Eyepiece questions

[BadgerD]

Hi all. I'm writing an article about swapping eyepieces between telescopes. Of course I need to cover the topic of barrel lengths. I thought it would be good to show a picture of a .965, a 1.25 and a 2 inch eyepiece next to each other. Unfortunately, I don't own a .965. So, if someone had a snapshot of that or could easily take one, I would be much obliged if you wouldn't mind sharing. 

Also, I have a technical question. I know (in large part from reading this forum!) that for smaller focal ratio telescopes, higher quality eyepieces may be necessary. But is this more true with short focal length eyepieces or long focal length eyepieces? Or does that matter? Thanks in advance. 

Edited March 31, 2020 by BadgerD

[andrew s]

If you had ever tried to use a 3mm Ramsden eyepiece you would know. 

In general the more you need to bend the light (short absolute focal length) the greater the aberrations.  To avoid these you need more complex optics.

Telescope  objectives are trivial to design compared to eyepieces. 

Regards Andrew 

 

[JeremyS]

@BadgerD you might find this article on eyepieces on the BAA website helpful.

[John]

Here are the 3 sizes for comparison. As the photo says, the .965 inch ones are not available new now, as far as I'm aware:

 

 

[Louis D]

1 hour ago, John said:

As the photo says, the .965 inch ones are not available new now, as far as I'm aware:

I just picked up a cheap 70mm aperture, 300mm focal length telescope to turn into a finder scope for kicks, and guess what?  It came with two 0.965 Huygens eyepieces, a 20mm and a 6mm, so they're still out there being produced for inclusion in cheap telescope kits.

[johninderby]

NAS.    -     New ancient stock. 😁

[Louis D]

There are also 3" eyepieces like the 30mm ES-100 and Siebert makes 2.5", 2.7", 3", 4" and 4.3" eyepieces for observatories.

[johninderby]

Eye watering prices on the 4” and 4.3” diagonals. 🙀

https://www.siebertoptics.com/SiebertOptics-eyepieces-observatory.html#2.7

Edited March 31, 2020 by johninderby

[Louis D]

8 minutes ago, johninderby said:

Eye watering prices on the 4” and 4.3” diagonals. 🙀

https://www.siebertoptics.com/SiebertOptics-eyepieces-observatory.html#2.7

But when you've just dropped 100+ large just on the optical tube assembly for an observatory class instrument, those numbers seem like peanuts.  They're mostly used for observatory outreach events since almost all professional astronomy is done using instruments these days.

[RT65CB-SWL]

Here is my 0.965" / 6mm Ortho & 1.25" adaptor...

It is almost as good as my Circle-T 6mm Ortho, (shown below), alongside the 12.5mm.

Edited March 31, 2020 by Philip R

[John]

I used to use some of the (V) (Vixen) .965 inch eyepieces engraved "Or." They worked rather well. I took two apart to clean them and found that the optical design consisted of 2 doublets rather like a plossl or symmetrical rather than the triplet plus singlet arrangement of the abbe ortho. The Vixen ones still worked nicely though.

 

[JeremyS]

The Pextax XP3.8, which was 0.965-inches, was one of the finest high power eyepieces I have owned. Wished I hadn't sold on.

[Dave1]

So I own 0.965", 1.25", and 2" eyepieces.

When selecting eyepieces you have to bear in mind the speed of the telescope you intend to use them in. 0.965" eyepieces of Ramsden and Huygens design typically do not work well in medium to fast telescope. In F15 telescope they work very well indeed, I have personally verified that. But I have read around F12 they become challenged. Kellners in 0.965" will be more acceptable of fast telescopes. Orthoscopic eyepieces in 0.965" are also very good and could work well down to F7. Only last week I used a 0.965" 4 mm Ramsden and compared it to 1.25" 4 mm Ortho. The difference in eye relief wasn't all that different. And on the moon details on view were very good in both. The only real difference was field of view. If you can deal with very short eye relief don't be put off. 

As a generalised statement, in fast telescope F5-6 or faster, you will need complicated eyepieces for high magnification if you want a perfect view. You can use simple eyepieces with less elements in longer eyepiece focal lengths, the view still will not be perfect but to some is acceptable. It depends how critical you are as an observer.

If you are after new 0.965" eyepiece there is maybe 2 manufactures that I know of that still make them to order. One being Siebert Optics in America. The other being ATC in Czech Republic. Although if the prices are high, I don't see the point. Secondhand yes maybe if priced competitively. 

David

 

Edited March 31, 2020 by Dave1

[JOC]

1 hour ago, Louis D said:

There are also 3" eyepieces like the 30mm ES-100 and Siebert makes 2.5", 2.7", 3", 4" and 4.3" eyepieces for observatories.

 

1 hour ago, johninderby said:

Eye watering prices on the 4” and 4.3” diagonals. 🙀

https://www.siebertoptics.com/SiebertOptics-eyepieces-observatory.html#2.7

Well that answers a question I often had about whether observatories use the same EP sizes that we all seem to (1.25" and 2") on their huge telescopes.  It seemed almost inconceivable that with all their enormous costly mirrors it still boiled down to what they plonked in a tiny focusser, just like us back-garden mob.

[andrew s]

2 minutes ago, JOC said:

 

Well that answers a question I often had about whether observatories use the same EP sizes that we all seem to (1.25" and 2") on their huge telescopes.  It seemed almost inconceivable that with all their enormous costly mirrors it still boiled down to what they plonked in a tiny focusser, just like us back-garden mob.

Only foŕ outreach events. All pro-astronomy is done with electronic detectors. The eye brain system is too easily fooled.

Regards Andrew 

[John]

49 minutes ago, JOC said:

 

Well that answers a question I often had about whether observatories use the same EP sizes that we all seem to (1.25" and 2") on their huge telescopes.  It seemed almost inconceivable that with all their enormous costly mirrors it still boiled down to what they plonked in a tiny focusser, just like us back-garden mob.

For outreach they use a Meade 55mm plossl in the Alvan Clarke 24 inch refractor at the Lowell Observatory. It gives 178x in that scope, apparently:

[RT65CB-SWL]

9 hours ago, johninderby said:

Eye watering prices on the 4” and 4.3” diagonals. 🙀

https://www.siebertoptics.com/SiebertOptics-eyepieces-observatory.html#2.7

I see they accept an AMEX payment... "That'll do nicely!"

...and: "Don't leave home without it."

Edited March 31, 2020 by Philip R

[Louis D]

1 hour ago, Philip R said:

I see they accept an AMEX payment... "That'll do nicely!"

Was there ever a British Express equivalent?

[John]

5 minutes ago, Louis D said:

Was there ever a British Express equivalent?

The advice we have had when visiting the USA is that American Express is the one card that they prefer us not to use !

 

[andrew s]

My first eyepieces had RAS threads so maybe these should be included.

Regards Andrew 

[JeremyS]

12 minutes ago, andrew s said:

My first eyepieces had RAS threads so maybe these should be included.

Regards Andrew 

Mine too. In fact I still keep one of the eyepieces around to remind myself how terrible these old eyepieces were, compared to the modern ones.

But they were beautiful.

[andrew s]

12 minutes ago, JeremyS said:

Mine too. In fact I still keep one of the eyepieces around to remind myself how terrible these old eyepieces were, compared to the modern ones.

But they were beautiful.

...and conductive having frozen my eye to them on more than one occasion. 

That's one reason I gave up visual along with a love of creature comforts and poor eye sight. 

Regards Andrew 

[JeremyS]

1 minute ago, andrew s said:

...and conductive having frozen my eye to them on more than one occasion. 

Ah so, not just me, then 🙂

Then there was the pain that was swapping eyepieces. Unthreading one eyepiece and then screwing in a new one. With numbs hands.

Thank heavens for push-fit eyepieces.

The young generation don't know just how good they have it.

🙂

 

[RT65CB-SWL]

14 minutes ago, andrew s said:

My first eyepieces had RAS threads so maybe these should be included.

Regards Andrew 

 

3 minutes ago, JeremyS said:

Mine too. In fact I still keep one of the eyepieces around to remind myself how terrible these old eyepieces were, compared to the modern ones.

But they were beautiful.

I have one too. Beacon Hill Telescopes made me the 1.25" adaptor. 

 

[johninderby]

Did someone mention RAS eyepieces. 😁

https://www.ebay.co.uk/itm/Victorian-RAS-Eyepieces-c1875-Brass/303173408204?hash=item46968b15cc:g:VXgAAOSwOFdc8TBT