Nalu Loc: Southern Arizona

Really! Why then does the active sensor show up sometimes, and sometimes not.

CHG_CANON Loc: the Windy City

This comment (mkahn) caused me to pull up work from the Cleveland airshow in DPP and ask to see the AF points. The point is red (displayed) in the quick view of the first 50ish in the scroll caused me to decided the author of this post is mistaken ...

I will focus and recompose, a purposeful action, with BFF. Here, AF is not active and a point will not show in DPP. But, when the thumb is holding the BFF (always set to AI Servo for me) and my index releases the shutter, the active AF point appears in the resulting image.

amfoto1 Loc: San Jose, Calif. USA

It would be helpful to know what gear you're using.... I see you were shopping for a Canon 5D Mark IV earlier and asking questions about a seller... but I don't know if that's the camera you're using. The lens(es) you have are important, too. A lot of the responses so far have been Nikon-centric, using terminology that's specific to that brand. I'll describe my methods in Canon terms, in case that's what you're using.

I use BBF for all sorts of sports/action photography.

With Canon cameras, for fastest focusing and moving subjects it's important to use AI Servo mode (not One Shot and definitely not AI Focus). And USM lenses are generally the fastest focusing and can be necessary for moving subjects.

Cameras vary in their AF performance. 5DIV should be pretty capable. I use 7D Mark II, which have a discrete chip running the AF, like 1D-series cameras do. Most other Canon use a single processor handling both the images and the AF. In addition, the 1D-series and 7D-series have dual processors to support fast frame rates (do do 5Ds/5Ds-R, though in those cases it's to handle those cameras' extremely large image files at a slower frame rate).

Most of the time I use a single focus point and simply set the frame rate to the camera's fastest possible. When there's plenty of light I also generally stop down a little to increase depth of field, which can sometimes "cover" minor focus errors. Telephotos I use are Canon EF 70-200mm f/4L IS USM, 70-200mm f/2.8L IS USM, 100-400mm L II IS USM, EF 300mm f/4L IS USM, EF 300mm f/2.8L IS USM and 500mm f/4L IS USM. I leave IS enabled (Mode 1), because on Canon cameras it helps stabilize the image in the viewfinder, which can be helpful when tracking moving subjects with long telephotos. Also, I think Canon IS helps AF perform better (I know Nikon users feel the opposite is true with VR... that it slows focus a bit).

Depending upon which camera you have, you also might be able to set focus versus shutter release priority. I set mine for max possible focus priority, even if it sometimes slows frame rate or causes a slight delay in shutter release... Out of focus images do me no good at all, hence that priority setting.

With any moving subject, you're going to miss focus sometimes. The faster, more sudden and/or erratic the movement, the harder it will be to achieve focus in a high percentage of shots. You can improve your odds if you can pre-focus close to where you expect the subject will appear. With a breaching fish like you describe, I might use my cameras' "Small Zone" or "Expansion Point" focus patterns, instead of Single Point. The latter is more consistently accurate when it's possible to use it... but with a subject like the marlin it might be better to have multiple AF points activated, even if it means a bit lower "hit" rate.

I took 5000 images at an equestrian event last Sunday... am editing them now. So far I've seen maybe two dozen where I missed focus. And I'd wager most of those were my fault, not the camera or lens'... sometimes I press the wrong button or my hand cramps up after a long day shooting!

Grimmster Loc: New Jersey

Try Steve Perrys www.backcountrygallery.com There is a great write up on Nikons AF sytsem.

Nalu Loc: Southern Arizona

So, tell me if I am mistaken. When the BBF is properly depressed, the AF indicator will light up in the viewer, lower right hand corner on most Canons, at least my 5DIV and in DPP4. With the AF point not showing up in DPP4, the probable the explanation is that the operator, me, is not holding down the BBF sufficiently, which can happen if you get distracted tracking a subject. For me, one reason to use shutter button. At least you are only having to concentrate on one finger. Simple things for simple minds! In my mind, the author's situation, shooting game fish, does not mandate using BBF, simply a matter of preference. Either focusing method will suffice as long as you are in AI Servo.

Appreciate your comment here. Helpful to me.

CHG_CANON Loc: the Windy City

Honestly, I'm too busy worrying about composition and / or keeping my typically single point located on a moving subject to worry about a confirmation circle in the lower corner of the frame ... My vII lens are near instantaneous as well as I've adjusted the AF settings to shoot first, not delay and wait for focus confirmation. BBF isn't for everyone. For me coupled with AI Servo, when not using BBF, it's awkward to use my cameras otherwise.

speters Loc: Grangeville/Idaho

BBF is best, especially for fast moving subject (no half press to fuss with, just the easiest way to keep the focus on whatever critters)!!

ShaKato Loc: Florida

I too agree that BBF is the best way to shoot. I use it when photographing jumping dolphin and I've never been disappointed.

Tracy B. Loc: Indiana

I believe you can have your camera set up for Al Servo, but by just touching the back button down once will automatically switch it to One Shot.

Nalu Loc: Southern Arizona

Exactly, and with me, sometimes I don't notice that the AF is not on.

Resqu2 Loc: SW Va

Not near the same situation but I have two small, fast pups and a Canon 6D which is know for not being a great action camera and could never get great shots of them running and jumping till I learned about BBF. Now it seems like I can’t miss a shot. Really changed how I feel about the 6D.

Paris Hanson

Once I learned BBF I haven't used any other method, use it for portraits as well, very easy to learn you can use it for any kind of photography, makes it easier to expose for the sky and then recompose on subject, try it and see if it works for you, I will never go back to shutter halfway down

saltwaterphil Loc: va beach, va

Sorry I'm late responding.....Thanks for the feedback