Newt or SCT for planets?

[originaltrilogy (Petr)]

I would like a C14 but cannot afford.

Can you get slow newtonian for planets instead if you have sturdy mount?
Newtonians seem cheap but not many are f10? Where can you get ones for planets?
Is it hard to make one yourself?

[mental4astro (Alexander)]

Doesn't matter if your Newtonian is f/5 or f/10, using appropriate eyepieces and/or barlows will give as good views of the planets as an f/10 SCT. My 8" f/4 newt gives me as good views as my C8 at the same magnification.

Slow newtonians are not really made anymore. You really don't want to carry around a 12" f/10 newtonian with a 3m long tube to accomodate the focal length. The mount would need to be overengineered too.

You can make your own mirror. Not overly difficult, and there is a thread on this in the DIY forum. Have a look. A slow mirror is much easier to make than a fast one too.

Mental.

[originaltrilogy (Petr)]

I want for photography, so need long focal length. I won't be carrying, is for permanent setup on a huge old clockwork mount I found. I also thought slow mirror might be cheaper as easy to make.
Thank you for help. How much money is one roughly so I know if I am dreaming or not?

[mental4astro (Alexander)]

Just the OTA, a 6" starts around $400. This is a good scope, not a dodgey thing.

Look at andrewscom.com.au, bintel.com.au, myastroshop.com.au. There are others, but I've delt with these folks many times.

A C8 is no slouch either, though an SCT is much more pricey. Planetary and lunar photography is also possible with a dobsonian mount too. Tracking isn't as essential as today's software programs (many of them free too) is capable of dealing with image movement. Some folks even get away with DSO photography too with dobs. Depends on your pockets and the mount youhave at the moment.

[originaltrilogy (Petr)]

I have a c9.25 now, but want to sell it and get something bigger. Cannot afford C14 so looking at newtonian for value.

[mental4astro (Alexander)]

What's wrong with your C9.25 for the planets? That is a mighty fine instrument for them. A newtonain may be a step backwards as to get a gain in aperture you need a proportionately larger mount. You won't be coming out in front dollar wise in this way.

Have you attempted all the possiblities with your C9.25? Maybe you can ask in the solar system photo forum those wizards on how to get the most out of your existing gear. Larger isn't always better.

[icytailmark (Mark)]

dont buy a c14 if your not gunna have it setup permanetly because its very frustrating to carry it outside and align etc. Im currently in the process of building my observatory with a pier for my c14. I suggest you buy a newt on an eq mount if your new to planet imaging because the c14 focal length makes it tough to get the planet on the camera chip and keep it on there.

[gbeal]

Newt from me as well, I have a 10" f5 newt, which is usually in a dob base, but with a set of tube rings also serves as a lunar/planetary (and more lately, solar) scope.
Don't be fooled by the f5 side, it is a stunning scope, and if you want more focal length/image scale simply use a Barlow. I use a 2.5x and 5x PowerMate. Hard to beat for all round use.
Gary

[icytailmark (Mark)]

check out this

http://www.bintel.com.au/Telescopes/...oductview.aspx


this is another option you could consider.

[alocky (Andrew lockwood)]

The key advantage a long focal ratio newt has is the smaller secondary obstruction over the equivalent SCT. A well designed f7 newt can have a reasonably sized fully illuminated fov with a 20% obstruction, compared to the typical 33% of a cat. Trade off is mounting the optics grows exponentially more difficult with size.
There are many parameters involved but putting it simply, more aperture gives more resolution (notwithstanding seeing conditions) and smaller obstruction improves the contrast. You want both.
Making a good mirror suitable for planetary work is not easy or simple. It will be the third or fourth mirror you make. Only take mirror making advice from someone willing to let you look through one they've made.
Regards,
Andrew.

[tlgerdes (Trevor)]

if you are thinking of imaging planets, then the longest natural focal length is what you really should look for. You will get this an SCT or Maksutov.

300mm f5 newt = 1500mm focal length
300mm f10 sct = 3000mm focal length

Yes, you can put barlows and powermates etc onto a newt, but you can also do the same for sct's

[Wavytone]

Petr, for observing the planets, in increasing order of quality:


Short-focus Newtonians (typically f/5 or less) are intended for wide-field imaging, not high magnification. Adding barlows and/or ridiculously short eyepieces is about the worst solution for planetary observing.

(Fast Newt = worst choice)

SCT's at f/10 are "all-rounders', able to show pretty much anything but they aren't the optimal solution for anything, either - f/10 is too slow to be much good for imaging, and not long enough to excel at high magnification. Worse still, they have a very big secondary mirror which degrades image quality, and usually have barely adequate optics - most SCT's I have looked through do not produce an acceptable diffraction pattern on a bright star.

(SCT = poor choice)

So... you want long focal length, small secondary obstruction (or none), good optics with the minimum number of surfaces, and without using barlows:

Maksutov's in the range f/15-f/20 are usually the choice for planetary observers wanting high magnification in a compact easy-to-transport scope. Small secondary coupled with optics from a good manufacturer generally results in an excellent image, pretty much the equal of a good refractor of the same aperture and focal ratio.

(Mak = better choice)

Long focal ratio newtonian - at least f/8 and ideally f/10 - these do give excellent high-power images though big and bulky to use. I had an f/8 20cm for a while, but its sheer size forced me to part with it at a time when I simply didn't have the space for such a big scope. Another example is the 16" f/7 which ASNSW had at Mt Bowen - this was an exquisite scope for observing the planets, but definitely not portable.

(Long FL newtonian = very good)

Refractors - for a given aperture, a long focus refractor will pretty much outperform everything else, except for one telescope design (below). in this respect I mean an ED APO with a focal ratio not less than f/10, and preferably f/15. Big, heavy, and hideously expensive once you talk about 15 cm apertures or more. The cheap short-focus refractors (f/7 typically) are again designed for wide-field imaging, not high magnification.

(big long refractor = excellent choice)

Schiefspieglers = a two or three mirror telescope with folded optics offering long focal ratio (f/20 or more) with an unobstructed light path, folded into a compact box. These look pretty weird but easily give the best images bar none.

Some years ago Barry Adcock (ASV) showed some images of Mars and the moon that he took using a home-made 12" schiefspeigler that looked like they came from the Hubble.

(Schiefspiegler = best choice)

[Wavytone]

Petr, for observing the planets, in increasing order of quality:


Short-focus Newtonians (typically f/5 or less) are intended for wide-field imaging, not high magnification. Adding barlows and/or ridiculously short eyepieces is about the worst solution for planetary observing.

(ast Newt = poor choice)

SCT's at f/10 are "all-rounders', able to show pretty much anything but they aren't the optimal solution for anything, either - f/10 is too slow to be much good for imaging, and not long enough to excel at high magnification. Worse still, they have a very big secondary mirror which degrades image quality, and usually have barely adequate optics - most SCT's I have looked through do not produce an acceptable diffraction pattern on a bright star.

(SCT = poor choice)

So... you want long focal length, small secondary obstruction (or none), good optics with the minimum number of surfaces, and without using barlows:

Maksutov's in the range f/15-f/20 are usually the choice for planetary observers wanting high magnification in a compact easy-to-transport scope. Small secondary coupled with optics from a good manufacturer generally results in an excellent image, pretty much the equal of a good refractor of the same aperture and focal ratio.

(Mak = better choice)

Long focal ratio newtonian - at least f/8 and ideally f/10 - these do give excellent high-power images though big and bulky to use. The usual problem is that the mount needed is big, expensive and heavy. I had an f/8 20cm for a while, but its sheer size forced me to part with it at a time when I simply didn't have the space for such a big scope. Another example is the 16" f/7 which ASNSW had at Mt Bowen - this was an exquisite scope for observing the planets, but definitely not portable.

(Long FL newtonian = very good)

Refractors - for a given aperture, a long focus refractor will pretty much outperform everything else, except for one telescope design (below). in this respect I mean an ED APO with a focal ratio not less than f/10, and preferably f/15. Big, heavy, and hideously expensive once you talk about 15 cm apertures or more. A good mount is also a big problem.

(big refractor = excellent choice)

Schiefspieglers = a two or three mirror telescope with folded optics offering long focal ratio (f/20 or more) with an unobstructed light path, folded into a compact box. These look pretty weird but easily give the best images bar none.

Some years ago Barry Adcock (ASV) showed some images of Mars and the moon that he took using a home-made 12" schiefspeigler that looked like they came from the Hubble.

(Schiefspiegler = best choice)

[el_draco (Rom)]

Originally Posted by originaltrilogy

I would like a C14 but cannot afford.

There is a good C 14 on sale in the equipment forum. Take a look. These are excellent all round scopes.

[Poita (Peter)]

I get a gorgeous diffraction pattern on bright stars in my 9.25 Edge SCT. Like anything, there are good and bad ones.
Most of the best planetary imaging I have seen comes from SCTs as well, so they aren't as bad as many people seem to think, especially if cooled correctly and collimated properly.
A poorly cooled, badly collimated SCT will give crappy views.

Having said that, Wavytone is pretty much on the money with his breakdown, but it looks like you have a permanent setup and a monster mount, so the portability arguments are irrelevent in your case.

[Poita (Peter)]

Where would one find a Sheepsprinkler?

[Shiraz (Ray)]

If you want to do images, have a look at what the planetary imagers who post on IIS use: 9.25-14 inch SCTs or 12-16inch f4.5-f5 Newts. If you can't afford an SCT, get the biggest aperture Newt you can afford + good quality Barlow, remembering that the mount will cost more than the scope. Scope quality is not as big a factor as might be imagined at these apertures, since a thermally stabilised large scope of commercial quality is almost always going to be better than the atmospheric seeing - in over a year of high res imaging with a 12inch f5 Newt, I have only once found conditions where the scope resolution was the limiting factor.

[silv (Annette)]

Where would one find a Sheepsprinkler?

(sorry possibly, Schiefspiegler is just a funny german lastname.
but schief means askew and spiegler is like the profession of a "mirrorer" if such a profession would exist. )

[Poita (Peter)]

Yeah, my heritage are Deutsche, Sheepsprinkler was one I heard at a star party years ago, made me laugh.

But it was a serious question, does anyone make them for general sale?

[silv (Annette)]

Thanks for recycling the word, then. gets a special meaning when read from within NZ...

I found one German shop, selling their hand made Sheepsprinkler for 2000euro +
http://www.wolterscope.de/produkte/p...ste/index.html