UNDERSTANDING THE MACRO LENS

[Nici]

I love shooting Maro. I invested in a Sigma 105mm 1:2:8 DG Macro. I have taken some real nice shots with the lens both in Manual and AF modes. What I struggle to understand is the reading on the barrel of the lens. When I shoot it at Full setting all seems pretty much in focus. As soon as I shift the lever to .45m or to .312 - 0.45 - Infinity, I loose all focus. Mainly, I don't pretty much get the other two settings or what they should be. I have now stuck to "full" mode. Can anyone please explain to me what the other two settings are and how to use them, especially the infinity setting (.312 - 0.45m) as I would love to get the full advantage of the lens.

Thanx

 

[Overread]

I think something might be getting mixed up in how you're describing the settings; however I get what you mean:

1) Macro lenses have a unique focusing system; the infinity to close distances for focusing have a very quick turn on the focusing wheel to move through the focusing distance. You can try this yourself in manual mode and see just how little you have to turn the wheel to move the focus a lot. This is a rather "rough" focusing setup - its possible to manually focus certainly and AF won't have problems; but it means you've little fine control that other lenses might have.

2) As a compensation the greater part of its focusing fidelity is in the close to macro distances. Again you can see this for yourself by just focusing the lens closer and closer and seeing just how much you have to turn to focus.

3) As a result of point 2 the lens features a focus limiter switch. The limiter switch typically has 3 modes.
a) Mode that allows all focusing from its closest to furthest distance.
b) Mode that focuses from a close up distance to infinity - this is used so that if you know you're not taking any macro photos you can enable the mode and when the AF hunts for the focus point it won't have to go through all the macro range; thus cutting down on any focus hunting that might take place and thus speeding up the time it takes to get focus
c) Mode that focuses from close up to macro; basically the same as mode b but in reverse; cutting out all the long distance that you don't need.


If manually focusing I leave the switch in mode a - whilst if using AF I'll use the most suitable mode for what I'm shooting. That is typically mode b since macro work tends to be done best in manual rather than auto focus because of the amount of pitching back and forth that you physically do when handholding - it puts a lot of strain on the AF and often AF at macro distances is hit and miss. Thus most use manual focusing.



Note in many macro lenses if you have the focus set to a range which is outside of that defined by a range set when you move the focus limiting switch the AF might not engage or it might engage wrong. You have to use manual focusing or all the focus distance (mode a above) to get the focus roughly in the right zone then engage the focus lock.



Note I've called them modes a,b,c but that is only in the context of this post; the manual might call them differently; but they should be clearly marked on the lens. Have a play and see how you find them.

 

[Derrel]

Your lens uses a rather unusual system with the DF or Dual Focus and the focusing ring "clutch" mechanism, detailed here: Sigma 105mm f/2.8 EX DG Macro Lens Review

The reviewer does a POOR job of conveying the information, with lacking distance markings. but let me put it this way: Any lens that has a Limit switch does that to "lock out" certain target distances, to prevent the lens from focusing either too far, or too close, and or to speed up focusing, by limiting the focusing range. MANY lenses use a Full/Limit switching system, and there are a few varieties of these, and not all are the same. Using the Limit position can really improve focusing performance.


from the review:" As can be seen in the above photo, the Sigma 105 Macro has a focus limit switch. Use the limit position to reduce focus hunting time by limiting the focus distance to 12.3" - 14.7" (313mm - 370mm) or 14.75" - 8 (400mm - 8). The minimum focus distance is 12.3" (313mm) which provides a working distance of 4.8" (122mm) from the end of the lens (without the hood in place)."

************

So, it seems that the Limit switch restricts focus to a very narrow range of 12.3 inches to 14.7 inches. The author's use of the exact wording of 14.75" - 8 (400mm - 8)

seems to me to indicate what he MEANT to state was that the second position of the Limiter allows focus from 14.75 inches back to 8 inches. This is as badly bungled a piece of camera reviewing as one could find, forgetting to double-check one's writing, and mixing Imperial with metric distance units and failing to use distance symbols. Trying to decode Brian's sloppy writing and poor explication, it seems as if there are two, different limit ranges, one range for AF, the other range for manual focusing.

One range is from 12.3 inches to 14.7 inches, and a second limit range would be made up of the 14.75 inch to the 8.0 inch range of distances. These close distance ranges are very useful for with a telephoto-length macro lens.

As you have discovered,when using the Limit feature for macro, there is NO autofocusing for distant objects. The FULL setting allows focusing across the lens's entire focusing range. The LIMIT switch on your specific macro lens is for close-range shooting.

 

[Nici]

I think something might be getting mixed up in how you're describing the settings; however I get what you mean:

1) Macro lenses have a unique focusing system; the infinity to close distances for focusing have a very quick turn on the focusing wheel to move through the focusing distance. You can try this yourself in manual mode and see just how little you have to turn the wheel to move the focus a lot. This is a rather "rough" focusing setup - its possible to manually focus certainly and AF won't have problems; but it means you've little fine control that other lenses might have.

2) As a compensation the greater part of its focusing fidelity is in the close to macro distances. Again you can see this for yourself by just focusing the lens closer and closer and seeing just how much you have to turn to focus.

3) As a result of point 2 the lens features a focus limiter switch. The limiter switch typically has 3 modes.
a) Mode that allows all focusing from its closest to furthest distance.
b) Mode that focuses from a close up distance to infinity - this is used so that if you know you're not taking any macro photos you can enable the mode and when the AF hunts for the focus point it won't have to go through all the macro range; thus cutting down on any focus hunting that might take place and thus speeding up the time it takes to get focus
c) Mode that focuses from close up to macro; basically the same as mode b but in reverse; cutting out all the long distance that you don't need.


If manually focusing I leave the switch in mode a - whilst if using AF I'll use the most suitable mode for what I'm shooting. That is typically mode b since macro work tends to be done best in manual rather than auto focus because of the amount of pitching back and forth that you physically do when handholding - it puts a lot of strain on the AF and often AF at macro distances is hit and miss. Thus most use manual focusing.



Note in many macro lenses if you have the focus set to a range which is outside of that defined by a range set when you move the focus limiting switch the AF might not engage or it might engage wrong. You have to use manual focusing or all the focus distance (mode a above) to get the focus roughly in the right zone then engage the focus lock.



Note I've called them modes a,b,c but that is only in the context of this post; the manual might call them differently; but they should be clearly marked on the lens. Have a play and see how you find them.

Thank you so very much for this most informative response to my question. You have given the answer in "layman's" terms which has helped me to grasp it so much easier. I understand exactly what you've explained and will now but this info to good use.