What is the meaning of the red words?


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hwchoy

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#1
on the focus distance window of these two lenses there are additional red etchings indicating different focal lengths. how is one supposed to read the scales?




thanx in advance!
 

Ah Pao

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#2
White line - the focus distance of the lens. If it points to the white "5", it means the lens is focused at 5m away.

The red lines indicate the depth of field at the various focal lengths. For example, if it points at "5", and your lens is at 70mm focal length, that means that anything between 5-10m is "in focus". If you lens is at 135mm focal length, it means the DOF extends from 5m to ~7-8m. The short line beside the "135" mark is probably for the 100mm focal length (not enough space to engrave it on the lens, I suppose).

I'm assuming that the engravings for the DOF are marked at the lens' largest aperture.

Same thing for your 80mm lens.


EDIT: Nope, it's not DOF scales (as the later posts shows). For IR film focus shift instead.
DOF scales are marked both sides of the focusing scale for all the different apertures, usually on prime lenses. Got mixed up. :p
 

Ah Pao

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#4
I suspect for your 80-200mm lens, the DOF at 200mm is so shallow that it will be around the same point as your focus distance.
 

Artosoft

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#5
Ah Pao said:
White line - the focus distance of the lens. If it points to the white "5", it means the lens is focused at 5m away.

The red lines indicate the depth of field at the various focal lengths. For example, if it points at "5", and your lens is at 70mm focal length, that means that anything between 5-10m is "in focus". If you lens is at 135mm focal length, it means the DOF extends from 5m to ~7-8m. The short line beside the "135" mark is probably for the 100mm focal length (not enough space to engrave it on the lens, I suppose).

I'm assuming that the engravings for the DOF are marked at the lens' largest aperture.

Same thing for your 80mm lens.
DOF at which Aperture? And usually DOF put a scale with white colour at nearer and farther distance. This one only at farther distance.

I am not sure about this, but last time I know the red colour indicate focus distance for InfraRed Photography.

Regards,
Arto.
 

Artosoft

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#7
Ah Pao said:
I'm assuming that the engravings for the DOF are marked at the lens' largest aperture.
Ups..., I didn't see your mention about the largest aperture.... :sweat: .

Regards,
Arto.
 

catchlights

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#8
is for compensation of Infrared Wavelength Focusing when doing Infrared Photography

if it is for DOF indication, should be indicate f-stop, not focal length.
 

Artosoft

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#10
hwchoy said:
mmm… not tremendously useful for me then (IR I mean).

for a zoom lens, DOF indication would require focal length as well right?
and Aperture as well...

Regards,
Arto.
 

lsisaxon

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#13
catchlights said:
is for compensation of Infrared Wavelength Focusing when doing Infrared Photography

if it is for DOF indication, should be indicate f-stop, not focal length.
From the scale, it looks more like DoF. If it were for infrared focus, it would not shift so much more the wider you go. Plus, if the 80-200 is APO, then there shouldn't be another focus for IR.
 

lsisaxon

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#14
catchlights said:
if it is for DOF, why is on one side only and not both side?

best is you check on the lens manual.
More like for indicating the hyperfocal distance I presume. I'm not a Canon user.. :)
 

Artosoft

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#15
lsisaxon said:
More like for indicating the hyperfocal distance I presume. I'm not a Canon user.. :)
Hyperfocal distance need aperture value also.

Hmmm.... must do RTFM. I am also non CANON user.

Regards,
Arto.
 

Artosoft

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#17
lsisaxon said:
From the scale, it looks more like DoF. If it were for infrared focus, it would not shift so much more the wider you go. Plus, if the 80-200 is APO, then there shouldn't be another focus for IR.
Are you sure? If I am not wrong, the wider, the more Ir focus shift.

Regards,
Arto.
 

catchlights

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#19
lsisaxon said:
More like for indicating the hyperfocal distance I presume. I'm not a Canon user.. :)
I agreed with you of both, it looks strange to me as a IR indication mark, normally is only 0.25% shift, it wouldn't be that much.

I'm not a canon user too, don't have a manual to check out.
 

lsisaxon

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#20
Artosoft said:
Are you sure? If I am not wrong, the wider, the more Ir focus shift.

Regards,
Arto.
I think you are right. Doesn't quite make sense for the DoF to be marked this way and yes, IR would have shifted more the wider you go because of the shorter focal length. :)

Edited: Checked with a Canon user. It's for IR.
 

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