Where to get second hand lenses

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Where to get second hand lenses

Postby pipusmar » Sat Dec 29, 2018 10:52 pm

Good evening!

I recently moved to Fleet in Hampshire, and for the first time as an adult have access to a reasonably dark sky, quite a treat after nearly fifteen years in Greater London! I watched my first meteor shower this winter - AMAZING!

I've been star gazing through a pair of binoculars for a month or so and really enjoyed, and I am excited to have been lent a telescope my brother had in storage, a Meade ETX-80.

He has looked after it well, but I have been informed one of the objective lenses has gone walk about, and I will need to get a new one (or rather, a good second hand one).

Where would be a good place to buy such a thing?

Many thanks in advance,

Clare
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Re: Where to get second hand lenses

Postby Aratus » Sun Dec 30, 2018 1:13 pm

Do you mean that it has no eyepeices?
Do you mean the 80mm diameter lens at the front is missing?

If it is the first, then any 1 1/4 inch eyepiece will work. A 25mm eyepeice is good for wide angle. Something like an 8 or 10mm for greater magnification. A x2 barlow lens will give even better magnification.

If you mean the lens at the front is missing :o (objective lens) then you have a greater problem. It is a bit like getting a car without an engine. :( You might get a broken EXT-80 with the lens intact on eBay. It is worth trying. Alternatively you need to contact a telescope repair group. I notice that Meade send their out of warranty repairs to SCTelescopes I suggest you write to them. They might send you the part.

http://sctelescopes.com/
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
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Re: Where to get second hand lenses

Postby pipusmar » Sun Dec 30, 2018 9:15 pm

Thanks for your reply Aratus, that's all really useful information. I've just had a look at it. I am wrong, but in a good way - the front lens is there!! Eye piece 6 is present and correct (albeit very dirty). Looking at the parts listed in the manual I downloaded, it's missing the second eye piece labelled 1/2.

I think the main challenge after the ye piece will be getting the lenses clean :o

C.
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Re: Where to get second hand lenses

Postby Aratus » Sun Dec 30, 2018 11:51 pm

Very confusing! The main 90 degree eyepeice holder is the one marked '5' on your diagram. You can use that for both eyepeices - if you have them. If you turn the little release knob/screw the eyepiece will pull out, and you can exchange it with the other one.

The one marked 1 and 2 is designed primarily for a camera connecton, but it can also be used with a 45 degree prism. I assume that is missing. In this set up a 45 degree prism is mostly for using the telescope for birdwatching etc. You don't need it for astronomical viewing. Plenty of places sell them for about £30 or £40 if you feel you must have one. However, you will find having a x2 barlow much more useful

Looking at the specifications it should include a 26mm eyepeice & 9mm eyepiece. They should be marked as such. You need them both + the barlow to get the most out of the telescope
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
Aratus
 
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Re: Where to get second hand lenses

Postby pipusmar » Mon Dec 31, 2018 3:17 pm

That sounds doable, and I'm excited it has the opportunity for camera connection, as I'm very much hoping to try some photography once I know how the telescope works. I have checked and the eyepiece came screwed into position 5 is a 26mm. I will look for 9mm. Part of my reason for asking here is not buying something I don't need, so I won't bother getting the 45 degree prism.

Please could explain what you mean by a x2 Barlow? Is this another lens or one that you use together with the 26mm or 9mm for more magnification?

Where it had been in storage, the whole telescope was covered in that sticky dust you get after a decade - there was no brushing this stuff off! I read a few posts on how to safely clean it, and then decided to clean the body with alcohol hand gel (being very careful around joints near lens as I didn't want any liquid seeping in) and it came up pretty well. Only one side of the eye piece was very dirty as it had be stored screwed into the body, so I cleaned that with a microfibre glasses cloth, using a different bit of the cloth each time so I didn't rub the dust in. It's come up nearly perfectly, except for dust around the very edges.

The objective lens is not as grubby, but I'm more frightened of damaging it. People seemed to suggest you can get away with a fair amount of dust and still see, so I have left it alone for now. Does this seem sensible?

It was cloudy last night but I did look down the eyepiece and through the objective lens, and was able to see the other side of the room, so something is working!

Thank you so much for all your advice, it's much appreciated :)
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Re: Where to get second hand lenses

Postby Aratus » Mon Dec 31, 2018 7:48 pm

pipusmar wrote:
Please could explain what you mean by a x2 Barlow? Is this another lens or one that you use together with the 26mm or 9mm for more magnification?

A barlow extends the focal length of the telescope so yes, a 2x barlow will effectively double the magnification. In this case the 400mm focal length becomes 800mm

To find the magnification of an eyepiece divide the focal length of the telescope by the focal length of the eyepeice.
So the 26mm eyepiece gives a magnification of 400/26 = 15.4x.
With the barlow 800/26 = 30.8x

You can do that with any eyepiece that you can buy for it.
Bear in mind that a 3 inch telescope will not normally take much more than 120x magnification under average conditions. I wouldn't consider getting an eyepiece less than 8mm, but younger eyes might be able to use down to a 6mm. With a barlow that is 800/6 = 134x which is at the top end anyway.

Regarding cleaning - anything designed to clean photographic lenses will do for telescopes. The objective can get pretty dusty and make little difference to the image. However cleaning with the right stuff it is not a problem. Brush it with a lens brush to get rid of any grit. Use a fine tissue soaked in lens cleaning fluid. Rub from the centre outwards. Once it is properly clean, use a lens cap. If any dust settles after that, a fine lens brush will knock the dust off.

Eyepieces are more difficult to clean, and less forgiving if they get dirty. a 'Q' tip covered in a piece of lens tissue, dipped in lens cleaning fluid should be able to deal with gunk around the edge. You might have to do it several times. Use a clean tip and tissue every time. Use a lens cap on the eypiece, and you shouldn't need to clean it again for a very long time.
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
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