editor. Why are people so afraid to crop? Focus and recompose is fine if the two points are really really close. Otherwise, just focus and don't recompose, crop! Your other option is to position yourself in such a way that after you recompose, the new point of focus is the same distance from you as the original point of focus. People often forget that this option exists.

Remember, simple geometric distortion can easily be corrected after the fact. Framing can be corrected after the fact. Blurry pictures because you focused and recomposed at f/1.4, not so much.

 

[nickzou]

I've never had a problem with focus recompose as long as I remembered that rotating the camera is what changes the distance between lens and the target of focus. Strafing side to side and up and down has worked fine for me. It's why there's always a level somewhere on my camera. It's like your dads have never made you memorize trig tables when you were 11 or something.

 

[imagemaker46]

I've just focused and shot without thinking any further than that. As my Dad has always said "it's just point and click" It's that simple.