alex_stars

Hi all again and thank you all for your continued input. I still await a night to run through my tests before I can decide weather I want a zoom or not as an upgrade. Yesterday appeared to be a good night, but a very fast jet-stream (45 m/s) made it hard to decide upon anything. Of course I will post results as soon as I have some and I continue to appreciate the comments people post. Clear Nights, Alex

Hi all, the Hyperflex does sound like an upgrade option in the "sharper and more contrast" segment. Eye relief is a bit less but at 15mm still very comfortable I guess. (Not sure if my Seben is actually at 20 mm). Now regarding the suggested 7.2-21.5 Zoom, I seem to find a confusing variation of specs on different sellers homepages: Skywatcher Hyperflex 7E1: 60-40 FOV, 7 lenses - 4 groups, weight 190 g Auriga version: 60-40 FOV, 7 lenses - 4 groups Orion version: 60-40 FOV, 7lenses - 4 groups, weight 170 g Omegon "premium" version: 53-40 FOV, 7 lenses - 4 groups TS-Optics "premium" version: 53-40 FOV, 7 lenses - 4 groups, weight 170 g Lunt Solar Systems version: 53-40 FOV, 7 lenses - 4 groups Hmm. All the above are reported to have 15 mm eye relief. And then there is the other version, Hyperflex 7E2 with a 9-27mm zoom range, 60-40 FOV, also 7 lenses - 4 groups, and a reported eye relief of 18 mm. This 9-27mm zoom I found also from Auriga, where it is labeled with 15 mm eye relief. And nobody seems to know anything about that as I read: https://stargazerslounge.com/topic/204638-skywatcher-hyperflex-9-27mm-zoom/ Does anybody know why there are different FOV specs for the 7.2-21.5 zoom? Interestingly the 53-40 FOV ones are consistently higher priced....

Thanks @iPeace for the additional input. I have the feeling too that another standard zoom EP will not much improve upon my existing 8-24 mm one. Great to know that the Hyperflex performance is probably due to the barlowing. I will ponder and test more what I expect from my upgrade. Simple answers would be more contrast, certainly as every planet observer tries to max out that. However I think I test more my setup with my existing zoom, such that: observe a large part of a good seeing night @ 12 mm setting only. Imagine that is a fixed EP and note down what I like and dislike. Do the same for the 18 mm setting as well as maybe the 8 mm one. Compare and come up with more detailed list to answer your questions. Just for comparison for later on I would say now (order of importance): Sharper, more contrast views Field of view, maybe Bigger eye lens, don't know More eye relief. I really like the 20 mm of my Zoom. I will report back as soon as I got some more nights in with the current zoom setup.

Thanks @John, I guess in summary I am back to square one and not sure if I should upgrade to some fixed-FL EPs or to a better Zoom. Planets and the Moon are after all my main focus. 😕 I'll have to rethink this subject. Nevertheless thanks for all the input. More is of course welcome. Clear skies, Alex

I fully agree with the notion of zooming. That's why I got my entry level 8-24mm Zoom. However now I wonder on how to upgrade. The Leica ASPH certainly would be an upgrade, however out of reach at the moment. So I guess the initial question could be expanded to "which 12mm EP for planets, or high quality zoom?" @John which zoom do you prefer over your fixed focal length EPs?

OK. Wow. Certainly a nice zoom EP, but I would have to save up quite some pennies for that one. Nope currently not in the budget. But thanks for the idea of a high-end zoom.

Hi David, thanks I have considered that but was not sure how much an upgrade would improve from my standard zoom. Which high end zoom do you have in mind? Pentax XL 8-24?

Nice! Thanks. I saw the same Nirvana under quite some brands now (SW, TS, Auriga,...) and you are right, they are a real bargain. As said above I will keep it in the back of my mind and test more with my 8 mm zoom setting to see if I can work with such small exit pupils. The 7mm would result in an exit pupil of 0.47mm. Last time I used my zoom at 8 mm on Jupiter I had a few issues with floaters, thats why I want to test more... Anyhow great to know that the 7mm worked for your on your Skymax 180.

Again, thanks for the replies. No pressure intended, right? 😀 I really like your summary. I am fascinated with the Tele-Vue and Pentax EPs but they are currently above what I can spend on EPs. So you might just be right and I go for some Morpheus EPs as my upgrade from my zoom. A reasonable list of EPs could be: Morpheus 17.5 mm for 154x magnification and 1.17 exit pupil (fallback for not that perfect seeing nights) Morpheus 12.5 mm for 216x magnification and 0.83 exit pupil (for very good nights) Morpheus 9 mm for 300x magnification and 0.6 exit pupil (for the very best nights) Hmm. Nice to crunch the numbers. I guess I'd start with getting the 12.5 mm. Then speculate if the 17.5 or the 14 are a better fallback and later on aim for the 9mm.... if at all. I have a Hyperion 2.25x Barlow, which would take the 17.5 down to 7.7 mm. Guess that would be just ok for the very very good nights.

Hmm lot's to consider. Down to 7mm, wow. I will have to test my 8mm zoom setting more to see if floaters don't get out of control with such a small exit pupil. Good to know though that this is possible. Budget wise I was more in the around 200 Euro range, so I was not considering the Televue EPs. Thanks for pointing me to the TV calculator. CS Alex

Hi and thanks for the reply, Just a few answers to the valuable comments you made: I have a tracking mount and don't have to wear glasses (astigmatism only on one eye) I have looked through a 10 mm Plössl and the eye relief was ok. Thanks as well for pointing me to the wide field options, I did not consider them as I mainly focus on planets. CS Alex

Hi and thanks for your reply. I quite like the view at 12 mm with my zoom (Seben brand, like Skywatcher standard zoom). At 8 mm it has 60 deg FOV so i guess I am around 50-55deg at 12 mm. Eye relief is comfortable at about 20 mm. I don't think I would mind less though. Sometimes I go down to 8 mm but then quite some floaters appear in my eyes and the seeing these days is not that great, so I often end up around 12 mm. Looking forward to see where you take it from here. CS, Alex

Dear esteemed Stargazers, I would like to ask for some recommendations for an eyepiece I look for. First off, I have a 7" Mak with 2700 mm focal length. So I figure, a 12.5 (or 12.0) mm EP should be very nice to start viewing planets (my main interest) on good nights. This would result in 0.83 (0.8) mm exit pupil and 216x (225x) magnification. So far so good and I really would like to add some fixed focal length EPs to my collection as I only own 8-24 mm zoom. The conundrum starts with the choice of EP design and three choices I face shall I go old school style and buy a 12.5 mm orthoscopic EP (Takahashi or Masuyama)? or shall I buy a more modern design with more eye relief and go for a 12 mm Vixen SLV? or do I completely miss an eyepiece and should go for that? Thus I thought I tap into the collective wisdom of the community and ask for advice. Clear skies, Alex

Thanks. I will have to try that. However I read that one can get quite some inconsistent results depending on the flashlight position, eyepiece used and distance to wall combinations.

Hi All, I thought I report on an issue I recently faced with my Celestron AVX mount that features the new dual saddle plate. The plate takes two standards of dovetails, the narrow CG-5 dovetails and wider CGE. Most people know the CG-5 as a "Vixen Style" dovetail and the CGE is Celestron's version of a 3" (but not compatible with a Losmandy) dovetail. Now the issue. I own a 7" Mak (Skymax 180 from SW) which has a classical Vixen-Style dovetail. When you try to clamp the 7" Mak to the AVX, the saddle plate clamp does not really fit. Interestingly the 7" Mak has too large of a diameter to fit the AVX saddle, which comes to a surprise, given that a C8 or a C9.25 are popular choices for that mount. As you can see on image, on the left side, the clamp rests on the OTA and the dovetail does not touch the clamp on the bottom. When you tighten the fixing screws, tension is built up between the clamp and the OTA and not between the clamp and the dovetail. In addition this makes it quite harder to balance the OTA on the mount (the clamp-tube jams). In the end the OTA will get a dent at that location, I guess. Luckily I caught this right a way and my OTA is not yet damaged. Anyhow for some this might not be an issue, but I changed the AVX clamp and now use an aftermarket clamp from ADM. Thought I share this with the community as this might be interesting for some. Clear skies Alex

I had a chance to image Jupiter yesterday with Ganymede casting a shadow (31.07.2020 at 21:38:36 UTC) The apparent size was 47.2 arc-seconds and I imaged with my ASI 224 at a back focus of 82.5 mm (original visual back + 2 to 1.25" adapter and ASI 224 to sensor). Using that info and some error estimates, I get a EFL = 2417 +/- 23 mm at that back focus and a f2 = 126.9 +/- 1.5 mm. Translating that to the back focus of the original setup (original visual back + 2" diagonal at 164 mm back focus) results in a stock EFL = 2720+/-27 mm. So for most practical purposes I'd say I can confirm the f2 estimate of Magnus and we can assume that SkyMax 180 has indeed a stock EFL of 2700 with the shipped VB and 2" diagonal. Cheers and clear skies, Alex

Hi, how did you estimate the effective aperture your SkyMax is operating on? BTW, I agree with you, it is certainly the meniscus lens that brings the effective aperture down to about 170mm.

Great! 👍 Same here, very few clear nights lately. Let's hope for better weather and report back when we got our estimates in ;) Alex

Hi All, this morning (rainy day), I realized that I can measure the baffle tube length without opening up the OTA though the baffle tube opening at the end of the OTA (ha!). So I went ahead and measured the baffle tube diameter there (30 mm) and the baffle tube length from the OTA back all the way in, which I gonna call d4 = 268.0 mm. Since it was a perfect day for some math, I wrote up some ray transfer functions that describe the Skymax 180 and let us calculate what the maximum BF can be before the baffle tube cuts the light cone and causes aperture loss. My setup is as such: And here is a summary of the dimensions I use: Now I derived an equation for d1, given d2, f1, f2, x0 and x1 such that alongside an equation that calculates the back focus (definition of Magnus above) to be Following the red ray in my figure, I can set x0 = 90 mm (full aperture) and x1 = 15 mm (baffle tube radius) and work out the maximum back focus before aperture loss happens to be BF_max = 210.67 mm. That translates to an maximum EFL_max = 2872 mm. If somebody wants to follow my math you can have a look at my attached pdf. Also I have to say this is still preliminary as I ignore the meniscus lens in the analysis and that f2 is actually not yet confirmed. With respect to f2 I plan to infer that one day by imaging a planet at a given BF and then back-calculate f2. Basically confirming the assumption of Magnus that EFL = 2700.0 mm when the supplied VD and 2" diagonal is used. Enjoy and hope that is useful to others. Cheers, Alex Skymax180_equations.pdf

Hi Magnus, Any chance you got around and measured the length and diameter of the inner baffle tube yet? (Sorry for asking, I am still not comfortable to take mine apart....) Like Olivier I would be interested in those dimensions. We could calculate a few more optical parameters and in my case I would be interested to calculate the maximum usable back-focus before aperture loss starts so that one can work out which bino-viewer configurations are possible. Cheers, Alex

Perfect, that explains it quite well. I don't plan on changing the collimation, but it's good to know if I need to one day. Cheers, Alex

Hi Magnus, thanks for that fantastic tear-down of a skymax 180. Lot's of very valuable info for people like me who also own one. I am especially fond of the (Re)-Collimation instructions and the idea of a carbon tube later on along the way. Regarding the collimation, as I understand you, you only use the larger hex collimation screws, never the smaller sunk-in “locking screws”, right? Are the locking screws more or less to define the initial mirror position and then work from there with the collimation screws? Just wondering as I always was looking for a collimation instruction for the Skymax. Also do let us know if you ever get around buying a carbon tube for the Skymax 180, I would be very interested in such a modification. Maybe together with a good thermal insulation. Anyhow, thanks again for the great work! 👍👍 Cheers, Alex