Balancing the scope

[Moonshed]

I have not had my Bresser EQ5 mount that long and as yet have not used it for Astrophotography, until last night. I fitted my cannon to it with a Lumicon Easy Guider. It was very heavily out of balance and I could not correct it. If I take my scope off the dovetail bar and slide it in on the other end it is then overbalanced on that side. Where I need to put it is more or less the one place I can't, that's  where the locking bolt is the holds the scope to the bar. The photo shows what I mean. So how do I get round this? Obviously I can't just strap a counter weight to the scope, but can't see where I could fit it. Any ideas?

Thanks, Keith

[ChrisLX200]

A full-length dovetail bar on the underside of the OTA would help - and be more stable than the fitting you have there.

ChrisH

[Moonshed]

Thanks for the advice. I am sure a full length bar would be more stable but I wasn't aware they could be changed. Mine seems to be permanently fixed to the OTA and unchangable but perhaps I am wrong. Having said that I don't see how that would help because regardless of the length of the bar the balancing point would still be in the same inaccessible point? Maybe I am misunderstanding the situation?

[ChrisLX200]

It would give you more options, like adding a sliding weight system to the front part of the dovetail. Are you using a dewshield? that normally adds weight to the front too.

ChrisH

[Moonshed]

Thanks for that, I will have a look to see if I can change the dovetail bar, it would help. I hadn't thought about adding the dew shield as a counterbalance but will give that a go. Thanks for the advice, appreciate it.

[Waldemar]

I totally agree with ChrisH. The way your scope is mounted is very unusual and unstable. I have never seen a Celestron being mounted like that...
Imaging will be very hard if not impossible with this mounting... For that matter: the combination mount, telescope and DSLR that you have is very challenging anyway....

A long dedicated dovetail bar can be mounted on the topside of the scope as well... Does not matter whether it is up side down or not.

Waldemar

 

[usingen1]

18 minutes ago, Waldemar said:

I totally agree with ChrisH. The way your scope is mounted is very unusual and unstable. I have never seen a Celestron being mounted like that...
Imaging will be very hard if not impossible with this mounting... For that matter: the combination mount, telescope and DSLR that you have is very challenging anyway....

A long dedicated dovetail bar can be mounted on the topside of the scope as well... Does not matter whether it is up side down or not.

Waldemar

 

I also agree, not agood mounting and it also looks very shaky....

[Moonshed]

It is an unsatisfactory set up. What happened is I contacted Telescope House to buy a new mount and bought the Bresser EQ5 after they assured me my Celestron would fit on it with no problem. However, when it arrived it did NOT fit. My Celestron was made circa 1985 and the dovetail on it is what I would describe as female. The dovetail bar on the mount is also female. I contacted  them and their solution was to make up this bar that goes between the two. It is two 7" Revalation bars joined back to back. As you can see it provides very little movement for balancing, which up till now has not mattered, but now it does. Any ideas?

[Waldemar]

To judge by your pictures, the female mounting on your scope can be removed by taking out the two screws that connect it to the telescope.

Then you can mount a C-8 dedicated Vixen style dovetail that connects to both ends of the telescope like this one: http://www.robtics.nl/popup_add_image.php?pID=1518
Now you will have a solid connection and all the moving possibillities you need.

If I were you, I would complain about the solution they offered you at Telescope House. Apparently they have no idea what they are doing! To be honest I have never seen such a stupid solution!!
FLO will be able to sell you the right the right dovetail with mounting brackets for your C-8

Waldemar

[skybadger]

That's a bit harsh. Seems eminently practical to me. Until the demands start getting high, that perfectly does the job. Remember all the weight in that ota is in the mirror end and the mount is coupled tightly enough for visual at least. 

For now , putting a spacer between those back to back dovetails would be something you can do at home to get you going before more drastic action. It would give you the clearance you need at the expense of moving the counterweight a little..

M

 

[Moonshed]

Thanks for the advice it makes a lot of sense, I will order the parts from FLO straight away. That's the last time I go to Telescope House!

[Waldemar]

@ SkyBadger: With this solution, there is bound to be a lot of flexure, especialy with the extra weight of  a dew cap and a camera on the scope.... this is a very bad solution, very unprofessional
Spacers between the two dovetails will make things even more unstable. As you can see in the pictures, they even used bolts with too high heads,  they damaged the origional Celestron clamp.

If I can come up with a far better solution being an amateur, what does that tell about them?
So, what do you mean harsh... I think I was very mild... 

Waldemar

[Owmuchonomy]

I think my main concern there would be that the scope is 'under-mounted' to be honest.

[Moonshed]

I have ordered the bars from FLO and I think the £60 cost will prove to be worth every penny. Thanks again for  all the advice. I have to say I am very disappointed with Telescope House, I have been dealing with them for 25 years, but no more. Thanks Waldemar.

[Waldemar]

I agree Chris, that's why I made the comment: " For that matter: the combination mount, telescope and DSLR that you have is very challenging anyway.... " 
Although an EQ 5 should be capable of carrying a C-8....  Kind of depends what and how the OP wants to image... Many short subs could do the job. 

Waldemar

[Waldemar]

4 minutes ago, Moonshed said:

I have ordered the bars from FLO and I think the £60 cost will prove to be worth every penny. Thanks again for  all the advice. I have to say I am very disappointed with Telescope House, I have been dealing with them for 25 years, but no more. Thanks Waldemar.

You are very welcome, Keith. I am glad I could offer a solution.

[Moonshed]

Just for my clarification, do the the two dovetail bars join together back to back, and do the bolts come for that, to make a longer version of what I have now? It's just that you mentioned removing the clamp from my OTA and fit a bar to it, but if I do that I have no means of clamping the tube in place.

[ollypenrice]

I think that, before condemning TH, we need a bit more information. The modern method for mounting an SCT is to have a full length dovetail bar (male) running from front to back on the scope so that it can fit into the female puck which is the white clamp on top of the mount. Now if TH could have simply supplied such a thing I strongly suspect that they would have done so. However, the modern SCT full length dovetail bar fixes to the scope using 'accessory bolts' which fit into pre-drilled and threaded holes at the front and back of the OTA. However, we have no pictures here of the front of the scope and it may be that, at this time, the scopes were sent out without any such accessory bolts at the front. In this case Moonshed may have no easy way of securing the front of his scope to the full length rail he has ordered. It might also explain why TH went for the eccentric option of the female saddle plate-like clamp fitted only to the rear of the scope and the 'double male' short bar. I'm only guessing as to why they might have taken this odd course and I may be quite wrong.

If the telescope does not have any viable means of being attached to the full length bar at the front then the only obvious option would be to order a set of tube rings and attach these to the full length Vixen rail. Tube rings are disproportionately expensive but might well turn up second hand.

Long story short: if you unbolt the little black female clamp from the tube you should be able to use the same threaded holes in the OTA to hold the full length rail in place. But is there a corresponding pair of holes at the front? 

Olly

[Moonshed]

31 minutes ago, ollypenrice said:

 

Long story short: if you unbolt the little black female clamp from the tube you should be able to use the same threaded holes in the OTA to hold the full length rail in place. But is there a corresponding pair of holes at the front? 

Olly

You raise some interesting points. If I can fit a male dovetail to my OTA that would solve the problem, it would mean that the set up would have only one clamp, the one on the mount, and solve the problem of the two clamps being unable to pass each other. I only have one bolt on the front of the tube so I am not sure about how fitting would go. The picture shows it.

[Waldemar]

1 hour ago, Moonshed said:

Just for my clarification, do the the two dovetail bars join together back to back, and do the bolts come for that, to make a longer version of what I have now? It's just that you mentioned removing the clamp from my OTA and fit a bar to it, but if I do that I have no means of clamping the tube in place.

There will be two parts with a radius and one long dovetail that equals the length of your scope.

The two parts small parts (brackets) with a radius are attached to the front and back retaining rings of your scope. On those brackets the dovetail is bolted and will be hold in place by the clamp on your mount.
You will be able to use the full length of the dovetail  and obtain balance easily. On top of that the whole construction will be far more rigid.

If you can show what you ordered at FLO I can be more precise, but the system is like on any available C-8 on GE mount.

Waldemar

[Waldemar]

58 minutes ago, ollypenrice said:

I think that, before condemning TH, we need a bit more information. The modern method for mounting an SCT is to have a full length dovetail bar (male) running from front to back on the scope so that it can fit into the female puck which is the white clamp on top of the mount. Now if TH could have simply supplied such a thing I strongly suspect that they would have done so. However, the modern SCT full length dovetail bar fixes to the scope using 'accessory bolts' which fit into pre-drilled and threaded holes at the front and back of the OTA. However, we have no pictures here of the front of the scope and it may be that, at this time, the scopes were sent out without any such accessory bolts at the front. In this case Moonshed may have no easy way of securing the front of his scope to the full length rail he has ordered. It might also explain why TH went for the eccentric option of the female saddle plate-like clamp fitted only to the rear of the scope and the 'double male' short bar. I'm only guessing as to why they might have taken this odd course and I may be quite wrong.

If the telescope does not have any viable means of being attached to the full length bar at the front then the only obvious option would be to order a set of tube rings and attach these to the full length Vixen rail. Tube rings are disproportionately expensive but might well turn up second hand.

Long story short: if you unbolt the little black female clamp from the tube you should be able to use the same threaded holes in the OTA to hold the full length rail in place. But is there a corresponding pair of holes at the front? 

Olly

Hi Olly, I had an old orange C-8 from a fork mount and there were no problems mounting a full length dovetail on it, so I assumed that will be the case with this younger one as well... I hope you are wrong...

Maybe Keith can have a look and confirm that there are indeed mounting holes with thread in the front ring... If not I owe TH sincere apologies...

Waldemar

[Moonshed]

The bars I have ordered are the same as the one that Waldemar put in a link to. As I said, there is a single bolt on the ring on the front of the tube and I have shown it on the photo. If there is any doubt I can always give FLO a ring in the morning and see what they suggest.

[ollypenrice]

Isn't that front bolt slightly offset? TH must have half a million dovetails for SCTs so if they didn't go for that I still think there will be a reason.

Olly

[Moonshed]

I don't think it's offset its just the camera angle. I will check in the morning in the daylight.

[ollypenrice]

The other thing is that one bolt is far from ideal. I've just had a look at my own Meade SCT and the full length rail does not bolt to the OTA with central bolts. It has a flanges on each side which are quite wide and profiled to fit the radius of the tube. The rail is bolted to the tube by two well separated bolts, one pair at the front and one pair at the back. Clearly the problem that this sets out to solve is the tube rocking on the long dovetail (that is, when viewed from front or back, rocking sideways.) I cannot see central bolts being at all satisfactory unless the new rail is very carefully profiled to meet the OTA along the outsides of its length. If it contacts the OTA along the centre line the OTA will rock.

Olly