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HyperFlex 7E1, Seben 8-24 Zoom, BCO 18 & 10 compared


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Dear Stargazers!

as a follow up of the discussion on 12mm planetary eyepieces: [settled] 12 mm planetary eyepiece ortho or zoom I though I share with you my experience with my newly acquired EPs which arrived last Monday from Aunty FLO 😉. Just before placing an order, I had a change of mind and went for the 10 mm BCO instead the Q-turret barlow. So here is the list of EPs in this comparison:

  • Hyperflex 7E1 Zoom: 7.2 - 21.5 mm (which has already a very good reputation as we all know)
  • Baader Classic Ortho 18 mm
  • Baader Classic Ortho 10 mm
  • Seben Super Plössl Zoom: 8 - 24 mm (same as Skywatcher, Starguider, Zhumell, Agena, ....)


So here are the contenders. I am well aware that all those have been reviewed and compared, but I though I share my experience with them in the hope that somebody finds it useful.

The comparison was done with my 180 SkyMax Mak-Cass, set up with the original VB, an Omegon ADC, a TS-1.25" star diagonal and then the EPs. In this configuration, which works really well to correct for atmospheric dispersion, my scope has an effective focal length of 2940 mm. I had the chance to use the EPs two nights in a row, one with ok seeing and yesterday with good seeing conditions. After cooling the scope for about an hour (where I try to place the scope outside for cooling when the outside air temperature is the same as the storing temperature of the Mak, about 24 deg C) I went to work comparing the EPs. Each comparison was done for about an hour, where I switched EPs back an forth, using the orthos as baseline for quality.

Comparison on Saturn at 10mm, so the BCO 10, the Hyperflex at 10 and the Seben at 10 were compared. That's at 294x magnification:

  • The BCO 10 is really sharp (as expected) and to me surprisingly comfortable to use. I was initially sceptical about the 8 mm eye relief, however for me it works and thus gives superb views. 52 deg FOV is also very comfortable. The Cassini Division was clear and easily discernible.
  • The Hyperflex, even though with a smaller FOV, was very close to the performance of the BCO 10. Also expected, I read a lot of good reviews on the Hyperflex. Again Cassini Division nice and clear.
  • The Seben zoom also performed, however noticeably less good than the Hyperflex or even the BCO 10. Basically I missed some sharpness, obviously in comparison with the BCO, but also with the Hyperflex. For my eye it was harder to make out the Cassini Division through the Seben.

Comparison on Jupiter at 18 mm: BCO 18, Hyperflex and Seben at 18. That's at 163x magnification. Here a picture of how Jupiter should have looked like to describe what I managed to see:


  • Again the BCO 18 gave superb views, sharp with lot's of contrast (as expected for an ortho). Quite some structure visible in the cloud bands.The two main bands where easy to see, no problem there. I was able to see the short dark band below the lower main band, as well as the eddy structure to the right of it (referring to the picture above). I have to say I was impressed.
  • The Hyperflex zoom was quite up there with the BCO, maybe a bit less contrast, but I still could make out the short dark band.
  • With the Seben zoom I had a hard time discerning the short dark band as well as the eddy structure to the side of it. Would I not have known where to look, I would have missed that. So noticeably less contrast in the Seben.

Summary comments:

  • Using the BCOs as baseline, they both produce very sharp and contrast rich views. The 52 deg FOV is very comfortable to view planets. As said I was surprised how comfortable the BCO 10 is to use even though with its short eye relief (8 mm). Obviously not useful to people who have to wear glasses.
  • The Hyperflex zoom is quite close to the BCOs, even though with a narrower FOV. Sharpness and contrast are comparable. Probably one would not switch too often to the BCOs and happily observe with the Hyperflex.
  • The Seben zoom is a good EP, but not there with the Hyperflex or the BCOs. To my eyes its a workable zoom, but you miss out on details of the planets with respect to sharpness and contrast. I can recommend going for a Hyperflex (as so many have said before) if your are looking for a zoom EP.
  • These three EPs, BCO 10, 18 and the Hyerflex are a very functional base set for a 180 Skymax. BCO 10 very sharp on Saturn (looking forward to see Mars with that). BCO 18 produces contrast rich views of Jupiter. And the Hyperflex for everything between 136x - 408x 😉. Maybe another fixed focal length EP in the 14-15 mm range, just to bridge the gap between the BCO 10 and 18. However the Hyperflex does a great job at that already.
  • A yes, and I really can only recommend an ADC. Without it the cloud band details on Jupiter disappeared even in the BCO 18 and the typical blue/red colour seams were clearly visible.

Clear skies,


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Nice comparison :thumbright:

29 minutes ago, alex_stars said:
  • The BCO 10 ..... 52 deg FOV is also very comfortable...
  • The Hyperflex, even though with a smaller FOV, was very close to the performance of the BCO 10.

The Hyperflex has stated FOV of 40 @ 21.5mm and 60 @ 7.2.  I estimate it's about 55 @ 10mm, so it should have looked similar to, if not a little larger than, the BCO.  
(I have the Hyperflex but not the BCO so can't compare them as you have).

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16 minutes ago, globular said:

Nice comparison :thumbright:

The Hyperflex has stated FOV of 40 @ 21.5mm and 60 @ 7.2.  I estimate it's about 55 @ 10mm, so it should have looked similar to, if not a little larger than, the BCO.  
(I have the Hyperflex but not the BCO so can't compare them as you have).

Thanks, glad you enjoyed it. I did not estimate the FOV of the Hyperflex yet, I focused more on comparing sharpness and contrast. My impression was that it is a bit narrower than the BCOs.

Also @Louis D posted in the preceding thread (https://stargazerslounge.com/topic/361158-settled-12-mm-planetary-eyepiece-ortho-or-zoom/page/2/?tab=comments#comment-3937213) this:


My version from Surplus Shed has between 9mm and 11mm of measured, usable eye relief, a measured AFOV of 33 to 49 degrees, and weighs 180g.

which I had in mind I guess.

Either way, the FOV of the Hyperflex is not at all limiting when observing planets. Maybe one day I should do a detailed FOV estimate of both (BCO and Hyperflex) at 10 mm.....

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Nice review - thanks for posting it :thumbright:

I reckon my clone of the Hyperflex 7.2mm - 21.5mm zoom has an AFoV of around 38 degrees at 21.5mm widening out to about 55 degrees at 7.2mm. This is derived by comparing the illuminated field with other eyepieces I have of known (and trusted !) AFoV.


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