What does an extension tube do?

[joescrivens]

I have a 70-300mm Canon IS lens. In the instruction manual it mentions an extension tube - what does this do to my lens and how can I use it?

 

[grumpybadger]

It fits betweent the lens and the camera and so moves the back of the lens away from the sensor/film plane.

This means you can no longer focus at infinity but you can focus closer than the standad minimum focus distance of the lens. This is typically used for two things:

1. Macro photography
2. With longer lenses with a high minimum focus distance (my 500 is 4.5 metres) to reduce the focus distance to (say) 3 metres to help with things like small birds.

Paul

 

[joescrivens]

It fits betweent the lens and the camera and so moves the back of the lens away from the sensor/film plane.

This means you can no longer focus at infinity but you can focus closer than the standad minimum focus distance of the lens. This is typically used for two things:

1. Macro photography
2. With longer lenses with a high minimum focus distance (my 500 is 4.5 metres) to reduce the focus distance to (say) 3 metres to help with things like small birds.

Paul

I see,

so by using the extension tube could I turn my 18-55mm EFS lens into a macro lens?

 

[minky_monkey]

That`s what I do with my 50mm 1.4

If you use the cheap ones on ebay that don`t have the electrical connection between the body and lens, you lose the ability to change the aperture.

 

[joescrivens]

That`s what I do with my 50mm 1.4

If you use the cheap ones on ebay that don`t have the electrical connection between the body and lens, you lose the ability to change the aperture.

ok so if i buy this one i'll be set:

http://www.amazon.co.uk/Canon-EF-25...1?ie=UTF8&s=electronics&qid=1256577350&sr=1-1

 

[andrewc]

Yes, but much poorer.

Kenko make extension tubes which come as a 3 piece set for variable amounts of macroness, which come with pins to preserve electrical conductivity.

 

[joescrivens]

Yes, but much poorer.

Kenko make extension tubes which come as a 3 piece set for variable amounts of macroness, which come with pins to preserve electrical conductivity.

where can I buy them from and do they work with Ef and EFS lenses?

 

[joescrivens]

http://www.onestop-digital.com/catalog/product_info.php?language=en&currency=GBP&products_id=226

found them here, looks like it's ef and efs - were these the ones you meant?

 

[Mostly Vintage Cameras]

If the extension equals the focal length you get 1:1 reproduction, that is to say 50mm extension on a 50mm lens will produce an image life size on the film or CCD (1cm on a ruler would be 1cm on the negative/slide/CCD etc).

25mm extension on 50mm lens = 1:2 half life size
50mm extension on 50mm lens =1:1 life size
100mm extension on 50mm lens = 2:1 twice life size.

The down side is as you move the lens away from the camera body and film plane less light gets to the film/CCD so you get longer exposure times and secondly the higher the magnification the less depth of field you get.

The above holds true of any format of camera. A 1.6X crop camera will give you a different angle of view with a 50mm lens compared to a full frame digital or 6X9 cm film camera but the focal length and the therefore the effect of spacing the lens further from the film plane remains constant at 50mm.

Hope that helps