Orthoscopic eyepieces

[ChrisEdu]

What are these? How do they differ from 'normal' eyepieces? Are there any pros and cons relating to their use?

[GazOC]

They are great eyepieces and excellent value for money esp. secondhand.

Pros:

On axis much better views than widefield eyepieces

Cheap

Cons:

Poor eye relief

Narrow field of view.

[ChrisEdu]

They are great eyepieces and excellent value for money esp. secondhand.

Pros:

On axis much better views than widefield eyepieces

Cheap

Cons:

Poor eye relief

Narrow field of view.

Could you explain what on axis means? Why are they cheap? (Define cheap)

What does poor eye relief actually mean? I presume narrow field of view means you see a smaller area of the sky. Is this right?

Thanks.

[John]

The Orthoscopic is one of a number of different eyepiece designs, each having their own strengths and weaknesses. Gaz's post summarises the Orthoscopic pros and cons nicely.

For more info on the different designs I recommend this link:

http://www.spacegazer.com/eyepiece-designs-g.asp

This was written by an SGL member and I find it both accessable and informative.

John

[ChrisEdu]

I'll have a look.

[GazOC]

Chris,

They cost about £50 new and £20 secondhand, "on axis" basically means in the middle of the view you are looking at. "Eye relief" means how critical your eye position needs to be to use the eyepiece. So as long as you have a small object centred an ortho will give great views, but because the field of view is narrow you don't get that "immersive" views that the widefield eyepieces show you.

The reason they are so cheap is that they are just a great basic design thats easy to implement. The price trade off is that you lose the field of view and eye relief over more expensive designs but you do get better views on axis.

Gaz

[ChrisEdu]

I see. The article above was also very informative. Somehow, I think I'm going to end up with a collection of lumps of glass!

[Helen]

I see. The article above was also very informative. Somehow, I think I'm going to end up with a collection of lumps of glass!

You're learning... telescopes and eyepieces are like golf clubs, you need quite a few so that you've got just the right tool for the right task

Helen

[ChrisEdu]

I see. The article above was also very informative. Somehow, I think I'm going to end up with a collection of lumps of glass!

You're learning... telescopes and eyepieces are like golf clubs, you need quite a few so that you've got just the right tool for the right task

Helen

You obviously haven't seen me play golf!

[Merlin]

I have three BAADER orthoscopic eyepieces: 12.5mm, 9mm and 6mm focus. These are excellent general purpose eyepieces and they give longer eye relief than Plossls.

The eye relief of an orthoscopic is the same as its focal length, but a Plossl has only 70% of this.

Orthos are the best of the four-lens element eyepieces and they give sharper and bright views than the much more expensive complex eyepieces.

[Azelfafage]

Orthoscopics seem more suited to lunar/planetary stuff (narrow field not being so critical as when trying to observe DSO's).

A

[themos]

Does it make sense to put orthos on dobs? The narrow FOV and shallow ER would make it pretty difficult to chase planets around with them on. Or would I still be ok with a 7mm, say, at about 200x?

[John]

Does it make sense to put orthos on dobs? The narrow FOV and shallow ER would make it pretty difficult to chase planets around with them on. Or would I still be ok with a 7mm, say, at about 200x?

While I prefer UWA's, I've used a 7mm Ortho (Antares HD) in my SW 200P dob and it worked fine - I just had to brush up my nudging technique. I also found that I had to used a lower power / wide field eyepiece to get object in the field of view before I switched to the ortho wheras a 7mm Nagler is wide enough to pick things up straight from the finder field.

John

[themos]

They're certainly affordable, compared to a Nagler!

[John]

They're certainly affordable, compared to a Nagler!

Thats true Themos, on the used market the exchange rate is around 1 Nagler = 5 or 6 Orthos !. If I used driven scopes I would certainly consider swapping to Orthos for my sub-10mm FL eyepieces.

John

[lunator]

They are great eyepieces.

I have a full set and they get used every observing session

[themos]

I've put up a request on the Wanted section.