Does focal length of a macro lens matter? If yes, to what extent?


wizz747

New Member
Feb 27, 2010
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Singapore
#1
Hi all. I don't know much about macro lens/photography. As far as I know, macro lens allows one to get a magnification of a certain subject and usually, the minimum focusing distance is very small compared to normal lenses (telephoto zoom, wideangle, etc).

However, I'm not sure about something. Does the focal length of the macro lens matter? If yes, how much does it matter? Basically, the macro lens allows one to get a certain magnification of a subject. Then, how is the focal length of the macro lens important?
 

yilin

New Member
Jul 24, 2004
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Within Me
#2
The shorter the focal length of the macro lens, the closer you also need to be to the subject you are shooting.

Think will be ok if you are shooting static object, but for sensitive bugs might be better to get a longer focal len

... another thing is the shadow that can be cast over the subject when you need to be closer but could be eliminated with right lighting

:) my 2 cents
 

Last edited:

giantcanopy

Senior Member
Feb 11, 2007
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SG
#3
In general the lower the focal length, the smaller / lighter / cheaper the macro lens.
The longer focal length macro lenses give more working distance as mentioned.

Ryan
 

Oct 15, 2006
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Serangoon
www.flickr.com
#4
A typical or true macro lens can achieve a magnification of 1:1 (life size) at closest focusing distance. At 1:1, the subject size of say 1cm cast an image size of 1cm on the sensor.

A true Macro lenses can come in various FL, eg. 35mm, 50mm, 60mm, 100mm, 150mm, 180mm, 200mm.
They all have the same magnification at minimum focusing distance.
Apart from the physical look, size and weight differences, as well as prices.

The 3 main differences are:
1) Shorter FL = shorter WD (Working Distance from lens to subject), longer FL = longer WD
2) Shorter FL = wider AOV (Angle Of View), longer FL = narrower AOV
3) Shorter FL = wider DOF (Depth Of Field), longer FL = narrower DOF

Different FL served difference purposes, make sure what kind of subject/photography you're into before purchasing anyone of the macro glasses.

Cheers..
 

zac08

Senior Member
Feb 21, 2005
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East
#6
I know this is a little OT but does the focal length affect the depth of field ?
Definitely.

When shooting the same subject at the same perspective, a longer focal length will definitely give you less DOF.

Just try a simple subject with your zoom lens. Focus on a subject @ say 55mm or 70mm. Then zoom out to 200mm, you must then move backwards away from the subject to get the subject to be framed as you'd have done so for the wider angle. This will definitely give you less DOF. :)
 

giantcanopy

Senior Member
Feb 11, 2007
6,232
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SG
#7
Definitely.

When shooting the same subject at the same perspective, a longer focal length will definitely give you less DOF.

Just try a simple subject with your zoom lens. Focus on a subject @ say 55mm or 70mm. Then zoom out to 200mm, you must then move backwards away from the subject to get the subject to be framed as you'd have done so for the wider angle. This will definitely give you less DOF. :)
The 100mm at 2.8 takes one doll on a shelf of dolls. The 20mm at 2.8 takes the entire shelf of dolls. While the 20mm appears as if much more is in focus, when u crop down that same doll taken at 100mm and the one at 20mm f2.8, they give the same dof.

There are many other sites that has pictures to demonstrate, but my fav goes to
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

quote :
Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to make the subject appear bigger when one is unable to get closer. If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length!
 

zac08

Senior Member
Feb 21, 2005
11,755
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East
#8
The 100mm at 2.8 takes one doll on a shelf of dolls. The 20mm at 2.8 takes the entire shelf of dolls. While the 20mm appears as if much more is in focus, when u crop down that same doll taken at 100mm and the one at 20mm f2.8, they give the same dof.

There are many other sites that has pictures to demonstrate, but my fav goes to
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

quote :
Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to make the subject appear bigger when one is unable to get closer. If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length!
I mean, you move close up to get the same doll to fit into the frame for BOTH pictures...

Same doll fills frame in both 20mm and 100mm. see if you find any difference in the DOF.
 

allenleonhart

Deregistered
Sep 17, 2008
3,656
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0
#9
The shorter the focal length of the macro lens, the closer you also need to be to the subject you are shooting.

Think will be ok if you are shooting static object, but for sensitive bugs might be better to get a longer focal len

... another thing is the shadow that can be cast over the subject when you need to be closer but could be eliminated with right lighting

:) my 2 cents
lens actually
and yea ur right on most counts:)
 

Jamesf

New Member
Apr 1, 2008
178
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0
Island East
#10
Hi all. I don't know much about macro lens/photography. As far as I know, macro lens allows one to get a magnification of a certain subject and usually, the minimum focusing distance is very small compared to normal lenses (telephoto zoom, wideangle, etc).

However, I'm not sure about something. Does the focal length of the macro lens matter? If yes, how much does it matter? Basically, the macro lens allows one to get a certain magnification of a subject. Then, how is the focal length of the macro lens important?
To achieve 1:1 (life size) magnification:

Canon EFS 60mm : Distance between lens front and subject is about 9cm
Canon EF 180mm : Distance between lens front and subject is about 24cm (more expensive, bulkier and heavy)

Hope it helps.
 

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