Telescopes are a simple invention that make stargazing all the more marvelous, but can you imagine how difficult it would be if you could not adjust your telescope’s settings? Focusers are a must-have if you are looking for precision. Before you buy one, here is what you need to know.
What is a Telescope Focuser?
Focusers are important components of a telescope because they allow you to adjust the clarity of your telescope’s optics. As the name implies, fine tuning a telescope focuser alters and improves the “focus” of what you are looking at. Though there are some factors that will affect your viewing, no matter how in-focus your telescope is, a focuser is a useful tool that eliminates inaccuracies and interferences in your observations by making it easier to resolve your telescope’s image. Regardless of whether or not your model has a built in focusing system or mechanism, adding a focuser is a good idea and is a simple and affordable way to modify and upgrade your device.
What Does a Telescope Focuser Do?
Focusers vary in design and utility, but are considered a standard component of all types of telescopes. Though these variations are different means to the same end, how they work is something you should consider to make sure that you are choosing the best one for your telescope. There are two main types of focusers for both reflectors and refractors; the rack and pinion, and the Crayford focuser.
Rack and pinion focusers work by gears. In this case, rotational motion created by the pinion – a small gear – is converted into linear motion by the rack – a flat bar. As the gear turns, the rack adjusts your eyepiece according to your telescope’s inner optics, optimizing the resolution of its magnification and image. Though the mechanics of rack and pinion focusers is simple, it can cause complications. Backlash is the most prominent one. In layman’s terms, backlash is stalling, delays or wobbles caused by the necessary spaces between the teeth of the gear. This causes limitations in how far or smoothly the focuser turns which can lead to interferences which affect the precision of the focuser.
Crayford focusers are often thought to be an improved design. Rather than using gears, they work by a roller and a flat plate. This eliminates backlash as a problem entirely and enables smoother, faster and more accurate adjustments in your optics.
Schmidt-Cassegrain and Maksutov-Cassegrain telescopes have built-in focusers which adjust the primary mirror rather than the eyepiece. There are advantages to this. The focus range is higher and often more precise than what is observed in rack and pinion and Crayford focusers. It also means that your eyepiece retains its position, as the internal optics make the difference. However, backlash is still a problem and even worse, image shift is a possibility. As implied, adjusting the primary mirror could force it out of alignment. This is not the end of the world for most amateur astronomers, but it can cause significant inaccuracies the higher your magnification is, or obvious problems in astrophotography.
You can also opt for an electronic focuser. You are spoiled for choice in design and operation when it comes to digital alternatives, but their premise is the same. They are motorized and remotely controlled (either through a handheld controller, or software). Electronic focusers tend to be more efficient than their manual counterparts. A drawback is that they might not be compatible with your telescope or devices.
All this said, the bottom line is that focusers adjust or alter your telescopes optics to clarify or resolve what you are observing.
How to Align a Telescope Focuser
Unfortunately, there is little general information or instruction available on how to accurately set up a telescope’s focuser. The reason for this is that every telescope is different and as such, so is every focuser. There is no blueprint for how to align your optics with your focuser, as it is largely a matter of preference and circumstance. The best thing to do, if your focuser or telescope does not arrive with a manual or guide, is to contact the manufacturers for specific instructions. Regardless there are a few steps that you can take to make your set up easier.
Start by making sure that the focuser you buy fits into (or onto) your telescope. If you are considering an electronic one, you will have to check manufacturer specs to avoid incompatibility.
Aim for a sweet spot when installing your focuser. If it is too tight, its ability will be limited and you will lose a lot of range and capacity. On the other hand, if it is too loose, you may experience interferences, shaking or distortion.
You will also have to be sure that your telescope’s internal optics are collimated. There is no point in fine tuning a focuser to optics that are out of alignment. Collimation is not a difficult process, though you may need to invest in a laser collimator to get the job done.
Though you may be tempted, do not fiddle with the set screws of your focuser. Your product is likely to arrive with the screws and tools you will need for set-up, separate from what is already built in. Dismantling or loosening any of its components could damage its integrity and so render the focuser inaccurate.
Best Telescope Focusers
Telescope focusers are a relatively inexpensive addition to your set-up, and they will go a long way so long as you take care of them. Once you have determined what will be the best fit for your telescope, picking a favorite could be tricky as there are so many to choose from. Here are five top picks to point you in the right direction.
Orion 13039 2-Inch Crayford-Style Telescope Focuser
As a Crayford focuser, you will not experience any backlash or image shift with this model. It is designed to fit telescopes ranging between 8 and 12 inches, and is compatible with both 1.25 and 2 inch eyepieces. It is comfortable to handle thanks to the addition of rubber grips on its knobs. This focuser also offers adjustable tension, which will go a long way in preserving the focuser’s utility.
- It fits a wide range of telescopes.
- Made to accept both standard eyepiece dimensions
- Rubber grips enable comfortable control during adjustments.
- Crayford-style, so there is no risk of image shift or backlash.
- User can adjust the tension of the focuser.
- For a focuser, it is a bit heavy and might throw smaller or lighter telescopes slightly off balance.
- Dust plugs are not included with this focuser.
Orion 7395 AccuFocus Electronic Telescope Focuser
This is a great choice for amateur astronomers in need of an electronic focuser that is not over the top. Its simple in its design and operation though does not lack any sophistication when compared to other models. All of the components you need to install it are included in your purchase, and the focuser itself is easy to use. It is motorized for fast, efficient and accurate adjustments, and is operated with a handheld controller. It is made to prevent vibrations, and a highlight is that you can control the speed of the motor.
- Compatible with most Orion telescope models.
- Includes all components for installation.
- User can control the speed of the motor, choosing from levels ranging between fine and coarse.
- Handheld control is easy to understand and operate.
- Reduced vibrations improve accuracy.
- Battery (required) is not included with purchase.
- Though the focuser itself is excellent, the build quality is disappointing.
Orion 13032 2-Inch Dual-Speed Crayford Refractor Telescope Focuser
This focuser, designed with refractors in mind, has some fancy features for a manual model. To start with the basics, it is a Crayford focuser, so there will not be any interferences, backlash or image shift. It is compatible with 1.25 and 2 inch eyepieces, as well as diagonals and most other telescope accessories. This model boasts an 11:1 focus ratio, for extra accuracy and crisper results when fine-tuning details. Not to mention its dual-speed feature for faster, more efficient adjustments.
- Dual-speed control when adjusting the focuser.
- No risk of image shift, backlash or interferences.
- Compatible with all standard eyepieces, including diagonals.
- Excellent focus range for fine-tuning.
- Makes a great upgrade for standard or built-in Orion focusers.
- Though it has a cool collection of features, this model’s price is not competitive when compared with other models.
- As with the Orion Accufocus, the quality of its build could be improved.
Orion 13031 Basic 1.25-Inch Rack-and-Pinion Telescope Focuser
Recommended for beginners or as an upgrade for starter telescopes, this rack and pinion focuser does exactly what it needs to without adding unnecessary features. It is a budget-friendly choice that is easy to find your way around. What is great about this particular focuser is that it is built to fit all Newtonian telescopes with apertures of 4 inch and higher. It is compatible with 1.25 inch eyepieces and features dual knurled knobs.
- Universal fit for all aperture 4 inch and higher Newtonian telescopes.
- Excellent cost-effective choice.
- Perfect for beginners, or amateur astronomers with starter telescopes.
- Its simple design and installation enables easy operation.
- Dual knobs are knurled for improved grip.
- Does not include mounting screws.
- As a rack and pinion style focuser, there is a risk of backlash.
Astromania AccuFocus Electronic Telescope Focuser
Similar to the Orion Accufocus focuser, this electronic model gives you the same great features and precision, with a wider range of compatible telescopes, including Celestron, Skywatcher and Meade. As with the former, this focuser prevents vibrations with a handy controller. You can choose the speed of the motor, and all components for installation are included with your purchase.
- Compatible with Celestron, Orion, Meade and Skywatcher telescopes.
- Build components are included.
- Motor speed control (fine-coarse).
- Operated with an easy-to-understand handheld controller.
- Eliminates vibrations for extra stability and accuracy.
- Does not include the necessary battery.
- Due to a manufacturing error the speed controls are reversed.
Telescope focusers are necessary for stargazing. Without them, you will not be able to fine-tune your telescope’s optics to achieve a clear picture, so your viewing will be disrupted by interferences like blurs, distortion and shaking. If you are a serious astronomer, a focuser is a worthy investment.
They do not have to cost you an arm and a leg, and there is a range of styles and fits available to choose from. The most important step is to determine which style will work best with your telescope. With the exception of Schmidt-Cassegrain and Maksutov-Cassegrain models, there are little differences in how focusers fit and apply to your telescope. Both reflectors and refractors require them, even if only as an upgrade to outdated built-in equipment.
Even if you are just starting out and in fact, especially when you are starting out, focusers are not something you do not want to overlook. They will make your stargazing easier and more enjoyable, not to mention accurate, and that is where their worth lies.