Confused about light gathering

[Csuka]

I read that lower powered scopes provide more crisp and colorful images, could someone explain to me how this works, on first light optics the Skywatcher Heritage 130p says 30% more light gathering than 114mm, but the Skyliner 150p says 70% more light gathering than 114mm, so which one would provide better images? Also stupid example here but the Hubble telescope provides very crisp and colorful images and the magnification it has is immense, so does it just depend on a scopes light gathering capability?

[richbyers]

firstly hubble is in orbit outside the earths atmosphere that is why the images are amazing - well coupled with whatever glass they have in that baby

light gathering is important for deep sky object- dobsonians are good for this such as the 130p, so much so they are nicknamed light-buckets

generally the greater the area (bucket) that gathers light, the easier it is too see dso's and the more fainter ones can be seen

thats why the really big dobs need a ladder to see through!!

rich

[Csuka]

firstly hubble is in orbit outside the earths atmosphere that is why the images are amazing - well coupled with whatever glass they have in that baby

light gathering is important for deep sky object- dobsonians are good for this such as the 130p, so much so they are nicknamed light-buckets

generally the greater the area (bucket) that gathers light, the easier it is too see dso's and the more fainter ones can be seen

thats why the really big dobs need a ladder to see through!!

rich

So even though the 150p is the bigger scope and has more magnification it would provide more crisp images?

[richbyers]

yeah...so a 200mm dob would be a step up from the 150 dob

the P stand for parabolic mirror which also enhances the pictures quality so you'd want one with that (mine isnt)

[Csuka]

yeah...so a 200mm dob would be a step up from the 150 dob

the P stand for parabolic mirror which also enhances the pictures quality so you'd want one with that (mine isnt)

So why do people say it's better to have lower powered scopes? Or is that just for scopes that don't capture any more light but have higher magnification?

Sorry about all the questions but this has confused the hell out of me as i'm completely new to the subject. =p

[richbyers]

i think the lower power ones give brighter images which in astronomy is a must- in telescopes power isnt held as a priority really, its light-gathering

[Thirdway]

Refractors, which by their design have less light gathering, usually have better contrast as well as less need for collimation, and suffer less from tube currents. Therefore they are considered to be generally better at planetary viewing where high contrast is important, unless really expensive they are not great with DSOs

The design of the average newtonian is to maximise light gathering, they are generally considered to be optimal for DSOs, however I'm beginning to understand that a Newtonian is equally capable of high contrast if designed that way. Get rid of the tube itself and go for a truss design and you can get rid of tube currents. An off the peg newt will still perform extremely well For planetary and is great for DSOs.

So, a newt, more bang for the buck. The refractor, more expensive, less labour intensive, usually smaller.

A 200 isn't much more expensive than a 150. If your getting a light bucket then you might as well get the bigger one.

At £270 a 200p Dob will really let you learn. It's a serious bit of kit that would once have cost at least £1000. It's painless education. If you like the hobby then there are many ways to go.

[Flaxinator]

With reflector/newtonian scopes, It's not so much about magnification than the amount of light it gathers, the more light the more/further/fainter objects you can see

[umadog]

Actually it is mostly about magnification, since telescopes don't make the object brighter. Instead, they allow you to magnify it a lot without it becoming dimmer. Larger aperture means more magnification before the image becomes too dim. Your ability to see details in an object depends mostly on how much you can magnify it. If the exit pupils are the same size then you should see pretty much the same thing with a 20" at 50x as in a 10" at 50x. If course, you'll have very different focal ratios to achieve that.

There is no difference between Newtonians and refractors in terms of these things. They essentially work identically, after all.

[rowan46]

I think most of the time the term is used to describe eyepieces a low power eyepiece gives less magnification and hence a brighter image. when looking for dso's a low power eyepiece is usually used and then magnified until the image gives way. larger scopes give brighter images and more resolution edit actually I think umadog explains it better

[swamp thing]

Refractors, which by their design have less light gathering,

This isn't strictly true unless you are comparing scopes of the same price rather than aperture.

A 6" scope is a 6" scope and both will have the same light gathering ability, only the frac will be three times the price.

Newts offer cheaper aperture gains as they are cheaper to make and mount than fracs.

But don't be thinking that fracs are any slackers on DSO,s cause they're not. It's just they cost more to get there.

[glowjet]

All of the forgoing are the hard facts in the relation of aperture and mag associated with refractors and reflectors, there are also a few other subtle differences, which have not been mentioned, reflectors have a central obstruction which does have an effect on the final image, as against a refractor which has no obstruction, this is why there are many devotees who use this type of scope. There is also the question of air quality, especially here in GB, a small refractor, with good optics, is often able to obtain a better visual image of a subject than a reflector of larger light gathering capacity, this is often down to the column of air through which the light passes, the narrow column for the refractor will contain less contamination, like moisture, than the larger area that its brother the reflector has to look through, just some other points to be borne in mind

[symesie04]

Also just a thought but I think worth you noting before you purchase, as many are sadly disapointed with their first views, and that is the fact that once you start looking at objects outside of our solar system you will not see very much in colour at all. In fact many see no colour whatsoever.

[Stu]

Also, don't forget that the term dso covers many different object types and sizes.

For faint fuzzies, galaxies and larger faint nebulae, a large newtonian would be ideal as it gathers alot of light.

For smaller, planetary nebulae and globular clusters, a moderate sized mak would do a good job as they are brighter and need more magnification.

For open clusters like m45 and the double cluster, for me you can't beat a decent apo refractor. They give a nice wide field of view ( up to 4° is possible, and they give wonderfully tight star images with perfect diffraction patterns.

Of course, these are just examples and you will, for instance, get fantastic views of globs and planetary nebulae from a large newtonian too. My main point was that not all dso's are faint nebulae or galaxies and a wide field refractor is sometimes just as good, if not better on certain targets.

All of which justifies why many of us have more than one scope

Stu

[umadog]

Interestingly, if the secondary obstruction is under 20% or so by diameter then the telescope will perform the same as an unobstructed scope. The effect of the secondary obstruction is over-rated. The diffraction effects produced by the secondary vanes are absent in a refractor, and many find this more aesthetically pleasing. Also, a refractor has better thermal properties and deals better with tube currents. This is a big deal. If you get the cooling right in a large reflector then it's quite capable of beating a refractor on planets. Everything has to be just right, though, (collimation, cooling, etc) otherwise the views will be worse. I think the bad reputation a large reflector has over refractors WRT to planets is due to the reflectors either being poorly set up or having bad optics (it being harder to make a large mirror than a small one). If you do it right then the views are distinctly better in the bigger scope, even when both are seeing-limited to 200x.