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I have an 8" meade schmidt cassigrain 2000mm. That is suppose to be perfect for photographing the sun. I'm using a cannon eos and the t adapter. The sun fits side to side, but is too large top to bottom.

How do I correct that?

Tony Wagner
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This will sound weird --- I had a similar problem with a Celestron 8”. I solved by unscrewing the “T” adapter. You will likely see that a cavity exists between the telescope body and the “T” mount. You can, with a little creative thinking, mount a supplemental lens in this hollow.

We commonly attach a Barlow lens between eyepiece and eyepiece tube. The Barlow is a negative power lens system that elongates the focal length of the objective lens. Thus the Barlow adds magnification. Again the Barlow is a negative power lens.

Now reading glasses you can buy at the drugstore are positive lenses. So are the close-up lenses we use on our cameras to make macro pictures when our camera won’t allow close focusing. If you install a positive lens between the camera and the telescope body, you will be shorting the focal length and the image seen by the camera will shrink.

Go to the drugstore and buy some inexpensive reading glasses like +2 or +3 or +4. Hold one of the lenses between your “T” adapter and the telescope body. I will bet the +3 does the trick. Now measure the cavity and see if camera close-up lenses (some say filters) are available for this diameter. Experiment with reading glass lenses. If you find a + power lens that works, this tell you the power you need.

An eyeglass optical shop can cut eyeglass lenses to fit. You might find that such lenses are already available, check your telescope accessory sources.

Alan Marcus
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  • I'll measure the dia. of the t adapt. and pick up some +3 next trip to town. It seems odd that others can slap a camera on a 8" and get good pics of the sun without any mention of this problem?? – Tony Wagner Jun 20 '17 at 20:20
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    It's simply the format of you camera is too small. Most use a 35mm format 24mm height by 36mm length. Likely you are using a compact digital 16mm height by 24mm length. You are imaging at the prime focus of the 2000mm objective. This image projected is too big for your camera format. – Alan Marcus Jun 20 '17 at 20:23
  • Thanks, that did it. My Canon EOS Rebel is NOT a full frame. I switched to my old Canon 700 and I could see the whole sun. I'll get some film as a backup and see if I can locate a full frame digital (used). I'm hooked on the instant gratification :-) – Tony Wagner Jun 20 '17 at 22:23
  • Being retired I have time to calculate sun’s image diameter. Sun’s distance 92,960,000 miles and diameter is 86,4575.9. The ratio is” 864575.9 ÷ 964575.9 = 0.0093.

    The image formed by a telescope traces out a similar triangle. We can calculate the image diameter 2000 X 0.0093 = 18.6mm.

     – Alan Marcus Jun 20 '17 at 23:03
  • Thank you Alan, I'm semi retired. I left electro-mechanical eng. about 20 years ago and went into facility maint. My math suffered over time.Now I'm running a motel that has a constant income from fishermen and hunters. Beautiful area and not far from the area of totality. – Tony Wagner Jun 21 '17 at 00:01
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You could also add one of the f6.3 reducer/flatteners. Either a Meade or Celestron version should work, assuming yours is a standard SCT. You'd probably also want the appropriate SCT T adapter to get the correct spacing between the reducer/flattener and the camera - flatteners are fairly picky about the distance between the sensor and the flattener; if you use the wrong distance then you won't get optimum results.

Nonstandard SCTs with better correction - like Celestron's Edge HD models - need a reducer/flattener designed to match them. I suspect this probably applies to Meade's ACF models as well.

JerryTheC
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