bargain achromats

[janoskiss]

Anyone after an achromat should check out AOE's current prices (http://www.aoe.com.au/refractors.html).

I was just browsing for a mount for my ED80 when I spotted the new specials on refractors. Ranging from 80mm on AZ3 for $249 to 102mm on EQ5 for $599.

I'm almost tempted to scrape together enough for yet another scope. Would the 4" f10 make a good planetary scope? I could also use the mount & tube rings with my ED80.

[elusiver]

how many scopes do u have jano.. didn't u just get the ED?? will it ever be enough :P :D

el :)

[ving]

been looking at them too...
the price of the 102mm barely covers the mount!

wonder what the quality is like?

[janoskiss]

That was my thinking exactly David. What I'm really after is a half decent mount + tube rings + mount plate for my ED80. With the 102mm package I'd be pretty much getting a free scope. Even if I don't like the scope and decide to sell the OTA + finder + diagonal + EPs real cheap, say $200 total, I still would have gotten a good deal.

[cahullian]

with the 102 mm the tri pod is alumunium not steel but it looks very interesting. Might think about one for my trip south of the border later in the year.

[cahullian]

would an EQ aluminium mount be any good?
Does anyone own one?

[ballaratdragons]

Steve, you could piggy-back mount the spare refractor onto one of your other scopes!

[ballaratdragons]

What is the difference between these 2?
I know nothing about refractors. I've never had one. But I am interested in one of these!!! They are on the site Steve provided above.

AOE90S 90x600mm F6.6 Price...$299.00

AOE90L 90x900mm F10 Price...$299.00

Is one better for deep space or what?

[ving]

focal length ken, the 900mm will give more magnification but like adding a brlow to your scope it makes the image dimmer and narrower too. the 600mm will give a brighter image and wider, but the trade off is less magnification.
:)

the mounts are probably interchangable even tho the f6.6 is shown on a az mount and the f10 on an eq.

so yeah the 600mm is better for wider field and deep space i'd assume

[ballaratdragons]

Ta David,

I am thinking of one for my boys (and me). If the f6.6 is a very good scope I would like to get them (us) one.

Unless someone explains to me why the f10 would be better.

And it says you get to pick which mount you want. I think EQ!

[janoskiss]

The 102mm is a bit too long to piggyback on the Dob, but the short tube 80 or 90mm would make a great finder. I've been meaning to buy a right angle finder anyway. Just got to work out what's the most cost effective option. The ED80 has an oversized 4" OTA, so the tube rings of the smaller scopes would not fit it.

Got a quote for EQ5 + tube rings from AOE: $548. So that's just $51 extra for the 4" f/10 + accessories. I read several reviews about 100-105mm f10 Chinese achromats, and the general impression I got is that this sort of scope at best could equal the ED80 on some targets and would be inferior on others. I wonder what the resale value of the 102mm OTA would be. :confuse3:

[janoskiss]

Ken, the main reason f10 is better because flaws inherent in the design of these scopes are worse at shorter focal lengths. All else being equal, spherical and chromatic aberrations get worse as the f-number goes down. This becomes more important at high magnifications, i.e., planets.

BTW, at the same magnification both the short and long tube scopes will be just as bright as each another. It's just that you'll need different EPs to achieve the same magnification.

One thing to consider is just how wide you want to go. With a 30mm PL (which is probably the longest FL EP you'd use), the 90x600 will give you 20x, i.e. about 2.5 degree FOV, and the 90x900 will do 30x or about 1.7 degrees. So at its lowest magnification you'd get away with not having a finder on the short tube, but you'd need one with the f10.

[ballaratdragons]

So a good compromise between the 2 f ratios might be:

AOE80S 80x600mm F7.5 Price...$249.00

Yes or No?

[janoskiss]

No. Mask down the 90mm to 80mm and you would have turned the 90mm f6.7 into an 80mm f7.5. For an extra $50 the increased aperture of the 90mm is probably worth it.

[ballaratdragons]

Sounds to me that the: AOE90L 90x900mm F10 Price...$299.00 is the way to go then.

And get it on the EQ mount. It is an: EQ-3A Equatorial. Hope they are OK for that size and length of scope.

[janoskiss]

EQ-3A looks identical to what I have, and what I have is a wobbly, flimsy and badly designed mount. I'd say the AZ3 will probably be a lot more stable & easier to use.

[janoskiss]

Ken, another variable in the equation: Coatings. See below. I'd say contact AOE by email or phone and discuss the pros & cons with them. I've found them to be very good at providing information, and willing to patiently answer question after question.

[ving]

yeah i was thinking of getting one at one stage for beckie (me) because it would be a great starting point for her (me). :P

:poke:
of course she isnt interested so I'd have to have it ;)
and of course cheryl say "you dont need another scope david!!!" :help3:

wouldnt buy one behind her back of course... I'd do it infront of her back :wink2:

[ballaratdragons]

David, to save arguments with you wife, I'll go you halves in one.

I get it for the first 5 years and then you get it for the next 5.

[Starkler]

My thoughts are that anyone with a dob here looking for a second scope may be better served by a short focal length refractor for rich field viewing. The longer f10 types are closer to the focal length of the dobs and wont do anything better than what your dob does, and be considerably dimmer and shakier.
A long fl refractor on an eq3 with aluminum legs will be diabolical.

[ballaratdragons]

:lol2: :lol2: :lol2:

I was explaining to Cheryl how the boys would like one of these Refractors :D

"It would be good for their Science Projects". ;)

[ballaratdragons]

Geoff,

Are you suggesting that this one: 'AOE90S 90x600mm F6.6 Price...$299.00' would be better for me . . . I mean my boys than the f10 even though it's on a wobblotronic EQ3?

[Stu]

janoskiss, I was just about to write that and you beat me.

The AOE 127mm F9 and 152mm f8 are the same scopes as the Meade AR5 and AR6. The 127mm version is the better of the two as far as aberations go and I've heard and read a lot of people say it's "in a different class" (...when you get a good one, as the collamation is not adjustable in the 5-inch).

I have wobbled the 6-inch on an EQ5 and LXD75 and the LXD75 was much more stable. After all, that was why Meade ugraded the LXD55, everyone complained.

The smaller scopes are made by someone else. They are all cheaper than the skywatcher/saxon version though. Three cheers for AOE :drink:!

ballaratdragons, if the kids want to look at planets, I'd get the F10. You can always upgrade to the 20" RCOS later... ;) Just make sure it doesn't fall on one of the kids. :ashamed: I'd do the paving before that point...

[ballaratdragons]

The Kids???

Oh yeah, them!

It would be for me, and I would let them use it sometimes. Might even piggy back it. I already have a GS12" f5 Dobbie. But would put it on the tripod on the nights they use it.

[cahullian]

I am thinking of getting the 102 mm with the EQ5 Aluminium tri-pod for $599.00 sounds like a good deal. Anyone know anything about the EQ 5 Aluminium mounts?
Will I need to save for an EQ 6 later on?

Gazz

[Stu]

In that case get the short focal length. You'll use it (as a guide scope) more than they will. I've just come in from outside. I just got a sore neck star-hopping in scorpio, I wish I had that right angled finder!!!

think I'll get the short scope as well...

[ballaratdragons]

Stu says: In that case get the short focal length.

John says: Yep. piggy-back the F/10.

No wonder newbies get confused in here!!!!

[janoskiss]

Ken, I don't know how good or bad your Dob is at high magnification, but when I got my old 60mm refractor off ebay for $25, I was astonished how well that little scope performed on Jupiter compared with my 8" Dob (allowing for the reduction in brightness of course). I've been after a better refractor ever since, and finally got the ED80 last week. The ED80 is lightyears ahead of the Dob in terms of contrast. But there must be something wrong with my Dob and it's not collimation. I'm going through Geoff's mirror de-stress howto and hopefully that will improve things.

So maybe if you look through an f10 refractor you'll be surprised by the contrast too. Star camp will be good for comparing scopes. :thumbsup:

"Yep piggy back the f10"?? It's 2/3 the length of the 12" Dob? The eyepiece will be at knee level. :confuse2:

Spot on Ken! :rofl:

[ballaratdragons]

Thanks Steve. I will compare at the Star Camp. Hopefully there will be Refractors of differing f ratios.

Have to remind Stu of the Star Camp next time he is in here. oops! I just did.

[Starkler]

Ive looked through a $25K astro physics refractor at Jupiter and im still happy with my dob :shrug:

[janoskiss]

Wow, thanks Geoff! That really puts it in perspective. I need to get to work on my Dob!

[Thiink]

Hm interesting. One of those would make a great grab and go scope, and with the 1.25" focuser means I can reuse my EP's. It'd be which one to go for that would be the problem. I already own an average 60mm refractor with below-average alt-az mount (DSE job). Are the short tubes any good for planets, or wide field only? Maybe the EQ5 would be the ticket, I dont want another crap mount..

I have dark skies about 15mins from my house, and the dob is just too big to cart around for quick viewing sessions (that and the base doesnt fit into the car easily).

[janoskiss]

Probably no good for planets.

[ving]

twas my 60mm ebay scope that got me into this stuff in the first place! :)
thinking of replacing the focuser on it (and other stuff) so i can use 1.25 eps on it..... I'll just add that to the to do list.. :poke:

[Stu]

EP at knee level...I didn't think of that.
Maybe it would suit the kids better.

Starkler is bringing up that age-old debate again:
1800's - Speculum Reflector vs Galilean Refractor
1900's - Glass Mirror Newtonian vs Achromat
2000's ??? - Dob vs APO???

You're either with me, or you're against me! :rofl:

Attack! Attack! :poke:

[ballaratdragons]

Don't forget:

2000's - Computerised & GPS GoTo's vs Dobbies & PushTo's

[seeker372011]

you can get a 0.963 to 1.25 convertor for $10 from BATSC in melbourne

I used one to convert a $50 GoLo scope -a 60 mm refractor into a really light weight guide scope that can be piggy backed on my 8 inch newt

[Starkler]

Dont get me wrong here!
I wasnt suggesting that the view through my dob was better than that of the AP apo i viewed through. The apo certainly gave a darker sky background but for me it wasnt a 'knock your socks off' kind of view worth paying big bucks for me personally. I would love to have that scope and my dob side by side on a night of excellent seeing to see what both can really do.

I mentioned it for the benefit of those who might be hoping that a 4 inch achromat is going to somehow deliver superior planetary views to their GS dobs. I fear these people will be dissapointed unless their dobs arent set up and collimated properly. Getting that right is cheaper and easier than shelling out for a new scope to do something the dob should be superior at anyway.

[ballaratdragons]

Good point Geoff. I will take that on board! Thanks.

[GrampianStars]

what refractor 12" ? what have you got a 30" dob ?
I'm not easily convinced
the ED80 kills my 8" SCT on planets

[slice of heaven]

Now you've done it Geoff :poke: :fight: :)
Seems confusion reigns supreme in this thread.

[Starkler]

I also have an ED80 but no way can I resolve the same detail with that as I can in my 10 inch dob and I wouldnt expect to with 80mm of aperture.
It really sounds to me that there is something wrong with the sct.
Dave47tuc used to own a 10inch lx200 which gave good planetary views (sold to mojo I hope he is using it, its too nice a scope to be collecting dust).

Im not bagging refractors, I just dont believe that a 4 inch achromat will beat an 8 inch gs dob (properly set up and collimated) on planets. Theres two factors working against the achromat, aperture and colour.

[slice of heaven]

Its not only the sct Geoff, there seems to be a few scopes in trouble in this thread.
Especially if 60mm and 80mm refractors are knocking off 8",10" and 12" newts.
Properly setup the big ap wins handsdown.

[Starkler]

When we had our Vic meet a few months ago, there were three other GS dobs there, two that I got to look through. Both of them had obvious issues.
If at least two out of three from this small sample had issues, I wondered how many others out there were like this. Thats what prompted me to put together the GS optics how-to http://www.iceinspace.com.au/index.php?id=63,206,0,0,1,0&hashID=23aa67c42d1165da5b7862c1ea93 21d8

In the case of dave47tucs scope, his primary was clamped in too tightly.
I havent heard back about Migs scope yet.

[slice of heaven]

Maybe that link should be thrown up more often to keep people aware of the issue.
I'll remember I said that.
As you've stated its a common problem that needs to be addressed.

[[1ponders]]

I have the HD-102EQ f/10 Celestron/Synta Achromatic refractor on an EQ3/4 mount with the diabolical aluminium legs. It has way to much lever arm movement for that size mount but should work well if they really are EQ5 quality mounts. Pitch the legs of the tripod in the bin and put some solid wooden legs on it.

If the refractors from you link are the same as mine, and I'm betting they are, its not a bad little planetary scope, but it has an abysmal cheese grater focuser. Though once you clean the Synta snot grease out of it and regrease it the improvement is quite dramatic. I've even used mine to image through. (see here http://www.iceinspace.com.au/forum/showthread.php?t=2304 ) Naturally the CA is much worse when imaging, but it does give a pretty good sharp image for a cheap refractor.

After seeing the amount of CA in my f/10 I'd imagine in the faster focal length scope it would be pretty abysmal. It would probably make a good finderscope or guidescope, but too colourful as a regular visual scope.

[ving]

good idea..
thanks narayan :)

[ausastronomer]

David,

Importantly the shorter scope will have SIGNIFICANTLY more false colour on bright objects than the longer scope. Basically the short scope is best suited for low power wide field deep sky work and the longer scope better suited to lunar/planetary double stars.

CS-John B

[ausastronomer]

Geoff is 100% correct here, no 4" refractor is going to compete with an 8" dob in terms of "visible lunar/planetary detail" a properly set up 10" dob will outperform or compete with the best 6" refractors. A 5" and smaller refractor is not even a contest to a 10" dob.

I will post something on the GS dob optics thread about what to check for optically with your GS dobs.

http://www.iceinspace.com.au/forum/showthread.php?t=3370

CS-John B

[dugnsuz]

Hi All,
New to this excellent forum - first post.
I've recently contacted Dan at AOE re this package.
I was worried about the flimsy aluminium tripod.
Dan said he'd upgrade to the tubular steel version for an additional $40.
That's a spicy meatball!

Cheers

Doug Robertson.

[ving]

hey thanks doug, and welcome to the forum :)