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Webcams, Planets and Barlows... OH My!

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#1 tommax


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Posted 16 March 2013 - 12:05 AM

Quick question for all you experienced web cam users...

On barlows, is it better to use 2, 2x barlows or a single 3 or 4x?

I currently have a nice barlow, one of the Televue 3x Barlows but the seeing where I am at seems to not work out very well and with my 8" LX 200 it can be a challenge to keep a planet in the sight window.

Most of the time I wind up using a Meade 2x Shorty and have been considering getting a second and possibly selling off my TV as it also seems a bit tall for imaging with...

Anyways, what do you guys use and what would you recommend?


#2 yock1960



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Posted 16 March 2013 - 08:06 AM

Need a bit more info. I assume by planet you mean Jupiter in having trouble keeping it on the chip. But what camera abe you using? There are resources available for you to calculate your image scale for a given camera, scope and focal length, whether you are reducing or increasing, as with a barlow. One is CCDcalc. Download that and you can quickly experiment with all sorts of scenarios.

Folks use all manner of Barlows and or extension tubes. Length can be a concern, but probably not with a webcam. Just make sure that everything is properly tightened and the cable is not dragging on anything.


#3 tommax


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Posted 16 March 2013 - 12:05 PM

Thanks Steve,

I use CCD Calc, it is very handy. Jupiter is a bear to get at real high mag at least for me at this point in my experience and it is not very often with my weather that the opportunity presents itself.

I guess the real question was what were you guys finding to be the best barlows, on a clear enough night is there any compelling reason to use a 4x over 2-2x?

One reason I ask is I have a barlow I barely if ever use that I could sell and get enough to buy 2, 2x's or if there are quality ones for example as I state I have the Meade #07278 shorty barlow, is the Celestron X-Cel a better barlow? especially for imaging with? I would rather have a better 2x barlow than a 3x I rarely get the opportunity to use and would rather ask the initiated than buy each if there is a fairly clear consensus.

#4 RedLionNJ


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Posted 17 March 2013 - 11:16 AM

I would think you would rarely (if ever) want to exceed f/25 or thereabouts for Jupiter or Saturn. Take a look at the better images being posted in this forum and on places like Facebook - in general, most are somewhere between f15 and f25.

If you have terrible seeing most of the time (like I do), you'll rarely even get to use f25. And f10 just really doesn't cut it unless you DO have good enough seeing, allowing you to drizzle the result (in which case you maybe shouldn't have been using f10 in the first place).

Also bear in mind that while most SCT's are nominally "f10", the actual focal ratio you get will depend on the separation of the mirrors, as well as the spacing between the other optical components (barlow, sensor).

There also appears to be a significant difference in image quality between a generic Barlow and something like a PowerMate, although they both serve the same purpose.

Good seeing, excellent collimation, tight couplings (no sag). It sounds so easy :(


#5 Kokatha man

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Posted 17 March 2013 - 06:22 PM

Hi Tom - personally I'd never advocate doubling up with barlows...at the very least you'd be working through quite a lot more glass and one barlow and extension tube can provide any of the useable amplifications you'd ever want to use!

Here's the TeleVue graph http://www.televue.c...d=52&Tab=_photo displaying said image scales with an extension tube but you can make a general interpolation for other makers' barlow from it - and I also think the point about using a "quality" barlow is very relevant! :)

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