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The Warthog

Eyepieces - the very least you need.

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I've recently come across this further guide to eyepieces which I thought was well written and useful :(:

Robins Eyepiece Guide

A good read.

I must say though, I breathed in some coffee, when I read the following, under the picture of a KK 'volcano top' ortho....

"The classic Celestron ortho,

this was a starter eyepiece

and not recommended now"

Really :p

:D

Andy

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Hello everyone. New to the hobby here and have my first scope coming in tomorrow. I ordered the Meade ETX 80AT-TC. It should be something good for me and my 9 year old son to grab and go with. It is an F/5 scope and comes with plossl 9.7mm and 26mm ep's which are close to what is recommended here. However, it mentions having a x2 barlow with those pieces. The scope has a built in barlow flip but wondering if it wouldbe worth buying a real barlow or if the one built in is just as good.

Edited by hodgespa

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Just for illustration - bundled Vixen Plossl Eyepieces (20 & 6mm) with the A80Mf vs Baader Hyperion (3.5 & 13mm) and Baader Aspheric (31mm) which is natively 2". They need a bit of a clean ;)

You can actually see the difference in quality in the last 'through the EP' photo. On the right is the bundled 20mm and the image is both not as detailed and not as contrasty. Also you can see the slight fisheye of the 31mm.

So for my two scopes..

Vixen A80Mf - 80mm aperture, 910mm focal length, f11.4. This has really taken a backseat with the Pentax below:

910 / 3.5 = 260x, in your face lunar! However touching the EP, scope with the Porta mount makes the image bounce around!

910 / 6 = 151x, you can just make out M42 stars and through averted vision just see the outline of the core nebulosity. Very dim!

910 / 13 = 70x, good - this is my workhorse with the vixen. A good upgrade - can see more of M42's stars and nebulosity and still separate the core stars.

910 / 20 = 45x, this EP is 1/2 as bright as the 13mm!

910 / 31 = 29x - not tried it, although the 31mm has a 1.25" adaptor - the Pentax's 105mm aperture brings in more light for a better image!

Pentax 105SDP - 105mm aperture, 675mm focal length, f6.38. I only use the Baader with this:

675 / 3.5 = 192x, great for lunar and planets

675 / 13 = 52x, great all around workhorse for lunar, planets and finding DSOs

675 / 31 = 22x, big sky and DSO view with a mass of stars. I need to switch focus adaptor here (the Pentax will take up to 63mm! :o)

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post-22611-133877604624_thumb.jpg

Edited by NickK

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HI

Does this formula work for MAKS as well, with there really long focal lenghs?

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Yes it works for maks, the formula is based on the focal ratio of the scope not the focal length. So the maximum magnification for a mak is about 6mm (half of F12) and for a fast dob it would be 3mm (half of F6). And many people would say those mags are too high...

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Hello everyone. New to the hobby here and have my first scope coming in tomorrow. I ordered the Meade ETX 80AT-TC. It should be something good for me and my 9 year old son to grab and go with. It is an F/5 scope and comes with plossl 9.7mm and 26mm ep's which are close to what is recommended here. However, it mentions having a x2 barlow with those pieces. The scope has a built in barlow flip but wondering if it wouldbe worth buying a real barlow or if the one built in is just as good.

I also have an ETX 80 AT.

I suggest not using the built-in Barlow for several reasons.

1. It requires MAJOR refocusing between the two settings, so much so, once you choose a setting, you may well leave it there for awhile. Going between the 2 settings is a real drag and works the focusing knob & linkage/gear much more than is probably good for the scope in the long haul. You may have found this out already.

2. More importantly (and hopefully this has NOT occurred yet), the mechanism is prone to failure/breaking/jamming and the unit is prone to falling off the "arm" that it is retained on. I have heard enough "horror stories" and also a friend who had take his apart to re-attach it.

Mine did function (I used it very sparingly at first), but the unit was not that smooth to operate so I have not used it since. I also received a Barlow lense as part of an eyepiece set that came with the scope as a package deal. It is MUCH easier to use switch out Barlow and requires minimal refocusing, if at all, depending on the eyepiece in use. Sometimes I will just "lock" the eyepiece in without letting it go all the way down into the receiver (flush) for a brief view.

If you can get a Barlow, I would leave the built in flip Barlow alone and in the "off" position.

Other than that, I have had a great time with the ETX. I hope you enjoy yours as much as I have.

Hope this helps.

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I also have an ETX 80 AT.

I also received a Barlow lense as part of an eyepiece set that came with the scope as a package deal. It is MUCH easier to use switch out Barlow and requires minimal refocusing, if at all, depending on the eyepiece in use.

OK, so I posted elsewhere about my ETX-80 flip barlow problem (knob not tight, barlow slides in unless I hold knob). I've had a couple of people suggests fixes but I'm starting to lean towards fixing it in place and buying a serperate barlow. A coupld of questions:

1) What barlow did you get as I've seen a couple of people post that the barlow they bought won't focus as not enough focus travel

2) Have you used it with a webcam? I have a modded philips but can only use it with the barlow flipped in (can get enough focus travel without barlow).

Thanks in advance.

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1.) I have 2 Barlow’s. One came as part of an eyepiece set (Zhumell), and the other was an extra from a scope purchased at second hand shop (Celestron).

Celestron 2x Barlow, Ultima SV series. Model #93506-1 ¼

Zhumell 2x Achromatic Barlow.

Both of these should work fine (they do for me), with or without filters on the eyepieces, even when doubled up together (4x?).

These units are both about 3” (7.6 mm) in length. I am not sure if these are considered “shorty” Barlow’s. I believe Meade makes a 3x Barlow for use with the ETX 60/70/80 scopes.

2.) No, I don’t use a web cam and just recently purchased adaptors (basic and T-ring) to use my Eos Rebel (1000D) with the scope, but I don’t think you will have the same problem with an aftermarket Barlow.

The difference in the amount of refocusing (tube travel/turns of focusing knob) between the aftermarket units I have and the built-in flip is pretty dramatic, 1 or 2 turns with the aftermarket units, as opposed to what seemed like 10 to 15 turns with the flip Barlow.

This is a site that might be able to help; they have answered some questions for me, very polite.

http://www.astronomics.com/main/search.asp?catsearch_header=Astronomics&keyword=Barlows&x=13&y=5

I admit I am no expert on these matters, and didn’t have to do any research, as one them was part of a gift and the other was a surprise. The Celestron was in a bag down in the optical tube (along with another eyepiece and compass). I don’t think the clerk knew, he said it was spare thumbscrews for the tripod!

Hope this helps you out.

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Wow,,,,I have ploughed through the whole thread, brilliant, thanks to everyone who has written with advice. I have a SW 200P, f5... so, bottom line, I have the two EPs that came with the beast, a super 25mm wide angle and a super 10mm. I have already bought a Plossl 40mm and a 2 x Barlow. From reading the thread this would seem to be sufficient.... yes ?..... no ?

I must say that since joining this site yesterday my interest and confidence has improved no end,,, might soon be brave enough to go outside in the dark and hopefully see something bright and shiny !!!

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Thanks Warthog - some great tips here. This is a very expensive hobby I've fallen into isn't it!

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This is a great post that has really helped me to better understand the importance of choosing the right eyepieces, especially if you have a low disposable income. Thanks Warthog.

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HI. going back to WH,s original post for a moment.

what would the number to multiply by be to find the optimum useful

ep,s for a f6.3 10" newt.

thanks in advance

ken

(i baint be no good at them mathematics things)

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Ken,

Your 10" F/6.3 newt has a focal length of 63" or 1,606mm. If you divide the focal length of the scope in mm by the focal length of the eyepiece you get the magnification, eg:

40mm eyepiece = 1606 divided by 40 = 40x

20mm eyepiece = 1606 divided by 20 = 80x

and so on.

a 32mm or 40mm would be the lowest useful power eyepiece in your scope and a 6mm (268x) would be about the highest (given our typical viewing conditions). A couple of eyepieces in between them would be useful as well - say around 90x and 150x (18mm and 11mm or thereabouts eyepieces).

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Your article has just answered so many questions I had! time to start shopping. Thankyou.

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great advice wh i have a skywatcher 130p which has a focal length of 900 i think its a f6 just bought five plossl ep's 6.3 mm 10 mm 15 mm 20 mm and 40mm what do you think i should use the x2 barlow lens with if anything also have a 25mm wide angle long eye relief which gives me alot of viewing pleasure many thanx for for your information looking forward to our reply jimmythemoonlight :)

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Great info and after a couple of read throughs i got it, (i am a complete beginner folks)

So now i know what im after i went searching the net etc and came accross this , (hope its ok to put up the link) which seems too good to be true, they are marked plossl and come in near enough or exactly the size im after , can anyone comment if they would be anygood, seems cheap for 4 eye pieces when the cost stated would only just about buy 1 anywhere else ????

Set of Four 1.25" PLOSSL Lens for TELESCOPE, Brand New | eBay

if anyone can cast an opinion over them for me it would be much appreciated..

cheers paul

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@BigP - They're cheap for a reason!

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I'll be buying my first scope in the next few months. I was already thinking about decent EPs so this post proved highly informative (most folk might agree with me that selecting/buying EPs is probably harder than selecting/buying a scope). I think a common mistake made by many newbies is the feeling that they need an 'armada' of EPs of different focal lengths, FOVs and optical types. In reality, I think most folk use only 2 or 3 EPs on a regular basis.

After some research (due, in part, to recommendations by Rod Mollise) I have shortlisted the following EPs for an 8" f/10 SCT:

Televue panoptic 24 mm, 68 deg apv, 85x

William Optics uwan 16 mm, 82 deg apv, 127x

University Optics abbe orthtoscopic 9 mm, ~47 deg apv, 226x

- Pete

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