Davey-T Posted December 16, 2016 Share Posted December 16, 2016 A review of this in January AN nice fast, big FOV and helical focuser ? not sure how that's going to attach to a motor focuser, presumably it's to keep the OTA short enough to work but seems a bit strange Dave https://www.vixen.co.jp/en/lp/vsd.html Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 It was a while ago now but it was reviewed in Sky @ Night by Steve Richards, and before that I had one on test/review. The FOV was as flat as a pancake, even on full frame sensors it was near perfection. However the colour correction left a lot to be desired, and even with the micrometer adjustable helical focuser it was impossible to find a happy compromise for focus that didn't result in an unpleasant colour halo in one or more colours when using a colour camera, or a mono camera with a luminance filter. I'm sure the AN review would mention this though? Such a shame because it was almost the perfect scope, fast, flat, and apochromatic. If it hadn't been for that issue I would have pulled the trigger on one because it really is nicely made. To fit a electric focuser some sort of bracket and belt arrangement I would think? Tim Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 http://www.skyatnightmagazine.com/review/telescopes/vixen-vsd-100-f38-astrograph Link to comment Share on other sites More sharing options...
Davey-T Posted December 16, 2016 Author Share Posted December 16, 2016 23 minutes ago, Tim said: It was a while ago now but it was reviewed in Sky @ Night by Steve Richards, and before that I had one on test/review. However the colour correction left a lot to be desired, and even with the micrometer adjustable helical focuser it was impossible to find a happy compromise for focus that didn't result in an unpleasant colour halo in one or more colours when using a colour camera, or a mono camera with a luminance filter. I'm sure the AN review would mention this though? Price has gone up by £600.00 as well. Tim According to Ninian Boyle it completely eliminates chromatic aberration, astigmatism, coma and spherical aberrations. Perhaps you got a duff one, though for the price I'd hope there wouldn't be any duff ones. Dave Link to comment Share on other sites More sharing options...
ollypenrice Posted December 16, 2016 Share Posted December 16, 2016 Only pictures taken with this or any other scope are really of ultimate interest. If Steve and Tim found it bloated in OSC and luminance then I can only assume that it does. This sounds as if it might be of interest narrowband imagers, though. Controlling the full spectrum at fast F ratios has never been easy... Olly Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 3 hours ago, Davey-T said: According to Ninian Boyle it completely eliminates chromatic aberration, astigmatism, coma and spherical aberrations. Perhaps you got a duff one, though for the price I'd hope there wouldn't be any duff ones. Dave According to the Pentax/Vixen Japanese team that I corresponded with it did too, however the reality of the telescope that Steve and I used, (yes it was the same one) is that Yellow/Green light could not be brought into tight focus at the same time as red or blue. The Japanese teams instructions for attaining best focus also indicated that they were aware of the limitations. I have pictures on my observatory PC somewhere if you would like to see. As Olly mentioned, narrowband pics taken with it were phenomenal. It is at least two years ago that this took place, so perhaps they have tweaked the design a little. Is there a serial number on the lens photo in AN, if there is one? Link to comment Share on other sites More sharing options...
Davey-T Posted December 16, 2016 Author Share Posted December 16, 2016 13 minutes ago, Tim said: According to the Pentax/Vixen Japanese team that I corresponded with it did too, however the reality of the telescope that Steve and I used, (yes it was the same one) is that Yellow/Green light could not be brought into tight focus at the same time as red or blue. The Japanese teams instructions for attaining best focus also indicated that they were aware of the limitations. I have pictures on my observatory PC somewhere if you would like to see. As Olly mentioned, narrowband pics taken with it were phenomenal. It is at least two years ago that this took place, so perhaps they have tweaked the design a little. Is there a serial number on the lens photo in AN, if there is one? Can't see one. Wouldn't want to pay nearly £6000.00 for something that only does NB, they also do a reducer to make it f/3 which must aggravate the CA situation. Dave Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 Thinking about it, the serial number might have been stamped on a plate on the side. The telescope that came to Steve and I had a low number, I think it was 000021 or so, but i dont recall taking any pictures of that. I have found a few pics with a mono camera so far, but it is the ones from my DSLR which might reveal the issue, still looking for them. I dont know if @steppenwolf retains any Luminance images? This one was just a few subs in Ha and Oiii as a test. Full frame camera used and not cropped I dont think. Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 This cropped image is my favourite result from the VSD. M51, comet PANSTARRS, and a lucky iridium or other satellite flare. Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 Looking at the dates on the subs, the scope was with me during May 2014. I think it first came in the back end of 2013 and then went back to Opticron for Astrofest, before coming back. Link to comment Share on other sites More sharing options...
Tim Posted December 16, 2016 Share Posted December 16, 2016 31 minutes ago, Davey-T said: Can't see one. Wouldn't want to pay nearly £6000.00 for something that only does NB, they also do a reducer to make it f/3 which must aggravate the CA situation. Dave Exactly Dave. If I had bought it, I would have sent it back. Such a shame. The reducer wasn't ready at the time I had it. Even at f3.8 the depth of focus was so shallow that the helical micrometer markings were essential for manual focusing as tiny movements of the focuser made a big difference. Link to comment Share on other sites More sharing options...
steppenwolf Posted December 17, 2016 Share Posted December 17, 2016 As Tim has stated and my own review confirms, the flat field characteristic of this instrument is phenomenal but on the example we had to test there was an issue with colour. I don't keep my test images forever, only those that I like and then place on my website or use when giving talks so I don't have my OSC test samples any more. However, I did like the results achieved in narrowband which is an area where this telescope can excel. The image below is a bi-colour captured using the telescope and it demonstrates the flat field quite well. The focuser was beautifully crafted and could be motorised by a belt drive but it does require very small movements as the depth of field is very shallow at f3.8. I have no explanation for why Ninian didn't find the same issue as the problem of green/yellow versus red/blue focus was acknowledged by the manufacturer at the time of my review but perhaps they have made a change to the optics? I hope this is the case as it would turn a killer narrowband instrument into a killer wide field instrument for all wavelengths. Bi-colour Narrowband image of the Veil Nebula captured with the VSD 100 and a QSI WSG-8 Link to comment Share on other sites More sharing options...
Davey-T Posted December 17, 2016 Author Share Posted December 17, 2016 Looking around for reviews, Ninian seems to have just paraphrased the Vixen blurb and Tony Hallas can find no fault Would have thought all examples would have the same quality control at this price level. Just goes to show that producing multi lens fast, flat fields ain't easy as per folks experiences re WO Star 71 and Tak FSQ 85. Dave Link to comment Share on other sites More sharing options...
andrew s Posted December 17, 2016 Share Posted December 17, 2016 Given no telescope is perfect (at any price) maybe this is not one for use with OSC or a L filter but I rather got the impression that anyone using filters RGB & or NB refocused for each filter (or used fixed offsets) anyway. Regards Andrew Link to comment Share on other sites More sharing options...
steppenwolf Posted December 17, 2016 Share Posted December 17, 2016 Quote but I rather got the impression that anyone using filters RGB & or NB refocused for each filter (or used fixed offsets) anyway. This is perfectly true, you cannot rely on filters being parfocal and in any event, focus needs to be checked with temperature change throughout an imaging session but, there are good reasons for capturing Luminance (L) data and this will still be compromised in the same way that OSC data will be compromised. Link to comment Share on other sites More sharing options...
andrew s Posted December 17, 2016 Share Posted December 17, 2016 19 minutes ago, steppenwolf said: This is perfectly true, you cannot rely on filters being parfocal and in any event, focus needs to be checked with temperature change throughout an imaging session but, there are good reasons for capturing Luminance (L) data and this will still be compromised in the same way that OSC data will be compromised. That is why I said OSC and L in the part you did not quote. You could do the L with a suitable broadband filter if needed. Regards Andrew PS I am not trying to make a big deal of this just there will be different compromises and solutions. Link to comment Share on other sites More sharing options...
Davey-T Posted December 17, 2016 Author Share Posted December 17, 2016 I think the AN review was done using a DSLR, which Vixen appear to say it's ideal for, also some mention of it being useful for normal daylight photography. Dave Link to comment Share on other sites More sharing options...
ollypenrice Posted December 17, 2016 Share Posted December 17, 2016 I think it would be a shame not to able to use an L filter if shooting broadband. You could make a case for saying that it's less necessary with a very fast scope and that RGB (from individually focused channels) would go as deep given time, but then you'd rather be defeating the object of the very fast optics. I had a spell of trying RGB plus narrowband without L but have concluded that it's really only worth doing on very extended emission nebulae leaving little background sky. The moment you have a fair amount of background sky you need the deep L layer to discover that there's no such thing as a background sky! Olly Link to comment Share on other sites More sharing options...
steppenwolf Posted December 17, 2016 Share Posted December 17, 2016 Quote That is why I said OSC and L in the part you did not quote. My point was that the 'L' channel is significant in RGB imaging, nothing more, nothing less! Link to comment Share on other sites More sharing options...
andrew s Posted December 17, 2016 Share Posted December 17, 2016 14 minutes ago, steppenwolf said: My point was that the 'L' channel is significant in RGB imaging, nothing more, nothing less! I agree but just how wide does or should the bandwidth of the 'L' channel be? I suspect no commercial lens based telescope can focus at the diffraction limit from the atmospheric UV cut-off at say 390 nm to say 1000 nm in the near infrared. Regards Andrew Link to comment Share on other sites More sharing options...
steppenwolf Posted December 17, 2016 Share Posted December 17, 2016 I'm with you, Andrew, I suspect that no commercial lens with cover the wavelength extremes that you suggest but an apochromatic lens system should adequately cover and focus very closely at the same point, visible red through to visible blue. In the tests carried out by Tim and I, this otherwise exceptional instrument fell short of this requirement. To reiterate, I hope that Ninian's sample is typical of the current product because that would make it a remarkable instrument. Link to comment Share on other sites More sharing options...
Tim Posted December 17, 2016 Share Posted December 17, 2016 5 hours ago, Davey-T said: I think the AN review was done using a DSLR, which Vixen appear to say it's ideal for, also some mention of it being useful for normal daylight photography. Dave Yeh, I never did get that really, cannot see how you would achieve tight enough focus. During my reviewing period I took the scope to a star party and got together with a professional photographer. We tested it to death in daylight, with a DSLR for any sign of CA, against high contrast objects, aerials against a bright sky for instance, and could find none. However the ultimate test of colour correction uses a point source, a star, and there it fell down. Such a shame. I'm still looking for the star pics I took with a DSLR and VSD. Link to comment Share on other sites More sharing options...
Ruud Posted December 17, 2016 Share Posted December 17, 2016 What a telescope! From the diagram I think that the focal ratio of the doublet at the front must be f/7. The corrections that Vixen manages to do with the three lenses at the rear is incredible. Link to comment Share on other sites More sharing options...
ollypenrice Posted December 17, 2016 Share Posted December 17, 2016 For me it will be 'what a telescope' when it has passed the acid test and produced some great astrophotos. At the asking price of nearly £6000 'great' has to mean great, not just 'very good indeed.' Olly Link to comment Share on other sites More sharing options...
Davey-T Posted December 17, 2016 Author Share Posted December 17, 2016 13 minutes ago, ollypenrice said: For me it will be 'what a telescope' when it has passed the acid test and produced some great astrophotos. At the asking price of nearly £6000 'great' has to mean great, not just 'very good indeed.' Olly Plus £450.00 for tube rings Dave Link to comment Share on other sites More sharing options...
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