None orthogonal Tak Reducer - NA Nebula

[kirkster501]

Been months since we had a clear night in Nott's.  Last night was still slightly milky skies but beggars can't be choosers.....

I noticed that on my FSQ85 reducer the grub screws at the scope end were a fraction loose such that the images I'd just taken - only five fortunately - were out on one side due to the focuser not sitting precisely squarely.  Corrected it now but heres the result of this at F3.8.  Blobbiness at the top left and, to a lesser extent, bottom left.  At least, I hope this explains it!

Steve

[ollypenrice]

These are the three tiny grub screws on the reducer itself? If so I had this myself. I suspect that Tak want to build in a bit of tilt-adjustability but it isn't terribly well done if that's the case. I just put the reducer (scope end down) on a flat surface and pressed the rest downwards as I tightened the grub screws. Thereafter they remained perfect.

Olly

[kirkster501]

Good tip and way of doing it Olly. I may redo it. Thanks

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[x6gas]

I too am having the same issue with the orthogonality of my Takahashi reducer.  For a company that makes such fantastic optical systems I wonder why on Earth they thought the mechanical construction of this reducer was a good idea.  When I first got the reducer (and before I tried to fit it) I assumed that the ring with those grub screws was to be used as a fine adjust for the metal back distance but, of course, it's at the wrong end of the reducer for that so I can only assume that Olly's guess is correct and that it's intended for tilt adjustment.  If so a very poor solution...

I've tried Olly's suggestion to get the adjuster ring snug against the bottom ring of the reducer so we'll see if it has improved...

[kirkster501]

Yes, I am not happy with it either mate.  The grub screws easily round off as well.  I am looking at getting some thumb screws from Boneham and Turners for this and following Olly's method.  Allen bolts are utterly useless when as small as they are on the reducer - they round off very easily, with nasty results if you can't get the bolt out.....

[ollypenrice]

A few words from the Sphinx-like Takahashi themselves would go a long way here, no? Don't hold your breath. I'd try Texas Nautical Repair if the problem persists.

Olly

[kirkster501]

Not too sure what the M size is of the Allen screws on TAK reducer.  I will take mine to Boneham and Turner  and get a few thumbscrew versions of that size and see if that would work and nothing in the imaging train will foul.  When, I do I will get a dozen or so - they only cost a few pence per piece - and send some pictures.

[kirkster501]

Some PM's I have received indicate we are not on our own with this issue......

[x6gas]

Some PM's I have received indicate we are not on our own with this issue......

I can't say I'm surprised.  I hope that following Olly's advice will have eliminated my problem (and hope to be able to check tonight).  If not then I'll be looking to put some kind of spacer or washer between the reducer and the scope so that tightening down the screw thread will actually tighten the reducer against the scope.

If Takahashi felt that tilt adjustment is required then they really should have done the job properly.  And while they were at it they could have put a nice helical space adjuster on the camera side of the reducer to allow fine adjustments to metal back.  The glass is expensive enough, after all...

[swag72]

I can certainly vouch for whatever Olly did with the reducer. It clearly did the trick and is still going strong........... There's the kiss of death no doubt  

[x6gas]

I'll be looking to put some kind of spacer or washer between the reducer and the scope so that tightening down the screw thread will actually tighten the reducer against the scope.

I'd actually managed to get a reasonably flat field but I forgot the golden rule of good enough being good enough and not striving for perfection... Also my curiosity got the better of me and I wanted to know how it goes together.

The idea above won't work because there is no shoulder for the locking ring to push against.  It's entirely at the mercy of a circular dovetail.  I suspect that trying to tighten the grub screws too much could throw the reducer out of true so it's probably better to just nip the screws up.  So long as they can't come loose this should be fine as any pull downwards will tighten the grub against the chamfer of the circular dovetail.

I dislike the grub screws on this too as I am paranoid about getting them out if I should ever need to.  At least Takahashi use a standard M3 thread for the grub screws (it would be more in keeping with their usual modus operandi to use an obscure and impossible to come by Whitworth thread!)  I've replaced mine with some standard PC hex chassis bolts: about the right length, easily tightened and undone with a screw driver and if the cross slot ever mars then I can still use a hex socket to get them off.