Here is the place to talk about all those equipment(Telescope, Mounts, Eyepieces, etc...) you have. Not sure which scope/eyepiece is best for you? Trash it out here!
Kamikazer wrote:any idea where i can find a 6" newt f/6 (preferably f/7) or slower, made by a reputable manufacturer? (like celestron or meade)(just looking around...no money yet)
Are you looking at an equatorially mounted newt or a dob? The 6" ones are usually F/5 (GEM-mounted) or F/8 (dob). I do not think Celestron and Meade make newts anymore. There are some Mak-Newts at 6" F6, though.
Skywatcher/Synta, Guan Sheng and Discovery are your options for a plain vanilla newt. Orion ones are actually from Synta. Guan Sheng are supposedly a bit better than Synta and is available from Kahn Scope (Canada). There are local dealers for Skywatcher/Synta newts though.
the schmidt-newt from meade...
if i'm not mistaken, it is a regular newt with a corrector plate of an sct
the 6-incher has speed of f/5...will the corrector plate remove coma?
and i'm not looking for dobs
Kamikazer wrote:the schmidt-newt from meade...
if i'm not mistaken, it is a regular newt with a corrector plate of an sct
the 6-incher has speed of f/5...will the corrector plate remove coma?
and i'm not looking for dobs
I don't think it is simply a regular newt with a corrector plate. I think it has a spherical mirror with a Schmidt plate instead of a parabolic mirror in a regular newt. Anyway, yes, the design should eliminate any comatic or spherical aberration.
i was pondering thru elton's statement for the past few days. now i finally come up with a conclusion. increase magnification does not make your scope use less of it's aperture, it just make your scope use lesser of it's fov.
a simple experiment to prove my point. centre on mars and keep it in the centre of the eyepiece(tracking or whatever method). now get a aperture mask, maybe 30-40% of your scopes aperture and cover the front of the scope. u will realise that the image becomes dimmer.
the reason is that the entire aperture of the scope is being used, even at high magnification. just that at high magnification, the amount of the fov of the scope u use will be lesser.
light from the sun reaches mars and then is being reflected to earth, therefore we see mars. the light is being reflected in all direction, that's why we see mars in jurong, and also changi or even further away. the light reaches the entire aperture of telescope and is being converge to a point. your eyepiece will handle the rest of job of bringing it to our eyes.
if u turn your eyepiece around, u will find that a 30mm eyepiece will have a much bigger piece of glass than a 7mm eyepiece. this is because the light from the area beside the object you wish to view(mars in this case) is not required on a eyepiece with a higher magnification.
so now back to the topic of barlow reducing coma. i will first have to explain what affects the image quality.
usually when we say a scope has a longer focal ratio, 2 things can happen. either it has a longer focal length for the same aperture(ie 150mm aperture, f/8 which have 1200mm focal length or f/4 which have 600mm focal length). or it can have lesser aperture for the same focal length(ie 600mm focal length, aperture of 150mm for f/4 or aperture of 100mm for f/6).
for the same focal ratio, as the aperature gets larger and larger, abberation will get worst. by masking an area of the scope, what we are doing is reducing the aperture and also increasing the focal ratio. both will improve image quality.
but in the case of using a barlow, what we are doing is only increasing the focal length. there is a slight chance of the image getting better on cheaper eyepieces in terms of sharpness and edge distortion, but as i said, slight. coma might not even be reduced.
a possibility of using a barlow to reduce coma is to stick the barlow all the way into the scope, therefore acting as a aperture mask, blocking part of the light reaching the eyepiece. i'm not responsible if you scratch ur secondary mirror as a result of doing so.
kayheem wrote:
Are you looking at an equatorially mounted newt or a dob? The 6" ones are usually F/5 (GEM-mounted) or F/8 (dob). I do not think Celestron and Meade make newts anymore. There are some Mak-Newts at 6" F6, though.
Skywatcher/Synta, Guan Sheng and Discovery are your options for a plain vanilla newt. Orion ones are actually from Synta. Guan Sheng are supposedly a bit better than Synta and is available from Kahn Scope (Canada). There are local dealers for Skywatcher/Synta newts though.
Kay Heem
how good are their optics?
are they as good as those from good manufacturers(celestron, meade, etc) ?
kayheem wrote:
Are you looking at an equatorially mounted newt or a dob? The 6" ones are usually F/5 (GEM-mounted) or F/8 (dob). I do not think Celestron and Meade make newts anymore. There are some Mak-Newts at 6" F6, though.
Skywatcher/Synta, Guan Sheng and Discovery are your options for a plain vanilla newt. Orion ones are actually from Synta. Guan Sheng are supposedly a bit better than Synta and is available from Kahn Scope (Canada). There are local dealers for Skywatcher/Synta newts though.
Kay Heem
how good are their optics?
are they as good as those from good manufacturers(celestron, meade, etc) ?
as proven by Chuan Yee, as long as you don't get those ABC branded mirrors, even a 10" synta mirror may outperform an 8" Zambuto.
Given that the Zambuto will probably result in better images, the differences is too subtle for me to see. of course the hard core perfectionist like cc will comment otherwise but images on the 10" dob with chinese mirror is brighter and clearer than the one with 8" zambuto mirror...
there, I said it! now let's wait for cc and gang to flame me....
The Boldly Go Where No Meade Has Gone Before Captain, RSS Enterprise NCC1701R United Federation of the Planets
Airconvent wrote:
as proven by Chuan Yee, as long as you don't get those ABC branded mirrors, even a 10" synta mirror may outperform an 8" Zambuto.
Given that the Zambuto will probably result in better images, the differences is too subtle for me to see. of course the hard core perfectionist like cc will comment otherwise but images on the 10" dob with chinese mirror is brighter and clearer than the one with 8" zambuto mirror...
there, I said it! now let's wait for cc and gang to flame me....
RICH!!!!!! I have been misquoted by you again!!! ARGGHHH I am going to leave my mark on ur ETX105 next time I see you!!!!
I love aperture more than over-the-top optical perfection... See what I wrote previously in SingAstro when answering a post on how image quality differs between a mass-produced 8" SCT and a scope with a high-quality 8" mirror such as a Portaball:
Okie, based on my own experience, my (ex-Vincent Snr) 8" Portaball w Zambuto mirror easily outperforms 8" SCTs in image sharpness, contrast and brightness (but at a higher price of course and minus all the electronic & GOTO wizardy, which is a plus or a minus depending on how u look at it).
The only 10" SCT I have seen through throws up a brighter image but is not as sharp nor contrasty. Chuang Yee's ex-10" Discovery gave the 8" Zambuto a good run for its money though. DSOs are noticeably brighter and more details are visible. On planets, the two scopes perform similarly, w perhaps an edge to Portaball.
BTW, Chuang Yee's scope was from Discovery Telescopes.
acc wrote:
RICH!!!!!! I have been misquoted by you again!!! ARGGHHH I am going to leave my mark on ur ETX105 next time I see you!!!!
I love aperture more than over-the-top optical perfection... See what I wrote previously in SingAstro when answering a post on how image quality differs between a mass-produced 8" SCT and a scope with a high-quality 8" mirror such as a Portaball: Okie, based on my own experience, my (ex-Vincent Snr) 8" Portaball w Zambuto mirror easily outperforms 8" SCTs in image sharpness, contrast and brightness (but at a higher price of course and minus all the electronic & GOTO wizardy, which is a plus or a minus depending on how u look at it).
The only 10" SCT I have seen through throws up a brighter image but is not as sharp nor contrasty. Chuang Yee's ex-10" Discovery gave the 8" Zambuto a good run for its money though. DSOs are noticeably brighter and more details are visible. On planets, the two scopes perform similarly, w perhaps an edge to Portaball.
BTW, Chuang Yee's scope was from Discovery Telescopes.
cheers
cc
ok ok...i know some people are very very very passionate about their scopes..like some people are passionate about their dogs...so I take some precautions here anyway, based on your threat, time to pop by to sim lim square to but some screen protector for my ETX!! 8)
but as I mentioned, image quality is better in the 8" zambuto but isn't it exciting to be able to see fainter objects on the 10" discovery dob?
rich
The Boldly Go Where No Meade Has Gone Before Captain, RSS Enterprise NCC1701R United Federation of the Planets
I am going to leave my mark on ur ETX105 next time I see you!!!! 
