Thursday 13 August 2009

Focus limiters

Certain lenses like macro and telephotos have a switch on the side that can limit the amount of distance that the lens can focus-why would you have these and in what situations would you use them?
Well firstly they will speed the AF up by only using the distance that you need to shoot in rather than the full- close in to far away, for instance if you using a Canon 500mmF4 I.S the focus limiter button has settings of 4.5m to infinity,4.5m to 10m and 10m to infinity,if you are shooting birds on a perch (branch) and the perch is say 6m away set the focus limiter button to 4.5m to 10m as you do not want or need the lens to focus either side of that, if you are shooting birds in flight then set it to 10m to infinity as the birds will not be closer than 10m and if you find that need to shoot both close and distant subjects then use the 4.5m to infinity, The 500F4 I.S has a minimum focusing distance of 4.5m so if anything is closer than that then you either cant focus,will have to move back or use extension tubes
My Nikon 600F4 VR has just 2 settings of 10m to infinity and FULL which will take me from the closest focusing distance of 5.5m to infinity, If again i shoot birds in flight i will set the switch to 10m to infinity, by not having to focus from 5.5m to 10m the AF will be faster and the lens less likely to hunt
Macro lenses are another type of lens that have focus limiters as one they are slower to focus than standard telephotos and you tend to work at certain distances,Look at my Sigma 180mm F3.5 macro below


you will see the switch has 3 settings 0.46-0.61,0.61-infinity and FULL which will be 0.46 {minimum focusing distance) to infinity,True macro lenses magnify to 1:1 which is at minimum focusing distance so if you are using AF with your macro lens and you want maximum magnification then set the limiter to 0.46-0.61 if however that makes the subject too big and you have to move back then use the middle setting and if your subject is farther than 0.61m then you will have to use the FULL setting
This may sound abit time consuming and fiddly but it will help you by having better/faster AF

Dave

4 comments:

  1. Dave, A quick question if I may . Do the minimum focussing distances quoted by the lens manufacturers refer to using autofocus or do they apply in manual focus as well? The reason I ask is that my 180mm macro canon seems to focus manually down to much closer that the 90 cm in the manual. The longer lenses 500mm or 300mm I haven't noticed that I can focus manually any closer than the official distances.
    Pete

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  2. Hi Pete
    I the figures quoted are for AF, My 600 is quoted as having a minimum focusing distance of 5.5m which it does have using AF however in manual focus i can get it down to 5m,I find it strange that the Canon 180 macro has a minimum focus distance of 90cm when the Sigma is 41cm,What does it say on the focus limiter
    Dave

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  3. Sorry Pete that should have said 46cm, I have looked at B+H website for the Canon 180 and it says that the minimum focusing on the Canon is similar to the Sigma lens

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  4. Dave yep my mistake I think its around 18 inches with the autofocus.
    Pete

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