ST80 Mods for Imaging

[kev]

Great results Gina.

Sent from my iPhone so excuse the typos!

[Gina]

Thanks both

[Gina]

Now thinking again about alignment mechanisms.  The present system is both too stiff to adjust and not stiff enough to avoid flexing   Seems the solution is not in 3D printed plastic - unfortunately a 3D printer is not the solution to all problems

Been thinking in terms of thrust ball bearings or maybe thin PTFE sheet.  Even milk bottle plastic worked well for the azimuth adjustment of the EQ8 mount.  Maybe a similar system would work for the RA scope alignment.  I have some 0.25mm thick PTFE sheet somewhere

[Dave Lloyd]

What's HOO?

[Gina]

HOO is where the Ha and OIII are out on the RGB channels viz. HOO stands for Ha, OIII, OIII and Ha is applied to the R channel and OIII to bot G & B channels.  (RGB = Red Green Blue)

[Dave Lloyd]

Thanks, I really, really must get that M.E.P.C book.

[Gina]

Been searching my many boxes for pieces of aluminium that might be suitable for making alignment plates for the ST80s and found two pieces that I bought a while back for another project for which they are no longer required.  These are 200mm x 150mm x 4mm thick.  Larger than I was thinking of but I think will be suitable for this project and could save buying new.  The diagram below shows how I might use these.

I have coloured the diagram to help explanation.  The light grey is the heavyweight main scope mounting plate - 400mm x 250mm x 10mm thick.  The darker grey is the ST80 mounting plate I'm proposing.  The scope ring pads are shown in black, the focus gears in yellow and the stepper motor in blue.   Not shown is a plastic block between the motor and the ST80 mounting plate.  Attaching the focus stepper motor to the new mounting plate ensures that the relationship between large focus gear and motor pinion is maintained while the alignment is adjusted.

With this arrangement the plate and scope mounting rings can form one solid structure whereas the arrangement I have at present has the scope rings mounted and adjusted separately.

The new plate can slide on the main plate to adjust the RA alignment - like the EQ8 azimuth adjustment, with pivot bolt one end and adjuster the other end.  I have yet to work out a Dec adjuster.

[Horwig]

I know you like toys Gina, but is a stepper controlled adjustable alignment plate absolutely necessary? Surely, once aligned and locked down it's not going to drift. Would a length of threaded bar through a captive nut sort of arrangement not do it, with set screws then to hold it's position.

Not that I'm even thinking of cramping your style you understand.

Keep up the good work, reading your posts gives me something to do whilst it rains.

Huw

[Gina]

I won't be using steppers for alignment Huw   In fact I plan to do exactly as you suggest with a threaded rod

And I think the Dec adjuster will be a simple rocker arrangement with screws in tapped holes.

[Horwig]

:mad:  Gina, I've looked again at the drawing, It's either the red wine or the lack of grey cells, the bits in yellow and blue are the focuser, not the automated adjuster I was imagining, what a chump, back to the red wine with much embarrassment.  

Huw

[Gina]

Not to worry Huw - we all have such moments   I have had too sometimes even though I don't drink - just rather "long in the tooth" as they say

[Starlight 1]

Hi Gina, I love seeing your posts way over my head, So what you are trying to make is something that works the same way as a red dot finder works.

PS as in left and right and up and down.

[Gina]

Basically, yes, that's right   But it's carrying a lot more weight than a finder   And needs to be a lot more accurate and rigid.

[Gina]

I think I have a plan...

The width and thickness of the mounting plate will be a big help in providing rigidity.  Two bearings near the edges of the long sides will provide good rigidity to stop sideways twisting.  One of these bearings will provide a pivot/fulchrum for rotary and lever type motion while the other will allow motion along the main common plate at right angles to the line between bearings (hopefully another diagram will make this clear).  A captive nut and threaded rod will provide adjustment in the RA direction ie. along the surface of the plates.  A knob attached to this will provide manual adjustment.

For the Dec adjustment the mounting plate will rock on the two bearings like a see-saw with two screws in threaded holes in the thick scope mounting plate (the 10mm thick one).  Adjustment is by loosening one and tightening the other.  Or I might see if I can incorporate a spring to allow adjusting just one bolt and then tightening the other when the right angle is set.

Diagram to follow...

[Gina]

I'm afraid the diagram will be a while - I've come across some snags with the current thinking and need to make some changes.  Working with the hardware and SketchUp together has come up with some clashes

The large focus gear gets in the way of one of the adjuster bolts.  However, once the focus is reasonably close there is no need for a full 360 degrees of teeth to mesh with the pinion so I can redesign that part as a sextant or less.  This would also mean the radius can be increased meaning less pressure on the gear teeth.

[Davey-T]

Don't know about you Gina, it's making my brain hurt 

Dave

[Gina]

Here is a SketchUp screenshot of my new large focus gear design.  Shown in the fully anticlockwise position up against the scope ring and again in yellow.  It has twice the radius of the previous gear so just half the pressure on the teeth.

[Gina]

Don't know about you Gina, it's making my brain hurt 

Dave

I admit, I am struggling a bit

[Gina]

Now back to the alignment adjusters...   Hmmmm................................

[Gina]

I've got a lovely clear sky and two imaging systems working trying to set up on the Pacman for some more Ha and OIII data.  BUT I seem to be having a problem with the EQ8 mount.  I set CdC and EQMOD ASCOM to park to the Home position and roughly aligned the scope to point to the pole.  Then I slewed to the moon but it was several degrees off.  So I did what I always do - realign the mount onto the moon using my finder scope.  And yes, moon nicely centred in both imaging frames.  BUT CdC now shows the frame several frame widths away from the moon yet I havent touched CdC and the tracking is set to Lunar.

I have tried to get AstroTortilla to plate solve and slew to the Pacman using an image from the other night.  That image solved fine and the scope ended up pointing in approximately the right direction.  But when I tried to plate solve an image from the Esprit (the scope I use for setting up) AT wouldn't solve - not even with the coverage set to 180 degrees and using 15s binned 8x8 (I usually plate solve with 10s and 8x8 which has worked fine).  I'm getting over 200 stars to plate solve on which should be more than enough.  But it just won't.

I'm baffled - anyone any ideas please?

[msh1]

have you synced on the moon in cdc

mark

[Gina]

have you synced on the moon in cdc

mark

No.

[Gina]

Damn - lost my post   Have to retype it

I've found my target by roaming round the sky in the vicinity, adjusted it to the centre of the frame and set up PHD guiding.  Now capturing data in Ha and OIII with the ST80 and Esprit respectively.  As before 5m subs binned 2x2.  The seeing doesn't seem quite as good tonight as the other night though.

CdC is showing the imaging frame way off the mark.

[Gina]

Back to alignment adjusters...

I think I shall put the fulchrum for the Dec adjustment at the objective end of the mounting plate.  Then use a screw in a threaded hole in the 10mm plate pushing up against the scope plate (4mm) with a spring to push the plate against the screw, at the other end.  I have sucessfully used ABS plastic as a spring for other projects so I think I'll do the same here (unless I can find some suitable steel springs).  After adjusting, the plate can be fixed with screws in each of the four corners going into threaded holes in the 10mm plate, the clearance holes in the 4mm plate being big enough to allow sideways movement for the RA alignment.

For RA alignment I plan to use the bolt head of the objective end scope ring fixing as a pivot in a matching hole in the 10mm plate (already drilled).  The final fixing screws in the corners that end will be slightly slack to allow slight movement, with washers to space the 4mm plate away from the 10mm plate to allow for both up and down Dec adjustment.

I have yet to add the RA adjuster screw to the diagram but here's what I've done so far.

Overall View

Corner Detail

Plastic Spring (Green)

Dec Adjuster Screw

[Gina]

Most of the RA alignment adjuster (blue).  Haven't shown the square nut that's captured in the blue bracket slot, for clarity.  Nor the locked together nuts on the far side of the block that match the ones shown and stop the threaded rod moving in/out.