Old "Refractor v Reflector" debate

[Donkeiller]

I know this has been done to death, but in the latest edition of "Sky at Night" observing guide, under "equipment needed" they say

"Small Scope- Reflector/SCT under 150mm, refractor under 100mm" and

"Large Scope- Reflector/SCT over 150mm, refractor over 100mm"

What are they implying here?

[Jon65]

Hi

I'm guessing here,and didn't see the article.Are they referring to imaging or general all round use.

If your budget and needs is for a small scope; consider a Ref/SCT under 150mm primary mirror size and under 100mm for the objective lens in the refractor,a Mak up to 100mm could also be added to the list.

And the opposite if your budget and needs are for a large scope start looking at over 150mm for a ref/sct and over 100mm for a refractor but no more than say 150mm for the Mak.

Jon

[spaceboy]

I think it is a guide to what equipment is recommended to see any particular object. Usually you will see a small icon next to an image of the object. IE: Something like M45 would be suitable for a small scope/ binoculars (should show an icon of a refractor, maybe binoculars or say small) where as some thing like M1 would require a large scope. (should show an icon of a SCT, dob or say large)

SPACEBOY

[brianb]

Trying hard to avoid rising to the challenge here: They've got it wrong. With modern dielectric mirror coatings, the disadvantage of reflector over refractor has vanished. The light grasp is pretty much the same & so is the contrast. Now I'm talking about equal optical quality here, and also in perfectly steady air: in turbulent air, the refractor has an advantage, though nowhere near as much as 50%: 10% is probably about right.

Handling differences are of far more practical importance than optical design.

[zcapp96]

I always remember that patrick moore would say the minimum for a refractor was 3" or 6" for a reflector. I think that it is a belief that with the central obstruction the 150mm reflector would perform on a par with a 100mm refractor (I would disagree). Or it could be about weight.

[brianb]

I always remember that patrick moore would say the minimum for a refractor was 3" or 6" for a reflector.

That was in the 1950s / 1960s when a 3" f/15 achromatic refractor (there weren't any other sorts then) cost about the same as a 6" f/8 Newtonian. Even then, with aluminimum coatings of not particularly good quality, the Newt would blow the refractor away for planetary work (resolution & contrast) as well as light grasp.

[zcapp96]

That was in the 1950s / 1960s when a 3" f/15 achromatic refractor (there weren't any other sorts then) cost about the same as a 6" f/8 Newtonian. Even then, with aluminimum coatings of not particularly good quality, the Newt would blow the refractor away for planetary work (resolution & contrast) as well as light grasp.

Not just then, I remember many a sky at night in the 80's and 90's and in his books. It was his staple advice!

[great_bear]

but no more than say 150mm for the Mak.

Why no more than 150 for the Mak?

[great_bear]

It was his staple advice!

That's the trouble with "staple advice" - it can be hard to change even when it's wrong. It sticks like porridge.

[jgs001]

It's an indicator of the size of the instrument you'd need to see it nicely I think...

In the deep sky tour in the March issue, M81 and M82 show you need a small scope... and you can see them in a small scope... I have... wouldn't say it was easy though. M101 and M51 recommend a large scope, I think you'll get more out of viewing them with a large scope than a small scope... I've not looked at either through any scope though... I did try... but never managed it.

[ollypenrice]

These days the difference, for me at least, would be summed up by, 'It ain't what you see, it's the way that you see it.' Refractors give a 'look' that I like. Very hard to definine and totally subjective. I am sure Brian is right on the light throughput. I don't for a moment think faint nebulosity greatly benefits from being seen in a refractor. For me it's the stars and the background sky.

A lot of these old rules of thumb need to go in the bin.

Olly

[Jon65]

Why no more than 150 for the Mak?

The reason why I would not buy a Mak greater than 150mm aperture is because of the very long cool down times.

I've read in the forum the SW Skymax 180mm, even though a great planetary and lunar scope can take up to four hours to cool down.

Set up at 6pm ready for observing at 9-10pm,best have another scope to hand I think.

Jon

[thommo10]

Hi all

Having read the above comments would a SW startravel 102 be comparable ie image quality of the Orion nebula, to my 150mm f/6 Newt that I bought back in the Eightes from Astro Systems or better

[great_bear]

I've read in the forum the SW Skymax 180mm, even though a great planetary and lunar scope can take up to four hours to cool down.

Set up at 6pm ready for observing at 9-10pm,best have another scope to hand I think.

Jon

cut-and-pasted from my own post in another thread:

[but] you don't think "Oh, let's do some astronomy!", pick up the Mak from it's position in the living room next to the log fire, and then plonk it on the mount outside and waste four hours doing nothing whilst it cools down.

Instead, you keep the thing in a secure place in the cold (a garage, or a basement, or the shed), and when you want to do astronomy you just go do it!

In real life, you adapt to such things, and use the device appropriately.

[GazOC]

The reason why I would not buy a Mak greater than 150mm aperture is because of the very long cool down times.

I've read in the forum the SW Skymax 180mm, even though a great planetary and lunar scope can take up to four hours to cool down.

Set up at 6pm ready for observing at 9-10pm,best have another scope to hand I think.

Jon

I've found it to be 2 hours at worst. If kept in a shed/ garage its pretty much ready to go straight away.

[Moonshane]

I think all this just confirms what we all know. one scope won't do everything and all scopes have plus and minus points. I think I'd change the word 'needed' though. any single scope of decent quality will be great on the sky and show hundreds / thousands of objects not visible to the naked eye.

I agree that stars are more 'attractive' in a refractor but there's nothing like aperture once you have seen the few brighter objects about. as we know, there are refractors and there are refractors - compare a skywatcher short tube with a Tak etc and you'll see a difference too.

personally, I just love dobs. easy to use, set up and pack away - great aperture for the money too.

[Macavity]

I learned a lot from (practical comparison of) my ST102 and MAK127. Tho', as I now (relatively cheerfully) aknowledge limitations in my physical and financial status, much of my remaining funds are plowed into a (new!) roll off observatory.

I think, many of us, were brought up on (can quote!) SPM's words. As pointed out, times / technology change? My feeling is: Start with modest scopes. Do the comparison for yourself. I do sometimes wince at (contradiction) "evangelical" threads. Some of this is about risk taking... (self) discovery? Don't reject the QUIRKY... In that vein: An Ioptron / MAK150 / Watec combination [part teasing].

BUT, if I do "win the lottery", I might think of SOME way to handle / accommodate

an "Six Inch Astro Physics"(?) APO, a HUGE Dobsonian etc. etc.

[zcapp96]

When I was at UCL we had a choice of a 24" reflector or a 24" refractor. (Yes I did say a 24 inch refractor) Jupiter looked quite good through one of those!