dawson Posted April 9, 2013 Share Posted April 9, 2013 Apart from the longer focal length, are there any optical differences between skywatchers startravel and evosyar models? I just ask as there is a startravel 120 on ASB for £135. I hear lots of praise for the evosyar, but never heard the startravel mentioned. Thanks. James Link to comment Share on other sites More sharing options...
Brantuk Posted April 9, 2013 Share Posted April 9, 2013 Often wondered this myself - seems almost like two ranges where only the names are different and one range would do...... Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 Sorry for the typos, clearly y and t and too close for my fat fingers on the iPhone! Jd Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 I've asked the same question on SGL, i'll report back any findings for future reference. James Link to comment Share on other sites More sharing options...
Guest Eddy Posted April 9, 2013 Share Posted April 9, 2013 (edited) Startravel series are achromatic refractors whereas all the evostar are doublet apochromatic I think, so yes there's a difference optically, on my tablet so you'll have to Google difference between achromatic and apochromatic Edit: Unless only the ED ones are apochromatic, I don't know without researching Edited April 9, 2013 by Eddy Link to comment Share on other sites More sharing options...
philjay Posted April 9, 2013 Share Posted April 9, 2013 Erm sorry eddy but evostars arent all apos im afraid Startavels are short focus scopes, to make them portable, travel - getit:-) Evostars are longer focal length. Therefore optically they are conciderably different Link to comment Share on other sites More sharing options...
Guest Eddy Posted April 9, 2013 Share Posted April 9, 2013 Thought that might be the case after a quick look on FLO and it didn't express that they were apochromatic, I had just presumed with the ed80 Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 But will the two have similar lens inside, just different length tubes? Link to comment Share on other sites More sharing options...
T A WOW Posted April 9, 2013 Share Posted April 9, 2013 The lenses will likely be similar but They will have a shorter focal length (ergo shorter tubes) than the evostars so CA will be more apparent. Not sure if they'd use different types of glass though. You'd need to do a bit more research ti answer that. Link to comment Share on other sites More sharing options...
Daz Type-R Posted April 9, 2013 Share Posted April 9, 2013 Just to clarify a point made above about CA, in case you don't know James it stands for Chromatic Aberration .In optics, chromatic aberration (CA, also called achromatism or chromatic distortion) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). The refractive index decreases with increasing wavelength. If you did know all this, sorry for wasting your time. Link to comment Share on other sites More sharing options...
philjay Posted April 9, 2013 Share Posted April 9, 2013 The glass in both scopes is the same, crown and flint elements which make up the achromatic doublets used in the fraunhofer design airspaced doublets which these scopes use. However because the startravel is a short focus F5 and the evostar is long focus, F7 or whatever. The startravel has more curves on the lenses to bring the focus of the light to the shorter focal length. This means that chromatic aberration is more evident in the shorter focal length scopes because it is more difficult to get the separate colours R, G and B to come to a focus. That's achromatic scopes for you. And no, before you ask , putting a barlow to artificially increase the focal length in a short focus scope wont improve the CA all it does is magnify the CA and makes it twice as bad for a 2x barlow or three times worse for a 3x etc. Therefore if you wish to get a fairly colour controlled SW achromatic scope it is better to go for the evostar. But if your into DSO visual and aren't bothered about CA, because you don't get much colour in DSOs then the startravel may be for you. Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 Thanks tobias, daz and phil; i dosn't know about CA so that was really useful. I won't persue this scope any more.. Out of interEst, if one was imaging in mono, either pure b&w or using coloured filters, does the CA fault still make an appearance? Cheers and hopefully see some of you on friday. James Link to comment Share on other sites More sharing options...
philjay Posted April 9, 2013 Share Posted April 9, 2013 Yes, bloated stars, they get bigger the longer the exposure, ive got lots if em from when i used an st120 for imaging, and filters wont help much Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 Ok. Thats useful, thanks. James Link to comment Share on other sites More sharing options...
Guest Kheldar Posted April 9, 2013 Share Posted April 9, 2013 I don't think it's been stated, but there's Evostar and Evostar ED - the two are quite different in quality Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 What does the ed stand for? Whats the dofference? Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 Some interesting replies and quite impressive dso images with someone ising the travelstar 102 on sgl: http://stargazerslounge.com/topic/182953-startravel-vs-evostar/#entry1898590 James Link to comment Share on other sites More sharing options...
Guest Kheldar Posted April 9, 2013 Share Posted April 9, 2013 What does the ed stand for? Whats the dofference? Can't remember what it stands for but it's result is an "almost" APO scope, there's the barest minimum of CA with the ED scopes which is why they are recommended as a good first "proper" imaging scope so often (the ED80 that is.) Link to comment Share on other sites More sharing options...
Brantuk Posted April 9, 2013 Share Posted April 9, 2013 Extra Dispersion glass = ED Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 Ah. Link to comment Share on other sites More sharing options...
Guest Ely Ellis Posted April 9, 2013 Share Posted April 9, 2013 Is it something like Extra Dispersion or Enhanced Dispersion glass. James, if I make it to Wymsewold on Friday, I will bring my scope, it is the Celestron version of the Evostar 120, then you can have a look. Cheers Martin Link to comment Share on other sites More sharing options...
philjay Posted April 9, 2013 Share Posted April 9, 2013 Extra Low Dispersion glass Link to comment Share on other sites More sharing options...
Guest Ely Ellis Posted April 9, 2013 Share Posted April 9, 2013 (edited) Ah, Kim got in there before me. At least I was on the right track, I must have learnt something! Cheers Edited April 9, 2013 by Ely Ellis Link to comment Share on other sites More sharing options...
dawson Posted April 9, 2013 Author Share Posted April 9, 2013 Thanks martin, that would be good to look through your scope. James Link to comment Share on other sites More sharing options...
Guest Tweedledum Posted April 12, 2013 Share Posted April 12, 2013 Had an st 120, it was a great scope, accept its limitations with a hint of ca. Brilliant grab & go, snow, sand and dog slobber proof. Travelled in boot, roof box and back seat, just usable on az3 but great on az4. For a cheap scope it punches above cost, and if it breaks on travel then you have not lost a great deal, consider the cost of a 2" uhc / Fringe killer at 80 quid, 55 more and you have the scope. Link to comment Share on other sites More sharing options...
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