refractor vs reflector for planets

[algol]

basically what the title says, i have a 130pm skywatcher newt. and was wondering what size of refractor would be needed to improve the planetary views of what i already have at the minute?

not thinkin of upgrading already more of a temptation thing for just planetary use.

[philsail1]

"Algol"

To give a simple answer - many, many refractors would give you equal and probably much better views of the planets than you are getting with your 130mm Newtonian. But (and it is a BIG "but"). You would have to spend much, much more money than you did for your 130mm scope!

I had the 130P (with single axis motor drive) and I thoroughly enjoyed it. Eventually caught "aperture fever" and started spending my way to "bigger and better" scopes!

Now have the equipment listed below - and do you know, the views I get are bigger, but I cannot detect "that much more" than I did with the 130P! And the bigger scope takes a lot longer to set up.

To obtain the views we all dream of, we would need a scope the size of the "Keck" telescope!

However, if you are thinking of "up-grading" in the future, just post your question and you'll receive plenty of advice on what scope (refractor if you want to go for one of those) to go for!

As you can see, I have the TAL100RS which "I" think is a great scope for the money (£180). It's not a portable scope, and needs the HEQ5 mount to hold it steady, but it suits my particular needs. Individual "need" is a crucial factor in everyone's choice of scope.

That's about all I can say "Algol," but whilst you are just mulling over what kind of scope will be your next, have a look at the "attributes" of various scopes. At least you will be able to narrow your choice down, and can then ask some serious questions as to the merits of your choices.

Best wishes,

philsail1

[Andrew*]

IMHO Phil's given you a great answer. The scope you have is a cracker for the money and if you wanted to improve on it you could either move up to say an 8" newt for higher resolution, or say a ED100 or 120mm achro for higher contrast. One other thing to consider of course would be a 5" or 6" mak that are said to perform superbly on the planets. I've yet to peek through one though.These upgrades all mean serious money and whether that money would be well spent is a matter of great debate.

HTH

Andrew

[algol]

cheers for the help guys, i'd already seen the 120 apo and thought it looked ace for the money to be honest, also the C10 celestron newt for 509 is awesome.

not thinkin of it yet prob be a year or two before i up my newt but i was considering a 120 apo for next year maybe ready for jupiter rising, as i've been toldthat the view through an apo beats a newt on planets eg contrast etc.

[Andrew*]

Yeah, wait for the big planetary year (is that 2009?) then get the best planetary gear you can afford. Getting planet stuff this year is pretty pointless really :?. Looking forward

Andrew

[algol]

exactly mate that is what's going through my head to be honest, get to learn the basics at min then get planetary gear next year or so.

[Ajohn]

I bought an old meade f9 5ins ed apo some time ago. In terms of viewing it outperforms a 10ins sc on all objects that it can register. It's just limited by magnitude. The problem with the sc's is that huge 2ndry obstruction. It washes out contrast and even though the detail may be there the eye just can't register it. My 1st experience of that was jupiter on a C8 wow I thought and went for a higher power eyepiece. Serious disappointment- went back down again. As to macs I am not inclined to believe the claims without figures unless it's a newt type and has been deliberately designed for planets. It needs to have a very well made mirror and lens too. A better and maybe cheaper option is a newt with a 1/10 wave mirror and a small flat. That will involve a lot of expense these day or making it yourself - called atm. As I've come to the conclusion that the best views come from refractors and newts I might finish up buying a newt and refiguring the mirror - a lot less work than making a mirror from scratch. Also the people that sell atm stuff charge far to much for mirror blanks etc. The only problem then is that I reckon I would want a 10ins mirror to compete with the refractor and wouldn't be happy about it being faster than F6.That makes a donor telescope a bit difficult to find. An 8ins may be easier but I think that the refractor would outperform it in all respects. In the mean time I'm trying a faster slightly smaller refractor as the 5ins F9 is still a bit of a handful. Also imaging is an entirely different kettle of fish. Just think about what actually sets limiting magnitude.

John

[KaStern_Former_Member]

Hello Ajohn,

The problem with the sc's is that huge 2ndry obstruction.

I di not agree to this opinion. The obstruction in one of the not very important problems of the SC Telescope Type.

You can check that by applying a 33% obstruction to a first class Apo. U can use a blackened cardboard disk.

Will the contrast transfer break down? No, it will not. I have supposed to do that so often in german astronomy boards,

but noone did do that, or noone who did do that wrote about his results...

The real problems of the SC are:

- slight decollimation causes severe contrast loss

- the mass-product-SC is NOT fully user collimatable

- sometimes rough surfaces, especially the schidt-corrector-plate

- thermal problems. The Mirror with big thermal capacity is at the downside of the tube, warm air rises from the mirror,

whereas cold air sinks down from the corrctor plate. And the rays have to go 3 times through the instable air in the tube.

I bought an old meade f9 5ins ed apo some time ago. In terms of viewing it outperforms a 10ins sc on all objects that it can register.

That SC sems to suffer from a lot of problems. The old Meade ED Apo is not freee from fals colour, althouth ca is no longer disturbing.

I could compare a 6" to my 8" Newt viewing Jupiter with high magnification and it was no real competion, the 8" Newt displayed better

contrast and better colour fidelity. Linear central obstruction of that Newt is 19%.

If it was only the central obstruction the mtf curve of the 10 SC would be way better than of the 5" ED Apo!

But if there are multiple problems combined contrast loss can be severe.

Regards, Karsten

[Ajohn]

I must try that Karstern. If what you say is true I've been following folklaw on that one. I would agree that the quality of the product and it's set up will have an effect. Thanks for the idea I must try it. What I would expect to see is a reduction in the maximum usable magnification for optimum viewable detail. I should have a decent artificial star up and running at some point in the future. The garden is long enough to make effective use of it too. Apart from collimation this sort of thing is one of the reasons I want to make one. Just waiting for an hp inkjet cartridge to run out. Then I have to hope that I do own a scope that will actually show diffraction rings. I would expect to see a very marked change in the rings at 30%. What would then be useful would be to go on and see just what effect that has on the view of a planet.

I keep using the term visual because imaging is an entirely different kettle of fish even more so in recent years.

John