ED/APO for visual observations

[Caldwell 14]

Is the step up from Achro to Apo/ED (for purely visual use) worth the extra, are the views really £300-£750 better? (Evo 120-Evo ED PRO 120 as an example)

[nightfisher]

If you want APO views without spending nearly a grand, go for a skymax 127, no false colour and a longer focal length

[ollypenrice]

I think they are. Sorry to be the bearer of bad news, but, yes.

In the DS observing section I recently wrote a quick description of a night's visual oberving with our TEC140. The views are just incredibly beautiful. I'm still on cloud nine from last night's session and I'm doing astronomy one way or another nearly all the time.

The SW achromats are good. I've had the slower versions of the 120 and 150 and they are cheap and more than cheerful, but they are not fine apos.

I really think the only way you can decide whether they do it for you is to try them because not everyone will agree. I can only speak for myself in saying that a good apo is something truly delightful to use. In my opinion they give the best views in astronomy (aperture for aperture) but they are the worst value for money...

Olly

[DeejayP999]

Is the step up from Achro to Apo/ED (for purely visual use) worth the extra, are the views really £300-£750 better?...

For my money, the real benefits of an APO come if you're looking for a short focal length refractor for travelling, astrophotography or wide field views.

At f6 it's a no brainer: Apo wins everytime.

However, if you can get away with a longer focal length (say f10 or above) then the situation becomes more complex. Because although the views through an APO will be superior whether, for purely visual use, they're that much better than a decent long fl achro is moot.

[Caldwell 14]

Just curious really. If I was to up-grade (and I have no intention of doing so) I would get a Mak/Newton hybrid I think. I don't think I would go down the imaging route. Do Mak/Newtons need culmanation BTW? I'm told they are nearly as good as an APO, the Skywatcher one offers loads more Aperture than a refractor

[andrew63]

i think at the end it comes down to optics. Whether it's binoculars, an eyepiece or a refractor, there is just no substitute for a finely crafted well corrected lens. And until you look through one...

andrew

[John]

Is the step up from Achro to Apo/ED (for purely visual use) worth the extra, are the views really £300-£750 better? (Evo 120-Evo ED PRO 120 as an example)

I've no idea where to even start on how to place a monetary value on better views to be honest....

......other than to say that I want them, of course

I've owned F/8 - F/10 achromat refractors from 4" to 6" and liked them. Using a Chromacor corrector to remove the most of CA from 6" F/8's I could see a significant improvement though which convinced me to invest in an ED120 when one came along. If an affordable (to me) ED150 was available I'd be seriously interested (I missed out on one around a year back ).

I've only limited experience with the longer focal length acrhomats though which I ought to amend when I get a chance. The optical potential of a 6" F/15 looks very interesting but the mounting requirements seem daunting

[Caldwell 14]

i think at the end it comes down to optics. Whether it's binoculars, an eyepiece or a refractor, there is just no substitute for a finely grafted well corrected lens. And until you look through one...

andrew

I'm sure your right.

[Caldwell 14]

I suppose what I am asking (and I suppose this is subjective) is the difference "oh my god" better...or is it more...er yeah I see what they mean, that is rather nice.

I don't suppose I need to point out here I have only ever looked through a Achro

[John]

...Do Mak/Newtons need culmanation BTW? I'm told they are nearly as good as an APO, the Skywatcher one offers loads more Aperture than a refractor

Like all scopes, mak-newts do need collimation from time to time. They do hold their collimation pretty well though. I'm not convinced that the Skywatcher 190 mak-newt would deliver all the benefits of that design visually though as it's secondary obstruction is still, to me. a little on the large side. An Intes-Micro 6" F/8 mak-newt was sold on UKAB&S a week or so ago for £475. That really would have competed with a quality 5" apochromat and would have pushed a 6" one hard. Mak-newts do have more cooling requirements than refractors though.

[West End Wendy]

Is the step up from Achro to Apo/ED (for purely visual use) worth the extra, are the views really £300-£750 better? (Evo 120-Evo ED PRO 120 as an example)

I think it's worth mentioning that doublets such as the ED PRO 120 do have certain advantages over triplets - they're cheaper, lighter, require less cool down, and at the lower-price end of the market at least, you're less likely to get a poor-quality doublet than a poor-quality triplet.

The step up from achro to ED doublet seems to me to be a lot less painful than the step up to full APO and the penalty is a tiny increase in CA which, in focus at least, is barely perceptible visually.

Tim

[MjrTom]

I compared my Vixen 102mm f/10 Achro to a society members Skywatcher 100ED and to be honest I did not notice that much difference. Ok a small amount of CA but the views was just as sharp in my opinion.

[West End Wendy]

That old Vixen of yours looks lovely. ?

[kniclander]

I have a skymax 127 and a celestron 100ed and i would say that the views are marginally better/ more pleasing throught the frac (although a direct comparison is difficult becasue the f/ls are quite different). Having said that, I also use them both for binoviewing. binoviewing either (moon and planets) gives significantly better views (for me) than cycops viewing with either.

ps I'm talking generally about mags up to about 150x - at higher mags the longer f/l of the skymax would probably tip the balance in its favour.

[MjrTom]

That old Vixen of yours looks lovely. ?

It is

Quite a surprise just how well performing it is

[coopman827]

The field of view in a mak will be tiny - like looking thru a straw since most are f12 to f15. If DSOs are your target and a bit of CA is not bothersome to you, an achro can be very nice.

[ollypenrice]

The issue is complicated by the scarcity of slow achromats. It's true that a slow achro is almost apochromatic, just as is a good modern ED doublet.

If you compare a Startravel fast acchromat with a similarly fast apo then the difference is of the OMG magnitude. If you compare the slower SW achromats with the apo the impact is less than 'OMG' but it's there. If you compare a slow achro, below F10, with an apo then the difference is certainly not of the OMG magnitude in my view.

As above, saying you can get apo-like images from a Mak ignores the charm of a fast apo, which is that it can flit from ultre-widefield to planetary and do both brilliantly.

Olly

[MjrTom]

Well put Olly.

My Achro can only manage 2.2 degrees FOV due to its long focal length where as the faster and far more compact ED80 can muster 4.4 degrees with the 35mm Panoptic!

Similar in FOV to a 9x50 finderscope which are usually about 5 degrees FOV

[NickK]

I can't offer much experience other than I can make out more detail with my 670mm focal length pentax 105sdp than my 900mm fl vixen a80mf - even when the image is smaller. Partly that's down to the aperture but also the quality of the optics.

You will find that you will get more returns from higher cost EPs too..

[MjrTom]

On the flip side Nickk I get a better image both in sharpness and detail from my 102mm f/10 Achro than I do from my ED80 at f/6.3

The increased aperture and focal ratio allow this.

[John]

It seems to me that the ideal with refractors is to have as many visual wavelengths of light bought to focus at the same point as possible. Any wavelengths that are either not bought to focus at the same point, or are filtered out, are not contributing to the overall image quality as I see it.

[Mark at Beaufort]

I have an Astro Tech 102mm f/6.95 ED frac with a starlight feathertouch focuser.

I few years ago I had the opportunity to compare my frac with a 5" f/8 achro whilst viewing Saturn with both scopes side by side. I have no doubt that the image in the 4" ED doublet out performed the 5".

I am solely a visual observer and often place my 6" reflector and the 4" frac side by side on the SkyTee dual mount. The 6" is not quite as good on doubles, moon and planets but I can see slightly deeper on DSOs.

I must admit I have always fancied having a go with one of these 6" Bresser fracs solely for DSOs, specifically clusters and globs. Link - Bresser Messier AR-152/760 Achromatic Telescope OTA: Amazon.co.uk: Electronics - However, I think its unlucky that I would buy one just to experiment.

Mark

[MjrTom]

The 5" f/8 would need to be at least f/15 to really stand any chance of competing with the AstroTech 102ED in my opinion.

A 5" f/15 would need some major mount!

[Caldwell 14]

I suppose I really need to look through an apo/ed. I get only a really small amount of CA in my 4 inch fl10 scope and then only with jupiter (very minimal and appears to be very dark purple which I have to look for) Venus is a bit tricky unless I get a bit of cloud (and I do mean a bit) The moon is no bother at all, which leaves DSO which of course have none at all. Mars and Satrurn have no CA at all.

Which Is why I suppose I asked the question Is it worth the extra few hundred quid to go ED? and now when I question it again out loud to remove a tiny bit of colour from one planet, then I think I have answered my own question haven't I?

[John]

I guess it depends how much contrast and resolution is being "lost" to the CA in your current scope. To find that out you need try it alongside a similar aperture apochromat. Sounds like you need to find a friendly club or star party.

That still won't answer the question of whether the difference is worth X£'s - thats one for you.

In astronomy, many £'s are spent by many people in pursuit of fairly small performance gains though