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PostPosted: Wed Jun 08, 2016 12:36 pm 
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Bought on a local flea-market this morning in an unblemished condition for £45. The bins also have the tripod pillar attachment, one of those items that are often missing with secondhand bins, along with dust caps.
I'm hoping the bins will outperform the TENTO 20X60's. The latter are good, but the eyelenses are small in diameter compared to the CELESTRON's and thus restricting for a specs wearer.
Donner und blitz is forecast for this evening, so the Moon might not be visible for viewing in the bins.

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PostPosted: Thu Sep 01, 2016 3:46 pm 
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Lower end binoculars can have a reputation for being out of collimation when purchased and this can include the CELESTRON Skymaster series. There are tiny collimating screws concealed under the rubber armouring.
The secondhand 25X70's are okay, but I recently tried out a pair of new Skymaster 15X70's at a camera shop and they were badly in need of collimation. I demonstrated the problem to the salesman and he agreed as he peered down the road through them - although whether he sent them back to the depot or put them back in the shop window ( on the understanding that some customers buy binoculars without first looking through them! ), we'll never know.
Later, I thought that the binoculars had probably been in the shop's front window for a long time and in full sunlight, as they felt quite warm to the touch.
The Skymasters' 70mm spec have black plastic bodies, a material with a much higher rate of expansion than aluminium. It occured to me that constant exposure to heat might have thrown the camera shop bins out of collimation. In the cooler conditions of night-time, the bins might have shrunk back to being more-or-less collimated.

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Last edited by brian livesey on Sat Sep 03, 2016 12:06 pm, edited 2 times in total.

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PostPosted: Thu Sep 01, 2016 5:53 pm 
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Hi Brian,
All of these cheap Chinese 70mm binoculars are liable to collimation problems.
Finding one properly collimated and keeping so is pure luck.

They are lightweight though and when they work they are good.
I hate my 25x70, the performance is awful, maybe they have improved.

The Revelation 15x70 is amazingly cheap at under £50, and I think Telescope House has resorted to testing each one before dispatch.

Regards,
David


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PostPosted: Thu Sep 01, 2016 7:31 pm 
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Location: New Farnley, Leeds lat 53.8N long 1.6W
David, I bought the Revelation 15x70s and a cheap photo tripod a couple of years ago on a whim, just to take to Cornwall for a family holiday. Collimation is ok and they have proved much more serviceable than their price suggested that they would be. On that trip they gave me the most pleasing view of Albireo that I have had in any instrument (sapphire on nine carat gold) and the beehive cluster was abuzz with stars. In twilight, under a light-polluted Leeds sky recently, they drilled down to mag 8.7, chasing a fading variable star that was well beyond my 10x50s. Premium they're not; serviceable and good value they are.
Regards to you from Bob


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PostPosted: Fri Sep 02, 2016 1:43 pm 
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Why are your 25X70's "awful" David? About 70 per cent or more of the field-of-view in mine gives sharp star images. I attach the the bins to the binocular mirror-mount, which makes them rock-solid.
I'd like the brighter 15X70 spec too, for lower power sweeping and on the mirror-mount. by the way, as regards collimating, some people go so far as to peel the rubber armouring off the bins to get to the collimating screws. This is an unnecessary, ham-fisted, way to do it. All that's needed is to lift the rubber with a screwdriver, just enough to be able to get to a screw. The rubber will then sink back when the job is complete.

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PostPosted: Fri Sep 02, 2016 7:42 pm 
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Hi Brian,
The false colour is awful.
The resolution is awful.
The binocular is awful.
I got a bad one.

The 15x70 Revelations are good, especially the ones with multicoating on all surfaces.
If they are in collimation.

Regards,
David


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PostPosted: Sat Sep 03, 2016 11:54 am 
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The problems you cite in your own bins David, don't seem to occur in mine. To borrow a cliche, your bins must have been made on the late night shift.
This morning, I bought the Skymaster 15X70's that I've been drooling over to complement the 25X70's. They seem to be fully-collimated, but I'll find that out when I attach them to the binocular mirror-mount for the star test: even the slightest miscollimation will cruelly reveal itself in the rock-steady mirror view. All things being equal, the Skymaster series get good reviews on the web for their price.
By the way, it's surprising how many camera shop staff know so little about optical gear; they just want to make a sale. At least, my man didn't drop the bins on the carpet! :wink:

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PostPosted: Thu Sep 08, 2016 12:28 pm 
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It's been recently said on the grapevine David that the range of budget binoculars, including the Skymasters, are stopped down at the prisms, so that a 70mm aperture is reduced to 62mm or thereabouts. Can you elaborate on this?
Would this contravene the Trades Discription Act?

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PostPosted: Thu Sep 08, 2016 12:58 pm 
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Hi Brian,
63mm maybe.
Most binoculars don't hold up to claims.
Some are complete fabrication.
The authorities are useless.
The internet lies and scams are beyond comprehension.

What do you expect for £50?
If they work they should cost £300. At least they would in the past.

Just go with the flow. It is not worth being upset.

Regards,
David

Some 10x50s are 10x39.
Optolyth Alpin 12x50 is 12x42. Owners love them. Light weight.

Foton 5x25 is 30mm stopped internally to 25mm. Oversized objectives.
The Soviets don't usually lie about optics although they lie about most other things.


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PostPosted: Thu Sep 08, 2016 3:45 pm 
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Do you know if my soviet-era TENTO 20X60's are stopped down? The only criticism I have is that the eye-lenses are too small for specs wearers. Of course, we can always take our specs off to use them!
Alas, there's some fungus on one of the prisms now, but at the edge of the field-of-view.

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PostPosted: Thu Sep 08, 2016 5:32 pm 
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Hi Brian,
I doubt if the 20x60 Tentos are stopped down.
I think they are 20x, so the exit pupil should be 3mm.

You could put a straight edge at the 60mm front and see if moving it inwards makes a difference.
At different position angles.

Or a 55mm mask and see if the exit pupil is reduced.

Regards,
David


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PostPosted: Fri Sep 09, 2016 1:56 pm 
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What a good idea for testing! The thing is David that I bought the X15 Skymaster's thinking that they'd collect a bit more light than the TENTO's, although I do like the Russian bins and wouldn't want to part with them.
At least, the eye-lenses are bigger in diameter on the Skymaster's. If I'd known about the stopping down earlier, I might have purchased the HELIOS Apollo 15X70's or a similar spec instead.

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PostPosted: Fri Sep 09, 2016 4:11 pm 
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Maybe 2 bits of masking tape 55mm apart at the front to see if exit pupil cut off, moving as necessary to find limit.

Regards,
David


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