Long exposures and motion blur (tripod vibration)

[Infidel]

I have a question related to exposure duration and motion blur. I would think that once the exposure duration is beyond 1 second or so (probably even shorter) any motion blur due to tripod vibration would be more or less equivalent, on up to 30 second exposures. In other words, I don't think cutting exposure time from 30 seconds down to 5 seconds would really make a difference, assuming the vibration is of the same amplitude and is present during the entire exposure in both cases. In fact, during a 30 second exposure, a minor, momentary jolt to the camera (e.g., mirror slap) would probably influence the final photograph less than the same jolt during a 5 second exposure, because in the longer exposure the duration of the jolt-induced movement would affect a comparatively smaller proportion of the total light used to make the exposure. Does this make any sense? If anyone can offer any further insight, please feel free to discuss.

 

[Derrel]

Duration and amplitude of the offending vibration, as a percentage of the total exposure time, seems to be what determines how detrimental mirror slap or camera vibration/movement ends up being.

Short exposures in the 1/4 to 1/30 second range seem to me to be the most serious problem exposures, in terms of mirror slap and or tripod vibration problems. In say a 1/4 second exposure, the slap from the mirror and the opening of the shutter together can cause vibration that lasts almost 50% of the total exposure time!!! With a faster shutter speed, like say 1/15 second, the doggone camera's mirror slap and shutter opening vibrations are present throughout the ENTIRE duration of the exposure!!!

Longer speeds, like say 1 second, will have perhaps 1/8 second with vibration present, then the vibrations dampen out, and the exposure is made with let's call it a "mostly rock-steady camera".

Of course, this is all about mirror slap and first-curtain vibration...there can also be some camera movement caused by a finger pressing the shutter release button, if you are not using a remote release, which is a huge benefit as far as eliminating one major source of vibration--your own trigger finger and hand and arm!!!

Carrying this farther, in long time exposures at night, which I often used to do, with exposures in the 45 to 120 second range with ISO 64 slide film, vibration was not much of an issue, since even a kick to the tripod legs was like 1/256 of the total exposure time...or less!

 

[Infidel]

Thanks Derrel, that clarifies my thinking on this issue. It's particularly useful to know the most troublesome shutter speeds, as you have described. Incidentally this leads to what, at least initially, is a counter intuitive conclusion, which is that motion blur can be worse with shorter exposures, given a certain range (1/4-1/30s, as you suggest). I know the use of VR-type technologies is discouraged when using a tripod, but would it nonetheless be of some benefit under these conditions?

My camera (D40) does not offer mirror lock up (it's in the menu, but not available to adjust), nor do I have a remote. That said, I do always use the self timer (2 sec) when making longish tripod-mounted exposures. Fifteen or so years ago when I was experimenting with my 35mm SLR, I had a mechanical cable release, and these days the wireless remotes are fairly inexpensive, so I think I will purchase one in the near future...if anything, for the sake of convenience (and to have a new toy).

 

[iskoos]

Never thought of that before to be honest. But when I read your question and Derrel's answer, it made sense...

 

[Derrel]

Nikon's earliest incarnations of VR are not good on tripods: tripods can cause vibration correction "loops", where the VR system tries to stabilize an already-stabilized lens, and the whole result is a terrible,terrible mess!

VR and IS and OS and Steady-SHot are all a bit different. VR and IS and not the same,exact systems, and VR has multiple incarnations, of varying sophistication. One of the counter-intuitive things I discovered was with the earliest Nikon VR lens, the 80-400 VR; it has an ACTIVE VR mode,designed to be used from moving platforms, like boats or cars or aircraft. When using the camera at very sloooooow hand-held speeds, like 1/3 to 1/8 second, I have found that using ACTIVE VR mode works better than NORMAL mode. Why? At speeds like 1/3 to 1/8 second, the human body is a pretty shaky platform...and ACTIVE Mode seems to be geared toward correcting very large vibration problems, while NORMAL mode is geared toward lower-amplitude tremors, at higher frequencies, or so I suspect.

Using the self-timer and/or a remote release are both good ways to alleviate tremors caused by the human hand and arm releasing the shutter via the button on the camera.

 

[Garbz]

As mentioned you don't want to use VR on a tripod. The lens manuals specifically say it should be off when using a tripod.

The solution to mirror slap is the exposure delay mode. This is present on most Nikon cameras and it's usually burried in the function menu somewhere. It'll raise the mirror, wait a second, then take the picture to eliminate the blur caused by the mirror movement.

Other than that what you say makes perfect sense. The mirror slap becomes completely immaterial past about 1/4 to 1/2 second exposures because the part of the image that is being shaken is simply not enough to expose the image. The post here: Mirror Lock Up - photo.net would indicate that the majority of the vibration occurs within 1/15th of the exposure, making 1/15th the worst shutter speed.

That said long exposures open you to other issues such as bumping the tripod, or passing cars.

 

[michaelleggero]

i know it's a plug for my own article, but if you go to my site and check my blog i've got an article about using live view and it addresses the mirror lockup in there a bit... the article is more about using the live view mode but most people dont' realize that live view is a mirror lockup

Mike

http://www.michaelleggero.com

 

[Parallax]

As an alternative, using the D300 and lacking a remote shutter release, I have used the mirror lock up itself to take these kinds of delayed tripod shots and avoid mirror and operator induced vibrations.
Just set to mirror lockup on the dial and press the release to lock it up-- wait 30 seconds and it will take the picture on its own. By then all the vibrations are gone.