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Burgess Optical - New Eyepieces Soon

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#76 Shneor

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Posted 03 August 2018 - 12:54 AM

Eye relief was not an issue for me. I did not measure, but my eye was nowhere near the eye lens. The fact that the apparent field ls larger than a typical monocentric only means that it's easier to find an object, since outside the inner two-thirds of the field you will just see an elongted blur, at least in a fast reflector.


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#77 ThomasM

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Posted 03 August 2018 - 01:41 AM

First post in this thread says more are planned in the next year.

 I was asking Burgess Optical via the contact formular and got the answer that further focal lengths are planned, namely 8 , 6 4 and 3 mm. This also means that the eyepieces might be well corrected for rather fast scopes. 3 mm focal length makes no sense for f/10.


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#78 leonard

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Posted 03 August 2018 - 01:44 AM

I calculate that for a 35 degree AFoV, a 10 mm eye lens provides 16 mm of eye relief.

Hello ,

 

          Jon , I must have missed the post where it’s stated the eye lens is 10mm in dia.

I have never seen a 10mm focal length cemented triplet of any kind with 16mm of eye relief .

But this could be something new , or I overlooked in the past . BillP’s review of the Siebert monocentric seems to be in line 

with the as expected eye relief of @ 7.5 mm of ER with a 35 degree AFOV . Don pointed this review out 

in the post above .



#79 ThomasM

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Posted 03 August 2018 - 01:57 AM

Eye relief was not an issue for me. I did not measure, but my eye was nowhere near the eye lens. The fact that the apparent field ls larger than a typical monocentric only means that it's easier to find an object, since outside the inner two-thirds of the field you will just see an elongted blur, at least in a fast reflector.

If you find time, could you please post a few pictures, e.g. the eyelense and also the entrance.

 

Thanks a lot.



#80 Jon Isaacs

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Posted 03 August 2018 - 07:32 AM

Hello ,

 

          Jon , I must have missed the post where it’s stated the eye lens is 10mm in dia.

I have never seen a 10mm focal length cemented triplet of any kind with 16mm of eye relief .

But this could be something new , or I overlooked in the past . BillP’s review of the Siebert monocentric seems to be in line 

with the as expected eye relief of @ 7.5 mm of ER with a 35 degree AFOV . Don pointed this review out 

in the post above .

 

It stated that the eye relief was 16mm.  It also stated that the AFoV was 35 degrees.  

 

Using those two, I calculated the minimum eye lens diameter based on simple geometry.. A line from the eye point at the edge of the apparent field of view must be inside the diameter of the eye lens. 

 

Dmin = 2 x ER x Tan(afov/2)

 

That is why I wrote:

 

"I calculate that for a 35 degree AFoV, a 10 mm eye lens provides 16 mm of eye relief."



#81 Jon Isaacs

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Posted 03 August 2018 - 07:39 AM

 I was asking Burgess Optical via the contact formular and got the answer that further focal lengths are planned, namely 8 , 6 4 and 3 mm. This also means that the eyepieces might be well corrected for rather fast scopes. 3 mm focal length makes no sense for f/10.

This is what Shneor said about the 10mm, 

 

"The fact that the apparent field ls larger than a typical monocentric only means that it's easier to find an object, since outside the inner two-thirds of the field you will just see an elongted blur, at least in a fast reflector."

 

That doesn't sound that well corrected. It's a monocentric, the designer doesn't have a lot of options in correcting the various aberrations.  

 

At F/10, a 3mm provides a 0.3mm exit pupil.  That's within reason for double stars.  

 

Jon



#82 ThomasM

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Posted 03 August 2018 - 08:42 AM

It stated that the eye relief was 16mm.  It also stated that the AFoV was 35 degrees.  

 

Using those two, I calculated the minimum eye lens diameter based on simple geometry.. A line from the eye point at the edge of the apparent field of view must be inside the diameter of the eye lens. 

 

Dmin = 2 x ER x Tan(afov/2)

 

That is why I wrote:

 

"I calculate that for a 35 degree AFoV, a 10 mm eye lens provides 16 mm of eye relief."

by the way,  with 5.5 mm field stop diameter you will not get 35 degree field of view for 10 mm focal length, you will get only 30.8-31.5 degree depending the correction of the eyepiece ( tangens or constant angular magnification condidtion)


Edited by ThomasM, 03 August 2018 - 08:45 AM.


#83 Starman1

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Posted 03 August 2018 - 08:46 AM

That assumes zero distortion, however.  If there is angular magnification distortion, a 35° field could fit in a 5.5mm field stop at 10mm focal length.



#84 ThomasM

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Posted 03 August 2018 - 09:14 AM

That assumes zero distortion, however.  If there is angular magnification distortion, a 35° field could fit in a 5.5mm field stop at 10mm focal length.

In principle yes, but for small  angles - here we talk about 15 degree half angle-  different types of correction  have almost no effect, look here:

 

 

https://www.google.d...533392094011834

 

especially this diagram, the ratio between field stop size and focal length it 0.55:

 

http://www.brayebroo...FOV/APP_fov.jpg

 

The distortion must be huge to explain the difference betwenn 30.8-31.5 degee (calculated) and the specifiyed 35 degree.


Edited by ThomasM, 03 August 2018 - 09:19 AM.


#85 Starman1

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Posted 03 August 2018 - 09:58 AM

I calculated a 31.5 degree apparent field for 0% distortion and a 5.5mm field stop.

However, what the charts don't show in your link is what happens when neither angular magnification nor rectilinear distortion are zeroed out.

It's possible to have both present in an eyepiece, in which case the geometric distortion curve in your first link doesn't hold.

Still, I agree with the most likely premise, which is that the apparent field is not 35° [edit: or the field stop is >5.5mm].  What it actually is will await a test by a user.


Edited by Starman1, 03 August 2018 - 09:59 AM.

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#86 leonard

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Posted 03 August 2018 - 11:20 AM

That is why I wrote:

 

"I calculate that for a 35 degree AFoV, a 10 mm eye lens provides 16 mm of eye relief."

 

 

                       Hello Jon ,

 

 

     Well and good , If the stated ER and FOV are correct .


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#87 Jon Isaacs

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Posted 03 August 2018 - 11:46 AM

That is why I wrote:

 

"I calculate that for a 35 degree AFoV, a 10 mm eye lens provides 16 mm of eye relief."

 

 

                       Hello Jon ,

 

 

     Well and good , If the stated ER and FOV are correct .

 

This is Burgess Optical, lots of unknowns.  My point was that it doesn't take a large eye lens to provide 16mm of eye relief. If the AFoV is 31.5 degrees and the eye relief is 16 mm, a 9 mm eye lens could be sufficient.

 

Jon



#88 nicoledoula

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Posted 04 August 2018 - 12:07 AM

It's only 3 elements, it can be barlowed and still use only 5. I'm interested and positive. 



#89 Shneor

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Posted 04 August 2018 - 12:56 AM

If you find time, could you please post a few pictures, e.g. the eyelense and also the entrance.

 

Thanks a lot.

There's a photo on the Burgess Optical web site. You know the diameter of the barrel is 1.25", you can see the eye lens and see how large it is.


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#90 ThomasM

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Posted 04 August 2018 - 02:54 AM

There's a photo on the Burgess Optical web site. You know the diameter of the barrel is 1.25", you can see the eye lens and see how large it is.

???

May be I miss something, as far I can see there is only one single photo on the Burgess Optical web site, it shows a side view of the eyepiece. The eye lense is not visible.

 

Please give a link, many thanks.

 

Thomas

 

p.s. since you own the eyepiece, could you please let us know the diameter of the eye lens


Edited by ThomasM, 04 August 2018 - 03:16 AM.


#91 starcam

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Posted 04 August 2018 - 07:03 PM

10mm measured it.


Edited by starcam, 04 August 2018 - 07:06 PM.


#92 leonard

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Posted 05 August 2018 - 12:53 AM

Hello ,

 

10mm measured it.

                   With this measurement confirmed , it seems the 16 mm of eye relief is true . If so , this would be unusual as the eye relief of a cemented triplet of 10 mm FL would run more like 7 to 8 mm . 

So I felt like I was missing something , some information maybe . Going back and reading Shneor’s post no. 1 I found the first thing that didn’t sink in , and that was that Burgess optical informed Shneor that 1 or more of the lenses was 

aspherical . Going to the burgess optical web site and reading what it has to say about the eyepiece puts more light on this mystery . First it calls the eyepiece a 3 element monolithic design , something new to me , nowhere does it say

it is 3 glass cemented lenses , something I  took for granted . And it does not say the three elements are cemented , just that there are only 2 air to lens surfaces .

                    So thinking at least one element is some form of optical polymer either molded or machined into an 

aspheric shape . At any rate this is not your grandfathers triplet .


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#93 emilslomi

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Posted 05 August 2018 - 05:56 AM

There is a thread on some Russian Steinheil triplets, which were advertized to have 200% of the focal length in eye relief. The author found them to deliver only about 125%. That would be pretty much what these monos promise. There is also a thread by BillP on some Siebert monos, which apparently promised a wider and flatter field than the usual monos. It would be cool if the Burgess mono would deliver some of what it promises on both counts. According to the tracking now in transit to Europe ... If this one turns out ok, I'd be interested in 4 and 6mm.

 

Eye relief is not really critical for me. I'm quite comfortable with a 6mm ortho, but I wouldn't want eye relief to be any shorter than with that one.

 

Cheers, Emil


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#94 Ain Soph Aur

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Posted 06 August 2018 - 01:24 PM

The Burgess 10mm arrived Saturday. Haven’t had a chance to use it, but looks like I may have partly cloudy skies this evening. It appears to be well put together, with a custom plastic molded container. I already have the 180 f/15 Mak out in the shade for tonight, will try lower f/l scope as weather permits.


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#95 starcam

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Posted 07 August 2018 - 04:23 PM

It has rectilinear distortion. Good for star/planet viewing.


Edited by starcam, 07 August 2018 - 04:24 PM.


#96 Starman1

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Posted 07 August 2018 - 04:55 PM

Well, technically distortion of any kind is bad for planet images.

But a balanced distortion can appear to the eye to be without distortion.

Moon viewing is where distortion appears worst, and we'll see what people have to say.

Or have you used it already?



#97 starcam

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Posted 07 August 2018 - 10:11 PM

It's not bad, but you said it has to have one or the other, to make the afov 35*.

You are assuming it's extreme but it's not.

Technically speaking you want neither, but in reality it's there.

Some one once said:

 

Eyepieces used for astronomical purposes tend to reduce angular magnification distortion (AMD) to a minimum to keep sizes the same across the field.

Eyepieces used for daytime viewing of terrestrial targets tend to reduce rectilinear distortion (RD) to a minimum to keep lines straight.

 

I haven't put it in the scope yet just viewed thru it. So it's not perfectly flat.(  |  ) barrel distortion. I stand corrected


Edited by starcam, 08 August 2018 - 11:24 AM.


#98 Starman1

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Posted 08 August 2018 - 09:48 AM

An eyepiece of <40° can have no noticeable distortion.

My comments were a general statement referring to eyepieces for telescopes, almost all of which have 50° fields and wider.

 

( | ) is barrel distortion, or negative rectilinear distortion.

 

Pincushion, or positive rectilinear distortion, would appear as ) | (

See: https://en.wikipedia...ortion_(optics)



#99 BillP

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Posted 08 August 2018 - 09:15 PM

There is also a thread by BillP on some Siebert monos, which apparently promised a wider and flatter field than the usual monos.

 

I have the 10mm from Burgess now...and a whole lot of clouds lol.gif   The eye lens is about 11/32" in diameter.  I have not measured the AFOV yet.



#100 emilslomi

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Posted 09 August 2018 - 01:17 AM

I have the 10mm from Burgess now...and a whole lot of clouds lol.gif   The eye lens is about 11/32" in diameter.  I have not measured the AFOV yet.

Sometimes it would be nice to be a little closer to the vendors. Mine is still in some international transit center in Florida ... sigh.

 

Cheers, Emil




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