Refractor specs

[mih]

Hi, i want to buy a refractor, equatorial mount. I already have a 6 inch Bresser Newtonian, f/5(750mm focal length) with two eyepieces, one 9mm and one 25mm and a barlow 2x and solar filter. I am seeing all these apertures like 90, 100, 70, while for reflectors like i have that is pretty low. Of course, for refractors, the focal ratio tends to be higher. What do I look for in a refractor? I want to be able to see some deep sky objects and planets. I am very confused, does the low aperture mean you gather less light and see worse? What does the focal ratio indicate? I just want to buy a good refractor, or maybe another reflector woud be the next step? Let me know!

Edited May 30, 2020 by mih

[ScouseSpaceCadet]

You have a decent 6" newtonian already. Why do you think you need another telescope? What are you not seeing now that you think a smaller aperture refractor will provide?

[mih]

14 minutes ago, ScouseSpaceCadet said:

You have a decent 6" newtonian already. Why do you think you need another telescope? What are you not seeing now that you think a smaller aperture refractor will provide?

I dont know, just asking if a refractor would have any advantages. Also I dont plan on buying it right now. In the future maybe. Sorry for saying that in the description. Or what should i get if I ever want to upgrade in the fiture

Edited May 30, 2020 by mih

[John]

Refractor optics cost more per mm to make because there are 4 or more optical surfaces to figure, polish and coat compared to just the two surfaces for a newtonian. A 150mm refractor is expensive and sizes above that comparatively rare whereas reflectors can easily be made in 200mm, 250mm, 300mm and up to around 500mm.

So if you want a larger aperture for deep sky objects, a reflecting telescope is the way to go.

Refractors have a lot of fans though for the purity of their image, their relatively robust collimation, their lack of a central obstruction etc, etc.

The subject of these different designs of telescope is the subject of many books, articles and, many, many posts, on forums

Here is a piece by our own Steve Richards ( @steppenwolf ) with a contribution from Paul Money, on these designs:

https://www.skyatnightmagazine.com/advice/buyers-guides/first-telescope-reflector-or-refractor/

 

[mih]

2 minutes ago, John said:

Refractor optics cost more per mm to make because there are 4 or more optical surfaces to figure, polish and coat compared to just the two surfaces for a newtonian. A 150mm refractor is expensive and sizes above that comparatively rare whereas reflectors can easily be made in 200mm, 250mm, 300mm and up to around 500mm.

So if you want a larger aperture for deep sky objects, a reflecting telescope is the way to go.

Refractors have a lot of fans though for the purity of their image, their relatively robust collimation, their lack of a central obstruction etc, etc.

The subject of these different designs of telescope is the subject of many books, articles and, many, many posts, on forums

Here is a piece by our own Steve Richards ( @steppenwolf ) with a contribution from Paul Money, on these designs:

https://www.skyatnightmagazine.com/advice/buyers-guides/first-telescope-reflector-or-refractor/

 

Thanks! I wanted to buy an eq mount, so i was thinking maybe i could get a refractor on an eq and put my reflector on it as well. Is that an option?

[John]

6 minutes ago, mih said:

Thanks! I wanted to buy an eq mount, so i was thinking maybe i could get a refractor on an eq and put my reflector on it as well. Is that an option?

Yes, that is quite possible.

Probably best to get a refractor that compliments what your 150mm newtonian can do so you get a different experience when you use each scope. They will have different strengths and weaknesses.

 

 

 

[mih]

4 minutes ago, John said:

Yes, that is quite possible.

Probably best to get a refractor that compliments what your 150mm newtonian can do so you get a different experience when you use each scope. They will have different strengths and weaknesses.

 

 

 

Ok, thank you so much!

[andrew s]

If it were my me I would put all the money into the best mount I could afford and get the best out of the Newt. You can improve the image with a a coma corrector, pump up the focal length with a Barlow or PowerMate and turn it down with a reducer corrector.

Regards Andrew 

 

[mih]

27 minutes ago, andrew s said:

If it were my me I would put all the money into the best mount I could afford and get the best out of the Newt. You can improve the image with a a coma corrector, pump up the focal length with a Barlow or PowerMate and turn it down with a reducer corrector.

Regards Andrew 

 

Yeah, i will also get a good mount for the reflector, but want to check out a refractor as well. Maybe ill compromise and get a mount and a refractor with no mount

Edited May 30, 2020 by mih

[mikeDnight]

If you're thinking of saving for a refractor, you probably better off looking at an ED which will give you good colour correction but will still have a relatively short tube length. These are easily mounted on an equatorial mount and will give some very pleasing views of pretty much every kind of object. Skywatcher offer some seriously nice 80mm, 100mm and 120mm ED refractors that are near impossible to beat for the money. An EQ5 would carry any of these well if the tripod is sturdy.  There are other brands you might consider too, but prices can get a little scary for the higher spec refractors, and you can find yourself paying a premium just to gain a slight edge in performance. To some its worth the price while for others it isn't. Also, for many, the larger aperture of a reflector has real appeal, while others would sacrifice aperture for superior image quality of a premium refractor every time. 

[mih]

22 minutes ago, mikeDnight said:

If you're thinking of saving for a refractor, you probably better off looking at an ED which will give you good colour correction but will still have a relatively short tube length. These are easily mounted on an equatorial mount and will give some very pleasing views of pretty much every kind of object. Skywatcher offer some seriously nice 80mm, 100mm and 120mm ED refractors that are near impossible to beat for the money. An EQ5 would carry any of these well if the tripod is sturdy.  There are other brands you might consider too, but prices can get a little scary for the higher spec refractors, and you can find yourself paying a premium just to gain a slight edge in performance. To some its worth the price while for others it isn't. Also, for many, the larger aperture of a reflector has real appeal, while others would sacrifice aperture for superior image quality of a premium refractor every time. 

By ED you mean an apochromatic one? Does Extra Low dispersion mean that when light passes through the lenses it does not go in all directions as much?

Edit: Ok, so ive looked it up, so the chromatic aberration is gone

Edited May 30, 2020 by mih

[Timebandit]

 

Hello. 

A lot of people prefer the refractor image on planetary, Luna and double stars to the reflector. In my opinion you get a slightly cleaner sharper image through a good refractor, compared to a reflector, So this is the advantage.

If I was in your shoes a and wanted a quality refractor for sensible money. Then I would start off with a SW 100ED. Purchased second hand. Great value for money especially purchased used .

 

 

[mikeDnight]

2 hours ago, mih said:

By ED you mean an apochromatic one? Does Extra Low dispersion mean that when light passes through the lenses it does not go in all directions as much?

Edit: Ok, so ive looked it up, so the chromatic aberration is gone

Yes! The extra low dispersion lens gives better control of colour spread. An ED apochromat will show an essentially colour free view, so star colours will be true and colours in planetary and lunar views will be natural and vibrant. 

[John]

Just for information, a newtonian reflector is also an apochromatic telescope

[Alkaid]

Aesthetics and ergonomics are also factors...it’s really nice to sit down behind a refractor, very relaxing.  Much better than standing up all the time with a newt and having to rotate it in the rings to get the eyepiece into a good position when moving to another part of the sky.

Refractors just look better too. (Hope I haven’t started a war now).  There was a guy on here that made me laugh when he said his wife had nicknames for his two scopes - the short fat 10” dob was named R2D2 and the elegant refractor was called Princess Leia.

[mih]

1 hour ago, John said:

Just for information, a newtonian reflector is also an apochromatic telescope

The more you know

[mih]

1 hour ago, Alkaid said:

Aesthetics and ergonomics are also factors...it’s really nice to sit down behind a refractor, very relaxing.  Much better than standing up all the time with a newt and having to rotate it in the rings to get the eyepiece into a good position when moving to another part of the sky.

Refractors just look better too. (Hope I haven’t started a war now).  There was a guy on here that made me laugh when he said his wife had nicknames for his two scopes - the short fat 10” dob was named R2D2 and the elegant refractor was called Princess Leia.

So you reckon i get a refractor?

[John]

Just now, mih said:

So you reckon i get a refractor?

Think through what you want it to do for you. Then work out if a refractor is the tool you need.

 

 

[mih]

5 minutes ago, John said:

Think through what you want it to do for you. Then work out if a refractor is the tool you need.

 

 

is a refractor a good tool for DSOs? Or is it better for planet viewing?

Edited May 30, 2020 by mih

[John]

38 minutes ago, mih said:

is a refractor a good tool for DSOs? Or is it better for planet viewing?

Aperture and dark skies are the best tools for observing DSO's.

The planets and double stars are more the refractor strong points.

The newtonian can do those as well though but the crispness of a refractor image is particularly nice for splitting double stars.

 

[Alkaid]

1 hour ago, mih said:

So you reckon i get a refractor?

My comment was actually meant to be tongue-in-cheek, but I do think that everyone in this game should have a try of all scope designs to see what works for them personally. Sure, why not? When people speak of the crisp view, they are not wrong. Refractors give a really nice view of star fields, open clusters, double stars, planets and of course, the moon. They work well on the brighter objects.

[Stu]

10 hours ago, mih said:

is a refractor a good tool for DSOs? Or is it better for planet viewing?

Depends on the DSO! Under a dark sky, refractors can be fabulous on larger deep sky objects like the Veil, Andromeda Galaxy and North America Nebula. For most other DSOs, aperture rules as they give much better resolution on globular clusters, and the ability to magnify smaller galaxies and planetary nebula for example whilst maintaining their surface brightness, making them much easier to see.

Refractors present much cleaner star images, and cut through poorer seeing conditions better, so I love them for double stars, Lunar and planetary viewing. Ultimately you would see more with a larger scope, but observing to me is as much about the aesthetics of the view as anything else so 4” refractors feature heavily in my collection 😁.

It is also worth noting that there are a few different sorts of refractor which are good at different things.

Fast achromatic refractors show lots of false colour on bright objects so not great for planets and the moon, but a 150mm f5 for instance shows good contrast on deep sky objects and have a wider field of view.

Slow achromatic refractors tend to have better colour correction and less spherical aberration but a narrow field of view, so are good for planets, the Moon and double stars.

ED and fluorite doublets tend to be medium or slower focal ratios (f6 and above). They are generally very well corrected for most aberrations and are visually apochromatic although will likely show some colour for imaging. They cool quickly and make good allrounders for visual. The faster ones are great for wide fields as well as planets, Moon and doubles and the slower ones are similar but a little more limited at widefield but a little more capable at the high mag stuff.

Triplet Apos have three elements in their objective and tend to be more imaging focused. They should be essentially free of false colour for both visual and imaging and also tend to have faster focal ratios so are better for imaging larger targets and widefield visual views.

Finally Petzval type designs have a doublet or triplet objective and then a rear doublet at the rear which is a reducer and flattener. This gives a very fast apochromatic scope with a flat field which is ideal for imaging so they tend not to be used for visual although there are no hard and fast rules!

I would think either a slow achro or an ED doublet would be worth investigating for your purposes and to complement your Newton if you decide to go down that route. The 100ED suggested by @Timebandit fits in this category.

Refractors also have the advantage of being able to be used with a Herschel Wedge for solar white light observing and with an erecting prism for terrestrial views.

So, I would decide what you want to achieve and then make a decision from there.

[mikeDnight]

11 hours ago, mih said:

is a refractor a good tool for DSOs? Or is it better for planet viewing?

Refractors can be good for all kinds of targets, including deep sky. Obviously the greater the aperture the deeper you'll be able to go, but how deep do you really need to go? There are countless deep sky objects that can be observed through a 100mm refractor, and a 120mm or 152mm refractor will take you deeper still. The best view i ever had of the Orion Nebula (M42) was through a 102mm Vixen F6.5 ED apo and a 20mm Nagler eyepiece. No other scope I've ever used, no matter how big, has ever given me a better view of that object. I've observed M51 (the Whirlpool galaxy) in many large aperture scopes, but the most memorable view was through a 150mm F8 achromatic refractor, which easily showed the spiral structure and the bridging arm between the two galaxies. Refractors make great all round scopes but their ability to produce piercingly sharp star images enables them to give some of the finest views imaginable of rich star fields and star clusters; views that no other design can match. A 150mm F5 achromat will give you arguably the finest view you'll ever have of the Double Cluster in Perseus. Other scopes may show it well but they'll never match the refractors view. So refractors can give you a lifetime of pleasure with deep sky targets in mind, but they can also excell at lunar and planetary too. 

I've attached some images to wet your appetite. This first one is a rich field achromat with a 152mm lens. This is a great deep sky refractor!

The second is another great deep sky scope, an NP101. At only 4" aperture you might think it wouldn't be so good, but its images of nebulae, galaxies, star clusters and comets are spectacular from a reasonably dark site.

Then there's the affordable but excellent Skywatcher 100DS Pro ED, which is a great all round refractor. If you like to do a bit of everything this scope will not disappoint!

Then there's the higher spec offerings from Takahashi, which again are great all round performers designed for very high powers when the seeing conditions allow.

 

There are many more you might consider too. Doublets are all you'll really need if you're a visual observer, as they cool quickly and will often be cheaper than a triplet. You might even find your reflector gets used less and less if you did buy a good refractor.

 

 

Edited May 31, 2020 by mikeDnight

[Stu]

3 minutes ago, mikeDnight said:

Refractors can be good for all kinds of targets, including deep sky. Obviously the greater the aperture the deeper you'll be able to go, but how deep do you really need to go? There are countless deep sky objects that can be observed through a 100mm refractor, and a 120mm or 152mm refractor will take you deeper still. The best view i ever had of the Orion Nebula (M42) was through a 102mm Vixen F6.5 ED apo and a 20mm Nagler eyepiece. No other scope I've ever used, no matter how big, has ever given me a better view of that object. I've observed M51 (the Whirlpool galaxy) in many large aperture scopes, but the most memorable view was through a 150mm F8 achromatic refractor, which easily showed the spiral structure and the bridging arm between the two galaxies. Refractors make great all round scopes but their ability to produce piercingly sharp star images enables them to give some of the finest views imaginable of rich star fields and star clusters; views that no other design can match. A 150mm F5 achromat will give you arguably the finest view you'll ever have of the Double Cluster in Perseus. Other scopes may show it well but they'll never match the refractors view. So refractors can give you a lifetime of pleasure with deep sky targets in mind, but they can also excell at lunar and planetary too. 

I've attached some images to wet your appetite. This first one is a rich field achromat with a 152mm lens. This is a great deep sky refractor!

The second is another great deep sky scope, an NP101. At only 4" aperture you might think it wouldn't be so good, but its images of nebulae, galaxies, star clusters and comets are spectacular from a reasonably dark site.

Then there's the affordable but excellent Skywatcher 100DS Pro ED, which is a great all round ago refractor. If you like to do a bit of everything this scope will not disappoint!

Then there's the higher spec offerings from Takahashi, which again are great all round performers designed for very high powers when the seeing conditions allow.

 

There are many more you might consider too. Doublets are all you'll really need if you're a visual observer, as they cool quickly and will often be cheaper than a triplet. You might even find your reflector gets used less and less if you did buy a good refractor.

 

 

******SGL Health Warning*******
 

Mr Hezzlewood suffers from a highly infectious form of refractorholism for which there is no known cure. The symptoms include a complete aversion to mirrors and the need for fluorite glass to be used everywhere, including the windows of his house. Proceed with caution, it can get very expensive!!

😉

[John]

These crazy refractor people !

You can't rely on what they say of course - they are smitten after all

Of course I have not fallen into their trap - I only have 5 refractors ........