Explore Scientific 120 degree - come on !!!!

[alan potts]

I think John hit the nail on the head, If it could be done to the same standard as the other Televue 100 and shorter 110 degree eyepieces. Don't forget the 25mm 100 that ExSc made on their own, not very good if the review I read on Cloudy Nights is anything to go by.

I would love to have one of the Nikon eyepieces to put along side my Televues to see for myself how much difference there is but the corner shop has sold out of them.

Alan.

[Moonshane]

Not sure if I have this correct but if I had a 40mm 120 degree ep  in the diagonal would it give me nearly 1 1/4 times "more" light pollution than my "little" 40mm Plossl (50 degree field)???

I don't think that's right. the sky darkness (in the visible field) depends on the exit pupil. if you used a 20mm 100 degree eyepiece vs your 50 degree 40mm plossl the sky would be twice as dark (approx) in the 20mm 100 degree.

if you look through a toilet roll and then naked eye, the sky would be the same brightness I'd wager.

[Macavity]

I think the exact figures (120, 82, 68 deg. etc.) AFoV contain a certain amount of "latitude"? <G>  I once bought an "82" degree (non-TV) eyepiece with a view to neatly framing the Moon. In practice, it accommodated ~7/8 Luna!

The general eyeball impression was of ~80 deg AFoV, but the focal length - nominally 10mm, was actually more like 9mm? Later versions of the eyepiece carried the revised spec! "Premium" eyepieces are more likely to deliver on these values. Not quite "premiership", but my Vixen LVs agreed best with my ad-hoc measurements?

But there are many other things. WA eyepieces employ significant "magnfication distortion" (Pincushion distortion?) to minimise distortion of stars at the edge of field. A certain "Seasickness" while rapidly scanning the skies is reported. Then there is the fact that movable mirror CATs have a fair variation in focal length...

Aesthetics and "framing" seem the greater object of wider fields. But that perception

seems based of factors of two or three, rather than the odd ten percent or so.

P.S. I too am a bit doubtful re. "Purging". My double glazing "units" claim some sort of exotic "purging"? But (precisely!) once a year show some internal misting. The conventional wisdom is that they are "blown" require "immediate replacement" etc. Mebbe So! But they ain't gonna be replaced on a budget! Having spent a little time making small volumes "airtight", basic rubber seals and a bit o' silica gel might not achieve perfection? That's my story and I'm sticking it - Unlike rubber on glass? 

[Northern Soul man]

I don't think that's right. the sky darkness (in the visible field) depends on the exit pupil. if you used a 20mm 100 degree eyepiece vs your 50 degree 40mm plossl the sky would be twice as dark (approx) in the 20mm 100 degree.

if you look through a toilet roll and then naked eye, the sky would be the same brightness I'd wager.

Moonshane, Thanks Mate but I'm still in the dark (yes, I know another pun) the example I used was that the eyepieces would have identical focal lengths (so the same exit pupil, is that correct???), just the Afov is the factor that I was pointing towards 120 degree against 50 degree - so a lot more sky in the 120 degree than the 50 degree??

Then there must be a different way to calculate these things because the exit pupil would be the same (mirror/lens diameter divided by the magnification for the given ep - 200mm scope (F10) the 40mm focal length in BOTH ep's are the same (40mm) giving a mag of x50, the exit pupil would be 200/50 giving a 4mm exit pupil in both ep's - but for the 120 degree having the same exit pupil as the 50 degree, surely can't be correct as you have "a lot" more sky (120 degree) than the 50 degree - given the same exit pupil!!

I've never been one for the mathematics of the hobby, but I'm struggling here guys - I think I need to do a lot more reading than observing - Bring on the rain!!!.

Thanks to all for their replies - nice 1  Paul.

Oh can anyone lend me £758.

[Naemeth]

Moonshane, Thanks Mate but I'm still in the dark (yes, I know another pun) the example I used was that the eyepieces would have identical focal lengths (so the same exit pupil, is that correct???), just the Afov is the factor that I was pointing towards 120 degree against 50 degree - so a lot more sky in the 120 degree than the 50 degree??

Then there must be a different way to calculate these things because the exit pupil would be the same (mirror/lens diameter divided by the magnification for the given ep - 200mm scope (F10) the 40mm focal length in BOTH ep's are the same (40mm) giving a mag of x50, the exit pupil would be 200/50 giving a 4mm exit pupil in both ep's - but for the 120 degree having the same exit pupil as the 50 degree, surely can't be correct as you have "a lot" more sky (120 degree) than the 50 degree - given the same exit pupil!!

I've never been one for the mathematics of the hobby, but I'm struggling here guys - I think I need to do a lot more reading than observing - Bring on the rain!!!.

Thanks to all for their replies - nice 1  Paul.

Oh can anyone lend me £758.

The exit pupil is only determined by the focal length of the eyepiece and the focal ratio of the telescope, apparent or true field of view doesn't come into it.

Imagine it this way (even though it is not perhaps the most accurate way to describe it): The telescope gathers a 360 degree field of view, the eyepiece being a certain size means only a small portion of this is used, for 50 degree eyepieces this means about 14% of the field of view is used, for a 120 degree eyepiece it's more like 33%.

HTH

[Moonshane]

I'd refer back to my toilet roll analogy. the exit pupil is the same (that of your eye) and the sky brightness is the same with either your naked eye or your toilet scope despite the wider field of your eye.

it's the aperture that gathers the light, not the eyepiece so the same amount of light is coming in no matter what eyepiece you use, assuming the same magnification, you just have more of the 'mask' removed with a wide field.

[Stu]

Personally I think this one is a case of marketing requiring something to try to outgun the competition, but missing the point!

I have several ethos eps, including a 3.7mm Ethos SX which has a 110 degree fov. I can honestly tell you that the 110 degrees had nothing to do with purchasing it! I bought it because it is a focal length which is pretty much optimum high power for my 106 apo, and has all the Ethos characteristics in terms of contrast, sharpness etc.

I find the 110 degree fov a bit much to be honest, and am quite happy with 100 degrees!

I think someone needs to come up with a far more radical approach to ep design before this sort of thing will take off.

Cheers

Stu

[Bart]

Bring on the rain!!!.

Heretic!!!

Come over here, you can have all the clouds you need!

Barry

[AlexB67]

I'd refer back to my toilet roll analogy. the exit pupil is the same (that of your eye) and the sky brightness is the same with either your naked eye or your toilet scope despite the wider field of your eye.

it's the aperture that gathers the light, not the eyepiece so the same amount of light is coming in no matter what eyepiece you use, assuming the same magnification, you just have more of the 'mask' removed with a wide field.

Just to add, perhaps I did not explain well yesterday, in the end of the day the sky background is determined by the number of photons collected, i.e. light gathering and then how it gets concentrated into the exit pupil.   You could think of it  as kind of flux I suppose, or area density. Following on from that, you can do a bit of intuitive math  without too much recourse or understanding of in depth physics, and hopefully satisfy your self that the contribution to the sky background darkness comes out  to be proportional to 1 / Mag ^2.  Then, you can see given the alternative definitions of Magnification, either by exit pupil, or focal length, in the end of the day it boils down to the same thing, but thinking in terms of exit pupil is more intuitive. In following the  argument through FOV never enters it, so therefore it is independent of it.

[Pliadian]

What in the, I say. What in the hell is this? The phone number or the price!  Yikes, run away, run away...

[hoops86]

Surley to justify spending that much on one eyepiece your scope has to be at least 4 times the price!?!?

Im pretty sure even if i was a multi millionaire i still wouldnt consider spending that on one eyepiece!

[jetstream]

Nice one Guys, I know but you mention the average astronomer (me), using their scopes under really light polluted skies with nights of poor seeing and the dreaded dew - with me, the more sky I put into the ep (low power) the more light I get from the light polluted skies - the more light I get in the less contrast I get, not sure how they work, but, lets face it, with the fields that are stated - would this be correct????

This can be a complicated subject and includes the objects viewed-light source points or extended objects with varying surface brightness.In light polluted skies I use a smaller exit pupil,same as you.Some thoughts on the matter:http://starizona.com/acb/basics/observing_theory.aspx,http://clarkvision.com/visastro/omva1/,I would venture a guess that the apparent FOV has no bearing on getting more light from light polluted skies.The more magnification you use,for a given focal length, the smaller the exit pupil which darkens the sky for light source points (stars).In Clarks paper,look at the bottom of the page for the conclusions.In light polluted skies I use 1mm-2mm exit pupil,dark skies 2mm & up.When  using the smaller exit pupils it is important not to exceed the available sky seeing limits.I personally love widefield low to med mag eyepieces and I am buying another one soon.

[Pig]

Surley to justify spending that much on one eyepiece your scope has to be at least 4 times the price!?!?

Im pretty sure even if i was a multi millionaire i still wouldnt consider spending that on one eyepiece!

Never say never

[estwing]

Surley to justify spending that much on one eyepiece your scope has to be at least 4 times the price!?!?

Im pretty sure even if i was a multi millionaire i still wouldnt consider spending that on one eyepiece!

I said that....also said I would never have more than one scope!

[Northern Soul man]

Thanks guys for all the help and advice, I'll take it on board and try and get my head around it!!!.  Not sure about the actual maths and physics involved into producing the "next big selling point" regarding ep's, but I'm sure that the manufacturers spend thousands on research and development - makes me wonder what the earlier pioneers of astronomy would have made of it all?  When these guys were trying to "see" better, it was down to the next project they were going to "make" themselves to progress, as with technology, it only seems like the last few years that the humble ep has been scrutinised for bigger better, thinking back to the Huygens, Ramsdens, Erfle's, Ortho's and Plossl's of yesteryear seems a very long way off to what we have today, but these designs still are recommended today - I think the Clave Plossl's are still a sought after ep amongst some astronomers today.

Thanks again Guys for the help, advice and brainy stuff - its beginning to sink in after about 25 years - wonder what the next 25 years will bring - a £2000 ep - maybe??

I know someone's going to put a link to one up next!!!

Thanks again.   Paul.

[John]

Surley to justify spending that much on one eyepiece your scope has to be at least 4 times the price!?!?

Im pretty sure even if i was a multi millionaire i still wouldnt consider spending that on one eyepiece!

It does not seem to work like that. I have 4 scopes, the most expensive of which cost around £700. My eyepieces would cost something in the region of £3K to buy new I guess. They do serve 4 scopes though and will give me a lifetimes observing.

[Pig]

Its surprising how much you can afford when you want something  and this hobby is very addictive.

[RikM]

Surley to justify spending that much on one eyepiece your scope has to be at least 4 times the price!?!?

Im pretty sure even if i was a multi millionaire i still wouldnt consider spending that on one eyepiece!

 A good eyepiece can bring out the best a scope has to offer.

I think of it in the same way as how a good amplifier can make even a cheap guitar sound good. The guitar supplies the input, the amp makes it sound nice. The telescope supplies the light, the eyepieces makes it look nice.

Like John I don't have any expensive telescopes, I think my 250PX at £440 is at the top, but I have about £1,600 in eyepieces and they make all the difference to me.

[AlexB67]

This can be a complicated subject and includes the objects viewed-light source points or extended objects with varying surface brightness.In light polluted skies I use a smaller exit pupil,same as you.Some thoughts on the matter:http://starizona.com/acb/basics/observing_theory.aspx,http://clarkvision.com/visastro/omva1/,I would venture a guess that the apparent FOV has no bearing on getting more light from light polluted skies.The more magnification you use,for a given focal length, the smaller the exit pupil which darkens the sky for light source points (stars).In Clarks paper,look at the bottom of the page for the conclusions.In light polluted skies I use 1mm-2mm exit pupil,dark skies 2mm & up.When  using the smaller exit pupils it is important not to exceed the available sky seeing limits.I personally love widefield low to med mag eyepieces and I am buying another one soon.

It is an interesting subject IMO. I requested his book on inter library loan, observing the deep sky and still awaiting, but should get it eventually.  http://www.amazon.co.uk/Visual-Astronomy-Deep-Roger-Clark/dp/0521361559. it is rather costly to buy, but it should be an excellent read I feel, Clark goes into some detail on this whole topic for extended objects.  I wonder if anyone here read it and their thoughts on it  

[iksobarg]

so, its been a while. How many of you sceptics went and got 120s?

Anyone? Impressions?

Thanks,

John

[quaoar]

I bought one, a 9mm 120 degree around when they first came out. I didn't use it much I much prefered the views through my Televue Ethos and Naglers. Other people I observe with tried it a few times and quickly came to the same conclusion. I ended up selling it just recently to make more room in my EP cases. If you like eyewatering EP prices try buying a 34mm ZAO I  or ZAO I 25mm lol.

[Charic]

Jupiter alone would still look better in my scope with the 8mm Starguider or the 6mm William Optic and about 93.5% cheaper than the ES.

Using the  ES 120 virtually  in Stellarium, Jupiter  looks  so pathetic in all that space, and why spend so much on an EP (£1122.oo UK)that will effectively just  end up as a finder EP?

[John]

Jupiter alone would still look better in my scope with the 8mm Starguider or the 6mm William Optic and about 93.5% cheaper than the ES.

Using the  ES 120 virtually  in Stellarium, Jupiter  looks  so pathetic in all that space,....

How do you know this without actually trying it, rather than just simulating it ?.

My most used planetary eyepiece with my 12" dob is my Ethos 6mm. Believe me, Jupiter does not look in any way "pathetic" with it !

[Chris]

I agree with John, My ES100's Wowed me when I looking at Uranus with my C8. They have Wowed me any other object for that matter!

[Dude_with_the_tube]

Stellarium by any means is a great piece of software but ONLY for locating things,but will never show you anything close to the actual performance of any eye piece used in real.All major images in Stellarium are made by professional equipment and doesnt not necessarily copy the actual image we see in visual mode.

I understand you favour your budget BST`s Charic what is perfectly fine,but i wouldnt and strongly suggest not to comment on eye pieces/equipment you never tried yourself.There are people who do buy equipment based on others point of view and reviews made (myself included).I have tried Ethos and they are absolutely great eye pieces for both DSO and high power planetary views,same i can say for EX SC 100 degree range,views both these provided where breath taking.They just didnt grow into me as i found that 100 degree views are not something i truly enjoy,however,there are plenty of people who actually do.Never tried 120degree EP ,but would love to.Would i buy one if i really like it? I dont see any reason why not and i have no issue of saving up for a long time if necessary,just to get the thing i would really enjoy.Some of the scopes used by forum members here cost far more then that 1000 quid eye piece,however,no one ever questions that? Same could be said for some peoples eye piece collections.

Suggest you get one of the premium eye pieces and try one you might be very surprised of results

Clear skies.