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PostPosted: Sat Sep 29, 2018 1:05 pm 
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Some people like to use an opera glass for very low, wide-field, views of the night sky. Imagine paying £600,000 for a glass.
This is the expected price in an auction in New Orleans for an opera glass that was purportedly used by Abraham Lincoln on the night that he was assassinated at Ford's Theatre in Washington in 1865. The wealthy Forbes family included previous owners.
Being an ancient glass, it would be interesting to know if the lenses have suffered devitrification over time.

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PostPosted: Sun Sep 30, 2018 8:57 am 
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Anyone having access to back-copies of Popular Astronomy, may be interested to look out the January -March 2003 issue, pages 25-26, in which you will find an article "Astronomy with an opera glass" in which I discussed this subject in some detail , both pros & cons. I spent from about £2.50 to about £25.00 for the ones that I used! £600,000 seems a bit steep! Regards maf.


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PostPosted: Mon Oct 01, 2018 11:10 am 
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We specs wearers have a difficulty with the Galilean opera glass, as we can't get close enough to the eye lenses to get the benefit of a wide-field. Mind you, for wide fields, I much prefer a 7X50 glass.

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PostPosted: Mon Oct 01, 2018 3:43 pm 
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My first observing instrument was a 3x30 opera glass. Cost me 30bob in 1963. More than a week's holiday job money working on a local farm. It served me well even after I saved up to buy my first real telescope, a cardboard and wood 4-inch f8 Newtonian kit with spherical mirror - advertised in Meccano Magazine as I recall :)

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PostPosted: Wed Oct 03, 2018 6:57 am 
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Two of main drawbacks of the standard opera glass are the inability of adjusting the interpupillary distance and lack of independent eye-focus. Regards maf.


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PostPosted: Wed Oct 03, 2018 10:16 am 
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I happened to come across an opera glass yesterday in a charity shop, for £5, and couldn't resist a purchase, after checking the interpupillary distance and infinity focusing.
The glass is obviously post war, as there are plastic parts to it, but it isn't a child's toy binocular. There's a simple metal focuser and the body is covered in brown leatherette. The inside of each barrel was high gloss black that I've since painted matt black.
The aperture is 40mm, but stopped down to 30mm or less. As is typical of a Galilean glass, it's like looking down a straw, but I do get the full stopped down field even with specs on. There's no obvious chromatism, despite the objectives and eyepieces being simple convex lenses. Magnification looks to be 2.5X to 3X.
It's too cloudy at the present time to try them out overhead, and the cloud seems to be set this way for some time to come in the North West.

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PostPosted: Wed Oct 03, 2018 2:00 pm 
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brian livesey wrote:
We specs wearers have a difficulty with the Galilean opera glass, as we can't get close enough to the eye lenses to get the benefit of a wide-field. Mind you, for wide fields, I much prefer a 7X50 glass.


Glassers, gave them up YEARS ago, for monthly contacts, put in once change every 30 days

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PostPosted: Thu Oct 04, 2018 7:07 am 
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One positive thing about buying old opera glasses is that if the lenses are mucky inside and out one can just unscrew them and clean them and screw them back in. There is no fear of getting them out of alignment and no prisms to worry about.
Are the lenses in you're not cemented doublets and therefore achromatic. I cannot imagine the objectives not being this? You say that the lenses are simple convex but surely in Galileans the eyepieces are concave , negative lenses! Regards maf.


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PostPosted: Thu Oct 04, 2018 3:14 pm 
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The Vixen SG 2.1x opera glass is a bargain at £239. :)

I use various opera glasses and afocal teleconverters from Nikon and Minolta cameras giving up to 32 degree flat real fields.

Regards,
David


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PostPosted: Fri Oct 05, 2018 10:37 am 
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The eye-lenses are wafer thin and there could be slight concavity on one side of them. It's difficult to judge. The objectives are single element and convex on both faces.
The glass might bring out an enhanced Milky Way in very dark skies, but probably not much in light-polluted places, as here.

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PostPosted: Wed Oct 31, 2018 3:39 pm 
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Just came across an old 40mm operaglass in a recycling emporium. Metal. No label, showing make or source, anywhere thereon. Roughly x2 to x3. Quite clean and easily cleaned up further, and seemed ok although interpupillary distance not adjustable and no indendendent eye focus of course, but at the "not huge" cost of £3 bought it! Will keep me occupied for a while! Regards maf.


Last edited by mike a feist on Thu Nov 01, 2018 7:35 am, edited 1 time in total.

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PostPosted: Wed Oct 31, 2018 4:24 pm 
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I've junked my opera glass. Let's face it, we don't want to go back to the 17th Century. Modern binoculars are much more effective.

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PostPosted: Wed Oct 31, 2018 7:10 pm 
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All the operaglasses that I collected around the time that I wrote that article for the SPA magazine I gave away a long time ago. The one just bought for a silly sum will probably end up in a similar the place eventually! It is not so much the old optical technology that works against it, but the lack of interpupillary adjustment. At very low magnification (something like between 2 and 3 times is hard to accurately meassure) the lack of independent eye focus is not such a great problem for me as I can use it as a monocular should I wish to. And at £3 it was hardly a risky purchase!
I toyed once with the idea of possibly buying one of the modern expensive ones that David mentioned (Vixen ) but a bit too pricey to buy without trying them out first. I noticed one of the astro-mags has a full page (inner cover) advertisement of something very similar but a different make and £100 cheaper? But once again these are never going to be seen in a local shop so that I could try them out first!
Regards maf


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PostPosted: Thu Nov 01, 2018 4:15 pm 
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Having just re-read my old article in Popular Astronomy (SPA) magazine, I wrote (erroneously , I now think!), that because Galilean operaglass has a negative eyepiece, one cannot use an operaglass to project the Sun onto a screen. However, using a negative eyepiece behind the objectives is really just like using a Barlow and increases the focal length of the object glass, and therefore, if correctly placed, an operaglass can be used to project the Sun! Yes? As the Sun was just about to set behind Southwick Hill, I attempted to project the Sun with a bit of cloud across it on the opposite wall...and adjusting the distances, there was a Solar disc (and it was not just a bright circle of light because the bits of cloud were visible! ! David's comments about using as telextenders, really made me think about this. Comments on this would be very welcome. The Sun has now set so cannot experiment any more to day! Regards. maf.


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PostPosted: Thu Nov 01, 2018 5:58 pm 
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Hi Mike,
The Nikon TC E2 is I think the favoured afocal teleconverter used to make a 2x opera glass.
So long as your IPD is 62mm or more.
I paid £15 each for mine, mint.
I'll try to check if this is the correct one.
Some people make 3D printed housings for them.

The cheaper version of the Vixen may be the original Russian version that predates the Vixen.

There is a list somewhere of all good afocal teleconverters.
Used as a monocular some are huge, maybe up to 100mm aperture.

The Konica Minolta 1.5x, 1.65x for me because long sighted, has an amazingly large flat field, but too big for opera glass. 32 degree full field. 1.5 mag gain in severe light pollution. Can see whole constellations, setting back the clock 20 years to lesser light pollution skies.

Regards,
David


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