Do you need a filter to see Nebulas?

[janoskiss (Steve H)]

The focal length is always specified along with the eyepiece make & model. For e.g. the Meade you've quoted above:

Meade 5000 06.7mm (1.25")

Here 6.7mm is the focal length.

Magnification = focal length of scope / focal length of eyepiece.

[Eardrum73]

ohhhh so thats the focal length...

lol i alawys thought that number was the eyepeice apeture or something....

Me = noober

[acropolite (Phil)]

Eardrum, I would try any Meade EP in your dob before you buy, because they don't always perform in fast scopes (e.g. your dob) That's not to say they're poor quality, but most seem to agree that they're optomised for Meade SCT's which are generally f8 and higher.

[RAJAH235]

Eardrum, I have Meade 4000 SP's & they are 5/6.4/9.7/12.4/15/32 & UWA 14mm, + #140 barlow. I also have a 7.4mm Televue plossl + 18 & 25m MA cheapies. They all work extemely well in my 10" 4.5 DOB.
Why not pick a brand & stick with it? You can always buy Naglers or Panoptics later if nec/needed. HTH. L.

[Eardrum73]

Hi all,

Thanks for all your responses....

Reading elsewhere in the forum it is said by many that 200x is the limit in terms of visual magnification.

But after reading an article about mars in Sky & Space Megazine (October issue) it said that for larger scopes we should try an get 300 to 400x magnification for observation.... this kinda of contridicts the 200x is the max rule... can anyone shed any light on this for me?


As for eyepeices,

what do you think of the following setup? (I have a 12' DOB, with FL 1500)

Option 1
1)Meade 5000 6.7mm 15mm eye relief with Orion Shorty Plus Barlow which should give me 447x magnification.
This will set me back $385 from Bintel.

Will this work to see the details in mars? (instead of a round orb of light like I am getting now.) will the meade eyepeice perform well with my GS dob?


Option 2
2) Andrews Ultrawide 2' 12mm, 80 FOV eyepeice. (Don't know what the eye relief is yet....) with a Andrews 2' Barlow at $79. This should give me 250x maginification.
This will set me back $298 from Andrews.

The only thing with this is that it is not 400x magnification liek option 1 and I am unsure of the quality of the barlow and the eyepiece.....

Sky and Space megazine said 300x to 400x should be good viewing for mars when it peaks in late october... but I am worried that if I spend $385 and realise that I can't make use of the magnification that all that money would be down the drain... which option should I go for (or perhaps none of the above, you can see a better option) and why? pls help.

[janoskiss (Steve H)]

Magnifications of over 300x can very rarely be achieved. I'd say don't spend so much money on something you could use for no more than a few hours a year.

The long eye relief requirement limits your choices at shorter focal lengths (FLs). The ED2's are an option you might like to consider at $79 each from AOE, with FLs as short as 2.3mm. Then there are the GSO superviews at medium and FLs. At FLs of 20mm or more, Ploessls will also have at 15mm eye relief or more. These are all sensible budget options. If you've got money to burn Televue Radians or Pentax XWs seem to be the most highly praised choices (20mm eye relief).

[davidpretorius]

from the televue website
"
HIGH-POWER VIEWING
Once you’ve selected an eyepiece set based on field stop sizes, calculate the magnifications produced with your scope. For planetary or double star observing, you’ll want an eyepiece in at least the 150x range. For determining maximum power, a good rule of thumb is to use no more than 60x per inch of aperture for scopes with apertures up to 6". Higher magnifications may still be pleasing but will not likely reveal any additional detail. Realistically, the atmosphere will usually limit your planetary observing to a maximum magnification of about 300x, no matter how large your telescope aperture.

Basically, you’ll be choosing low and medium power eyepieces by field stop increments to "frame" the subject, and high power eyepieces by magnification increments (based on your scope’s aperture), to reach the optimum contrast and resolution for viewing planets and double stars. "

[square_peg114GT]

The ED-2s are reported to be very fussy about eye placement, blacking-out if if you don't keep your eye positioned just right.

Unless you have an astigmatism, try removing your glasses for viewing. Also, at higher powers the resulting smaller exit pupils may fall inside of the astigmatic portion of your eye. Remember:
EPmm = Dmm / Magnification;


where EP is exit pupil in mms
D is the objective diameter (again in mms)
Magnification is the effective focal length of the objective divided into
the focal length of the eyepiece.

300x in your 300D scope produces a 1mm EP, which may not be effected by an astigmatism.


Another trick for those needing long eye relief is to get to high powers by barlowing longer FL eyepieces. A barlow changes the effective focal length of the telescope not the eyepiece, so the eyepiece retains it's eye relief when barlowed. Ex. - a typical plossl has eye relief = ~.75xFL, so a 15mm eyepiece with a 3x barlow results in the same 300x (in your scope) as a 5mm eyepiece, but with longer eye relief (11.25mm vs. 3.75mm).

In general, I think the new owner of a fast dob (< f/5) should buy a few stop-gap eyepieces to tide you over until you invest in some quality wide-field eyepieces. Celstron Ultimas, Orion Ultrascopics or Orion Highlights (not sure what equivalents you have down under) should do just fine. Avoid the bargain wide-fields - You're gonna end up replacing them. JMHO

[iceman (Mike)]

1)Meade 5000 6.7mm 15mm eye relief with Orion Shorty Plus Barlow which should give me 447x magnification.
This will set me back $385 from Bintel

The 6.7mm on its own (without the barlow) will be your most used eyepiece for the planets. As Steve said, it's very rare that the seeing will allow the type of magnifications you're going for. Most times you try it, you'll end up with a fuzzy out of focus ball and you won't see any fine detail on the planet.

Of course you want to be able to push the magnification when the seeing IS great on those rare nights, but usually you'll be around 200x or less.

You'll want a barlow for every focal length - so getting one of them is a must. The Orion Shorty Plus is a great choice - it's really the best of the middle priced range, after the Televue range.

I'm not a fan of the ED-2 series, as Pegster said, they're fussy about eye placement and I found that the 14mm I tried didn't perform well in my f/5 10" dob. They might be better at shorter focal lengths (asimov likes them) but if you could try before you buy, that would be the best bet.

Sky and Space megazine said 300x to 400x should be good viewing for mars when it peaks in late october... but I am worried that if I spend $385 and realise that I can't make use of the magnification that all that money would be down the drain... which option should I go for (or perhaps none of the above, you can see a better option) and why? pls help

As I said above, 300x or higher will only be possible on nights of really good seeing. So don't spend a fortune going for that - spend you money on a good eyepiece to get you around 200x, and the barlow for nights of GREAT seeing. As I said, you'll use the barlow for your other eyepieces too.

So Option 1 looks like a good deal.

The Meade s5000 range don't appear to be quite as good as the s4000 range (at least in the Ultra Wides), but they're at a reasonable price and the plossls or super wides might be better than the 14mm ultra wide i've tried.

[Eardrum73]

Thanks for the help and feedback guys... I think your post help me heaps...

Eye placement is a crucial factor for me. I have Andrews 1.25' 40mm with 25mm eye relief and it actually cast a "shadow" or a "black shade" depending on where I place my eye. it actually has to be pretty exact, any slight movement will bring about the shadow. With eyeglasses its just a nightmare!

the other plossils don't have this problem. My most comfortable eyepiece is the GS 2' 26 mm with 30mm eye relief.... no shadows, easy to view, clear.... but unfortunately only 58x magnification.
Perhaps I will try and find a 3x barlow as Square Peg said and see if it can increase it 170x.

The Pentax UW or Televue Raidians with 20mm of eye relief sounds like something i should look into.... (I just hope they are not the wallet lightening types.....)

Iceman... you mean option 2 is the better choice don't you?

[iceman (Mike)]

Iceman... you mean option 2 is the better choice don't you?

No, I don't think Option 2 will be the best way to spend your $$ as you'll need to upgrade to something sharper before long (imo).

Option 1 is good because you'll use the 6.7mm on it's own for the planets, and the barlow for when the seeing is GREAT. Both are good quality items that you won't need to upgrade and you'll get plenty of use out of them.

[Eardrum73]

Ahhh I see... thanks for that!!!!!!!!!!

[Starkler (Geoff)]

I think many of the writers talking about very high magnifications are people living in places with exceptional seeing that most of mortals dont experience, such as Florida in the US.

In my Melbourne based experience, times are rare that going over 200x gains me anthing. My most used planetary combo is a 14mm barlowed which gives me 196x.
200x corresponds to a focal length of 7.5mm in your scope.
If you buy say a 15mm and a 12mm quality plossl such as televue, along with a good barlow, you will have a flexible set of medium powers for dso viewing, and medium and high planetary magnifications all giving quality views.

[davidpretorius]

Geoff, a noobie question?

Is 15mm and 12mm too close together. Is it a double up?

[janoskiss (Steve H)]

Eardrum, one more thing to keep in mind. Barlowed long FL eyepieces might have problems with eye placement too, because the Barlow actually extends the eye relief. My 25mm GSO Ploessl is comfy on its own but real touchy in the Shorty Plus. In my limited experience, the barlow can also accentuate some of the design/build flaws of an eyepiece, like internal & stray light reflections.

Dave, I'd say no, 15 and 12mm are like 30 and 24mm in a scope with twice the FL. 30 & 24 don't sound like doubling up at all, do they?

[davidpretorius]

thats true!!

[Eardrum73]

Hi all,

Over the weekend I had a chance of looking through a GS 68 degee eyepeice vs a Meade Wide view, both projected crisp clear views ( Although I was looking at the sign across the street on a spotting scope) and for the same FL they looked exactly indentical. perhaps with the more experience eye maybe you guys can spot the diffrence. But I will have to say its a very minute difference.

The meade eyepieces for its price seem to project about the same image as the GS ones. For almost 3x less the price, i would go for the GS wide view eyepieces anyday! (thats if I was heading down that path....)

I am begining to think that I should follow - the all or none law!

Either get the cheap stuff (which is GS eyepeices whoes quality seems comparable to eyepieces at 3 to 4 times its price ).... or go for the top of range like a televue.....

I haven't had a chance to look through and compare so I can't make any comments..... but I hear Televues are suppose to be the best of the eyepieces.... also the best bank busting one.... at 500 quid a pop!

[davidpretorius]

Eary,

hang five and let me try all the eyepieces i can lay my hands on at star camp.

Three categories, cheap=series 500 and gs, moderate = meades etc and premium = televue.

Each will be compared back to a series 500 at the same target at roughly the same time on the f5 dob

Mars will be out and so will saturn and dark skies will show up the dso's ie orion!

Which is the best planetary, best dso, double star resolution.

I will try and repeat on another sct etc, to see if there is any difference.

I want to know for all three ranges of eyepiece; contrast, image quality across the entire eyepiece, eye relief, barlow potential, double barlow potential etc. What is the overall feeling for the eyepiece etc.

I was able to double up a 2.4x and a 2x barlow and my 12mm series 500 worked well on mars ,the 6.5mm didn't work at all.

Hopefully, there will be a comprehensive list from a newbies point of view of where they all sit, and is there a good feel for value for money?

[Eardrum73]

11 days eh? I look forward to reading it..... should be interesting reading. Can't wait actually!!!!

But wow it sounds like a mountain of work...

Maybe I sould email Sky and Space megazine and see if they want to buy an eyepiece review article by an author named Davidpretorius...

[davidpretorius]

iis can sell the royalties, for every mag sold!!!!

except greg bryant's mates, cos he is a top bloke!