Slider: How to get complete image in singlepost?

Hello, I’m new to WP, I started about a week ago. I have a slider in the homepage that shows caption from featured image and it works fine. The problem I have is that when I go to singlepost it still shows a caption of the featured image (not complete).

I though about uploading an image that has 585px width so it shows the complete image but it’s not visually compatible with the lightbox gallery.
The lightbox gallery include the featured image and image for it have 900px with (because I want it like that): if the featured image has only 585px width, gallery would be ugly. (some image 900px width and one 585px width)

So I though about two way around:
1. Remove the slider featured caption from singlpost: tha allows me to insert manually an image on top of singlepost.
2. Making the slider to resize the image to 585px width so it shows the complete image and the gallery doesn’t look ugly.

Hard to understand?

This is what I see now:
http://www.flickr.com/photos/fotodiaf/6792728090/in/photostream

This is what I want:
http://www.flickr.com/photos/fotodiaf/6792728224/in/photostream

This is the post I’m talking about:
http://www.diostesalve.cl/?p=100

Is there anybody out there?