Shop by Price
Shop by Brand

HoTech SCA Laser Collimator With Crosshair

HoTech SCA Laser Collimator With Crosshair
Price:  £145.00(Inc. 20% VAT)

Model:  SCA-1.25C
Brand:  HoTech

2 Year Warranty On All New Items
(Excluding Batteries & Globes)

There maybe a misconception that SCA only centers in the focuser, instead, SCA is the first and only device that performs both parallelism and centering at the same time very well. Unlike other adapters in the market that only advertise one or another.

The HoTech laser collimator separates itself from all other laser collimators with its innovative self-centering adapter technology (SCA). This mechanism allows precise and REPEATABLE installation in all brands of 1.25" and 2" telescope focusers thus provides accurate collimation. All laser collimators in the current market have one fundamental problem, slop in the adapting mechanism between the laser collimator and the telescope focuser.This problem is recognized and often discussed among astronomers but so far there has been no definite solution in the market.

No matter how tightly the tolerances machined on the laser collimator or the focuser, a small gap is required to allow installation of the laser collimator. Once the laser collimator is inserted, the required gap becomes a problem. A laser collimator is secured with one or more thumbscrews or unified compression ring. Both methods introduce very critical issues, namely inconsistant adaption from off-axis (axial) and none parallel-axis installment that instantly destroys the precision of your collimation instrument along the entire optical axis.

Our Self-Centering Adapter cleverly eliminates the focuser slop by linearly compressing the built-in rubber rings. By doing this, the diameter of the rings expands to compensate the gap.Because all rings evenly expand radially in diameter from the compression, this automatically centers the laser collimator in the focuser draw tube. And most importantly, our SCA laser collimator can be tightly installed in the focuser for a repeatable installation to provide an accurate collimation.

In summary, our SCA adapter serves three critical functions. First, its expansion rings accommodate almost all focuser's manufacturing tolerances. Second, it automatically centers the adapting laser in the focuser. Third, it provides at least two evenly distributed circular contacts on the focuser's inner tube surface preventing the adapting laser from pivoting and parallel to the focuser.Once the slop factor is taken away, you can quickly collimate your telescope in confidence to achieve perfect collimation every time.

Current Collimators' Problems

  • The Thumbscrew Gap
  • Adapting with Unified Compression Ring

Problem Solved with SCA Technology

SCA Eliminates Drawtube Slop

All drawtube have manufacturing tolerances.And it requires larger diameter to accept various eyepieces and adapters.When a standard collimator is inserted, the gap between the drawtube and the inserting device became a slop problem.The rubber rings in the SCA expand radially according to users own adjustment to fill the gaps.This makes your collimator seats firmly in your drawtube becoming part of your telescope for a secure and repeatable installation.

SCA Keeps Laser Perfectly Parallel to the Focuser

The patented multiple expanding o-rings design provides solid 360 degress even grip to the inner focuser surface keeping the adapting laser perfectly parallel to the focuser tube elimating any possible tip or tilt error from the conventional thumbscrew locking mechanism.
SCA Eliminates unstable locking from thumbscrew or unified compression ring

The optical axis is shifted when the inserting device is locked in by thumbscrew.In some cases, some poorly made unified compression ring can cause unstable tilt when locking in the drawtube due to loose tolerances between the compression ring, inner groove, and the uneven tip of the locking thumbscrew in a drawtube.The SCA adapts the collimator itself without using the thumbscrew or the unified compression ring.

SCA Accepts the Imperfection of a Drawtube

Small imperfection inside the drawtube like dents, scratches, and uneven burrs, the rubber rings compensates the errors and faithfully centers the collimator in the tube.In addition, even if the drawtube is slightly deformed in diameter, egg-shaped, the rubber rings in the SCA will compensate the differences and faithfully centers the collimator. A metal collet design will not be able to transform itself to the deformed shape to compensate the imperfection of a drawtube for a sturdy adaption.

More SCA Laser Collimator Features:

Laser Engraved 45º Targeting Faceplate

The targeting faceplate displays the returning laser spot with a clear visual reference during adjustment. That allows you to align your primary mirror from the rear of the telescope and eliminates traveling to the front of your scope repeatedly during collimation.

Collimating without the targeting faceplate, you will not be able to adjust the primary mirror in real time referencing the laser dot.In other words, you often get lost on which adjustment screws you used due to traveling back and forth for referencing the direction you have adjusted.This results in considerable time to complete the collimation and defeats the purpose of quick and easy laser collimation.
HoTech understands the importance of this, so the faceplate is a standard feature in our laser collimator.All astronomers deserve to have it without paying any extra!
HoTech understands the importance of this, so the faceplate is a standard feature in our laser collimator.All astronomers deserve to have it without paying any extra!

Also, our faceplate viewer’s pattern is laser engraved to ensure a long lasting sharp targeting grid for best visual effects. Unlike other collimators, the target is not a sticker that will peel, or paint that can rub or chip off. We understand that you are paying for a precision instrument that is supposed to be well made.

Finest Projecting Laser Dot

Keeping the laser dot to the finest point is the key to precision collimation. But when you look closely at the laser dot from brand to brand, most laser dots appear large, not really a fine point as you imagined.This means there is guess work involved when you try to center the dot; not just centering the laser dot to the center of the faceplate, but also centering the center of the dot itself.This does not make any sense when you are trying to take the advantage of the collimated laser beam's characteristic "which has a low beam divergence, so that the beam radius does not undergo significant changes within moderate propagation distances." In other words, the laser beam size within the collimation distance (laser collimator to the primary mirror and back to the faceplate) should remain a constant fine point. As you know, most laser collimator brands are not laser manufacturers.They install an off-the-shelf laser module or pointer and align the laser in a tube without REALLY considering the user’s application, namely the operating distance for a laser beam size.HoTech has been designing and building laser modules and systems for over 20 years for various professional industries.We know exactly how a laser should work.We limit our laser beam to the finest size in the correct operating distance for optimal effect.Our understanding and experiences with the laser design permit you to have an effective and precision collimation.


Proprietary Crosshair Laser Collimator Available
With our proprietary laser crosshair, user can zero-in the laser with ease during the final collimation on the secondary and the primary mirror. The crosshair model still exibits a precision laser center dot, but with a touch of four extended laser lines from the center dot. The extension lines (crosshair) of the laser dot is the most intuitive way to guide the laser pointing for an accurate adjustment. During the secondary mirror collimation, a single dot laser projecting on the approximate center of the pre-loaded donut is difficult to identify if the laser dot is exactly on the center.The crosshair laser can easily help user to adjust the secondary mirror to point the laser on the exact center with the help of the crosshair line. During the final primary mirror collimation, the returning laser dot often hides into the laser exiting hole preventing user to identify if the returning laser is at exact center of the hole. Again, the crosshair will visually guide the user to center the laser dot with ease even when the center laser dot disappears into the exiting hole.It is a very effective and essential feature to the SCA Laser Collimator in obtaining at even higher degree of accuracy with ease. Click here for a video tour on YouTube.

High Accuracy Laser Alignment

Our laser collimator is well centered and aligned which are critical factors for an accurate collimation.But you will be surprised that many laser collimators in the market fail in this regard.The reason is in the design and understanding of the product itself.

We considered all aspect of parameters in our design.Parameters like the alignment mechanism, mechanical and optical structure of the laser itself, and more are taken as part of our design.For instance, some laser collimators install an off-the-shelf laser pointer in the casing.It is very cost effective (for seller), but it inherits numerous problems.In many cases, the laser pointer might not install perfectly centered in the casing due to pointer size variations and the added alignment mechanism.So the laser itself is not positioned on the true alignment point and optical axis. As the result, the laser can never be center-aligned in the enclosure.It is possible to align the laser beam parallel to the optical path but always with an offset along the optical axis.This means the laser beam is off no matter how you center adapt the laser collimator to the focuser. The result of off-centered laser will introduce astigmatism into your telescope which is similar to figure 1's scenario.

Light Weight Design and All Aluminum Body Machined with High Precision CNC

Many laser collimator manufacturers give users the wrong impression, “big and heavy means rugged and stable.” Instead, HoTech engineers successfully cut the unnecessary weight on the laser collimator because we understand that additional weight on a telescope (especially open structure Newtonians) will create imbalance and structure sagging. The heavier the device is, the more inertia it will have during an impact from an accidental drop.In such an accident, the inertia force can cause more damage to the internal alignment mechanism because there is more energy required to dissipate from the impact.Therefore, the lightweight design on our laser collimator makes you gain reliable precision collimation.And of course our laser collimator uses aero-space grade lightweight aluminum material and CNC machined with the tightest tolerances, then sand blasted and anodized to protect from harsh environment. Nothing has been sacrificed while you get a long lasting state-of-the-art collimation instrument.

Long Lasting Battery Life
By using the CR123, 3V battery as our laser power source, our laser collimator has over 65 hours of continuous use battery life time. The included CR123, 3V lithium battery operates well under a typical cold night and it has a 10 years shelf life. This is a great advantage that you don't have to worry about changing the tiny hard to find cell batteries frequently in the dark like other collimators.

Collimation for your SCT
Commercially made SCTs all have slight optical and mechanical alignment errors. The error typically is in the centering of the secondary mirror. As the result, when a laser is installed and emitted from the focuser, the beam will seldom return dead center, even though star testing would indicate perfect collimation. The secondary mirror (convex shape) expands the fine laser dot to a larger spot, and magnifies any axial error by about 5 times. The error of deviation for a typical well collimated SCT will return laser beam at around 0.125" to 0.250" off center. To compensate the optical and mechanical alignment errors of SCT, a different collimation approach is required in compare with Newtonain telescope. Please refer to our newly developed Advanced CT Laser Collimator to detail.

Diffraction Grating Pattern Lens on our SCA Laser Collimator
Since our SCA Laser Collimator is already accurate with the SCA technology, fine laser dot, and the built-in 45 degrees faceplate, there is no need to use the DFG pattern to align the primary mirror of a Newtonian telescope.The purpose of using DFG pattern is to gross alignment the primary mirror.The user aligns the primary mirror by referencing the shadow of the secondary in the projected DFG pattern on a wall, and user counts the DFG dots around the shadow to center in the shadow.This method cannot achieve accurate alignment because the gap between each dot can make a big alignment difference.At the final alignment stage, the user must bring the laser dot back to the laser exit (the center of the 45 degrees faceplate).Our built-in 45 degrees faceplate allows you to align your primary mirror from the rear of the telescope eliminating traveling to the front of your scope repeatedly during collimation like other collimators.Therefore, there is no need to use DFG lens in conjunction with our SCA Laser Collimator.

"We used your 2-inch SCA collimator to help bring our 15-inch Obsession Dobsonian telescope back into service. The telescope was initially so far out of collimation that the laser beam reflected off of the primary mirror didn't even reach the secondary mirror at all. That was easily fixed and the magic of the SCA made final collimation a breeze. The star images were excellent and the telescope was enjoyed by a group of about 50 people under wonderful skies. I confess that
I had never used a laser collimator before, but using the Hotech laser collimator was much easier than I had imagined. I now know that it is a fantastic tool that makes it easy to keep a telescope in tip top shape for observing."
Scott Kardel - Caltech Astronomer, Palomar Observatory Public Affair

Be the first to Write a Review for this item!

Some items that are showing as in stock are in stock at our holding warehouses, not at the shop. To double check the stock levels at the shop, please contact us on 01909774369 or

The delivery times for most items is 1 - 2 days but again, please double check stock levels on important orders before placing an order via the website.

The delivery costs for courier next day are for mainland UK only. If you live in the Scottish Highlands/Islands, Channel Islands or Northern Ireland, then a shipping surchage will apply. please contact us for prices. Smaller items can still go 1st class via Royal Mail.

Please note that if you are wanting to take advantage of our Saturday and Sunday timed services or next day pre 12 or pre 10:30 services, you MUST check that the stock is here at the shop before placing orders. Also, orders using the Saturday and Sunday services must be placed before 1pm the previous working day. Also, please remember to check that the stock is here at the shop before placing orders. If the stock is not at the shop, we won't be able to ship on any of the timed services. 

Please note International customers will need to contact us for a shipping price prior to ordering via the website. We don't ship all items internationally. It is at our discretion what we ship outside of the UK. This all depends on the size and weight of the items. Please get in touch with us for any postage costs. Please note we do NOT ship telescopes or heavy items outside of the UK. This is due to massive postage costs and problems regarding returns.

If you have any questions regarding stock levels or delivery, please get in touch.

Zygo Interferometer Testing For ED Refractor Telescopes!

We are extremely pleased to announce our Zygo Interferometer is now installed and ready for use! Our experienced staff can test refractor lenses up to 120mm aperture and provide a comprehensive 2 page report showing the optical quality and Strehl ratio, plus much more information. We are using the very latest Zygo MX software to provide a more detailed report compared to other standard reports.


The interferometer is essentially a measuring instrument. Within the interferometer is a calibrated laser that is pointed through the optical test surface, then onto a high quality reference sphere, then back through the test subject then to an internal camera which gives us the measurement on the screen. From this, we can adjust the position of the test optic and the reference sphere to obtain a perfectly calibrated system. The more central the laser to the test optic and then on return, the better and more accurate reading and measurement we can take. This takes a lot of adjustment to get the best results from the optical surface. Once the measurement has been taken, we are provided with a series of results that show the optical quality of the surface plus other information. Continue reading for an explanation of the individual values and you can also see a test report that was done on one of our RVO Horizon 60 OTAs. 

We are offering certain telescopes with a Zygo test at an extra cost. Mainly ED doublets and triplets. All available telescopes with a Zygo test report are listed here. Just select Zygo Test Report from the drop down box at the top of the listing and we will test the optics in house and provide a full 2 page report with your scope. This will show you the optical quality of your telescope optics. We can also offer this service on your refractor telescope. Please get in touch for more details about this. 

At Rother Valley Optics, one thing we pride ourselves on is customer service and quality of our equipment. When we test your telescope, we will ensure that it is of the highest quality otherwise, we will reject the scope under our strict quality control and test another model for your peace of mind. One of the main values to look at when testing a refractor is the Strehl ratio. The higher this number, the higher quality lens you have. At Rother Valley Optics, we will guarantee the highest possible Strehl ratio for your telescope.  We will aim to provide 0.95 Strehl or higher on Takahashi, RVO Horizon, William Optics and many more! Generally, the higher the Strehl ratio, the lower the Astigmatism and Coma meaning a better image quality from your instrument. 

Other measurements such as the PV and RMS are important too. With these measurements, the lower the number the better as it shows less curvature on the lens. The flatter an optical lens, the better it will perform. The PV rating (Peak To Valley) is a measurement from the highest point (Peak) to the lowest point (Valley). From this we get the RMS (Root, Mean, Square). This is a similar figure to the PV and measured exactly the same way. The RMS is basically an average height difference from the PV so again, the lower the better. As you can see form the example below, we measured an RMS of just 0.027 wave which is a very good value.

We also measure the Power with our systems which is essentially the error from the reference sphere to the test optic. The reference sphere we use on our system is a very high quality sphere so the closer to zero the Power, the less error between the 2 elements thus ensuring a higher quality optical surface. 

You will also see some more values such as Astigmatism and Coma. Again, these are measured by the interferometer when we take measurements of the optical surface after adjustment. These are values which ideally would be at 0 but as our test optics are all curved lenses, there will always be astigmatism and coma present. The lower the number, the less of these aberations you will effectively see but with most refractors, you can buy field flatteners which will compensate for the coma anyway. The astigmatisms value is explaining the error between the symmetrical curvature of the lens. Basically, no lens will be perfectly symmetrical, the lower the astigmatism, the more symmetrical the lens surface is. 

Once the Zygo test report has been completed, the optical alignment is thoroughly tested and tuned to ensure they are spot on before they leave us. 

All available telescopes are on the website at the link below and ones we've tested already that are available straight away are also listed.

Here is an example of the test what we provide. This was a test on one of our Horizon 60 ED OTA's.

For any questions about this amazing new service, please either call 01909774369 or email


Related Products
Baader Mark III Laser Collimator

Baader Mark III Laser Collimator£84.00


The Baader Laser Collimator has a precision etched reticule featuring hundreds of tiny cross-hairs that light up brightly when the reflected laser beam touches them. Easily visible from any viewing angle.

HoTech Advanced CT Laser Collimator

HoTech Advanced CT Laser Collimator£549.00

The Advanced CT Laser Collimator brings the collimating star to your telescope within arm reaching distance. With its short-range capability, you can perform collimation indoors - day or night.

OVL Laser Collimator 1.25''/2''

OVL Laser Collimator 1.25"/2"£45.00


This 1mW red laser collimating device boasts some of the best and most practical functions collimators can offer. A large display window allows the user to clearly see the face of the device.