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YKSE

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About YKSE

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    Bridge, badminton, mushroom picking.
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    Gothenburg, 57°, Sweden

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  1. Congratulations to the fabulous scope, Dave, I think you can give the magic word "I'm done" a proper meaning after this beauty.
  2. Nice haul Doug You may bag a few more galaxies in Makarian chain, if you go a little higher mag, say 70x or even 100x. Those smaller ones may benefit from higher mag, despite fainter.
  3. To my understanding, the dominant aberration in C8 is usulally FC, the FC is about the same magnitude as about a 700mm FL refractor, younger eyes can have the ability to acommodate it, but not me, I can see the FC, with my 70° AFOV eyepieces, even though nothing serious. Another potentail aberrations in C8 is SA, that'll be caused by much too long back focus when extra stuffs are added there, such as binoviewer without OCS. If the aberration seen significant or not, it's much dependant on personal references, IMHO. My impressions is that most SCT owners use EPs around 70° AFOV as their wider field EPs. Vignetting seen in C8 is more likely caused the EPs or diagnals than the scope, using EPs with 46mm field stop (such 40mm Skywatcher AERO) will have just perceivable vignetting when I look for it, the 38mm rear port size of C8 doesn't cause any serious viegetting as one might fear, simply because our eyes are not very sensitive to gradual vignetting.
  4. Maybe that's like in most cases, when someone has bought something with great excitement, not many want to be like the innocent boy? This is my general impression/requirement about truss dobs, for someone hasn't bought anything yet https://www.cloudynights.com/topic/560243-seeking-a-12-to-14-dob/?p=7599728
  5. I think your reasoning looks correct. Effective focal length with a barlow can be calculated as mentioned here http://astunit.com/astunit_tutorial.php?topic=barlow As to the aberration effects of a barlow, I'd like to think it as the total effect of a system, i.e. including the scope, diagonal, EP, etc, as mentioned by experienced visual observers, such as Nils-Olof Carlin: http://web.telia.com/~u41105032/barlow/Barlext.htm
  6. I don't think 2" diagonal itself will introduce any vignetting, your main concern with a 2" diagonal in a 6SE should be if the diagonal clear the mount base when the scope is pointing near zenith. The picture in your link is kind of puzzling, a 2" diagonal with SCT fit should like the stock 1.25" focuser, i.e. with female SC thread directly mounted on C6's rear port, like this one http://www.teleskop-express.de/shop/product_info.php/info/p87_TS-Optics-SC-thread-2--Star-Diagonal---99--Quartz---Compression-Ring.html
  7. Very itneresting, Nigel the added spherical aberration with a prism diagonal, will it be under- or over-correction?
  8. Yes, you can read as twice as sharp by some numbers, but under 5-6 argmin is not very easily seen except on bright stars. Distortion has nothing to do with FC, it's the geometrical distortion, easily seen in daytime targets with straight lines. You might seen more lateral colours with 24pan than 24 ES. That's what that chromaticity means, I guess.
  9. OK, good to know, good luck with your upgrade. Just a quuote of optical measurement information the ES 24mm vs 24 Pan in a f4 scope (Those angular miniutes etc size means how big a star's spot size) ---------------------------------------- ES 24mm 68° - in the center less than 5 angular. Minutes. - on the zone (70% from the center to the edge) 11 angular. Minutes due to curvature and astigmatism. - on the edge of the field of view - 20 ang. Minutes. The main aberration is curvature and astigmatism. There is a noticeable (5-6%) positive distortion ("pincushion"). The image of the diaphragm edge is sharp and unpainted. There are also no traces of increase chromaticity. Pan 24mm With a 1: 4 lens. Excellent image of the luminous point on the axis of less than 2-3 angular. Minutes. On the zone (70% of the center to the edge) the star image increases to 6-7 angles. Mostly due to astigmatism. At the edge of the field of view (one and a half degrees from the edge of the diaphragm), the aberration spot grows to 10 angles in size. Minutes, the main aberration is astigmatism and coma. The chromaticity of the increase reaches 20 ang. Minutes (i.e., of the order of 1%). Distortion is positive (pincushion) not less than + 3-4%. ----------------------------------
  10. Is it the same in the 12" dob as in 120ST?
  11. Well, that might be some simple explanations 120ST with its 600mm focal length is known to have quite noticeable field curvature(FC), and 19mm Pan is often mentioned with some FC too, the curvatures in 120ST and 19mm might happen to be the opposive sign so that it canceals each other, therefore sharp to the edge with 19mm Pan, while through 24mm ES you get to see the FC in the scope. Have you tried to focus on the edge stars? can it be brought to sharp focus?
  12. May I ask what do you see the main benefit upgrade the 24mm ES to 24 Pan?
  13. Congratulations to the new addtions. C8 is very compact for it's aperture, doesn't need to collimate as often as a newt, but you do need to check and do the collimation from time to time. If you're not familiar with collimating a SCT, I'd warm recoomend this guide https://www.astromart.com/articles/article.asp?article_id=548
  14. There're quite a number of these 2" to 1.25" reducers nowadays, and with different flange thickness, they can be used as par-focalizing adapters too, as I see it. Here's the info I've able to gather (mostly from specification on internet), it'll great if others can confirm/contribute with their measurement. Dimensions are illustrated by this picture: Here's we have so far: