Hello, my name is Adam. I'd like to ask for help in purchasing an eyepiece for my SkyWatcher BK 909 AZ3 90/900 telescope. I'd like to see, for example, Jupiter's belts and Saturn's rings. I was considering buying a 5mm eyepiece, but I'm not sure if it's a good idea.
As for now, I have two eyepieces: a 25mm and a 10mm, which came with my telescope.
Why not try a 2X Barlow? That will give you two the same thing as a 12.5mm and 5mm ocular. You’ll also get greater eye relief so it will be easier to use.
Tony Gondola · Jan 24, 2026, 02:20 AM
Why not try a 2X Barlow? That will give you two the same thing as a 12.5mm and 5mm ocular. You’ll also get greater eye relief so it will be easier to use.
That's a very good idea. I've read about the Barlow lens, and it makes sense. Instead of spending $75 on a 5mm eyepiece, I can just spend $20 on a Barlow lens. Besides, it's better because it zooms in on the image depending on the eyepiece and the Barlow lens it's mounted on.
Thank you for your help.
Hi, Adam.
When I started this hobby a few years ago I had the same questions.
Albeit not a ‘prime’ eyepiece, I decided to try a zoom to see what works and consider primes later on. i.e. get something I knew would cover all bases and be of fairly high quality.
I got the Baader Hyperion 8-24mm Mk IV. It fits 2” and 1.25” holes and has been such a delight to use.
I’ve only bought one other prime since because the Baader does most of what I want visually on my Celestron EdgeHD 8 (2030mm) and Esprit 120ED (840mm, close to your 900mm). I mostly to photography these days, but whenever I want to do visual (or show others things), I pull out the Baader zoom. On my first scope (William Optics Zenithstar 81, 559mm) I had not troubly picking out Saturn’s rings.
Perhaps something to consider.
Cheers.
Paul
BigLizardAstro · Jan 24, 2026, 07:21 AM
Tony Gondola · Jan 24, 2026, 02:20 AM
Why not try a 2X Barlow? That will give you two the same thing as a 12.5mm and 5mm ocular. You’ll also get greater eye relief so it will be easier to use.
That's a very good idea. I've read about the Barlow lens, and it makes sense. Instead of spending $75 on a 5mm eyepiece, I can just spend $20 on a Barlow lens. Besides, it's better because it zooms in on the image depending on the eyepiece and the Barlow lens it's mounted on.
Thank you for your help.
I wouldn’t get one that cheap! Get one that’s roughly the same cost as that 5mm you were thinking about.
Bear in mind that higher magnification does not necessarily mean a better and clearer image. For example, if you are magnifying an image by say 200 times, you are also magnifying the atmospheric effects by that much as well as the effects of Earth’s rotation. You will find yourself constantly adjusting the aim of your telescope on an untracked AZ mount to see an unstable view at too high of a power using too short of a focal length eyepiece. I have a SkyWatcher 102mm on an AZ mount (500 mm focal length) and I get great views of Saturn using a 2x Barlow and a TeleVue 11mm Plossl. A fringe killer or contrast booster also helps on achromatic refractor telescopes like mine. I have to adjust the aim of the telescope quite a lot on my AZ mount, but it's manageable.
Steven Fanutti · Jan 24, 2026, 05:03 PM
Bear in mind that higher magnification does not necessarily mean a better and clearer image. For example, if you are magnifying an image by say 200 times, you are also magnifying the atmospheric effects by that much as well as the effects of Earth’s rotation. You will find yourself constantly adjusting the aim of your telescope on an untracked AZ mount to see an unstable view at too high of a power using too short of a focal length eyepiece. I have a SkyWatcher 102mm on an AZ mount (500 mm focal length) and I get great views of Saturn using a 2x Barlow and a TeleVue 11mm Plossl. A fringe killer or contrast booster also helps on achromatic refractor telescopes like mine. I have to adjust the aim of the telescope quite a lot on my AZ mount, but it's manageable.
thank you very much for your tips