Newt with Barlow or separate OTA?

[lewis_riches]

Hi, guys!

So, a quick hypothetical one, here:

Say I have a good, solid mount (A Celestron AVX, for example) and I buy a decent Newtonian for deep-sky astro-imaging. I now want to take my set-up out and look at some planets but d'oh! I have not the focal length for such an endeavour (sad face). Would a decent 5x APO Barlow lens be a worthy solution for this? Would buying a separate OTA with a higher focal length (and waiting to save up the funds) be worth it instead of the former option? Given that it's a fast Newt we're talking about here (f/3.9) surely the optics can handle such a increase in focal length?

My concerns are that introducing such a high-power Barlow (regardless of how good it is) will introduce noticeable chromatic aberrations on bright objects and do I really want two OTAs when storage space is limited when I could get what I need out of one?

Thanks in advance. Clear skies!

[nightfisher]

In theory this works but say you have a newt with 600mm fl you would be better of with a decent x2.5 and on planets the newt will give diffraction spikes

[John]

I guess one issue is that an F/3.9 newt is going to have a fairly large secondary which won't help planetary contrast. A barlow will give you the magnification to have a look at planets at a larger image scale though.

[ollypenrice]

I think you're inventing a problem. Being conservative a 6 inch Newt ought to be able to give good planetary views of at least 180x and, from the UK, that is often enough. Using the same formula of 30x per inch an 8 inch would give you 240x and it needs a good night's 'seeing' (freedom from turbulence) to allow this. You can read all sorts of stuff about great views at 500x but I wouldn't get too excited about that kind of stuff. If you get a good stable night and have a well collimated Newt working at about 30x per inch and a magnification of about 200x you are going to get a good view of the planets.

Olly

[riklaunim]

There are many planetary photographers that use very big and very fast Newtonians for astrophotography. There are no problems with chromatic aberration. Just perfect collimation and focus are required to achieve best results.

[Dave In Vermont]

For the least impact that extra glass will bring into play in the optical-pathway, I'd be inclined to get a TeleVue (or similar) 2.5X PowerMate and keep that in reserve - if needed.

Dave

[lewis_riches]

Thanks guys! Still undecided about what to do but this has given me plenty to think about. Looks like I'll be getting a lot more out of my cheap-and-nasty AstroMaster 130 in the interim.