MLU - is it really that critical on exposures longer then say, a minute?

[hoffy]

Howdy,

OK, second question about longer exposures in a couple of days - I feel so dirty

The question is as simple as that - is MLU really that critical when doing longer nightime exposures, using longer then 1 minute? Wouldn't the shake on such an exposure not really bother the negative?

Now, there is a reason behind this question. I want to be able to shoot a shot using a pneumatic release from a distance away and I want to be able to hear if I accidentally let go of the bulb!! Anyhow, just a thought.

Cheers

[Vaughn]

If you have some fine bright light sources it might (stars, distant street lights, etc). Perhaps a small sandbag draped over the top of the camera might reduce the duration of any shake due to the mirror.

[ath]

With exposures that long MLU is totally unimportant. Important is a sturdy tripod to avoid picking up blur due to wind or creeping fixtures.
MLU is said to have its maximum benefit around 1/8 s or so. With longer times an increasing part of the exposure takes place when the vibration due to mirror slap has relaxed.

[hoffy]

That's what I kind of thought, but haven't really checked. Typically I use MLU when shooting on the tripod, regardless of the camera (as long as it has that feature of course).

Now, I wish I had spent a bit more money and bought a release with a needle valve in it....sigh

[bsdunek]

Or, just cover the lens with your hat, open the shutter, then use your hat as the shutter. Just don't touch the camera during the actual exposure. Wind (or earthquakes), as Andreas mentioned, is a different story.

[DREW WILEY]

What is your camera? A popular camera with amateur astrophotographers is the Pentax 6x7, and you're pretty much doomed without lockup. That big mirror hits hard. A lot also depends on the actual lens and tripod mounting system you are using and whether or not harmonic vibrations are set
up synchronously with the shutter itself. It's a bit involved if you're get serious about image quality.
The most knowledgable guy I know on this subject is Francis Sakamoto, a former Pentax and Celestron dealer, but still an enthusiastic telephoto photographer himself. Check his website.

[hoffy]

The camera is a Bronica SQAi.

[Poisson Du Jour]

As you are planning a long night-time exposure, there will be little risk of introduced vibration during the actual exposure. Problems I have experienced with star trail photography are numerous and unique e.g. animals wandering about and colliding with the tripod, spiders seemingly finding their appearance attractive and making the front of the lens a looking-glass, condensation on the lens, wind and then clouds. You really do need the moon and stars to be aligned 'just-so', and once that is done, worry about MLU...

OK...The primary purpose of mirror lockup is to reduce (but not entirely eliminate) vibration caused by the abrubt movement of the mirror swinging up, then the shutter opening and closing and the mirror returning to position; that is to say it isn't just the mirror, but also the shutter that plays into the equation, and big focal plane shutters cause as much hue and cry as the equally big mirrors. If the camera you use has a reputation for introduced vibration from mirror movement (e.g. Pentax 6x7 / 67, of which chapter and verse has been written and repeated ad nauseum), it is a priority for slow speeds. There are many additional tricks to apply additional to MLU to prevent vibration, which chiefly will be noticeable below 1/60th.

[O|||||||O]

Well, the question has been answered, but now I'm wondering about this:

Now, there is a reason behind this question. I want to be able to shoot a shot using a pneumatic release from a distance away and I want to be able to hear if I accidentally let go of the bulb!! Anyhow, just a thought.

I don't think MLU would make any difference one way or the other for this. It would sound exactly the same either way if you accidentally let go of the bulb. Only the beginning of the exposure would sound different.

[hoffy]

Maybe I should explain - with MLU on the SQAi, the mirror gets locked up when you advance the film and only gets reset when you re-advance the film. So, when you do an exposure, all that you hear when you take the shot is the faintish click of the shutter opening and then closing. If you are far enough away from the camera or there is other ambient noise, you hear nothing.....(I know from experience!!!)