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New scope for Watec


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I recently got a Watec camera and have been trying it out using a 4.5" f4 Newtonian (I've attached a couple of images below).

I plan to get a larger scope to use with it and I'm wondering what to go for. So far I'm considering either an 8" f4 imaging Newtonian or the 8" f5 Skywatcher Newtonian with the shorter tube for imaging that will allow me to use a focal reducer and get to about f3.3.

I'm leaning towards the f5 scope because it will be better for visual work and at f3.3 with the reducer it will give brighter images using the Watec. If anyone has any thoughts on these or alternative scopes I should consider for the Watec then I'd be interested to hear them.

In relation to this, I wonder if anyone has any comments on the following...

I have seen it written in several places that the Watec effectively increases the aperture of a scope by a factor of 3-ish. Being a visual observer only until recently I had been thinking that this meant the bigger the scope the more I would see with the Watec. However, based on what I've read it seems that f ratio is the key to image brightness, so for two scopes with the same f ratio the image brightness won't change regardless of aperture (although of course the field of view and image resolution will change). This makes me wonder what the advantage of a big scope is when used with a video camera and also how meaningful the 'triple your aperture' statement really is. If anyone can enlighten me about the benefits of more aperture with a Watec I'd be grateful!

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I have used the watec for about 18 months now with a 3 inch refractor, a 6 inch F8 refractor and currently a 10 inch F4.7 Newtonian and yes of course the larger the aperture the more you will see but I pretty much always use the watec with the scopes at full focal ratio, I don't really put the reducer in because it simply makes the image scale too small especially for galaxies so the 10 inch is left at F4.7 instead of F2.9 if using the reducer but the times I have put it in I personally diddnt think it made such a big difference. I even put the 2x barlow in to view very small objects and with the 10 inch the image brightness is just fine and if it is-int then you could always use the long exposure function on the Watec.

I would go for the 8 inch F5.

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In retrospect, I'd go for an 8" F5. Though, if you want to get into large-chip imaging, the Skywatcher Quattro series? My TS/GSO 8"/F4 is a "fine thing" - It shows definite prospects for videoing "ultimate DSO's" (galaxies etc.)! But I do wonder whether the general "faffing about" with (double requirement re.) collimation, going from F5 to F4, is of any real value for smaller-chip imaging? Idem re. the abandonment of low power VISUAL possibilities (secondary mirror shadows) etc. :)

I sense my focal-reduced MAK150 delivers much (unexpectedly so!) with mid-range DSOs. As above, the aperture effect is (subjectively) less than expected? Nevertheless, the extra 2" (of the 8") seems WELL worth it... But perhaps at F5, rather than F4. I wryly note the only thing that attracted significant DEW, the other night, was the F4's larger secondary. But then, a quick blast with my (largely forgotten!) hair drier, solved most problems... :)

Edited by Macavity
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Regarding apparent aperture gain, I used my Watec 120n on a 12" SCT at F3.3. The resulting images of faint objects were better than visual in my 30" F4.1 Dob. I've never seen the central star in M57 visually with a 16" but it shows easily with the Watec in a 6". You cannot of course increase the resolution of the telescope by this means.

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