Focal extenders are similar to a Barlow or tele-negative lens, but there is one important difference between the two that you will want to take into consideration, especially if you plan to use the Explore Scientific Focal Extender for imaging and astro-photography.
When you use a standard Barlow or tele-negative lens to increase the magnification of your optical system, your results will be dependent on where you place the Barlow in the optical chain. For instance, if you put a 2X Barlow lens in front of your diagonal instead of behind it (Barlow-Diagonal-Eyepiece as opposed to Diagonal-Barlow-Eyepiece), you won't get 2X magnification in both set-ups. The magnification varies with placement. However, with an Explore Scientific Focal Extender, even if the distance is changed, the magnification remains the same. You can place your Focal Extender anywhere along the optical chain between an eyepiece or a camera, and if you are supposed to get 2X magnification, you will get 2X magnification.
When it comes to imaging, this is a critical difference, because you may want to introduce an accessory like a flip mirror or filter wheel in between the Focal Extender and a CCD camera, which would increase the distance to the focused image. This difference in design allows users to rest easy, whether they are pumping up the magnification of a lower power eyepiece for visual observations or using their Explore Focal Extender in imaging applications.
More Magnification Choices without Sacrificing Eye Relief A good Focal Extender adds some real versatility to your telescope accessory line-up. First of all, it allows you to increase the magnification of any eyepiece with the same barrel size that you already own. In other words, 3 eyepieces offer 6 magnification choices with the addition of a focal extender. Secondly, most of the time, lower magnification eyepieces have better eye relief than higher power models. When using a focal extender to increase your magnification, you get to enjoy the generous eye relief of the lower power eyepiece, and that's quite a bonus, especially for eyeglass wearers or for those with fast telescopes who can really push high magnification eyepieces. Remember, we make focal extenders in 2X, 3X and 5x models, so there is something for every style of telescope.
Optimized Optical Design Explore Focal Extenders are optimized through each design, fabrication, and testing process to produce high contrast, high resolution images.
Durable Coatings & Finishing Touches Each of the four elements in your Explore Scientific Focal Extender is fully multi-coated with EMD enhanced coatings, resulting in bright, sharp images; and every element has blackened edges to reduce internal reflections and increase contrast.
Tapered Barrel for Extra Security The insert barrel of each extender is double-tapered to allow smooth insertion to, and removal from, a telescope's eyepiece holder, focuser or diagonal, however the wide dimension of the taper helps prevent the focal extender from falling out of the telescope should the set-screw holding it in place become loose.
Producing optics for amateur astronomers that can be relied upon to deliver research-quality images requires a solid design, careful fabrication, multiple tests, and continued diligence to make sure we are always doing everything we can to produce a cutting edge, quality product. This is what we do at our facilities at Explore Scientific, and to insure your satisfaction, we back each eyepiece with the Explore STAR Transferrable, Extended Life of the Product Warranty, so you can keep exploring!