Home · Register · Search · View Winners · Software · Hosting · Software · Join Upload & Sell

Moderated by: Fred Miranda
Username   Password

  New fredmiranda.com Mobile Site
  New Feature: SMS Notification alert
  New Feature: Buy & Sell Watchlist
  

FM Forums | Forum & Miscellaneous | Join Upload & Sell

  

Archive 2013 · Plane Of Focus (Wide Angle Lens)
  
 
SweetMk
Offline
• •
Upload & Sell: Off
p.1 #1 · p.1 #1 · Plane Of Focus (Wide Angle Lens)


I have wondered about this for a while, and I am too lazy to set up 100 beer bottles to take a picture.

Is the plane of focus of a picture a curved surface or a flat plane? When you focus a wide angle lens, say at 20 feet according to the numerical indication on the lens. does that equate to a flat plane 20 feet from the camera, or a curved surface at a 20 foot radius from the lens?

I guess all lens' are the same, but, telephoto shoot such a narrow angle, the plane is sort of flat either way.

Thanks for the assistance!!




Feb 26, 2013 at 01:24 AM
mpmendenhall
Offline
• • • •
Upload & Sell: Off
p.1 #2 · p.1 #2 · Plane Of Focus (Wide Angle Lens)


All lenses are definitely not the same in this respect. The "ideal" to which lenses are expected to aspire is a flat plane of focus; when lens resolution is measured for, e.g., an MTF chart, testing is done for resolution on a flat surface. Actual lenses can have "field curvature," meaning the surface of best focus is not a flat plane (this is especially common in fast wide angles, though even long focal lengths can display this). The focus surface can be curved in a variety of ways --- sometimes the focus gets closer to the camera, sometimes further away, towards the corners of the image. This is a common cause for decreasing sharpness towards the image corners when flat subjects (or scenery at infinity) are photographed.


Feb 26, 2013 at 06:05 AM
jcolwell
Offline
• • • • • • •
Upload & Sell: On
p.1 #3 · p.1 #3 · Plane Of Focus (Wide Angle Lens)


+1

As far as telephotos go, I think my CZ Sonnar 100/3.5 has slight concave curvature of the plane of focus, at infinity focus distance. IOW, the edges can be in focus while the centre hasn't quite made it to sharp focus. That's the way it behaves at f/3.5 on the generic CY to EOS adapter that I'm currently using. At f/8, it's sharp everywhere, even behind me.

I'l check it again when my Leitax kit arrives.

As far as I can remember, most of the wide angle lenses I've owned that have noticeable curvature of the plane of focus are convex, but as Micahel says, any particular lens can be very different.



Feb 26, 2013 at 12:15 PM
SweetMk
Offline
• •
Upload & Sell: Off
p.1 #4 · p.1 #4 · Plane Of Focus (Wide Angle Lens)


I had no idea this was variable, I thought there would be one standard surface of focus.

Now I have something else to learn!! Or not! I guess this is why I have noticed variable results of DOF.

Is there a guide that might help anywhere?



Feb 26, 2013 at 11:26 PM
EB-1
Offline
• • • • • • •
Upload & Sell: Off
p.1 #5 · p.1 #5 · Plane Of Focus (Wide Angle Lens)


SweetMk wrote:
I had no idea this was variable, I thought there would be one standard surface of focus.

Now I have something else to learn!! Or not! I guess this is why I have noticed variable results of DOF.

Is there a guide that might help anywhere?


You will need some proper test results. The cheapie lens tests that use a camera are all the rage these days, but do not normally provide field curvature results. It is important to note that the curvature varies with distance and most lenses are a compromise. The better lenses have some correction as the distance varies, but that is not perfect either.

EBH



Mar 02, 2013 at 04:37 PM





FM Forums | Forum & Miscellaneous | Join Upload & Sell

    
 

You are not logged in. Login or Register

Username   Password    Retrive password