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Explore Scientific 120 degree - come on !!!!


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There are Nikon and Takahashi eyepieces that cost around £1K and the 21mm Ethos was £720 before the recent price reduction.

The price of the ES 9mm 120 will be a bit less outside the UK of course.

Heres some notes on it's performance for those interested:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5726357/page/0/view/collapsed/sb/5/o/all/fpart/1/vc/1

I'm still not convinced that this nitrogen or argon purging has any real benefit for the average astronomer but I might be wrong  :undecided:

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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????

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I'm still not convinced that this nitrogen or argon purging has any real benefit for the average astronomer but I might be wrong  :undecided:

I wonder too.  I suppose  whatever gases may be in an eyepiece in air could affect degradation perhaps like traces of water or something else and corrode the inside in the long term  :undecided: Now in  the case of spectroscopic applications there a very good reasons besides that I know about, but in this case, not sure what other reasons.  

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I can't help feeling these extreme WA EPs are, well, a bit 'gimicky'. 120 deg seems almost unbelievable to me. Having said that, I can't help noticing that my own EP collection is slowly... but surely being replaced by 82 deg models. Perhaps we'll all be using 120deg as standard some day, who knows. 

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It just all seems a bit much to me. I don't mean the price, I mean the FOV. I have a 100 degree ES and to be honest I have to move my eye around to take it all in. Does anyone know the FOV of the MK1 Eyeball? Anyhoo none of that really matters for me as I just can't justify spending that much on an EP.

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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)???

Sky  back ground  brightness is largely determined by magnification and focal length of the eyepiece, as I understand it, so no. To see the same image say with smaller exit pupil, bigger FOV shorter focal length or a less FOV and a longer focal length will not result in the same sky background brightness.  Did I get that right  ? ( scratches head ) need to check my calculations to be sure and have not done so :embarassed:  I think that kind of reasoning is true in a simple model anyway, but with LP all in there perhaps there is more to it. I am of course ignoring additional scattering that you may get in a cheaper eyepieces and other various effects that could affect contrast also, and for an expensive eyepiece all those things should be improved, in part that is also what you pay for.

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I'm still not convinced that this nitrogen or argon purging has any real benefit for the average astronomer but I might be wrong

Totally agree.

I think the theory behind it is that by purging, you are removing any residual moisture in the air inside the EP and so preventing any future fogging from inside (like in swimming goggles).

In practice though, even with purging and sealing the EP, moisture and air will always find its way into the system after a few weeks or months.

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Hi Alex, not sure mate, If I use the the same telescope with ep's with identical focal lengths - would this give me an "Increase" in light pollution using the 120 degree as opposed to the 50 degree so would the exit pupil be the same in both ep's as the exit pupil is the ep focal length divided by the focal length of the scope????   PLEASE HELP NEEDED???

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Hi Alex, not sure mate, If I use the the same telescope with ep's with identical focal lengths - would this give me an "Increase" in light pollution using the 120 degree as opposed to the 50 degree so would the exit pupil be the same in both ep's as the exit pupil is the ep focal length divided by the focal length of the scope????   PLEASE HELP NEEDED???

A simple sort of way of looking at  is that the background is determined by magnification, but contrast and other things will complicate it in a given eyepiece.  Assuming the scope is a constant, and the eyepiece magnification is solely determined by focal length the sky background goes as 1 /  mag ^ 2. I am doing this sort of top of my head I can check some calculations I have on this later on my other PC and correct it if I am wrong, so it is as I said I think as above,  the FOV does not enter it is quite a simplistic way of looking at it. Hope that makes sense.

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On advantage of ultra wide eyepieces is that they can show as much sky as one with a normal field of view but at a higher magnification. Higher magnification tends to darken the background sky if there is any light pollution around so that can be helpful for seeing fainter objects. As an example, in my 12" dobsonian, the 9mm 120m degree eyepiece will show a true field of view .68 of a degree across at 177x which is the same amount of sky as a 21mm plossl would show at 76x. Whether you can actually "see" the whole of a 120 apparent field of view is likely to vary I guess.

Another advantage in a fast scope is keeping the exit pupil to a reasonable size while showing a lot of space.

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My earlier post in this thread links to a review post on another forum which does reveal a few issues although still pretty impressive for a 120 degree eyepiece.

I reckon Tele Vue would do it if it could be done to the same standard as the Ethos and the Delos but won't if they are not 100% confident of that.

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Quote Northern Soul man: "...Just like your thoughts on this???? - Is it only me or is this getting a little "astronomical" (pardon the pun) now and at £758 - come on!!!!"

I possibly could afford the £7.58.

Seriously, I suppose there are some amatuers think that £758 is 'value for money'.

I have spent £758 on 2x TV Plossl's, 1x TV Radian & 1x TV Nagler zoom. To me that is/was 'value for money'.

At this point I'll quitely leave the room, grab my coat and take my TV eyepieces with me.

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Quote Northern Soul man: "...Just like your thoughts on this???? - Is it only me or is this getting a little "astronomical" (pardon the pun) now and at £758 - come on!!!!"

I possibly could afford the £7.58.

Seriously, I suppose there are some amatuers think that £758 is 'value for money'.

I have spent £758 on 2x TV Plossl's, 1x TV Radian & 1x TV Nagler zoom. To me that is/was 'value for money'.

At this point I'll quitely leave the room, grab my coat and take my TV eyepieces with me.

I expect your eyepieces will all perform at least as well, if not better, than the ES 9mm 120 in all things apart from the size of the field of view.

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I guess it just seems a lot for one eyepiece. But we must remember there are plenty of more expensive options that have been pointed out in this thread before, the Leica ASPH 8.9mm-17.8mm is about the same price, depending on the exchange rate ;).

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