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doormij

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About doormij

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  1. No your wrong, there are several optical manufactories of optical equipment, you can actually order a binocular made to your specification or just a version of the shelf with your name printed on, all within the limits of their capabilities, flat field binoculars is not yet on their list or shelf I guess, but if you give them the optical formula they make it for you, low quantities are no problem like 100 units. They are privately owned companies, and they make (I guess) 95% of all the binoculars sold in the world including those from Zeiss... (Swarovski is still being made in Austria). The latest eyepieces sold by APM are designed by European optical designers contracted by APM/ Mark Ludes, and made in China, just like the eyepieces sold by Baader (Hyperion and Morpheus). Garrett
  2. The Nikon 10x50 WX has a 99% flat field: stars remain sharp to the edge of the 90 (!) degree apparent field thanks to the 2 field-flattener lenses between the eyepiece and the roof prism, rectilinear distortion of the Nikon WX is high, but angular distortion is very low; this is the best optical formula for a astronomical binocular you can get. Distortion is characterized in two ways. In positive or rectilinear distortion, the magnification increases toward the edge of the field: this causes straight lines to appear curved outward, even when the image is stationary. In negative or angular magnification distortion, the magnification decreases toward the edge of the field: this causes straight lines to appear projected onto a spherical surface curved toward the viewer, which is especially noticeable when the optical axis is moved — the image then appears to "roll away" near the field edge. But there are no straight lines in space, so we don't bother for this Rectilinear distortion ? (except for the moon and planets maybe). You can not make a binocular with flat field and both zero rectilinear and angular distortion; my Swarovski EL 10x50 has 95% flatfield and very low Rectilinear distortion but high angular distortion (straight lines on the edge are still straight but slightly less magnified) Light absorption for field flatteners is low: a few percent, the huge prism absorbs much more light. Image: Nikon WX Garrett
  3. With 'flat-field' lenses between prism and eyepiece it would be 99%... something for the Mark 3 upgrade!
  4. 20mm according to the APM specs, considerable less in real life?
  5. Thanks W. Bill Paolini... I have the APM 100mm ED APO, that's a F5.5 non flat refractor, edge sharpness could be a disappointment with the 17.5mm? Garrett
  6. 1) The anti reflection coating, at a certain angle the reflection of the daylight is as bright as in the left image. 2) False pupils (arrow) cause -at a certain angle- weak images of bright objects like the moon or streetlights despite being way out of view (10 degree or so). Reading http://www.scopeviews.co.uk/Swaro10x50EL.htm I read: 'the eye relief is to little for those wearing glasses', I wear glasses and there is plenty of eye relief; I set the eye-guard on position two. With a price tag of 2408 euro that's a lot of money, but a refractor as good as this binocular with tripod, binoviewer and 2 Delos eyepieces is likely double this amount. (and with the Swaro you get 10 year warranty/ service not one year as with the telescope).
  7. My latest: EL 10x50 roof, very good but not perfect, small: fit in my hand palm.
  8. Thanks for the mini review for the Lunt 10x50! I'm looking for the 7x ED version which should be equal if not better. The up coming ED version should not have any visible color aberration, but they are 20% more expensive. To my surprise the UK warranty is 3 years longer then a similar APM-brand version, but understand neither Lunt or APM can not repair any of these gas filled binoculars, they send it to China, with very long turnaround. If you have a faulty binocular after the warranty period, you better buy a new one. Many other brand of binoculars have Lifetime warranty, 2 years for APM is just preposterous. Garret van der Veen
  9. The Sony A7 s has more noise then the Canon 6 d or 5 dmk3, on http://www.centralds.net/cam/?p=7911 they write: "In our tests we found that the noise level is higher than that of 6D, 5D markIII but the low light, high iso performance of A7s is so special" Here the link for the Canon 6 D: http://www.centralds.net/cam/?p=7828 The darkframe comparison images show this clearly, here a combined darkframe image of the two cameras: What we all want is a real test under the stars, this means both cameras (a7 and the 6D) on two small telescopes (small lenses) on one mount, take several images: short and long exposure, high and low iso, brite nebula and a dark area of the sky and make the raw available for anyone to process. Garrett
  10. I will try collimate the scope with a weight on the focusser on a later date. It will not stress the corrector but it can stress the entire focusser on the tube, with a Newton the focusser is mounted on the side of the tube, maybe the tube bend. Yesterday I spent the evening to collimate the scope with the aid of the videocamera function of the Canon 5d on a defocused star by tweaking the primary mirror, well, I tried to do that: if I had a fine concentric diffraction rings on a defocused star in-focus, it was non-concentric on the other side... Then I tried the to get round stars, by tweaking the primary again but now the star on the monitor (still video) was exactly in focus... during adjusting the primary, I could see the shape of the star changing from more or less round to oval, when it was round (difficult to see because of the seeing!) I lock the bolts (push/ pull bolts) and did a series of exposures of M13. After stacking, the stars are more round then in my example of m92 in my first message of this topic. This means for round stars I must have exactly the right collimation, wich is very difficult to find... Now a good example, this image of ngc3079 wich was made on May 19th this year, it has perfect round stars. But 2 days before that night I made test images because of the non-round star shape issue, and indeed those images shows non round stars. But I did't change anything to the scope, a lucky exact collimated scope on that night? My conclusion for now is: 1) for round stars the scope must be collimated just right. 2) collimation of the scope is not stable, 3) with luck I have round stars on my images. 4) Or something on my scope is't right, tube stability, optical quality, the Wyne corrector... My scope is a very expensive ASA 16" Newton Astrograph, I have a way to long list of troubles with this scope and the Brand. Garrett van der Veen, The Netherlands
  11. Collimate with extra weight on the focusser, yes thats is a good idea, and that can be made simple: a counterweight tied to the focusser with a string. Garrett
  12. To Ronin: any true (fast) Newton telescope needs a coma corrector. Last spring I had mixed results, some like the image above and some with perfect round stars, I change nothing to the scope, the scope is permantly mounted for imaging. My guess is the collimation of the scope changes. If I collimate visual there is hardly any weight on the focusser, but for imaging the total weight is 5.8 kilogram (13 pound) (the camera is Peltier cooled with water cooling assist), this extra weight may change collimation, hence the question how to collimate the scope with the videofunction of the imaging camera on a defocused brite star, to get perfect round, concentric diffraction rings on a defocused star (in and out). But maybe there are also other problems/ things involved like tube currents, wind during imaging... (because in the m 92 image only brite stars are not round) Garrett, The Netherlands
  13. I have collimate my large Newton Astrograph with all my visual collimation tools -laser, Cats-Eye- to perfection, checked also the mirror clamps; all three are not touching the mirror. Then I made a image of m 92 with the Wyne coma corrector, and as you can see the brite stars are not round, on some of my older images they are perfect round! With the videocamera function of my Canon 5 d imaging camera I notice the diffraction rings of a defocused brite star are not concentric. So I want to collimate the scope with the Wyne corrector on a defocused star with the Canon 5 d video function, how to do that??? by tweaking the primary or secondary or the focusser? Garrett
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