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08-21-2009, 02:57 AM   #1
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Pentax PF-100ED scope

A lens is never too long. That's what every wildlife photographer will tell you. Even more so if the main subject is some timid bird. Suitable tele lenses are too expensive for most of us. Fortunately there are alternatives like mirror lenses and scopes. The later are being also made by Pentax and can be used with Canon, Nikon and of course Pentax SLR cameras. I had a chance to try out the flagship of Pentax scopes the PF-100ED.


Up until this opportunity I had no experience with scopes. I did however try some binoculars from various price ranges. Besides the scope one needs an eyepiece. I got the XL 8-24 zoom eyepiece and despite zoom the picture was incredibly bright and clean. So instead of staring at TV we spent the evening on a balcony staring at the moon. The scope is packed in a bag that doesn't have to be removed when in use. One can just unzip the necessary openings and use scope with bag on as protection. A more in depth review of scope can be fond here: Birdwatch - Pentax PF-100ED scope

The main difference between telephoto lens and scope is that latter has fixed aperture and is completely manual (manual focusing an exposure). Focusing is done with a very smooth knob with a lot of travel and just right friction. Still focusing through the view finder is far from easy mainly due to fixed aperture (estimated f10-11) that makes view finder dark and grainy. Focusing is hard also due to focal length which magnifies every little shake. And yet there is no margin for error. Due to fixed aperture depth of field stays the same during the exposure. All fore mentioned properties make scope suitable only for objects that stay still long enough to get them in focus or are predictable enough and can get caught in focus.
Focal length also makes composing harder. It happens too often that in effort to correct composition one looses main object from frame all together.

Optically a scope is no match for a pricey tele lens, but with some luck with focusing one can get decent image quality that is as good in corners as in center. For better image quality I'd recommend a camera with good ISO performance.

I was surprised with efficiency of Shake Reduction. I was positive that I won't be able to use SR at all as it can be set only up to 800mm. So I condemned my self on shooting with IR remote and 3sec timer (mirror up). After first week of testing I found out that 3 sec is just enough for a pheasant to get out of the frame. With little patience left I set SR to 800mm and started shooting holding camera and scope on tripod with released head. And what do you know - pictures at 1/180s were as sharp as those shot with mirror up. The attached photo of pheasant was made in this manner (SR on, no mirror up)

Test pictures

Center and edge sharpness:

Magnification of moon with scope (bigger) and with 1100mm mirror lens (smaller)


Comparison with 1100mm mirror lens. The mirror lens (upper images) has virtually no CA but it's softer.

I'd like to thank my local dealer Foto Beseničar, for a free rental of the scope.

I made a short clip as an illustration of how severely weather and stomping on grass 1/2m away from tripod can affect image
YouTube - Spektiv

08-21-2009, 03:45 AM   #2
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"Free rental" - over here we call that a "loan"

I'd love to turn up to a sports game with that!!
08-21-2009, 03:54 AM   #3
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Very good info. Thanks for the test and putting this together. One think that always confuses me is the actual focal length. From the FOV, it would appear to be around 12-1300mm, correct? How do you calculate the focal length?
08-21-2009, 04:07 AM   #4
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Another league of telephoto capability being presented here...
MF must be hard to nail at that FL, even at f/10.
But way to go Pentax SR!
Awesome summary.
Thanks for sharing it here.

08-21-2009, 05:50 AM   #5
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QuoteOriginally posted by Peter Zack Quote
From the FOV, it would appear to be around 12-1300mm, correct? How do you calculate the focal length?
I literally measured the moon diameter on photo made with mirror 1100mm lens and one made with scope.

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