127 replies to this topic

[Sarkikos]

I have one of these:  ASTRO-TECH DOVETAIL ACCESSORY ADAPTER FOR VIXEN-STYLE DOVETAILS  https://www.astronom...k.html?___SID=U   

 

I attached the dovetail accessory adapter to the end of the 7" dovetail, with the open side facing out.  Then I clamped a chunk of iron into the adapter.  The piece of iron is 6.9 oz.  I tried this setup with the AT72EDII and a 3.7 Ethos.  I need more weight to balance the eyepiece.  

 

Last night I ordered three small counterweights with 1/4-20 bolts and threaded holes: two 7 oz and one 10 oz.  This will provide a total weight of 1.5 lbs, if I need it.  I can screw these weights onto the back of the adapter, and clamp the adapter onto the dovetail.  

 

Another way to help adjust balance is to loosen the clamp on the accessory adapter and slide it up or down the dovetail as needed.  A longer dovetail would make this more effective.

 

Mike

Edited by Sarkikos, 12 November 2019 - 09:19 AM.

[Sarkikos]

I use the AT72EDII mostly at home for bright DSO and double stars.  I don't usually take it to dark sites, except maybe on a vacation with my family.  If I'm going to a dark site, I like to take larger scopes.

 

So I don't really need to balance for the heaviest eyepieces, such as a 31 T5 or 41 Pan.  Besides, wide exit pupils give washed-out views under light pollution.  My home is in a red zone.  Here I like to avoid eyepieces which give the widest exit pupils.

 

But I do want to balance for the shorter focal length Ethos, like the 3.7 and 4.7, and the Baader Zoom or Leica Zoom, as well as some wide-field medium focal-length eyepieces.

 

Mike

Edited by Sarkikos, 12 November 2019 - 09:33 AM.

[gwlee]

A 1.6# 35 Pan balances easily with a just an 8” vixen rail and gives a 5.1 degree TFOV, but find I seldom use it with the AT72ED2. Seem to have settled on a 1# 27 Pan for low power in this scope. It gives a 4.0 degree TFOV AT 16x with a 4.5mm exit pupil. Believe this EP would probably balance with 7” rail, but haven’t tried it yet. Intend to try it with DM’s “2x7” dovetail from my 92mm scope to confirm. 

[Sarkikos]

My default mid-range wide-field for grab-n-go at home is a 24 Meade 5000 UWA, deshrouded of course.  It's 1.5 lbs.  Too heavy to balance in the AT72EDII unless I'm willing to rotate the scope in the rings until the focuser knobs point up and down, to avoid the dovetail.  I'm not willing. 

 

Mike

Edited by Sarkikos, 12 November 2019 - 01:09 PM.

[gwlee]

My default mid-range wide-field for grab-n-go at home is a 24 Meade 5000 UWA, deshrouded of course.  It's 1.5 lbs.  Too heavy to balance in the AT72EDII unless I'm willing to rotate the scope in the rings until the focuser knobs point up and down, to avoid the dovetail.  I'm not willing. 

 

Mike

As shown in the photo in post #29, I don’t need to rotate my AT72ED2 focuser more than a few degrees off horizontal to get it to clear the rail, definitely nothing close to “up and down.” It still looks a bit odd to me because I am accustomed to perfectly aligning my focusers with the horizon, but it’s proven to be perfectly functional, largely unnoticeable in use, and avoids adding dead weight to this grab-and-go scope to balance it. Either approach will work; neither is as elegant as I would like.

 

Like most things with telescopes it’s a tradeoff. Longer scopes are less likely to to require adding dead weight or rotating the focuser with a longer rail to balance them and have less field curvature, but give up some portability. If you find that you must add 1.5# or more of dead weight to the scope to get it to balance, you might consider putting the same amount of weight into a bigger scope that will perform better and balance without adding dead weight or rotating the focuser. 

Edited by gwlee, 12 November 2019 - 03:13 PM.

[Sarkikos]

As shown in the photo in post #29, I don’t need to rotate my AT72ED2 focuser more than a few degrees off horizontal to get it to clear the rail, definitely nothing close to “up and down.” It still looks a bit odd to me because I am accustomed to perfectly aligning my focusers with the horizon, but it’s proven to be perfectly functional, largely unnoticeable in use, and avoids adding dead weight to this grab-and-go scope to balance it. Either approach will work; neither is as elegant as I would like.

 

Like most things with telescopes it’s a tradeoff. Longer scopes are less likely to to require adding dead weight or rotating the focuser with a longer rail to balance them and have less field curvature, but give up some portability. If you find that you must add 1.5# or more of dead weight to the scope to get it to balance, you might consider putting the same amount of weight into a bigger scope that will perform better and balance without adding dead weight or rotating the focuser. 

On my MicroStar the AT72EDII focuser knobs are closer to up-and-down if I want them to clear the dovetail.  

 

Field curvature in many of these fast refractors can be virtually eliminated or at least improved very much with the right field flattener.  I've found the TSFLAT2 to flatten the field nicely in several of my refractors.

 

I have bigger refractors.  But I want to use the small AT60ED or AT72EDII for fast, easy grab-n-go at my house, or to carry in a small bag to observing sites in my neighborhood (the local golf course, for instance).  I can't see lugging my ST120, SW120ED or 150mm f/5 achro for a mile or so.  Well, maybe the ST120.

 

All scope and mount setups are compromises.  I'm trying to find the best compromise for these small refractors for me and my purposes.  Going to a bigger scope isn't compromising.  It's giving up. 

 

Mike

Edited by Sarkikos, 12 November 2019 - 06:16 PM.

[25585]

Some ideas here?  https://www.cloudyni...scope-eyepiece/

[Sarkikos]

Some ideas here?  https://www.cloudyni...scope-eyepiece/

Did this guy try out any of these setups at night, pointed at zenith?  I bet you he would have had trouble with at least some of them.

 

I have a 501HDV, similar to the head in his first pic.  The fluid balance is nice.  But ultimately since the load is top-mounted, it's not enough to make up for a really heavy eyepiece in the focuser.  Like he says,

 

I will stick with my 20mm Pentax XW on that scope unless I want to look at bugs in my garden.

 

Mike

Edited by Sarkikos, 12 November 2019 - 08:46 PM.

[Sarkikos]

My little counterweights are due to arrive tomorrow … if FedEx delivers them to the right house.  

 

Mike

[gwlee]

On my MicroStar the AT72EDII focuser knobs are closer to up-and-down if I want them to clear the dovetail.  

 

Field curvature in many of these fast refractors can be virtually eliminated or at least improved very much with the right field flattener.  I've found the TSFLAT2 to flatten the field nicely in several of my refractors.

 

I have bigger refractors.  But I want to use the small AT60ED or AT72EDII for fast, easy grab-n-go at my house, or to carry in a small bag to observing sites in my neighborhood (the local golf course, for instance).  I can't see lugging my ST120, SW120ED or 150mm f/5 achro for a mile or so.  Well, maybe the ST120.

 

All scope and mount setups are compromises.  I'm trying to find the best compromise for these small refractors for me and my purposes.  Going to a bigger scope isn't compromising.  It's giving up. 

 

Mike

I would like to experiment with a field flatter to see how it works for visual use.

 

I had the same balance problems to address with my AT72ED/AT72ED2 3-4 years ago and considered various options including replacing the AT72ED2 with something slightly larger that didn't have as great an inherent balance problem with 2-inch accessories. 

 

A 72mm f6 triplet would be about the same size as my AT72ED2, weigh slightly more due to the extra glass, but might be easier to balance due to the extra weight being in the best place to counter heavy EPs. It might actually weigh less than your AT72ED2 after you add 1.6 or more pounds to you AT72ED2 to balance it. 

 

An 80mm F6 triplet would be about two inches longer, so might be easier to balance due to the longer tube and extra glass being in the best place to compensate for heavy EP, and might actually weigh less than your AT72ED2 with balance weights. 

 

An 80mm f7 doublet would be about five inches longer, so easier to balance, and it might not weigh much more, than your AT72ED2 with balance weights depending on how much weight you need to balance your heaviest EP. 

 

In each case, the extra weight comes with some extra benefit, so it's not dead weight. Given a choice between adding 1.6# of dead weight, or 1.6# of extra aperture or glass with less CA. I would choose functional weight over dead weight if I could handle the extra length. Larry said the MicroStar was intended for 80mm scopes, so your mount would probably handle a slightly bigger scope OK.  

 

My other choices for balancing seemed to be limited to sticking with lighter weight 1.25" EPs, rotating my focuser, or, adding dead weight to the scope. I chose to go with a slightly longer dovetail and rotate the focuser because it works fine, adds almost no weight, and costs nothing extra. It still looks a little odd to me, but I am trying to get over it because it works so well. 

 

If you don't object to adding dead weight to your scope, adding balance weights will work and won't cost much. I tried it and thought it was the least elegant solution for a grab-and-go scope, so didn't pursue it. 

 

Trying to find the best compromise never ends. At the moment, I am experimenting with a 92mm f6.7 scope. It's definitely longer and heavier than the AT72ED2, and requires a much heavier mount, but it's still easy enough for me to use for a grab and go duty at my home that requires a lot of tree dodging. However, it's far too heavy for me to consider packing it a few miles, which I do occasionally with my AT72ED2 to catch a view of something that isn't visible to me from home. 

[Sarkikos]

OK, I finally got around to trying out the new counterweights on my AT72EDII mounted on MicroStar Deluxe. 

 

I put a 3.7 Ethos in the Baader T2 BBHS Sitall Mirror Diagonal.  I attached a 2" barrel to the diagonal to provide a more secure grip in the visual back. 

 

For this first trial, I screwed all the new counterweights onto the AT dovetail adapter, for a total of 1.5 lbs.  (One Bushman Panoramic Counterweight  (10 oz) plus two SmallRig 2285 Counterweight (7 oz ea).  Possibly the setup would balance with less weight.

 

Another option I might try is a longer dovetail.  This would allow use of less weight for the counterweights, and a longer range of position for the AT dovetail adapter.  But it also might require a longer equipment bag.

 

Mike

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Edited by Sarkikos, 18 November 2019 - 09:19 AM.

[Sarkikos]

Here is a close-up of the AT72EDII, showing how close the focuser knobs are to the AT 7" dovetail.  If I rotate the OTA in the rings to avoid the dovetail, the focuser knobs will be nearly vertical.  Also, since I have two finder shoes on the OTA, if I rotate the OTA in the rings, the finders will be in positions that would be uncomfortable for me.  Notice the 6x30 RACI and laser finder in the first pic of my previous post.

 

These are reasons why I don't - or can't - position the dovetail behind the focuser knobs. 

 

Mike

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Edited by Sarkikos, 18 November 2019 - 08:51 AM.

[jeffmac]

Well, I have a Sky-Watcher 72mm. I have the same balance issues with large, heavy eyepieces. I'm using an Orion Versa-Go alt-az with it. I didn't think I'd like it but I tried a very large heavy-duty rubber band for tension and it works beautifully. This is essentially the same idea as the spring-loaded counter weight on a video tripod. I also like it because it is easy to attach the band and it adds no extra weight to the set-up. Well, not technically....maybe a fraction of an ounce. Not elegant but inexpensive and effective.

[Sarkikos]

Would you post a pic of how you take care of imbalance with the rubber band? 

 

Mike

[paulh83]

Did this guy try out any of these setups at night, pointed at zenith?  I bet you he would have had trouble with at least some of them.

 

I have a 501HDV, similar to the head in his first pic.  The fluid balance is nice.  But ultimately since the load is top-mounted, it's not enough to make up for a really heavy eyepiece in the focuser.  Like he says,

 

 

 

 

Mike

I also had a 501HDV and found it awkward when using my TV-76. I sold it and got a M1V. Overall, it was a better solution for me. 

Edited by paulh83, 20 November 2019 - 09:27 AM.

[Sarkikos]

The 501HDV is fine for small telescopes with light-weight eyepieces.  I never had a problem balancing a C90 on the 501HDV.  The fluid balance is sufficient when pointing toward zenith.  It's also OK for the AT60ED, as long as you don't use heavy eyepieces.  I even have the AT60ED rings attached to a plate rather than a dovetail, so it can attach quickly to the 501HDV.   

 

A C5, however, is borderline.  I know some observers have even mounted a C6, but I think that's too much.  I also had my 25x100 binos on it, though that really is pushing the capacity.

 

I still have my 501HDV.  I just don't mount anything on it besides the smallest and lightest telescopes.  

 

Mike

Edited by Sarkikos, 20 November 2019 - 09:44 AM.

[jeffmac]

Would you post a pic of how you take care of imbalance with the rubber band? 

 

Mike

I'm sorry Mike. I don't have the means to post a picture right now, but I had to get creative and think about it for a while. In essence, what I did was to put a screw with a washer into one of the tube rings. The band goes around this and the other end attaches to the mount head. The attachment is not symmetrical but it works. The creative part is figuring out how to attach the band to the mount head. My mount is different than yours but the band hopefully can be attached to yours with an "S" hook. As long as there is at least a little constant tension on the band at all times, it will stay attached. It really is very easy both to attach and remove the band. Takes only a few seconds.

[Sarkikos]

A couple nights ago I took out my ST80 with the counterweight setup.  I had a 10mm Ethos in the focuser.  (I was testing a TSFLAT2 field flattener.)  One  SmallRig 2285 Counterweight (7 oz) was enough to balance the scope.

 

Mike

Edited by Sarkikos, 30 November 2019 - 09:27 AM.

[Tyson M]

OK, I finally got around to trying out the new counterweights on my AT72EDII mounted on MicroStar Deluxe. 

 

I put a 3.7 Ethos in the Baader T2 BBHS Sitall Mirror Diagonal.  I attached a 2" barrel to the diagonal to provide a more secure grip in the visual back. 

 

For this first trial, I screwed all the new counterweights onto the AT dovetail adapter, for a total of 1.5 lbs.  (One Bushman Panoramic Counterweight  (10 oz) plus two SmallRig 2285 Counterweight (7 oz ea).  Possibly the setup would balance with less weight.

 

Another option I might try is a longer dovetail.  This would allow use of less weight for the counterweights, and a longer range of position for the AT dovetail adapter.  But it also might require a longer equipment bag.

 

Mike

Those counterweights look slick!

 

I myself use heavy eyepieces with a small fast refractor (AT92 with 31N or 17ES).  Balance is solved by adjusting the dovetail on the rings closer to one end, which I am sure someone has already mentioned.  The focuser knobs is close to hitting the dovetail but I get by with it like yours is pictured.

[Sarkikos]

I could not position the dovetail farther back on the AT72EDII without hitting the focuser knobs.  I would have to rotate the OTA in the rings until the focuser knobs are nearly vertical.  I don't want to observe like that.

 

Mike

[jag767]

You mean like this? Easy, at 8x I can get away with not using a mount 😁

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[TNmike]

Mike,

 

I put a longer dovetail (8” generic vixen from Astronomics) on my AT72ED2 to get it to balance with a 35mm Panoptic, and I must rotate the focuser a few degrees, so the focuser knobs clear the longer dovetail. It works perfectly, but looks a little odd to me because the knobs are no longer parallel with the horizon. I have set up mine, so the right knob with the fine focus mechanism is a touch higher than the left. 

 

gary

Gary, how thick would the spacers need to be between the mounting rings and dovetail for the left side focuser knob to clear the dovetail, if the focuser wasn't slightly rotated but horizontal instead?

[dhormann]

I have a TV-85 that I mount on a 14” D Plate with a single Stellarvue riser and a TV clamshell ring.  This gives me a bunch of adjustability.  My heaviest eyepiece set-up is a 17.3mm TV Delos (.90 lb.) with a 2X Powermate (1.2 lbs.) and 2” star diagonal (1.3 lbs.) for a total of 3.4 lbs. (1.54 kg) hanging on the focused.  So far, balancing has not been an issue.  I believe I could mount one of the 41mm Panoptics without drama, but that’ll have to wait until the money tree grows another crop!

 

Doug

 

[Sarkikos]

I have a TV-85 that I mount on a 14” D Plate with a single Stellarvue riser and a TV clamshell ring.  This gives me a bunch of adjustability.  My heaviest eyepiece set-up is a 17.3mm TV Delos (.90 lb.) with a 2X Powermate (1.2 lbs.) and 2” star diagonal (1.3 lbs.) for a total of 3.4 lbs. (1.54 kg) hanging on the focused.  So far, balancing has not been an issue.  I believe I could mount one of the 41mm Panoptics without drama, but that’ll have to wait until the money tree grows another crop!

 

Doug

Yes, mounting a small refractor on a riser on a 14" D Plate would raise the focuser knobs above the plate, allowing the telescope to be shifted forward to provide balance with heavy eyepieces.  But as I mentioned in my Opening Post, "I don't want to increase the size and weight for grab-n-go."  A big D Plate would definitely increase the size and weight for grab-n-go.  The D Plate would also require a larger, more heavy-duty head and tripod.  Not what I want to do.

 

Mike

Edited by Sarkikos, 03 December 2019 - 06:59 AM.

[Wouter1981]

You mean like this? Easy, at 8x I can get away with not using a mount 😁

Wrong thread. This should be in the thread "how do you balance your eyepiece for small refractors" ;-)