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Forums > Back > How to use my old "newfound" FD lenses
#11
[quote name='Vieux loup' timestamp='1304885872' post='8136']

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?

[/quote]



Well, the symptom is as follow:



1) The distance scale on the lens appears to be wrong.

2) When the lens shows "infinity", things at infinity aren't sharp ... instead something

(much) nearer is sharp.

3) The situation is completely equivalent as when using a lens with an extension tube.



If you have a look on how a lens focusses, you will see two methods:

- by extension ... the optical groups are shifted forward (away from the focal plane) to focus nearer.

- by internal focussing ... not all groups are moved ... sometimes only an internal group is

moved, so the length of the lens does not change.



If you compare "focusing by extension" with adapting FD to EF (or Nikon), you will find that

in principle the same thing happens ... in one case by moving the focus ring, in the other case

by mounting the lens in the "wrong" position. As you likely know from your own experience,

long focal lengths need more extension to focus to something near than short focal lengths

do ... so for a 20mm lens a few millimeters change focus from infinity to below one meter,

while for a 400mm lens these few millimeters only focus down to say 50mtr.



This means, the maximum distance you can focus on (with such an adapted lens that is not

correctedfor infinity focus) is further away the longer the focal lengths is. Short lenses it will

become more or less useless (exept macrolenses, where the effect might be quite welcome).



Some (but by far not all) FD-lenses can be modified to fit EF ... in some cases this modification

is reversible, in others it is not. But you really need a hand for this in order to get a proper result.

There are quite a few things that need modification for this.



Rainer



PS It's in german (which might or might not be overly helpful for you), but have a look on

the pages linked here ... [url="http://www.4photos.de/camera-diy/Foto-Selbstbau.html"]http://www.4photos.d...-Selbstbau.html[/url]

This guy has modified quite a few FD-lenses to fit EOS/EF.
  Reply
#12
[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='Smile' /> ! 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.
  Reply
#13
[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='Smile' /> ! 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]

Here is one calculator to give an indication. If you're just looking at effect of extension on infinity focus, then just put in the lens focal length, set D to zero, and add extension as needed.



I'm still working on a FD 50mm f/1.2 non-L to EOS conversion. Replacing the bit around the mount section will allow infinity focus in this case, but metalwork was never my strong point...
<a class="bbc_url" href="http://snowporing.deviantart.com/">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.
  Reply
#14
[quote name='Rainer' timestamp='1304889396' post='8144']

Well, the symptom is as follow:



1) The distance scale on the lens appears to be wrong.

2) When the lens shows "infinity", things at infinity aren't sharp ... instead something

(much) nearer is sharp.

3) The situation is completely equivalent as when using a lens with an extension tube.



If you have a look on how a lens focusses, you will see two methods:

- by extension ... the optical groups are shifted forward (away from the focal plane) to focus nearer.

- by internal focussing ... not all groups are moved ... sometimes only an internal group is

moved, so the length of the lens does not change.



If you compare "focusing by extension" with adapting FD to EF (or Nikon), you will find that

in principle the same thing happens ... in one case by moving the focus ring, in the other case

by mounting the lens in the "wrong" position. As you likely know from your own experience,

long focal lengths need more extension to focus to something near than short focal lengths

do ... so for a 20mm lens a few millimeters change focus from infinity to below one meter,

while for a 400mm lens these few millimeters only focus down to say 50mtr.



This means, the maximum distance you can focus on (with such an adapted lens that is not

correctedfor infinity focus) is further away the longer the focal lengths is. Short lenses it will

become more or less useless (exept macrolenses, where the effect might be quite welcome).



Some (but by far not all) FD-lenses can be modified to fit EF ... in some cases this modification

is reversible, in others it is not. But you really need a hand for this in order to get a proper result.

There are quite a few things that need modification for this.



Rainer



PS It's in german (which might or might not be overly helpful for you), but have a look on

the pages linked here ... [url="http://www.4photos.de/camera-diy/Foto-Selbstbau.html"]http://www.4photos.d...-Selbstbau.html[/url]

This guy has modified quite a few FD-lenses to fit EOS/EF.

[/quote]



Rainer thanks, this is fantastic. I do understand Herman and should contact this man.<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />
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