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Here's a brief look at the Celestron 2800mm F/10.   Scroll down for the review.

Lens

Celestron 2800mm F/10 Nexstar GPS

Box contents

Front and rear caps, and a users manual.

Cost

Around $2599 starting price with tripod.

Build quality

Good

Additional information

Requires T-ring and focus adapter for your camera, about $50 for both.

Specifications below

 

Optical configuration

One zero power collector plate, one sperical primary mirror, and a secondary mirror.

Angle of view

0.72°x 0.50° (35mm camera)

Aperture

F/10--big hole!!

Full frame and APS-C

Adaptable to any modern camera.

Depth of field and focus scales?

Nothing

Minimum focus, image plane to subject

About 66 feet, or  20 meters. 

Minimum focus, end of lens barrel to subject

About 64 feet, or 19.5 meters.

Hard stop at infinity focus?

No

Length changes when focusing?

No

Focus ring turns in AF?

N/A

Filter size

The lens front cover is 317mm in diameter.

Filter ring rotates?

N/A

Distance encoder?

N/A

Max magnification

About 660x useful power, realistically, under average viewing conditions, less than 220x.

Min. F/stop

F/10, fixed

Sony teleconverter compatible?

Yes, but it's crazy to use one.

Dimensions W x L (my measurements)

Optical tube is 12.25" x 22"   (311mm x 559mm)  overall length including camera adapter and focus knob about 25" or 635mm.

Maximum  extended length (my measurements)

About 25" or 635mm.                                                      

Weight bare (my scale)

Optical tube is listed as 65 lbs (29.5 kg), and the tripod is 26 lbs (11.8 kg)


Requisite product shots.

April2009/2800sdz.jpg
With A900.
April2009/2800bk.jpg
Backside
April2009/2800a900.jpg
Camera with T-ring and focus adapter
April2009/2800clssd.jpg
Right side
April2009/2800ft.jpg
Corrector plate (blue part), mirror in back, around center.
April2009/specsheet2800z.jpg
Specification sheet

 
 
The A900 was used for this review.                   
 
This is a quick review of the Celestron 2800mm telescope when configured for terrestrial viewing with a compatible camera, in our case, a Sony A900.  This will not be a review of the telescope as it was designed for, like nighttime star gazing.
 
This is not just a larger version of the Sony 500mm reflex lens, which incorporates auto-focus and a different optical design, though they both use mirrors to channel light through the aperture.  My copy has a carbon fiber optical tube, a fork mount and a Telrad reflex finder.  
 
If you're thinking of getting a lens to really pull the scene up close, this telescope may, or may not be what you're looking for, depending on application.  For birds, sports or action type photography, the much smaller and faster 500mm F/8 reflex lens would be much better.  If you want to take pictures of planets, the moon, or stars, and occasionally want to check out the distant harbor or neighbors back 40, this telescope would be very useful.  Don't buy this huge telescope for daytime use only, as it's extremely hard to get a good shot because of heat shimmer, hazy atmospheric conditions, and movement caused by wind, mirror actuation and user.  For all shots below I used at least ISO 400, mirror lock-up, and a corded remote.  You'll need to use manual mode on the camera to allow the shutter to fire because of "no lens attached" reading, and focus looking through the viewfinder while focusing with the telescope knob.  The EXIF data will show the aperture as F/1 and focal length as 0. 
 
Let's check out the "lens" as we'll call it, and compare it to the Sony 500mm F/8 reflex, reviewed here
 
Focusing takes 37.5 turns of the knob from close-in to infinity. 
 
Coma.  None.
 
Color looks blue when compared to Sony and Minolta lenses. 
 
Bokeh is typical reflex/mirror design donut shapes.
 
Color fringing.   None observed.


Light fall-off or corner darkening below is moderate, though you can't do anything about it. 
 

April2009/2800vig.jpg

 

Sample images next.

 

April2009/500over.jpg
Full scene, Sony 500mm F/8 reflex lens
April2009/2800over.jpg
Full scene, 2800mm F/10 Celestron

 

Above are the two full scene (uncropped) shots from the lenses.  The object for our comparison is the flower pot in the center, by the brick steps, (hard to see in the first pic).  The distance is about half a mile, or .47 miles, (756 meters) as measured by Google earth, and my car odometer.  The color differences are obvious, the telescope renders images somewhat blue, but I also took the 500mm reflex shots last, when the sun was lower and the colors warmer, so the differences in color aren't quite as dramatic as they seem here.

 

April2009/500b54.jpg
Sony 500mm F/8 reflex center crop
April2009/2800cf.jpg
2800mm F/10 center crop
April2009/500b54a.jpg
Sony 500mm F/8 reflex center crop upsized to same as 2800mm shot.

 

The 2800mm is really pulling in the scene here, with a huge jump in resolution over the 500mm as expected, especially by looking at the last shot which I upsized to show as a direct comparison.  The 500mm shot was 1/400 sec at ISO 200, the 2800mm was 1/1000 at ISO 800, which I really needed as any less shutter speed resulted in blur, even using mirror lock up and a corded remote.

 

To get a better idea about the detail size, the black lamp post is 3" (75mm) wide.  So I'm figuring the flower pot is about 18" (457mm) wide.  It looks like you may be able to make out 1" (25mm) newsprint from almost half a mile (756 meters) away!!

 

April2009/2800moon.jpg
Moon shot with 2800mm. 1/160 sec, ISO 400


This moon shot shows how much area is covered using a full frame camera.  You can't really get the entire moon in, but then again you don't shoot the moon when it's full, as there are no shadows to convey depth and detail.  This shot was a little blurry (do to high winds and an angle close to the horizon; I have better shots of course, but with a different camera system) so I'm not going to show any crops this time, I'll try again when I have more favorable conditions.  Incidentally, this moon picture was taken in daylight, before the sun went down.  I used levels adjustments to make it look better. 
 
 
My final thoughts. 
 
This review was just for fun, I wouldn't recommend the telescope as a daylight super telephoto camera lens, it's just to much trouble.  You need a high shutter speed for sharp shots, which requires a high ISO, and when you factor in heat shimmer, wind, haze in the atmosphere, and user error, it's very hard to get good shots.  I think an 11", 2800mm telescope is way too much, but you may consider a smaller one, around 1000mm focal length, which, in my opinion, is about all that's practical in normal applications.