Balancing for Imaging

[Langy]

Everywhere you read it always says about balancing the telescope, which yes I can see why that when you are looking for that object in the sky and the clutch is off you can take your hands of the telescope and it hopefully doesn't move too much when you tighten the clutches.

Now when you are taking images through the telescope, especially with a DSLR there is movement when the mirror raises and the shutter curtains open and close therefore possibly adding vibration to the telescope nicely balanced on the tripod.

When I take a picture with my DSLR in low light and a large lens I will try not to just stand there with my arms tucked in to the chest but will try and find something to lean against, therefore removing the chance of moving, where even the wind could effect the image.

So my thought it that if you are all lined up with your subject, why not have the telescope out of balance, where the camera is pulling down on the telescope which should make any movement that much harder. For longer exposures this wouldn't be a problem but where you are exposing at around a second or less any movement could mean that the subject is moving.

I'd like to know what people think of this theory.

[jambouk]

Unbalancing kit is commonly practiced, but largely to reduce "backlash"; mine is unbalanced because i'm lazy.

James

[LouisJB]

I read somewhere that leaving it a little unbalanced so that it pushes against the direction of the motors is a good thing.

I normally just get it roughly balanced so there isn't tons of weight for the mount to move, but don't bother getting it totally perfect. If I were manually moving the tube around for visual I'd get it nicely balanced so it stays where you put it. For guiding / imaging I think approximate is good enough and perfect balance not needed or necessarily even wanted. Of course it should be nearly balanced, or the mount may struggle and have to work hard to move the scope.

Might be wrong, but just based on what I read, somewhere.

[Leveye]

Balancing your rig slightly heavy "To the East" makes the gears mesh better, pushing instead of pulling and reduces backlash.

[todd8137]

Rember if you you do move the weight slightly to the east when you flip the meridan push the weight the other way ! I get balance on bot axis firt there a lot to be said about balance nod imaging and I always put all my image stuff on the mount then balance ,do not balance the mount with a ep in do it with your camera and all the bits on astronomy shed as,a great vid on this

Pat

[RobH]

For imaging, try to achieve perfect balance with all the gear on, and in focus ( the draw tube length will affect balance), then slightly unbalance so it's east heavy, but only by the equivalent of a couple of grams or so.

[Pete Presland]

its just a slight bias to the east and makes perfect sense when you think about it, i think of it along the lines of, it sort of stops the mount getting ahead of itself (not sure if that makes ense or not  )

[Richie092]

For imaging, try to achieve perfect balance with all the gear on, and in focus ( the draw tube length will affect balance), then slightly unbalance so it's east heavy, but only by the equivalent of a couple of grams or so.

Good thinking Rob - I try to get it as balanced as poss but never thought about the leverage effect of the draw tube.

[nucleardwarf]

Does your camera have the facility to raise the mirror  and " park" it, to stop vibration?  You lose the facility to see through the viewfinder but it stops the clack of the mirror.

[ollypenrice]

For imaging, try to achieve perfect balance with all the gear on, and in focus ( the draw tube length will affect balance), then slightly unbalance so it's east heavy, but only by the equivalent of a couple of grams or so.

Exactly this. It does work well for RA.

There is an equivalent for Dec as well, but running one end heavy doesn't work well because, if you approach the meridian, the scope is vertical and falls into balance again. The clever anti backlash dodge for Dec is to be slightly polar misaligned and to guide in one Dec direction only. This stops the autoguider bouncing the scope back and forth across Dec backlash. However, it is best not to have any Dec backlash, or to have only a vanishingly small amount, then you can run near perfect PA.

Olly

[Langy]

Does your camera have the facility to raise the mirror  and " park" it, to stop vibration?  You lose the facility to see through the viewfinder but it stops the clack of the mirror.

No I have a Canon EOS 30D which must be around 7 or 8 years old now. Even though it only takes 4MB images it still holds it's own with most photography.

Other than that I have a Canon PowerShot S45 that is now over 10 years old, I did post a couple of afocal images on another post from that camera. Having the manual settings makes life so much easier in these situations, which is why I bought the S45 as it is as close to an SLR as you probably can get with a compact, certainly of it's time.

[Tim]

Rob's answer is spot on. However a lot depends on your mount. They are all slightly different once loaded up so you may need to experiment a bit. My EQ6 and HEQ5 I run heavier on the weights, slightly, but my main mount complains if it is anything but perfect balance.

I wouldn't have thought that being camera-end heavy is the solution though, maybe try making it heavy on the weights side.

Don't forget to keep away from the kit during exposures, vibrations going up through the legs of the tripod will likely be more responsible for shaking than the mirror lock.

In the past I have overcome your problem by holding a black sheet in front of the lens, starting the exposure, let it settle for a few seconds, then remove the sheet for the desired time, then put it back and close the shutter.

[lensman57]

Hi,

The issue of balance is different to the vibration induced by the camera shutter in particular  with newtonian scopes that have large, thin and  hollow steel tubes.

To induce a little bit of " Eastern " bias is solely to compensate for the lack of precision in the gear train of the mounts axis, these gears are hardly precision in engineering terms and there is just too much gap between the gears. Unbalancing sort of meshes the gears together and is supposed to reduce backlash, although I am not convinced of this 100% as particularly with a guided mount unless the aligment is so accurate and the guiding parameters  spot on the mount will over shoot periodically and has to be pulled back in which case the gears will unmesh for a very short duration and will have to settle again. As for the camera vibration, some highend  DSLRs have a facility to delay the shutter firing after the mirror has risen ,Nikons do have it but I have seen it for my 1000 or 1100d, if so activate it. If you are using software such as APT to control the camera then a mirror up facility maybe present for your camera. I don't think this problem is that important in comparison with other challenges that you encounter in AP. Alternatively there is always 10 Micron mounts that  do not need guiding and these do have precision built in  but you do pay for precision.

Regards and clear skies,

A.G

[RobH]

I have an Astrophysics AP1200 GTO CP3, which I think most would regard as precision engineering, but it still works better with a small bias to the east, so it's not simply about getting sloppy gear chains to mesh. As regards overshooting during guiding, I set my guide parameters so that unless the guide star shifts more than half a pixel or more, then guide commands don't get sent. This avoids this problem.

[ollypenrice]

Yes. I meant to say 'zenith' when I wrote 'meridian' on my earlier post, too.

An amusing variation of Tim's black sheet (which was often known as The Hat Trick in the days of film) is to use an umbrella in front of the scope. You can remain at the back with the camera while blocking the light with the open brolly!

Olly

[Langy]

So I guess the bias to the east is simply that as the axis will slowly be rotated east that it then puts less strain on the rotation as it will be a fall in weight rather than pulling on the weight.

Now I have the basic 130EQ without any motor drive (which may be purchased later in the year.

What would be the rough calculation used for how long of an exposure I could take?

When hand  holding a camera you use the simple rule of shutter speed should be no less that the focal length of the lens, even though this is rough and a good steady hand can take shots at much lower shutter speeds.

[dph1nm]

I have never been convinced about this east heavy theory. I have tried both east and west(!) heavy on my HEQ5 and it makes not one iota difference to the accuracy of the tracking.

NigelM

[Langy]

I would guess that it's not about the accuracy but more that you are putting less load on the drive as it works as the weight will be pushing it to turn rather than as a brake.

That's my thought anyway.

[ollypenrice]

I have never been convinced about this east heavy theory. I have tried both east and west(!) heavy on my HEQ5 and it makes not one iota difference to the accuracy of the tracking.

NigelM

This is perfectly normal. There is neither rhyme nor reason in guiding. A mount that has been perfectly happy for months can suddenly throw the dummy out of the pram unless you slightly alter the balance. Who knows why? Sometimes my Tak likes to be in perfect balance, usually it wants to be east heavy. There is no doubt though, that many mounts like to be a little east heavy. That doesn't mean they all do. What a business!

Olly

Olly

[lensman57]

I have an Astrophysics AP1200 GTO CP3, which I think most would regard as precision engineering, but it still works better with a small bias to the east, so it's not simply about getting sloppy gear chains to mesh. As regards overshooting during guiding, I set my guide parameters so that unless the guide star shifts more than half a pixel or more, then guide commands don't get sent. This avoids this problem.

I have no doubt that you are right. I also believe that a lot of the problems with balance are to do with the assymetric loading of the axis with relation to  the scope, guide camera, imaging camera, dew strips, wires and so on. As the mount rotates with the gear the center of gravity also gets altered   and this I am sure influences the inertia and the list of the problems go on. I think it is best to remove anything unnecessary including the finder scope prior to guiding and also to have the guide scope and camera as close to the main body of the scope and not hanging to one side , these might just help the matter.

Regards,

A.G

[martin_h]

Blimey your mounts must be better made than mine, I can move my weights 3 inches up or down the shaft and still be "balanced" LOL. A bit stiff in RA then?

[Langy]

So I guess the bias to the east is simply that as the axis will slowly be rotated east that it then puts less strain on the rotation as it will be a fall in weight rather than pulling on the weight.

Now I have the basic 130EQ without any motor drive (which may be purchased later in the year.

What would be the rough calculation used for how long of an exposure I could take?

When hand  holding a camera you use the simple rule of shutter speed should be no less that the focal length of the lens, even though this is rough and a good steady hand can take shots at much lower shutter speeds.

Does anyone have a calculation for this?