Need advice Re Camera mirror lockup

[peter brown]

I am a very beginner and am looking for a modified Canon Dslr with decent resolution...6-10 megapixels.I have a nikon D80 but from my reading on this great site, I probably need a camera with the IR filter taken out. The only ones I see are Canon ie D10 but when I researched a bit, it doesn't have mirror lockup, which is apparently very desirable. Could someone let me know if the lockup is necessary, and if so, how some of the great photos I have seen from the D10 were managed?

Thanks heaps in anticipation

Peter Brown, Mount Beauty

[Dennis]

If your DSLR doesn’t have mirror lock up, you can use the “top hat” method for “Bulb” or long exposures.

Basically, you place a loose fitting cover (like a top hat) over the end of the ‘scope to completely block the light, and then open the shutter of the DSLR using e.g. a cable release. Wait for say, 10 seconds for the vibrations to die down, then very carefully remove the loose fitting cover and your exposure then begins.

To close the shutter, re-fit the cover (carefully) and then close the shutter using the cable release.

This is how I used to do it in the days of SLR’s using 35mm film. The cable releases had a locking grub screw to hold the shutter open.

The down side is that you have to do this for every sub frame if you are going to combine say, 10 x 3 min exposures.

Cheers

Dennis

[Matty P]

Hi Peter,

From what I understand the use of Mirror lockup for long exposure astrophotography is not needed. I personally don't use Mirror lockup when imaging. If you have a solid mount it is not nessesary to lockup the mirror before an exposure.

Mirror lockup is only nessesary when precise focus is needed to reduce camera movement and vibration from the reflex mirror.

Please correct me if I am wrong.

:thumbsup:

[monoxide]

i'd still use mirror lockup,
the mirror slapping up is enough to cause the scope to jump a little even if your mount is really solid.
i wouldn't say its 100% neccessary but its a good idea to use it if you can, its one less thing that can potentially ruin a sub before you even really start exposing it.

[Dennis]

My personal experience is that when using both a Pentax *ist DS (violent mirror slap) and Canon 40D (much less violent mirror slap) I can get blurred Moon images (1/125 sec and slower) as well as “double” stars on long exposure DSO images, where the bright stars have a fainter double just to the side, a ghost resulting from the vibration caused by mirror slap.

This has happened on a Vixen GPDX GEM mount and a Takahashi EM200 GEM mount with a 4” F9 refractor and Mewlon 180 F12 Cat despite having the ‘scopes carefully balanced and using a remote release or the software utility to fire the shutter.

As a result, I no longer risk ruining a shot so now always use mirror lock up. As Matty writes, a heavy, solid mount should minimise this or even prevent it happening.

Cheers

Dennis

[[1ponders]]

Using my 300D I installed the Russian Hack with gave the camera mirror lockup, best thing I did for my camera. That's imaging on a G11 mount. With my newer 20D the mirror slap is much more pronounced. Unfortunately the standard remote timer doesn'7 seem to work the mirror lock properly, I've had it modified. ;) Hopefully when I get it computer controlled I'll have another work around.

The bottom line: If you can get mirror lockup, use it.
:thumbsup:

btw I was under the impression that the 10D had mirror lock. The Russian Hack for the 300D gives the 300D the same functionality as the 10D.

[wmzaphod]

It really does depend on which camera you have and the mount....



There is a version of the Canon 20D that has the IR filter removed. It has mirror lockup (and it needs it too) :)

[Terry B]

I use a 40D on an EQ6 and don't bother with the mirror lock up. I start guiding before I start the exposure and can watch the guide star in real time using guidemaster. When the exposure starts there is no discernible movement of the guide star so don't see that I have anything to gain by using the mirror lock.
If your setup isn't as heavy then it might be needed.

[Dennis]

Another consideration is the type of ‘scope and focal length of ‘scope the DSLR will be attached to.

Typically, refractors are long so the DSLR is fitted on a long moment arm, dangling on the end of the focuser. A catadioptric ‘scope (generally) has a shorter tube so there is less of a moment arm.

Cheers

Dennis

[Hagar]

Hi Peter. a modded camera is not needed initially. You can certainly make do with your current D80. The modification I think you are refering to is to replace the IR/lowpass filter in your camera with a standard IR filter. The standard filter allows the passing of more of the Ha band. Depending on the item being photographed this may or may not be required. Some cameras are already quite Ha sensitive.

Mirror lock up is also a contentious issue with a lot of people saying it is required but with a properly balanced scope on a rigid mount you can live without it. Both my Canon 350 and 40D had mirror lockup but I very rarely used it. If you allow a reasonable time between shots, say 5-10 seconds, you will notice very little in the way of scope movement. Cameras like the 40D have a live view facility which in effect locks the mirror up when activated anyway and the shutter action is then very small.

I would give the D80 a go first and see what you really need.
I haven't seen you for a while, so how is the observatory works progressing?

[Dennis]

Here is a comparison showing the non-use and the use of Mirror Lock Up (MLU). The photos aren’t pretty, but I was just playing around in the lounge room, trying hard not to disturb my wife and guests!

Canon 40D with 400mm F5.6 lens on a tripod, using remote shutter release.
Photos taken under a 40W table lamp showing various shells in an acrylic moulding some 4 metres away from camera.
Raw captures at ISO800 1/60 sec at F5.6 with no processing or sharpening.
Cropped from full frame.

Top photo – without MLU.
Bottom photo – using LiveView hence MLU active.

I have highlighted the grey ellipse area on each photo to show the additional detail recorded in the shell when using MLU.

Cheers

Dennis

EDIT
Full frame photo added, resampled down to 1024x683, to show where the crop came from.

[wmzaphod]

I'm surprised (pleasantly) it made that much diff on a 40D. The 40D is much smoother than the 20D - just goes to show eh :)

[Terry B]

Interesting result. I agree that for the short exposure you used it has made a differnce but I wonder if there would be any discernable difference with a 5 min astro exposure. I think that any shake would be swamped by other sources of noise.

[peter brown]

Hi Hagar
Just got word today that my Sirius cubby is ready for transport. Guess it will be here in about a week to ten days. Got my ultrawedge from the States so it will be all go soon. Now I just have to find theSCP before constructing my base for pier. Catch ya down the town or with the other senior citz.
Cheers PB

[Dennis]

Yes – there is a big difference between a tripod (on a carpet floor) and an astronomical set up.

However, when trying to squeeze every last drop of image quality from your set up, it is worth optimising everything you (sensibly) can, to remove any potential sources of image degradation, leaving only those factors beyond your control.

Cheers

Dennis

[thomasz]

I am not sure. I think you pay through internet.