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Doubler/Booster Recommendation Please

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Old Friday 7th December 2018, 07:58   #26
Hans Weigum
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[quote=henry link;3790557]
...The main optical limitation with these things isn't usually the booster's image quality or brightness, but the poor image quality most binoculars show when their magnification is doubled. The bad effects of aberrations are usually more than doubled when the smaller exit pupil allows the eye to take in the binocular's full aperture aberrations in daylight, usually not a pretty sight...


I am rather puzzled how the discussion in this thread can limit itself on how to fit an after eyepiece converter to a binocular, when Henry Link clearly explains why such a configuration optically makes little sense.

My personal experience is, that camera type of teleconverters in front of a mono-/binocular produce much better results. They probably are better optically corrected for the purpose, allow for a wider field of view and usually do not reduce luminosity. They make the second prism system with all its drawbacks redundant and usually have a lower magnification, more reasonable for such a combination, which cannot anyway fully replace picture quality wise, at higher magnifications real spotting scopes.

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Old Friday 7th December 2018, 16:01   #27
Binastro
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Some afocal front teleconverters are so large that they wont work on a binocular, but may work on a monocular.
I have several of these, and will try them, although I haven't until now.

I have tried boosters on the Canon 18x50IS and the results are not good. This was hand held and the booster not rigidly mounted.
However, a 7x binocular behind the Japanese Celestron 20x80 was very worthwhile, although 4x or 5x would have been more suitable.
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Old Saturday 8th December 2018, 16:53   #28
Binastro
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I tried the Canon TC-DC 58N front teleconverter with a Leica 8x32 BA.
The converter is 1.75x. Made in Japan.
Front outside diameter 74.5mm.
Rear 58mm thread.
Weight 185g maybe.
2 inches long. 3 inches wide.
But maybe only 3 elements.
Multicoated and well made.

The rear lens aperture is about 29mm.

For me, I couldn't quite get to focus even at far distance,.
There was also false colour, maybe because it was not perfectly centred.
It doesn't touch any binocular glass.

This might work for other people with different eye prescription and more accommodation.

Although rear boosters may not give perfect results, they probably are the simplest solution to higher magnification in a small device.

It did work well with my computer screen glasses and unaided eyes giving maybe 1.9x magnification with ~30 degree field.

I may try it with another binocular, but it is not good for me with a Leica 8x32 BA.
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Old Saturday 8th December 2018, 22:05   #29
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I just tried the Canon 1.75x teleconverter mentioned in post 28 on the Canon 18x50 IS.
Both Canon,so should work?

The adapter screws into the 58mm thread of the binocular, as if they are made for each other.

Indeed, there is enough focus travel for me to just focus on an illuminated white background square sign at about 100 yards distance.
The focus on the side with the front afocal adapter is quite different to that without the adapter.
The adapter does not look out of place on the Canon 18x50IS, neither is the binocular too heavy.

However, although the writing is much enlarged probably to 30x or slightly more instead of 18x, the text is sharper with the side without the adapter.
The side with the adapter is much dimmer, probably because the aperture is stopped down to 29mm or less.
The IS makes both sides very steady, almost tripod steady unbraced.

There is a very strange extended area to the large square illuminated sign. It seems to be spherical aberration, I think, although I am not sure.
There is not much false colour on the illuminated sign, although I noticed bad CA on an out of focus neon strip kitchen light with the adapter side.

Unfortunately, the Moon is not around so I can't test on that, and my normal test objects at 120m are covered in plastic sheets and scaffolding.

But it seems this front afocal adapter and the Canon 18x50IS are not a match. In fact, it seems worse, although there might be a situation where distant writing could be read through the poor image with the adapter, but not seen without.
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Old Saturday 8th December 2018, 23:13   #30
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Quincy,

I posted a report on the current Opticron UTA a couple of years ago. I think this was the link that Pete meant to post.
https://www.birdforum.net/showthread.php?t=329496

David

Last edited by typo : Sunday 9th December 2018 at 08:01.
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Old Sunday 9th December 2018, 16:23   #31
Binastro
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This morning at 3 a.m. the fast clouds eventually had some cloud gaps and I was able to view some of Orion with the Canon 18x50IS and 1.75x afocal front teleconverter.

The star images were very strange.

Betelgeuse was shown as a very extended lowish intensity disc about 12 arcminutes in diameter.
In the centre was indeed the almost point image warm coloured star Betegeuse.
This might be very severe spherical aberration, but I am not sure.

At the moment Comet Wirtanen is visible in binoculars. It too shows as a large expanded faint disc, i.e. coma. I am not sure what the central condensation looks like and whether is is star like or diffuse. The apparent diameter is similar to the moon, 20 or 30 arcminutes depending how dark the sky. It has been seen with unaided eyes and averted vision.
This is similar to the star images shown with the Canon 18x50IS and the teleconverter.
I don't think that I have seen such large star images before in an optical instrument.

The field size was about 2.2 degrees using star separations, which suggests that the magnification is 32x with no loss of AFOV, whivch is 3.85 degrees normally at 18x50.

The images with the teleconverter are low contrast and dim. With this large halo effect.

The set up looks good. Pity it doesn't work.
I am not sure what is happening here.
I am not yet sure of the clear aperture at 32x or whether there is a clear cutoff.
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Old Sunday 9th December 2018, 20:23   #32
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The front lens diameter of the 1.75x teleconverter is about 65mm.
The weight of the teleconverter is 193g.
The weight of the Canon 18x50IS with the teleconverter on one side is 1384g.

The exit pupil of the normal binocular is ~2.8mm.

The exit pupil of the binocular with the front afocal 1.75x teleconverter is ~1.6mm.
This is despite the rear lens of the front teleconverter being 29mm diameter, and the magnification with the teleconverter being about 32x.

The teleconverter is designed to fit a digital camera with a lens of front clear diameter of 20mm maximum.

The variables are the positioning of the teleconverter along the optical axis and the design of the teleconverter.

Whether a very large front afocal teleconverter can be designed to work well on a 50mm binocular, I don't know?

I suppose that if a medium size front afocal teleconverter was possible for binoculars it would have been made.

What we actually have are rear boosters, zoom binoculars, interchangeable eyepiece binoculars. turret eyepiece binoculars and maybe internal barlow lenses in binoculars.

As far as I know there are no front afocal teleconverters for binoculars, although they may exist?

Last edited by Binastro : Sunday 9th December 2018 at 20:36.
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Old Monday 10th December 2018, 12:13   #33
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I hope the OP doesn't mind this link of my use of the extenders.

https://www.birdforum.net/showthread.php?t=219014
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Old Monday 10th December 2018, 15:09   #34
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Thanks mooreorless.
Interesting read.

Does anyone know when rear boosters where first used on a binocular?
Did Zeiss have an early model?

It may be that the front afocal 1.75x Canon teleconverter acts as the first telescope and that the 65mm aperture becomes the aperture of the two telescopes.
The front lens of the teleconverter is very curved, which may explain the very severe apparent spherical aberration.
But I am not sure why I get the very unusual in focus star images.

And why does it work well on the 20mm aperture digital camera lens and so badly on the 8x32 BA?
I tried it on the 10x25 Docter binocular but could not focus even at a distance.

If held at a distance in front of the binocular the magnification seems to increase further.

I suppose that the Canon 1.75x teleconverter may be a Galilean system and front boosters are normally regular optics, which may account for the strange behaviour?

Last edited by Binastro : Monday 10th December 2018 at 15:13.
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Old Monday 10th December 2018, 16:24   #35
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Quote:
Originally Posted by Binastro View Post

It may be that the front afocal 1.75x Canon teleconverter acts as the first telescope...

I suppose that the Canon 1.75x teleconverter may be a Galilean system...
Hi Binastro,

Both of these statements are true and explain the poor result. Remember, the aberrations of the first telescope are magnified by the second telescope, so if the first scope is low quality the image will be very poor after it's magnified by the second scope. The aberrations of the second telescope are actually improved in this arrangement because it's stopped down to the exit pupil of the first telescope.

As you said, teleconverters are simply short Galilean telescopes and like all such telescopes are optically pretty poor, useful only for low magnification like an opera glass. They cannot stand an 8x boost, much less an 18x one. A conventional Keplerian scope would be impossibly cumbersome as a front booster since it would require an "eyepiece" with half the objective lens focal length for 2X as well as some kind of image erecting system.

I recall Bushnell selling a front booster for it's binoculars many years ago. I'm sure it must have been the optical equivalent of a Galilean teleconverter and probably worked about as badly.

Any monocular from the past, including the 3x12 Zeiss, could always have been used behind a binocular as a booster. The only thing that makes the current 3x12 Zeiss monocular a "booster" is an adapter for attaching it to a binocular eyecup.

Henry

Last edited by henry link : Monday 10th December 2018 at 16:42.
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Old Monday 10th December 2018, 16:47   #36
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Thanks Henry.

Regards,
B.
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Old Wednesday 12th December 2018, 09:53   #37
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Thanks to all having contributed here to the question regarding performance of boosters in front of the objective.


https://www.scopelist.com/BE10xT-Bin...er-901793.aspx

Why did Safran/Vectronic disregard the drawbacks seemingly inherent in the concept with such an expensive booster dedicated to an equally expensive binocular. The dedicated residual light amplifier (night vision adapter) to the Vector fits after the eyepiece however.

http://precisionrifleblog.com/2013/1...tor-23-review/

The poor vision performance of Vector - booster combination shown here in comparison seems to confirm earlier statements.

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Old Thursday 13th December 2018, 20:07   #38
Binastro
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Thanks Hans for the link to the Vector 23 test.

However, some points I don't like.
The test does not specify the exact accuracy at 18 miles.
One would need to take GPS measurements at the start and end points to get 10 yard accuracy with a hand held unit or better with surveyors equipment. I don't accept makers specs unless confirmed.
And also a second method, perhaps triangulation.

I don't like the reviewers use of 10x zoom, when I think he means 10x magnification boosted from 7x.
It doesn't zoom 10x, I think.
The cost of $2,000 is interesting for a 1.4x Galilean binocular. It might need special glass to work.

My old 7x Leica moncular RF works well through glass up to about 1000 yards.
But I haven't checked its real accuracy.

905nm lasers can probably be seen on a digital camera screen, even a cheap one. I don't think it needs anything fancy. I use this for infra red T.V. remotes.

The Disto 120 yard RF gives inclination. I can't remember if compass reading also. It doesn't seem to work through glass.

I fancy a Vector 23, but its a bit pricey.

As to front teleconverters.
It may be that the old Bushnell one for 7x35 Porros works better than my 1.75x Canon, because the aperture is only 32mm or 33mm instead of 65mm.
The Canon has very curved glass, the Bushnell maybe less so.

Galilean army glasses are 5x possibly 6x and are O.K. but very small fields.
Some Galileans have compound optics with high quality glass types and maybe good design, so probably work better than the 3 element Canon 1.75x.
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Old Friday 14th December 2018, 10:53   #39
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Further regarding the Vector 23 rangefinder binocular review.

If my memory is correct I read a long time ago about adaptive optics for large telescopes.
An infra red star was projected on a layer of the atmosphere 90km? up in the sky.
Infra red was used instead of visible light because the effectiveness was maybe the square or the cube of the wavelength, possibly the cube.

If so, this may apply to the Vector 23 using 1550nm instead of 905nm for most laser rangefinders.
If it is the cube of the wavelength, then it is just over 5 times as effective as 905nm.
So the 18 miles difficulty of measurement would equate to 3.6 miles for other rangefinders.

The accuracy may depend on how accurate the clock time is to receive the return signal.
I suppose atmospheric conditions may also be a factor.

Laser measurements to the Moon are accurate to about 10cm, by repeated careful measurements. These use reflectors left on the Moon.
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Old Friday 14th December 2018, 14:59   #40
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If I'm reading the text correctly it appears that the Vector 23 uses a front booster solely in order to extend its range finding distance at 10x compared to 7x by increasing the surface area of the aperture receiving the returning laser reflection. A booster behind the eyepiece wouldn't do that.

To the extent we can deduce anything from the non standard way they evaluated visual resolution the Vector 23 with the booster appears to be quite poor, around 30% worse than the best model in the test for a tester with "average" eyesight acuity for this group. The two parts of the statement below are in direct contradiction.

"Although they (Vector 23) appeared to have good clarity even with the external glass attached, the testers simply couldn’t make out the same level of detail with them as we could with some of the other models."

All high quality 10x42 binoculars really should show a similar level of detail for an average observer since the actual instrument resolution (multiplied by the magnification) ought to be at least twice as good the observer's acuity. If we assume that the best binocular in the this test (Leica Geovid) conforms to that standard then it would appear to be the only one in the test for which the observed resolution is limited by eyesight acuity. All the other binoculars in the test that show a visible reduction in resolution compared to the Leica must have true resolution (multiplied by the magnification) worse than the average tester's acuity. That seems unlikely, but if we just accept the 30% visual loss of resolution for the Vector 23 that would suggest at least a 65% reduction in its true instrument resolution compared to the Leica, which would be very poor indeed.

In fairness to the testers I don't think the nuances of the optical quality of these binoculars were of any more interest to them than the nuances of the optical quality of the scope would be in a review of surveyor's theodolites.

Last edited by henry link : Friday 14th December 2018 at 20:20.
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