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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

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  1. J

    Astigmatism as an Aberration in Optics

    No, Brock, I just used the edge condition as a basis for the "explanation" but pointed out in post #8 that astigmatism gets progressively worse towards the edges because the tangential and sagittal focal "planes" diverge. Btw, the astigmatism in a 10x42 FL along with its marginal eye relief was...
  2. J

    Astigmatism as an Aberration in Optics

    Brock, I think "bad" is a little strong, undesirable would be better. All bins probably have some astigmatism to a greater or lesser extent, though I can't see any in my 10x42 SV, and that's good enough for me. I wouldn't know how to boost the edge of a 60° AFoV anyway. I think we can safely...
  3. J

    Astigmatism as an Aberration in Optics

    No idea what that's got to do with optics. Perhaps the author was the sole occupant of my ignore list ;). John
  4. J

    zeiss 8/10x54 HT

    Henry, What a typically clear and simple demonstration! Perhaps you got the World Cup special edition for Italian fans. It does look like their flag out at the edges. John
  5. J

    Astigmatism as an Aberration in Optics

    Along with field curvature (not to be confused with distortion) it's the cause of a progressive sharpness loss towards the field edge. Unlike field curvature it cannot be corrected by refocussing. It's described here http://en.wikipedia.org/wiki/Astigmatism as third-order astigmatism and on...
  6. J

    Astigmatism as an Aberration in Optics

    There is often confusion between astigmatism of the eye and astigmatism as an aberration in an optical instrument, so I thought I would attempt an explanation. It has even been suggested that one could cancel out the other but this is not the case. I stand open to correction for the following...
  7. J

    Best Video Head with Arca Swiss type Quick release

    Kimmo, I was unaware of the introduction of the Sirui VH-10 and VH-15 heads, which would appear to be another couple of nails in the coffins of the established manufacturers. I have a Sirui L-10 tilt head on my monopod and an M3204 carbon fibre tripod. Their products are very well thought-out...
  8. J

    A Word on Coatings

    I took this step months ago and would encourage anyone interested in furthering their knowledge on Birdforum to do likewise. I wish he'd go away and start an American branch of http://en.wikipedia.org/wiki/Official_Monster_Raving_Loony_Party ;). John
  9. J

    Why no 8x56 or 10x56 SLC HDs in U.S.?

    Brock, That's conceivable but, in view of Swarovski's service reputation, I think unlikely. John
  10. J

    Best Video Head with Arca Swiss type Quick release

    Probably not, but AFAIK that was not the OP's requirement. John
  11. J

    Why no 8x56 or 10x56 SLC HDs in U.S.?

    Well, you could try Orniwelt. Their German prices would correspond to €1634 and €1679 for 8x56 and 10x56 respectively without sales tax. You would of course have to pay shipping and your own import duty. If Orniwelt are unwilling to export and you are still determined, you could PM me and I...
  12. J

    Best Video Head with Arca Swiss type Quick release

    See post #4. The Berlebach 510 weighs 700 g, not much heavier than a Manfrotto 700 RC2, and better in every way. There would be no point in stacking an Arca-swiss adapter on top of another QR system and I know of no other good lightweight heads lacking QR. John
  13. J

    Best Video Head with Arca Swiss type Quick release

    For the past two or three years I have used a Berlebach 552, which uses Arca-Swiss plates. It is stable, lightweight (820 g) and very well made (all CNC) and is rated up to 6 kg. There is adjustable tilt friction, independantly lockable pan and tilt, and a pre-load lever for scopes or cameras...
  14. J

    Conquest HD & SLC 15x56s A Review

    Lee, Many thanks for the excellent review. It's often suggested that the 15x56 format is a very specialised market but the interest this thread (and a review of the 15x56 SLC on Cloudy Nights) has generated would seem to disprove that. As you point out, the view through tripod-mounted...
  15. J

    Meostar 10x42 HD

    I would say that the eye relief of the 10x42 Meostar will almost certainly be inadequate for glasses wearers. The size of the eye lens is a fairly good indication of eye relief; see this thread: http://www.birdforum.net/showthread.php?t=243816&highlight=relationship+eye+relief. It is just not...
  16. J

    1 1/4" Eyepiece Adapter for Kowa TSN-883 or884

    Malcolm, I have used three different astro adapters on Zeiss Diascope and a Swarovski ATM scopes, so I think you have some options, even if you are going to have to get something made. A Kowa equivalent of this Baader Diascope adapter...
  17. J

    Zeiss Lens Wipes

    These will be familiar to many but as questions about lens cleaning crop up frequently, I thought it worth a mention. I came across them at my local drug store and they were no more expensive than the usual household items. Zeiss state that they contain no perfumes and that there are only two...
  18. J

    1 1/4" Eyepiece Adapter for Kowa TSN-883 or884

    Malcolm, You should estimate the diameter of the "window" in the scope body under the eyepiece. There would be no point in using eyepieces with a larger field stop than this as they would vignette. As a guide see this link...
  19. J

    The Price of Fluorite (Calcium fluoride)

    Thanks for those insights, Henry. In view of the price differences and the marginal optical advantages (and some physical disadvantages) of CaF2 over FPL-53 and similar fluorite crown glasses from Hikari and LZOS, it's surprising that CaF2 still finds applications in telescopes. Surprising too...
  20. J

    The Price of Fluorite (Calcium fluoride)

    I recently received a catalogue from Edmund Optics in which they are offering plano-convex fluorite lenses (uncoated) in diameters ranging from 12,5 mm to 50 mm for scientific applications. They have a surface quality of 40-20 scratch/dig. The 50 mm lenses cost €375 (or €300 for >6 pcs.), so...
  21. J

    Experience new birding

    Well, Lee I know it doesn't offer any significant advantages, but there is a BaK4HT and also a SK2HT, which could conceivably be used in SP prisms. HT now seems to be chasing ED, SD etc. as a marketing term, so if Zeiss can justify it I'm sure they will use it. Regards, John
  22. J

    Experience new birding

    The dealer, Orniwelt has often jumped the gun in the past. They're not showing anything new but they're showing the FLs as discontinued, so it looks like it's going to be 32 mm HTs. John
  23. J

    Minimum magnification with a big spotter?

    Lars, I believe the Celestron scope takes 1,25" astronomical eyepieces, which allow a maximum field stop of 27 mm. If the focal length is 540 mm the maximum achievable FoV would be around 2,9°, which you would get with a 24 mm Hyperion, 24 mm Televue Panoptic or 32 mm Plössl. If there are any...
  24. J

    UV filter size for Leica Apo 65

    Hi Frederico, I have just checked a Leica catalogue, which specifies E67. I think this must be M67 x 0,75 as there don't seem to be any other pitch sizes in that filter thread diameter. John
  25. J

    Comment by 'John Russell' in media 'Egyptian Goose'

    They're Egyptian Geese. Now common in Europe but didn't know you had them in South America too. John
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