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Vortex Impact and similar scopes

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/03/2007 at 12:52
lucznik View Drop Down
Optics Master
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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.

 

I will divide this into a few different “chapters” (or posts) to help make it more readable.  First I will address the theoretical aspects of the basic design of these scopes, as they are very different than what most of us have probably dealt with before.  I will then address the Impact scope specifically in two areas.  First, I will discuss the physical scope itself and then offer a review of the scope’s optical performance
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/03/2007 at 12:52
lucznik View Drop Down
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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.

Originally posted by betterviewdesired betterviewdesired wrote:

Because the Cat folds the optical path back on itself, optical designers can fit a large aperture, long focal length, instrument into a very small package… Even the best prismatic refractor spotting scopes aren't much use at anything over 60-80X. The average birding refractor is fairly useless even at 60X, yielding an image that is often slightly blurry, quite muddy, and very dim. High quality Cats… have no problem reaching those powers, with an image that is still sharp, contrasty, and bright, and can often go quite a way beyond. Many [people] see increased definition, better color fidelity, and more brightness than they have ever seen in a refractor scope.

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.
Mirrors, since they do not bend light at all, are inherently free of chromatic aberration and false color. What impresses [people] is the all-but-perfect definition and delineation of each individual shade and tint in the image.

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.

Originally posted by betterviewdesired betterviewdesired wrote:

…the effect of the central obstruction on image quality. Having the secondary mirror in the light path blocks some of the light, making for a dimmer image than you would get from a perfect lens of the same diameter. The secondary also introduces diffraction effects that reduce the overall contrast of the image. The amount of lost light is equal to the percentage of obstructed area… Remember, the central obstruction affects only brightness and contrast. You still get the resolving power of the full aperture.

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. 

Historically, such Cat scopes have not been super-popular with the hunting crowd for a few additional reasons; they tend to have slightly narrower fields of view at comparable magnifications than do prismatic scopes and they also tended to be a bit more fragile in their design.  Additionally, the mirrors were subject to tarnishing over time - reducing their image quality.  The smaller FoV is something the user just has to accept but, we will nevertheless, discuss it further later. With these new "waterproof, fogproof" models, I suspect the ruggedness problem as well as the problem with mirror tarnishing (as air no longer makes contact with the mirrors) has been to a large extent mitigated. Only time will tell but the inclusion of the Impact in the Vortex no-fault “VIP” warranty program is at least comforting.

Edited by lucznik
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/03/2007 at 12:53
lucznik View Drop Down
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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

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/03/2007 at 12:53
lucznik View Drop Down
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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...

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/04/2007 at 15:49
lucznik View Drop Down
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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.)

 

Brand

Model

Magnification

FoV (in ft.)

Vortex

Impact

@ 25x

89


What if the hokey pokey really is what it's all about?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/04/2007 at 19:49
FrankD View Drop Down
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lucznik,

 

Again, Excellent Post! What a thoroughly enjoyable read. I, too, spoke with Paul about this scope the other day as I was considering donating a few of them to one of the local nature centers. He suggested also checking out the Sandpiper and another of their models.

 

Ofcourse I am still going to give that big Skyline ED 80 a go once it hits the market. I would absolutely love for you to give that 65 mm Pentax a go with the 20x XW eyepiece. I believe you would be truly shocked by the performance level.

 

Thank you again for taking the time to put this whole thing together. It is posts such as this which make these forums an enjoyable place to visit.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/04/2007 at 20:05
anweis View Drop Down
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lucznick, thank you. It sounds like a decent 200 yard shooting range scope.

Frank, you will like the Skyline ED, but it's a bit on the big/long side, just don't drop it  .

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/12/2007 at 11:58
FrankD View Drop Down
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Quote Frank, you will like the Skyline ED, but it's a bit on the big/long side, just don't drop it

 

I am looking forward to getting it but, alas, nobody has them in stock yet. I think they become available some time at the end of this month....

 

...which puts me in another dilemna. I surely cannot afford a $700 scope without getting rid of something else. I had contemplated selling the Pentax 65 but may opt to sell one of my bins instead. Who knows?

 

I also would love to check out this little scope that lucznik reviewed. I think it would make a perfect option for those with a tight budget.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/14/2010 at 13:58
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Optics GrassHopper
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Back from the dead:

Anyone know who is really making these optics? I'm in the market and can get the Burris version at 50 percent off msrp (not really a great deal as it would seem) or this version. They appear identical yet Burris claims to make their stuff in Colorado and Vortex in Wisconsin. Something tells me neither is right and this is a foreign made product....  Anyone know for sure?
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