At what resolution do you have your Previews set?
Look in Aperture > Preferences then click on the Previews tab and select the resolution and jpeg quality you want.
Aperture uses these Previews for creating slideshows. For max quality set this to your display resolution.
If you change the resolution you need to remake the previews of the pictures that are already in your library:
Photos > Update Previews for Project.
Thank you so much for your input. I haven't used Aperture before and I hadn't gotten through the 900 page
pdf manual. Your advice fixed my problem. The resolution for previews was set at half size about 70% quality
that the programs apparently comes preset for. Changing the resolution in preferences and rebuilding the
previews made all the difference in the world.
Apple makes some wonderful software, but they certainly don't make much effort to pre-answer the obvious
questions. After reading your helpful information, I tried looking through the 900 page manual and found the
beginning of the useful information starting on page 237 under "Previews". It took me several minutes of
searching to come to this. I had been searching for the words "Slide Show" which are in abundance but was
not able to find a single reference to how to maximize the quality of slide shows. Surely I can't be the only
person upgrading from iPhoto who didn't think that slide show quality had to be pre-chosen for maximum quality.
The out-of-the-box slide show performance of Aperture seems to be similar to viewing a slide show on
Flickr- the relatively small "large" jpeg is pumped up to screen filling size. Fortunately, with Aperture
this can be fixed if you are able to find the instructions. I was ready to drag Aperture to the trash. I wonder
how many sales Apple might be missing on Aperture by not providing some helpful tips for first time users?