observational astronomy - SDSS ImgCutout webservice returns black image for dr12

The SDSS (Sloan Digital Sky Survey) ImgCutout webservice should return jpeg images for a given field that is defined by the parameters. The service can be tested here: http://skyservice.pha.jhu.edu/DR12/ImgCutout/ImgCutout.asmx?op=GetJpeg

A simple (and working) get query is given here:
http://skyservice.pha.jhu.edu/DR12/ImgCutout/getjpeg.aspx?ra=132.749&dec=11.656&scale=0.79224%20%20%20&width=400&height=400&opt=

If you enter the same information (the parameters) in the form of the first link and click on invoke you will get a black image only. You can test the base64 encoded result here: http://www.askapache.com/online-tools/base64-image-converter/

Now the question:

Do I require an additional parameter (non empty string) for either imgtype_ or imageField_ in order to not get the correct image? What are this parameters good for anyway?

(Is there a better place this question? It would be nice if there was a tag for SDSS)