Posts Made By: John Boudreau

Fine image Paul!

When it's been clear around here recently, I've usually had the opposite luck--- terrible seeing. Sometimes I can't even determine a focus point!

---John

If you want a color cam, in the long run it's usually best to choose the DBK series over the DFK. The DFK has an IR-cut filter bonded to the CCD coverglass, while the DBK has no such filter. If you decided to do some near-IR imaging with filters like the Baader 685 or Astronomik 742 and 807 IR-pass filters, the built-in IR-cut filter of the DFK will defeat that purpose.

For normal color-cam imaging, an IR-cut filter is definitely needed because some IR leaks into the G and B sensitive pixels. The IR-cut mutes this leak, and allows good color balance. So simply use a screw-in IR cut filter for normal color imaging. The DBK simply allows more flexibility vs. the DFK.

---John

Fine shot Steve! Nice structure in the SEB outbreak.

I was imaging Jupiter earlier that evening, but took a break after the GRS neared the limb to get some Uranus video in the good seeing. After I finished up with Uranus I tried Jupiter again, but the seeing was starting to deteriorate back to more typical New England @#%@* just as I started to record. No outbreak image for me yet. Oh well...

---John

The NexImage already has a IR-blocking filter bonded directly onto the CCD coverglass. If it didn't, you wouldn't be able to get good color balance of daytime scene with it.

One reason that the early Philips ToUcam models were so popular was that the IR-blocker was part of the lens assembly, which was removed to mount the 1.25" adapter. So one could use a screw-in IR/UV blocker in the adapter for good color balance, or remove it and use an IR-pass filter for near-IR imaging. You can't do that with a NexImage because it's CCD is permanently IR-blocked.

A few years ago I did some testing of the NexImage built-in filter, and it blocks IR as well as either an Astronomik IR blocking filter or the Baader IR/UV blocker (also sold rebadged as the optional Celestron filter). I did not have a good way to check on the UV end, but it did indeed have noticeable UV blocking too.

The only reason to use a screw-in IR-blocking filter on a NexImage is to protect the CCD from dust.

---John