How good can a Apochromatic telescope be?

[monkey_coral]

Yet another stupid question from my semingly endless supply, but I notice a lot of people have invested in a apochromatic telescope.

These appear to be pretty poor value in terms of aperture per £, yet people buy and rave about them. I have read that a refractor produces excellent views of planets, but for the money you could get an 8" or 10" reflector. Is the apo as good as an 8" or 10" reflector on planets? I understand that portability is potentially a big consideration.

Also if I was to elect to buy a 80mm apo, surely any DSOs are out of the question?

I am confuzzed!

[Moonshane]

I feel you come into one camp or the other (in the most friendly way). I personally prefer newtonians and specifically dobsonian mounted newts. I have a 16" f4 and a 6" f11. Also a 90mm f5.5 achromat which I use on wide field targets and for a quick peek. I'll always use the big dob if conditions and time allow. OK it's not as portable as some scopes but it fits in my small hatchback and can be set up in 5 mins.

Other members will only buy refractors or at least much prefer them.

Any scope will show DSOs, it just depends on what you expect. Even an 80mm refractor will show nice wide open fields with good views of open clusters and with dark skies, also some galaxies and globular clusters.

My view would be that a 4" APO will never compete with an 8" or 10" newt on any target if that scope is cooled and well collimated with the possible exception of double stars.

Others will probably argue differently but not me.

[dweller25]

I have a 8" Skywatcher Dob and a 5" Takahashi APO.

There is little to choose between the two when viewing the planets. The Dob beats the refractor on deep sky objects.

I could sell the Dob tomorrow and would have no regrets - I will never sell the refractor.

Hope that clears up the confusion

[monkey_coral]

Confusion ^2

[angusb1]

I have a 10" newt and am hoping to soon buy an apochromatic refractor because I can't take my big scope on holiday or up mountains to some of the really dark skies I have access to. Its horses for courses, I'd never sell my newt but the refractor should be very useful on holiday and I'm planning to use it for imaging as well, the newt is too big for anything but a very large mount.

To add to the confusion, I had a look through a 6" F12 achromat on Friday at Jupiter, some DSOs, the moon and some doubles and it was amazing.

[monkey_coral]

So their appeal really is down to portability?

[angusb1]

So their appeal really is down to portability?

That's certainly a big part of it for me.

[dweller25]

So their appeal really is down to portability?

Noooo....

Refractors have the optics at the right end and no obstructions that degrade the image. Also the eyepiece is in just the right place and to top it all off THEY JUST LOOK RIGHT

Not to mention the super tight star images and high levels of contrast that allow you to see planetary detail

Did I mention that refactors don't need to be collimated and cool VERY quickly - refactors don't know what a boundary layer is !!!!

But I will concede that Newtonians do represent the best value for money

[bish]

I think an 80mm apo makes for a great imaging scope. If you want the best results you pay the extra and you don't need the extra aperture.

[Earl]

For visual Apature is king, for Imaging F Ratio is king

I prefer Refractors as they are simpler to use.

[monkey_coral]

I currenty have a 6" SCT what would be the visual and imaging comparison between this and say an 80mm apo?

[Earl]

The 6" Sct will be great for webcam imaging of the moon and planets.

An 80mm APO will have a much wider field of view and be great for imaging larger Nebula etc.

off the top of my head the FOV of a 80mm will be about 6 times that of the SCT.

[Skybrowser]

Very few people can afford the price of an expensive Apo but they still sell well I guess. Someone told me the single most popular scope is an 8" Refelector and I understand why - more portable than a 10" or bigger and more aperture than a 6" so better viewing. That said, the expensive Apos I have looked through have been superb and I'm not sure that portability is the big driver on decision to buy one. For me, this hobby is about balance. Balancing the bank account of course, but perhaps more importantly, getting the right level of kit you can afford, with some aspirations to acquire some nice little extras along the way like eyepieces with green writing on them!!

Who wants to spend £600 on a single eyepiece? Some do, most of us don't. Likewise, would you buy an apo for £2K and upwards - I for one wouldn't, even if I could afford it. Personal choice yet again I suppose.

My next acquisition will be a big, heavy Dob. Cheap, big aperture and move-able until my back gives up!

[brantuk]

There is a certain aesthetic appeal of different scope types depending on the individuals character and aspirations. Me ... I'm just weak and had to have one of each cos I love 'em all lol.

But a good appo will focus all three primary colours in the same focal plane - great for photography. Whereas the aperture of a decent large newt will bring out all those faint fuzzys and show you deepest into space. A good cassegraine will yield very sharp views and images of planets and moon.

Portability, storage space, size, weight, etc are all just side issues for me that can all be solved one way or another. It's the variety of possible ways to do astronomy that floats my boat - I wanna do them all

[RikM]

I am very much a fan of Newtonians, but there is just something about the 'feel' of the view through a good refractor that is deeply satisfying. They are just nice to look through. You may not see as much detail or brightness as with a big Newt, but what you do see will look 'better'.

[cantab]

Sometimes, I expect it's the same reason people buy a mobile phone costing 5, 10, even 15 thousand pounds.

[MjrTom]

I have always been a refractor kind of guy.

Ok you can't see as deep with a refractor as you can with a reflector but the views from the refractor are just sublime. To have pinpoint stars across the whole field of view without any distracting coma is why I like them

Also as mentioned due to just starting a family and having an eight month old daughter means that my observing times can be quite short along with the variable weather we have in this country means I want a scope that cools down quickly and requires no maintenance.

This is the main reason after months of deliberation I realised that an SCT is just not suitable under my circumstances.

In addition to this due to health problems lifting heavy scopes is really out of the question.

I just accept that won't see as much as the guys with the big scopes but I get my fix when I go to the local astro society where there is various newtonians from six inch to twenty inches.

Maybe one day!

[John]

I've always got more satisfaction from the views that refractors deliver and apochromatic refractors even more so. I've owned many other types of scope too but I always seem to enjoy the refractors the most. It's a hobby so I think you should go with what you enjoy using

[wrinkly]

You only live once, unless you are James Bond, so buy one of each.

Sum it all up and get what looks good to you as we all have our favourites.

[Stu]

My most used scopes are apo refractors. They are smaller, more convenient, less hassle and just quicker to use than other scopes. As for the views? Well I use mine visually and love the contrast and pin sharp stars you get, lovely for doubles, open clusters and surprisingly good on planets.

I would love a 'big' newt, and will get one some day and I will love it for the deep sky views, but it will still be trickier and more time consuming to use.

Quite interested in exploring long focal length refractors to see how they perform

Stu

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[michael.h.f.wilkinson]

I have an 8" SCT and a 80mm F/6 triplet apo. If I were only allowed one scope I would mount the triplet as finder on the SCT .

If that were not allowed I would sell the triplet. The SCT is visually the much better scope on most objects in terms of light gathered and detail seen. In terms of apparent contrast the 80mm is better. With apparent contrast I mean the following: At a given exit pupil the mean brightness of the image is the same in both scopes (but at 2.54x more magnification in the SCT). However, the contrast between highlights and background will be (somewhat) better in a refractor, due to the lack of central obstruction. If the refractor is achromatic rather than apochromatic, this difference in contrast may be less pronounced, due to chromatic aberration.

If the central obstruction is small, as in the 6" F/8 Newtonian I had, it will give any apo of similar aperture a serious run for its money on planets. I have looked through a TEC 140, so do know what I am talking about, the TEC has an edge, but the 6" F/8 can get uncomfortably close. I am talking about a 1/12 wave optical system in good collimation. The same 6" F/8 probably equals or even beats most 5-6" achromats of similar focal ratio on planets. On wide field, due to reduced coma, the refractors will have the edge.

The 80mm can give me 5.6 deg true FOV . The SCT manages 1.38. Thus the views of truly wide field objects like the Hyades, North America Nebula, Rosette, Pleiades, M33, M31, and Veil are amazing with the 80mm. The SCT gives way more detail on planets and the moon, and on galaxies and other deep sky stuff. The viewing 7 galaxies in a single field of view, with hints of dust lanes in some, in the Virgo cluster with my SCT was just one of those jaw-dropping moments.

When I got the 80mm APO I also considered cheaper, larger aperture achromats such as the star-travel 104 and 120. The reason I chose the APO is that it would also work as a DSO imager in the future.

Horses for courses.

[angusb1]

The 80mm can give me 5.6 deg true FOV . The SCT manages 1.38. Thus the views of truly wide field objects like the Hyades, North America Nebula, Rosette, Pleiades, M33, M31, and Veil are amazing with the 80mm. The SCT gives way more detail on planets and the moon, and on galaxies and other deep sky stuff.

This is why we all "need" lots of telescopes . No one scope can do it all.

[michael.h.f.wilkinson]

This is why we all "need" lots of telescopes . No one scope can do it all.

Too true, if ever I get a 16" dob, or a C11, the C8 will not be going anywhere. Three scopes it quite modest, is it not?

[Macavity]

If / When video astronomy matures (beyond the "security camera" stage) I see less point in "aperture" - At least for the vaguely decrepit, like me... Or those who don't mind the "indirection" of the computer screen! Though, expense aside, a lot of APOs are quite [c]hunky. The [decent] mounting question remains perennial?

[michael.h.f.wilkinson]

If / When video astronomy matures (beyond the "security camera" stage) I see less point in "aperture" - At least for the vaguely decrepit, like me... At least for those who don't mind the "indirection" of the computer screen! Though, expense aside, a lot of APOs are quite [c]hunky. The mount question remains perennial?

Not when it comes to resolution, and simple light grasp. My C8 cannot hope to match the kind of shot of Jupiter currently POW, even if I had Neil's skills, simply because the 8" scope cannot resolve the detail a 12" can. Photon noise is going to be a problem in video imaging of DSOs on small scopes, unless you up the exposure times dramatically (which is why imagers take so many subs!). With all the improvements in equipment and processing, even professional astronomers still hunger for more aperture, and they have the Keck and similar class scopes to work with. Aperture fever is with us to stay!

"Ye cannae change the laws of physics, Capt'n."