Vortex Viper PST 1-4x


Review of the Viper PST 1-4x scope from Vortex


By Les (Jim) Fischer (BigJimFish on AR15.com and Snipershide)
March 30, 2011


I am happy to present my review of the Vortex Viper PST 1-4x. I know a lot of folks have been waiting for this one. At $500 street price, this scope falls into a price range that most people can afford and it features the best warranty in the business. Inexplicably, this scope also has very little competition at its price point. For whatever reason, few scopes fall between $350 and $750. If memory serves, this scope debuted at the 2010 Shot Show and released near the end of that same year. With six scopes on hand today, we should get a pretty good idea of how it stacks up and if it’s worth dropping a stack of cash on one.

Here is the Viper mounted on my 16″ AR:

Viper mounted on rifle


Here is the lineup of scopes that were used as references for the Viper in this review. From left to right: Zeiss conquest 4.5-14x44mm, Leupold CQ/T, Vortex Viper PST 1-4x, Vortex Razor HD 1-4x, GRSC Korean-made 1-4x (mine was a prototype), GRSC Japanese-made 1-6x Prototype.

The Line up


Table of contents:
-Physical description
-Reticle description, explanation, and testing
-Comparative optical evaluation
-Exit pupil and eye box discussion
-Illumination subjective and comparative evaluation
-Mechanical testing and turret discussion

Background: (The majority of this information was taken from an ArrowTrade article posted in the Vortex industry forum by Sam). Vortex is a family business in the truest sense of the term. It was founded by Dan Hamilton as a result of the optics experience and frustration he gained operating a Wild Birds Unlimited franchise and is now run by him and several of his sons. As many small business owners have found out, it is often necessary to do it yourself if you want it done right. This was the principle behind the founding of Vortex. Dan was unsatisfied with the optics options available to him to sell at his Wild Birds Unlimited store and, after unsuccessfully trying to enact change in the industry from the outside, decided to wade in himself. Vortex Optics originally made optics of primary interest to birdwatchers, such as binoculars and spotting scopes. However, they have continued to expand their product line and now also produce hunting and tactical scopes of interest to the ARF community. Though Vortex does not currently have manufacturing facilities, they do have facilities for designing and repairing their optics stateside. This allows them to offer a far wider price range of optics than most companies because their optics are produced in several different countries. All of their optics, regardless of price, come with the best warranty in the business. Unless you are truly new to the world of optics, you have doubtless heard many stories from individuals duly impressed with the warranty service Vortex offers.

Physical Description: The Viper is shorter and considerably lighter than its big brother the Razor. It also has an appearance more in line with what seems to be considered ‘tacticool’. The lines are more ridged, the turrets protrude more, and it is flat black. It also has the wart style illumination rheostat attached to the eyepiece. The machining looks good on the Viper and the Vortex name is featured prominently more or less everywhere. The turrets, variable rheostat, power ring, and euro-style diopter all turn smoothly and with the amount of resistance you would expect. Similarly, the clicks are clean and tactile. To be perfectly honest, the turrets actually feel considerably better than those of the Razor and since they also include adjustable zero stop shims, they have more features as well. I remember several months ago Vortex delayed the release of the Viper to rework the turrets because they were unsatisfied. Mission accomplished. My only complaint about the appearance of the Viper is the labeling on the power selector ring. Setting is marked, but with reticle multiplier and the magnification. Though it might be convenient to note that at 3x the reticle is 1.3 times the normal size, I think it’s more confusing than it’s worth. Like the Razor, the Viper comes equipped with little fiber optic indicators for the magnification and elevation turret. They don’t really seem to light up much, but in the case of the elevation knob, you can feel where the fiber is with your finger and I find that helps you confirm that the scope is set to your zero when it is dark.

Reticle (refer to the pic below while reading the description): The Viper comes in either an MOA or Mil ladder style reticle bracketed with a broken circle to aid with close quarters functionality. Turrets are always matched to the reticle. The Viper I have is the MOA version and has hash marks every two MOA and labels every ten MOA. Obviously, since this scope is 2nd focal plane, the reticle is best used for ranging at 4x. As most of you know, I prefer rapid ranging reticle designs such as the GRSC, the Vortex EBR-556, or the Trijicon TA-31F for 1-4x scopes. I think the Mil and MOA ladders have their place beyond, say, 600 yards, but I don’t think they are of much use for a 1-4x. That being said, lots of folks seem to like them and buy them so for those folks, the two options Vortex offers are probably very appealing, especially with matching turrets. I tested the reticle accuracy on a calibrated target and it is roughly 7.5% too large. As I have mentioned before, reticles being improperly sized is a very common occurrence. Nevertheless, given how perfectly spot-on the Razor’s reticle was, I re-measured the markings on the target as well as the distance to the target to make sure. It is unfortunate that the reticle is off by a measurable amount. Though I suppose since you are going to bust out your calculator, Mildot Master, or your awesome mental math prowess to do some calculations while you range; this will be just one more set of numbers to punch. I also tested the reticle for close quarters use. Because it is 2fp, the reticle is still very easy to see at 1x. This is good as I had the tendency to lose the reticle on the Razor when scanning with the scope. The Viper does not have this problem. I found the broken circle less effective for me than I expected, though. I thought that the pieces of the circle would more or less coalesce into a whole and draw my eye into the middle when scanning with the scope at 1x. I was surprised to find myself often focusing on the upper left portion of the circle instead of the middle, however. I did not predict this happening and I am surprised. I wonder if others will have similar experiences or if they will be drawn to the center as designed. In any case, the close quarters aspect of the reticle was a bit of a mixed bag for me. There was definitely enough of it to keep from losing it, but I found myself focusing on the wrong part. I am taking this scope out tomorrow with some buddies, so I will take a little survey to find out if I am unusual in this regard.

An image of the Vortex Viper MOA reticle 4x:

Viper on 4x


An image of the Vortex Viper MOA reticle 1x:

Viper on 1x


Comparative Optical Evaluation: The Viper was one of the middle-priced optics in my lineup and clarity-wise it finished in the middle of the pack. It was always clearer than the GRSC K and never as clear as the Razor or the GRSC J. In bright light, the Leupold CQ/T bested it, but on an overcast day it was better than the Leupold. Due to the very small objective lens of the CQ/T, its performance varies dramatically depending on lighting. Though the price of the Viper as well as its performance were middle of the pack, I don’t think that really does it justice. It was a lot clearer than the GRSC K and only a little less clear than the Razor and GRSC J. Both of these scopes double or more than double the Vipers price. The optical performance of the Viper really was very impressive at its price point. Optical aberrations such as curvature of field or excessive chromatic aberration were also not a problem with the Viper. As for the field of view, the Viper and Razor are amazingly close in this regard and the total spread between all the scopes, excluding the CQ/T, is really quite small. For what it’s worth, the field of view was slightly smaller than the GRSC K, bigger than the Razor, and bigger still than the GRSC J. My compilation photo below is very good for judging the field of view of the scope in the lineup. Please pay particular attention to the soccer goal in the 1x photo for a field of view comparison. In the 4x photo, the fence on the right side and far tree on the left are good benchmarks. All of these photos were taken in relatively low light (evening) to enhance optical differences in the scopes. The target is 50 yards away and is calibrated to the GRSC and EBR-556 reticles at that range. Scopes were not mounted on a rifle, which is why the soccer players don’t look worried.

Scope compilation photo with scopes set at 1x:

1x compilation


Scope compilation photo with scopes set at 4x (CQT is at 3x):

4x compilation


Exit Pupil and Eyebox Discussion: First, lets discuss the exit pupil. The exit pupil is the size of the disc of light at the point at which it is focused for your eye. Assuming you are using this scope for close quarters work and you are moving about, your head will not be completely stationary regardless of how good your cheek weld is. A larger exit pupil will allow you to keep view of the object through the scope despite your movement, though it is notable that due to parallax error the reticle will not be exactly where it should be when your head is far off center. People refer to range through which your eye can move about and still get a good image as the “eyebox”. Obviously, exit pupil is a very important specification on 1-(n) power scopes. Mathematically, the largest an exit pupil can be is the diameter of the objective lens / the magnification. I have noticed a trend for scope manufactures and optics websites to simply list the results of this mathematical formula as their exit pupil. Roughly half of the scopes in the table have this and dollars to donuts, it is incorrect on every one of them. For its part, Vortex does not list an exit pupil in any of its documentation, although several third party websites do have it incorrectly listed as 24mm. Exit pupil can be roughly tested by placing a brightly illuminated object at some distance from the optic and measuring the disc of light transmitted through the scope at its smallest point. Below is a photo of my measurement setup.

Exit pupil measurement setup:

exit pupil set up


What I found measuring exit pupil corresponded well to my experiences testing the scopes by bobbing my head around a bit. These hands-on experiences did not correspond to many of the exit pupil listings I have found for scopes. I am somewhat left with a quandary, as I have only been able to take measurements of the exit pupil of scopes that I have and these measurements are far from precise. I will have to decide whether to replace the values in the table at the front with my better measured numbers or leave the manufacturers’ reported numbers. In either case, be aware that numbers in the table at the front that look too good to be true probably are. Despite not having the exit pupil reported in the product literature, the Viper has the largest measured exit pupil in the lineup. Here are the numbers I measured for today’s scopes, in order of 1x exit pupil size:

Viper PST 1x, 16mm 4x, 6.4mm
Razor HD 1x ,13.2mm 4x, 6.5mm
GRSC K 1x, 13.1mm 4x, 6.7mm
GRSCJ 1x, 11.2mm 6x, 4.6mm
Leupold CQ/T 1x, 9mm 3x 4.86mm

Illumination Subjective and Comparative Evaluation: The Viper is one of only two scopes in the lineup today to be 2nd focal plane. The other is the Leupold CQ/T and it uses only a 1.5V battery instead of a 3V like the Viper. It was not surprising for me to find that at 1x the Viper is the brightest scope in the lineup. In addition to being 2nd focal plane and having a 3V battery, the Viper’s reticle also has ample reflecting surface for illumination in the form of the broken circle portion of the reticle. All that being said, whether you will find it (or, more generally, any 1-(n) power scope) to be daytime bright is another matter. No 1-(n) power scope that I have ever tested is even near as bright as a holographic sight, though this one is the brightest I have tested thus far. The photo below is a compilation of all the scopes in the lineup with fresh batteries at maximum illumination when set to 1x on a bright Ohio Spring day. I hope that this helps your determination of illumination brightness. At some point I should try to find an Aimpoint or Eotech owner locally to add one of those to my compilation photo for testing.

1x illuminated compilation photo:

1x illumination compilation photo


As for the illumination controls, the Viper has a 10-position rheostat with off positions between each illumination attached to the eyepiece. It looks like the first 5 settings are night vision only, as they are not visible to me at any time. The next 5 seem to be quite sufficient to account for different ambient brightness. Unlike the Razor, the battery cap on the Viper is knurled a little bit, though I was still unable to fully tighten it barehanded.

Mechanical Testing and Turret Discussion: In order to test the mechanical properties of a scope such as the accuracy, repeatability, and independence of the adjustments; I will be performing a box test and a power change test. These tests will be done using my Lothar Walther barreled Spike’s .22lr upper. This gives me the data desired without the time and expense of making up match .223 hand loads. In the first target you will see a simple box test. Since the time I began these reviews a few years ago, a lot of rounds have gone down the pipe of the Spike’s .22lr and it is starting to break in. The groups are tightening up nicely. For those of you not familiar with box tests, a box test is performed in the following manner. Zero the scope and shoot the first group. For the second group, you move your adjustments a specified distance to the right (24 clicks for 1/2 MOA adjustments on this target), but you still aim at the original point. For the next group, you move the adjustments the same distance down, but again shoot at the original aim point. You then adjust back left to shoot and finally back up for the final group. The result should be a square box on the target with the last group on top of the first. This test will determine not only if your scope properly returns to zero, but also if its adjustments (right/left and up/down) operate independently of each other (i.e. adjusting left does not also adjust slightly down or up). I also used this test to asses whether the adjustments were moving the point of aim the amount that they claimed to be (i.e. 1/4 MOA adjustments move the point of aim 1/4 MOA and not 3/8 or some other amount).

The target below was fired at 25 yards with the scope set to 4x. The point of aim for all groups is marked. Since the target and the adjustments are MOA, I have set it up so that each group should have the same relation to its respective black box on the target as all the others.

Viper box test


I am quite happy with this box test. The adjustments are independent, accurate, and return to zero. The fine elements in the center of the target also made the groups a pleasure to shoot. No complaints.

This next target is a power adjustment target. On the target each group represents a group fired at one of the two power extremes of the scope. No changes are made to the scope’s adjustments when firing these groups. Each group is fired using the upper left corner of the respective boxes as the point of aim. An ideally performing scope should show the same relative position of the center of each group to its target box. A scope whose point of impact shifts when the power is changed will show a corresponding shift in the group relative to the aim point.

Viper power change test


The only scope to ever pass this power change test totally unscathed was the Vortex Razor. Here you can see that the Viper showed a shift of probably 1/2 inch or 2 MOA. While no shift is ideal, virtually all scopes fail to accomplish this. The Viper’s numbers are not unusual or out of the realm of acceptable. The bottom line is that if you are looking to be precise at distance, you should use your scope on the power setting that you zeroed with, which should be 4x.

Generally I prefer capped low profile turrets on a 1-4x scope, but generally I also prefer rapid ranging reticles. Since the Vipers come in only Mil or MOA ladder reticles, it probably fits that they have these big sniper style turrets. After all, you will likely be using them to compensate for drop and windage. Quite surprisingly, the Viper’s turrets are better than those of its big brother the Razor in just about every way. The turrets on the Viper feel great. They are smoother than those of the Razor and have more definite feeling clicks. They are also 1/2 MOA instead of 1/4th. 1/2 is simply a better increment in a 1-4x scope. Lastly, the Viper comes with a set of little shims for setting up a zero stop if yon are so inclined. These are really very nice sniper styled turrets. I wish I had them on my Zeiss 4.5-14x.

Summary: I am impressed with this offering from the folks at Vortex. Though I disagree with the principle of a sniper style reticle and matching turrets on a 1-4x, Vortex executes them well. Furthermore, I am happy to see an MOA / MOA option in addition to the Mil / Mil option. The quality of manufacture of this scope is evident and better than one would expect at this price point. I suspect a great many people will find this scope very much to their liking.

For those of you looking for the simple pro and con list, here you go:

Optical clarity better than would be expected at $500
Optics show low chromatic aberration and curvature of field
Fit and finish are excellent
Adjustments are accurate, feel fabulous, and even have an adjustable zero stop if you’re into that sort of thing
Illumination is brighter than most 1-4x scopes
On the light and small side of the 1-4x class
MOA and Mil options available both with matching controls
Good price point
Best warranty in the business

I disagree with the 1-4x sniper scope concept
The broken circle did not totally agree with me at 1x
Reticle is too large for its markings by 7.5%