Piggyback or Side-by-side mounting?

[tooth_dr]

EQ6 + 250px + ED80

I'm moving along with the obs bow and trying to get the mounting configuration sorted for the scopes.

I've been considering the following:

ADM Guidescope Rings and systems - ADM Vixen-type Dual Mounting Bar

but before I buy I'm interested to hear about piggybacking these scopes, and potential problems in terms or flexure, weight, balancing, etc. I've found the rings on the 250px on it's own aren't very stiff, and probably not the dovetail either when loaded up with cameras, etc.

Thanks

Adam

[SteveP]

Adam

You've already got a great mount which is capable of carrying the load. However, the two scopes are very different in their weight and the distribution of the weight. I'm guessing a bit here but I assume the ED80 without any camera etc weighs 2.5-3kg (?) with a reasonable distribution of the weight along its length and the 250 must weigh 11-12kg (?) with much of the weight at the rear of the scope. From my experience side by side works best with similarly weighted scopes. Although I don't have your particular setup, I struggled to maintain a good balance sbs with my two refractors - one weighing about 7kg and the other about 11kg. In the end I opted for a piggy back arrangment which has given me much better balance right across the sky.

And yes, I wouldn't skimp on the tuberings and dovetails. ! know it's (yet) more expense but as I'm sure you're already aware the larger the scope, the more it flexes. You can get away with this is a single OTA imaging set-up but not in a dual set up, whether that's sbs or piggy back

It would be interesting to hear others experience of a large reflector with a small refractor

Steve

[steppenwolf]

Hi Adam, as you may recall, this is one of the setups I use. I have my guide camera piggy-backed on top of the 250 and it works for me. I also use an ED 80 for imaging with an ST80 piggy-backed on top for guiding and, having had what I suspect is differential flexure, I tried a side by side arrangement and it made zero difference so I only ever piggy-back my guide 'scope on either setup now. Before you splash your cash, I'd be tempted to try the piggy-back route and see how you get on.

[skye at night]

Had this dilemma myself in the past...

Side by side involves a lot of heavy investment in lumps of metal (which always wrankles with me as I tend to think what else? lenses etc.. the money could go on)...

but does use the loading capacity and counterweights of your mount better...

Piggy back requires a bit less in hardware and if it works is worth just going with.

Steve

[tooth_dr]

thanks for all the replies. Steve R - i always refer to your site for info as it has a good image of your three scopes piggybacked on your eq6. I will need to buy a new long dovetail to let me mount the ed80 on top of the 10", but worth trying that before buying the dual bar. Are there any dovetails better than others for my purpose?

[MikeD]

I have the same setup, EQ6 + 250px + ED80.

I went piggyback for a long time with the standard skywatcher dovetails

and it worked but there was a lot of flexure and as a result I found it hard to go above 5 minute subs at Prime on the newt without differential flexure causing star drift.

Recently I switched over to astrodevelopments M3 280mm basic mounting plate and homemade bars and guide rings for a side by side setup.

I am much happier with the side by side setup and even with all the extra weight of the new mounting system I still only use the same amount of weight (at the same position) as the piggybacked scopes.

Balance is not an issue with the side by side setup, I found it very easy to do.

So In my experience both methods work but for me the side by side has worked better, but I did it with a second hand mounting bar and made the rest for nothing ( total cost of £40 ish) I'm not sure I would have done it at full cost.

Hope this helps.

Mike.

[tooth_dr]

thanks for all the replies. Steve R - i always refer to your site for info as it has a good image of your three scopes piggybacked on your eq6. I will need to buy a new long dovetail to let me mount the ed80 on top of the 10", but worth trying that before buying the dual bar. Are there any dovetails better than others for my purpose?

[tooth_dr]

don't know what happened there, any surfing on my mobile. Thanks Mike, cannot view photos on my phone here but will look at them later at home.

[SteveP]

Adam

You shouldn't need a dovetail on top of your 10" for your ED80. A simple drilled plate would suffice. I would however recommend a new dovetail to attach the 10" to the mount. If your EQ6 has the Vixen fitting, then I'd also support Mike's recommendation of the Astrodevelopment m3 - it's very sturdy although a bit heavy. If your mount has a Lomandy head then I'd go with an ADM dovetail. I bought mine from FLO

Steve

[tooth_dr]

Thanks guys.

My EQ6 is standard so it has the vixen style fitting.

I had a look at the M3 stuff there and it looks very sturdy indeed.

Looking at the information above I have come to the following conclusions/solutions, and would be grateful for some guidance as to which is the better solution:

1) Get a new mounting bar for the 250px (not sure which though), attach the exisiting 250px dovetail to the top of the rings of the 250px, then mount the ed80 onto this. Piggyback solution sorted.

2) Get the M3 basic mounting bar, add a further M3 support bar for holding the 250px, and use the existing ED80 dovetail to attach it to the basic mounting bar. Dual mounting solution.

3) ADM dual mounting solution.

2) and 3) look like similar costs so really comes down to which is going to perform better.

What are the general thought on this? Or am I on the wrong track as I frequently find when it comes to trying to figure stuff out by looking at pics lol

Thanks again

Adam

[SteveP]

Adam

A couple of comments on the 3 options which are all good solutions

Option1 I'd still recommend the m3 as a replacement dovetail for the 10" - it is machined to be either used as a Vixen or Losmandy type dovetail and when fitted into the EQ6 head will provide a good wide platform for the tuberings

Option 2 Looks a complete solution if you prefer the sbs route

Option 3 It still doesn't resolve the inherent weakness of your existing dovetail. A more robust alternative may need to be factored into the costs

Which method (piggy back or side by side) do you now prefer? That may well determine what you think is best for your setup

Steve

[tooth_dr]

Thanks for you time and reply Steve, I forgot about the more rigid dovetail needed for the third option. I think I will have to eliminate it based on £££.

More questions (sorry!):

If I was to piggyback, do I simply attach the 250px tube rings to the M3 basic mounting plate? If so, I noticed the basic mounting plate comes in two lengths, is the shorter one sufficiently wide to give the scope itself enough support or do I need the longer one?

I would also like to be able to add my camera into the equation for some widefield shots with a lens only. The sbs setup would lend itself better to this as the camera would be closer to the mount being mounting on top of the ED80, but maybe this isn't an issue given small weight of camera, short focal length, etc?

But basically I need the basic mounting plate for either sbs or pb? If so what length is best!

Apologies again

Regards

Adam

[SteveP]

Adam

There's no need to apologise ... this forum is designed for people to share their own experiences and therefore help others!

I suggest the longer version given your scope. I've just measured mine - it's about 14" long (in old money) and has 2 single holes drilled at each end on about 12" centres. That's where you'd attach the 10"'s rings. I assume they only have a single fastening point? This means they're going to be wider apart than currently so should reduce tube flexing a little

Having the longer length should also give you some more leeway in getting the larger scope closer to the mounts centre if you decide to go sbs and mount the dovetail crossways

Does that make sense?

Steve

[Beyond_Vision]

I use a Vixen SBS plate which is extremely strong and has several pre-drilled holes for mounting a variety of hardware. I use two Vixen dovetail clamps bolted to it. The kit costs £150 and is very rigid. The dovetail on the SBS is vixen/synta compatible as are the clamps. The clamps have two clamping screws to ensure no movement.

» Opticstar - advanced CCD imaging solutions.

I have had no problems balancing a 7.5kg 4" Triplet Apo along side a little WO66SD. The other advantage is that it's easier to swap OTA's as it's just a matter of undoing two clamping screws swapping scopes and rebalancing. With a top mount there will be more disassembly.

Regards

Kevin

[tooth_dr]

I had written a large piece of text but decided on a picture instead lol

How does this look. It's decision time as I'm fed up with only one scope mounted at the minute and I want to do some guided deep sky imaging.

Thanks

Adam

[tooth_dr]

Hi Kevin

Thanks for the reply.

That looks very very nice what you have running there. It looks like I need a decent mounting plate either way and a stiffer dovetail for the 250px.

[SteveP]

Adam

Good picture ... you clearly have artistic skills!

That's very similar to one of the examples on the Astrodevelopment site so ought to work for you as well.

What's your reasoning for going with the shorter m3 plate? The longer one, although a little more expensive gives you more flexibility either in sbs or piggyback. I have my doubts as to whether the shorter plate could be used as a conventional dovetail with such a large scope

[tooth_dr]

Thanks

WRT the shorter plate, I suppose I just thought I could attach the 384mm mounting bar to this, and then to the EQ6, and that would do for piggybacking? It's only another £19 so I'll go on your advice, longer one it is!

[MikeD]

I would go for the 384mm mounting bar, I got the 280mm because it came up 2nd hand.

Mike.

[davinchi]

Piggyback mounting puts the center of gravity far from the center of the mount, requiring more counterweight or putting it also further away, wich makes the mount prone to shake. Dual mounting keeps the center of gravity next to the center of the mount, wich helps balancing the mount. I hope this helps, i was in the same dilema with my C11 and ED80 and went dual mounting..

[tooth_dr]

Thanks Mike for your reply, more or less finalising things now.

Regards

Adam

[George]

Originally I had my ED80 piggy backed onto my 250PX, this setup worked quite well but I had one annoying problem.....tube creep

The ED80 would never keep alignment in the adjustable tube rings, sometimes on a night to night basis, I eventually put this down to the 250's aluminum tube flexing during extreme temperature changes over a 24 hour period. The problem was the bridging bar that sat on top of the 250's tube rings (blue bar in photo) was not beefy enough to counteract the flex.

This summer I decided to try side by side mounting of my scopes, with cash being tight I made my own which can be seen in this thread.

http://stargazerslounge.com/diy-astronomer/82677-poor-mans-dual-mount-plate.html

All seemed well with this setup but it was a pig to balance properly at first but with some perseverance it can be done...or so I thought. My first imaging session east of the meridian went flawlessly and the ED80 kept alignment with just the odd small tweak over many weeks. My second imaging session west of the meridian was a disaster, after 5 minute of tracking I started to get star trailing, PHD was fighting the mount all the time. If I flipped east the problem would go away, I have always set my scope east heavy and it worked well even with meridian flips but with the side by side setup I always had problems.

Back to the drawing board, I rescued yet another piece of 8mm thick aluminum plate from the machine graveyard at work and decided to go back to the piggyback setup but with a substantial new bridging bar which would hopefully cure the tube creep. The new bar is 8mm x 150mm x 650mm, this might be overkill but better to over engineer than to under engineer Ive drilled holes every 30mm along its entire length so I can place the adjustable rings anywhere along its entire length and also move the whole setup on the 250's rings to change the balance.

Which ever method you decide to use you will need a substantial dovetail as this is the linchpin to anything you put on your mount, do not skimp on this

[tooth_dr]

Cheers for that info George, very informative. I've also looked at the link you provided. Can you tell me what size the dovetail for the 250px.

Thanks

Adam

[daz]

Just to add my support for the SBS and M3 option...

I have an ED80 and a 12" F4 newtonian. Even when I had my 8" Newt, I used the M3 support bar rather than the standard Skywatcher dovetail.... its like ali-foil in comparison!!

Go with the longer basic bar as well, it will be worth it in the end!!

The M3 is absolutely rock solid kit!

[George]

I had mine custom made by Raysrings, there are some pictures here

I'll post the dimensions later.