| This Explore Scientific 4" refractor has:
• big 4" aperture fully multicoated achromatic doublet refractor optics
• collimatable objective lens cell for fine-tuning the images
• big 8 x 50mm finderscope
• 2" dielectric star diagonal with 1.25" eyepiece adapter
• tube rings with carry handle and Vixen-style dovetail plate
• bright high contrast deep space views, plus excellent performance inside the solar system
• lifetime transferrable warranty
This highly portable 4" achromatic refractor optical tube (only 25.5" long, with a weight of 11.3 pounds) is a sensational value! It has a 102mm (4") diameter multicoated doublet objective lens (663mm focal length f/6.5). Its diffraction limited optics are sharp and well suited to serious deep space observing of binary stars, star clusters, and the brighter nebulas and galaxies, in addition to excellent high contrast planetary and lunar images. The objective lens cell is fully collimatable, using push/pull collimation screws, so you can optimize your image quality.
The 4" Explore Scientific is a great grab-and-go scope for quick looks at the sky when mounted on a suitable altazimuth mount. It’s good enough optically to be the heart of a reasonably-priced serious observing system when mounted on one of the many equatorial mounts and go-to altazimuth mounts from Celestron, Meade, iOptron, and others.
Some chromatic aberration is visible on stars and objects of 2nd or 3rd magnitude and brighter, as you would expect in an achromatic refractor with such a fast focal ratio. However, the spurious color is well controlled and not unreasonable, thanks to careful optical design, and has little effect on deep space observing. Most observers feel the relatively limited amount of chromatic aberration visible is a small price to pay for the scope’s many other virtues of portability, sharpness, contrast, and optical clarity.
Details About This Optical Tube . . . - Achromatic refractor optics: 4" (102mm) aperture, 663mm focal length, f/6.5 air-spaced crown and flint glass doublet lens. Tube diameter is 3.96" (100.7mm) and the tube length with dewshield installed is 25.5" (648mm). Scope weight is 11.3 pounds (4.67 kg).
- Collimatable lens cell: The 4" Explore Scientific lens is precision collimated at the factory to give optimum performance. Although you may never need to adjust optical alignment, the ES102D allows for collimating the lens set should the telescope ever require it due to a fall or very rough handling.
- Multicoated optics: Fully coated on all surfaces with multiple layers of antireflection materials for high light transmission and good contrast.
- Internal light baffles: Multiple internal knife-edge baffles in the optical tube mask and deflect unwanted stray light for improved contrast.
- Dew shield: The removable 190.5mm (7.5") diameter dew shield slows the formation of dew on the lens in cold weather to extend your undisturbed observing time. Also improves visual and photographic contrast by shielding the lens from off-axis ambient light (the neighbor’s yard light, moonlight, etc.)
- Dust covers: Front and rear dust covers are provided.
- Dual-speed Crayford-style focuser: 2" focuser, with adjustable tension and lock knobs. The 2" eyepiece holder uses a non-marring brass compression ring to hold the supplied 2" star diagonal in place without scratching the diagonal barrel. The precision-made 2" focuser has dual-speed focusing. There are two coarse focusing knobs. The right knob also has a smaller concentric knob with 10:1 ratio reduction gear microfine focusing. This provides exceptionally precise image control during high power visual observing or critical DSLR or CCD imaging. The focus knobs have ribbed gripping surfaces so they are easy to operate, even while wearing gloves or mittens in cold weather.
- Dielectric star diagonal: 90° viewing angle first surface mirror 2" star diagonal with 1.25" eyepiece adapter. The diagonal uses durable 99% reflectivity for maximum light transmission and long life.
- Finderscope: 8 x 50mm straight-through achromatic design, in a dual-ring six-point adjustment bracket with a quick release mounting shoe. Focuses by loosening the trim ring behind the objective lens cell, screwing the lens cell in or out to focus, and tightening the trim ring to lock in the correct focus.
- Dovetail tube mount: The optical tube comes with two split and hinged tube rings for installing the optical tube on your mount. The rings are connected to a dovetail mounting plate that slips into the standard dovetail groove on Astro-Tech Voyager, Explore Scientific, Celestron, Meade LX80, and Vixen mounts. A carrying handle is conveniently fitted to the top of the tube rings
- Lifetime warranty: All Explore Scientific telescopes and telescope accessories are covered under a One Year Limited U.S.A. Warranty against defects with proof of purchase, but you can extend this limited warranty to a lifetime transferrable Explore STAR warranty good within the United States by simply filling out the product registration and submitting it to Explore Scientific within 60 days of purchase.
This extended warranty program is also available to the person who receives your gift of an Explore Scientific telescope. You don't need to give them the purchase receipt, just remind them to fill out the registration and submit it, and Explore Scientific will take care of the rest.
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