Its all a question of Balance

[darrellx]

Hi All

I have two Balancing questions for you, which have come about because I have just weighed all my equipment.

First, there is a 200g difference in weight between my lightest and heaviest eyepiece. If you setup and balance your scope with say a light eyepiece then during the viewing session change eyepieces to a heavier one, I suppose there is no point in rebalancing the scope. I don't. Does 200g make a real difference?

Following on from this, and say you change to do some photography during the session, I would be changing the weight by around 600g. (I have an EOS400d) This is significant. At the moment, to rebalance this is what I do.
Park the scope.
Change equipment.
Rebalance.
Re-align.

All this takes time. Is there an easier way? Or do you not even bother with a 600g difference in weight?

Thanks
Darrell

[Astro78]

you could always grab a 200g magnet and find that magic spot on the scope where it balances, then remove for your lighter eyepieces. Depending on the length of your tube, the same magnet would work for the camera too.

[AlexN]

That would all depend on the total weight load, and the mount being used...

If you were at 1/4 of the total weight capacity of say, and EQ6 or something bigger, 200g is really not going to make much of a difference.. If you were closer to 6/8ths the total capacity of the mount, and had a 200g imbalance, the weight difference might be more of a problem...

Also, how far is this imbalance from the fulcrum? I found that a 150~200g imbalance on the end of my old 152 F/8 refractor (1300mm physical length) was rather substantial, however 200g imbalance on my C11 (690mm physical length) did not make too much difference at all..

[leon]

I would not be concerned with the 200 gram weight, but the 600 is an other story and would re balance.

Leon

[Wavytone]

Make two ballast weights about 200g and 400g, with an easy attachment method (even Velcro will do). Pill or drink bottles with sand in them will do nicely, as you can add or subtract to these whenever you need.

Put an attachment point on side of the tube opposite to the eyepiece (this will help keep the centre of gravity central, too).

Balance the scope for the heaviest item.

When using the lighter eyepieces, add ballast to the scope, either 200g, 400g or both to get 600 g.

[AlexN]

Doing that will keep you balanced in dec, but give you an imbalance in RA, as you're adding more weight to the telescope side of the RA axis, but not to the counterweight shaft.. So you'd still need to rebalance and re-align the mount.. I suppose you could then make the same sort of weights for your cw shaft too, but honestly it would probably be less frustrating to just rebalance and re-align in the end..

[marki]

Like Leon said, 200g would not make much difference. I can think of three possible options to prevent having to rebalance and reallign.

1. Buy an TV ethos (13mm approx 590g or 17mm approx 700g).
2. Buy a flip mirror system and balace with everything aboard then flip to the eyepiece to allign and the camera to image.
3. Buy a chronos mount and forget about it all together.

Mark

[darrellx]

Hi All

I think I have a solution. Thanks for the comments. If a 200g weight variation would be acceptable before a rebalance would be required, here are two examples.

For my 200mm on the Eq5. Lets say I normally start with just a 20mm eyepiece - weight 121g.

Later during the session, I might want to use my Canon at prime focus - weight 615g.

Then even later I might want to use my DMK21 - total weight 356g.

So how would it go if I setup the balance for the DMK (the middle option for the weight ranges), then any weight variation would only be 200g or so. Either hevier or lighter.

I could then do a similar thing when using my Meg90. Setup and balance for the middle of the weight options - 600g for a 2inch diagonal and an EP. Then if I changed to any other option, the weight variation would only be 200g or so. My Canon with a reducer weighs in at 868g, and my DMK setup is 486g.

Darrell

[Omaroo]

Maybe you just need to plan what you are going to use your session time for Darrell, and stay with it for the length of the session. If I plan a photographic night, I set up that way and do just that for the whole night. I don't go back and forth between cameras and eyepiece. It takes too long to get focus back before you can start long image takes. A night isn't long enough to do everything. Wish it was though... :)

[AlexN]

mm true.. I used to swap between an eyepiece for centering objects then the camera to image, and usually rushed the focusing effort, and generally achieved pretty average images... Once I sorted out my alignment issues, I now tend to trust my go-to's and centre objects using the CCD... Once its all balanced etc, I leave the setup as is for the entirety of the night..

[gregbradley]

Can I ask why you would start with an eyepiece if you were planning to image or do you like to do some visual beforehand?

If I were doing photography I start with the camera and get it balanced and then do focus etc using the camera.

If you need to do polar alignment using the drift method this is also best accomplished using the camera. Andy Shotglass's startarg overlay is good for that. It has instructions and everything and it is cheap.

Of course this assumes you are using a laptop or computer and you may not be in which case you are stuck with swapping.

One simple solution is to make a mark on your dovetail where each balances with both eyepiece and camera setups. Then simply move the OTA along the saddle so that mark lines up on the dovetail. Of course perfect balance requires having the camera at focus as it could shift a lot.

Greg.

[omnivorr]

... or run two scopes ;)

[darrellx]

Greg, to answer your question first, I usually plan a session and have somewhere around 6 or 12 objects that I would like to look at. When I get out there, and I am able see one of the objects particularly well (maybe the see is good on a particular night), I tend to want to take some shots. So I don't really plan to do much photography, it just seems to happen.

I take the point raised by Chris and AlexN - not only to plan what I am going to view for each session, but also decide what to do (view or photo) and stick to it.

Maybe when the weather clears and I can get out more often, I wont need to try and fit it all in on one night.

Thanks for your comments.
Darrell