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Stacking Barlows

Started by rocketsteve, 06/30/2003 03:09PM
Posted 06/30/2003 03:09PM Opening Post
This morning, I brought out my Orion XT8 dob for a real quick peek at Mars. Initially, I was viewing with a 3x-barlowed 17mm EP (approx. 212x mag.), but then I wanted to switch to a 2x-barlowed 25mm EP. I removed the 17mm from the 3x barlow, and mistakenly inserted the 2x-barlowed 25mm into the 3x barlow. When I realised what I did, I wanted to see if I could bring Mars into focus, and to my surprise, the planet came into perfect focus and was absolutely huge. The southern polar cap was just as plain as could be and the divisions between the darker and lighter areas were very distinct. Now if my math is correct, for my scope, a 2x-barlowed 25mm EP becomes an unbarlowed 12.5mm EP, which is then 3x-barlowed and thus becomes an unbarlowed 4.166666mm EP, yeilding a total magnification of 288x. Is this the correct answer or have I missed something?

Posted 06/30/2003 05:35PM #1
Sounds right if both the barlows are operating at the rated factor. My Ultima barlow varies from about 2.2x to 2.4x in my SCT. It's 2.2x in my refractor.