Refractor vs Reflector

[Bullfrog (Jeremy)]

I've recently acquired an old Skywatcher 120/600 refractor. I have not had any experience with refractors and would like some advice.

I have a little 114mm refractor and have been lucky enough to be the custodian of a Meade LX90 8in SCT for the past 12 months. I have used both of these scopes a lot for both visual and astrophotography. I have produced some reasonable images from both. Obviously the LX90 has produced the better shots.

I have noticed that many astrophotographers use refractors and would appreciate if someone could explain the pros and cons of refractors.

The scope is in reasonable condition. Its has a William Optics 10:1 focuser that works very smoothly. The objective lens has a few spots on it. What would be the best way to clean it?

Any advise is welcome.

[dannat (Daniel)]

for cleaning lik to use zeiss wipes, but have also had god success with blue windex..im guessing they are dried dew marks -do they look wispy/spider web nb tis can be fungus

the adv of refractors is they are lightweight, easier to mount & you don't need to worry about collimation as much

cons can be they have a longer focal ratio e.g. f7, also they have a relatively short focal length so are not as suitable for planets/ deep galaxies- they also cost a lot more per inch of aperture

[cometcatcher (Kevin)]

The Skywatcher 120/600 refractor is an achromat. As such it has some chromatic aberration that throws blue rings around stars. Not so bad for visual but for photography can be unwanted. ED or APO refractors are best for photography but are more expensive.

There was a thread on the 120mm F5 here.

http://www.iceinspace.com.au/forum/s...d.php?t=117525

My latest toy is a Skywatcher ED100 refractor and it's a great no hassle scope.

[OzStarGazer]

I bought a refractor last month (I wanted to buy it in September because it is so cold now but it was on sale...) I bought is because they say refractors are better at producing sharper images, so they are particularly good for moon and planetary viewing. In my case I was not able to use prime focus with my dob because of its focusser, but it works well with the refractor, except that there is not much to see... Dobs are better for wide-field viewing. I don't know much about reflectors that are not dobs...

[astro744]

Originally Posted by OzStarGazer

Dobs are better for wide-field viewing.

The width of the field is a function of focal length and field stop diameter for visual and sensor size for imaging. Unless you have 4" f15 refractor, the focal length of most commercially available refractors is much less than reflectors and hence are capable of a wider field.

[OzStarGazer]

Originally Posted by astro744

The width of the field is a function of focal length and field stop diameter for visual and sensor size for imaging. Unless you have 4" f15 refractor, the focal length of most commercially available refractors is much less than reflectors and hence are capable of a wider field.

I was thinking of a small "dob" like mine...

By the way, something that surprised me is with my new refractor is that I tried my 8mm eyepiece with a Barlow lens (2X) by pointing at a partially illuminated house (a wall in the distance) at night (no planets or anything in view unfortunately) and it worked. It is a 90mm (aperture), 1000mm focal length refractor. The magnification with the Barlow is 250 which should be too much for my scope, but although the focus was not perfect it was pretty good ("almost there"), and lots of details were visible. Maybe because it was a relatively close terrestrial object (no air turbulences?). It was really an experiment, I didn't think it would work at all at that magnification.

[N1 (Mirko)]

Originally Posted by OzStarGazer

and lots of details were visible. Maybe because it was a relatively close terrestrial object (no air turbulences?). It was really an experiment, I didn't think it would work at all at that magnification.

Dobs work for terrestrial too if you don't mind the orientation of the image and your target isn't too close. Looked at some cranes with the 10" the other week, which were sitting on an aerial pole about 100m away, give or take (about the closest the dob can focus without changing the configuration). I could actually see their eye lids blink.

The magnifying power of an astro scope is immense. Use responsibly.

[julianh72 (Julian)]

Originally Posted by N1

Looked at some cranes with the 10" the other week, which were sitting on an aerial pole about 100m away, give or take

When I helped my father un-box and set-up his Meade LX90 200 mm SCT a few months back, we were in the backyard in daylight, and we needed a "reasonably distant" target to get the finder-scope roughly aligned. I pointed the scope at a joint in a concrete kerb about 30 metres away, racked in and out to find focus, and got a nice close-up view of some ants going about their food-foraging business. If we had a camera attached, the footage would almost have been worthy of a David Attenborough documentary!

[OzStarGazer]

I used my dob for terrestrial viewing to align my finderscope too.
Anyway, I could see pigeons' poop on a roof pretty well. Not exactly exciting, but still...

[N1 (Mirko)]

Originally Posted by OzStarGazer

I used my dob for terrestrial viewing to align my finderscope too.
Anyway, I could see pigeons' poop on a roof pretty well. Not exactly exciting, but still...

Yuk.

[Bullfrog (Jeremy)]

Cheers for the help guys

Kevin I read that post you linked, great information. Really in depth coverage about refractors. It's given me great insight into what I can expect.

Now I've just got to get all the mounting gear so I can start using it.

Bullfrog