[pacerr]

. . . and tube-extensions to reduce minimum focus distance.

Not only does it reduce the minimum FD, it also reduces the maximum focusing distance and limits the total focusing range.

You can use this to your advantage when a close-in subject is allowing the AF to break lock and search throughout the min-to-inf range. Spreading a limited focusing range across the full rotation of the focusing ring also adds a degree of fine-tuning capability for both auto- and manual focus lenses.

I routinely take advantage of this characteristic by using 10 - 50mm of extension on 90 - 300mm lenses even when not interested in the extra magnification or close-ups although there is a slight EV penalty. The effect of extension rings on the focusing range is a useful tool not offered by TC's or macro lenses in general.

H2

Edit: from later post --

OBTW, since most extension tubes (PK) don't have the necessary data contacts for AF, a converted screw-drive PK/A or Pz-AF TC shell is required for AF.

With manual focus it seems much easier to finesse the view finder which is how I normally use this technique but it'll work with CIF too. I don't find it particularly useful with AF but it does work. (I.e., the DA 50-200 on hummers with a Pz-AF 1.4 TC.)

Let's say a given bare tele-lens focuses from 9 ft to infinity with the focus ring covering 270-degrees of rotation. With an extension it might focus from, say, 5 - 55 ft. Since the mechanics of the focusing mechanism haven't changed, each degree of rotation now covers only a fraction of its original range -- in effect, fine tuning the focus adjustment.

Since it takes the same amount of mechanical rotation to cover the full range of the available field of focus there's no actual AF speed advantage if it actually breaks lock and hunts lock-to-lock but IME it seems that it's less likely to do so. Since small details cover a larger area at closer range there's less 'distraction' and a larger target for the AF system.

Normally we think of extension tubes as a close-up device but here we're also using the longer end of the focusing range. Try it on your next backyard safari, you might find it interesting.

---

Last edited by pacerr; 11-10-2011 at 09:35 AM.

[dadipentak]

Not only does it reduce the minimum FD, it also reduces the maximum focusing distance and limits the total focusing range.

You can use this to your advantage when a close-in subject is allowing the AF to break lock and search throughout the min-to-inf range. Spreading a limited focal range across the full rotation of the focusing ring also adds a degree of fine-tuning capability for both auto- and manual focus lenses.

I routinely take advantage of this characteristic by using 10 - 50mm of extension on 90 - 300mm lenses even when not interested in the extra magnification or close-up range although there is a slight EV penalty. The effect of extension rings on the focusing range is a useful tool not offered by TC's or macro lenses in general.

H2

very useful tip!

[jpzk]

I'm not sure about the "fly by night" part, but I'd be curious as to why this 'new' lens ONLY has a 1 year SELLER warranty - if I remember correctly, Sigma lenses usually have a 6 year warranty???

Check out this FAQ response on Sigma's website:
SigmaPhoto.com - FAQ's .

Thanks, Chip !

I've looked into it ... better pay a bit more and get peace of mind.

JP

[imtheguy]

@imtheguy and @dadipentak have been after me forever to post some blazing sharp photos with the A* 400/2.8

Yes, dadi and I were mildly concerned but you outdid yourself by carting that anvil around the zoo. Way to go clinton.

[imtheguy]

very useful tip!

I aplogize for my density but I do not understand the situation (other than MFD) where an extension makes focusing easier. Can somebody put this into very simple words for me?
Thanks.

[dadipentak]

I aplogize for my density but I do not understand the situation (other than MFD) where an extension makes focusing easier. Can somebody put this into very simple words for me?
Thanks.

As I understood it, tubes narrow the focus range which means less hunting. .

[imtheguy]

As I understood it, tubes narrow the focus range which means less hunting. .

Should be easy enough to run some tests tonight and find out. Thanks.

[Clinton]

Yes, dadi and I were mildly concerned but you outdid yourself by carting that anvil around the zoo. Way to go clinton.

@DrJulie was Papoosing the 250-600 along side me. We drew some interesting looks, although a local camera shop was offering to let people try out their big glass the same day so we didn't look quite so conspicuous.

[littledrawe]

Should be easy enough to run some tests tonight and find out.

...and the mad scientist retreats to his laboratory....

[pacerr]

. . . an extension makes focusing easier . . .

OBTW, since most extension tubes (PK) don't have the necessary data contacts for AF, a converted screw-drive PK/A or Pz-AF TC shell is required for AF.

With manual focus it seems much easier to finesse the view finder which is how I normally use this technique but it'll work with CIF too. I don't find it particularly useful with AF but it does work. (I.e., the DA 50-200 on hummers with a Pz-AF 1.4 TC.)

Let's say a given bare tele-lens focuses from 9 ft to infinity with the focus ring covering 270-degrees of rotation. With an extension it might focus from, say, 5 - 55 ft. Since the mechanics of the focusing mechanism haven't changed, each degree of rotation now covers only a fraction of its original range -- in effect, fine tuning the focus adjustment.

Since it takes the same amount of mechanical rotation to cover the full range of the available field of focus there's no actual AF speed advantage if it actually breaks lock and hunts lock-to-lock but IME it seems that it's less likely to do so. Since small details cover a larger area at closer range there's less 'distraction' and a larger target for the AF system.

Normally we think of extension tubes as a close-up device but here we're also using the longer end of the focusing range. Try it on your next backyard safari, you might find it interesting.

H2

[traderdrew]

K-5 with Sigma 500mm F/4.5 prime lens

[dadipentak]

Nice work, traderdrew!

I'm liking the K-5+Sigma 500/4.5 combo, too

[traderdrew]

Nice work, traderdrew!

I'm liking the K-5+Sigma 500/4.5 combo, too

Thanks! Those small birds wear me out because I hand hold the lens all of the time and they hide. Suddenly pointing a lens at them doesn't help either. Sometimes I rest my lens on my knee or my chest will be on the ground. I'm thinking of buying a monopod.

[dadipentak]

I'm thinking of buying a monopod.

A very good idea! I rarely hand-hold: I figure if I'm so serious about getting good bird photos that I bought a $5K lens, I need to go the extra bit and use a 'pod of some sort.

[pacerr]

This might be an idea for consideration.

Monopod, Travel Tripod and Camcorder Tripod Outfitter | Trek-Tech ) -- MagMount PRO.


#4 (permalink)

H2