Circle T Japan eyepiece help please

[Darrensnk]

Hello, I'm new to astronomy and came across these eyepieces. Being in need of some I bought them so now just trying to find some information on them. Most things I find are "volcano" eyepieces which people seem to think highly of, just wondering if these would be similar. I haven't tested them yet as I need to buy an adaptor now.  Any info will be greatly appreciated. AH 40mm K 25mm OR 12.5mm all have a sticker with a T in a circle and Japan on it. Thanks

 

 

 

[Mr Spock]

These are 0.965" eyepieces so will need an adaptor for use with 1.25" fittings.

The 40mm is an Achromatic Huyghenian and will have a very narrow field of view - about 30° if memory serves.

The 25mm is a Kellner. A simple three element eyepiece which will be reasonable quality in longer focal length scopes. Probably about 50° fov.

The 12.5mm is an Orthoscopic and will be very good quality with a 40° fov.

[F15Rules]

Good advice from Mr Spock above 👍.

EdIT: in my hurry to post before being called back to the real world by my wife, I showed the wrong adapter..🤦‍♂️..

The adapter shown below in Louis' post is the correct size, and will enable your 0.965"  eyepieces to work in a 1.25" focuser.

My appreciation to Louis for correcting my error..

Hope that helps,

Dave

Edited December 24, 2023 by F15Rules
Error in original post.

[Louis D]

10 hours ago, F15Rules said:

Good advice from Mr Spock above 👍.

This adapter will enable these eyepieces to work in a 1.25" focuser😉

https://uk.vicedeal.com/products/0-965-to-1-25-eyepiece-adapter-telescope-astronomy-24-5mm-to-31-7mm-metal-mount-adapter-for-binoculars-monocular?variant=UHJvZHVjdFZhcmlhbnQ6MTcyNTgyMjMw&gad_source=1&gclid=CjwKCAiAyp-sBhBSEiwAWWzTnjmInk_hbmno5fz_ba-4iFFO-j_3byRGTstcz9YeANOGUWB47NfEwhoCBWgQAvD_BwE

Hope that helps,

Dave

Wrong way round for that adapter.  That one is for using 1.25" eyepieces in an 0.965" focuser.  This is the adapter needed for these eyepieces.

[Darrensnk]

Thank you for the information and the link to the adaptor. This might be a silly question but it the add for the adaptor it says requires additional back focus. Does that mean I need to buy something else also to use it.

 

 

[Roy Challen]

1 hour ago, Darrensnk said:

Thank you for the information and the link to the adaptor. This might be a silly question but it the add for the adaptor it says requires additional back focus. Does that mean I need to buy something else also to use it.

 

 

Depends on the telescope you'll use them with. If the focuser doesn't rack out far enough, you may need an extension tube, the exact length you'll need to measure yourself. On the other hand, it may work without one.

Edited December 26, 2023 by Roy Challen

[Don Pensack]

Generally, additional back focus means the same as additional IN focus.  When an adapter is used with an eyepiece that pulls it out more from the focuser, additional in-travel of the focuser is necessary.

0.965" (24.5mm) eyepieces are typically so short, though, that only a trace of in-travel is necessary, if any.

[Darrensnk]

Thank you all for the information

[Darrensnk]

I've managed to look through them, the 40 and 25mm are quite clear and give nice images (for my amateur eyes). The 12.5mm not so much unfortunately. I held it to the light and looked through it to see a web of something so I tried to take a photo.

I tried cleaning the outside lens but it is still there. Would it be worth a professional clean if that's possible or is it sadly a lost cause.

[GrumpiusMaximus]

That could be lens fungus?  Could you get a picture of the outside of the lens?

[bosun21]

That's most definitely a bad case of fungus IMO. Personally I would just bin it and put it down to experience. That's one of the pitfalls of buying old eyepieces from someone you don't know (especially on eBay).

[Louis D]

Those old eyepieces are pretty easy to disassemble with a lens wrench/spanner.  Once apart, you could try soaking the fungal coated elements in bleach or mildew remover to see if you can kill the fungus and then start cleaning the elements.  If it's between lens element in the cement, it would require a lot more work to loosen the lens cement to separate the lens elements to get at the fungus.

Of course, any lens coatings are probably etched beyond hope by the fungus.

I'm just tossing out ideas to make lemonade out of lemons.