All planetarium projectors have their strong points and their weak points. During the development of Digistar we were able to increase brightness and reduce image size considerable, but we were never able to achieve the pinpoint sars produced by Spitz planetarium projectors. Zeiss projectors produce a nice star field, but the images are significantly larger than Spitz stars. Digistar images are larger than Zeiss stars. Digistar offers significantly more flexibility than the others, and allows 3D travel, proper motion demonstrations, and rastered images. The others do not. Planetary position accuracy is also better with Digistar. From what I have seen of the new Digistar, the bright stars are actually many pixels in size.This is an attempt to simulate higher brightness, but it doesn't work well for me. Others have made similar comments as well. Brightness in the original digistar was limited by the amount of energy you could put into a phosphor and still have a linear response. At a certain level, you can pump more energy into the phosphor, but local heating and other effects will cause the brightness to peak, and then slightly decrease. This is my biggest dissapointment in our original plan. As I mentioned, we dramatically improved the image from when we first started, but it still need even more. The latest Digistar gets mor light by making the stars bigger. To a certain extent, the real stars do look bigger as their brightness increases, but not as much as Digistar represents. Even the Zeiss machines show larger images for brighter stars, but not as much as Digistar. So, Chuck, the bottom line is that software changes wil not really solve the problem. It is a hardware limitation. There are some algorithms we tried and had some success with, but the basic problem is trying to get a larger number of photons out of a projection CRT. Yes, we contemplated lasers too, but the problems of deflecting the beam at sufficient angls and at a speed required to image 6713 stars (the number of stars brighter than magnitude 6.5 in the Yale Catalog of Bright Stars) were even greater than the ones faced by using projection CRTs. We would have had to limit the number of stars to around 2000 and perhaps a 60 degree field of veiw. There were also speckle and color issues to deal with. That's probably more than you've ever wanted to know. I hope you were able to find your answer in there somewhere. ________________________________ From: Siegfried Jachmann <siegfried@jachmann.org> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Thursday, February 9, 2012 10:04 AM Subject: Re: [Utah-astronomy] Clark Planetarium Old "Jake" had a much better star field. That would be a Brent question but I think in order to get brighter, i.e., Jupiter, they have to go to a bigger image. On Thu, Feb 9, 2012 at 9:31 AM, Chuck Hards <chuck.hards@gmail.com> wrote:
On Thu, Feb 9, 2012 at 8:28 AM, Siegfried Jachmann <siegfried@jachmann.org>wrote:
They have star shows. They have a newdigistar projector. It's no better than the old digistar. We took the grandkids and I was again thoroughly disappointed in the quality of the star images. Bright stars are big blobs, Jupiter looked like a big nebula, the narator made several mistakes, i.e., did you know the Milky Way has 300 "trillion" stars in it. The operators struggled through the program. Purists will be disapointed.
There's no excuse for untrained operators. Could the imaging shortcomings be solved with software fixes? _______________________________________________