Piero

The new mirror cell was built based on the Kriege design. There are more modern designs, but this is simple and effective. It is a 6-point mirror cell. A 6-point mirror cell gives the same performance of a 9-point mirror cell but is much simpler, therefore it is easier to get it right. Also, it can be upgraded to 18 points any time. All metal is stainless steel 304. I did not find too difficult to work with. After drilling the holes, I cut (yes, that's correct) the bottom of the original mirror box, so that this could be used as a frame for welding the new cell. The cell was tack-welded in the frame first. Then the welding was completed and the mirror cell was cleaned / sanded: Finally, it was sprayed with grey primer and then flat black: A real Glatter's sling was installed. This is the assembled mirror before cutting the cable to the correct length:

Mirror cell Well, this is the part I disliked the most. Here's the original: When dismantling it, I also found out that the triangles are quite asymmetric with each other. Quite embarrassing really. It is not that difficult even for an amateur to cut aluminium and make precise holes at the same position. Apart from aesthetics, these errors affect back mirror support.. See here: Despite of being advertised as an excellent mirror cell, here is a summary of the problems for this design: 1) sling cable positioned at 1/2 mirror thickness instead of at mirror COG. Also, cable was 1/4" thick, whereas it should have been 1/8" thick 2) sling cable passed through side stoppers, squeezing the mirror 3) triangles were asymmetrical (points in inner ring were 10mm off from what they should have been!) 4) triangles locked by screws whose threads blocked triangle floatation 5) triangle barycentre (holes of collimation bolts) not optimized by PLOP. Likely determined arbitrarily (looks like to be 1/2 radius) 6) 3 side stoppers blocked the mirror so tightly to cause serious aberrations 7) 2 panels of 18mm thick plywood caused the mirror to cool down incredibly slowly and in an unpaired manner. Also, the cooling fan was almost ~65mm away from the back of the mirror. This was too distant to be effective. Needless to say that his horror mirror cell had to go. Literally, I removed the metal from it and it went down the green bin as that is the place it belongs to.

UPDATE After building my 16" f4, the future for this telescope became somehow uncertain. It was put on sale for about 4 months, but apart from a couple of potential buyers, it did not attract much, despite of the large discount. Therefore I decided to remove it from the second hand market and redesign it in order to make it more portable and compact. I will soon move out to a new location at some point this summer, so the 16" will be used at home, whereas this 12" will be left at ambient temperature in the garage, ready to be picked up for short trips to the darker countryside. Changes.. well many. I addressed all the components of the original telescope that I did not like much or that I would have liked to be be different. In contrast to the previous pages in this thread, in which I applied small but critical changes in order to fix the telescope making it functional, these new changes are radical.. Here we go:

Yeah, I agree! It would have helped you a lot! Anyway, your project is stunning as it is. 💯

On the 20th Dec, the blueprints of the JWST were released by NASA: https://www.nasa.gov/image-feature/blueprints-of-the-james-webb-space-telescope

Can you help me understand what part of the visual shows the tilt error of the secondary? In your first image, the secondary mirror is "more present" towards the left. And you can see that the reflection of the primary mirror on the secondary mirror touches the secondary mirror to the right. It is possible that the previous owner was more concerned about obtaining circular shapes. The issue with that is that the edge of the secondary mirror is the weakest part of the mirror and should be avoided if possible. Your telescope is fast (f/4) and is meant for AP. Therefore, it makes sense to offset it a bit at least and avoid using the edge of the secondary mirror anyway. To adjust the tilt do I need to loosen the central screw and adjust the secondary by hand or will the loosening of the screw in itself perform a slight adjustment? Or should I instead be using the three thumbscrews also present on the secondary holder? First of all, I would just play with the three thumbscrews behind the secondary holder. If this is not sufficient you might need to play with the height of the secondary by regulating the central screw. This is a nice collimation guide: https://www.cloudynights.com/articles/cat/articles/collimation-and-the-newtonian-telescope-v4-r2599 .

Between the two, I would go for the Morpheus for the reasons stated by Don previously and because the Morpheus are more competitive cost wise. The ES were bargains some years ago.

This was taken ages ago, using a Catseye TeleCat collimator and my 12" dob after playing a bit with the secondary holder. The collimation is not perfect in this photo (in particular the primary mirror axial alignment is slightly off), but you can see that the primary reflection is reasonably within the secondary mirror. This last point is fine for visual. For imaging, try to get as precise as possible.

First of all, your technique for aligning 1) the focuser axis against the primary central spot and 2) the primary mirror axis, is okay. You can get a bit more precise, but the technique is sound. Your secondary mirror is oriented towards the focuser. However, there is a visible tilt error due to the lack of offset, which should be fixed because the primary mirror is currently reflected using the edge of the secondary mirror. To do so, you will need to slightly loosen the secondary holder and tilt the secondary towards the focuser. Doing so, one reflection might appear slightly oval, but that doesn't not matter. What matters is that the whole primary is reflected using the central part of the secondary (not its edge). For completeness, in the "new model of collimation", offsetting the secondary is achieved by moving the secondary towards the primary and tilting the edge of the secondary towards the focuser. The secondary holder remains centred within the tube. This kind of offset technique is easier and more flexible than the old way of regulating the spider or offsetting the holder mechanically. I would first try to adjust the secondary tilt using the three collimation screws behind the secondary holder. You might find that you need to adjust the central screw. Don't be afraid of collimating your telescope. Whatever error you introduce, can be fixed. It's just down to practice. Besides, good Catseye central spot you have! They are the best and they offer some advantages (e.g. autocollimator), but that's not relevant right now.

Reading the previous posts, it seems to me that a dream telescope is whatever is large. However, the same dream telescope can be a nightmare telescope if other factors (in addition to the cost) are considered. Some of these factors: - basic logistics, like moving the telescope outoodrs / indoors - climbing up and down the ladder - moving the ladder every time the telescope is moved - for some of us, redo the eyepiece case due to different telescope specs - telescope too large to pass through doors or a full garage / cabin to dedicate for this telescope - difficulty in minimising lights coming from a neighbourhood either overly concerned about robbers or excited by brightening houses - lack of proper dark sky to take advantage of that aperture - not be kin to go to live to a very remote, but dark place In summary, I think a dream telescope is what we can afford and makes sense for us. As we live quite well compared to other people, I think nearly all of us have already got their dream telescopes. 🙂

I already have my dream telescopes. What I would like is to observe more, particularly considering that light pollution is not getting any better over time.

And here an answer as it seems to me that most of what I said has been misinterpreted. I never talked about comparing a TV/Tak 60 with a 60mm (achromat) finder.. of course those are not comparable. And I wouldn't certainly try to compare the views of a 60mm with an 18" dobson. The two telescopes are different and have different purposes. My point is that a 60mm is a limited telescope apart from wide field (assuming it is a short tube.. a long f.l 60mm seems to me an excellent choice for a nostalgic person of the 60-70s as I cannot really see what other benefit one can get from these nowadays). Yes, one can use a 60mm for planets, but it is not a telescope conceived for that, given that it has a 0.5mm exit pupil at 120x (besides in my book I would not call this power combined with the resolution of a 60mm ED refractor to be "sufficient for some satisfying planetary views". Under the best seeing conditions, the GRS and the Cassini division are just detectable and this using top notch planetary eyepieces. Belts on Jupiter are visible but the very few visible details are really minor. Mars at that power - no comment). The majority of accessible DSOs are detectable, but the view gets quite dark with a bit of magnification (1.5mm exit pupil at 40x..!). In any case, the point here is not whether buying one makes sense or not. As I said I have one and used as my main telescope for 3-4 years. In the OP's circumstances to me the idea of getting a small refractor for quick observations is completely sound. Having said this, a 60mm aperture does not do miracles and is intrinsically limited. Whether the OP wants to spend £1K for a 60mm, that's up to him/her. My suggestion remains to look at the second hand market because those 60s gets substantial devaluation. Besides this, there are other good ED alternatives, which could make more sense for 15-20 min sessions observing under poor seeing conditions.

Wow! This is a great project and is coming out really well! Congratulations! Looking forward to seeing how it evolves!

I currently have 2 refractors: a TV-60 f/6 and a Tak FC100 f/7.4. Between the two, the Tak is used 99% of the time nowadays. Having said this, my main telescope is a reflector and I would be satisfied with just that plus the TV-60. The problem for me is solar observing. The 100mm is largely better than the 60mm on this and the reflector cannot be used for this.

Your idea of buying him a telescope is really beautiful, but choosing the right one is not very easy. In addition to a telescope, you also need eyepieces, a star atlas or phone app, and some other gadgets. I would also get him a book like `Turn left at Orion` and let him be involved in the decision making. You could get something together and spend time observing together. Also, it is worth considering buying second hand equipment in this website: https://www.astrobuysell.com/uk/search.php . A lot of items are in excellent conditions (like new).

Sorry, but I disagree with this. Maybe this is the case for the 100mm aperture, but not for the 60mm. I did consider selling my TV-60 (bought new for £850, case excluded). At that time my asking price was £550 with case, which I considered a honest price. I got offers for £400, which I refused. That is about 60% discount for a 4 years old telescope in excellent conditions.

There are both a TV-60 and a TV-76 available on astrobuysell.. Each of these would be my first choice rather than getting a new Tak-60/76 refractor. I can understand the obsession with refractors and Takahashi in particular, but the laws of physics are still valid and a 60mm objective is still a 60mm objective.. its best use is wide field observing which is low power with some zoom ins to medium power. I do have a 60mm and it was my only telescope for 3 years. I spotted / observed about 400 DSOs with it, so I know what I'm talking about. It's a very nice telescope and it allowed me to observe during that time. Having said this, it also has major limitations due to its small aperture. If I had to do this again and options were available, I would opt for a low cost 60mm fast refractor like the Altair one. It's quite close optically, the financial loss if you decide to sell it is way more contained and it accepts 2" diagonals (and therefore filters). By the way, I also have a Tak FC100. It's a nice telescope for planets, DS, and large DSO with the right low power eyepiece. It falls shortly with the vast majority of DSOs, given the small aperture, despite of what the Tak club likes to believe and say about this telescope. Don't get me wrong, please. They are very fine refractors, but a larger decent quality aperture, collimated, mounted in the correct way, and left to cool properly will beat them all the time and will allow you to see more. So in summary, I suggest not to spend a fortune here, and check the second hand market.

Hi Gerry, coma spreads the light over a much larger surface, and this depends on the focal ratio. A threshold target can simply be invisible due to coma. This is valid unless you call that target "threshold" as observed without a coma corrector, which means that the same target is quite well visible if a coma corrector is added. In an F4, coma is so severe that dim stars can be washed just about half the field of a 70 Deg eyepiece. Stars are point sources, therefore much easier than dim low contrast galaxies. Saying that a Nagler zoom set at 6mm has less transmission than a Delos 6mm means that the image in the former is somehow dimmer than the image in the latter. Given that the design of the former is much simpler, I doubt that. I haven't observed through a Nagler zoom, but I can accept the possibility that it shows less contrast than the Delos 6mm. This would mean that certain faint features can be detectable in the delos, but simply washed out in the zoom. I saw that with a Nagler T6 3.5mm vs Delos 8+PM2.5x: nearly identical image brightness, substantial difference in terms of features when observing details on Jupiter.

I am aware of that plot in Alvin Huey's website. It's here: https://www.faintfuzzies.com/AboutUs2.html . I do have some doubts about the validity of it though. In fact, 1) there is no information about the data (and how these were collected!), 2) what is the Y axis ?. As it is that plot seems artificial, if not even speculative. Even after by-passing the row data issue, I am not convinced that differences between eyepieces are "magnified" with aperture as the plot suggests. According to that idea, I should not have noticed any difference between eyepieces with my TV-60, whereas I should start noticing them with my 16". Instead, I saw plenty of eyepiece differences with my TV-60, and the way I can explain this, is because these differences are between 30-150x, far below an average seeing. Therefore, as the telescope was easily operating at its limit, any difference was due to the eyepiece. In contrast, with fast telescopes of 22" or 30" apertures, a 6mm eyepiece is not even close to the theoretical telescope resolution (~1mm exit pupil), but the delivered magnification is high enough to require almost superb seeing conditions, something which is only rarely met. Also, those folks observe with ~f4 telescopes without coma corrector. I tried to observe with my 16" f4 without coma corrector for curiosity and the views were degraded nearly on-axis. Now, I don't want to comment on whether a PC2 is required or not in a fast dobson, but my doubts remain: how can one spot substantial differences between eyepieces and spot extremely faint targets in the presence of severe coma like that when details tend to be washed out? And from a theoretical perspective, let's consider the term called `coma free region` which identifies the region where the introduced coma is smaller than the Airy disc. This region is tiny at f4 (e.g. 0.022mm x f/ratio^3 ) and is generally defined on the Rayleigh criterion. If one is assessing top quality eyepieces on threshold targets, it means that s/he is judging way above a Strehl of 0.8. Taken this in consideration, the `coma free region` (which is actually just a dot really..) is even smaller.. So.. to me there is something which does not work quite right there.. Regarding transmission with modern eyepieces, the only eyepiece which I repeatedly thought it had more transmission than the others is the Vixen HR. Having compared the 2.4mm against a Vixen SLV 5mm with my TV-60, it was quite obvious to see that the image in the HR was almost as bright as the image in the SVL despite half focal length of the former eyepiece. This was also quite striking considering the short exit pupil of the 2.4mm ep using a 60mm refractor (150x). Apart from that standalone case, the other eyepieces I compared showed a noticeable difference in contrast, not transmission to my eye (for instance, both the Docter and the Zeiss zoom show more contrast than the Vixen SLV, Delos, Naglers, Morpheus I've tried).

That's interesting, John. My copy was fine on-axis and showed a bit of chromatic aberration near the edge. The eyepiece was completely functional to my eye. Having said this, the delivered view was okay / good, but not something that I would have called "impressive". In other words, it was not an eyepiece I would have kept.. and in fact, I let it go! 🙄

To the OP: There are so many good eyepieces nowadays, that I am not sure the definition of `planetary eyepiece` still applies, unless one just intends something like "I want a focal length to observe planets with my telescope X". I would rather consider a telescope with larger aperture rather than a set of ultra expensive / famous eyepieces. Besides, planets are visible for about 1 season in one year and from UK latitudes they are also quite low. Regarding the 10mm BCO, my copy bought new was functional but nothing special. Possibly, its low cost is due to poor QA?

The Vixen HR is a 5 element, 3 group design (ref: https://www.vixenoptics.co.uk/Pages/hr_eyepieces.htm).

@faulksy Nice work, Mike! Are you going to mount the wheelbarrow handles to those two holes on the horizontal bar? If this is the plan, I would consider a mechanism to lock the mirror box to the rocker box, to prevent the former from sliding frontally as the inclination changes when the telescope is moved around.

Here we go for me: - TV-60: 24mm, 9mm, 3.4mm. All used equally. - 4" Tak: as above, plus 5mm and 2.4mm. All, apart from the 2.4mm, are used equally. - 12" F6 dob: 30mm, 25.1-6.7mm zoom (also w/ Barlow). All used equally. - 16" F4 dob: 30mm (or 24mm), 12.5mm, 8mm, 6mm, 4.5mm (also w/ Barlow). Most used is 12.5mm, least used is 30mm (or 24mm).

My TV-60 allowed me to observe in a time of my life where it was literally impossible otherwise. Now that things are more settled, my home made 16" dob is hard to beat. It offers me surprises every time it goes under the stars. The original design of key components in my 12" dob was a mess in my opinion, and many other parts could have been designed better. Despite the numerous issues and frustrations it caused me, without those problems I would never have considered the idea of making my own telescope (which, I have to say, has been one of the most beautiful experiences in my life). As the mirror is good, I have a plan to refactor this 12", but this will only happen some time next year. Finally, after being "feathertouched", my Tak FC100 has received much more star light than anticipated. In conclusion, all these tools have given me something valuable, although in different ways.