Quote:
Originally Posted by MortonH
Do orthos play well with Barlows or do they lose something when you do that? I'd like one around 5mm but that would mean awfully short ER. More tempted to try a 9mm with Barlow. What do you think?
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Hi Morton,
I have all of the UO HD orthos from 4mm through to 25mm. The 4mm and 25mm are series 2 HD's and recent additions, which I added last year when they were released. The 6mm, 7mm, 9mm,12.5mm and 18mm are series 1 HD's and I have had those for about 12 years. I had previously owned a full set of UO Volcano top orthos (4mm through 25mm) for well over 10 years. Notwithstanding that I have a case full of premium widefields, the orthos still see a good bit of use. I just love the clean clinical view they offer.
Most orthos are fairly similarly engineered and constructed for a given focal length and how they barlow is a lot more dependant on the focal length of the ortho and the specific barlow, than it will be on the brand of ortho. The shorter focal length orthos (12mm or less) will generally barlow very well in any high quality barlow. In many cases it can be an advantage to barlow a short focal length ortho because it extends the short eye relief. The longer focal length orthos (18mm and 25mm) can barlow very well in some barlows and not so well in others. Some barlows can extend the eye relief excessively making it harder for some people to find and hold the exit pupil (usually shorter barlows like Orion Shorty Plus, or Celestron Ultima) and some barlows with a narrow clear aperture (eg UO 2.8X KLEE) can cause them to vignette, notwithstanding that these barlows are high quality. I have found the Televue 1.8X and 2X barlows, as well as the 2.5X TV Powermate, work fine with the longer focal length orthos, as does the Zeiss, Baader, TMB and AP BARCON barlows. Any good quality 2" barlow, or powermate should work well also.
Cheers,
John B