Why are refractors of limited use?

[nckjsmitj]

Why is it that refractors are often quoted as having limited uses? Most websites seem to box these scopes as good for observing solar system objects but not other types of objects?

My binoculars are fab at viewing many object types and I assume a refractor is just a single giant bino (well monocular really).

So what is it that limits a refractor compared to other types of scope?

N.

[RikM]

I don't think that refractors are limited use, just that refractors above a certain size tend to get a bit pricey and you need aperture for deep sky viewing. I have a 10" Newtonian that cost about £400, I expect you would need to add a couple more zeros to get a 10" Apo refractor.

[nckjsmitj]

Is that it then? Those within the reach of mere mortals are 'on the small size' and that is why they have such restrictions?

[Stephen]

Is that it then? Those within the reach of mere mortals are 'on the small size' and that is why they have such restrictions?

What restrictions?

[RikM]

I think what most descriptions mean is that with relatively small aperture but nice sharp optics (no diffraction effects from secondary spiders etc.) and decent focal length, refractors may be best suited to lunar, planetary and double star observations. That doesn't mean they are necessarily bad for deep sky viewing though.

[barkis]

I guess the reason might be the refractors are commercially at least, inhibited by their objective sizes.

I would consider anyone who owns a 150mm Apochromatic refractor, very fortunate. I could never afford such an instrument.

I do own a 150mm f8 Achromatic frac. and indeed I'm happy with the views it affords me. Sure it has some chromatic aberration, yellow fringes on the brighter objects, not least the moon, but I just ignore it. As for deep sky objects, I can easily observe galaxies and nebulae, and double stars too. The light grasp isn't brilliant, but I have a reflector of larger aperture I can turn to.

So, probably size restriction is the main reason for refractor dissentors. The large objective intruments, are inch for inch, much more expensive to buy than reflectors, plus the mounts required for the bigger fracs, by and large have to be big, and solid, especially in the field of astro photography.

In a nutshell then, it is expense, and objective size limitations imposed by costs. There are some quality Apo's though, in the 80 - 120mm range

Ron.

[Stu]

The main limitation with refractors is the cost and difficulty of manufacturing them at larger sizes. 4 or 5" is about the largest affordable and this means they don't have the light grasp of larger dobsonian scopes.

Refractors, and particularly apochromatic refractors are excellent on planets, open clusters and double stars, aswell as brighter nebulae. They have very good contrast and wonderful tight star shapes. In dark conditions they will manage reasonably on galaxies but really you need an 8 or preferably 10" or larger scope to show those well.

Longer focal length fracs (often achros) are better for planetary use, lunar and doubles whereas the medium/shorter f/l apo scopes can give wonderful widefield views which are not achievable with newts, whilst also performing well at high power.

Stu

[John]

I love refractors and don't find them restricting other than in pure light grasp terms, because, for the reasons given already, really large refractor apertures are very costly. When I want to observe faint deep sky objects I use my 250mm newtonian. Most of the rest of the time I'm using either my 102mm or 120mm refractors.

[garethmob]

i know for imaing big fracs have a higher focal length and so slower scopes, wouldnt that effect the viewing, take longer to see an object or am i just too tired tonight ? lol

[rowan46]

for many imagers refractors are the weapon of choice. you don't need apparture for imaging but you do need good optics. Small apo's are relatively affordable, have good optics and being small don't stress the mount too much.

[neil phillips]

I love refractors and don't find them restricting other than in pure light grasp terms, because, for the reasons given already, really large refractor apertures are very costly. When I want to observe faint deep sky objects I use my 250mm newtonian. Most of the rest of the time I'm using either my 102mm or 120mm refractors.

This may be true for visual but for imaging, fracs, are really quite limeted, yes a 9 " apo refractor would be exceptional imaging.

But the cost is way ott. a 3 or 4" apo on lunar and planets, or 10" newt. A good newt would kill it stone dead. Left in the dust on planets.

Even a 5" tak would not out perform my 245mm Europa. small sharp contrasty images, but really very limeted in total focal length.

Try pushing a 5" tak To 13 M focal length on mars, and there is the rub.

I would love a 10" Tak dont get me wrong, hell a 7" would be dynamite. But sorry similair can be got for a few hundred quid. with less contrast and crispness, but for imaging unless someone is loaded. Good refractors are very limeted. if someone wants to give me a massive apo for jupiter next year, yeah i will take it

[nightfisher]

This may be true for visual but for imaging, fracs, are really quite limeted, yes a 9 " apo refractor would be exceptional imaging.

But the cost is way ott. a 3 or 4" apo on lunar and planets, or 10" newt. A good newt would kill it stone dead. Left in the dust on planets.

Even a 5" tak would not out perform my 245mm Europa. small sharp contrasty images, but really very limeted in total focal length.

Try pushing a 5" tak To 13 M focal length on mars, and there is the rub.

I would love a 10" Tak dont get me wrong, hell a 7" would be dynamite. But sorry similair can be got for a few hundred quid. with less contrast and crispness, but for imaging unless someone is loaded. Good refractors are very limeted. if someone wants to give me a massive apo for jupiter next year, yeah i will take it

I have a 7" APO..........its a skymax 180, the mak`s really do fill a gap

[ollypenrice]

Because of my work I have all sorts of scopes available from small apos to a half metre Newt. (The pay ain't great but the work makes up for it!!!) They all do 'something' best.

The most optically and mechanically perfect one is a Tak astrographic refractor. It gives the best widefield imaging results that can be had at any price in my view. I don't want square stars or spikes in widefield images so all short FL secondary spider scopes are out, for me. Faster reflecting systems without spiders exist but take too much collimating and focusing for my taste. The Tak is F3.9 or F5.3. Fast enough and it is 100% plug and play.

The 5 inch apo (TEC140) gives the most beautiful deep sky views and the big Dob gives the deepest. The TEC is a fine mid FL imaging scope but slow at F7. I doubt you can get much better planetary views in anything bar a bigger refractor but maybe you can. Not much better though, that is simply not possible.

You want to image small galaxies and planetaries? Enter Yves' 14 inch ODK. I guess it would be no slouch on the planets either but we don't use it that way.

There is no 'one best scope' just as there is no 'one best car' or 'one best house.'

And to quote Monty Python, '...I think this is good!'

Olly

[Atlas]

I have a 6" Refractor. It can see and image everything I wish. Only cost the equiviant of 500 pounds.

Excellent at viewing and wonderful at imaging.

[chiltonstar]

A point not mentioned is "ease of use". I've had a 4" long focus refractor for 30+ years, although now I tend to use an 80mm orion ED, or a Mak 127mm more. The 'fracs have the enormous advantage that they are "ready to go" immediately, which is important in the UK climate! Neither reflectors nor Maks (or SCTs) (Mak was mentioned previously as a good 'frac substitute - I agree) can be used without a temperature equilibration delay, and often the weather degrades in this time! And of course, you don't need to collimate 'fracs......

Chris

[Catweazel]

Have to agree with chiltonstar on the ease of use, when you are only going to get 45 minutes of clear sky, my Evostar 5" frac is a godsend, and is very nice on planets, lunar and double stars, and pretty good on many DSO's; it just doesn't have the range (depth) of my 200P reflector, and is a non starter for imaging, but in the end, it's just horses for courses, as they say

[Moonshane]

here's my reasons - scroll down to post #15 http://stargazerslounge.com/diy-astronomer/183426-aperture-mask-16-f4-dobsonian.html