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Chronos
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Incorrect. The relay lens is not a barlow.
Just to clarify - by "smaller mount" you mean shorter tube. That's why they are called "short tube" reflectors. You get a longer focal length than you would normally expect out of a tube that length -- by using an internal Barlow.chemisttree said:The company's motivation appears to be the use of a smaller mount.
chemisttree has it right, russ. It is more expensive to accurately figure a faster mirror, but by using that mirror in tandem with a permanent barlow, you can approximate the performance of a scope with a longer f/l. The trade-off is that you get a short OTA with less vibrational momentum to damp, so you can use a cheaper, lighter mount and get acceptable results. The extra cost of figuring the steeper mirror is more than offset by the savings they get by using a cheaper, lighter mount, especially if the mirrors are figured someplace like China. My 6" f:8 A-P APO has a long tube, a heavy objective cell in the front and a heavy cast/machined focuser at the rear. As a result the mount has to be much beefier than you would need for a 6" f:8 Newtonian. Mounting it on the tripod is quite a handful, but it is rock-solid even in windy conditions and damps very quickly.russ_watters said:Just to clarify - by "smaller mount" you mean shorter tube. That's why they are called "short tube" reflectors. You get a longer focal length than you would normally expect out of a tube that length -- by using an internal Barlow.
The part of that that makes sense...it isn't there. And no offense, but your lack of explanation implies you haven't thought it through.Chronos said:Long focal length mirror, corrector lens, shorter tube . . . what part of that is too hard to understand?
It doesn't say a longer focal length mirror, it just says a "longer optical focal length". Ie, normally a scope of that physical size would have to have a shorter focal length. This one doesn't because the relay lens lengthens it.The optical design of Meade Digital Series reflecting telescopes includes an achromatic relay lens, permitting longer optical focal lengths to be housed in shorter optical tubes.
http://answers.yahoo.com/question/index?qid=20071122041842AAnXToeThe two most common problems with inexpensive Meade scopes seem to be mounts that aren't stable, and short Newtonians that use a relay lens (permanently attached barlow) to get a longer focal length. [emphasis added]
Optics use a relay lens (like a built in barlow) to achieve longer focal length...
http://www.cloudynights.com/documents/convert2.pdfHow to convert a hybrid short tube Newtonian to an enjoyable RFT [rich field telescope]
russ_watters said:Well anyway, I'm glad you pushed me to research it because lookie here what I found: http://www.cloudynights.com/documents/convert2.pdf
It's exactly what the OP was looking for! The guy even used the exact same scope! Among other things, it has the true specs of the mirror: 114mm, f/4 (448mm fl). And detailed (holy cow, are they detailed!) instructions for making the conversion.