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Piero

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Everything posted by Piero

  1. Thanks John. I looked at astrozap shrouds and they are nice but it seems they make them for commercial scopes only. Teeter customise them, and they are not very expensive either. But this doesn't include customs..
  2. I am considering a new elastic light shroud for my 12" f6 dobson. Apart from the obvious ones sold by Teeters and Astrosystems, are there options here in the UK or in the EU? Where did you get yours? Cheers, Piero
  3. The skywatcher 8" f6 dobsonian is good, but the bresser is better in mechanics in my opinion. The rocker box supporting the tube is really well designed. The altitude bearings allow one to track smoothly. The primary mirror collimation bolts are excellent. The focuser doesn't even compare.. The skywatcher is okay, but requires some upgrade to make it work really well, whilst the Bresser might only need a finder upgrade. If it were me, I would get him the Bresser as birthday and Christmas present.
  4. Great thread! I was not aware that they also sold a 10" version. That telescope design is very good!
  5. I've always liked these Bresser dobsonian. Great move to go away from those tiny rounded altitude bearings, as used by Skywatcher or Revelation, and instead adopt proper altitude bearings as in larger dobsons. Nice list of mods too! Congratulations
  6. Any 200-300mm dobson can reveal outstanding views of the lunar surface, with a plethora of details. It will show you plenty of details on planets, and DSO under reasonably decent skies. If you decide to go for a dobson, make sure to get a decent collimator.
  7. Thanks John. Anyway, my point is just that I don't consider aperture fever the purchase of a 200-300 Dobsonian. That's just a telescope that does a good job and all targets. To me aperture fever is an impulse purchase of larger telescopes without understanding why they are there for. I think SGL members are quite responsible on this actually.
  8. Considering "on-axis" like the central dot in the field of view, the views through the PC2 should be almost identical to the views without PC2, minus a tiny loss in light transmission due to the extra glass. Outside that dot, the view through PC2 should be better, because the light is not smeared due to coma. This affects all targets, so yeah, DSO, moon, and planets are included. To my understanding, the plot to the right essentially shows that without PC2, the view degrades below a Strehl of 0.82, quite quickly as one moves away from the central on axis dot of the field of view. Beyond that point the telescope is behaving sub-optimally, as described in Suiter's book with the MTF tool.
  9. Here's some data regarding the TV paracorr2: ( Source: http://www.televue.com/images/TV3_Images/Images_in_articles/Paracorr_2_chart.jpg ) => That's a massive improvement.. The plot to the right is what a lot Newtonian owners prefer to ignore. As you can see, there isn't really a "coma-free region" without a coma corrector. In my understanding, when the curve is above the Airy disc radius, the optics behave < 0.82 Strehl.
  10. I think a more sensible upgrade from a 114mm something like a 200mm, as stated above by others. A 200mm is a great all-around telescope showing a lot of different types of targets. Having own a 114mm F8 newtonian in the past, I would definitely recommend to upgrade it to something larger, like a 200mm F6 dobsonian. As a side note, this is NOT aperture fever in my opinion though, but simply the fact that you want a more capable telescope which is still within portability, storage, weight, etc. Aperture fever is when someone has NOT yet explore the potential of his/her own telescope (generally 150-300mm) and decides to upgrade thinking that the larger instrument will show what the current smaller telescope is not. This can lead to disappointment though.
  11. I use one from Geoptik for my Tak. It works very well.
  12. I don't want to hijack this thread, so I will answer this, but I'd suggest to move this conversation to a separate thread as it is clearly off-topic. To test whether astigmatism is due to your eye or the telescope, a simple tool is the magnification. Assuming that the eyepiece in use is astigmatism-free, an increase in astigmatism at low power is more likely due to one's eye, whereas an increase in astigmatism at high power is more likely due to the telescope. Life can be hard for the amateur astronomer though.... issues with the mirror cell, for instance related to mirror lateral supports or triangles can show astigmatism, but also spherical aberration. When minor, the signature of the latter can be difficult to analyse whether due to the supports or the mirror changing temperature.
  13. Hi Robert, I don't have the TV paracorr2, but would like to assess whether my current equipment has problems with it or not. Thanks for the links regarding the ES HR CC.
  14. for Alvin's observing guides. > I am not sure whether the paracorr2 sharpens the Delos, meaning that it makes them "sharper on axis". However, because the whole field does not have coma, the whole field will be sharper. The fact that the Delos are more similar to the Docter with the paracorr2 , to me is more related that on axis the Docter looses a little bit of transmission, actually becoming closer to the Delos. Said this, on-axis is 1 point, off axis is an area. Therefore, in general the benefit of a coma corrector is considerable. I think you chose wisely when you decided to get one with your telescopes. I am considering one myself, despite the fact that I have a F6 dobson. This because I do see coma. Although not distracting, I like the views delivered by refractors, and the only way to get these views with a newtonian is to add a coma corrector. > The PCII makes the whole field (up to 42mm field stop if I remember correctly) coma free. > Regarding the 16mm 82 deg, my though is about using it with the VS60 finderscope to get a 14x60 finderscope, with 5.7 deg AFOV and 4.23mm exit pupil. At that power, many DSOs are visible in the finder directly, hence facilitating star hopping. At F3.78, the eyepiece must be free of off-axis astigmatism though, so a Nagler would be the best choice, although expensive for a dedicated use like this. Will see
  15. I don't know and won't be able to test this as I sold my 20mm Lunt HDC as 100 deg is too much for my likes and I tend to jump from 30mm to 12.5mm. The APM UFF 30mm is quite close to the Docter if I remember correctly, but I've never measured the distance. I'd be interested in knowing the TV paracorr2 setting for the 12.5mm Docter UWA too.
  16. Thanks for your information, Don. May I ask you what is the TV Paracorr 2 setting for the 30mm APM UFF, please?
  17. No problem. Yes, the paracorr2 makes the stars tighter, within the Rayleigh limit, across the field of view. Note that the paracorr2 doesn't make the Newtonian collimation more forgiving, but the opposite. The tolerances for the focuser axial alignment become tighter: 0.03 * D : no CC 0.005 * D : Paracorr1 (6x) 0.0007 * D : Paracorr2 (42x) where D is the telescope aperture. Which atlas have you ordered if you don't mind me to ask? With a 24" under dark skies as yours, I suspect that even Uranometria is "limited". Probably, the best guides to use are those in Alvin's faintfuzzies.com for 20"-30" dobsonians. Regarding the "Sharp to the edge without coma corrector".... well, to be short, I don't believe that... Even the concept of "coma free" can be quite misleading. The only coma free region is on axis in a perfectly collimated Newtonian. The "coma free region" only means that although coma is present, this is within the Rayleigh limit of 0.82 Sthrel. If the optics are better enough, coma is certainly visible in this area too. Some time ago I was testing the effect of coma in my F6 dobsonian. To make it more evident, I thought about mimicking the coma by misalignment. So what I did was to collimate the telescope as well as I could. Then I pointed a bright star and defocused it so that the diffraction rings were visible. Then I left this drift towards the edge. Interestingly, it was possible to see the signature of coma. This was noticeable as soon as the star was no longer on axis and the first diffraction ring was affected from about as little as 30 degrees off axis from the centre. When the star is focused, this is less obvious of course, but doesn't mean that it is not there. This was in a F6 dobsonian free from astigmatism (you know my mirror cell...) and minimal spherical aberration. Repeating a test like this on a F5 or below, for sure, doesn't get any better.. so yeah, a coma corrector is beneficial in my humble opinion. Star hopping. I have a telrad and an Antares VS60 RACI finder (great Canadian finder ). I use the telrad for pointing, although I often manage to broadly point with the RACI finder directly. Then star hopping is done using the finder and the eyepiece. I don't really use the 30mm APM UFF for star hopping. This eyepiece is used for large low power targets or when I like to scan an area of the sky with a larger field of view. Normally, the docter is in the focuser and so star hopping is done with that eyepiece (145x) plus VS60. This combo works quite well for me. I've also done star hopping with the Zeiss zoom (150-200x) plus VS60. Again, no problem. I like the VS60 a lot and prefer it to 8x50 finders. The reason is that I'm quite accustomed to the light gathering of the TV60, which is also a 60mm clear aperture. One day, I might try something like a 16mm 82 deg and install a cross axis. Doing so I could get more magnification facilitating the detection of DSOs in the finder directly.
  18. Yes the paracorr2 makes the whole FOV diffraction limited. It also decreases the focuser axial alignment tolerance by about 10 times. Glad to hear that it is working with the Zeiss zoom and the docter.
  19. Yes, I hold it with my hand and use it for star hopping. I've also downloaded Alvin's Herschel 400 guides (3 vols) on this tablet. That should be a lot of fun and within the limits of this dobson. Glad to hear that your new encoders are working well with your 15". The Zeiss zoom is one of my main blocker from getting a paracorr2. I love that eyepiece, but I suspect that the fact that it is not fully parfocal across the zoom range, could affect the setting of the paracorr2. Also, when you said that the paracorr2 sharpened the views of your Delos eyepieces, do you mean on axis?
  20. That's a very fine piece of equipment for small / medium scopes as the ones you mention. Good luck with the selling.
  21. I am interested in this item if in excellent conditions. If you are keen to sell yours, please let me know.
  22. Turn left at Orion was one of the first books I bought. Although there is some valuable information, I never managed to take it to the field.. So.. yeah, I rarely use that book. Do you also use U2k Guide?
  23. It's excellent! This is also well made and free. Said this, it's a bit like Uranometria: very strong on DSO (e.g. galaxies), but a bit poor in terms on labelling and double stars. I've read very positive comments on those three volumes.
  24. I have a TV60, which is quite similar in specs. With it, I want a 24mm, 9mm, and then 3.5. Al Nagler suggested: 24 Pan, 9mm Nagler, and TV Nagler zoom. I completely agree with him on this. I have 24 Pan, Nikon MC1 zoom 21_9mm, and Vixen HR 3.4mm and 2.4mm.
  25. As I said before.. I am going to stick with my trusty APM UFF 30mm..
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