What Are Close Focus Binoculars?
The term close focus refers to how close you can focus on an object through the lens of the optical device, usually binoculars, and see the image crystal clear. When it comes to close focus, the best close focus binoculars tend to have lower magnification and a smaller objective lens.
For those of us that are interested in butterflies, moths and other insects, and would like to observe them in their natural habitat, close focus viewing is a must. Even birdwatchers with a keen interest in identifying the sex, or seeing the variants in colour, shape, size etc will have far more success with close focus binoculars.
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What Are The Limitations Of Close Focus Binoculars?
One of the main setbacks for close focus binoculars that we often hear about here at Binocular Base is the inability to focus long distances. The majority of close focus binoculars that have exceptionally close focus (3 ft-1metre) are awesome for watching wildlife close-up but not too good with long focus. We have found that you are either going to have two pairs of binoculars out with you, or reach a compromise.
You see almost all of the top quality binocular manufacturers produce at least one or two models with a close focus of around 6 ft 6 inches (2 metres) and enough magnification for general use too. But those models that are specifically designed with a close focus of less than 2 metres tend to not have enough magnification for general use too.
If a close focus of around the 2 metre range is close enough for you, then we can suggest any number of top quality brands that will be useful for practically all of your binocular needs. But if you really want a pair with 1 metre close focus or below, then for normal functionality (distance) you’ll need to bring two pairs into the field with you.
Let’s face it, decent optics aren’t cheap (if they are too cheap they’re usually cheap and nasty) so instead of buying one pair for North of £130, you’ll be needing another pair too. Plus you then have to carry both pairs with you and keep them close to hand so you don’t miss any close up birds, butterflies, moths and so on.
The Close Focus Compromise
As we just mentioned you’ll either need to take two pairs of binoculars out wildlife watching, which in all honesty isn’t really practical. Or you’ll need to compromise on how close, close focus can be. There are some binocular brands that have extremely close focus binoculars which also have reasonably high magnification values.
However, there’s a trade off, for some reason the manufacturers seem to have omitted waterproofing and fog proofing, which although not vital, would be a useful feature (especially living in the UK) to protect your investment. Plus the way the objective lenses move when you turn the wheel to focus on something close up requires a battery that will need to be changed regularly.
Another slight problem with these super close focus binoculars is they are Porro prism binoculars. As any experienced nature watcher will tell you, porro prism binoculars are easy to damage. The offset prism arrangement can get misaligned which causes eye strain, which leads to headaches and in severe cases migraines.
With all that said, for the money (anywhere between £80 to £125) you get what you pay for. We would recommend waiting for the better brands to catch up with this macro focussing before buying. In our opinion a regular pair of binoculars with 8x magnification and an objective lens size of 25mm, a close focus of 2 metres, waterproofed and fog proofed for slightly more money (£130), will be far better value long term.
What Numbers Are Important For Close Focus Binoculars?
We’ll go through the basics in a bit, but there seems to be a direct relationship with close focus and the field of view. So let’s start with the field of view and how it’s affected by close focus.
What Is The Field Of View (FoV)?
In plain English, the FoV is how much you can see through the lens of the binoculars from left to right while looking straight ahead. It will be listed in the specs as the angular FoV, or as the linear FoV. With decent binoculars the angular FoV ranges from 6° to 8° and the linear FoV will range from 315 feet per 1,000 yards to 420 feet per 1,000 yards or in metric, 105 metres per 1,000 metres to 140 metres per 1,000 metres (which are all the same values, expressed in 3 different ways).
Why is the FoV Affected By Close Focus?
The way focusing works on binoculars involves magnification, increased magnification lowers the field of view. This is because as you close in on anything, you lose the surrounds of whatever the butterfly, insect, moth or bird is in. A wide FoV is great for finding the creature you want to observe close up, but as you magnify that creature, you lose the FoV around it.
Magnification, Objective Lens Diameter And FoV
To find the magnification and the objective lens diameter, look at the actual body of the binoculars. There will be a series of numbers split by an X that indicates the magnification and the diameter of the objective lens. Look for something like this, 7×25, 8×32, 10×42.
Taking the first set as an example, 7x means 7 times magnification, which means you will see the object 7 times larger through the binocular lens than with the naked eye. With an objective lens diameter of 25 millimeters. The objective lens size is important in a number of ways,
- The larger the objective lens is, the more light allowed to enter the binoculars. The more light that enters the binoculars, the brighter and clearer the image will appear through the binocular lenses (exceptionally handy in low-light conditions like dawn, dusk or extremely dull days).
- The size of the objective lens diameter affects the overall weight of the binoculars (the larger the objective lens, the heavier the glass weighs, which makes the binoculars heavier).
- The objective lens size is used to determine the size of the binoculars.
Compact binoculars have an objective lens of less than 30mm
Midsize binoculars have an objective lens of between 30 to 40mm
Full size binoculars have an objective lens of greater than 40mm
It’s not just close focus that affects the FoV, it’s the magnification in general. Hold a printed sheet of paper up in front of your face, not too close but close enough to see the whole sheet. Now move the sheet of paper closer to your face until only the middle section is visible. You can’t see the whole sheet now, just the section in front of your eyes.
That’s the field of view in a nutshell, and an easy way to demonstrate how higher magnification cuts the field of view. If you were to move that sheet even nearer to your eyes, that’s close focus.
Are Close Focus Binoculars Worth It?
We’re getting asked this question almost daily just later over here at Binocular Base, and we have to say for the most part yes they are. It depends on the brand, and your expectations but overall, yes close focus binoculars have their place in the world of binoculars. Of course with close focus you’re either going to lose on magnification or some useful features.
But used correctly, close focus binoculars can open up a whole new world – Right in front of your eyes (literally). Some of the poorer quality models don’t feature waterproofing or fog proofing but given time, that will come. The way the commercial world is, if there’s a demand for anything, it soon gets fulfilled.
Frequently Asked Questions
Close focus on binoculars means the distance between the binoculars and the closest object that can be focussed on and still keep the image sharp.
To date, the closest binoculars can see is around 18 inches (½ metre).
The minimum focus distance for binoculars is between 1m to 2m (3ft to 6ft).