Focus Trap??? Which cameras can I use focus trap with?

haring · April 13, 2011

- Is there a list of DSLRs I can use "focus trap" with? Canon, Nikon, Sony, Leica, Mamiya, Hasselblad, etc...?
- Can I use with any lens on cameras which capable of the focus trap feature?

I have a few old manual lenses and it would be great to focus on moving subjects...

Thanks a lot!

hgernhardtjr · April 13, 2011

My understanding of what you want to do is the following: on some SLR cameras, when using a manual focus lens you can set the camera to auto focus; then hold the shutter button down and adjust the focus. Once the camera "captures" focus on an object that comes into view, it will automatically take the photo.

Is this what you mean?

If so, I have not used that rarely-available feature for many years ... although I know some of the expensive "pro" cameras will do it. Function 16 in most (if not all) dSLR Series 1 EOS cameras can be used, like if you want to take photos of, say, hummers ... especially if it can trigger burst mode so you can get a great shot. Beyond that, I have not even thought about it in a number of years. Perhaps someone else can be of assistance and come up with a list.

I am pretty sure, though, it will not be inherently available on non-"pro" cameras ... but when it comes to computers and cameras, never say never and never say always, things change so fast and so many things are deeply hidden in the software/firmware/hardware.

ziggy53 · April 13, 2011

Many cameras have an option to allow image capture only after focus acquisition or to allow image capture regardless of focus, and I believe that the default is usually the former. If you pre-focus and allow the subject to enter the scene with the former setting I believe those cameras will "trap" at the point of focus detection, but it may not be focussed on the part of the subject you desire. This makes the feature of somewhat limited usefulness.

On my Canon bodies I can use old Pentax and Nikon lenses with a "chipped" adapter and subsequent focus confirmation. Unfortunately auto-aperture is not possible and so the lens must be used wide open for best focus confirmation speed. If the lens is not sharp wide open or if you need to stop the lens down for DOF control or any other reason, this negates much of the usefulness of the focus confirmation.

I did have rather good success using an old Vivitar 500mm, f6.3 prime (Pentax/M42 screw mount) and focus confirmation in the following series (exposure and processing could have been better):

I do think that manual lenses on a modern dSLR for any sort of sports/action would be more of a lesson in frustration, so I cannot recommend it for that application. If you want to try it, Canon bodies work nicely just because of the wide variety of lenses and adapters available due to the short flange-focus distance of Canon bodies and the availability of cheap "chipped" adapters.

Dan7312 · April 13, 2011

Isn't this Eisnestaedt photo an example of using a focus trap? He focused on the chair and waited for the waiter to skate by...

http://www.gallerym.com/work.cfm?ID=68

ziggy53 wrote: »

Many cameras have an option to allow image capture only after focus acquisition or to allow image capture regardless of focus,

Carpy · April 13, 2011

Yo Haring

Here's a few words from my Nikon D80 Manual

AF-C Continuous-servo AF

For moving subjects. Camera focuses continuously while shutter-release
button is pressed halfway. Photographs can be taken even when in-focus
indicator is not displayed

Is this the sort of thing you are looking for ?

Carpy

ziggy53 · April 13, 2011

Carpy wrote: »

Yo Haring

Here's a few words from my Nikon D80 Manual

AF-C Continuous-servo AF

For moving subjects. Camera focuses continuously while shutter-release
button is pressed halfway. Photographs can be taken even when in-focus
indicator is not displayed

Is this the sort of thing you are looking for ?

Carpy

Focus trap (more often called "Trap Focus") is where you preset the focal point of the lens and then wait for the subject to traverse the plane of prime focus. I believe that the OP is interested in a camera that automates this process and only allows tripping the shutter when the cameras AF mechanism detects focus acquisition.

http://en.wikipedia.org/wiki/Autofocus#Trap_focus

AF-C/Continuous-servo AF/AI-Servo focus is something that only applies to AF cameras with AF lenses and which uses the camera to predict subject motion to provide more accurate AF of moving subjects.

ziggy53 · April 13, 2011

Dan7312 wrote: »

Isn't this Eisnestaedt photo an example of using a focus trap? He focused on the chair and waited for the waiter to skate by...

http://www.gallerym.com/work.cfm?ID=68

I believe that you could discuss focus trap as a method and technique of manual focus photography, but I think that the OP is inquiring which cameras have the AF automation technology. I could be wrong?

Carpy · April 13, 2011

Found this with regard to nikon

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9479603

Maybe

Carpy

ziggy53 · April 13, 2011

Carpy wrote: »

Found this with regard to nikon

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9479603

Maybe

Carpy

Yes, that is a description of the setup and use on some Nikon cameras.

Like I said before, sometimes the camera will trip on the wrong part of the subject so it's not a perfect method for all subjects and all situations. (In fact in most circumstances it works rather poorly so I rarely use it.)

NeilL · April 13, 2011

Dan7312 wrote: »

Isn't this Eisnestaedt photo an example of using a focus trap? He focused on the chair and waited for the waiter to skate by...

http://www.gallerym.com/work.cfm?ID=68

tnx 4 link

Neil

www.SGphoto.us · April 16, 2011

that link is for doing focus trap with an autofocus lens, seems pretty pointless in my opinion. just use af-c or af-s, thats what that technology is for, however, now days focus trap would be pretty useful while using a manual focus lens, i just don't think you can do that though on a Nikon. I have tried, i couldnt figure it out. That would be highly useful to me, iven if it does have its limits.

haring · April 17, 2011

yes, is is useful with MF lenses.

Sand · April 17, 2011

Would this be helpful for getting a photo of a moving object and a fixed object when both are the same distance away (i.e. a race car crossing the finish line)?

Focus Trap??? Which cameras can I use focus trap with?

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