Esprit 100mm f/5.5 ED apochromatic triplet refractor with field flattener

by Sky-Watcher Print

What would you like to print?
(Reviews and Documents/Videos will not be printed)

Basic Product Information
Full Description
Tech Details
Supplied Accessories
Recommended Accessories

More product information
This premium quality Sky-Watcher Esprit 100mm ED triplet apochromatic refractor has:

• 100mm f/5.5 apochromatic triplet optics using Ohara FPL-53 ED glass
• thread-on Schott glass doublet field flattener
• rotatable dual-speed rack and pinion 2.7” focuser
• 2" star diagonal with 99% reflectivity dielectric mirror coatings
• Canon EOS DSLR camera adapter
• 9 x 50mm right-angle correct-image finderscope
• tube rings with a Losmandy-style "D-plate" dovetail for installing on a German equatorial mount
• aluminum clad foam-lined hard case
• two-year warranty

The substantial Sky-Watcher Esprit 100mm apochromatic triplet uses a lens of Ohara FPL-53 extra-low dispersion (ED) glass, flanked by two carefully chosen mating lenses of premium BK-7 Schott optical glass. The trio delivers crisp, high-fidelity wide-field images of celestial objects. The views are unmarred by the faint but annoying halo of unfocused violet light (chromatic aberration) often seen around bright stars and solar system objects in other large aperture fast focal ratio doublet and triplet refractors. A separate thread-on Schott glass doublet field flattener provides pin-point star images across the entire 40mm image circle for superb astrophotography.

The 100mm Sky-Watcher Esprit triplet utilizes the most modern optical glasses and fabricating techniques to deliver the ultimate in small aperture high-fidelity astronomical observing and imaging. Each lens element is individually inspected for purity and absence of striations and other image-degrading imperfections. Each element is then pitch polished to exacting standards of optical fabrication and performance by highly skilled opticians and tested on an optical laser bench to rigidly controlled optical standards. The result is a high-quality, diffraction-limited optical system performing to the theoretical limits of its aperture – one that will give you years of imaging and visual observing satisfaction.

Features of this Sky-Watcher refractor . . .

Apochromatic ED triplet refractor optics: 100mm (3.94”) aperture, 550mm focal length, f/5.5 focal ratio. The triplet objective lens uses mating elements of premium BaK-2 and BK-7 Schott optical glass, from one of the world’s most-respected glass manufacturers. The center ED element is precision-polished from high grade FPL-53 ED (Extra-low Dispersion) glass from Ohara, Japan's premier glass maker.

Fully multicoated optics: Each air-to-glass surface in the Sky-Watcher Esprit 100mm triplet objective lens has high transmission antireflection multicoatings on all air-to-glass surfaces for high light transmission, minimal light scatter, and excellent contrast.

Retractable dew shield: The aluminum dew shield retracts to allow the scope to fit into its hard carrying case, and extends when the scope is in use. The dew shield slows the formation of dew on the lens in cold weather to extend your undisturbed observing time. It also improves the contrast, similar to the effect of the lens shade on a camera lens, when observing during the day or when there is excessive ambient light at night, such as a neighbor’s backyard security light. The telescope measures 18.3" long with the dew shield retracted and 24.5" long when it is fully extended.

Thread-on doublet field flattener: When you are ready for imaging, the Esprit 100mm includes a doublet field flattening lens that can be threaded onto the optical tube to transform your scope into an exceptional wide-field imaging Instrument. Using optical grade Schott BK-7 glass and multicoatings on all air-to-glass lens surfaces, the field flattener provides sharp, in-focus stars across a large fully-illuminated 40mm image circle. This is ideal for DSLR cameras (APS-C sensors and even those with 35mm equivalent sensors, although there will be some vignetting at the corners of a full-sized sensor) and for virtually all CCD cameras. Back focus is 69.8mm. A Canon EOS camera adapter (the most popular DSLR camera brand for astronomical imaging) is standard equipment. Optional Celestron M48 camera adapters are available for Nikon and Sony/Minolta Maxxum cameras.

Dual speed 2.7” rack and pinion focuser: The precision-made and mechanically ultra-smooth, backlash-free, rack and pinion focuser has a giant 2.7" diameter drawtube with a 2” accessory adapter. This rotatable focuser offers dual-speed focusing and has an engraved focusing scale. There are two coarse focusing knobs. The right knob has a smaller concentric knob with 10:1 reduction gear microfine focusing over the full 112mm focuser travel. This provides exceptionally precise image control during high magnification visual observing and critical DSLR or CCD imaging. The large focus knobs have ribbed gripping surfaces so they are easy to operate, even while wearing gloves or mittens in cold weather. A lock knob lets you adjust the tension on the drawtube to accommodate varying eyepiece/photo accessory loads, as well as firmly lock in a photographic focus.

2” dielectric star diagonal: The supplied standard equipment 2” mirror star diagonal of the Esprit 100mm slips into the focuser drawtube’s 2” eyepiece/accessory holder. The 2” compression ring diagonal has 99% reflectivity dielectric mirror coatings for high light transmission. A 1.25" compression ring accessory adapter is standard.

Finderscope: The Sky-Watcher Esprit 100mm comes with a 9 x 50mm right-angle correct-image finderscope that is fully multicoated to insure maximum brightness and contrast. The finder shows the star field in its correct upright and right-reading orientation, as it appears to the naked eye and on star charts.

Mounting rings and dovetail: The Sky-Watcher Esprit 100mm apo has dual hinged split-ring tube rings to fit the 5.75" diameter aluminum optical tube. They are bolted to a Losmandy-style "D-plate" dovetail that fits directly into the dovetail slot on the head of many of the most popular medium to heavy capacity German equatorial mounts, such as the Celestron CGEM DX and CGE Pro and the Losmandy G11.

Shipping/storage case: The scope comes in foam-fitted aluminum-clad shipping/storage hard case.

Two-year warranty: The Sky-Watcher Esprit 100mm triplet apo is protected by a two-year limited warranty against flaws in materials and workmanship.

Highest Useful Magnification:
This is the highest visual power a telescope can achieve before the image becomes too dim for useful observing (generally at about 50x to 60x per inch of telescope aperture). However, this power is very often unreachable due to turbulence in our atmosphere that makes the image too blurry and unstable to see any detail.

On nights of less-than-perfect seeing, medium to low power planetary, binary star, and globular cluster observing (at 25x to 30x per inch of aperture or less) is usually more enjoyable than fruitlessly attempting to push a telescope's magnification to its theoretical limits. Very high powers are generally best reserved for planetary observations and binary star splitting.

Small aperture telescopes can usually use more power per inch of aperture on any given night than larger telescopes, as they look through a smaller column of air and see less of the turbulence in our atmosphere. While some observers use up to 100x per inch of refractor aperture on Mars and Jupiter, the actual number of minutes they spend observing at such powers is small in relation to the number of hours they spend waiting for the atmosphere to stabilize enough for them to use such very high powers.
Visual Limiting Magnitude:
This is the magnitude (or brightness) of the faintest star that can be seen with a telescope. The larger the number, the fainter the star that can be seen. An approximate formula for determining the visual limiting magnitude of a telescope is 7.5 + 5 log aperture (in cm).

This is the formula that we use with all of the telescopes we carry, so that our published specs will be consistent from aperture to aperture, from manufacturer to manufacturer. Some telescope makers may use other unspecified methods to determine the limiting magnitude, so their published figures may differ from ours.

Keep in mind that this formula does not take into account light loss within the scope, seeing conditions, the observer’s age (visual performance decreases as we get older), the telescope’s age (the reflectivity of telescope mirrors decreases as they get older), etc. The limiting magnitudes specified by manufacturers for their telescopes assume very dark skies, trained observers, and excellent atmospheric transparency – and are therefore rarely obtainable under average observing conditions. The photographic limiting magnitude is always greater than the visual (typically by two magnitudes).

Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

1.16 arc seconds
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
Back Focus:
The weight of this product.
16.3 lbs.
Telescope Type:
The optical design of a telescope.  Telescope type is classified by three primary optical designs (refractor, reflector, or catadioptric), by sub-designs of these types, or by the task they perform.
Based on Astronomy magazine’s telescope "report cards", scopes of this size and type generally perform as follows . . .
Terrestrial Observation:
Observing terrestrial objects (nature studies, birding, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial observing. Scopes with apertures under 5" to 6" are generally most useful for terrestrial observing due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes. 
Lunar Observation:
Visual observation of the Moon is possible with any telescope. Larger aperture scopes will provide more detail than smaller scopes, thereby getting a higher score in this category, but may require an eyepiece filter to cut down the greater glare from the Moon's sunlit surface so small details can be seen more easily. Lunar observing is more rewarding when the Moon is waxing or waning as the changing sun angle casts constantly varying shadows to reveal craters and surface features by the hundreds.  
Planetary Observation:
Very Good
Binary and Star Cluster Observation:
Very Good
Galaxy and Nebula Observation:
Terrestrial Photography:
Photographing terrestrial objects (wildlife, scenery, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial photography. Scopes with focal ratios of f/10 and faster and apertures under 5" to 6" are generally the most useful for terrestrial photography due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes.
Lunar Photography:
Photography of the Moon is possible with virtually any telescope, using a 35mm camera, DSLR, or CCD-based webcam (planetary imager). While an equatorial mount with a motor drive is not strictly essential, as the exposure times will be very short, such a mount would be helpful to improve image sharpness, particularly with webcam-type cameras that take a series of exposures over time and stack them together. Reflectors may require a Barlow lens to let the camera reach focus. 
Planetary Photography:
Star Cluster / Nebula / Galaxy Photography:
Optical Coatings:
Fully multicoated
View Finder:
9x50mm RA
2 years
There are currently no Cloudy Nights reviews associated with this product

User Ratings/Reviews from our Customers (
Overall Product Rating: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics(0.00)   # of Ratings: 0   (Only registered customers can rate)

We haven't recommended any accessories for this product quite yet... check back soon or call one of our experts (1-405-364-0858).
This product does not have supplied accessories... or supplied accessories have not been assigned.
No documents have been associated with this product.
No videos have been associated with this product.
There are currently no formulas associated with this product
Esprit 100mm f/5.5 ED apochromatic triplet refractor with field flattener

Click icon(s) below & hover image above for zoom

Esprit 100mm f/5.5 ED apochromatic triplet refractor with field flattenerAnother view of the Sky-Watcher 100mm Esprit triplet ED apo refractor.The hard case for the Sky-Watcher 100mm Esprit triplet ED apo refractor.
   · No ratings/reviews   Only registered users can submit ratings - Register Here
Our Product #: S11410
Manufacturer Product #: S11410
Price: $2,499.00  FREE ground shipping - Click for more info
Congratulations. Your order qualifies for free ground shipping within the 48 contiguous United States.

 E-mail this product to a friend E-mail this product to a friend

Your Email:  
Your Friend's Email:  
Confirm Friend's Email:  

  200 characters or less

An email containing a link to this product has been sent to the email address you provided.

Clear Skies!

 Have a question? Do you have a question about this product?
 Found a better price? Found a lower price? Click to let us know... or call 800-422-7876 before you buy.

If you’ve found a lower delivered price on this product, let us know about it below. We’ll do our best to meet or beat that price and will get back to you within one business day with our best offer. Thanks for giving us the opportunity to give you a better deal.

Your Name:  
From Who:  
Context:  Magazine AdOnline
Website Address:  
Cut and paste the web address into the box above
Your Email:  
Confirm Email:  

We’ll do our best to meet or beat that price and will get back to you within one business day with our best offer. Thanks for giving us the opportunity to give you a better deal.

Clear skies,

The Sky-Watcher Esprit 100mm ED apochromatic triplet refractor has the premium high contrast/high resolution/flat field optical performance you need to let you use it as the heart of your observing and wide field imaging system.

. . . our 38th year