05-08-2011, 09:23 PM
(This post was last modified: 05-08-2011, 09:24 PM by Brightcolours.)
[quote name='Vieux loup' timestamp='1304885872' post='8136']
Thanks again Rainer for bringing me back on the straight and narrow <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' /> ! What does it mean in practical terms to loose focus to infinity. You focus up to a certain distance I guess and then you loose the focusing ability? Are there any rules about how far out you loose the focusing?<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/unsure.gif' class='bbc_emoticon' alt=':unsure:' />
[/quote]
I am sure there is a way to calculate that, but I do not know the formula.
The longer the lens, the less you will lose. The shorter the lens, the more the focus range will collapse.
2 examples to illustrate this:
I have a 12mm extension tube. So, the lenses are put 12mm from the position they are designed for.
On my 70-200mm f4 lens, at 200mm, the focus range changes from 1.2m (MFD) - infiniti into: 1m - 3.5 meter.
My 35mm f2 lens focusses from 40cm (MFD) - infinity. With 12mm tube it collapses to: 17cm - 20cm.
As you can see, the shorter the focal length, the bigger the impact.
This means that the 50mm lens will only be usable for close up photography. And the teles probably to about 20 meters?
You can of course just use the for close up stuff, with maybe an extension tube set to get closer by. But if you want to use them in their designed roles, Sony Nex (my preference format wise) and 4/3rds (micro or regular) are the cameras to look at.
Thanks again Rainer for bringing me back on the straight and narrow <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' /> ! What does it mean in practical terms to loose focus to infinity. You focus up to a certain distance I guess and then you loose the focusing ability? Are there any rules about how far out you loose the focusing?<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/unsure.gif' class='bbc_emoticon' alt=':unsure:' />[/quote]
I am sure there is a way to calculate that, but I do not know the formula.
The longer the lens, the less you will lose. The shorter the lens, the more the focus range will collapse.
2 examples to illustrate this:
I have a 12mm extension tube. So, the lenses are put 12mm from the position they are designed for.
On my 70-200mm f4 lens, at 200mm, the focus range changes from 1.2m (MFD) - infiniti into: 1m - 3.5 meter.
My 35mm f2 lens focusses from 40cm (MFD) - infinity. With 12mm tube it collapses to: 17cm - 20cm.
As you can see, the shorter the focal length, the bigger the impact.
This means that the 50mm lens will only be usable for close up photography. And the teles probably to about 20 meters?
You can of course just use the for close up stuff, with maybe an extension tube set to get closer by. But if you want to use them in their designed roles, Sony Nex (my preference format wise) and 4/3rds (micro or regular) are the cameras to look at.