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

hoffy · Feb 16, 2012

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 · Feb 16, 2012

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 · Feb 16, 2012

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 · Feb 16, 2012

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 · Feb 16, 2012

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 · Feb 16, 2012

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 · Feb 16, 2012

The camera is a Bronica SQAi.

Poisson Du Jour · Feb 16, 2012

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 · Feb 16, 2012

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

hoffy said:
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 · Feb 16, 2012

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!!!)

Poisson Du Jour · Feb 16, 2012

Where will you be in relation to the camera, in front, behind, on top or where?? If in front, you should be able to see the aperture blades close down which is good enough an indicator/confirmation that the shutter has fired?

Wade D · Feb 19, 2012

If you are far enough away not to hear the shutter opening and closing then that could be problematic with a standard bulb.
An idea would be to adapt the bulb from a blood pressure cuff for the purpose. The bulb can be locked after squeezing via the screw valve that is part of it. When the time period is done then open the valve to complete the exposure.
This, of course, depends on an air tight connection to all components. Otherwise leak down will cause a failure to remain open for the indicated exposure.
The mirror slap issue with long exposures is negligible. During the last full moon I made landscape exposures using a SRT 101b with and without MLU. There was no noticeable difference. All negatives were sharp with an 8X loupe.

hoffy · Feb 19, 2012

Cheers. I went out on Friday night to give it a try...but:

Before I went out, I gave things a try - Idiot....the mirror is always reset by the winding action, not the photo taking, so when the bulb is released all you get is the click....face palm...
It was too windy when I got to my location (about 50 metres walk)...so there was no point.

As mentioned elsewhere, I have plans to make an electronic remote release....but I have spent a bit too much over the last month or so.

Cheers for everyones advice!

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

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