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ZWO ADC Atmospheric Dispersion Corrector - ZWOADC

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ZWO's Atmospheric Dispersion Corrector is used to reduce the effect of atmospheric dispersion on lunar and planetary images. This device dramatically reduces the prismatic smearing caused by the passage of the light through our atmosphere and allows planetary images to be taken which show noticeably finer detail.

Commercial ADCs are relatively new. Their significant benefits, however, justify more astronomers knowing about them. As well as being an advantage to imagers, they can also help visual planetary observers, increasing the amount of surface detail seen through the eyepiece.

Why you would use an ADC?

Light from any star or planet that enters our atmosphere at an angle will suffer refraction effects which bend to light to a slightly steeper angle. This refraction effect makes the object appear higher in the sky than if the atmosphere wasn't there. The degree of refraction depends to a small degree on various things like temperature, humidity, observers and height above sea level, but does increases strongly with decreasing altitude of the object - for example, the image of the sun at sunset can actually be elevated by over 0.5°, which is slightly more than one solar diameter.

 Like most optical media the refractive (bending) power of the atmosphere is actually dependent on the wavelength of light. This is called optical dispersion. Atmospheric dispersion means that actually the degree of 'lift' that the refraction causes depends not only on the angle of the light, but also the colour of that light. Atmospheric dispersion spreads the light from any point source into a vertical spectrum of colours whose length increases the lower the object is in the sky.

The diagram of viewing Saturn illustrates this dispersion effect as light enters the atmosphere and also the lifted elevation of the image. The lift is wavelength dependent and hence the image is separated into different colours. A planet exhibiting bad atmospheric dispersion effects will have a blue fringe on the top edge and a red fringe on the bottom edge.

Atmospheric dispersion correctors use two prisms adjusted to cancel out these distortions caused by the atmosphere.  You can read in much more detail in this excellent article by Martin Lewis:

Returns Policy

You may return most new, unopened items within 30 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

Items that have been opened, damaged or are otherwise unsaleable will be subject to a minimum 10% restocking fee, to be assessed by Telescopes Canada upon receipt of the returned goods

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the 'Complete Orders' link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.


We can ship to virtually any address in the world. Note that there are restrictions on some products, and some products cannot be shipped to international destinations.

When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.

Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.

Typographical Errors and Order Cancellations

Telescopes Canada reserves the right to cancel an order due to an error in pricing by Telescopes Canada or one of our suppliers, equipment being no longer obtainable, or other events which are out of our control.

Client-Initiated Cancellations

Client-initiated order cancellations are accepted prior to delivery of the equipment to the customer, thereafter it is a return.

Material: H-K9L(Schott BK7)

Surface Accuracy: λ/10@632.8nm

Deviation Angle: 2°

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