Konig Eyepiece

[Albireo380]

I saw an ad for a 32mm (2") Konig on e-bay last week. I am sure I have seen these advertised in Sky & Telescope, but didn't know anything about them. The advertiser raved on about how good ab EP it was (but then, he was trying to sell it). It ended up going for about £40. I didn't bid, as I didn't know what I was bidding for.

Anyone tell me any more about these EPs? Are they Ortho's - or what :?:

Tom

[GazOC]

They are a design of eyepiece, they are supposed to get nice, wide views at a resonable price.

University Optics make them, so they can't be too bad....

Check Excelsis theres a few reviews on there if memory serves...

[FLO]

The Konig is one of the earliest wide-field eyepiece designs; though 60 degrees FOV isn't considered that impressive these days (Meade's standard Series 5000 Plossl range offers the same).

They have a good reputation on slow scopes (f6 or above) but suffer at the edges on anything faster.

[FLO]

Are they Ortho's - or what :?:

No,

Although they share the same number of elements in their design, they are not Orthos. A modern Konig with good glass, multi-coatings and edge-blackened lenses will be be bright but it won't have the Orthos flat field, freedom of false colour and incredible contrast.

[John]

I was following an e.bay ad for a 32mm Konig last week and actually bid for it - I got beaten by about 10 pence with 0.5 secs to go - hmmmm....

The only thing is that this was a 1.25 inch eyepiece and UK based although it looks like a 2 inch - the body is over 2 inches wide and the eyelens is about 45mm across. They offer the widest field available in 1.25 inch format but need 0.8 inch inward focusser travel compared with a standard plossl because the field stop is placed in the body of the eyepiece rather than in the chrome barrel as per most eyepieces.

I believe the field is around 52 degrees.

I wonder if this was the same eyepiece ?.

John,

North Somerset

[FLO]

They offer the widest field available in 1.25 inch format...

I believe the field is around 52 degrees.

82 degrees is about the limit these days for a 1.25" eyepiece (though I am not aware of one around 30mm?).

[John]

My understanding is that the field of view of any eyepiece is ultimately limited by the internal diameter of it's barrel. In the 31.7mm format this is about 29mm. Because of this limitation, as the focal length of the eyepiece increases the maximum apparent field (AF) that can be achieved decreases - in 31.7mm format at 40mm, 44 degrees AF is possible, at 32mm, 52 degrees at 25mm, 70 degrees is possible and so on. I used to own a 10mm ultra wide field modified plossl design that offered 84 degrees and I think you can get a Nagler in 13mm in 31.7mm format which offers 82 degrees. If someone offers an 80 degree, 32mm eyepiece in the 31.7mm fitting I'd love to know how they do it !.

John,

North Somerset

[Albireo380]

Thanks Gaz,

Went to Excelsis and there it was - UO Konig, 32mm, 52 degree FOV - priced at $114.99. So I guess the ~£40 sale price was okay. I think the EPO John bid for was the one I was watching. It would be interesting to compare with a Meade series 4000 32mm - same aFOV. If I see another one I will bid and see what they are like - never like to miss a chance to increase my EP collection

Tom

[FLO]

My understanding is that the field of view of any eyepiece is ultimately limited by the internal diameter of it's barrel. In the 31.7mm format this is about 29mm. Because of this limitation, as the focal length of the eyepiece increases the maximum apparent field (AF) that can be achieved decreases - in 31.7mm format at 40mm, 44 degrees AF is possible, at 32mm, 52 degrees at 25mm, 70 degrees is possible and so on. I used to own a 10mm ultra wide field modified plossl design that offered 84 degrees and I think you can get a Nagler in 13mm in 31.7mm format which offers 82 degrees. If someone offers an 80 degree, 32mm eyepiece in the 31.7mm fitting I'd love to know how they do it !.

John,

North Somerset

John,

Sorry.

I misunderstood your reference to 'field'.

[Albireo380]

John,

I understand what you are saying re aFOV and FL - do you have any maths behind it? - how did you work out the aFOV when you know the FL?

Incidentally, there is a 13mm type 6 Nagler with 82 degree aFOV - it is a beaut - one of my favourite EPs.

Tom

[GazOC]

TFOV= eyepiece AFOV/(telescope FL/eyepiece FL)

= TFOV=eyepiece AFOV/(magnification)

[Albireo380]

Thanks Gaz, but that wasn't what I meant. How did he work out the maximum possible aFOV when the barrel width and FL were known? Why can't you get an AfOV of 82 degrees on a 40mm EP (1.25 inch)? There must be some formula that explains the maximum aFOV for an EP of a given FL. I just can't figure out what it is.

Tom

[Kaptain Klevtsov]

It must have something to do with the lens in the eyepiece. This bends the light so that, although all the light is coming in a narrow cone from the objective lens/mirror, the eyepiece spreads it out so that it "looks like" it's a wide view that you are seeing. Is that the answer to your question?

Captain Chaos

[GazOC]

Tom,

Do you mean at what point the barrel size (1.25") cuts the light off?

Gaz

[Albireo380]

Hi Gaz & CC,

I think CC has the essence of what I am trying to ask. There must be some cut - off point where the lens bends the light so much, you can't get a crisp field of view - so that may limit the FOV you can get from a barrel of 1.25". But I think your p[oint also comes into it as well Gaz. But there must be a simple equation that determines how much you can bend the light, still get a crisp image to the edge of the field - and pack it all into a 1.25" barrel. I think John must know what this is - as he stated definite aFOVs for a 1.25" barrel at each FL. Just wish I knew it too.

Tom

[GazOC]

Ah, right.

TFOV = eyepiece field stop / focal length of scope * 180/Pi.

The best you can get from a 1.25" fitting is 27.3mm.

So you can either use a simutaneous equation for a general answer or test each combination out. (I think!! )

[Albireo380]

Thanks Gaz, I am knackered and can't think straight. I think you are correct, but need a working brain to consider - sleep tight.

Tom

[Kaptain Klevtsov]

Is that in radians or degrees?

Captain Chaos

[GazOC]

Degrees....the second part is a guess. I can't really see any other way to do it. Then again, my maths are n't the greatest.

[Albireo380]

Arghhh! My brain hurts - and so to sleep.

Tom

[John]

Sorry I did not chip in earlier on the formula but Gaz's post a few back sets it out well. The Tele Vue web site (www.televue.com) has lots of useful info and fomulas regarding eyepieces (inclding general stuff - not just their own products).

The issue has also been confused over the years by some eyepiece manufacturers claiming fields of view for their eyepieces which they did not deliver in reality. An example of this is the Celestron 32mm Erfle (31.7mm fitting) which was marketed in the 1980's as having a 65 degree apparent field. I finally got to own one of these a few years back and found that it's field was the same (slightly less actually) as my Taiwanese 32mm Plossl - around 50 degrees. Even when I removed the field stop from the inside of the chrome barrel the Erfle's field was only about 52 degrees - the same as the Meade 32mm 4000 series plossl as it happens - another illusion shattered - I had wanted one of those Erfles for about 10 years !.

John,

North Somerset

[Albireo380]

Thanks John,

The Tele Vue article makes it all clear.

If: tFOV = (EP field stop / telescope FL) x 57.3 degrees

My 'scope would work as follows (with a 32mm series 4000 - 29mm field stop) : (29 / 2000) x 57.3 degrees = t FOV of 0.83 degrees

Now, working back to aFOV aFOV = tFOV x Magnification in 'scope : In the above example 0.83 degrees x 62.5 mag = aFOV 51.875 degrees

Meade advertise their 32mm series 4000s at 52 degrees aFOV - and so they are 8)

I can now work out what combination of field stop, mahnification and Focal Lengths are possible in a 1.25" and 2" EP.

Thanks for your help.

Tom

[Alma]

I've owned both the 1.25" Konig 32 mm and the 2" 32mm MK80 eyepieces in the past, the latter I've heard is a modified Konig design.

The 1.25" was was acceptable but I always felt I would have been happier with something like a Televue 32mm Plossl.

The 80 degree afov MK80 was a great eyepiece.... smaller and much lighter than a 31mm Nagler and much better as a daytime performer in spotting scopes (the 31mm Nagler is awful for daytime use). The MK80 isn't as sharp to the edges as the Nagler so best for scopes f7 or longer. I did eventually replace it with a 31mm Nagler but kind of wish still that I hadn't sold it. I've never felt that way about any other eyepiece I've sold.

[cs1cjc]

There is a good diagram and explanation at:

TELESCOPE EYEPIECE

[AndyH]

I've owned both the 1.25" Konig 32 mm and the 2" 32mm MK80 eyepieces in the past, the latter I've heard is a modified Konig design.

The 1.25" was was acceptable but I always felt I would have been happier with something like a Televue 32mm Plossl.

The 80 degree afov MK80 was a great eyepiece.... smaller and much lighter than a 31mm Nagler and much better as a daytime performer in spotting scopes (the 31mm Nagler is awful for daytime use). The MK80 isn't as sharp to the edges as the Nagler so best for scopes f7 or longer. I did eventually replace it with a 31mm Nagler but kind of wish still that I hadn't sold it. I've never felt that way about any other eyepiece I've sold.

I too have owned the 1.25" 32mm Konig and 2" MK80.

I agree on the latter being an excellent eyepiece, whilst not a proper konig. Only reason I sold mine was, it was a toss up between that and my Tal 2" Uber WA that had to go. No contest. The Tal at roughly 95 degree tfov, is a lovely piece of glass.

The 1.25" konig(U.O. branding) was nice and just as good as a TV 32mm plossl I once had, but the Generation II Tal 'plossls' are regarded as a konig design(I've not read 100% confirmation on this) and can get close to the same field of view with a more pleasant view. I've got 4 or 5. All with varying field stops

I had an early flat top U.O. 16mm konig which was nice(but had basic coatings) and would like to source a newer U.O. version. I still regret selling my 16mm U.O. 'super' erfle. Some folk think this can be a better eyepiece than the konig 16mm. It can still be had from K.K. in Japan. Perhaps one day I'll get one.

I still regularly use a 12mm U.O. konig. A lovely eyepiece. As with all konig designs, it is super sharp, as good as an ortho in my opinion. Doubt I'll ever let this one go.

I'd like to be able to source the rarer 8mm konig one day. I reckon the eye relief would be awful, but I'd love to give it a go.

Bear in mind I don't use fast scopes.

Cheers,

Andy.

ps: thanks for opening up an old thread. It should happen more often. Lots of great stuff buried deep within SGL.

Edited October 9, 2011 by AndyH