Reflector or Refractor?

[Tron]

What gives better images?

Apo refractor or reflector (at the same aperture and not about cost)?

[Doc]

It doesn't really work like that.

A 4" APO will be much better then a 4" Newt, but will cost about 20 times as much. For the same price as a 4" APO you could buy a 12" Newt from a company like Orion Optics so in theory an excellent scope. At this size the newt will win on planets, DSO's, etc.

The APO should excell at maybe giving a more pleasing image of stars as there is no diffraction spikes to contend with.

[jimmyjamjoejoe]

Depends what you mean better i guess. The refractor won't suffer from coma, and have better contrast with no central obstruction, but the reflector will lose less light due to fewer optical surfaces.

Thats just theoretical though, i haven't tried them both.

[Tron]

"(at the same aperture and not about cost)"

[swamp thing]

Blimey! Are you trying to start a fight.

:boxing:Second out, round one.

[Tron]

Depends what you mean better i guess. The refractor won't suffer from coma, and have better contrast with no central obstruction, but the reflector will lose less light due to fewer optical surfaces.

Thats just theoretical though, i haven't tried them both.

So apo refractor would be better then due to contrast mostly.

What % of light would be gained with a reflector (on average).

My assumption is same aperture (after factoring out the central obstruction for non-offaxis reflective optics).

[Moonshane]

I don't know much about imaging but don't think that contrast is a big issue. after all many imaging newts have large secondaries (and hence lower contrast) than other 'standard' newts.

One thing I do know about imaging is that it's about reducing chromatic aberration which ruins shots. an APO and a newt have no CA.

BUT imaging newts have faster focal ratios and this results in faster data gathering. they also generally have longer focal lengths and therefore are more suited to smaller targets. APOs are often more suited to much wider targets but have a slower focal ration and hence take more time to gather the same data.

many imagers for this reason among others choose to have several scopes for different targets.

[Ags]

Why would you compare reflectors and refractors at the same aperture? Newton invented reflectors precisely because they could be made larger than refractors. It's like asking "What is better - a car the size of a motorbike, or a motorbike?" You can't take size out of the equation.

[Tron]

I don't know much about imaging but don't think that contrast is a big issue. after all many imaging newts have large secondaries (and hence lower contrast) than other 'standard' newts.

One thing I do know about imaging is that it's about reducing chromatic aberration which ruins shots. an APO and a newt have no CA.

BUT imaging newts have faster focal ratios and this results in faster data gathering. they also generally have longer focal lengths and therefore are more suited to smaller targets. APOs are often more suited to much wider targets but have a slower focal ration and hence take more time to gather the same data.

many imagers for this reason among others choose to have several scopes for different targets.

So basically reflector for very very faint targets and Apo refractor for bright targets (lunar, solar etc) or all others.. And an Apo would be "sharper" than a reflector because of the coma issue?

An Apo has no CA? Or just negligible?

[Ags]

A reflector still beats a refractor on bright targets because for the same money you can get more aperture and so more resolution.

Reflectors have no CA.

[Moonshane]

I am not an optician but one definition of apochromatic is

'corrected for spherical aberration at two wavelengths or colors and for chromatic aberration at three wavelengths.' So I suppose it would be neglibible or none depending on your viewpoint. If you cannot see it or image it then I suppose it's irrelevant.

I don't feel you can pigeon hole scopes for specific use. The best scope for a particular target is the one which gives the best field and image scale. This applies visually too to some extent although visually, contrast is probably more important.

The hubble Telescope is a fast reflector and I don't see any issues with sharpness of coma in the images it produces. Many APOs of f6 approx. also have a much less than flat field but this is where I am beginning to fall off the cliff of ignorance. As I said, I am no imager.

[Doc]

An Apo has no CA? Or just negligible?

You would be hard press to see any in a good APO.

The other night I compared the moon through my 152r Achro bresser and my WO GT81 APO and the difference was astonishing. Loads of CA in the Bresser and I could detect NONE in the WO GT81, even tried both of them on Vega with the same results.