which one 7 or 9 mm for my 8" SCT

[astropolak (Joe)]

Hi there
Can anyone tell me if I should look at 7 or 9mm eyepiece for my LX90 SCT.
Hoping to buy myself a Christmas present but afraid to make a mistake here.
My worries are that the 7mm may be too powerful for my scope in polluted Sydney sky.
And - yes I am looking at T6 Naglers.

Regards

[iceman (Mike)]

Hi there astropolak.

Light pollution isn't too much of an issue, but I think that 7mm would be too powerful for an SCT, and may only be able to used on those rare nights of above average seeing.

The 9mm is probably a better option for you and would be able to be used on a wider range of targets more often.

However, a few questions as well:
1. What's the FL of your scope?
2. What eyepieces/barlows do you currently own?

[ving (David)]

yes, alot depends on the FL of your scope too... divide the FL of your scope in MM by the size of the EP to get the magnification.
eg: 1200 fl / 9mm ep = 133.33 magnification.
I am guessing that you FL is alot longer? if so your magnification would be higher. are you looking to use it for planetary work?
i use 184(ish) magnification in VERY good seeing. other wise its not practical.
if you are splitting doubles you can go higher

[astropolak (Joe)]

Thank you for your response.
My LX90 has a focal length of 2000mm.
I currently gave:
14mm Meade 5000 Plossl
6,9,32,40 mm cheap Bintel Plossls
7-24 Vixen zoom
20mm Meade QX
42 GSO Superview
2x APO 1 1/4 barlow (Orion shorty)
Cheap and nasty 2" diagonal from Andrews plus standard 1 1/4 prism diagonal

Obviously I am looking at improving my viewing experience here - my zoom eyepiece does a great job at 7mm but I am not convinced that it offers me best quality images...

RGDS

[Robby]

The seeing will need to be really good for you to use a 7mm. At 285x it is really too much power.
I'd recommend the 9mm. As ice says it has far more uses.
Cheers

[h0ughy (David)]

Follow Mikes advice there, look at the 9mm. I own a 12" and the 9 is very comfortable in it, the 8 would be ok as well. the scope is already a f10, by uppingthe power too much you loose out on the light and clarity to observe any detail, that is my experience anyway and IMHO.

[rmcpb (Rob)]

Astropolak,

Just looked up the specs on your scope and it has a focal length of 2000mm and an aperture of 203mm.

Let's start with your aperture first. On a night of really great seeing and I mean really great seeing the maximum magnification your scope will support is about 400x. The rule of thumb used here is the aperture in millimeters multiplied by 2.

With your focal length a 9mm lense will give you 222x (2000/9) magnification which is within this range BUT if you considered a 10mm and get 200x (2000/10) this would probably be a more useful lense. Add a good 2x barlow and you have your theoritical limit with the 10mm, the 9mm barlowed would be over this limit.

From the Meade website that scope comes with a 26mm lense giving you 77x and, if barlowed 144x.

Add another about 17mm giving you 117x or 234x barlowed and you will be getting a good range of magnifications.

Just some thoughts.

Cheers

[[1ponders] (Paul)]

Hi Astropolak.

I have the same scope. Ditto to just about everything already said. For planetary viewing I find I'm mostly using either a 10mm or a 15mm with a 2X barlow, assuming the seeing will let me. I have a 6.4mm but I rarely use it as its just that bit too much for average conditions. Even on those rare nights where the sky is being kind then the 10 plus barlow is just too much. BTW collimation will make a hell of a difference too. If I'm well collimated I can get away with pushing it just a bit in magnification and still have reasonable viewing, but if I'm out even a bit - forget it.

[astropolak (Joe)]

Rob, thank you for this. In mailing this messages I am slowly working my way to "Buy and Sell" section of this Forum.
I have not warmed up to using barlow too much, in fact adding 3 more glass elements to 5 or 6 or 7 element eyepiece hardly makes for better viewing.
I am hoping to get one "GREAT" eyepiece for planetary viewing...if there is such thing...

RGDS Joe

[astropolak (Joe)]

Paul
I am amazed how much worthwhile advise comes from you guys - it is great.
On the subject of collimation, I have Bobs Knobs on my LX90 adjusted to perfection (or so I think) but have never seen the famous "Airy Disk" - have I got a dud scope or what?. I I see in focus is boiling stars dancing around...

RGDS Joe

[rmcpb (Rob)]

Point taken, however, buying a specialist eyepiece just for high power use is an expensive option. The barlow option is more often taken and, if the barlow is a good apocromatic one, the views are really great. Add to that the retention of the original eyerelief of the original lense and the barlow option becomes a strong one.

Cheers

[Merlin66 (Ken)]

I picked up an original Ziess 6mm Mono many years ago..... like looking down a tunnel but the images are 300%

[Striker (Tony)]

I would go for the 9mm....

But saying this your going for a very expensive eyepiece that your really only going to benifit from on a faster scope....I have had some naglers and yes their great eypieces but I would never go down that track again unless I had a F6 or faster scope.

I say buy 2 well respected eyepieces instead of the Nagler....you not going to benifit from a Nagler at F10.

You may want to improve your cheap and nasty diagonal...again...no good having a nice eypiece if the diagonal isn't up to it.

[janoskiss (Steve H)]

Originally Posted by astropolak

Rob, thank you for this. In mailing this messages I am slowly working my way to "Buy and Sell" section of this Forum.
I have not warmed up to using barlow too much, in fact adding 3 more glass elements to 5 or 6 or 7 element eyepiece hardly makes for better viewing.
I am hoping to get one "GREAT" eyepiece for planetary viewing...if there is such thing...

I recently got a set of UO HD orthos. Great sharpness & contrast. Beats everything else I've tried on planets (incl nagler, panoptic, plossl ...). And the 9mm still has plenty of eye relief (w/o glasses of course). The 7mm is getting a bit tight but still quite usable. They do have a 45 degree FOV, but for planets this is a non-issue. They barlow really well too in the shorty-plus, better than any other EP I tried. (Only 4 elements per EP which will help with the glassophobia too.)

And they are a bargain at around $125 new. (Or you could buy a 13mm Nagler T6, and I know someone who will swap you a set of four HDs for it. But it won't be me!)

[[1ponders] (Paul)]

Originally Posted by astropolak

but have never seen the famous "Airy Disk" - have I got a dud scope or what?. I I see in focus is boiling stars dancing around...

RGDS Joe

That makes two of us. I cam close one night but still no banana. Living near the Coast near the base of a mountain range (well the australian version anyway) I get a lot of turbulance.

[xstream (John)]

Astropolak,
My wife has an LX90 and 9mm Nag. At 222x there isn't a lot of nights you'll find that you can use it unless you live in one of those rare spots that has a high avg. of excellent seeing.

My suggestion is go for a medium power, 12mm T4 Nag if you want a wide field eyepiece.

Between that and a 32mm TV wide field Anna finds these are her most used eyepieces, and she would never part with either.

[asimov (John)]

I agree with Tony. A Nagler with your FL is not really needed.....desireable perhaps, but not essential for great views.

[Robert_T]

Hi Joe, I have to agree with Tony's comments regarding the value of going with a Nagler on your F10 SCT. At the power's you'd be getting using 7, or 9mm for that matter, it would have limited use for deep sky observation (perhaps double stars and resolving globulars?). That leaves the planets and moon. Assuming it's mainly planetary observing you'd be doing (?) the 82?deg fov of a nagler is really just giving you a good and expensive view of black space (ok maybe a few moons round jupiter too). If you want quality high power eyepieces for planetary, as Steve mentions the UO HD orthos are hard to beat and at $125 you can get 2 or 3 for the price of similar Nagler.

Re your comments on Barlows, you might want to consider the Televue powermates. Used with quality eyepieces it would be hard to pick any degradation...

cheers,

[ausastronomer (John Bambury)]

Originally Posted by xstream

Astropolak,
My wife has an LX90 and 9mm Nag. At 222x there isn't a lot of nights you'll find that you can use it unless you live in one of those rare spots that has a high avg. of excellent seeing.

My suggestion is go for a medium power, 12mm T4 Nag if you want a wide field eyepiece.

Between that and a 32mm TV wide field Anna finds these are her most used eyepieces, and she would never part with either.

Hi,

I am going to throw a spanner in the works and agree 100% with what xstream said in not being able to use the 9mm eyepiece all the time due to atmospheric turbulence. The 9mm eyepiece gives you 222X in your 2000mm FL scope. I think you would get infinitely more use out of of either the 11mm Nagler T6 (181X), the 10mm Pentax XW (200X) or the 10mm TV Radian(200X). FWIW I rate the 10mm Pentax XW as superior to the Nagler T6's and Radians, having used them all. The Pentax has a slightly smaller AFOV compared to the NT6 which I dont really notice anyway, but for planetary performance it is sharper, has better contrast and higher light transmission than the Nagler t6's. It also has much more eye-relief but offsetting that is the fact that it is also larger. For planetary work I also find the Pentax XW's give cooler more neutral tones than the Naglers. I also find the Radians to be warmer than the Pentax XW's. Whichever you were to choose between the 3 I have mentioned you will end up with an exceptionally good eyepiece, the differences between them all are pretty subtle but as I said having used them all I think you would fall in love with the 10mm Pentax XW.

CS-John B

[Starkler (Geoff)]

If buying for planetary use on a tracking scope, why not a 9 or 10mm UO ortho ?
As Steve says, very little will beat it when it comes to contrast.