A question came up in a recent comment about how use CiF (catch-in-focus, aka focus-trapping) for unattended shooting and while I was thinking up a response, it occurred to me that it might be good to broaden the audience a bit with a post here and possible expansion at some point to a full article.
Note: This tutorial assumes one already knows how to set up and and use CiF with the desired lenses on one's camera. Troubleshooting for CiF in general is probably a bit out of scope.
How it works:
In short, when the camera is using CiF in continuous shooting mode, exposures will be made at the set rate whenever in-focus is detected for as long as the shutter button is depressed. When using a wired remote or intervalometer, one can leave the shutter depressed for extended periods of time in a manner similar to doing a timed exposure in B mode. An intervalometer provides the advantage of being able to set a firm limit on how long the shutter press will last.
Things to be aware of:- There are better ways of doing unattended "event driven" shooting than using CiF in this way, but those require specialized equipment and/or software.
- There may be many trapped exposures depending on what you are photographing. For example a hummingbird feeder may be quite active.
- There may be very few trapped exposures on things like a game trail
- The camera will be ON for the entire session. It might be good to limit sessions to a reasonable time span either by setting a timer for yourself or using an intervalometer.
Preparation and Gear:- Your camera should support the following:
- CiF (duh!)
- External power (wall outlet or battery pack)
- Wired remote shutter release
- Heat and power are potential issues. You will want to configure:
- Rear display off
- Top display light off
- Instant review off
- Camera and other kit (flash and such) may need protection from weather, people, and animals.
- You will need a sturdy tripod or other camera support.
- You will need a wired remote capable of locking the release button in the down position or timing the duration of "button press". I suggest a remote with built-in intervalometer to do the latter. (Yes, I did mention that a third time.)
- You will need a battery pack or AC adapter capable of powering the camera for the full session.
- You will need memory cards of sufficient capacity
- You may need some way to manage heat or cold
Considerations when doing setup, testing, and dry runs:- CiF is limited to the center point...sorry.
- CiF requires light and works better in the bright than in the dim.
- Prefocus point and exposure settings are important
- There might be a benefit to taping down the lens focus ring.
- The camera will not go to sleep as long as the shutter is pressed, but may do so if using an intervalometer. Many models will send a half-press before the full press to wake up the camera, but not all.
- It may possible to use the IR remote (depends on brand/model) or WiFi tethering, but with the caution of that running those features increases the heat and power load on the camera.
- CiF may be less precise with a stopped-down manual aperture lens (e.g. M42). DOF applies to the focus trap as well as to the focus screen
- If the subject lingers, there might be a lot of near duplicate shots
- Consideration should be given to which of H, M, or L continuous rate settings suits your subject. The L setting may be best for many (most?) subjects.
- Flash may be your friend if fast recharge is in the mix. Remember heat and power implications associated for the flash. They shut off when overworked or when the battery dies.
- Framing wide with a longer than "normal" lens (allows greater distance to the subject) might be to your advantage as might shooting other than wide open. One can use a wide angle up close, but trapping may be more sensitive than is useful. It is best to test this out ahead of time.
- With fast subjects (e.g. birds or small mammals) they may move a fair distance after being focus-trapped and before the shutter fires.
- If using an intervalometer, be creative with its settings, say multiple short sessions with short interval between for a set number of repetitions.
- If you don't have time to thoroughly test your setup up, your likelihood of disappointment will be high.
Basic Example: ...in progress...
I think that about does it.
Steve
Last edited by stevebrot; 12-19-2020 at 02:41 AM.
Reason: details...details...details...