Achro Vs Apo?

[Damo636]

Hi Guys? Other than the obvious lack of colour, what other advantages has an apo (for visual use only) over a cheaper long focal length achro?

Take for example the Evostar 100 ED and a Lyra Optic f11 achro, would the apo outperform the latter in any way other than giving colour free views?

[AndyH]

Given that if both lenses were equally well figured and polished, then no, in my humble opinion.

Andy.

[Caldwell 14]

Given that if both lenses were equally well figured and polished, then no, in my humble opinion.

Andy.

I concur with a small caveat, there will be nights when you may be able to eek out a little more detail from an ED, I'm just starting to see this now. CA does rob a little detail.

[Caldwell 14]

I nearly bought a Lyra Optic f11 achro, very nearly, I bought my ED100 second hand and in fantasic condition for the same price (and that without buying a diagonal and a finder, the Lyra comes without them) shop around and wait is my advise

[John]

I concur with a small caveat, there will be nights when you may be able to eek out a little more detail from an ED, I'm just starting to see this now. CA does rob a little detail.

Yep, I'd agree with that too. Experiments with eliminating 90% of CA in achromats using a Chromacor have demonstrated to me that CA does reduce both sharpness and contrast in planetary viewing, all other things being equal.

Of course a sufficiently slow achromat will reduce CA to a level where it's impact is negligable but you do then have the mounting challenges that a long OTA presents to deal with.

[Damo636]

I have a soft spot for long focal length refractors &

read that a 4" f15 will be all but CA free,

trouble is, something like that (Skylight for example)

are twice the price of an ED100

[Alan_B]

Interesting thread this as I also considered the Lyra F11. At £260 cheaper than the Evostar (minus the finder & diagonal costs - never considered them thanks Caldwell)

Now I have to rethink.

Sent from my Nexus One using Tapatalk 2

[AndyH]

Depends how bad the CA is to begin with though.

A scope with heavy CA will probably always lose out to ED doublet. Whereas if the achro has minimal CA, the views are very close between the two.

I think the finishing of the lens is/can be more important than CA, when we're talking small amounts.

Andy

[Damo636]

I had the Lyra f11 and sold it to fund the bigger dob. Always regretted having to let it go but I have a plan hatching that might allow me to acquire another in the near future. I just can't decide whether or not to go the extra mile and opt for the ED100. The Lyra are really nice but now coming very close to the price of an ED by the time the diagonal/finder is added.

[ollypenrice]

Usually the Apo will have a faster F ratio so give you the possibility of lovely widefield views. I'm a bit of a sucker for these views but I also think the long slow achro has a vintage charm. (Hey, what a helpful reply!!!)

Olly

[Damo636]

Good point re the widefield views Olly.

[Caldwell 14]

Usually the Apo will have a faster F ratio so give you the possibility of lovely widefield views. I'm a bit of a sucker for these views but I also think the long slow achro has a vintage charm. (Hey, what a helpful reply!!!)

Olly

I concur with that too! ED100 fl9, Lyra fl11. (what a lovely scope, but you do look through them and not at them at night)

[Damo636]

Just to throw something else into the mix, how would one of these compare with a 100mm ED.... http://www.firstlightoptics.com/pro-series/skywatcher-skymax-150-pro.html

I have seen them described as a poor mans apo? Obviously the increase in aperture will give brighter views but can they match an ED on sharpness and contrast?

[ollypenrice]

When they've cooled down, yes. That might take a while, depending on storage.

Olly

[Alma]

I'd kind of turn that around and say that in order to achieve a faster f ratio you NEED to have apo grade glass in order to reduce the spherical as well as chromatic aberration.

A true apo should show the reduced aberrations in the form of a very precise snap to focus as well as a sharp image and lack of false colour.

I'm an old-fashioned guy, so to me the term "apo" also means a triplet lens rather than a doublet, but I don't think that's necessarily a prerequisite for a lens to be termed "apo".

[nightfisher]

Just to throw something else into the mix, how would one of these compare with a 100mm ED.... http://www.firstlightoptics.com/pro-series/skywatcher-skymax-150-pro.html

I have seen them described as a poor mans apo? Obviously the increase in aperture will give brighter views but can they match an ED on sharpness and contrast?

Yes, maks do give APO views, when correctly cooled, i have a 7" APO (mak) and the views will beat any readily available achro, but i still really like my achro refractors, my Tal is very well corrected

[John]

The Russian mak-newtonians (Intes & Intes Micro) do a great impression of a quality apo refractor and are truly apochromatic of course. I found the views through my old Intes MN61 6" mak-newt pretty much just as good as my ED120. I could not keep both though so, as cooldown time is important to me, I kept the ED120.

[Damo636]

My scopes are all kept outside so cooldown time would be minimal. Thanks guys. Nothing might come of this but you have given me some food for thought

[nightfisher]

I would stick my neck on the line and say a 150 pro mak will beat a 120ed frac on lunar and planets, but will have a smaller field of view

[iwatkins]

I've got a Lyra 150mm f/8. It uses an IStar optics and in turn mounted in a collimatable counter cell. It's well set up and the CA is not bad at all. Venus its obvious but doesn't affect the contrast that much. Other targets it doesn't affect the views at all. (still not got first light on the moon, but I expect that to be well controlled based on Venus views)

It's sits between my 80ED and my 180Mak with regards to focal length so I've not been able to do a direct comparison. But image quality wise, I would say it is beaten by the 80ED but it's close to the 180Mak.

If we are talking just the optics and CA then this OTA can be beaten. But that isn't the whole picture to me. Having a collimatable objective is very useful, having a well tuned and rotatable focuser is also important to me. Having the tube very well flocked (flockboard) and not having contrast issues. Having someone I can talk to if I have problems and that person knowing the OTA intimately is also worth lots.

I bought this scope primarily as a white light solar scope and it surpasses all my expectations on that. But I am in no way disappointed by the night views either

Cheers

Ian

[Alma]

The Russian mak-newtonians (Intes & Intes Micro) do a great impression of a quality apo refractor and are truly apochromatic of course. .........QUOTE]

Yep, I'd go along with that. I had an Intes Micro MN56 Mak Newt once and the planetary/lunar views were easily the equal of the top name 4" triplet apo I have now. But, you can't beat a fast apo refractor for flexibility - they can do everything from decent planetary to great wide field views, something no other scope can achieve in the same way i.m.o.

[hunterknox]

I went on a bit of a mad quest for the ultimate all-round scope last year and so have had a couple of 100EDs, a couple of Tals and currently have a Lyra F11, which I'm using mostly for solar stuf. Other than CA there's little to choose between the Lyra and 100EDs optically, apart from the difference in focal length. The Lyra's mechanically much slicker than the basic 100EDs, more comparable with the Equinox scopes, but that's about it.

Of the 3 scopes I have to say the Tal would be my choice, but I'm a bit weird so it wouldn't necessarily be my recommendation to others.

As an aside, I also have an 80mm f15 scope and can still see the CA in that - it's more noticable than in the 100EDs at any rate. A 100mm f15 would theoretically be a little worse in that respect.

Never did find the one scope that can do it all, by the way, but the 120ED was the closest I got.

[tony4563]

I have both the 150 and 180 maks.

I intended to sell the gold tube 150 when I bought the new 180 but for some reason... I just cant let go

Side by side the 180 is almost a third longer in length and a heck of a lot weightier!

Sure the images are a little brighter in the 180, but for its size and aperture, the 150 is really hard to beat. It sounds stupid, but its just SO "comfortable" to use.

That, and the fact that the images it produces were stunning.

Dont get me wrong. The 180 is a great scope, and gives great views when cooled down properly.

Maybe I'm just struggling with its slippery bulk and tiny FOV to enjoy it as much as I should be.

[John]

....I intended to sell the gold tube 150 when I bought the new 180 but for some reason... I just cant let go .....

How close does your Equinox ED100 get to the Mak 150 on the planets Tony ?

[AndyH]

I find that planetary views through bigger aperture scopes(in my case 8") can be affected far more often than smaller scopes due to the lack of good seeing here in the UK.

Bigger is not always best.