focal reducer for astrovideo

[Andrew C]

Does anyone know of a threaded 1 1/4" f/3 focal reducer suitable for use with a 12" f5 dob for astro video observing?

Thanks,

Andrew

[Derek Klepp]

Andrew if you are using a c-mount camera check out astroshop.

[mental4astro]

Andrew, the only type of focal reducer you'll be able to use on your dob is a 0.5X reducer. These come in both 1.25" & 2". Andrews carries both, the 1.25" being $29. Look under their Guan Sheng banner:

http://andrewscom.com.au/site-section-10.htm

This is the reducer I use with my astro video camera. Very effective.

Just note that you could run into focusing problems though. You may find that the draw tube needs to be wound out further than it can go. If that's the case just use an extension tube.

Derek mentions the reducer from Myastroshop. If I'm not mistaken it's the same item as the GSO one, just rebadged. Excellent item too.

Which astro video camera do you have?

Mental.

[Andrew C]

Hi guys,

I already have a 0.6X reducer so I don't think 0.5X would be a big enough next step. I have been using it successfully for a few years on the nosepiece of my Stellacam3 on a 6" f5 GEM mounted tracking newtonian scope, but I have recently been building a equatorial platform for my 12" f5 dob, and would like to get the benefit of wide field and low equivalent f ratio. 0.3X would be great (and about the same field as the 6" 0.6X combination but giving half the f value), but finding one is the challenge. I have no problem with focus, although with the focal reducer it needs in-focus (i.e. getting the camera + focal reducer combination closer to the primary) rather than out-focus, so I'm not sure what you mean there. My dob mount is the flextube type, so I can achieve that by not extending the secondary cage position fully.

Is there some optical limitation with 0.3X and newtonians (since 0.3X are available for SCTs), or is it just that for most newtonian configurations getting sufficient in-focus would not be possible?