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

Recent content by John Russell

  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...
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