Multi-telescope imaging rig

[Gina]

True but it might be summer before I'm ready   I shall be aligning during the daytime on the tree on the far hill so not as cold as nighttime (probably) so that should help.

[Gina]

I think I have come up with a design for the Dec adjuster

An M5 bolt mounted on a 5mm x 16mm x 5mm sealed ball bearing with a spur gear attached with a nut, forms the screw adjustment.  This runs in a 5mm threaded hole in a printed plastic lever that fits closely onto the scope mounting plate.  This allows the plate to slide through the fork for the RA adjustment while holding the Dec alignment.

I tried first with a captive M5 nut in the lever but there was too much slack which would allow the alignment to shift slightly.  (This was a problem with the previous RA adjuster.)  OTOH a thread cut in the plastic can be made to be quite tight and remove all slack.  Of course, this will only work for relatively infrequent use as in time the plastic thread would wear.

I have yet to sort out the stepper motor mounting and position but there are a few options.  eg. I could have the gears and motor on the other side of the main plate, or maybe arrange the motor to drive the screw directly.

[Gina]

I've been giving this whole system a lot of thought and wondering if I'm making things more complicated than necessary - I do have that tendency

My idea of having the four scopes on the EQ8 was that if I wanted to change from MN190, 1000mm FL imaging to the triple rig at 400mm FL I wouldn't have to haul one system off and put the other one on.  If everything is working properly this seems an eminently sensible thing to do but this utopia has yet to be achieved    Goodness knows how long it's going to take to sort everything out and in the meantime I have no imaging facility and I'm missing out on clear night skies and getting frustrated to boot!!

I do know that I'm currently taking too much on with all the other things I'm having to sort out so postponing some of the astro projects seems sensible.  I have already shelved some of my non-astro projects.

As for the telescopes, I'm thinking maybe I should put the MN190 on the mount alone and get imaging working again on that.  It will mean constructing a power distribution and focussing box for just the MN190 but everything will be much simpler.  The 400mm FL triple imaging rig could be put on hold for the time being.  The MN190 is light enough to lift onto the mount manually so I wouldn't need the hoist.

I'm thinking that I might mount just the three 400mm FL scopes directly on the big ali plate in a row.  I could use one of the ST80s with OAG for guiding instead of the MN190 as at present.  They already use extension tubes so incorporating an OAG wound be no problem. ATM the Esprit is fitted up with its flattener plus special FLO adapter to the EFW2 filter wheel so not convenient to fit the OAG to that.  I think the mechanical coupling between the three scopes will be a fair bit better than with the Esptit mounted on top of the MN190 scope rings.

Another advantage of using the 400mm set without the MN190 is that the roof can be opened and closed with the rig in any position whereas with the MN190 the mount has to be parked in a special position for the roof to clear.

As always, comments are very welcome

[Gina]

I'm thinking that with just the three scopes in a row with much more room to spare, I can use variable alignment guide scope rings for the ST80s (similar to these but home made).  The more rigid mounting system should mean that the alignment should only need doing once and all that complicated motorised remote alignment can go.  Thank goodness for that - it was getting rather ridiculous

[Davey-T]

Be nice to have something set up ready to take advantage of clear skies while you play around with other projects.

I keep setting mine up for Solar hoping the Sun might come out then taking the solar off and setting up for planetary, then taking that off and setting up CCD for DSOs.

In the meantime I've ordered some foam to redo all my flight cases ready for SGLX , stop me getting bored with clouds, garden is getting a bit neglected though 

Dave

[SnakeyJ]

I think we all need pots of cash and three dome observatory complexes - that and early retirement to concentrate on processing all that data ;-)

The triple side by side rig sounds very sensible and more manageable. Don't give up on all the projects, perhaps limit to 2-3 at a time - life is for learning ;-)

[Gina]

Be nice to have something set up ready to take advantage of clear skies while you play around with other projects.

I keep setting mine up for Solar hoping the Sun might come out then taking the solar off and setting up for planetary, then taking that off and setting up CCD for DSOs.

In the meantime I've ordered some foam to redo all my flight cases ready for SGLX , stop me getting bored with clouds, garden is getting a bit neglected though 

Dave

We haven't had suitable weather here for doing much outdoors.  Been very cold with a bitter wind and the ground is like a bog   Managed a few odd little jobs on my observatory though

[Gina]

I think we all need pots of cash and three dome observatory complexes - that and early retirement to concentrate on processing all that data ;-)

The triple side by side rig sounds very sensible and more manageable. Don't give up on all the projects, perhaps limit to 2-3 at a time - life is for learning ;-)

I've spent cash I didn't really have - a grant I was expecting didn't materialise and a bill I though I'd paid months ago resurfaced   Now I'm struggling somewhat but selling off unneaded bits of kit has helped   As for time, I am retired from paid work but still have non-astro things that need doing and sorting out which is taking a lot of time and effort

Yes, I'm happy with this latest decision - I think it will make things much easier   I have already attacked the power box from the 4 scope system and salvaged the components.  I'll want a smaller box for the triple rig.  From the Arduino Mega box I have extracted the cable for the MN190 focuser - easy job, just snipped the power lines and unplugged the data from the Mega. 

Haven't decided whether to change to a Nano as that is sufficient for three focusers or just keep the Mega, which is already wired up and ready to go.  Also, if I keep the Mega I could add dew heater control electronics if it looks advisable.  I have yet to install dew heaters on the ST80s and the Esprit needs a new one with a different resistance as the one I had made for it ran off 5v and I'm using 12v now.  Only thing using 5v is the USB powered hub and I'm dropping that from the 12v with a regulator chip.

I'm not giving up on the other projects, just prioritising.  I like to have more than one project going at a time so that if one is held up or I get tired of it there's the other to go at

[Gina]

Here is a circuit diagram of the triple telescope imaging rig power distribution and focus control and now with dew heater control added.  The use of complementary MOSFETs means virtually no heat generated and switching in the power line to the dew heater so the -ve line of the dew heater is always at ground potential.

[Gina]

Mistake!! That is NOT the circuit diagram for the triple imaging rig - it's for the single MN190 with dew heater control

THIS is the triple imaging rig with dew heater control though I'll probably get it going without the dew heater control first and add that later.  The Arduino Mega with feeds to the stepper drivers is already done so I'll just make up the power distribution box anew.

[Gina]

Mistake!! That is NOT the circuit diagram for the triple imaging rig - it's for the single MN190 with dew heater control

THIS is the triple imaging rig with dew heater control though I'll probably get it going without the dew heater control first and add that later.  The Arduin Mega with feeds to the stepper drivers is already gone so I'll just make up the power distribution box anew.

[Gina]

Made some progress on the mechanical side - mounted the Esprit on the top of the hefty aluminium plate and an ADM dovetail underneath.  The stepper motor to operate the Esprit focuser will be mounted on a bracket on the main plate and connected to the slo-mo knob with a timing belt.  Focus mechanisms for the ST80s are already in place on their own daughter plates (pinion and large segment spur gear as shown earlier in this thread).

I'm thinking of going back to the earlier manual alignment system for the ST80s, with a handwheel for RA and screw for Dec adustments with the four corner screws to lock down when the alignment has been completed.  With the vastly increased space I believe this will be feasible whereas it wasn't really with the MN190 scope in the way.  The locking screws could even have handwheels to tighten them rather than using an Allen key.

Here is a collection of photos showing the Esprit and ADM dovetail mounting plus the ST80 assemblies put in position.  (The Esprit is less it's dew shield in the photos.)

Main body of Esprit mounted on main plate.

ADM dovetail mounted on underside of main plate.

Focuser assembly (with field flattener and finder scope) attached to body of Esprit.

ST80 assemblies placed in position on main plate.

[Gina]

Been thinking about guiding.  I was going to use an OAG on one of the ST80s but there will be a long overhang and it will already have a 460EX pulling it down.  It's all screwed joints which helps but I've been wondering whether it would be better to use separate optics for the guide scope (LodeStar X2).  I have a 300mm SLR telephoto lens that I cound use.  I would welcome opinions, please

[Davey-T]

At your focal length I'd go for separate guide scope myself, save faffing around with OAG, no fear of overloading the EQ8

Dave

[Gina]

Yes, that's what I think.  I'm wondering now which FL lens would  be best.  Initially I though the 300mm f5.6 lens would be best being nearest in FL to the scopes (400mm).  But am I right there?  I also have 200mm f4 and 135mm f2.8 plus an 85mm f2 whaich has the advantage of already having a T2 adapter fitted.  I know many people use finder guiders with quite a short FL.  I have a couple of spare 9x50 Finderscopes.

[Dave Lloyd]

Super stuff Gina, I can only look on in amazement.

[DIYASTRO]

Hi Gina,

 have been thinking about this little problem myself since I started and hope to finish my final multiscope and have similar dilemma as yourself.

I think at the moment it comes down to tracking ability of the mount ...if very good then shorter /smaller guidescope with regard to f/l. the other side of the equation is light gathering power / field of view and  ultimately a view of suitable guide stars.

I do think that although a separate guidescope is more work it is infinitely better than OGA. .especially  if  it has capability of being 'tweaked' with regard to viewing angle to perhaps pick up suitable guide star.

This...My last? multi scope is a 4 x 100mm f4 imaging lenses with 4 canon 1000d's (but also able to use other cameras) using Ha,Hb,0III&SII with an 80mm at 190mm f/l (around f2.5) for guiding. All assembly mounted in my usual way in fork mount.

Hope to post images of this soon.

In essence, I have plumbed for a short f/l with wider field and lots of light to guide camera sensor.

Boyd

[Gina]

Thank you Boyd

Tracking ability of the mount is good but can probably be improved further by more careful PA.

With the LodeStar X2 and OAG on the MN190, I have had no problem finding a guide star even with that very narrow view, but maybe I've been lucky.  I agree with using a fairly large aperture and probably wouldn't want to go below the f5 of the MN190.  I think it's probably a case of "suck it and see".  The 300mm lens is quite a big heavy beasty and less easy to mount though I could use guidescope rings.  It would need mounting underneath the main plate as there isn't room for it on top.  I think the same applies to the 200mm f4 though a lot lighter and shorter.  There might be room for a 135 f2.8 lens and LodeStar on the top between Esprit and one of the ST80s.  Certainly room for the little 85mm f2 Jupiter Lens.

I'm a little bit confused by your last remark of "short f/l with wider field" for guiding when your imaging lenses are 100mm FL compared with 190mm for guiding though you don't say which guide camera you are using.

I look forward to seeing your photos

[Gina]

I checked the amount of space available between Esprit and ST80s and there isn't really room for a guidescope, even with quite a small lens, so I'll put it underneath.  The 300mm lens is currently in hiding so I think I'll try the 135mm f2.5 SMC Takumar lens.  Mounted using either printed plastic brackets or guidescope rings which I think I've got around somewhere

[DIYASTRO]

Hi Gina,

Sorry, I didn't specify very well but the four imaging lenses are 100mm dia. at f4 giving focal length of 400mm.

I am sure that since your tracking / mount is good that even a small guidescope would work since you have a sensitive loadstar camera. Placing the guide system undercarriage may have some advantages when balance is finally worked out so I would go with your feelings on that!

Hope you are feeling a lot better, you are keeping busy and I think that helps get rid of all sorts of things that try to put you down.

Boyd

[Gina]

Hi Boyd   I'm with you now - they're some big lenses

I'm feeling much better now, thank you   Still a bit of a cought but much better than it was and my general health is a lot better

Thank you for your concern