Calculator Help

Our online calculator (link) lets you determine the best Star Analyser grating setup for your specific equipment.

If you like, we can do all the work for you for free. Enter your equipment details in our Equipment form (link) and we’ll do the rest.

We encourage you to try out the calculator for yourself though.  The three fields below may require you to look up some additional information about your equipment.

Calculator fields

The page below will help you determine the values to plug into the three above fields.

Where can I find Grating to Sensor Distance for Field 5 in the calculator?

The Grating to Sensor Distance is the distance between your camera’s sensor and the grating when screwed into your nose piece (or filter wheel.)


If you’re using a standalone DSLR with its own lens (not a telescope), you don’t need to use the calculator. You should use our AD-58 adapter (link). If your camera lens is 35 – 100 mm, use the Star Analyser 200. If your lens is 70 – 200 mm, use the Star Analyser 100.

If you’re using your DSLR with your telescope acting as its lens, you’ll need our AD-T2 adapter (link). This adapter places the grating 60 mm from the sensor. Plug this value into field 5.

ZWO cameras

The distance from a sensor to the face of the camera body is called “back focus.”  You can look up the back focus of your ZWO camera in this document: link (Excel, easier to view) or link (PDF, three pages). Field 5 in the calculator is the sum of the back focus and the length of your camera’s nose piece. (The standard nose piece supplied by ZWO is 30 mm in length.)

NexImage cameras

The Grating to Sensor Distance on these cameras is 43 mm. Plug this value into Field 5. For Field 6:  pixel size is 1.67 µm. For Field 7: camera width is 3856 pixels

Skyris cameras

Back focus is 17 mm. The standard nose piece is 33 mm. Add these two and put the result in Field 5.

Other cameras

You can ask your vendor for the back focus distance of their camera for the Calculator’s Field 5: Grating to Sensor Distance. Or, you can measure the distance yourself:

Grating to sensor distance


The drawing to the left shows a camera sensor recessed behind the face of the camera enclosure.

To measure this distance:  Carefully poke a toothpick into the sensor opening and then measure how far in it goes. Sensors are frequently protected by a glass cover plate but be careful not to scratch the plate or the sensor itself. You should use standard static discharge precautions by grounding yourself and the camera, etc.  Your measurements don’t have to be exact. For example, don’t worry about eliminating the thickness of any glass cover plate on the sensor. Then add the back focus that you measure to the length of the nose piece (or filter wheel distance). This is the value should put in Field 5 of the calculator.










Where can I find Camera Pixel Size and Camera Width for Fields 6 and 7 in the calculator?

These values should be available from your camera vendor’s site.

For DSLRs, you can look up your sensor data in this online database: link. Enter your camera into the topmost banner field. Copy the “Pixel Pitch” field in the database results into Field 6 of our calculator. Then scroll down in the database results and copy the first number in the “Sensor Resolution” field to field 7 in our calculator. For example, if the sensor resolution field on the database results screen is  5196 x 3464, copy “5196” to Field 7 in our calculator.

For ZWO cameras, see the document linked to further up this page or see the ZWO site or an online retailer’s site. The highlighted rows in the document contain Pixel Size and Camera Width for each of their cameras.

Questions?  We’re happy to answer questions. You can text chat live or send us an email from this page: link.