C90 Maksutov spotting scope, 90mm, 1.25" 38x, photo tripod mounting block

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This Celestron spotting scope has:

• 90mm f/13.3 Maksutov-Cassegrain optics
• 45° viewing angle diagonal (eyepiece holder) 
• upright/right-reading images suitable for both terrestrial and astronomical use 
• 8 x 21mm erect image finderscope
• built-in T-threads for easy 35mm or DSLR camera attachment
• 32mm Plössl eyepiece (38x)

    Like all Maksutov optics spotting scopes, such as the ultra-premium Questars, the Celestron C90 is exceptional for observing anything that is small and distant and needs a lot of power to resolve clearly. It provides sharp, high contrast images of distant birds and wildlife, details that are free from the distracting spurious color you’ll find in comparably-priced achromatic refractor spotters. Optically very nice, this Celestron 90mm Maksutov has the optical performance to keep you busy observing the land and sky for many years to come.

Features of this spotting scope . . .

  • Maksutov-Cassegrain optics: 3.5” (90mm) aperture, 1200mm focal length, f/13.3 multicoated optical system. The 11” long optical tube weighs only 3.1 lbs with finderscope and eyepiece attached.

  • Multicoated optics: The system’s Maksutov corrector lens is fully coated on both sides with multiple layers of antireflection materials for high light transmission and good contrast.

  • Internal focuser: Focuses by moving the primary mirror fore and aft in the optical tube by means of a large focusing knob on the rear cell.

  • Close focusing: Twenty turns of the slow, but very precise, focusing knob of the C90 moves the focus from the horizon down to a very close 20’. This is not as great a burden as it might first seem, as only a few turns of the knob in the middle of its rotation range will cover most of the medium to long distance observing situations the C90 is designed for. However, the relatively slow multi-turn focusing makes the C90 more suitable for observing stationary targets from distant locations, rather than trying to follow fast-moving birds in flight.

  • Erect image eyepiece holder: Unlike conventional 90° star diagonals (eyepiece holders) that reverse the image, the supplied 45° viewing angle erect image 1.25” diagonal provides correctly-oriented images that are identical to what you see with your unaided eye (upright and correctly oriented left-to-right so that printing is correctly oriented and readable and you can easily follow subjects in motion).

  • Eyepiece: Fully multicoated 1.25” 32mm (38x) Plössl eyepiece with a 1.4° field of view (73’ at 1000 yards). While this Celestron C90 Mak has excellent optics with sharp images, its field of view is somewhat narrow, due to the scope’s long focal length. However, the narrow field is entirely in keeping with the primary task of the scope, that of long distance observing. The eyepiece has a usable eye relief of 18mm for eyeglass use. In addition, any of nearly 200 different 1.25” astronomical eyepieces can be used with the C90, giving exceptional flexibility in choosing observing magnifications. For example, the optional Celestron 8mm to 24mm zoom eyepiece listed below provides very flexible viewing, with a zoom range of 50x to 150x, allowing you to instantly modify the magnification to suit the target distance and lighting conditions.

  • Finderscope: 8 x 21mm straight-through crosshair design with erect right-reading images that give you the same image orientation you see with your unaided eye. Three collimating screws let you line up the finder crosshairs precisely with the center of the eyepiece field. The finderscope must be removed from the scope before the scope is stored in its case, but a quick-release dovetail bracket makes removing the finder just a matter of seconds. The finder can be reinstalled on the scope just as quickly, and the dovetail bracket system assures that the finder will be properly lined up with the main optics once in place on the scope. The finderscope eye relief is quite short at 8mm. It will severely vignette the field of view for eyeglass wearers.

  • Tripod adapter: The scope has a mounting shoe with two standard 1/4”-20 thread mounting holes to let you use it on any suitable heavy duty photo tripod. The front hole is for visual use. The rear hole will help better balance the scope on the tripod when a camera is attached for terrestrial photography.

  • Built-in camera adapter: The star diagonal holder threaded onto the Cassegrain focus at the rear of the scope has standard T-threads built in that allow you to connect a 35mm or DSLR camera to the scope by simply adding an inexpensive optional T-ring to fit your camera. This converts the C90M to a very high power 1200mm focal length (24x) f/13.3 telephoto lens for long distance terrestrial nature photography. Such high magnification requires the use of a very sturdy photographic tripod for the sharpest images.

  • Carry case: Nylon backpack style carrying case.

  • Lifetime warranty: This Celestron spotting scope is protected by a limited lifetime warranty.
Magnification is the ability of a telescope to make a small, distant object large enough to examine in detail. If you look at the Moon (250,000 miles away) with a 125 power (125x) telescope, it's essentially the same as looking at it with your bare eyes from 2000 miles away (250,000 ÷ 125 = 2000). The same telescope used terrestrially will make an object one mile away appear to be only 42 feet away (5280 feet ÷ 125 = 42).
The magnification of a telescope is determined by dividing the focal length of the telescope (usually in millimeters) by the focal length of the eyepiece used (again, usually in millimeters; but in all cases by the same unit of measurement used for the telescope focal length). For example, a 2000mm focal length telescope and a 10mm focal length eyepiece will give you a magnification of 200 power (2000 ÷ 10 = 200). The same 2000mm telescope with a 20mm eyepiece will give you 100x (2000 ÷ 20 = 100).
Field of view 1000 yards:
Near Focus:
Eye Relief:
Eye relief is the distance from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the circular image is formed, sometimes called the “Ramsden Disk.” This is where your eye should be positioned to see the full field of view of the eyepiece. If you must wear glasses because of astigmatism, you’ll usually need at least 15mm of eye relief or longer if you want to see the full field of view with your glasses on.

A note on our eye relief figures: Quite often, our eye relief figures will differ from those of the manufacturer. This is because we measure the “usable” eye relief, while the manufacturers specify their usually-longer (but technically correct) “designed” eye relief.

The eye lens of the eyepiece is normally recessed below the rubber eyeguard or rubber rim of the eyepiece to keep the lens from being scratched during use. An eyepiece might have a “designed” eye relief of 15mm (and the eye relief will truly measure 15mm from the eye lens to where the image forms). However, if the eye lens is recessed 3mm below the eye guard, the Ramsden Disk forms only 12mm above the eyepiece body (the 15mm “designed” eye relief, less the 3mm of eye relief made unusable by having the eye lens recessed into the body of the eyepiece). This “usable” eye relief of 12mm (measured from the rolled-down eyeguard – the closest point you can get your eye to the eye lens – to where the image forms) is the eye relief figure we would measure and list in this website.

Why is it important to list the “usable” eye relief? For those people who don’t wear eyeglasses while observing, a few mm difference between the eye relief they expect from the manufacturer’s literature and the shorter eye relief they actually get in real life doesn’t mean a lot. They can simply move a little closer to the eyepiece to see the full field, and never realize that the eye relief is a little shorter than they expected. However, some people must wear eyeglasses while observing, because of severe astigmatism. These observers can’t move closer to the eyepiece if the eye relief is shorter than expected because their glasses get in the way. For these people, the real life “usable” eye relief is more important than the technically correct but sometimes not fully usable “designed” eye relief. We measure and list the actual usable eye relief so that people in the real world can pick the eyepieces that will work best for them.

Exit Pupil:
The circular image or beam of light formed by the eyepiece of a telescope. To take full advantage of a scope's light-gathering capacity, the diameter of an eyepiece exit pupil should be no larger than the 7mm diameter of your eye's dark-adapted pupil, so that all of the light collected by the telescope enters your eye. (The eyepiece exit pupil diameter is found by dividing the eyepiece focal length by the telescope focal ratio.) Your eye's ability to dilate declines with increasing age (to a dark-adapted pupil of about 5mm by age 50 or so). For those in this age group, eyepieces with exit pupils larger than their eyes can dilate to simply waste their telescope's light-gathering capacity, as some of the scope's light will fall on their iris instead of entering their eye.
Twilight Factor:
A number used to compare the effectiveness of binoculars or spotting scopes used in low light. The twilight factor is found by multiplying the size of the objective lens (in mm) by the magnification and then finding the square root of that result. The larger the twilight factor, the more detail you can see in low light. A twilight factor of 17 or better if usually required for reasonable low light use.
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.
A binocular or spotting scope whose body is clad in rubber or polyurethane armor is said to be armored. Armor can be applied for looks, a better grip, noise-proofing, etc. An armored body does not guarantee that a binocular or spotting scope is waterproof, although most waterproof optics are armored.
Photographic Focal Length:
The effective focal length of a spotting scope/camera adapter combination when the scope is used as a telephoto lens. The photographic focal length divided by 50 will give you the magnification of the combination compared to your standard camera lens.
Photographic Focal Ratio:
The photographic “speed” of a spotting scope/camera adapter combination when used for photography. The smaller the “f/ratio,” the faster the exposure (to capture birds in motion), or the dimmer the light level in which you can successfully shoot.
The weight of this product.
5 lbs.
Limited Lifetime
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  • Soft case
  • 8 x 21mm erect image finderscope
  • 45° image erecting diagonal and 90° viewing port
  • 32mm 1.25" Plössl eyepiece (38x)
  • Flip-down lens cover
  • Eyepiece holder covers
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Celestron - C90 Mak, 45° And 90° viewing Maksutov-Cassegrain, waterproof, 38x

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Celestron - C90 Mak, 45° And 90° viewing Maksutov-Cassegrain, waterproof, 38xFeature image name not indicated
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Our Product #: C90M
Manufacturer Product #: 52268
Price: $199.50  FREE ground shipping - Click for more info
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MSRP: $345.95

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This Celestron spotting scope puts good quality Maksutov-Cassegrain optics for long-distance observing (both terrestrial and astronomical) into a compact and lightweight body that's easy to use in the field  . . .

. . . our 38th year