Back button focus and shutter speed: Hi, am posting an image I took of my granddaughter. Had the d750 set on BBF. AF-C, and tried 9, 11, S and so on. Every time I keep holding down the...

anneabc

Hi, am posting an image I took of my granddaughter. Had the d750 set on BBF. AF-C, and tried 9, 11, S and so on. Every time I keep holding down the back button AND RECOMPOSE, I miss the focus. You can see that in the image. I had the speed, unfortunately, on 1/200. Was shooting shutter priority. Do I keep holding the BBF button and recompose, or do I lift my finger to lock in the shot? Thanks for the help.

anneabc

Sorry, it was 1/250/sec, not 1/200/sec.

DaveO Loc: Northeast CT

Keep your finger pressed on the button and take your shot. If you release it, it goes to AF-S and locks focus at the distance you released at, which is fine if your subject stopped before you released the button. Many members have enjoyed the many benefits of this book by Steve Perry:

http://backcountrygallery.com/secrets-nikon-autofocus-system/

Check the site out and the many free tips on it.

Peterff Loc: O'er The Hills and Far Away, in Themyscira.

anneabc wrote:

Hi, am posting an image I took of my granddaughter. Had the d750 set on BBF. AF-C, and tried 9, 11, S and so on. Every time I keep holding down the back button AND RECOMPOSE, I miss the focus. You can see that in the image. I had the speed, unfortunately, on 1/200. Was shooting shutter priority. Do I keep holding the BBF button and recompose, or do I lift my finger to lock in the shot? Thanks for the help.

BBF is great, but you need to learn how to use it. Can you drive a stick shift? If not, BBF may not be for you, unless you learn how to do so.

anneabc

Peterff, that's what I did. Kept my finger on the bbf button the whole time. The focus kept changing and would not stay on her.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

anneabc wrote:

Hi, am posting an image I took of my granddaughter. Had the d750 set on BBF. AF-C, and tried 9, 11, S and so on. Every time I keep holding down the back button AND RECOMPOSE, I miss the focus. You can see that in the image. I had the speed, unfortunately, on 1/200. Was shooting shutter priority. Do I keep holding the BBF button and recompose, or do I lift my finger to lock in the shot? Thanks for the help.

The camera will only focus when the back button is pressed. But it will focus continuously if you keep the button pressed. If you want it to stop focusing so you can recompose, then you press it to focus, release to recompose. The settings for Dynamic Focus of S, 9, 11, etc are just telling you how many focus points are active around the focus point you have selected to focus with. Typically the camera will function best at 9 with subjects like you are trying to get.

If you want, you can move the selected focus point up, down, left or right to minimize the need to focus and recompose, which is what I would suggest.

Resqu2 Loc: SW Va

When doing shots like my dogs running around I set the focus to the center point only. That way the camera only focuses on that point and I know where to aim when following them. I keep my bbf pushed the entire time. Try it and see if it helps.

Feiertag Loc: British Columbia, Canada

Take your finger off the BBF once you are in focus then recompose. A thing you should be aware of is that pressing the shutter button, half way, you lock the exposure. Keep you finger on the shutter button, especially if you use spot exposure. Cheers.

Psergel Loc: New Mexico

anneabc wrote:

Hi, am posting an image I took of my granddaughter. Had the d750 set on BBF. AF-C, and tried 9, 11, S and so on. Every time I keep holding down the back button AND RECOMPOSE, I miss the focus. You can see that in the image. I had the speed, unfortunately, on 1/200. Was shooting shutter priority. Do I keep holding the BBF button and recompose, or do I lift my finger to lock in the shot? Thanks for the help.

If I understand the question........here is a somewhat simplified answer.

You are in continuous AF and using BBF. AND
If you are manually selecting an AF point.
After you focus on the subject you need to take your finger off of the button before you recompose. That way the focus stays where you put it, on the subject.
If you are in continuous AF, holding down the focus button and move the camera, the focus will change to the nearest object the selected AF point sees.
If, on the other hand, you are tracking a moving subject you need to keep the focus button depressed.

You are in continuous AF and using BBF. AND
You are letting the camera auto select an AF point.
You can leave you finger on the focus button and recompose all you want as long as your intended subject remains the object nearest the camera since the AF point will change as needed to to stay on your subject.
Auto AF point select will always try to focus on the nearest object.

Boy.....I hope this makes some sense.

Rab-Eye Loc: Indiana

I'll simplify: you're using continuous AF, so when you move the camera with the back focus button down, it continuously focuses, but the focus point is no longer on your subject.

Psergel Loc: New Mexico

Rab-Eye wrote:

I'll simplify: you're using continuous AF, so when you move the camera with the back focus button down, it continuously focuses, but the focus point is no longer on your subject.

Unless you are letting the camera select the AF point and your subject in the closest object to the camera.

DaveO Loc: Northeast CT

Rab-Eye wrote:

I'll simplify: you're using continuous AF, so when you move the camera with the back focus button down, it continuously focuses, but the focus point is no longer on your subject.

As I move the camera, I keep a single focus point on my subject. If my subject stops, I can let my finger off, recompose and shoot if I desire. Otherwise, why would AF-C be used? Why would I use BBF?

ronichas Loc: Long Island

Have you tried group focus. Nikon d750 does have this. I use it most of the time.

**When compared to the regular Single-Point AF Mode, Group-area AF activates five focus points to track subjects. This focus mode is great for initial focus acquisition and tracking of subjects when compared to a Single-Point or Dynamic AF, especially when dealing with smaller birds that fly erratically and can be really hard to focus on and track. In such situations, the Group-area AF mode might give better results than Dynamic AF, showing better accuracy and consistency from shot to shot.**

Mary Kate Loc: NYC

Peterff wrote:

BBF is great, but you need to learn how to use it. Can you drive a stick shift? If not, BBF may not be for you, unless you learn how to do so.

Well, that solves that problem.

DaveO Loc: Northeast CT

ronichas wrote:

Have you tried group focus. Nikon d750 does have t... (show quote)

When non-dynamic group-area is used, the points act more like one large point and do not provide the accuracy of dynamic points. There is no switching from point to point for the most accurate. This is explained in my reference in the third post of this thread.