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DaveL59

TAL-M refurb

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21 minutes ago, Stu said:

Err hmmm, it’s actually a light thimble, the Telementor is the peashooter 🤣🤣

my bad Stu, the old grey cells don't always play nice, of course I shoulda realised huh, thimble - a kinda teeny tiny bucket... 😄 

Just tried out the barlow combo on a distant (ish) tree canopy that was nice and bright while the sun peeked out. So focuser -> TAL-M x3 barlow -> TAL-1 x3 barlow -> 25mm Plossl. Worked pretty well. OK dim but that's expected with that amount of mag, adjusting focus I was able to see very close into the leaves on the tree as the branch wafted in and out of focus in the breeze. Focus seems soft though, again no surprise.

No idea what mag that actually gave me, the 25mm plossl should give x21 I believe (80/526mm FL) so with x3 barlow that'd make x63. What effect does a barlow in a barlow give I wonder? Would that add another x3 to the first barlow's x63 or be x6 to the EP's x21? So effective result is x189 or x126?

Either way it seems usable as a combo of the 2 barlows and kinda saves me messing about trying to fettle an extension tube. The acrylic tubes would cost around £8 each for the 2 diameters at 100mm length. Not too bad if I do decide to try that one day, easier than trying to work metal with hand tools too 🙂 

 

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doing a bit of reading around the web:

Stacking Barlows doesn’t add the factors, it multiples them – thus stacking a 2x with a 3x gets you 6x. Now, on your 1000 mm focal length scope, with a 25 mm eyepiece (40x) paired with that 6x stack, you’re getting a 240x magnification view!

Interesting, that'd mean the combo I have in 32mm fit would give a x9 effect. So I was using the TAL-M at x189 with the 25mm Plossl, wow I'm not surprised the image dimmed and got soft and hard to pin the focus, especially being a tree branch with the sun hitting the leaves. Impressive though that it was useful at all given the 80mm aperture, will be interesting to see how that combo works aimed at Jupiter and Saturn.

Might be worth getting a couple acrylic tubes and making up an extender too for a more in-spec x139 as the stacked barlow could be pushing the scope a bit far, will decide once I've tried it out tho 🙂 

 

PS - source of the above info:
https://orionbearastronomy.com/2019/02/11/pros-and-cons-of-barlow-lenses/

 

Edited by DaveL59

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