Barlow for imaging on Evostar 120ED

[Mark_C]

Hi all,

Just want to start off and say apologies if this question has been asked many times before but I'm not sure what brand of barlow I should be going for? And should I opt for 2x or 3x? Don't really want to spend a huge amount out like on a TeleVue Powermate but something that will do the job nicely at a competitive price. I notice the TAL series of barlows get reverence amongst many people here but it seems they stopped making them quite a while back, which is a great shame.

I'm hoping to start imaging Jupiter/Saturn/Mars using a Skywatcher Evostar 120ED (I believe is f7.5 @ focal length of 900mm) and something along the lines of a QHY5L-II mono (will be buying a camera fairly soon).

I realise the 120ED isn't exactly perfect to image the planets, as it seems to be more orientated towards DSOs, but I'm just starting out with the whole imaging regime and hopefully in time I will buy an OTA more suitable for this kind of work, such as a C9.25/C11.

Any recommendations would be most appreciated!

Thanks,

Mark.

[michael.h.f.wilkinson]

I like to image planets between F/20 and F/30. An F/7.5 scope should fare well with 3x or 4x barlows or (better for imaging) TeleCentric Barlows such as PowerMates, Meade TeleXtenders (now sold as Bresser SA Barlows), or the Siebert TeleCentrics.

[AstroAdam]

I use one of the 2.5x revelation apo barlows with my scope for planetary imaging.  

http://www.telescopehouse.com/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2etelescopehouse%2ecom%2f&WD=revelation%205x%202&PN=Revelation_Astro_2_5x_Barlow_Lens%2d1%2ehtml%23a1_21BL251#a1_21BL251

Got some good results with it (take a look at the most recent few posts in the planetary section on my website in my sig for examples).  The scope I use it with is a 200p reflector though, so you won't get as much useful magnification with the 120ED.  

I Also use a ZWO ASI120MC one-shot colour imaging cam, which has a nice small pixel size, and maximises what resolution your scope does have...

[michael.h.f.wilkinson]

BTW, in planetary imaging the key thing is to match the focal ratio to the pixel size of the camera. This automatically adapts the magnification to the aperture. For the ASI120MM (same chip I think as the QHY5L-II mono), F/16 to F/25 are often quoted as optimal, but good results have been obtained at F/40. For the DMK21 and similar cameras, F/25 -F/30 hits a sweet spot.

[Mark_C]

Thanks to all for the advice. It looks as though I will need to get a 3x barlow to achieve decent results with a QHY5L-II. I've narrowed down a few options, however the Celestron X-Cel 3x looks particularly interesting from FLO @ £69, has anybody had any experience with these barrows?