Hi Bharat,
Nice meeting you and your family at M.Barrage last Sat.
Here are my views on your queries:
1. As you are comparing a achromat with a Newtonian, generally yes at low power. At high power, the chromatic aberration of a achromat will compromise the image sharpness & contrast. This CA will reduce the image sharpness, contrast and resolution when you view the Moon, Jupiter, Saturn, Mars etc.
2. Yes it is noticeable.
3. The best planetary views are seen with a large Newtonian. A big premium newt will give better view than a apo. A rigid newt with premium optics, well-collimated and thermally stabilized will give sharp detailed contrasty planetary images similar to an apo, though there will be slightly lower contrast and maybe diffraction spikes. A smaller refractor can still be used for observing the brighter DSOs, but when it comes to DSO observation, bigger aperture is better, regardless of the type of scope.
Once I did a side-by-side comparison between a 3.1" f/7 'semi-apo' with a 4.5" f/4 newt on Jupiter. The newt beat the refractor easily, giving a bigger brighter, more detailed and equally sharp image. A 6" newt will collect 2.5 times more light, better resolution and allow higher magnification than a 4" achromat. I recommend the 6" newt over a 4" achromat.
I noticed the C102 Omni XLT achromat and the C150 Omni XLT newt are currently offered at the same price.
4" Refractor vs 6" Newtonian
While I recommend 6" newt over a 4" achromat, it is perfectly reasonable why someone else may choose the other way round, for a number of reasons:
1. A sharp high contrast refractor image is preferred.
2. Refractor can be used for terrestial viewing, not a newt.
3. A refractor requires minimal maintenance/setup and no collimation compared to newt.
4. Asthetically, a refractor is the classic telescope look, or looks better in your living room etc. This may be a factor
for newbies!
1. A sharp high contrast refractor image is preferred.
2. Refractor can be used for terrestial viewing, not a newt.
3. A refractor requires minimal maintenance/setup and no collimation compared to newt.
4. Asthetically, a refractor is the classic telescope look, or looks better in your living room etc. This may be a factor
for newbies!
rlow
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orly_andico
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Another thing is.. newts on EQ mounts can be a PITA unless you rotate the tube, which is a lot more inconvenient than loosening and rotating the diagonal.
So from a user-friendliness perspective the refractor is more convenient. Between a 4" achro and 6" newt I'd also go with the newt.. am not sure if the C150 is the "short tube with a barlow in the focuser" type though.. if it is, I'd go with the 4" achro since those barlowed short tubes don't have a good reputation optically..
I also gotta add: I used to be a "big aperture / low mag" kind of person back in Philippines. But.. with the lousy weather these days and the light pollution in Singapore, I bet most of us are going high mag lunar and planetary because often that's the only observation you can do. And when you get to that point ( > 100X ) the CA on an achro will piss the heck out of you. :-)
So from a user-friendliness perspective the refractor is more convenient. Between a 4" achro and 6" newt I'd also go with the newt.. am not sure if the C150 is the "short tube with a barlow in the focuser" type though.. if it is, I'd go with the 4" achro since those barlowed short tubes don't have a good reputation optically..
I also gotta add: I used to be a "big aperture / low mag" kind of person back in Philippines. But.. with the lousy weather these days and the light pollution in Singapore, I bet most of us are going high mag lunar and planetary because often that's the only observation you can do. And when you get to that point ( > 100X ) the CA on an achro will piss the heck out of you. :-)