Meade ETX-90-105-125 - Focal Reducer

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The F-0.66FR will work with the Mead ETX90 - 105 - 125.

The F-0.3EXT needs a modification tot he focuser as described by Dan below. (At least for the ETX-90) I don't know about the 105 and 125 at this stage.

Steven, I promised you feedback on whether the 0.3 adapter tube for the 0.6 focal reducer would work with my system; both arrived 20 Jan and I tested them on sunspots.

Meade ETX-90-RA, Maksutov-Cassegrain, fl=1250mm, f13.8 Philips ToUcam 840 I was able to get to focus with the 0.3, but I had to remove the original focus knob and use a piece of vinyl tubing over the shaft to be able to turn it in far enough. I got the idea from this site, which has a lot of ideas for ETX users:

Images showing focus shaft showing the difference between the 26mm Meade Plossl and the ToUcam 840 with 0.6 and 0.3 focal reducers.

 The photo for the paragraph below, "3magsfencepost".

I took shots of a nearby fencepost to measure the field. With the adapter only, the 640 width spanned 8.97 minutes of arc. With the 0.6 lens it was 15.47 minutes. With the 0.6 lens + 0.3 extension, it was 18.54 minutes. I used the measure tool in Photoshop to get the data for the calculations. The sun shots confirm the calculations. I got about a 0.58 reduction with the 0.6 lens, but only about 0.49 with my system adding the extension. BTW, the extension wouldn't screw onto the lens all the way, leaving about a 2.5-3mm gap; however, this is good for increasing the reduction! I may need to try a second 0.6 reducer to try to widen the field a bit more; I'm thinking about it. I'd think the limit would be how far I could turn the shaft in before it falls off, which would probably happen with a longer extension. As you can see by comparing the 'focus' shots, while the difference from eyepiece to webcam to webcam+0.6 was not that great, adding the extension took about another 5 turns. I'll leave the files posted until at least April.

Thanks, Dan Prall



Dans Images



Meade ETX-90 with Adapter - F-0.66Fr and F-0.3EXT images of fence post.