AF vs. MF for telephoto Macro

I am about to buy the Canon 100 mm macro lens to use with my D-Rebel in an Ike housing. I am curious to know how many of you who use similar lenses shoot mainly, or exclusively, with autofocus versus mostly with manual focus. I've heard varied opions, from "MF is worthless because you can't see well enough through the viewfinder to know if the subject is in focus" to "I use MF exlusively." I'd appreciate any insight you can offer.

Mark

Both are accurate statements at times. Seems to depend on the conditions. In high vis water, like the Caymans, I used a lot of autofocus with the Nikkor 105, very succesfully. However, in my local waters it seems like the autofocus is erratic at best, even with two q40 focus lights. Manual focus seems easier through a viewfinder, at least for my tired eyes, as I am looking at the subject itself, not an LCD representation a few inches away.

My $.02, YMMV

This is a question I have tried working on for my last few dive trips. I currently shoot a housed 10D and 100mm USM but have also been shooting the older 100mm macro lens with film cameras for the years leading up to my digital jump. Focusing accuracy depends on the camera and conditions for the most part but have found my greatest success shooting in AF. When I shoot MF, I tend to find my focus point and then move the camera forward until the subject hits critical focus. This is great if your subject is stationary but tough if your subject is mobile and aware of your movement. I have also found that DOF is greater(or seems to be) with digital which makes AF that much more effective since more of your subject is in focus. Because of the 1.6x crop factor, your 100mm shoots at a greater distance which ultimately increases your DOF. Good luck with your efforts.

I use AF exclusively for underwater macro work. It doesn't mean it's the best solution for all circumstances.

1) The camera does a better job than I do. I don't see that well through a mask and housing to obtain a consistent solid focus.

2) The 60mm focuses with great ease. The 105mm is quite difficult at times, but you can work it somewhat to minimize the hunting. If AF isn't going to cut it, I'll try continuous instead of single servo mode, it doesn't require a focus lock. I can also switch to manual focus on my housing and just move the camera.

3) It is but a single moment that you achieve focus. At that moment, any movement of you hand held camera will reduce focus.

I shoot MF almost exclusively on land when shooting from a tripod. Which is why I wasted dives because I forget to switch the lens back to AF.

"Because of the 1.6x crop factor, your 100mm shoots at a greater distance which ultimately increases your DOF. "

Nope. Imagine the area of a 35mm equivent photo, now imagine cropping it by 1.6x (cut out the photo with scissors, then blow it back up to full size) and then you have the 1.6x crop factor of digital. That's all that is happening. I've heard all sorts of claims about the crop factor that are completely wrong. "I get additional magnification with the crop factor." "All my lenses are longer, my 300mm is now a 450mm" None of this is true. All it does is crop your photos by the crop factor.

This should have no more effect on DOF than you cropping your photos in photoshop.

What I meant by the 1.6x crop facter increasing DOF is that it allows you to shoot at a greater distance from the subject which ultimately increases your DOF and ultimately increases your chance of getting your subject in focus. If you increase your distance between lens and subject with these macro lenes, you increase your DOF. Consequently, the closer to your subject, the shallower your DOF. I did not mean to mislead by my prior entry.

FWIW, I get my best results shooting pygmy seahorses by setting my 10D to AI Servo, if you do your job and keep the focus point on the animal, the camera will track him for you....if the camera can track a peregrine falcon in flight, in can track a pygmy seahorse!

Stu

I haven't tried 1:1 in the water, but after a couple of hours on the grass, I found the best way is to fix the focus on the lens and move the camera.

I started of using AF, but after numerous frustrating dives and missed opportunities I switched to MF. I especially got tired of all the zoom-zoom-zoom leading to missed shots due to AF inability to lock focus during night dives. I found that the modeling light did not really help in most cases. I am now only doing MF which in MHO is much better and easier. I do not find focusing with the Dreb hard, but maybe that is because I am a dinosaur that lived in the times before AF... Anyway, I find locking the focus and moving camera, just like Herb suggested works really well. I use 50mm macro 1:2 and same with lifesize converter for 1:1. 1:1 IS hard to shoot, both above and under water because the DOF is miniscule, and any litte shake of hand throws the focus off, but I would't say it's harder UW.

I've used the manual focus and move method also, on the few occasions I've used Macro underwater. My macro has slow AF (Tamron 90mm) and I've been thinking I'd have more luck with AF with the Canon 100mm USM, so I figure it is lens dependent to some extent whether AF or MF works best. If I do get the 100mm USM I'll let you know if my theory was correct or if I just wasted several hundered dollars!