Thalestris24

Yeah, as I said, with a belt mod, you don't want or need East heavy. You want perfect balance in all three axes. People often forget to position the scope vertically and check it's still balanced ok i.e. stays in the vertical position without falling to one side. Of course, you also have to make sure your guidescope is rigidly mounted without flex - more critical with longer focal lengths. Louise

Hi Well, starting from having your eq mount pointed north, then the RA axis will track the stars from the East to West. By arranging for the balance to be biased slightly to the East, it will ensure that the weight of the scope will be pushing against the cogs of the RA motor and not able to 'flutter' around in between the cogs. Having a belt mod eliminates the motor cogs and hence the RA backlash. You can still have similar problems in DEC but you can reduce that via balance adjustments also or by being slightly out of PA, so that the scope drifts in one direction and is easier to manage. Similarly, a belt mod eliminates motor gear backlash in DEC also. There can still be issues with the worm gear meshing but you should be able to adjust that to minimise any problems with it. Pointing at the zenith can also be problematic and you have to think about readjusting balance as the scope moves down to the West. I should probably mention that it's a good idea to start of with correct balance in all 3 axes that the scope can move in. Then, if you don't have a belt mod, you can do your East heavy tweaks. This balancing malarkey can be slightly more trickier with a Newtonian than with a refractor, partly because of how a camera is mounted. Hope that helps. If I've missed anything, I'm sure someone will chime in E&O.E. Louise

Just had another, same-sized box of goodies to accompany the 0.5" mirror! Ho ho ho Merry Christmas, Thorlabs!

Remarkably good for such short exposures ! I can hardly pick up even much of a hint of a nebula in half an hour or more of 5 min subs Louise

It's maybe worth bearing in mind that alignments are only as good as your inputs e.g. lat long, time of day. Time of day on computer also. Likewise inputs to your Stellarium or other planetarium software. Louise

Make sure you're well-balanced and fairly close to being polar aligned before calibrating with PHD2. Having the Rowan belt mod is the best way of dealing with backlash but, failing that, it's recommended to arrange your balance to be slightly East heavy. Louise

Just had a delivery from Thorlabs Gmbh via UPS. It was a rather large and heavy box for a 1" mirror and a diffraction grating: German sweets, lol. Brought a smile to my face! I presume it was a 'first order' present! A 0.5" mirror due from them tomorrow... Time for a coffee and a sweet Louise

After all that I've had a second invoice from Thorlabs for the short-shipped mirror! Not very economic to separately ship a single 0.5" mirror but I think I'm happy! At least I don't worry about where to get one from now. Louise

Could be useful for a quick check! Louise

It has to fit in a small holder: Louise

Nice try but wrong size and shape! Louise

Nah, they don't do mirrors, and cost with shipping would be silly for just 1 x 0.5" mirror. It probably doesn't have to be particularly high quality either - it's just for guiding (via the reflective slit). It needs to fit the 0.5" holder but perhaps an odd bit of mirror tile might do... If only I had one and the skills to cut it ha ha. Louise

Oops! It's actually the 0.5"/12.7mm diameter (guide) mirror that Thorlabs don't have. Edmund do a similar one which is half as thick and is nearly £13 + shipping... Seems a lot for a tiny mirror! If anyone knows of an alternative source, that would be good to know Louise

I assume it was a post-design change. Wondering whether it might be as well to use a smaller lens but I suppose, in that case, probably couldn't get the longer focal length. When it comes to it, I'll experiment with a few things. I need to find a source for the 1" mirror but with the smaller collimator aperture, maybe a smaller one will do. Louise

No, but as with cameras, will change the depth of field. Louise

I'm looking at the collimator lens holder which I think had its design changed. Ken was saying last night about how the collimator lens focal length (lens specified at 125mm but measured distance = ~115-120mm) should match the distance between it and the slit. The collimator lens holder has the aperture stopped down to F10 - I'm assuming that's to achieve the match? It seems a shame to discard the lens aperture but must be necessary? Eric? Louise

There was some 'gossamer' but easy enough to remove manually Looks like some things don't quite fit together so will need some shaving or maybe a reprint with a slightly reduced size. Louise

It's printed out ok! Yes, the top of the slightly bigger than T2 holes do need a little emery papering But this was only meant to be a rough print though it does actually seem quite good. Thanks everyone for all the support and advice Louise

Yeah, it's top view. I just edited to show a more up to date design, though it's essentially the same case. I'll let you know how it goes! Thanks Louise

Thanks, James

Oh good, thanks for the reassurance! What's the chance something will go wrong overnight? It should look something like this (without the internal components): Louise Edit: Changed to more up to date image

Um, I know it's late in the UK but... Anyone about who knows how a 3d printer will print across a sideways T2 sized hole? Clearly I'm asking this because I didn't switch on supports... When I started printing I didn't actually mean to print the whole thing - just the base really. Then I thought - nya might as well just let it go on and on ha ha. It actually printed across a smallish aperture ok - 9mm dia. But will it cope with the larger one? I was thinking as it curves gradually it might be ok since all circles are similar (in a geometric sense)? It's not near to halfway up a T2 hole yet but will be whilst I sleep. Fingers crossed... Louise

Yes, I have your book! Louise

If I can manage to get my head around the details of the design theory, and also learn Fusion 360 well enough, I might try hacking an 'improved' version of the spectrometer some time in the future . Of course, one step at a time! Louise

I don't have any drawings with measurements (unless I can somehow get them from the stl or gcode files?). I have a printout of the assembled case which seems to be close to actual. On the printout, the measured slit to collimator via the mirror is ~105mm which is short of the recommended 125mm fl. The collimator to grating distance is about 25mm. As I say, I can change the lenses if I need to but recycling unused, old finders if I can seems kind of nice. Louise ps the Simspec you gave me seems to allow some variation of lens focal lengths?