Best Compact Binoculars for your Budget & Preferences

BBR Video Version on YouTube: Choosing The Best Compact Binoculars based on your needs & budget

The 3 Main Designs (Styles) of Compact Binocular & Which is Best for You and Your Needs

In a category of binoculars where size really does matter, you only need to look at the photo below to see that not all compacts are created equal and this is especially true when you take into account the different body and chassis designs.

The Three Main Types of Compact Binoculars

So in this article, I take you through the three main designs and discuss their relative merits as well as shortcomings to help you decide which compact binocular is best for your specific needs and budget:

Vortex Vanquish 10x26 Binoculars - Typical Reverse Porro Prism Compacts
Typical Reverse Porro Prism Compacts: Vortex Vanquish 10x26 Binoculars

Reverse Porro Prism Compacts

So to begin with, let’s take a look at what is probably the most popular type, especially at the lower price levels, and that are the Reverse Porro Prism Compacts.  These Vortex Vanquish 10x26’s are a perfect example in that as you can see, because of the shape of the prisms they use inside and the way they are positioned, they have this distinctive shape where the objective lenses are closer together than the eyepieces. 

Now typically, standard-sized or large binoculars that use Porro prisms, the opposite is the case, with the eyepieces closer together than the objectives. But whilst optically excellent, you can see that this shape is anything but compact.

So in order to help keep the size down, they reverse the prisms in most Porro prism compacts. However, as small as they are, you can see, out of these examples I have on display here, these are the least compact, compacts and this is their main weakness. 

So In a category of binoculars where size really does matter, why would you choose a porro prism version over the others? Well, the main reason is price or more accurately performance versus price:

Strengths: 

Total Internal Reflection
You see, the Porro prisms used inside these binoculars are cheaper to make than Roof prisms in these as they do not require any special coatings to in order achieve a maximum level of light transmission through them. Nor do they have an issue in regards to something known as phase shift which I will go over in more detail when I discuss these other two options.

This means that at the cheap, entry-level price points you will more often than not get a better optical performance out of a Porro prism binocular because they are easier and less expensive, whilst a  cheap roof prism binoculars will invariably use lower quality or no coatings at all and thus not perform as well as a Porro prism 

Weaknesses:

Size & Shape
The shape of the prism and the way that the light exits it in a different plane to that which it enters means that it is not possible to make as small a shape as that of a roof prism binocular with the same or similar sized size lenses.

Reduced Stereoscopic View

Another weakness is due to the fact that the objective lenses are so close together, you get a slightly reduced Stereoscopic view, which can affect depth perception, which ironically is one of the strengths of a standard Porro prism instrument. 

Roof Prism Compact Binoculars: Steiner BluHorizons 10x26
Roof Prism Compact Binoculars: Steiner BluHorizons 10x26

Roof Prism Compacts

A different design of compct that is once again largly dictated by the type of prism used inside of them to correct the inverted image.

Known as a Roof prism and more specifically, in this case, the Schmid-Pechan design of Roof prism, they offer a number of advantages over the Porro prism design, but also come with a number of potential issues:

Strengths: 

Size & Shape
The advantage here is they have a more compact shape than a Porro prism, which is mainly down to the way the light both enters and exits the prism in a straight line and thus as you can see, you can position the objective lenses straight inline with eyepieces can result in a more compact overall shape than a Porro prism one with the same size lenses. 

Single vs Double/Dual Hinge Design: Minox 7x28 BD vs Swarovski 8x25 CL Pocket

Single vs Double/Dual Hinge Roof Prism Compacts

This size difference is not always as apparent when they are opened, like when you are using them, but once you fold them away, the difference, especially in width is more obvious:

So if you take a closer look at both the compacts in the image above, both use roof prisms, however, the Swarovski CL Pocket uses the two hinge body design, whilst the Minox 7x28 BD only has only one hinge in the center and thus once they are folded to put away or carry about, the Double hinge design is the clear winner and I would say makes a true pocket binocular.

True Pocket Sized Binoculars, the Double Hinge Design on the Steiner Wildlife 8x24 Binoculars
True Pocket Sized Binoculars, the Double Hinge Design on the Steiner Wildlife 8x24 Binoculars

Weakness:

Internal Reflection

So whilst you can make a more compact instrument, the downside to using Porro prisms is that their specific shape means and the angles at which light reflects off the surfaces means they do not transmit 100% of the light that enters them. 


This is because of the way that the light hits one of the prism’s surfaces at an angle that is less than what is known as the critical angle and thus total internal reflection is not achieved and some light is lost.

Thus to correct this, special, highly reflective mirror coatings are usually added to these surfaces to boost the level of reflectivity.

Of these, the best are dielectric mirror coatings that get extremely close to a 100% reflectivity level across the entire visible light spectrum but these are expensive and thus only usually found on high-end roof prisms binoculars.

Next comes, Silver mirror coatings that cost less, but also have a lower reflectivity level of between 95% to 98%.

Then lastly you get aluminum mirror coatings which typically have a reflectivity level of between 87% to 93%. This is the least expensive option and which is what you will usually find on cheaper roof prism binoculars and whilst acceptable, it does not match the 100% you get with a Porro prism.

Phase Shift

Another issue particular to roof prisms is something known as phase shift. 

Here, as the light reflects off the prism surfaces, it causes it to become partly polarized and thus it splits into two slightly out-of-phase beams.

Left uncorrected, this “phase shift” produces an image with less contrast and a lower resolution. So to correct this, special phase-correction coatings are applied to the prism which eliminates the difference in phase shift so that both paths will now have the same polarization and thus no interference degrades the image.

Once again this costs money and thus will often be omitted on low cost and even some mid-range roof prism compacts. 

Conclusions & Reccomendations

So in a nutshell, I’d say, the choice of which type compact binocular is best for you ultimately boils down to your budget and whether optical performance is more or less important than the physical dimensions:

Healthy Budget:

High-End and Mid-to-High End Compacts
If you have a reasonably healthy budget, then you can most certainly have your cake and eat it in that with a high-end Roof prism compact like these Steiner’s with their double-hinge design, you get a very compact, true pocket-sized binocular, with a performance that is as good as the best Porro prism compacts. 

So for the Best, Most Compact of Compact Binoculars, I would narrow my search down to ones using roof prisms that are phase-corrected and dielectrically or at least silver mirror coated with the double hinge design.

Recommendations:

Tight Budget:

Entry-Level Compact Binoculars
If you are on a very tight budget and looking at cheap, entry, and even some mid-level price ranges, and want to get the best optical performance at this level, you are usually better off sacrificing a little in the size department and going with a Porro prism compact. 

Also as a side note, whatever type you choose at the budget level, just check to make sure they use Bak-4 glass and not the inferior BK7 glass for the prisms. 

Recommendations:

Average Budget:

Mid-Level Compacts
At the mid-level price ranges, the water gets a little murky and the choice is not always as clear cut:

Do you go with a reverse Porro prism for the best optical performance, but not quite as small dimensions, or do you go for a Roof prism compact that may be smaller, but probably has silver mirror coatings. This will result in an acceptable optical performance, but may not quite be at the same level as an equivalent  Porro prism at this price range. 

Here it is important to note that the difference can be very minimal and can change between models and brands.

Recommendations:

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