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Some advice on Zoom Eyepiece


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5 hours ago, des anderson said:

Just to put my pennyworth in, save up and get a Badder zoom,either a 2nd hand or a new one. There excellence on the moon and planets are worth there weight in gold; there not bad on some DSO as well. Des

The problem I have with the Baader Zoom is the lack of eye relief when used with the screw-up/down eye cup.  I've tried them (Mark II and Mark III versions) at star parties with my observing eyeglasses, and I can't see the whole field of view at any setting with eyeglasses.  I found these numbers in this post on CN:

Here I list the measured USABLE EYE RELIEF.
1st is the total eye relief
2nd is the depth of lens recess
3rd is the net usable eye relief.

Hyperion Zoom at 8mm 16.7-4 = 12.7mm
Hyperion Zoom at 12mm 13.7-4 = 9.7mm
Hyperion Zoom at 16mm 12.3-4 = 8.3mm
Hyperion Zoom at 20mm 14.3-4 = 10.3mm
Hyperion Zoom at 24mm 16.9-4 = 12.9mm

In Bill Paolini's review of the Mark IV version, he measured the eye relief at 15mm to 19mm with 1.5mm of ER loss due to eye lens recession/concavity.  Perhaps it has improved in this version?

By comparison, I measured these usable eye relief numbers on the Regal/Olivon zoom (I have both for binoviewer usage, and they're mechanically identical) with the eye cup screwed off (how I use them and many other eyepieces with removable stiff cups):

  • Celestron Regal Zoom at 8mm: 16mm
  • Celestron Regal Zoom at 10mm: 15mm
  • Celestron Regal Zoom at 12mm: 13mm
  • Celestron Regal Zoom at 16mm: 13mm
  • Celestron Regal Zoom at 20mm: 13mm
  • Celestron Regal Zoom at 24mm: 14mm

I find the "feels like" eye relief to be more like 17mm to 19mm across the board because at no time do I have to press in and touch the top of the bare metal housing.  I can safely hover above the eyepiece and still take in the entire field.  I can't use them without removing the eye cup.  The Regal Zoom has a large eye lens that is 26mm in diameter which is the same size as the 18mm and 25mm Meade HD-60 eyepieces.  Both have a measured 18mm to 19mm of usable eye relief which matches closely with their "feels like" eye relief in use.

Clearly, since the Hyperion Zoom's eye cup can be removed, and if the eye lens is flush with the top of the housing as it is in the Regal, it would have as good or better eye relief than the Regal Zoom with the eye cup screwed off except possibly at 16mm.  Since the ones I've used at star parties weren't mine, I didn't attempt to remove the eye cup, so I can't confirm this.

I also find the Regal/Olivon zoom quite serviceable for the $60 to $65 I've paid for each, especially in binoviewers with a barlow element operating at about 3x.  The Hyperion Zoom is roughly 4x as expensive, so it would be hard for me to justify buying it because I just don't find myself using zooms in mono-viewing mode except when packing light for road trips.

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