is ES70 an Erfle?

[kilix]

Hello stargazers,

I am unsatiably curious and I cannot find an answer to my question.

So, yesterday and the day before I screwed up and it ended with me completely disassembling my 10mm ES70 eyepiece. When I struggled to get it together, I tried searching online for construction, I did not know the order of the spacers or orientation of the lenses. I did know what order the lenses are, but other than that, it was a guesswork. After 5th assembly, the eyepiece returned to it's previous state and now I am happy, as it is working correctly and it's completely cleaned.
What baffles me thou, is the fact, that I do not know what type of EP it is! It is sold as an Erfle, but the construction is nowhere near similar to Erfle (5element in 3 groups). So no matter what I searched for and what I researched online, there was nothing to be found to help me reassemble the thing.

This is a drawing I made from memory, according to orientation of the lenses and the spacers used it is like this:

I am not 100% sure on lens #2. One side seemed planar, one concave, but it may be, that the "planar" side is actually a tiny bit concave. I am also not 100% sure on the orientation of the lens #2, it may be, that it is oriented the other way around (drawing from memory). Other lenses I am 100% certain on orientation. #1 and #4 seemed identical. But I am not sure, those are tiny lenses (maybe 6mm diameter) and really hard to judge small differences by eye.
So, what type of an eyepiece it is? It is certainly sold as Erfle, but the construction does not seem like an Erfle to me.

Here a screen from an e-shop. Btw, the description is the same on multiple e-shops.

 

[John]

Lots of proprietry eyepieces are slight variations on a traditional design like the Erfle.

Manufacturers tweak the designs to get better performance and to give themselves competative edge / marketing points.

I thought the classic Erfle had 2 cemented elements while the ES70 seems to have just the one ?. The ES70's may not use the same design throughout their range though, unless it is what is known as a "scaled" design.

There are plenty of designs out there to choose from !:

 

[Dave In Vermont]

Whether it's called an 'Erfle' or sold by a company - like Orion-USA - as a 'Planetary Eyepiece,' with 5 lens-elements and a 70° FOV - from what I've read around - these were somebody's promotional eyepieces, or an over-run of production from somewhere, or who knows what. But they seem to have vanished in one form - only to re-appear with a different brand-name and description elsewhere.

I wouldn't be terribly excited or concerned.

Could you use an eyepiece-chart? One's below -

Dave

 

OUCH! Careful of my toes, John...

[kilix]

yeah, I've seen those charts numerous times and I kept searching, but as you can see, the eyepiece I have falls in no category

That's why I am curious as to what it actually is.
This eyepiece business is a terrible mess.

EDIT: I also know, that this particular eyepiece is not sold under the Explore Scientific brand anymore, it went to Bresser, and now it's sold as Bresser 70° series, not ES anymore.

[John]

21 minutes ago, kilix said:

yeah, I've seen those charts numerous times and I kept searching, but as you can see, the eyepiece I have falls in no category

That's why I am curious as to what it actually is.
This eyepiece business is a terrible mess.

EDIT: I also know, that this particular eyepiece is not sold under the Explore Scientific brand anymore, it went to Bresser, and now it's sold as Bresser 70° series, not ES anymore.

What it is, is a reasonably priced eyepiece that delivers a 70 degree apparent field of view and it works well in scopes of F/7 or slower focal ratio but shows some astigmatism in the outer parts of the field of view in faster scopes than that.

The ES68 range is more expensive but is a better corrected design in faster scopes.

I think it's best not to get to OCD about the exact internal design. If you enjoy the eyepiece then that is what matters 

I'm not sure that I agree that the eyepiece business is a terrible mess. The choice, value and performance quality today is better than I've ever known it during my 30+ years in the hobby

 

[kilix]

24 minutes ago, John said:

What it is, is a reasonably priced eyepiece that delivers a 70 degree apparent field of view and it works well in scopes of F/7 or slower focal ratio but shows some astigmatism in the outer parts of the field of view in faster scopes than that.

The ES68 range is more expensive but is a better corrected design in faster scopes.

I think it's best not to get to OCD about the exact internal design. If you enjoy the eyepiece then that is what matters 

I'm not sure that I agree that the eyepiece business is a terrible mess. The choice, value and performance quality today is better than I've ever known it during my 30+ years in the hobby

 

I love the eyepiece. Especially the 15mm version. For 50€ it's really good in my Mak (at f/11.8). The image gets a tiny bit blurry near the edges, but that does not bother me much. In F/5 scope, the usable view is only about 60% of the field, then it gets really distorted.

I think about getting 24mm ES68, as I have nothing between 15 and 32mm focal length (only the "Super barium" 20mm supplied with the scope, which I hate), but that will happen when my wallet recovers

It's not like I am OCD, but I am a really curious person and I NEED to know everything about everything Okay, maybe I am a bit OCD about knowledge. Maybe quite a lot. Maybe really lot.

[John]

Nothing wrong with curiosity - it's probably why many of us are in this hobby !

I'd try and resist any temptation to take things apart though, if you can. Ideally you want to keep the chances of getting any dust or other contaminents inside an eyepiece to the absolute minimum. The manufacturers are (usually) better at putting these things together than we are !

[YKSE]

There're some of these 5 lens in 4 goups eyepieces out there, modified erfle is mentioned here

http://www.burgessoptical.com/erfle-eyepieces.html

These 70° EPs are like of the same design:

http://www.universityoptics.com/125inch.html

and 9mm, 15mm, 20mm Willaims SWA are likely too:

http://www.williamoptics.com/eyepiecesDCL/swan9_spec.php

[Louis D]

Do some patent searches on eyepiece designs from Nikon, Olympus, Zeiss, Leica and others who make high-end microscopes.  You'll see lots of variations on 5 to 7 element wide angle designs that are optimized for long focal ratios as in microscopes.  Your diagram reminds me of some of them.

[kilix]

So, after testing it at night and failing miserably, I was forced to open the eyepiece again.
Finally, after multiple tries, this assembly works as intended (maybe it helps someone in the future):

 

Now it starts to vaguely resemble some kind of erfle modification.

Well, at least I'm not learning on Naglers

 

[Louis D]

23 hours ago, kilix said:

So, after testing it at night and failing miserably, I was forced to open the eyepiece again.
Finally, after multiple tries, this assembly works as intended (maybe it helps someone in the future):

 

Now it starts to vaguely resemble some kind of erfle modification.

Well, at least I'm not learning on Naglers

 

Comparing diagrams, you just had to flip 1/2 as a group around, so you were pretty close the first time.  Kudos to you for figuring it out and posting a very nice diagram.  For the record, what software did you use to create the diagram?  Most folks on the forums resort to drawing it on a sheet of paper and then snapping a photo of it.

[kilix]

2 hours ago, Louis D said:

Comparing diagrams, you just had to flip 1/2 as a group around, so you were pretty close the first time.  Kudos to you for figuring it out and posting a very nice diagram.  For the record, what software did you use to create the diagram?  Most folks on the forums resort to drawing it on a sheet of paper and then snapping a photo of it.

I thought that I had it right the first time, because image was quite OK when testing during the daytime - viewing a distant antenna through telescope. During the night it showed significant blur everywhere - about 50% off axis field was distorted. I don't know how I could've missed it during the daytime test.

And software is ZWCAD 2013 - almost 1:1 copy of AutoCAD by chinese programmers.

[Rick_It]

Try to google "Evolution of the eyepiece", there is a very nice 50- page PDF on the topic.

It does not look like an Erfle:

ERFLÉ I - A 1-2-2 design.

ERFLÉ II - A 2-1-2 design

ERFLÉ III - A 1-2-2 design.

 

 

[Louis D]

Out of curiosity, I did some patent mining and came up with this Fuji patent for an eyepiece that looks pretty similar in arrangement.

[25585]

I came across this thread Googling Burgess Erfles. 

Erfles being the eye piece type I started with, I have an attachment to the design and name. But get frustrated seeing "Erfle" advertised but the word (or "Er") not on a product!

Those I have that are branded with type are; a Circle-T 20mm, an Antares modified 35mm,an Antares 40mm & a Cassini 27mm. 

TS & GSO advertise "Erfle" but the E-word is absent. 

Takahashi used to make them, as did Vixen.