• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Zeiss Diascope successor (1 Viewer)

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
 
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.
 
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?
 

Attachments

  • Art star 2.jpg
    Art star 2.jpg
    51.1 KB · Views: 279
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
 
Last edited:
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
 
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.
 
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.
 
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.
 
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.
 
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... o:D
 
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).
 
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?
 
Had a quick look through a Gavia

  • sharpness was superb
  • minimal CA @ 30x but noticeable at highter magnification (conditions: gray sky and backlighting + I'm quite sensitive to CA)
  • contrary to SzimiStyles' observations, I found the focus & zoom rings to be rather stiff in this sample; smooth but relatively high resistance
    (had a brief gander through a Meopta S2 82 right after and the difference in ease of focussing was significant to me)
 
I had a chance to try the Gavia out in my local reserve shop today, priced at £1595.
.... r 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).

For what it's worth I was in precisely that position and decided to spend that extra for the Kowa - a better instrument optically (and it really counts at high power), a good stay on case to protect it, more accessories available and my preferred focusing method tipped the balance. Additional cost per birding trip really isn't that high! Personally, it would have needed to be nearer the £1200 mark to offset the benefits of the big beast.
 
Warning! This thread is more than 8 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Users who are viewing this thread

Back
Top