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Eye piece dilemma


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Hi,

having spent a long term deciding which telescope to get (went for 6SE), I now have to work out which lenses to get. I find my heart is easily seduced by the Celestron kit with its strong silver case ,black foam interior and the array of lenses and filters.

However, my head + reviews is thinking that I should go for better quality and smaller number of lenses. Maybe an 8, 17 (25 came with telescope ) a Barlow and moon filter.

 

Has anyone got any suggestions or advice? Is it possible to get this combination of lenses that are better quality than the kit versions, but around the same price of the kit.

 

Many thanks 

Martin

 

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There's nothing actually wrong with the Celestron Eyeopener Kit. There is some misconception that all kits are rubbish. This is possibly due to the fact that the first Celestron kits often contained substandard eyepieces and were a marketing gimmick supplied with some old entry level Celestron scopes. The Plossls in later stand-alone kits were all perfectly decent and were manufactured  by both GSO and Barsta (BST) at one time. I don't know about now though. The filters were OK but suffered from some thread incompatibilities.

 

This 'Astro Essentials' kit has 'StellaLyra' eyepieces and filters which are actually manufactured by GSO. These are excellent value for the money and are distributed under several brand names.

 

If you want a wider field on a 150mm SCT GSO SuperViews are an economical EP. I even use these in short tube achromats. I find them ergonomically quite pleasant to use. Bear in mind your SCT is f/10 and has a 1500mm focal length. A 15mm eyepiece will give 100x and a 10mm will give 150x. If you want to observe many DSO's you will need an eyepiece that will deliver at least a 3mm exit pupil or preferably greater. With SCT's all you need to do to calculate the exit pupil is divide the eyepiece focal length by 10 (which is the focal ratio of your scope).

 

UeHK4u7l.jpg

 

Altair used to sell the SuperViews at one time and I have a bino pair for my 127mm MCT. Unfortunately SCT's and MCT's aren't very good for rich field observing (due to their limited field of view). However they can excel at high lunar/planetary magnifications and for viewing brighter DSO's.

Edited by Nightspore
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Hi, that’s interesting about the kits because there are a lot of negative reviews for them, although the main problem seems to be poor eye relief And paying for bits you might never use. The Astro kit is a very good price, I might also look at second hand lenses.

 

many thanks for your comments .

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34 minutes ago, Martin said:

Hi, that’s interesting about the kits because there are a lot of negative reviews for them, although the main problem seems to be poor eye relief And paying for bits you might never use. The Astro kit is a very good price, I might also look at second hand lenses.

 

many thanks for your comments .

 

There's a lot of mythology about astronomical equipment, especially EP kits. This is often perpetuated on some forums (*cough* Cloudy Nights *cough*) by people who almost certainly have no actual experience with the items in question. 

 

The only negative thing I found with the Celestron Eyeopener Kit was that the filter threads were often incompatible with the supplied eyepieces threads. Which is why I recommended GSO filters which generally have universally compatible threads.

 

K12mhXx.jpg

 

Eye relief preferences vary and I'm happy with as little as 3~4mm for short focal length Plossls and orthoscopics. The chart above is about typical for ortho's. 

 

a51A5enl.jpg

 

For wide field EP's anything much longer than about 13mm and I find I can have eye placement issues with some individual eyepieces. With an f/10 SCT you won't need wide field eyepieces that are excessively overcorrected for edge astigmatism, which is why I recommended the SuperViews. The requirements for faster scopes are more stringent. Oddly there are even differences between fast refractors and fast Newtonians. I find Celestron Lumimos eyepieces work quite well in refractors up to f/4.9, yet glare badly in Newtonian scopes faster than f/5. Secondhand eyepieces are an option but catadioptric scopes are generally optically more forgiving. 

 

HL3bDRkl.jpg

 

It's not always about how expensive the retail price is. The 5mm eyepieces above are quite different prices, yet optically I can detect no difference. 

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Hi Martin and welcome to the yard.

 

It sounds like you are just where I was about a year ago: having just purchased my first telescope I realised that there were some important decisions to be made re EPs. Although there are many on here with more experience than myself, I thought I would offer a few remarks that may (or may not) help.

Firstly, don’t be shy to ask any questions you have to this forum. The folks on here have helped me no end. You have already had one answer from Nightspore and I must say that he has also answered many of my questions and I have always found his advice to be spot on. If you view the areas on the forum re ‘equipment reviews’ and ‘show us your Astro gear’ you will find a number of threads re eyepieces.

 

The type of eyepieces you acquire can be affected greatly by your choice of target. Some benefit from a higher magnification and others from a lower power. Magnification isn’t everything and your highest useable magnification will be limited by your scope. 

 

There is a good used market in Astro gear and although initially cautious to buy used, i now scan it on a regular basis. It has enabled me to try numerous eyepieces and then just sell on the ones I didn’t like at no real loss.

Different EPs have different characteristics: eg fields of view and eye relief. So you may well find that one type suits you better as you find it more comfortable than a different type. An example of this would be my own experience with Plossl EPs which I find uncomfortable in short focal lengths. Therefore I sold the ones I had in the short focal lengths but kept a 32mm Plossl which I really like. But then others will have different experiences.

Finding the EPs that suit you and your chosen targets takes time. Be patient and if you are able to try a friends then do so.

As for the used market, I have used auction sites, gumtree and a specific Astro site called Astrobuyandsell. (Although I am UK based and am assuming you are also)

 

I rushed out and bought a moon filter as it seemed a good idea. I have since found out that definition can be enhanced by using some coloured filters, which can also be used on planets and also enable good views of the moon before it becomes completely dark. (Much of the advice concerning this came from Nightspore). If you search the threads on the forum re viewing the moon you will find the thread. My specific moon filter now lays unused in a drawer.

 

The lower pic in Nightspore post above shows a TMB planetary clone. He put me on to these and consequently I purchased 2 on Amazon. I can’t fault them.  The price on Amazon fluctuates so Keep your eyes open for a deal.

Edited by Marmot
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6 hours ago, Martin said:

 I’m really impressed with how quickly you guys have responded. Lots of quality advise to think about. 
thank you. 

 

You're welcome. I forgot to mention an old trick with cat's (or any slow scopes). 

 

iNg4Krel.jpg

 

By threading an 0.5x reducer directly into the barrel of an eyepiece it effectively doubles its focal length. The 25mm TV Plossl above basically becomes a 50mm Plossl. Depending on the individual eyepiece there may sometimes be some vignetting. Also it's possible the secondary mirror can be seen with very long focal lengths, although I've never seen it on my MCT's or SCT with a '50mm' eyepiece.  1.25" 50mm eyepieces are rare. In a scope with a 1500mm focal length this would now give a 30x magnification and an exit pupil of 5mm.

 

0EIHGsZl.jpg

 

Some larger SCT's have provision for a reducer-corrector to be threaded directly into the visual back. I have one for my 235mm SCT. I believe you can thread one into your scope. This effectively gives the scope a focal ratio of f/6.3. An 18 or 19mm eyepiece would give around a 3mm exit pupil. A 25mm Plossl would give a near 4mm exit pupil. Again, there may be some vignetting with eyepieces with wide FOV's. 

 

 

 

 

Edited by Nightspore
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