Question about Coronado SolarMax 40 Telescope

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40mm Solarmax Filter

I have an original Coronado 40mm Solarmax filter set. I don't know the BF size. Based on the price I paid, it sounds like a 5mm. When I ordered I told them It would be used on a Celestron C5. How can I determine the BF size?

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Measure the aperture of the output (eyepiece end) of the blocking filter. That diameter in mm determines the BF size.

That is not the only difference among all the bloacking filters but is the way to determine which one you have.

Regards, Marc

Posted on Dec 05, 2008

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Can I use this telescope to view the solar eclipse and if so, how do I do this safely?

Only if you have a white light filter. You can make one or you can buy one, I have done both.
Here are a couple of helpful links. The first one explains white light filters.

This link is a place that sells the material.

Cheers .,. Bob

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Do NOT attempt to look at the Sun through a solar filter! These can crack from the heat and you will be blinded instantly.

Most telescopes use a standard fitting eyepiece with a 1.25 inch outside diameter barrel. You can measure the mount where the eyepiece goes to make sure that yours is this size, then search on eBay or Amazon for "1.25 eyepiece" and you will find many available. None of these will be made by National Geographic, but any make will fit.

The other variable will be the focal length of the eyepiece, which is what determines it's power. The power of the scope will be the focal length of the main objective divided by the focal length of the eyepiece, so a 9mm eyepiece will give a higher magnification (and be dimmer and harder to focus and find objects) than a 20mm eyepiece. It is usual to have two or three different focal length eyepieces for viewing different objects.

You will find a large variation in prices, which is partly due to the difference in quality and type of construction of the eyepieces. Kellner eyepieces are simple and cheap, whereas Possl or orthoscopic ones are more complex and cost more. There are reasons why people will pay more for the better eyepieces. Avoid eyepieces marked with the letters "H" or "SR" before the focal length.

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Here are two companies:

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You will NOT get 525 power from that small telescope. Yes I know the box said that but it was a lie.

An eyepiece might cost as much as you paid for the entire telescope. NEVER buy a telescope that advertises magnification on the outside of the box.

Here are some eyepieces:

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Yours is probably either a .965 or 1.25 inch.

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HI lyuen: its possible the finder scope/window is not aligned properly , or these type of scope need very careful focusing. otherwise it will be difficult to see the sun.
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