A few thoughts...

Shotgun mics are highly directional, so how will you capture two instruments with one of those? Might be better off using the 90 or 120 degree pattern on the internal mics to capture these two instruments.

Or, if the vocals are nixed, then put the shotgun on the guitar and the large condenser (especially if multi-pattern) on the cello and violin.

Or use the mid-side stereo technique on the trio as a whole, if the large condenser has fig8. And let the musicians balance themselves.

You're right, I may see if I can borrow another condenser from a friend. If I can, and it's multi-pattern; what's your opinion on how to mic them both? This is my first time recording cello/violin.

My idea was to back the shotgun off of of the cello & violin to widen the range. It's the only other mic I have. I would use the stereo pair on the recorder but they don't sound as good. I use them mostly for ambient room sound.

I have to use the condenser on guitar and main vocals (only the backup singers are nixed).

Also, I'm a film maker, too (hence the shotgun...). It's going to be a live music video. Here's a previous one I did, and you can see my set up.
[[url=http://[/URL]="http://vimeo.com/20…"]"My Will" by Duck & Goose on Vimeo[/]="http://vimeo.com/20…"]"My Will" by Duck & Goose on Vimeo[/]

Four sources and two mikes makes it tough. You will get a lot of room sound if you back way off with the shotgun mic.

I think I would just go for the M/S stereo recording, if you can get a fig 8 condenser. Use the fig8 mic for the S and the shotgun for the M mic.

Not optimal, because the shotgun is probably hypercardioid.

Is the vocalist playing the guitar?

Yes, the vocalist is playing the guitar.

Hmmm, i've never tried the M/s technique before. I'll have to experiment over the weekend.
Thanks!

Yeah, I would try it with the vocalist/guitar in the center, with the violin on one side of the vocalist and the cello on the other side.

Then use M/S to capture the stereo image of it all.

If you are new to this I would not try M/S. Try [="http://en.wikipedia.org/wiki/ORTF_stereo_technique"]ORTF[/]="http://en.wikipedia…"]ORTF[/] or [[url=http://="http://en.wikipedia…"]XY[/]="http://en.wikipedia…"]XY[/]. You want a matched pair of condensers for this (at least as closely matched as possible).

If getting a matched pair is a problem, from what I've read the internal mics on the Zoom are not all that bad. Can you use those to record the whole ensemble as two tracks and then use your condenser as a spot mic on the vocalist for a third track?

+1