Why are macro lenses slow to AF?

DNT · 10-07-2012, 11:11 PM

Howdy All,

Can anyone point me in the direction or explain to me as to why macro lenses are slow to AF? I'm not having any luck with google as the search results tend to return the general line 'macro lenses are slow to focus' but there's no why.

I"m currently shooting the 100mm f/2.8L from Canon on a 300D and it's brilliantly fast in perfect daylight but when the light drops because of factors like shade, it can be quite slow at times whether it be a macro or telephoto shot.

Last night I was doing my research as to which pentax macro lens to get (35mm vs 100mm) but also read their AF can also be slow. I can only assume it's just the way a macro lens is constructed compared to a non-macro lens. As you can see I don't have great technical knowledge so any help would be appreciated.

It's not something that I mind as manual focusing is a piece of cake but it's just to satisfy my curiosity as to why?

Cheers,
DNT

Adam · 10-07-2012, 11:36 PM

Macro lenses are slow to AF simply because their focusing throw is really long due to fact that the optics need to be moved further in order to focus on stuff that's close to you. Some macro lenses have AF limiters to prevent hunting, such as the old FA 100mm F2.8, F 100mm F2.8, and FA* 200mm F4.

DNT · 10-07-2012, 11:42 PM

ahhh ok that makes sense. (had to google focus throw hehehe)

Cheers Adam!

lytrytyr · 10-07-2012, 11:42 PM

The DA 35 Macro Ltd is one of my favorite lenses,
and the only AF macro lens I use.

Once, I was taking a photo of the speaker at a presentation,
and made the dumb mistake of pointing the center focus point
straight at the empty whiteboard.

The poor lens chugged itself all the way through to the extreme close up range,
and then all the way back to infinity.
At this point, the lens became the center of attention
for the entire audience, and the speaker.

So to focus quickly with that lens at normal distances,
choose a contrasty target, and pre-focus manually with the quick shift.
MF is best for macro shots anyway.

elliott · 10-07-2012, 11:44 PM

Also, the longer the focal length, the further it has to travel to get the same magnification. You can obtain 1:1 macro with a normal 28mm lens on 25mm of extension tubes, but a normal 50mm would require 43mm of extension tubes to obtain the same magnification. So the 100mm is going to be traveling much further than the 35mm, which might make the 100mm slower to focus.

**maxfield_photo** · 10-07-2012, 11:45 PM

With the limiter engaged, my FA 100 macro is blisteringly fast, it's really from 2 feet to MFD that takes the longest.

DNT · 10-07-2012, 11:51 PM

Originally posted by lytrytyr

So to focus quickly with that lens at normal distances,
choose a contrasty target, and pre-focus manually with the quick shift.
MF is best for macro shots anyway.

Yeah I quickly discovered that at an outing with my wife's cousin when shooting dolphins @ Seaworld on a cloudy day

Seaworld

Only have the 100mm macro and the 18 - 55mm kit lens hence the macro usage. Never tweaked settings and shot so fast in my life till that day hahaha

But yes, macro work I generally use MF over AF.

DNT · 10-07-2012, 11:59 PM

thanks for all the replies people!

Jean Poitiers · 10-08-2012, 03:59 AM

My D FA 100 WR is not that slow IMHO but will hunt under certain conditions ... I use a lot of MF and will use AF (approx. focus preset first) on moving small things like bees, that tend not to be stationary as opposed to the flower itself. Salut, J

**Lowell Goudge** · 10-08-2012, 04:37 AM

Also note that when focusing closed especially the light falls off due to image enlargement and this may also cause a reduction onAF performance

bwDraco · 10-08-2012, 07:03 AM

Originally posted by DNT

ahhh ok that makes sense. (had to google focus throw hehehe)

Cheers Adam!

For reference, the focus ring travel of the Pentax D FA 50mm macro lens is about 285 degrees, or more than three-quarters of a full rotation. This is entirely normal.

-----Off topic-----

Originally posted by DNT

100mm f/2.8L from Canon on a 300D

emphasis added

Wow, that's a really old camera body to be using an L lens on...
-----End off topic-----

--DragonLord

KHatfull · 10-09-2012, 11:13 AM

Originally posted by Adam

Macro lenses are slow to AF simply because their focusing throw is really long due to fact that the optics need to be moved further in order to focus on stuff that's close to you. Some macro lenses have AF limiters to prevent hunting, such as the old FA 100mm F2.8, F 100mm F2.8, and FA* 200mm F4.

And with the limiter on it's really fast. I just got mine a couple weeks ago. While it's not as fast as an IF lens the limiter sure makes a difference for non-macro subjects.

One of my complaints with the Tamron 90s, and one of the reasons I ultimately decided to sell the Tamron and keep the FA100 (the other two being the heavier weight of the FA100 and the "Clamp" swtich).

10-07-2012, 11:11 PM	#1
DNT Junior Member Join Date: Sep 2012 Location: Brisbane Photos: Albums Posts: 43	Why are macro lenses slow to AF? Howdy All, Can anyone point me in the direction or explain to me as to why macro lenses are slow to AF? I'm not having any luck with google as the search results tend to return the general line 'macro lenses are slow to focus' but there's no why. I"m currently shooting the 100mm f/2.8L from Canon on a 300D and it's brilliantly fast in perfect daylight but when the light drops because of factors like shade, it can be quite slow at times whether it be a macro or telephoto shot. Last night I was doing my research as to which pentax macro lens to get (35mm vs 100mm) but also read their AF can also be slow. I can only assume it's just the way a macro lens is constructed compared to a non-macro lens. As you can see I don't have great technical knowledge so any help would be appreciated. It's not something that I mind as manual focusing is a piece of cake but it's just to satisfy my curiosity as to why? Cheers, DNT

10-07-2012, 11:36 PM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Macro lenses are slow to AF simply because their focusing throw is really long due to fact that the optics need to be moved further in order to focus on stuff that's close to you. Some macro lenses have AF limiters to prevent hunting, such as the old FA 100mm F2.8, F 100mm F2.8, and FA* 200mm F4. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

10-08-2012, 07:03 AM	#11
bwDraco Veteran Member Join Date: Jul 2010 Location: New York Photos: Albums Posts: 1,071	Originally posted by DNT ahhh ok that makes sense. (had to google focus throw hehehe) Cheers Adam! For reference, the focus ring travel of the Pentax D FA 50mm macro lens is about 285 degrees, or more than three-quarters of a full rotation. This is entirely normal. -----Off topic----- Originally posted by DNT 100mm f/2.8L from Canon on a 300D emphasis added Wow, that's a really old camera body to be using an L lens on... -----End off topic----- --DragonLord Last edited by bwDraco; 10-08-2012 at 07:09 AM.

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10-07-2012, 11:42 PM	#3
DNT Junior Member Join Date: Sep 2012 Location: Brisbane Photos: Albums Posts: 43 Original Poster	ahhh ok that makes sense. (had to google focus throw hehehe) Cheers Adam!

10-07-2012, 11:42 PM	#4
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	The DA 35 Macro Ltd is one of my favorite lenses, and the only AF macro lens I use. Once, I was taking a photo of the speaker at a presentation, and made the dumb mistake of pointing the center focus point straight at the empty whiteboard. The poor lens chugged itself all the way through to the extreme close up range, and then all the way back to infinity. At this point, the lens became the center of attention for the entire audience, and the speaker. So to focus quickly with that lens at normal distances, choose a contrasty target, and pre-focus manually with the quick shift. MF is best for macro shots anyway.

10-07-2012, 11:44 PM	#5
elliott Inactive Account Join Date: Dec 2008 Location: North Carolina Photos: Albums Posts: 1,720	Also, the longer the focal length, the further it has to travel to get the same magnification. You can obtain 1:1 macro with a normal 28mm lens on 25mm of extension tubes, but a normal 50mm would require 43mm of extension tubes to obtain the same magnification. So the 100mm is going to be traveling much further than the 35mm, which might make the 100mm slower to focus.

10-07-2012, 11:45 PM	#6
maxfield_photo Site Supporter Join Date: Mar 2011 Location: Cincinnati, OH Posts: 1,216	With the limiter engaged, my FA 100 macro is blisteringly fast, it's really from 2 feet to MFD that takes the longest.

10-07-2012, 11:51 PM	#7
DNT Junior Member Join Date: Sep 2012 Location: Brisbane Photos: Albums Posts: 43 Original Poster	Originally posted by lytrytyr So to focus quickly with that lens at normal distances, choose a contrasty target, and pre-focus manually with the quick shift. MF is best for macro shots anyway. Yeah I quickly discovered that at an outing with my wife's cousin when shooting dolphins @ Seaworld on a cloudy day Seaworld Only have the 100mm macro and the 18 - 55mm kit lens hence the macro usage. Never tweaked settings and shot so fast in my life till that day hahaha But yes, macro work I generally use MF over AF.

10-07-2012, 11:59 PM	#8
DNT Junior Member Join Date: Sep 2012 Location: Brisbane Photos: Albums Posts: 43 Original Poster	thanks for all the replies people!

10-08-2012, 03:59 AM	#9
Jean Poitiers Pentaxian Join Date: Apr 2011 Location: Lost in translation ... Photos: Gallery \| Albums Posts: 18,076	My D FA 100 WR is not that slow IMHO but will hunt under certain conditions ... I use a lot of MF and will use AF (approx. focus preset first) on moving small things like bees, that tend not to be stationary as opposed to the flower itself. *Salut, J*

10-08-2012, 04:37 AM	#10
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,888	Also note that when focusing closed especially the light falls off due to image enlargement and this may also cause a reduction onAF performance

10-09-2012, 11:13 AM	#12
KHatfull Senior Member Join Date: Aug 2012 Posts: 98	Originally posted by Adam Macro lenses are slow to AF simply because their focusing throw is really long due to fact that the optics need to be moved further in order to focus on stuff that's close to you. Some macro lenses have AF limiters to prevent hunting, such as the old FA 100mm F2.8, F 100mm F2.8, and FA* 200mm F4. And with the limiter on it's really fast. I just got mine a couple weeks ago. While it's not as fast as an IF lens the limiter sure makes a difference for non-macro subjects. One of my complaints with the Tamron 90s, and one of the reasons I ultimately decided to sell the Tamron and keep the FA100 (the other two being the heavier weight of the FA100 and the "Clamp" swtich).