can you compare

[the bishop]

Hi

I have been thinking about this for some time and so this is

probably going to be the daftest question of the day...

I understand there are different types of scope using variations on light gathering,

some mirrors, others use lens and some a bit if both...yes?

But.... here it comes

Is there an umm a type of comparison chart between the scopes?

Meaning for example what would be the equivalent scope in terms of...

and I hate to say it coz it’s the wrong word but power or ability of say a

3”refractor? What would be the reflector size equivalent??

does that make any sense? Or is it just not possible to compare

Thanks

gra

[rwilkey]

Hi Gra, not come across such a comparison chart but that would be really handy I think, however, light-gathering power does make a difference, but in my view aperture is not king. I have a 4" refractor and an 8" reflector and to be honest I have never been disappointed with the refractor, I swear the objects are just as bright, however, the reflector does show more detail especially in things like globular clusters, but with open clusters the telescopes are equal in my view. Love your location btw!

[cantab]

There's a generally-held view that refractors punch "above their weight" in comparison to reflectors. It's true that reflectors do have a central obstruction, but the effect is minor and can't account for the reported worse per-aperture performance. I suspect the idea largely comes from looking through poorly-collimated reflectors and comparing them to refractors that can be factory collimated and will stay that way.

[Carbon Brush]

Then of course a simple size relationship reflector vs refractor is not enough.

I have compared 3 refractors, all 80mm objective with similar focal length.

No1 Thought it was OK until 2 & 3 were viewed. CA evident, but tolerable. Contrast/clarity down.

No 2. CA a bit better. Contrast much better.

No 3. A world ahead. Near enough zero CA and clarity/contrast excellent.

There would of course be performance differences in similar size and focal length reflectors, depending on optical and mechanical quality.

No easy answers!

[the bishop]

No easy answers YOU SAY...too true...thats the story of my life

It is a puzzler I admit!!

Obviously I had far too much time on my hands... well thats what the wife said!!

I just thought... I wonder if there a “general” sort of cross reference comparison

Between the scope types

Please note this is just for an example...but say a 3” frac would for arguments sake

roughly = a 5” newt or something like that??

But it would seem that there is far, far more to it than that,

I haven’t compared one type side by side with another type

I tend to agree that refractors sort of punch above their weight for size as it were

But that said a comparison chart would be good though...

Rather than are you a dso or a planet observer, yes, yes I know before you say it... ha ha

gra

ps it really is the side of a se Wales mountain

and boy was it cold last night ...but nice and clear till midnight

[John]

I've used lots of different telescopes and telescope types over the years (I've owned more than 25+ of the things !). My experience generally is that a good refractor performs about as well as a good, collimated and cooled, reflecting telescope of around 1 inch larger aperture.

As the aperture increases though, often the seeing conditions limit the performance and can affect an open design more than a closed design of smaller aperture, eg: a refractor. So sometimes, under moderate or poor conditions, a smaller refractor can deliver performance that appears to rival that of a more significantly larger scope.

I also wonder how many reflecting systems are not properly collimated when being used - mis-collimation can have a significant effect on performance, especially on the planets and binary stars. Refractors tend to be much less demanding with regard to collimation so, again, this could narrow the performance gap and also perhaps fuel the perception that they "Punch above their weight".

[the bishop]

re:

I also wonder how many reflecting systems are not properly collimated when being used - mis-collimation can have a significant effect on performance,

especially on the planets and binary stars. Refractors tend to be much less demanding with regard to collimation so, again, this could narrow the performance gap and

also perhaps fuel the perception that they "Punch above their weight".

yep im sure your right here... its a good point well made!!

gra

[umadog]

I also wonder how many reflecting systems are not properly collimated when being used - mis-collimation can have a significant effect on performance, especially on the planets and binary stars. Refractors tend to be much less demanding with regard to collimation so, again, this could narrow the performance gap and also perhaps fuel the perception that they "Punch above their weight".

I agree. Also, refractors are easier to baffle and have fewer issues with tube currents. In addition, the lack of diffraction spikes gives the views a cleaner look that it's more aesthetically pleasing. You get the perception of "diamonds on velvet" with a refractor. If you want that stuff, then there's no substitute. If you want to pull in lots of light then you want a mirror as your objective.