alex_stars

That's a very reasonable plan, no question and I fully hear you on the "long term endeavour" of saving up to a Mewlon. I bought my OMC140 used for about 1/3 of the price of a new Mewlon 180, so there you go. I kind of got stuck on my stopgap scope and I do enjoy it. Towards the Mewlon it might be cool to try the CC8 first, especially used. It shares some features with the Mewlon, like an open design (similar cooling?) and the spider vanes (and diffraction) holding the secondary mirror. So you might get a feel of how a Mewlon might be.

Hi @Ags when it comes to planetary visual observation, which is what I do mostly, I so far tried: 5" Skymax (too small) 180 Skymax (a nightmare to cool, seriously) and with bad focus behaviour (as the mechanism in the skymax 180 can be of poor quality, at least compared to better quality scopes) in my unit 5" APO f/7.8 (the TS one), really nice views but too big too handle for me, else really great OMC 140 Mak, which is a beast it itself (cooling) and can be of poor build quality, however great if it works Currently I'm stuck with the OMC140, which I spent quite some time optimizing (see here) and testing/collimating (see here). This is a great scope, at least my unit, others might be different, however I dream of a Mewlon 180. If I would redo my journey with planetary scopes with the knowledge I have now, I would straight go for the Mewlon 180. You can skip the Skymax 180 (which is actually a 172 mm AP scope with a 34% CO, see here) in my opinion, but hey just my thoughts on the matter. And BTW, I really like Maks too, not joking. Looking forward to see what you end up with! All the best.

To test the new insulation, I recorded more thermal data last night. Similar to the post above, I recorded temperature just below the insulation on the tube (green line), inside the baffle tube at the location of the primary (blue line) and the outside air temperature (red line) As we can see in the temperature difference plot, after about 3 hours of adjusting to the outside air, the difference between the OTA outside and the centre is at its minimum, and then raises to about 0.5 °C, where it remains constant throughout the 16 hrs. Thus a couple of hours adjusting period before observing should just do nicely to avoid any major thermal currents in the tube. Still have to confirm visually if the tube currents are minimal, cause currently there is only 🌧️ CS, Alex

Thermal Insulation, part II I was not completely satisfied with the thermal performance of my two layers of aluminium bubble wrap and recently redid my thermal insulation. The reason for doing so was that I compared thermal conductivity (k) values for different insulation materials and wanted to aim for the best insulation I could find in order to maximize the thermal inertia of the scope. Here are the values I looked at: thermal conductivity of aluminium coated bubble wrap: approx. 1 W / m K [that would be Watts per meter and Kelvin] PE, EVA and similar foams: approx. 0.035-0.04 W / m K air: approx. 0.025 W / m K So air, if you could keep it still, would be best, but I went for a 1 cm thick EVA foam plate with aluminium coating on one side, which you can find in the form of camping mats. Here are some images: Made a new finderscope mount (stainless steel) so that the insulation fits nicely in between. Crafted a paper template for the back, including small holes for the collimation screws (just in case I want to work on those) Double sided tape to fix it to the OTA finished scope on the mount. Closed the back with aluminium tape. Now I just need to wait for clear skies to test the thermal behaviour. CS Alex

Interesting indeed. My 2017 OMC-140 deluxe carbon tube OTA has no cooling vents. Did/does the OMC 200 have those?

Hi, not sure if it is relevant still, but I own a carbon-fibre OMC 140 (deluxe version). The advantage of the pre-carbon tube would be a better cooling behaviour. The carbon tube is a nightmare to temperate, so I personally do not see any advantage of the carbon OTA. If, and that is a big IF, the focuser is working flawless and the primary mirror is not tilted (due to cork rings giving in), than I think it is worth considering. A SW 150 Mak costs more new and is a whole category lower with respect to the focusing mechanism. I owned a SW 180 Mak and a 127 Mak and both were not comparable to the OMC 140. However I would not buy any OMC-140 without trying it on-site and check for the issues mentioned above. If it is all good, I think the price named is ok, not a bargain, but OK.

just a quick add-on to this collection of information. I wrote up my favourite daytime collimation technique in a different thread. That method extents the method described above. https://stargazerslounge.com/topic/406851-precise-daytime-collimation-of-a-makutov-cassegrain-projection-method/ CS Alex

you can also find my German version here https://forum.astronomie.de/threads/praezise-kollimation-eines-maksutov-cassegrain-bei-tag-projektionsmethode.339785/

Greetings fellow stargazers, At the moment I am tinkering a lot with my Mak (OMC-140) and therefore I am constantly re-collimating the Mak. Yesterday I worked on the real star again, but today I would like to introduce you to a possibly "new" method. At least I haven't seen it anywhere in this form. It is based on two well-known daytime methods and combines them: The "daytime method" described by Robert Casady The "kitchen table method" described by Russ Slater Both methods should also work for all Cassegrain type scopes. I only have a Mak so I can only confirm that it works very well that. Now what do you need to try this method: checked A4 sheet or graph paper (if you want to be very precise) a piece of cardboard, similar size than the A4 a compass to draw circles pen double sided tape a mobile phone with flashlight (LED next to the rear camera) photo tripod your telescope and the wrenches to collimate a table your eyes (and optionally a camera or a Cheshire eyepiece [can also be homemade] And now it's time to tinker I) The collimation target: To make one, you first draw a crosshair in the middle of the A4 sheet, whereby the lines should be at least as long as your telescope aperture. Then you take the compass and draw concentric circles from the centre of the crosshair. In my case the telescope has an aperture of 140mm and a central obstruction of 44mm, so I make the following circles with these radii: 25mm, 35mm, 50mm, 63mm, 70mm and 90mm. One circle should be slightly larger than the telescope's obstruction (that's 25mm for me) and one slightly smaller than the aperture (that would be 63mm for me). Now the A4 sheet is glued to the cardboard and the central hole from the compass puncture is enlarged with a needle to about 1 mm in diameter and extended through the cardboard. At the back of the cardboard you tape the mobile phone with the LED switched on behind the hole in the target so that you have a collimation light source. The collimation target in the end looks like this: The target is now clamped on the photo tripod and is ready to go. II) Alignment of the telescope: Put the telescope on the table with the dovetail bar down and place the collimation target in front of it. I start with the front edge of the telescope about 50 cm away from the collimation target. You have to align the telescope and the collimation target so that the optical axes are the same. To do this, you first set the height of the tripod such that the innermost bright circle of light that is reflected by the telescope is exactly at the level of a drawn circle and the horizontal crosshair line. For horizontal adjustments you can move the tripod or the telescope. I align my scope and target by centreing the smallest shadow ring and the following bright (is the brightest) ring so that it fits exactly into my R=25 mm circle (see picture). III) Collimation Now you can go ahead and work with the collimation screws until all projected circles (dark and light) are as concentric as possible. The picture above shows a good collimation for me. Important! If you turn a collimation screw, the inner brightest ring moves out of the circle on the collimation target. After each movement of a collimation screw you have to (!) re-center the brightest ring on the collimation target to align the optical axis. You can do this either on the tripod (especially if it has moved vertically) and also horizontally on the telescope itself by turning it slightly on the table. The checkered paper or graph paper helps with the exact adjustment. You will be surprised how accurate and sensitive you can adjust with this method. IV) Final Collimation check After you are done with the projected circles, you should look through the eyepiece clamp or use a camera (or Cheshire eyepiece) to check the adjustment from eyepiece clamp side of the scope. In the middle is a huge Poisson spot (rather a disk, right?) which helps you to find the optical axis here as well. If you are satisfied here too, the telescope is officially collimated. You can of course fine-tune the collimation on a real (or artificial) star. Colleagues who do a lot of photography in particular will agree. But I have to say that for me, who only works visually, this collimation method is completely sufficient. I hardly ever see a reason to improve on a star when I check. Have fun trying this method and post a comment with your experiences. That would be great! CS Alex Additional info: This method assumes that the secondary mirror is centred in the tube and also centred with respect to the centre of the eyepiece clamp. At a commercially available Makustov you can't adjust the secondary mirror position anyway. If a de-focused star does not have its Poisson spot centred when the de-focused star is centred in the eyepiece, then it is likely that the secondary mirror needs to be re-centred. Either complain to the manufacturer (if you just bought it) or try it yourself, but that's another story. I've never had to do this. It is also assumed that the baffle tube and the eyepiece clamp are in the middle of the tube and are not tilted in relation to the optical axis. These types of adjustments cannot be made on a commercially available Mak either, so the same applies as above for the secondary mirror.

As I had my OMC-140 opened up today to clean the mirror (just blowing air) I thought I'd post some images for comparison with the other ones posted above: Micrometer focusing screw and how it is mounted in the foreground. The screw to the left is one of the collimation screws. Detail of the focusing mechanism. Noteworthy is also that the mirror now rests on a plastic washer and not only a cork washer as in the old days (mine is a 2017 model according to the previous owner). When you look at the baffle tube from above, you'll see that a cork washer is still present. Anyhow all looked good to me and the mechanics really do work smoothly. Disassembly of the back-side primary mirror is really easy: mark the orientation of the rear cell with respect to the carbon tube (I used red tape as can be seen above). Loosen all the screws at the rear end of the carbon tube, which are on the carbon tube. You do not need to loosen any screws on the backside of the scope where the visual back is mounted. Start with the dovetail mount and its opposite counterpart. Those a four screws. Continue with the three tiny screws which are at the same radial locations as the collimation screws. Place the scope downward on the table (meniscus lens downward) and pull (gently) the back of the scope upward to remove the rear cell. Assembly is just those steps backwards with the addition of a quick collimation at the end. Clear skies everybody, Alex

Hi All, just a follow up for other owners of the Giro Ercole Mini, and probably the Ercole model as well. I got in contact with the manufacturer of the mount at "Teleskop-tecnica" or "Tele Optik Tecnica". Anyhow Giovanni told me the following, which is of interest to everybody owning such a mount. A slight radial play is normal and as long as it disappears with tightening the friction brake a little, the mount is fully functional and not damaged in any way! The Ercole mini is greased at the factory even though the bearing bushings (collar bearings) from IGUS do not require that. This is done to make the movement even more smooth. There are two bearing bushings in the azimuth axis and a bearing plate between the moving parts of the base (ie the head itself and the bottom where the mount is mounted). Over time the grease leaves the bearings and some radial play becomes noticeable, but the function is not diminished. User tip no 1: Don't try to grease the bearings, it is not necessary! User tip no 2: Always keep the azimuth axis break slightly engaged (tightened) when transporting or mounting the mount to avoid that the bearing plate opens a little. User tip no 3: Use counterweights to balance the azimuth axis, this makes the azimuth movement smooth (I guess we know that 😉) and lets any axis "play" disappear. Double thumbs up for customer support at Teleskop Tecnica 👍👍 and I'm gonna enjoy my mount! Clear Skies, Alex

Hi all, I just bought a Giro Ercole Mini mount used and was wondering how much radial play (hope that's the correct term) the azimuth axis should have, given the azimuth axis break screw is fully open. Maybe to explain further. If I open the altitude axis break and try to tilt the axis with my hands, I feel no play whatsoever. I observe the same when the mount is fully loaded with my approx. 5 kg scope. However when I fully open the azimuth axis break and "wiggle" the azimuth axis, I feel that I can tilt that axis a bit. It is also visually observable on the whole mount, not much, but the azimuth axis is not "play" free. I can almost get rid of that radial play when I tighten the azimuth break just a bit. Then the azimuth axis still moves quite freely but the radial play is almost gone. In practice, when I observe, I have no issues with the mount. When loaded I can move the azimuth axis nicely and very smoothly even with the azimuth break fully open. But I was wondering if the observed radial play on the azimuth axis is normal, or if the pervious owner has overloaded the mount and thereby damaged the plastic bearing bushing on the azimuth axis. Any comments from Ercole Mini owners would be very much appreciated. Clear Skies, Alex

True, very accurate collimation should be done on a real star. Thanks for the feedback! I sometimes check visually the diffraction patterns on bright stars when I take out the scope, but on those occasions I don't image through the eyepiece.

Collimation check, artificial star Today I had the time to check my collimation on the OMC-140 with an artificial star setup at home. I dropped a needle on some aluminium foil to make a "tiny hole", placed it in front of a strong LED light and then had a look at that artificial star with my scope from about 15 m away. A quick photo with my smartphone showed this: The black cross-hair is from my 23 mm eyepiece, however the red, concentric circles I added later with software. To me this looks quite acceptable for the purpose of collimation. However the artificial star is not far enough away to test for defects in the optics, but that is some other task for later. Comments are welcome!

Thanks for the fast reply @Victor Boesen. Funny you mention the Girol Ercole Mini. I just go one used for a cheaper price than the Castor II so I went for that one. I will post my experience here after I set everything up. Alex