What's that focusing technique called?

gman

gman

Suspended / Banned
Messages
11,100
Name
Graham
Edit My Images
Yes
I guess this will bring on some daft reply hehe but in all seriousness what's the actual term used for when you are going to shoot something at say 17mm but you zoom in to 50mm to focus and then lock the focus and zoom back out to 17mm and take the shot?

Supposed to give you sharper focus (?), something like hyperfocusing but I can't remember?
 
No, hyperfocal is where you don't focus on the subject but elsewhere to maximise the DoF.

Zooming in to focus and then zooming out is risky unless you're using a lens that doesn't change focal distance when zoomed. There is a fancy name for lenses that do that but I can't recall it right now.
 
pxl8 said:
There is a fancy name for lenses that do that but I can't recall it right now.
Click to expand...

It's a parfocal lens, no idea about that technique though... I have used it for astro shots though, and not had a problem.
 
pxl8 said:
No, hyperfocal is where you don't focus on the subject but elsewhere to maximise the DoF.

Zooming in to focus and then zooming out is risky unless you're using a lens that doesn't change focal distance when zoomed. There is a fancy name for lenses that do that but I can't recall it right now.
Click to expand...

Its you mentioning hyperfocualing....:lol:
 
I would say it is called "common sense" focusing, that is what I do all the time, and it is one of the great things about "live View" you can zoom massively to check your focus. All zooming in does it get you closer to check your focus is ok then you zoom back out and take the shot, your auto focus may not like it too much as what it can see will have changed, but if in doubt just manually focus when zoomed, then zoom out and you should be fine. I find it more usefull with zoom lenses, when using my 70-200 I will often check focus at 200mm then pull back to whatever I need to get the composition. Then other times I am just lazy and rely on the red focus confirmation light in the view finder :p
 
Jimmy_Lemon said:
I would say it is called "common sense" focusing, that is what I do all the time, and it is one of the great things about "live View" you can zoom massively to check your focus. All zooming in does it get you closer to check your focus is ok then you zoom back out and take the shot, your auto focus may not like it too much as what it can see will have changed, but if in doubt just manually focus when zoomed, then zoom out and you should be fine. I find it more usefull with zoom lenses, when using my 70-200 I will often check focus at 200mm then pull back to whatever I need to get the composition. Then other times I am just lazy and rely on the red focus confirmation light in the view finder :p
Click to expand...

Not sure why it's common-sense JL ???

You're relying on your lens being a parfocal one (i.e. where the focus doesn't change when zooming); with a good modern autofocus you rely on the camera to do it for you

I use a 70-200 often and find the camera is always right, providing I ask it to focus on the right bit and then perhaps use focus-lock too

Shooting kids, or any moving subject, I suspect would cause you to be more likely to be OoF a bit with your in-out zoom focussing ??? :thinking:

DD
 
gman said:
shoot something at say 17mm but you zoom in to 50mm to focus and then lock the focus and zoom back out to 17mm and take the shot
Click to expand...

No that will not work!:nono:

It would work on my old manual Zeiss zoom lenses for Contax, it could be that they were true zoom lenses. Later autofocus zooms by Zeiss, you needed to re-focus after each change of focal length. I believe they were correctly described as varifocal lenses but I might be wrong.

Edit - The later ones where you have to refocus are varifocal. The earlier "true" zoom lenses were also known as parfocal lenses.

This certainly applies to my current Canon zooms as well.

What you're thinking of is hyperfocal focusing - where you place your main subject matter somewhere within the zone of sharp focus at any particular focal length and aperture. Its much easier with a depth of field scale on the lens barrel.:)
 
Sorry Jerry12953 - what he's described is in no way Hyperfocal focussing - see PXL8's comment for that - #3

In t'olden days when I were a nipper, this was a common suggestion to try to ensure accurate focus with the then manual-only zooms - these days I just don't see the point - if you use the camera correctly and understand when it may struggle a bit autofocus is much better and faster

DD
 
http://www.rogercavanagh.com/helpinfo/30_parfocal.stm

"With manual focus and a true parfocal zoom, the recommended
technique was to take advantage of the highest possible
magnification to guide focus. So you'd zoom in, focus, zoom
out and recenter and shoot. You can use focus lock with an
autofocus camera and accomplish the same thing.
However, many modern AF zooms are not parfocal. They are at
least slightly varifocal, meaning that focus changes as you
zoom. For such a lens, you're better off if you zoom first,
then focus, then (if necessary) recompose and shoot".

Nikoins cant do it at all
 
Blimey I need a drink now... Oi Delipher pass me the sherry.... :runaway:

:lol:
 
jerry12953 said:
Its much easier with a depth of field scale on the lens barrel.:)
Click to expand...

Careful! Those depth of field scales are rarely calibrated correctly.

I suppose Nikon DX and Canon EF-S might be calibrated to the sensor size, but I'd need to do some testing and calculations to work it out.

I prefer to rely on my own calculations, and only use the depth of field scale on my film cameras, where I know it's correct.
 
You must log in or register to reply here.
Back
Top