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Old Saturday 6th August 2016, 17:33   #51
Troubador
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I have a request for those who will get a look at the new Zeiss scope at Birdfair.

Could someone among you try to do a quick 60X star-test? Ideally someone who is familiar with star-testing can do this, but anyone can learn how do do it by Googling something like "telescope star-test" and practicing a little.

Hopefully there will an example of a glitter point of the sun returning from some small round shiny object between maybe 20m and 50m (too close and it may not be small enough to act as a point source, too far and there may be too much air turbulence to see clear diffraction rings). A car in sunlight has many such glitter points in the head/tail lights and trim areas or you could bring your own little shiny object. Rack the focus back and forth and observe the diffraction rings on either side of focus and the point of light at best focus. These reveal the level of spherical aberration and various defects like astigmatism, coma, turned edge, zones, pinching and poorly made roof prisms. One accurate description of a star test is far more informative of the true optical quality of a particular scope specimen than all the subjective descriptions we are likely to read of what birds look like through it.

Henry
Henry, the Zeiss booth overlooks a short area of grass (with no access), then water and reeds and beyond a wide area of lake with some islets. There are no twinkly metal or glass bits out there as far as I can remember. There will be highlights off water but I wouldn't think this would be of a constant quality.

Lee

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Old Saturday 6th August 2016, 19:13   #52
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Henry I have just remembered there is a single-storey building about 30 metres away and I think it has windows so there could be a glint off the glass at some time during the day.

Didn't remember this at first because, well, you know how it is: you go to Bird Fair, set in the middle of a bird reserve, in order to assess bird-watching instruments by looking at, yes, birds, and you tend to ignore buildings .

Anyway I have found a great tutorial on star-testing on the internet and printed it off and will give it my best shot if I get an opportunity.

Lee
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Old Saturday 6th August 2016, 20:47   #53
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Lee,

DO NOT USE A REFLECTION OF THE SUN FROM A FLAT GLASS PANE!! Sorry for yelling, but that would send a full sized dangerously bright reflection of the sun into your eye that would be plenty bright enough to destroy your eyesight!. A small spherical or convexly curved object MUST be used, so that the reflection of the sun seen through the scope appears as a tiny star like point. The smaller the object (ball bearing, glass bead, Christmas tree ornament, light bulb, etc) the closer it can be placed to the telescope and still form a point source. I sometimes use a small silvered glass ornamental ball about 20mm in diameter at about 50m for star-testing small telescopes and binoculars. A good place would be near the building with the sun behind you. Place the object in the open air with no hot surfaces like pavement between you and it. It's best if it's at least a few few feet above the grass, perhaps on top of a tripod or dangling from the tripod handle.

Thanks for volunteering and please be careful.

Henry

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Old Saturday 6th August 2016, 22:34   #54
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just wonder why not start the zoom range at 25x...
FOV will suffer a bit from it,
Hi,

that question is easily answered - they traded a smaller zoom range for higher AFOV at the low maginification end, as did all manufacturers with wide-angle zooms to varying degrees.

With the new Zeiss we have a 2x zoom with an AFOV of around 60 degrees at the low mag end and around 80 at the short end, as with Leica, Meopta and the Swaro ATS/STS wide angle EPs.
The Kowa WA zoom for the big bodies and the Swaro ATX/STX eyepiece module have 2.4x with about the same AFOV range as the 2x models mentioned above, which makes them quite sweet.

For astro scopes there's 1.7x zooms with a constant AFOV of 80 degrees (Speers Waler Zoom or the discontinued Astro Zoom Kit).

Joachim
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Old Sunday 7th August 2016, 09:21   #55
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Lee,

DO NOT USE A REFLECTION OF THE SUN FROM A FLAT GLASS PANE!! Sorry for yelling, but that would send a full sized dangerously bright reflection of the sun into your eye that would be plenty bright enough to destroy your eyesight!. A small spherical or convexly curved object MUST be used, so that the reflection of the sun seen through the scope appears as a tiny star like point. The smaller the object (ball bearing, glass bead, Christmas tree ornament, light bulb, etc) the closer it can be placed to the telescope and still form a point source. I sometimes use a small silvered glass ornamental ball about 20mm in diameter at about 50m for star-testing small telescopes and binoculars. A good place would be near the building with the sun behind you. Place the object in the open air with no hot surfaces like pavement between you and it. It's best if it's at least a few few feet above the grass, perhaps on top of a tripod or dangling from the tripod handle.

Thanks for volunteering and please be careful.

Henry
Thanks Henry and you can shout as loud as you like about this.
You don't get to carry intruments outside at Bird Fair and there is no access to the grass area between the Optics Marquee and the lake to place an object.

But I will take the star-test tutorial printout and see what opportunities arise.

Lee
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Old Thursday 11th August 2016, 23:13   #56
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Perhaps take an artificial star along?
http://www.rothervalleyoptics.co.uk/...llimating.html
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Old Sunday 14th August 2016, 20:57   #57
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Originally Posted by henry link View Post
I have a request for those who will get a look at the new Zeiss scope at Birdfair.

Could someone among you try to do a quick 60X star-test? Ideally someone who is familiar with star-testing can do this, but anyone can learn how do do it by Googling something like "telescope star-test" and practicing a little.

Hopefully there will an example of a glitter point of the sun returning from some small round shiny object between maybe 20m and 50m (too close and it may not be small enough to act as a point source, too far and there may be too much air turbulence to see clear diffraction rings). A car in sunlight has many such glitter points in the head/tail lights and trim areas or you could bring your own little shiny object. Rack the focus back and forth and observe the diffraction rings on either side of focus and the point of light at best focus. These reveal the level of spherical aberration and various defects like astigmatism, coma, turned edge, zones, pinching and poorly made roof prisms. One accurate description of a star test is far more informative of the true optical quality of a particular scope specimen than all the subjective descriptions we are likely to read of what birds look like through it.

Henry
I may get to have a look at this scope on Friday as it's being released to the RSPB optics shops as soon as its released at the Bird Fair. I think it will depend on Viking Optical bringing a sample over to my local reserve and they may all be busy/at the Bird Fair.

In any case I will get a chance to artificially star test it in due course as there is a roof light in the reserve shop that makes a good artificial star and I'm there in my volunteer capacity every two weeks, (and if a good bird turns up sooner).

This is the first Zeiss scope the RSPB shops have stocked (to my knowledge), so it will be interesting to see how it it received.
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Old Sunday 14th August 2016, 22:15   #58
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Hi,

that question is easily answered - they traded a smaller zoom range for higher AFOV at the low maginification end, as did all manufacturers with wide-angle zooms to varying degrees.

With the new Zeiss we have a 2x zoom with an AFOV of around 60 degrees at the low mag end and around 80 at the short end, as with Leica, Meopta and the Swaro ATS/STS wide angle EPs.
The Kowa WA zoom for the big bodies and the Swaro ATX/STX eyepiece module have 2.4x with about the same AFOV range as the 2x models mentioned above, which makes them quite sweet.

For astro scopes there's 1.7x zooms with a constant AFOV of 80 degrees (Speers Waler Zoom or the discontinued Astro Zoom Kit).

Joachim
I guess you could draw that conclusion.
Perhaps bigger AFOV looks a bit more impressive and is more "modern".
Not sure it's the most versatile in practical use. A larger exit pupil and FOV (@20-25x) for example is sometimes preferred.
But it might be better for digiscoping.

Nikon and Meopta (and Swaro on ATS) offers two different zooms, one with larger AFOV and one with a bigger zoom range, so one can pick what suits you best (or both).
I guess Zeiss will not for the Gavia. They offer the Diascope with a 25-75x zoom instead.

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Old Monday 15th August 2016, 07:45   #59
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Hi Zeiss Team,

Do you have any plan for New 65 mm scope in Conquest Gavia series in near future.

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Old Friday 19th August 2016, 21:18   #60
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I had a chance to try the Gavia out in my local reserve shop today, priced at 1595.

First impressions, good build quality but maybe easily scuffed rubber armoring. Smooth even focusing clockwise to infinity. There appears to be no case supplied in the box, maybe it's coming.

I tried it out on the internal artificial star in the shop, I'll do my best to describe what I saw. Outside focus pretty good circular rings well defined, maybe slightly thicker at ten o'clock but only slightly. Purple flare to outer edge of "star".

Inside focus the inner rings were missing replaced by a white disc and were not so well defined, so spherical aberration not as well corrected as some scopes I've tested. Don't know what the disc indicates but the rings were still pretty round so good collimation.

The artificial star was not resolved as well as some scopes I've tested and I got the impression there was a bit of CA there too.

The scope had a bit of vignetting at the very close focus end. I checked this a few times as I wasn't sure if there was any at all but I'm pretty sure it's there I'm guessing there is a way of knowing for sure by shining a light inside the objective lens end?

I couldn't manage to take any pictures of the star images.

In the reserve shop the Gavia is pitched against the Swarovski 65HD with 25-50 zoom or for 400 more you can buy a cased Kowa 88 with 25-60 zoom. I know what I would do if I was in a position to spend that sort of money (on a new scope).

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Old Sunday 21st August 2016, 18:12   #61
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Hi dipped,

I got your PM. Sorry for the delay in responding to your post. Thanks for doing the test.

I have a few questions:

What kind of artificial star did you use and how far was it from the scope? I ask because an 85mm scope needs a very small artificial star to form a genuine point source at a short distance. Also spherical aberration is usually worse at close distances.

When you say "inside focus" do you mean moving the focus in the direction of infinity?

How far out of focus were the patterns you evaluated? In other words how many rings could you see? I ask that one because the non-circular appearance of things like astigmatism, coma and pinching is most evident at only a few rings out of focus and tends to even out and become more circular at higher ring counts.

I'm not sure I know what you mean by "vignetting" at close focus. If there is a loss of clear aperture you can check it be shining a collimated flashlight beam through the eyepiece end from about a foot or more behind the eyepiece. Then measure the diameter of the bright circle projected on a flat surface just in front of the objective lens. I wouldn't expect any loss in the Gavia since it uses a focusing lens rather than a moving prism.

Henry
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Old Sunday 21st August 2016, 18:21   #62
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Did anyone have a chance to look at it at the Bird Fair? I had a very quick look and it seemed a very sound instrument but without any technical knowledge or time for meaningful comparison couldn't go beyond saying that it appeared to give a pleasant sharp image. As for the lack of a case, even if Zeiss don't have an official one I'd be surprised if one of the big optics companies didn't produce one to fit.
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Old Monday 22nd August 2016, 00:48   #63
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Hi dipped,

I got your PM. Sorry for the delay in responding to your post. Thanks for doing the test.

I have a few questions:

What kind of artificial star did you use and how far was it from the scope? I ask because an 85mm scope needs a very small artificial star to form a genuine point source at a short distance. Also spherical aberration is usually worse at close distances.

When you say "inside focus" do you mean moving the focus in the direction of infinity?

How far out of focus were the patterns you evaluated? In other words how many rings could you see? I ask that one because the non-circular appearance of things like astigmatism, coma and pinching is most evident at only a few rings out of focus and tends to even out and become more circular at higher ring counts.

I'm not sure I know what you mean by "vignetting" at close focus. If there is a loss of clear aperture you can check it be shining a collimated flashlight beam through the eyepiece end from about a foot or more behind the eyepiece. Then measure the diameter of the bright circle projected on a flat surface just in front of the objective lens. I wouldn't expect any loss in the Gavia since it uses a focusing lens rather than a moving prism.

Henry
Hi Henry

Artificial star about 40 feet away small spot in upper part of light in attached picture. This was at 60x on my phone with point slightly defocused, to give you an idea of the size I'm working with. It "works", with a 95mm swaro ATX.

I've tested a number of scopes and seen v good SA correction at the range noted above. Maybe they are over corrected?

Yes inside focus towards infinity.

I could vary the rings from 3-4 to above. I didn't bring my 2.5x extender but will bring it next time to have another look.

I don't have access to a collimated flashlight but I will have another look in 2 weeks, but it appeared to lose a bit of aperture at very close range. This was different to other scopes I've tested (cheaper) where there is a steady reduction in aperture when you focus to near from far.

Hope this helps a bit, I'm not an expert but I think I know when I see good/bad samples even if I don't know what's causing the bad aberrations and I have to say I have seen some strange effects.

Hats off to you and others who manage to photograph the artificial stars as I am struggling with my 4x zoom compact. I have access to a Lumia G2 with 14-42 zoom, maybe that would be better on a tripod behind the eyepiece?
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Old Monday 22nd August 2016, 19:55   #64
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Dipped,

Thanks, 40' is OK as long as the diameter of the glitter point is no larger than the radius of the Airy disc of the scope.

I notice that you said focuser movement is clockwise toward infinity. If you see the scope again could you look though the objective lens while moving the focuser and try to determine whether the focusing lens moves forward or backward when changing the focus from close to distant? That would tell us whether the focusing element is positive or negative.

Looks like Pete Gamby has settled the question of who actually makes the Gavia scope. In the Kamakura thread on the Binocular Forum he said the Gavia is one of several "tailored versions of the (Kamakura) EDV-81".

Just about any flashlight is collimated well enough for the clear aperture test. Just make sure it's a least a foot or so behind the eyepiece.

Henry

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Old Tuesday 23rd August 2016, 12:33   #65
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Old Friday 26th August 2016, 11:19   #66
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Henry

You have probably realised from other posts that the weather at Bird Fair was hopeless for star testing. Using the technique on sparkly water during brief sunshine on the Sunday created strangely beautiful effects due to the changing geometry of the sources of the sparkles but I couldn't see any suitable gleams elsewhere. Sorry.

Lee
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Old Friday 26th August 2016, 12:05   #67
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I had a chance to 'play' with the scope for a while. I had great expectations before the Birdfair but left the stand with mixed emotions. Basic impressions.
  • Optical quality is great and I saw not much difference from the other big players.
  • Colour tone is close to neutral, maybe a bit into blueish.
  • Very disappointingly shallow depth of field. Just a millimeter turn on the focus ring and subject was out of focus.
  • Build quality and weight is excellent.
  • Focus ring is extremely smooth and easy to manage.
  • Sharpness was outstanding to me.
  • No considerable light loss at zooming in.
  • No sharpness loss at zooming in or out.
  • Touch and handling is very nice.

I'm not sure this will be my next toy. After moving between exhibitors like Leica, Swarovski, Zeiss and KOWA, I thought KOWA was still the winner.
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Old Wednesday 31st August 2016, 17:19   #68
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I had a chance to 'play' with the scope for a while. I had great expectations before the Birdfair but left the stand with mixed emotions. Basic impressions.
  • Optical quality is great and I saw not much difference from the other big players.
  • Colour tone is close to neutral, maybe a bit into blueish.
  • Very disappointingly shallow depth of field. Just a millimeter turn on the focus ring and subject was out of focus.
  • Build quality and weight is excellent.
  • Focus ring is extremely smooth and easy to manage.
  • Sharpness was outstanding to me.
  • No considerable light loss at zooming in.
  • No sharpness loss at zooming in or out.
  • Touch and handling is very nice.

I'm not sure this will be my next toy. After moving between exhibitors like Leica, Swarovski, Zeiss and KOWA, I thought KOWA was still the winner.
Starting mag at 30x, will impair on usable DOF, even more so with a scope with large aperture I suspect.
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Old Wednesday 31st August 2016, 17:35   #69
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HI is this scope (Gavia) better than Zeiss Victory Diascope? What are the main difference between the two scope. If one has to choose between the two, which one will be better.
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Old Wednesday 31st August 2016, 21:21   #70
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HI is this scope (Gavia) better than Zeiss Victory Diascope? What are the main difference between the two scope. If one has to choose between the two, which one will be better.
Diascope is still the top model in the Zeiss range.
Gavia is made in japan by Kamakura.
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Old Thursday 1st September 2016, 11:34   #71
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Gavia vs. Diascope

Just remembered 2 comments:
- bayonet system isn't equal within 2 models so you can't swap eyepieces - Diascope would gain with the Gavia wide zoom and the Gavia would gain with the 3.5x Diascope zoom...;
- Diascope isn't known by having a good quality control (many lemons, dust inside optics, ...), so a new updated version is needed, specially if it comes with a >=100mm version...
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Old Friday 2nd September 2016, 23:06   #72
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I had another look at the scope today and contrary to my post 60 it focuses counter-clockwise to infinity and the focusing lens moves towards the objective whilst doing so. I must have got confused in all the excitement and made a mistake.

I forgot to bring a torch with me but my phone "torch", did appear to show a constant aperture over the focusing range consistent with Henry's post that the scope uses a focusing lens not prism. (And I saw the lens move as above).
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Old Saturday 3rd September 2016, 15:05   #73
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I had another look at the scope today and contrary to my post 60 it focuses counter-clockwise to infinity and the focusing lens moves towards the objective whilst doing so. I must have got confused in all the excitement and made a mistake.

I forgot to bring a torch with me but my phone "torch", did appear to show a constant aperture over the focusing range consistent with Henry's post that the scope uses a focusing lens not prism. (And I saw the lens move as above).
Is there any modern scopes that use a focusing prism?
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Old Saturday 3rd September 2016, 15:23   #74
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Plenty of the cheaper ones.
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Old Sunday 4th September 2016, 10:48   #75
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Plenty of the cheaper ones.
Ok thanks, sounded like a cheap solution...and the Gavia is not cheap.
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