ZWO Camera Troubleshooting Guide

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The Sun just set, and it looks like the forecasts were correct: there isn’t a cloud in sight. You set everything up, including your ZWO camera, which whirs to life. After you reach your target cooling temperature, you start the image capture program… only for the first image to come through with a huge bright patch in the corner. Perhaps you don’t even make it that far and instead receive an “Exposure Failed” message. Maybe you don’t even reach your set cooling temperature. Or, your image capture program doesn’t see the camera at all.

Even with ZWO being the leading astrophotography camera brand and offering fantastic products, there will occasionally be situations where something goes awry. Often times however, while these issues may seem and feel catastrophic, actual camera defects and failures are exceedingly rate, with the vast majority being simple things you can resolve with this guide!

The steps outlined in the article below have been compiled by our experts and are based on hundreds of successful troubleshooting interactions over the years, and tips we’ve received while working with ZWO’s excellent support team! We highly recommend reading the Most Common Issues section regardless of what your issue is. Not only do the steps here resolve the vast majority of issues, but in the event your issue does need to go to ZWO, these are some of the steps they will ask that you perform if you haven’t already.

A Note About This Guide: At the beginning of each section, we’ve included a summarized version of the testing procedure. We recommend reading through the full section first and then using the summary as a guide while walking through the troubleshooting steps.

Most Common Issues: A Deeper Dive

Exposure failed messages, oddities in images, and failure to recognize the camera are among the most common issues our gear experts see. If you’re experiencing one of these issues with your ZWO camera, or anything in between, the following steps are the place to start!

First Steps

Checking Power: It may seem like this is only relevant for cooling issues; however, ZWO Pro models are more than just an uncooled model with a separate cooling system slapped on. These designs require more power than USB alone can usually provide and accordingly will not function without 12v 3A DC power. Some earlier Pro models could be used without external power if the cooler was turned off, but this is no longer the case and external power is required regardless of whether you will be using cooling or not.

While it truly should be as simple as just verifying that your power supply is rated to 3A, an unfortunate reality our experts have encountered again and again are power supplies that don’t actually meet their rating. It is for this reason, we recommend ensuring you are using a high-quality power supply from a reputable manufacturer. If you’re using a power distribution solution, try removing this from the equation and powering the camera directly if possible. If you are unable to do so, double-check the output is rated for 3A output and the supply in use can comfortably cover the demands of the camera and all other equipment connected.

A final failure point within the power system are the actual cables. Inspect the cable for fraying/cracked insulation along its length, and replace any cords or AC adapters that show damage. It is rare, but on occasion, these can fail without being visibly damaged. A good way to test that the cable is passing power along is with another piece of equipment.

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USB Cable/USB Port: After power concerns, issues with the USB cable are the next most common culprit of camera issues. They’re also some of the most frustrating to deal with, as there is rarely any visible sign that a cable has failed. So, when something suddenly stops working, it is common for suspicion to fall on the more delicate/intricate components like the camera rather than a simple cable. This often leads to a lot of time and effort spent trying to fix a camera that isn’t broken. That being said, if you believe you’ve ruled out cable issues, we highly recommend double-checking—even if the cable is brand new!

The two methods of checking a cable are fairly straightforward and are as follows: swapping it out with another cable or swapping out the camera for a different device. Of course, there is always a chance (though it is very small) you have two bad cables, so we recommend checking with a separate device if you continue to have issues after a cable swap. One thing of note with faulty cables is sometimes the failure is position-dependent, so be sure to move the cable around while testing. We’ve seen plenty of cable failures where a cable will work long enough for a device to show as connected and work briefly, only to fail after a few minutes of use, so be sure to be thorough with this troubleshooting technique.

Though USB port failures are less common, it is still something to check. First, examine the USB port on the camera and the PC to ensure there are no broken plastic pieces or obviously bent pins. Then, try connecting the camera to a different USB port and re-testing.

If you're still having issues after checking the USB port and cable, this does not mean the camera is broken or defective, just that you will need to do a bit more digging. So far, we’ve been focused on hardware troubleshooting, but now, let’s take a look at software!

Software Troubleshooting: It may seem pretty straightforward. If the software lists ZWO cameras as compatible, it should just work. These are the most popular brand of astronomy cameras, so things should just be plug-and-play. However, the reality is some software suites are less “turn-key” than others. The way programs interact with a certain model could have bugs as well, so one camera may work while another does not. Software updates especially can introduce these bugs.

Note: If you’re using your ZWO camera with an ASIAIR, you can skip this section.

First, if you have not already done so, make sure that you visit the software section on ZWO’s website and download and install the native camera driver, if available for your operating system, as well as the ASCOM driver, if the imaging program you’re using requires it.

For the reasons listed above, it is always a good idea to test your ZWO camera with ZWO’s first-party software suite. By using first-party software, you can just about eliminate the chance an issue is caused by a third party’s implementation of drivers. While ZWO ASI Studio may not be your imaging tool of choice, starting here will inform whether you need to pursue further troubleshooting with the camera or contact the software developer. The suite is available for free on ZWO’s website, so it won’t cost you anything, and in the event you need to contact ZWO for further assistance, they often require that you check with this suite if you haven’t already.

An additional resource to check with is the free program SharpCap. There is a paid Pro tier, but for checking images, or whether the camera can even successfully take images, you don’t need to purchase this tier. While this is a third-party program, many of our users and experts have had great success using it with ZWO cameras, and accordingly, it is a great way to do a “double-check.”

If you’re still encountering issues with the camera when using ZWO’s ASI Studio and SharpCap, then you likely will need to review our more specific troubleshooting sections, but first there are a few more simple checks you can perform.

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A Few More Simple Checks

Remove Any USB Hub/Extensions: While there are hubs, particularly powered ones, that will work just fine for astronomy equipment, we occasionally do see some do not. In addition to this, it is always possible the hub itself is malfunctioning or failing, so we suggest testing your camera when it is directly connected to your computer to rule out this possibility.

Extensions are similarly known for occasionally causing issues, especially over longer and longer distances, whether it is a powered extension or not. Again, to rule out this possible failure point, we recommend trying the camera directly connected to your PC.

Remove Any Other Equipment: Though other equipment interfering with your camera connection is not a common issue, it is still worth isolating the camera as much as possible when troubleshooting a ZWO Pro camera with USB 2.0 passthrough ports. If the camera works when accessories are disconnected from it, then it is worth investigating if the equipment itself is working properly. Additionally you will want to assess if the device itself is suitable for the hub on ZWO Pro cameras. Devices using the USB port for power only, such as USB dew heaters, draw more power than the ZWO camera USB port is designed for and should not be used.

Still Having Issues? If, at this point, you are still experiencing exposure failure messages, connection issues, or if the camera is not being recognized, then jump to our section about contacting ZWO. If, however, you are able to take an image but are seeing artifacts/oddities in it or are experiencing issues with the camera not reaching the desired temperature while imaging, then you’ll want to move on to the more detailed sections below.

Image Issues: A Deeper Dive

So, you’re able to take images with no problem but find they have odd artifacts? While camera failures/malfunctions can be the culprit, it is more common for the issue to lie elsewhere in the imaging train. It may seem like a daunting task at first, chasing down the source of an image issue, but with these tips, you’ll be diagnosing these issues like a pro in no time!

Calibration is a topic on which we could spend quite a bit of time. That is why we created an article, Understand Calibration Frames. For calibrating out amp glow specifically, we recommend checking out the Dark Frame section of the linked article, which covers capturing and applying these frames.

Assessing Tilt: When part of your image is in focus, but a corner or side is not, this is known as tilt. This occurs when part of the camera sensor is tilted away from the image plane formed by the optics. How this occurs is a bit more involved as it is possible the sensor itself is tilted, or the imaging train itself is flexing/sagging slightly, or perhaps the sensor has a bit of tilt introduced from an adapter/spacer/accessory.

Adjusting for tilt can be done with accessories known as tilt plates/tilt adapters, and for a number of ZWO cameras, these are even included with the camera. However, if you are looking to assess if tilt is coming from the camera sensor itself or the imaging train, then proceed with the following test:

• Point your telescope at an object and focus on it.
  • This does not have to be done at night with stars; you can absolutely do this assessment during the day. Just ensure whatever you point the telescope at fills the whole frame, is relatively flat, and has enough detail that you’ll be able to spot any out-of-focus sections.
• Take an image.
• Slightly rotate the camera only. This does not need to be drastic, 45-90° of rotation is plenty to check for sensor tilt.
  • The best way to do this is to unscrew the camera slightly. This ensures you’re not rotating any optical elements, spacers, adapters, or accessories that might be introducing tilt along with the camera. Make sure you are careful when doing this, and you stay with the camera at all times when it is not fully screwed down/attached. You want to be present to catch the camera, but don’t add any pressure, which may artificially introduce tilt.
• Refocus.
• Take another image.
• Compare the two images.

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Troubleshooting Other Image Issues

Gradients. Soft/amorphous spots. Splotches. Images without stars. What these all have in common is most of the time these are caused by some physical phenomena: dust, dew, spacing issues, issues with filters, focus, etc. While you may feel you’ve ruled these out, we strongly recommend you read through the following to double-check before reaching out to ZWO’s warranty support team.

The Bench Tests: Before looking at anything else, you’ll want to assess the performance of the camera on its own. Accordingly, you’ll want to do the following to establish a baseline:

• Remove the camera and any connected accessories from your imaging train.
• Connect your camera to your PC or ASIAIR, and open the image capture software of your choice.
• Point the camera at a surface as flat and uniformly lit as possible. A ceiling or wall is perfect for this.
• Adjust the exposure time until you’re seeing a gray image in the preview; if you have a program with a histogram, aim to put the “hump” or “curve” towards the center.
• Take an image. We’ll call this one the ‘Light’ image.
• Now, put the lens cap on the camera and place it in as dark an environment as possible. You want to eliminate as many possible places for light to get in as you can; think inside a bag covered by a towel, if possible.
• Adjust the exposure time to something short, but not too short, like 2-5 seconds.
• Take an image. This one we’ll refer to as the ‘Dark’ image.

The Light Image: Check this for any signs of splotches, blobs, or other similar artifacts. If any are present, then physically inspect the “window” that protects the sensor chamber, as well looking at the sensor inside the chamber, for signs of dust, particulates, smudges, etc. Clean these using a kit like the Apertura Cleaning Kit. If there's dust or particulates on the sensor itself, please refer to ZWO’s cleaning guide and ensure you are using cleaning solutions/tools specifically for cleaning these delicate chips.

The Dark Image: Check this for signs of obvious gradients. Should one be present, double-check check your testing setup is adequately blocking out stray light.

If you are able to generate the two above images without issues (or are able to track down the source of the issue as outlined), then chances are very, very good your camera is fine! But that begs the follow-up question: Where is the issue coming from if not the camera sensor?

While diagnosing other issues in the optical train could likely be its own separate article, we’ll go over some common issues, what they look like, and how to address them!

Back Spacing

Presentation: Not able to see stars at all or can only see large splotches of white; images look poor in general, with notable distortions on the edge of the frame that the corrective element should be addressing.

Cause: With field flatteners, coma correctors, and focal reducers, there is a very specific distance between the camera sensor and the corrective element. If it is not at this distance, optical performance will be impacted.

Fix: We have a whole article dedicated to this subject: How to Connect a Camera to a Telescope! However, if you find you can’t see anything at all, try the following:

• Bring your imaging train out during the day and point it at a distant object. The further away the object, the better.
• Attempt to focus on this object.
• If you can focus, take note of where the focuser position is (if you don’t have an SCT) or perhaps even lock your focuser in place. Then, at night, try starting from this position.
  • If you can’t focus, then you will want to review the linked article for tips on setting your camera spacing.

Dust or Particulate in the Imaging Train

Presentation: Out-of-focus dark spots/blotches.

Cause: Particles in the optical path block light, but since these are not what the optics are focused on, they appear as large and transparent blobs rather than small, sharp, solid specks of black.

Fix: Inspect the optical train for signs of dust or particulates, including the scope and any field flatteners, coma correctors, focal reducers, or filters. If accessible, you can try cleaning this with something like the Apertura Cleaning Kit. You also can use flat calibration frames to “fix it in post”. The reality is you usually will want to use both. See our article on calibration for more information on taking and applying your flats!

If none of the above feels applicable to your issue, or if these steps do not resolve your issues, then we advise a systematic approach if possible: remove the filter wheel, take an image, and check for improvement. If it doesn’t improve, remove the field flattener/coma corrector/focal reducer, take an image, and check for improvement, etc. This may not solve your issue immediately, but it will give you a big advantage in narrowing your search for a solution, as well as troubleshooting with support.

Cooling Issues: A Deeper Dive

While not unheard of, actual failures of the cooling system are fairly rare, and the distance between occurrences has only been increasing with recent production ZWO cameras. When issues do occur, typically following the steps in the Most Common Issues section will resolve them. If they don’t, then you will need to contact ZWO. Before you move on to that step, be sure to read this one first!

In lieu of actual defects, more often, there are misconceptions about how the cooling system operates and what it can do. We’re happy to relay that knowledge, and the way manufacturers advertise these systems has been improving. To clarify, the cooling figure listed by manufacturers like ZWO, QHY, etc., is a delta. This figure refers to how much the cooling system can lower the starting temperature, not what temperature it can ultimately reach. For example, a camera advertised with a -35° C cooling feature can cool a camera sensor starting at 40° C to 5° C, not -35° C.

In addition to understanding the figure is a delta, it is also important to know this figure is not absolute but rather what the cooling system can achieve under optimal circumstances. It is not uncommon to see a cooler only providing 32° C of cooling instead of the full 35° C.

PSA: If you are going to push your cooler to the max cooling or close to it, ensure you are cooling and disengaging cooling in stages. For example, if you’re aiming for 30° C of cooling, cool 10°, wait a few minutes, cool another 10°, wait a few minutes, then cool the last 10° (and then follow this in reverse when you’re done). Cooling your camera sensor down or warming it up too fast can damage the camera.

One last thing to understand is how your software handles cooling. Some programs will allow you to set a target temperature, in which case you’ll need to note the starting temperature and calculate just how low you can go with the cooling. Other programs, however, will allow you to set the target amount of cooling you want, or in other words, what delta you want. Usually, these programs will show your starting temperature as ‘0’. It’s important to determine which system your software uses because a target temperature of -20° C is a lot different than -20° C delta if you’re starting at 30° C!

I’m Still Having an Issue—Contacting ZWO

If you’ve made it to this section, then you have unfortunately exhausted all the common remedies for ZWO camera issues and will need to engage ZWO’s technical team for more in-depth troubleshooting and possible repairs. We know how frustrating it can be to reach this point, so we’ll be providing a few more tips to help move the support process along as quickly and smoothly as possible!

Step 1. Gather Your Documentation: Manufacturer support processes can be tedious at times, so to cut down on the amount of back-and-forth emails (and thus cut down the time this takes), you’ll want to check off as many of their “need to have” boxes from the start. This includes:

• A copy of your receipt, either a scan of the physical invoice or a screenshot of your digital receipt email.
• Images of the issue in question. This should include images from the camera showing the issue, screen captures from your computer or program showing the issue, and/or any images of your physical setup that may help demonstrate the issue or confirm your setup is correct.
• A detailed description of what issue you’re experiencing, along with information such as:
  • Did this suddenly occur or has it seemed to develop over time?
  • If it was a sudden occurrence, did anything else noteworthy happen around that time?
  • All of the troubleshooting steps you’ve tried from this article and any individual research you’ve done to resolve the issue. This is an important part. Take your time to be thorough here. The clearer you can be that you’ve isolated the issue to the camera and have tried all the basic troubleshooting steps, the sooner you can get to the advanced steps and/or send the camera in for repairs.
• A list of your equipment and, if you’re using a computer, a list of the programs you’re using. Also include what OS your computer runs (Windows, Linux, or Mac).
• Your contact information, including your current address.

Step 2. Contact ZWO: You will want to navigate to ZWO’s official website to ensure you’re using the most up-to-date contact form or email. While drafting your first outreach to them, be sure to include all the above information, pictures, and documentation. There are many ways to approach this initial outreach. We’ve created a template to make things easier:

Hello ZWO, I purchased a(n) [[ZWO camera model]] from High Point on [[date of purchase]]. [[Describe the issue that you’ve encountered with the item. Be as detailed as possible. Include things such as whether you’ve noticed the problem develop gradually or suddenly and if it appeared suddenly, what was happening at the time it appeared.]] [[Describe here what you’ve done to troubleshoot/isolate the issue. Again, be as detailed as possible here. Troubleshooting is a part of most manufacturer’s warranty processes, and the further along you can demonstrate you are in that process, the quicker it typically goes.]] Please find attached my proof of purchase [[and if at all possible, images and/or screenshots of the issue you’re encountering]]. My contact info is as follows [[Name]] [[Current address]] [[Phone number]] [[Email address]] Thank you in advance for your assistance with this issue. I look forward to hearing from you, and if there is any additional information you need from me, please don’t hesitate to let me know. Regards, [[Name]] Copy Text

Step 3, Keep An Eye on Your Inbox: Once your case is submitted to ZWO, keep an eye on your inbox for their reply (and your spam folder). Their agents will be able to advise what further steps to take from there, whether it be further troubleshooting or camera repair.

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Glossary

Backfocus/Backfocal Distance/Backspacing

All optical systems have a point at which an in-focus image is formed, and for astrophotography it is at this location that the camera sensor should be placed. When the telescope is used without corrective elements, this is done easily with the focuser mechanism; and so long as an image can be brought into focus, optimal optical performance will be achieved. However with corrective elements, oftentimes there is a certain distance that the camera sensor needs to be placed away from the rear of the corrector for optimal performance. This will be listed as the backspacing or backfocal distance for the corrective element.

Calibration Frames

Calibration frames are types of images that are applied to light frames to remove unwanted artifacts caused by a number of different factors. Dark frames are images taken at the same temperature as the light frames, and are necessary to remove hot pixels or other fixed noise for a cleaner image. Bias frames are similar in this aspect, though their purpose is to reduce the sensor’s readout noise seen within the light frames. Another type of calibration frame are flat frames, which remove dust motes or unwanted gradients for a uniform, even field.

Image Circle

This specification refers to the area where an image is formed by the optics/ corrective element. This is useful for assessing whether a certain camera sensor size will be supported by the optics, or if vignetting/ poor performance will be seen in frame.

Sensor

A camera sensor is the main component of a DSLR, deep sky camera, or smart telescope that turns incoming light into data that can then be displayed on digital devices like mobile phones or computers. Accordingly, these are just as important as the optics of a system for a quality image. There are a wide variety of specifications that are important for a sensor - physical size, pixel size, resolution, dynamic range, amounts of image “noise”, and other technologies such as back-side illumination. As a result there is also a wide variety of sensors available that attempt to balance these in differing ways for different applications and price points.

Sensor Size (Full Frame, APS-C, Micro 4/3, Etc)

Imaging sensors come in many different proportions, such as 4:3 or 1:1, and physical sizes. There are some common combinations that have received a name - full-frame, APS-C, micro four thirds (4/3). The most important component of sensor size for astrophotography is the measurement from corner to corner (diagonal) of the sensor, which can then be compared to a telescope/ corrective element's image circle to assess how well the two may pair.

Vignetting

Vignetting is seen as the darkening of the corners of the frame within an image. This happens when the camera sensor is not exposed to enough light, resulting in a shadow effect along the borders of the image. This issue presents itself for a number of reasons, though most commonly occurs when using incompatible sensor sizes and image circles, and using too small of filters for the imaging assembly.

Visual Back

The visual back is the connection from the focuser where visual accessories are attached. Typically this is used to describe a component of a refractor or SCT, which can be removed to allow for a corrective element (or a different visual accessory) to be connected.

Exposure Time

Exposure time is the amount of time the camera sensor is allowed to collect light. In general, the longer the exposure time, the more light collected, and the brighter the image will become. This should be selected with caution though, as an exposure time that's too long can oversaturate the pixels and blow out the image, resulting in a loss of signal. Determining the correct exposure time is highly dependent on the aperture of the optics as well as the gain settings used. A larger aperture will produce a brighter image than that of a smaller aperture with the same exposure time. In a similar fashion, an image with a higher gain setting will be brighter than a lower gain setting image with equal exposure time. Finding the perfect balance between the aperture, gain, and exposure time will maximize image quality.

USB

Universal Serial Bus or USB is a protocol for data transmission, and is by far and away the most common way astronomy equipment will communicate with a PC in a wired capacity. There are a number of USB connectors, such as USB-A (the rectangular port you’re likely familiar with), USB-B, USB-C, and micro USB; as well as a number of different revisions (2.0, 3.0, 3.1, etc.) that have brought more speed, power, and reliability to the protocol.