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Review - Baader Zoom 8-24mm Eyepiece
Posted: 7 November 2014
Updated: 2 December 2014

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photo Hyperion Zoom 8-24mm Mark III Eyepiece
Baader Planetarium

While helping out in the OPT booth at the Arizona Science & Astronomy Expo, 1-2 November 2014, I purchased a Hyperion Zoom 8-24mm Mark III Eyepiece from OPT. My main reason for purchasing a zoom eyepiece was to use it at star parties when I'm representing the Oracle Dark Skies Committee. Having a good zoom eyepiece will be considerably more convenient with people in line to look through the telescope than swapping eyepieces multiple times.

This review will discuss using the Baader Zoom Eyepiece on two telescopes: my 8" LX200-ACF in the observatory and my ETX-105PE (one of the telescopes I use at star parties).

The eyepiece is a complete system, as seen in the photo below. There is a nice soft case for it, the eyepiece, an adapter (for Canon DSLRs, although it wasn't obvious to me what part that was or how it attaches to the eyepiece), two different eyepiece cups, and an end cap. The eyepiece is compatible with both 1.25" and 2" eyepiece holders. There is no instruction sheet nor warranty information included, and none could be found on their web site. The OPT product page does state that the warranty is one year.


8" LX200-ACF

My initial tests of the Baader zoom eyepiece were on the 8" LX200-ACF. I first used it with the 2" nosepiece and inserted the eyepiece into my 2" star diagonal:


When removing the 1.25" nosepiece I discovered that it is actually in two sections (and so is the 2" nosepiece). If you are not careful you can unscrew both sections completely. There is no problem doing this; you just have to put them back together again. My first real (and only) problem was that I could not figure out how the included eyecups were supposed to be attached. So, I left them off; I really didn't feel the need for them anyway from my dark site.

The first object I viewed was a waxing gibbous moon. Using the 24mm focal length, the moon's disk did not quite all fit in the field-of-view (FOV) on the f/10 8" telescope. With the center of the FOV in-focus the very edge of the FOV was just slightly out-of-focus at 24mm. Changing the focal length by rotating the eyepiece tube was smooth from 24mm to 8mm, with clickstops at 20mm, 16mm, and 12mm. Edge focus improved as the magnification was increased. The focus is essentially parfocal throughout the range and there is no change in the eyepiece length as the zoom amount is changed.

This image taken with an iPhone 5s afocally (handheld) shows the various zoom amounts:

Click or tap on image for larger version

I then viewed Mars, which was very low in the southwestern sky. Mars is currently very small so no details were visible. But the convenience of having a zoom eyepiece was readily apparent. I switched to the 1.25" nosepiece and there was no discernable difference, which isn't surprising since the eyepiece is really sized for a 1.25" holder.

Next, I viewed M13 (Great Globular Cluster in Hercules). The view was good throughout the focal length range, although it was somewhat faint at 12mm and 8mm focal lengths. I also viewed M57 (Ring Nebula). It was also good at all focal lengths. The bright sky from the waxing gibbous moon was a factor in how good these two objects appeared.

I did some solar observing using the zoom eyepiece and an 8" full-aperture solar filter. It was very handy to locate a sunspot at the lowest magnification and then zoom into the sunspot to see more details.

My last tests of the Baader Zoom Eyepiece were done using a 2X Barlow Lens (left) and a 3X TeleExtender (right):

photo photo

At all focal lengths except 8mm, the views of Mars and the moon were good using the 2X Barlow Lens. 8mm (effective 4mm) was too much magnification for the 8" telescope (and exceeded the theoretical maximum magnification for an 8" of 400X). With the 3X TeleExtender, the zoom eyepiece focal lengths of 24mm, 20mm, and 16mm were good. 12mm and 8mm were pushing the magnification too much. In general, a Barlow Lens or TeleExtender can be used with the zoom eyepiece. If the seeing conditions allow you can probably use the entire range of focal lengths.


I used the Baader zoom eyepiece on my ETX-105PE:


It worked as expected, although there was one minor nuisance with the eyepiece on the ETX. The eyepiece holder screw on the ETX was blocked by the width of the eyepiece, as seen here:


The screw can still be tightened and loosened but access to it is difficult. Of course, the problem can be eliminated by NOT inserting the eyepiece all the way into the eyepiece holder. If a filter is attached to the zoom eyepiece, the eyepiece will not go all the way into the hole so the screw is accessible in that case.

I first viewed Mars, low in the southwest. The view was surprisingly good, with a hint of the North Polar Cap being visible using 12mm and 8mm. I viewed the nearly full moon. The entire lunar disk was visible in the FOV at 24mm, 20mm, and 16mm. This is an afocal image of the moon taken at 24mm using a handheld iPhone 5s:


The view using a moon filter was easy on the eye and sharp at all magnifications. Also viewed M13 (Hercules Globular Cluster) and M57 (Ring Nebula). Both were fine objects in the ETX at all magnifications. I did notice a slight focus change when focused using 24mm and then zooming to 8mm. If I focused using 8mm, there was no obvious change in focus going back to 24mm.


If you have an afocal adapter that can handle the large diameter of the Baader Zoom Eyepiece, being able to change the magnification without needing to swap to another eyepiece can be a big convenience. I don't have an afocal adapter that can accommodate the 2.25" zoom eyepiece diameter so wasn't able to do astrophotography through the eyepiece except by handholding the camera lens over the eyepiece. But on brighter objects like the moon, you can easily do handheld afocal images at various magnifications using the same eyepiece. If you use a Canon DSLR, you can use the Baader Canon adapter for eyepiece projection astrophotography.


The mechnical and optical quality of the Baader Planetarium Hyperion Zoom 8-24mm Mark III Eyepiece are excellent. The ease of changing magnifications without needing to swap eyepieces or generally change focus really makes using a high quality zoom eyepiece a joy. It is a necessity if you frequently allow others to look through your telescope.

The OPT product page for the Hyperion Zoom 8-24mm Mark III Eyepiece has a lot of additional information about the eyepiece, including specifications, so check that out if you want to learn more.

This zoom eyepiece will get used a lot in the observatory, especially when I have visitors. And it will be a tremendous asset for use at star parties.

2 December 2014

A reader provided this information:

In your review of the Baader Hyperion 8-24 zoom eyepiece you indicated that you did not see how to change from the large to the small eye cup. Based on your review I bought one from OPT and received it today. I discovered that to remove the large eye cup you grasped the metal part just below the eye cup, above the rubber grip area, and unscrewed that section. Then you can snap the small eye cup over the remaining section. This allows more room for your nose when looking through the eyepiece.

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