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Leica 1.8 times extender

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Old Monday 4th August 2014, 14:00   #1
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Leica 1.8 times extender

I suppose this should be under spotting scopes, but I have only ever contributed to the binocular forum.

Birdwatching Magazine for September 2014 has an article on this new piece of kit announced by Leica.
They say that they think this is the first time a quality optics firm has produced such an item.

Questar have always had an inbuilt switchable Barlow lens since the 1950s. That is for 60 years.

TeleVue have various specialised Barlows up to 5 times increase in the focal length of the objective.
There are numerous other telescopes that use Barlow lenses.

The first use of the Barlow lens, invented by Peter Barlow, not of Coronation Street, seems to be in a Dollond telescope in 1833. So this is hardly something new.

I have long wondered why the Leica Apo telescopes of 77 mm aperture and upwards have not supplied dedicated Barlow lenses.
These telescopes, I think, can easily take a top magnification of 150 times without the optical image breaking down. The only limitation is the atmosphere and the fact that the brightness of the image reduces at high magnification.
These telescopes can certainly be used for observing, for instance, the planets.
I hope that Leica also supply perhaps a 2.8 times, so-called, extender to enable say 140 times magnification.

It is quite strange how conservative some of these well-known makers are.

I would also think that image stabilisation should be common by now in even lower priced binoculars, as even the cheapest digital camera may have image stabilisation.

Anyway, Leica are certainly not the first to use Barlow lenses.
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Old Monday 4th August 2014, 14:08   #2
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There's already a thread on the subject of the Leica extender on the Spotting Scope Forum here:

You might want to move your post there.

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Old Monday 4th August 2014, 14:57   #3
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. Dear Henry,

I'm not, unfortunately, computer literate so I don't know how to move my post.

Perhaps one of the moderators could move my post to the correct place.

Thank you for pointing out that this had already been discussed elsewhere. I only just saw the reference this morning when I got the magazine.
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Old Monday 4th August 2014, 15:00   #4
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Old Tuesday 12th August 2014, 16:20   #5
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I think the claim is true, this is an extender accessory separate to the scope, not an inbuilt barlow lens. I know the latter has been looked at by various scope manufacturers over the years, but as I understand it, its just not possible to put a barlow-type device in a spotting scope
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Old Tuesday 12th August 2014, 17:07   #6
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Thanks Steve,
a Barlow lens does not have to be built in. In fact built-in Barlows are rare and normally it is a separate item.
With cheap long focus telescopes it is often a single element, these give poor results. With better telescopes it is usually a doublet.
Better ones, especially with short focus refractors, are sometimes three or four element. They may then be called Apochromatic.

But there is the problem of matching the whole system and here sometimes the Barlow component may be specific to one particular eyepiece and one particular barrel and prism. This Barlow will work with other eyepieces but may be not as well as the specific eyepiece it has been designed for.

Vivitar lenses in some cases had matched Barlow's which were specific to the particular lens. They probably would work with other lenses but not as well.

An extender, such as Leica's is in essence a Barlow even though it might be called something else.
A Barlow lens is simply a negative element to increase the focal length of the objective.
This has benefits with telescopes as the eyepiece can still be fairly long focal length and have good eye relief.
And instead of having to work at say F/5 it is working at F/9.

But as has been found with the Leica extender/Barlow it doesn't work apparently with the straight through telescope because of physical limitations. This is a problem of geometry.
With some telescopes such as the PST H-alpha, a Barlow lens may help being able to take photographs by throwing the focal plane backwards so that the camera can focus.

Photographic tele extenders, which again are Barlow lenses, come in two element, four element and seven element variations, typically. Again they may be matched to specific lenses, such as a 300 mm F/2.8. They typically come in 1.4 times and 2 times versions.

Cheap variable Barlows, such as 2x -3x achieve the variable magnification just by adding a small extra tube. The lens is the same. All you are doing is altering the position of the negative lens and adding a bit of extra length. You may actually just have a system to change the position of the glass elements to give the variability.

Barlow lenses or tele-extenders work particularly well with mirror lenses either photographically or visually.

With a high-quality short focus spotting scope such as the Leica Apos, the Barlow component or extender is obviously carefully designed to give the best optical performance both centrally and off axis.
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