Frac questions?

[dezzie]

I am reading up on refractors as I fancy one to go with my big binos, thinking apo are best but finding out some are more suited to astro and some general viewing, after seeing some images taken with an altair 80 and being wowed if I ever go down that route, but looking at 115 and 150 mm scopes that are half decent just for looking through would probably suit me better as I want a scope with less hassle I can use straight out the box that will last me for years, I like the write ups on the skywatcher range but getting confused as to what to expect from a decent 5 or 6 inch or do I get an apo 100 and still get great images and potential for astrophotography later?  the images through the 80 mm look awesome and I cant understand how something with an aperture that small can get objects that big and detailed or is it actually photos taken in a wide field then cropped and zoomed?

[John]

I've owned quite a lot of refractors up to 6" in aperture. While I do love the images they serve up, when they get above 5" in aperture they do get pretty unwieldy and pose challenging mounting requirements - really challenging if you want to image with them - the mount will cost at least as much as the scope, possibly somewhat more.

I'm not an imager but small apochromatic refractors do seem to produce some great results in the right hands. They won't be anywhere near that satisfying for visual astronomy though. Our eyes just cant compete with CCD's, stacking multiple images and post capture processing !

Apochromat refractors above 5" get very expensive and achromats above that do show quite a bit of false colour making them much less suitable for imaging.

Perhaps you could say bit more about your general interests and ambitions and there may be other scope options ?

[bingevader]

Lots of images, stacked and manipulated.

The mount is also very important.

Take a look at the Getting started with imaging section and the Imaging section itself before going any further, it's an expensive hobby if you decide to go down that route.

Failing that, the best you can afford.

Cheers

[ronin]

Think that you will find that even on many scope sold as "apo" they will show some CA. Reason is simple they are ED doublets and ultimately doublets are not apo's.

You seem undecided about the AP side and that is therefore relevant. If you stuck to visual only then there are a number of ED Scopes that would be fine in the 4/5 even 6 inch sizes, but at 6 inch they get costly even if ED doublets. The outer parts of the image they form could well have distortions.

If you were to go down the AP line then a good triplet would be better but the cost is somewhat higher.

Many at 6 inch could be achro's, simply owing to the cost.

So when you say decent 150mm do you mean decent 150mm achro?

The 150 Evostar is an achro, f/8 and would show CA.

If you want ED then they seem to stop arounf 110-120mm, the TS 120/900 ED Doublet comes in at £1500-1600

Something like a TS 150mm triplet is £5000.

So standard first question: Budget? What are you looking to spend.

Second: exactly what do you want one for.

[dezzie]

yes I was thinking a 120 to 150 achro on an eq5, not interested in go to mount, looking at the skywatcher apos, they seem to fit the bill, it will be probably for viewing by eye but those images of stuff with the apos tease me somewhat but I know I haven't got the budget to get into it, its more a one off lifetime scope to take out to dark sky sights and sit in the garden with so probably will definitely be the achro route I take, whats the difference between the standard length and shorter star travel scopes of equal aperture? I know the focal range is less so whats there purpose?

[dezzie]

oh and its a general scope, I wanted to go bigger so I can at least get some decent galaxy and nebulae to look at aswell as planets, I know aperture is best and a dob probably more suited but I like the wide field of view and just the no hassle set up and care of the fracs!

[dezzie]

oh and budget of 800 to 1100 at the most!

[John]

You mention both an achro and an apo in the above posts.

A 6" F/8 achromat on a decent equatorial mount costs around £800-£1000 new. For an apo you can multiply that by 4.

An 8" dobsonian (newtonian scope on a simple dobsonain mount) will outperform the 6" F/8 achromat on everything and costs around £300. I'm a refractor fan but I know what I'd choose.

[Herbig]

Hi, I have an 80mm Skywatcher Equinox Pro which I use for AP and visual, objects are not very big in this scope but they are sharp and contrasty.  When the seeing is good you can push up the power. You should be able to buy this with an EQ5 within your budget.  Secondhand with an HEQ5 if you want to do AP.

[rowan46]

Apparture is best but there is plenty to see in a smaller scope especially  if its quick to set up and portable enough to take to darker skies. If you like a wider view  a shorter scope and low power is best. long refractors are better on planets and doubles.  I only have a small refractor and enjoy even the views from city skies its not great on globular clusters but open clusters brighter larger nebulas even some doubles are fun and under darker skies the milky way is superb. If you are getting a smaller scope spend the money and get an apo or good doublet great for picking out the different coloured stars. If you are getting a large achro get a longer one evostar rather than  starseeker as the longer focal lengths make their colour correction better.

[ollypenrice]

Don't confuse what can be imaged in small scopes with what can be seen. They are totally unconnected.

Your range 'possible' of galaxies in a small refractor will be quite limited in visual use. Structural detail will only be possible in a handful of galaxies though hundreds of small smudges can be seen.

I've had refractors ranging from 60 to 150mm, achros, semi apos and apos. I like them but accept their limitations. The slower of the SW 6 inch scopes isn't bad though construction is cheap and cheerful and they are close to worthless on the used market. I haven't sold my 6 inch SW achro for this reason. It would fetch £200 at most so I just keep it 'in case.'

While it may be technically true that doublets are never true Apos I think that in visual use many are so close as not to matter. The ED100 at F9 is, reputedly, a stunningly good example at a low price. I'm sure the Tal enthusiasts will soon appear as well! Personally I'd be looking for a used premium scope like the lovely TeleVue 85, which is consistently under-valued on the used market, is built to last several lifetimes and wil not disappoint. It can also be recollimated and repaired easily. I have a TV Pronto for which I paid about £250. It's a keeper!

Olly

[laser_jock99]

A minor point- but often overlooked, Newtonian mirror only scopes are also true apochromats!

[Moonshane]

another point is that with poor quality eyepieces it's often not the scope that generates CA.