Another primer on Mak cooling

[LewisM]

In restoring a Mak scope, I have had to totally remove the paint. This has left a rather attractive bare aluminium OTA, and I was thinking ... would it help in cooling a Mak faster if it was left bare?

I seem to recall some doing similar things to OPEN tubes like Newts, but insulating Maks, so would I actually be better served painting the tube?

I like it shiny :) (plus no paint 'n polish blues :lol:)

[Wavytone]

Hi Lewis...

There really is a reason why telescopes and observatory domes should be white.

A bare aluminium OTA is about the worst choice possible as it’s an excellent thermal conductor. I guess you also aren’t aware that cooling a mak is also not the best thing to do to stop the internal tube current. It has been pretty well established that insulating the OTA of maks (and SCTs) will both stop the internal tube current and prevent the OTA from cooling rapidly - this helps significantly with keeping the corrector dew free.

If I were you I’d have it powder coated in pearl white, there are places that will do it for a reasonable cost. Or have some sort of close-fitting insulating sleeve that fits over it.

Secondly pearl white will stop the scope getting hot if it’s in the sun, and minimises the radiative cooling to the sky at night.

I know some will dispute this however some years ago I had the chance to test about 100 cars and some samples of sheet metals with an optical pyrometer to find out how they perform in the real world in order to assess the range of temperatures that would occur in trains stabled in maintenance centres, and power required for air-conditioning night and day winter or summer.

Pearl white was consistently the best followed by the lacquer whites.

[LewisM]

Dang it, more painting...

How about satin pearl enamel? I have that already from a prior restoration.

Thanks Nick.

I already have made a thick EVA foam insulation tube that tightly fits the tube (I made a dew/light shield for a Tak refractor recently so know how to do it rather neatly).

I'll start masking tonight. HO HUM!

[Wavytone]

Satin or gloss won’t make any difference. Personally I’d get it done professionally as it should be grit blasted - paint adheres much better to a rough surface than smooth - and apply a primer before the final coats.

A DIY effort is going to look pretty awful IMHO.

I did some research recently as I’ve been thinking of repainting the MK91 OTA.

Or you could have one of the weird bi-colour paint jobs with a white base then a coloured clear coat over that. These aren’t DIY though. Maybe add some yellow/red flames, a long antenna with foxtail (extra wifi reception) and mount it on some wide chrome mags under for portability...

[Kunama]

A very nice score on the Santel Lewis, bargain of the century !!!

I tend to disagree with Nick on the bare aluminium thing and I think there are quite a few who would also go with bare aluminium though perhaps not on fully enclosed Maksutovs. Horses for Courses comes to mind.....

There is a good reason why Antony Wesley, Trevor Barry and Phil Miles all use bare aluminium tubed Newtonians for their superb planetary imaging....

Look forward to you treating this Mak to some "MichelangeLewising".

(Lewis's DIY efforts are way above the usual DIYs we see...)

[LewisM]

Thanks Matt - indeed, a super score!

It won't be bare metal - it's going to be Antique White USA from Dulux. All mixed up in epoxy 2pack ready to go.

[Wavytone]

Well I’m stunned to find you’ve joined this exclusive club, Lewis. Which Santel ?

I’m well aware this seems completely contrary to the long established mantra (must cool the OTA and force-ventilate it) but it has only been recently accepted that there really is an alternative - insulation - that is entirely effective at stopping the internal tube current and helps with dew as well.

If you do use insulation, the colour of the OTA is irrelevant if you’re going to wrap it in a cover of some sort. You could leave it bare or paint it black with pink polka dots if you like.

[LewisM]

Etch primed and ready for the top coats when the weather permits.

I should do a blog like Marc and the CN212 resto we did together

[Wavytone]

So which Santel is it - the 6”, 7” or 9” ? Pics ?

[LewisM]

6"

[Wavytone]

Have you tried it optically ? I think the CO is 33% so will be interesting to see if it’s any better than typical 6” SCTs

What’s the focuser on the back ?

[LewisM]

I think a cardboard toilet roll tube will be better than typical 6" SCTs :lol:

Helical focuser.

[Wavytone]

Hmm so it was not original. Any paperwork or a test certificate with it ?

And does it have the black intes finder with their unique attachment - there are at least 3 different variants depending on vintage...

[LewisM]

No, the focuser is original - paperwork proves it.

Intes finder is unique, yes... I wouldn't say the attachment is that "unique". Good, but hardly unique.

[Wavytone]

So its not this configuration re focuser and finder ?
http://www.stellaroptical.com/Images/Santel-MK6-b.jpg

Who issued the test certificate ? StellarOptical, Mike Palermiti, or Santel itself ?

FWIW In case anyone else is thinking of acquiring a large OTA secondhand from the US there is a way without paying a fortune - sign up with a freight forwarder (like MyUS) that charges by weight only - not volume - and have the vendor ship to them at their domestic rates. Then the freight forwarder will consolidate it in a larger shipment to Australia - which is where the big savings come in. And they can still use Fedex for that.

Shipping the MN86 this way cost a fifth of what the quotes were to ship it direct from the vendor. It was so reasonable that it was worth having the scope shipped inside its transport case rather than ditch that to cut the cost.

[LewisM]

The new paint was done yesterday afternoon.

Today, I redid the finder base and the primary backplate.

The front of the corrector plate is now spotless (came away as a BLACK kimwipe!). The primary was spotless already (and looks like it won't need a resilver for even another 20 years).

All mounting hardware either resprayed satin black, or cleaned with turpentine.

Interior blackening is FLAWLESS and VERY non-reflective, so nothing required there. Front tube cap resprayed satin black, with a touch of personalisation that will be revealed when it is finished. New data plate arrived from my printer today.

Starting on cleaning the visual back and focuser.

Decided at this point to use an new old-stock Vixen finder, as I find the Intes finder NOT user friendly eye-relief wise (for me). I may yet modify and fit a Baader Vixen shoe onto the spare screw spots.

This one was too far gone exterior finish wise to keep it totally original, hence I had the data plate made that indicates "RESTORED 11-18". No bluff and BS here. It is what it is.

[multiweb]

It should say "LEWISED".

[LewisM]

Is that a PC way to say it's Effed?

[multiweb]

ye of little faith.

[Wavytone]

So when will “first light” take place ?
And does this mean a Mak vs Tak event ?
Will those little Jap scopes be driven out by a Russian invasion ?

[LewisM]

I always let paint cure 3 weeks to a month, so first light is a ways off yet. No rush with the crap weather anyway.

[Atmos]

I’d be interested in putting a M250 up against a few Maks!

[Wavytone]

Hi Colin, did you mean a Meade 10” SCT ?

[LewisM]

Colin means a Tak Mewlon 250

[Wavytone]

Here's the bad boy :) and it's mint, despite its age...

[netwolf]

Drool... will just have to dream and live with my skywatcher 7” for now. Very hard to find

[raymo]

Everything is relative; I'm sure that there are people out there that would
love to get their hands on your SW 7 Mak.
raymo

[Wavytone]

Well, if you have one in good shape, look after it.

[LewisM]

Ok confession time - it’s not a Santel :) Just a plain Jane Intes from 1994.

Now that Tom foolery over, here it is now restored. I decided to make it in the more recent white as the original “spiky” grey wasn’t going to happen. I did however match the grey on the finder base and the rear backplate. The original grey on the tube had suffered someone leaving masking tape on it,which they then removed taking a massive piece of paint off.

I have had the Intes decals made, but may not put them on. The silver data plate I had made will be enough (not yet fitted - probably later today).

[LewisM]

Incidentally, the Intes grey is VERY close to early Tak green. It matches Dulux “Moorlands” perfectly (Intes, not Tak). I airbrushed it on and had a hard time seeing what I had painted. Absolutely perfect match.

White is Antique White USA, made up as 2 pack and gunned on. 3 coats, semi gloss (more half way between gloss and satin :lol:)

[Wavytone]

Lewis having seen the bare metal, did you have any idea whether it was machined, rolled (and welded) or pull-truded ? Two of mine are 3mm thick aluminium and I have a feeling they’re machined out of thicker tube, not rolled sheet.

[LewisM]

100% MACHINED from solid. This is VERY VERY military - the walls are indeed 3mm thick! No seams, no welds, and in fact, mine has a step mid-tube where it becomes even thicker for the primary.

[FlashDrive]

OK Wavey .... your being cruel now .... :prey:

[LewisM]

First "light" - looking 200 metres away to the car park :lol:. Which was a challenge given the f/10 focal ratio, meaning I was running out of focus! (had to actually ALMOST remove the EP to come to focus).

Verdict: NOICE, really really really NOICE! Tak nice, no doubt about it! VERY pleasing colour rendition, VERY contrasty and exceptionally sharp. The helical focuser inbuilt into the diagonal/visual back is VERY smooth and rather easy to use.

No chance of using it on the stars for a while though. Ho hum.

Using it on a Manfrotto 3030 tripod isn't ideal, but it got the test done at least. Now I regret selling my vixen GPD - got to find another one now!

Also shown is the custom data plate I had made for it, complete with Intes logo, Russian "Made in Russia Moscow 3.94" and "RESTORED 11.18". The decal that was on the backplate (where the data plate is now) replaced the very worn, peeling one on the diagonal, so NOTHING was thrown away (even the original decals are still attached to an A4 card stock sheet in a photo album - they came off in one piece). The original finder is sitting in my spares drawers (I swear the "Tourist" branded scopes sold in Russia in the 80's and 90's are the SAME scope without the reticle!) - the Vixen 6x30 works wonderfully in this role.

[Wavytone]

Ah ok it’s an early MK65 with the cemented secondary mirror. Now I understand about the helical focuser. Later versions had a modem star diagonal and the handle on top of the OTA.

Congratulations Lewis, this is only the start. Push this to the max on the moon and planets and look carefully, very carefully. I’ll also suggest you consider making a dew shield for this that extends 150-200mm, it will enhance contrast near bright objects (Jupiter and the moon especially).

I bet your Taks will turn a shade of pale green.

[LewisM]

This has a handle on the OTA. The secondary is not cemented either - it is aluminised to the meniscus. The diagonal is incorporated into the visual back, with a helical focuser at the EP holder side.

[Wavytone]

Ok, yet another variant...

[LewisM]

Rarer than a Santel :P :lol:

[LewisM]

Tried it today terrestrially in bright daylight (rather than dusk yesterday), trying a range of EPs.

It LOVES the Parks/Antares 25mm and 15mm "pseudo-Masuyamas" (then again, all my telescopes do), nice with the Masuyama 20, VERY nice with the Tak LE12.5 and Vixen NLV 15 (though I felt the Antares 15 was better for colour rendition, since I prefer warmer tones). The NLV needs the rubber eyecup rolled down for me too.

VERY flat field too - leaves at the edge of the field looked for all intents and purposes identical as those near the centre. Defocusing solar reflection spots on parked cars showed also very nice rings and a centred secondary, so I guess I reassembled it spot on :lol:

Have a GPD coming eventually, so the mounting issues are also sorted out.

[LewisM]

Having used it now on the Moon (early morning), I disagree with this comment.

The image is EXCELLENT indeed, but NOT as good as a refractor, simply because of the "shadow" of the secondary. It is quite noticeable to my sensitive eyes on bright objects, and in my opinion, distracting. I find this with ALL reflecting telescopes - one of the most obvious to me is the Mewlon (REALLY distracting) and any of the Schmidt-Cassegrains. It is something my eye-brain cannot "put aside", and it doesn't matter what size secondary there is - I always see it.

As I said, the image presented is exquisitely sharp, but the differential dimming is a distraction to me.

So, no, the Tak refractors are whistling merrily.