What determines the minimum focus of a lens?

[Yousuf Abbasi]

Take a 50mm lens, for instance. How come with some lenses I can focus as low as 1-inch from in front of the lens, whereas with other lenses the closest subject in focus is 5-10 inches away?

What determines the minimum focus distance of a lens, and can it be changed?

:emote_popcorn:

 

[Noah Kadner]

Not really- it's to do with the optical configuration of the lens. That's why you have different focal lengths as well as special close focus and macro lenses. All of this is very clearly laid out in the manufacturer's specifications- things like focal range, sensitivity, etc.

Noah

 

[Yousuf Abbasi]

Not really- it's to do with the optical configuration of the lens. That's why you have different focal lengths as well as special close focus and macro lenses. All of this is very clearly laid out in the manufacturer's specifications- things like focal range, sensitivity, etc.

Noah

Yes I'm aware its to do with optical configuration (what else could it be?). I've seen lenses converted to close focus... just trying to understand what are the drivers determining focus distance.

 

[sander kamp]

On lenses where the whole lens block moves for focussing it is how far the lens block can move away from the sensor/film plane. With macro lenses the lens block can travel very far, sometimes multiple turns. If you can put something in between the camera and the lens, like rings with mounts, you will be able to focus closer.

Now I don't know how it works with lenses with internal focussing and it might also be that proper macro lenses have a different optical formula.

 

[Jeff Kilgroe]

Internal focusing lenses are the same basic concept but their optical design allows for the front element to remain stationary, therefore allowing all moving elements to be encapsulated within the lens for no external shifting components. The close focus ability of a lens is usually limited by the range of travel for the focusing elements within the lens. Other optical characteristics can play a role as well, but it all varies from one design to another. Some lenses are able to be converted to macro if they are re-barreled and / or fitted with a different mount that can allow greater travel distance for the optical focusing elements.

 

[Matthew Duclos]

It depends on the lens. Several replies in this thread are correct.

For example, a Zeiss speed can be modified for close focusing with a simple alteration to the focus stop mechanism.
This is possible because the entire optical group moves simultaneously and there are no stationary elements relative to the film/sensor.

The other note by sander is also true. It's a simple as adding an "extension tube".
You'll gain excellent close focus ability, but you won't be able to achieve infinity focus.

Close focus is mostly determined by optical-mechanical limitations.

 

[Yousuf Abbasi]

It depends on the lens. Several replies in this thread are correct.

For example, a Zeiss speed can be modified for close focusing with a simple alteration to the focus stop mechanism.
This is possible because the entire optical group moves simultaneously and there are no stationary elements relative to the film/sensor.

The other note by sander is also true. It's a simple as adding an "extension tube".
You'll gain excellent close focus ability, but you won't be able to achieve infinity focus.

Close focus is mostly determined by optical-mechanical limitations.

This is what I wanted to know. Thanks a lot guys.