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Barlow for DSLR->Telescope that attaches to telescope threads?

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#1 SkyfallerTac


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Posted 27 October 2021 - 10:16 AM



I would like to ask if there is such a thing as a barlow for DSLR that allows the camera to be screwed onto the telescope thread rather than be held by a thumbscrew pushing on the side of the barlow (normal eyepiece slot). I like to image when stuff is high in the sky and it wrecks my nerves to see expensive equipment just hanging its entire weight by a little thumbscrew. 



Telescope 2" thread -> Threaded connection -> Barlow -> Threaded connection -> Camera T2 Adapter -> DSLR

#2 james7ca


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Posted 27 October 2021 - 11:05 AM

If by a "Telescope 2" thread" you mean M48 x 0.75 (same, nearly, as most 2" filter threads) then many 2" barlows have a female 2" filter thread on their input side (opposite that from where the eyepiece is inserted). Thus, if the telescope has a male M48 thread then it should screw right onto the 2" filter threads on the 2" barlow. If the telescope does NOT use a male M48 thread then you'd need either a gender changer or a threaded adapter to go between the telescope and the 2" filter threads on the barlow. Similarly, many 1.25" barlows are threaded for 1.25" filters, so again all you'd need is an adapter to go between the male M48 on the telescope (if that's what it is) to a male 1.25" filter thread on the end of the adapter (so as to mate with the female 1.25" filter threads on the barlow).


Those kind of adapters are probably available from Agena Astro:  http://agenaastro.co...ccessories.html


Next, you'll have to find a barlow that has threads on the output side that will fit (probably) to a standard M42 x 0.75 or T-thread into your camera's T2 adapter. I know that there are a few barlows that offer male threads on their output side, some are 1.25" (GSO?) and the 2" Tele Vue Powermates also can be fitted with an adapter (from Tele Vue) that converts the output to a standard T-thread (and the Powermates have 2" filter threads on their input). The Astro-Physics Advanced Convertible Barlow can also be used with threaded connections on both sides, but it's male M48 on the input and male M42 (T-thread) on the output (the latter would work with the camera's T2 adapter but the input side would probably require a gender changer -- again see Agena Astro. However, the A-P barlow has a rather long backfocus so you might have to add a short T-tube between the barlow and the camera's T2 adapter to get the correct spacing.


Other than that you might check out Siebert Optics: https://www.sieberto....com/index.html

Edited by james7ca, 27 October 2021 - 11:09 AM.

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#3 barbarosa



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Posted 27 October 2021 - 11:42 AM

GSO makes a 2" Barlow with a removable lens cell. The cell is m48 threaded on both sides. This model is sold under several brand names, GSO, Apertura, TPO, Zhumell, etc. I've used it this way and it works, though you may have to rummage through the adapter drawer. Probably not the best Barlow available but seemed OK used with a ZWO camera and a f/7 refractor for the  gas giants and the moon 

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