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Vortex Impact and similar scopes |
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lucznik
Optics Master Joined: November/27/2004 Location: United States Status: Offline Points: 1436 |
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Posted: April/03/2007 at 12:52 |
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I will just apologize right up front that this is going to be a bit lengthy. I have been intrigued with the Vortex Impact (and the identical Hawke Optics Nature and Burris XTS-2575 - which is an incredibly stupid name by the way) since its introduction to the market. Basically my decision to buy one of these scopes came down to two primary reasons: 1. I have long been interested in the design of these scopes which is wholly different from the standard prismatic spotting scope to which most of us are accustomed. (Much more on this to come later.) 2. While I need a spotting scope to fill my needs right now, I really want an ED scope, which I can’t just yet afford (at least, not without incurring grand and terrible punishments from the domestic goddess.) This scope, with its under-$200 price tag, will allow a stop-gap for both of these issues. |
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lucznik
Optics Master Joined: November/27/2004 Location: United States Status: Offline Points: 1436 |
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Why it’s unique and CAT scopes in general. These are all catadioptric scopes (often simply called "Cat" scopes) which means that they use mirrors rather than prisms to "bend" (actually they reflect) the light path. The following is taken from www.betterviewdesired.com and explains far better than can I the concepts involved with these scopes.
In addition to usable high powers, many [people], when they first look through a high quality Cat scope, are amazed at the snap in the image. They might use words like "sharp," or "bright" to describe what they see, but what they are actually seeing is a negative quantity...the almost total lack of chromatic aberration. As noted in [the] past… no lens can bring all the colors of light to exactly the same focus. Lenses bend light as it passes through, and each color is bent at a slightly different angle. The presence of out of focus color in the image is called chromatic aberration… [and] even the best ED and Fluorite… spotting scopes… show some out of focus color. Of course not all is perfect with these scopes. For one, they incorporate a central obstruction on the Objective Lens that of course, affects the overall performance of the scope. As has been mentioned before in these forums; all optics involve compromises. These scopes counter the dimness "problem" with the use of larger-than-normal Objective lenses. However, it is not as big a deal as you might think. For example, (assuming I've done the math correctly) these little compact scopes have an Objective that is fully 70mm in diameter giving an area of 3846.5mm. The central obstruction is about 20mm in diameter, which has an area of 314mm. Subtracting the one from the other you get an ara of 3532.5 mm which is still 706.5mm more area than a standard 60mm prismatic scope. Actually this is roughly equal to a prismatic scope with a 67mm Objective. Of course, you retain (in theory) the resolving capacity of the full 70mm Objective Lens and of course, you keep the ability to (again, in theory) reach the higher 75x magnification without the loss of image quality seen in prismatic scopes. Edited by lucznik |
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What if the hokey pokey really is what it's all about?
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lucznik
Optics Master Joined: November/27/2004 Location: United States Status: Offline Points: 1436 |
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The Vortex Impact: the scope itself. The Impact comes as a package that includes the scope, a very nice carry case, a small “table-top” tripod, and covers for both the objective lens and eyepiece. Let’s address each of these briefly. Lens Caps: The eyepiece cap is a simple, plastic, friction-fit cap common to most compact binoculars. It’s nothing fancy but, the fit is good and tight and won’t come off easily by itself. The objective lens cap on the other hand, is fantastic. It is a screw-on deal made of hard plastic that cannot physically come off at all unless unscrewed, similar to my old B&L Discoverer. This is very positive protection for the objective lens and I like it a lot. More manufacturers should do this for their scopes. Tripod: The “table-top” tripod that comes with the scope is nothing to brag about. It definitely is not a “field-worthy” unit. The adjustments are fairly crude and not terribly user friendly. In addition, there is a heavily-greased spring on the back side of the tripod that is exposed and not only will readily gather dust but, if you’re not careful, will spread grease on your hands. Not cool. Carry Case: The provided carry case is really quite nice. It is a cordura case that is sized appropriate to hold both the scope and the tripod. It is well made and even includes double-stitching at the seams. In addition, there is a Velcro-attached, removable shelf to separate the tripod from the scope allowing better protection for both. The Scope: The Impact is a very cute little spotting scope. It is described as “compact” which it certainly is in comparison to other full-size Cat scopes but, it is still about the size (shorter but fatter) as a 60mm Nikon Fieldscope. It is however, noticeably lighter. The design of catadioptric scopes precludes them having a straight eyepiece, which bothers me a little but, I’m sure I can get used to the angled eyepiece. After all, birders love the things. When looking at the objective lens, the mirrors are very obvious. Unlike a prismatic scope where, if you look through the objective lens you see things as if they were really far away, when you look through this scopes objective lens, you see a distorted reflection of yourself. The scope at least appears to be well built and rugged but, I do need to mention a little problem I had with it within the first hour of it arriving at my home. There is a small piece of plastic just forward of the focusing knob that, in addition to giving the scope a sleeker appearance, seems to serve as an extra bit of protection for the knob from inadvertent impacts. This piece of plastic fell off almost immediately after the scope arrived. A careful look will show where it was held to the scope only by two tiny dots of super glue. It also reveals how inconsequential this piece of plastic is to the operation of the scope. With this in mind, I chose not to send the scope back for repair/replacement under the VIP warranty and instead, I just reattached the piece with two additional drops of (higher-quality) super glue. This little “tragedy” does not make me worry too much about the overall build-quality of the scope as (like I said) this piece of plastic has no effect on the operation |
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What if the hokey pokey really is what it's all about?
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lucznik
Optics Master Joined: November/27/2004 Location: United States Status: Offline Points: 1436 |
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The Vortex Impact: the optics. My scope arrived at around 9:00 p.m. last night so; there was no real chance to evaluate the optics. I will be taking it out this evening after work and giving it a more thorough examination and will update this part later with better information. I did take the time to set up the scope and look at some household items down the hall (about 15 yards.) This is a terrible way to assess optics but, for just a quick peek it was not without benefit. The short version is that I was rather pleased. I could not discern any image degradation toward the edges nor could I see any chromatic aberration (this last one I shouldn’t see anyway but, I also realize that conditions were not ideal for detecting this either.) I was able to zoom all the way to 75x and get a very satisfying picture of the writing on the box of Kool-Aid juice boxes on the kitchen counter. I’ll post more either tonight or tomorrow after I get to spend some more useful time behind this scope... |
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What if the hokey pokey really is what it's all about?
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lucznik
Optics Master Joined: November/27/2004 Location: United States Status: Offline Points: 1436 |
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The Vortex Impact: the optics - continued O.K., now where was I?
Oh yes, the optics….
I took the scope out for a pleasant evening of glassing eagles, mule deer, and antelope on a mountainside not far from my home. This can actually be done right off my front step though; you won’t generally see quite as many animals.
Field of View As noted earlier, the Impact (along with all other Cat scopes) has, resulting from part of its design, a relatively narrow Field of View as compared to prismatic scopes at similar magnifications. To give you an idea of what we are looking at here, I have composed a chart that compares the FoV of the Impact at its lowest 25x with the calculated FoV of a few comparable scopes at that same magnification. (I did also throw in the Pentax PF65ED with the 20-60 XF eyepiece.)
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