Quote:
Originally Posted by sunslayr
I can definitely understand where you are coming from, it can quickly become overwhelming with all the different options. Its a bit like asking what car should I buy? Like cars all telescopes have advantages and disadvantages there is no one size fits all 'best telescope'.
I the case of an imaging newtonian Everything must be perfectly in line to achieve the best results, this is can be a little difficult for a beginner which is why people often recommend a refractor ( Link to Astrobaby's guide). Not only does something like an F4 Newt require precise collomation but the focuser also has to be stiff enough to handle the precision involved and can often require and upgrade to something like a moonlite focuser which can add to the cost.
The central obstruction in a newtonian is the the secondary mirror that reflects the image from the primary into the camera or eye through the focuser. This 'obstruction' blocks some of the light and makes the image dimmer and reduces contrast.
Now normally a newt is large enough to compensate for this but If you want a wider field you start hitting the limit of what can be achieved by going faster with a reasonable price so you have to go smaller say 150mm F4. However while at 200mm the secondary taking up around 35% of the total aperture, at 150mm it is taking up almost 47%. That is why people avoid small imaging newtonians because a refractor is a more efficient at gathering light at those sizes.
Hopefully that helps a little. |
I see, that is an excellent answer and explanation, now i know about those small Newtonian, thank you very much