marcopolo

Hi Jeremy, thanks kindly. I wrote an article about it and it was published in Astronomy Now April 2023. Yes Edinburgh!!

Hi all, i've finished my 1930's scope refurb and put it back on top of a permanent steel/concrete pier. The EQ head is set up for a latitue of approx 56degN and i've put it **ROUGLY** into polar alignment. The way Iv'e set it up with the M12 mount bolts it has full 4 DOF movement. The motor drive will get completed by next month probably so I want to try and understand how to accurately polar align and what my options are or if I need to buy some auxilliary equipment that would help. The problem is when I do searches on how to polar align they nearly all apply to tripods with EQ heads or scopes with setting cicles on the side and bubble levels. Mine has none of this, and I can find very little on the alignment process for a permanent pier scope. Here are a few pics so you can see what I mean. The 3 positional M12 bolts have captive nuts (you can't see them) that let the head tilt any way you want and the ends of those bolts are just pushing against the top of the steel/concrete pier (so not embedded in hte concrete). The centre bolt is simply to adjust height and rotation and lock it back down. So full rotation and tilt. It's totally solid BTW! Best option i've seen so far is the drift alignment method. But i'm open to suggestions. I've seen ASIair but it appears to be a full imaging system not just polar alignment and a bit expensive looking. Thanks, Marco.

Guys, I succumed to the dreaded "iv'e just no spare time for this syndrome". I got this second hand unwanted present on gumtree for £30 basically unsued, unopened. It appears to have no fieldstops/aperture stops internally. It gives nice crisp images right out to the edge of the field of view which is is surprise (even with the generic kelner 25mm included). So i'm just goign to 3D print some simple mounting rings. Will report back once it's done and tested! Here is the scope: (the 400f.l./70mm version) https://www.amazon.co.uk/Telescope-Astronomical-Magnification-Erecting-Eyepiece/dp/B07FJVWLKM/ref=sr_1_2_sspa?crid=1AW7HZBKKQNXK&keywords=70mm%2Btelescope&qid=1677517490&sprefix=70mm%2Btelescope%2Caps%2C80&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

Vlaiv, that’s actually a good idea. The only thing that would annoy me would be the fact the tube would not be a nice shiny metal finish. I’d still like it looking “manufactured” rather than printed or blue petered.

Great info Loius, exactly the kind I was looking for.

One of ther reasons i'm asking if anyone tried it was because the optics could be horrifc!!

Hi Peter, no problem for me . I'm an ATM'er, built many scopes, mechanical engineer, have CAD, 3D printers and mahining access etc...It's just an optical consdieration.. FYI i'll put it on a slider rail so I can also use it to tune OTA balance.

Has anyone tired buying one of the sub-£50 amazon 70mm refractors and using/mounting that as a finder? They come in 300-400mm F.L flavours ao I was going to plonk in a 40mm generic plossl I have to give an aprox 8-10 x 70. Obviously that makes the exit pupil a bit large but they generally come with a 25mm kelner anyway. There's going ot be considerable Chromatic aberation and i'd imagine a fair bit of pruple fringing but as a finder it could be OK. Finderscopes in the 70-80mm arent exactly cheap or widely avaialable.

Hi, so i've had first light with it installed (will try get a photo uploaded soon) There's no astigmatism present in the unfocused Airy disc, nice sharp images. No change in collimation when the scope is pointed at different altitudes. No loss of collimation ove rtime (over 3 weeks now) - so i'm actually extremely happy with the arrangement. TBH the whole fabrication was a bit of a faff but it does seem to be successful.

Thanks Vlaiv. Appreciated! I’m a mechanical engineering so no excuses for poor work!!

Did you see mine? All assembly details, BOM, files and CAD available. I looked ages online couldn't find anything descent, so designed and built this. There have been variants of it made since even motorised so folk are quite happy with it. https://marcosatm.com/2020/06/04/2in-crayford-focuser/

Thats it all farbicated. I ened up just using firbreglass in the mould. Concrete was not happy for a few re a treat.

All good. I threw it in all the ground, dumped some concrete in. made the steel tube plumb, aligned the tube square edge approx N/S. No mis-haps. Apart for a bird foot pattern. that was inevitable.

Making good progress with the 1930's Newtonian scope rebuild on cast iron GEM EQ mount. About 180kg for the scope+GEM mount/head. This weekend is dopping the pier in. I've got a couple of questions though one regarding alignment and two regarding the concrete pouring. I'll start with the latter. 1.The steel i'm using is heavy duty 6in x 6in square section 1/4in+ thick steel. I've got good long sections so how deep I go and how much sticks up above ground is basically how far I choose to dig. The thing i'm wondering is. If I backfill the hole AND the inside of the tube at the same time is there the chance that when the concrete level rises in the tube ABOVE ground level, will it try to overflow round the outside or can I just make the concrete viscous enoguh not to do this? My gut instinct is it will be ok if I tap down on the tube top it will ebbed a bit in hte bottom of the hole and therefore not flow out into the hole from the tube. However this leads to my next question.... 2. Is it better to float the base of the steel tube ABOVE the bottom of the ground a bit say by 4-6in so you have a continuous concrete piece running inside of the tube to the dug hole? (I could float it for example with a small strap of wood). Or am I overthinking this and just throw it in and pour? If the latter the internal concrete in the tube is pointless other than to increase overall mass (vibration dampening I suppose) as it's not pysically tied to the concrete in the dug hole. 3. I was going to alight the square tube ROUGHLY N/S with polaris by clamping a long baton of wood to one side, put my phone compass on the end away from the steel and settign to about 1.5deg E on my phone compass. Magnetic declination at my loaction is -1.05deg (W), polaris is at 0.43 Az (E). I'm not too worried as i've built about 5deg adjustment into the wedge interface anyway. but it would be nice to be close. Does this sound reasonable? Thanks, MArco.

Yep, good idea. I’ll definitely float the surfaces to a polish a few times during drying then seal with something…

Hi all, Ordinarily i'd make a 6, 9 point cell out of Aluminium etc....standard route for most of my Dobsonians. However this scope is a 1930's refurb - 7 .5in F8 Newtonian on a VERY heavy GEM. (200+ Kg all in). The existing mirror cell if I can call it that is a heavy brass backplate holding the mirror in with shims and no support so to speak. I'm adding the mirror collimation plate to this arrangement, keeping the heavy brass scope backplate that is presently serving as the mirror cell. So that all said the weight will make little or no difference. I have some 9mm ply I could double up (18mm) and RTV to that. It was simply to try something new/different. I might just give it a go simply because I can easy 3D print a mould for the concrete, drop in some threaded m4-m5 threaded rod or some steel mesh as concrete reinforcement. Embed the M8 collimation bolts (1mm fine thread pitch) in the concrete which is the other advantage. I literally have all the ingredients lying around my workshop to do this. Honestly not much more logic than that...just a bit of fun. I can't see it failing too easily. Thanks, Marco.

...the tumblewheel blew silently across the field of view as the other astronomers contemplated the sheer stupidity of the question........

Hello all. There's no shortage of crazyness here so I was wondering. In a simple RTV cell arrangement you have the mirror collomation plate that the mirror is RTV'd to usually from 12-18mm Ply or similar, MDF etc... usually for scope mirrors in the 6-10in region I was wondering. Has anyone ever tried making a concrete disc for this, probalby reinforced with some steel mesh? One of the reasons i'm masking is that the thermal coefficients of expansion are not that dissimilar. I realise adequately thick RTV will take up that difference anyway. But i'm just curious. Also you could just embed the collimation bolts in the concrete. thanks, Marco.

Hi Keith, unfortunately on the side you can't see in the picture there are bad rips...... On taking it apart it has a pentagonal prism on which the coatings were quite badly damaged, I managed to find and order this: https://www.aliexpress.com/item/4000937851400.html The one in the scope is 28mm. This one is 25mm. There might be slight vinetting but that's fine. Also I found this for the leather after Dave's advice (thankyou). https://www.ebay.co.uk/itm/221994857297?_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D2165177d3d2b49f0a027b2537e38873b%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D221994857297%26itm%3D221994857297%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A681b96ac-1bcc-11ed-a8b1-aa28687f22ec|parentrq%3A9c52725a1820ad3929ca6227fff9ea80|iid%3A1

Hi, yes, I use Accuscrews.

That does help, Thankyou. Much appreciated. I’ll report back after I’ve found a solution(s), kind regards.

Hi all, The 1930's scope i'm doing the refurb on i'm trying to keep as much original as possible. The finderscope needs a bit of TLC so Iv'e got a couple of q's and a bit of advice needed as i've never disassembled a prism assembly before. 1. The barrel has a leather covering over it and the leather is unsavable. Does anyone know a UK fabricator, even better in Scotland, that will make me a new leather sleeve? Synthetic or real. 2. Looking down through the 50mm objective it is clear the prism is corroded/damaged. Has anyone got a good web link to a way or replacing the prism or refurbing a finderscope. It is of course a RA finder.? Finderscope pics here:

Hi Sathya and Rob. That's my crayford focuser linked up there. You can also get the STL's over at thingyverse if you want. I plan on doing a 1.25in version as i've had a few requests now. Also someone had done a remake with a motor, linked in thingiverse and a 1.25in version. cheers, marco. https://www.thingiverse.com/thing:4424419 https://grabcad.com/library/2in-crayford-focuser-mk1-1

???Did you not see my comment?

That's it all assembled and running perfectly. Very smooth action. Lifts 750g no problem without a brake installed (yet). Chriske, I've moved the focuser wheel outboard and made much larger. It's a cinch with gloves on now.