Forums
New posts
Search forums
What's new
New posts
New media
New media comments
New profile posts
Latest activity
Media
New media
New comments
Search media
Members
Current visitors
New profile posts
Search profile posts
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
General Photography
Macro
Questions about extension tubes
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Bob Blaylock" data-source="post: 572497" data-attributes="member: 16749"><p>A 100mm lens, focused at infinity, has its optical center 100mm away from the sensor, and has an angle of view that is based on the arccosine of the size of the sensor divided by twice that focal distance.</p><p></p><p> The simplest lenses focus by moving the entire lens away from the sensor, to focus on closer subjects. As the lens moves farther from the sensor, the angle of view becomes narrower. Move a 100mm lens out to 200mm away from the sensor, and now you're focused on something very close, and you have a narrower angle of view—the same angle of view than a 200mm lens would have when focused at infinity.</p><p></p><p> This is the phenomenon known as <em>“focus breathing”</em> or <em>“lens breathing”</em>. More sophisticated lenses try to minimize it by moving different elements in different ways, rather than by moving the whole lens at once. But when you use extension tubes, you're moving the whole lens at once. Stick 100mm of extension tubes on a 100mm lens, and no matter what that lens does to avoid breathing due to its own focus, you're still getting the full extra 100mm of focus breathing, and getting the angle of view of a 200mm lens. This isn't really a terrible thing, when you consider that you'd usually be using extension tubes to try to take detailed pictures of very small objects, and in that context, the narrower angle of view is helpful.</p></blockquote><p></p>
[QUOTE="Bob Blaylock, post: 572497, member: 16749"] A 100mm lens, focused at infinity, has its optical center 100mm away from the sensor, and has an angle of view that is based on the arccosine of the size of the sensor divided by twice that focal distance. The simplest lenses focus by moving the entire lens away from the sensor, to focus on closer subjects. As the lens moves farther from the sensor, the angle of view becomes narrower. Move a 100mm lens out to 200mm away from the sensor, and now you're focused on something very close, and you have a narrower angle of view—the same angle of view than a 200mm lens would have when focused at infinity. This is the phenomenon known as [i]“focus breathing”[/i] or [i]“lens breathing”[/i]. More sophisticated lenses try to minimize it by moving different elements in different ways, rather than by moving the whole lens at once. But when you use extension tubes, you're moving the whole lens at once. Stick 100mm of extension tubes on a 100mm lens, and no matter what that lens does to avoid breathing due to its own focus, you're still getting the full extra 100mm of focus breathing, and getting the angle of view of a 200mm lens. This isn't really a terrible thing, when you consider that you'd usually be using extension tubes to try to take detailed pictures of very small objects, and in that context, the narrower angle of view is helpful. [/QUOTE]
Verification
Post reply
Forums
General Photography
Macro
Questions about extension tubes
Top