Testing Different Optical Setups for Watec Videocamera on Meade 10" Scope

Nov 11, 2015

These are from tests done in cold (~44F) conditions, with dew a problem, at Cabrillo Observatory, looking at the Double Cluster in Perseus as it rose from roughly 40 degrees to 60 degrees altitude.

The 1.25" and 2" Diagonals give same orientation (ie neither are "erecting")

First test was to see if perhaps using the 1.25" diagonal and 40mm Plossel eyepiece gave good FOV's with the eyepiece in target location. The result - no; much better to stick with the 2" Diagonal and the Q70 Orion 70 deg eyepiece as you've been doing previously. The 1.25" diagonal and 40mm Plossel gives only about 60% of the diameter as the 2"+Q70 combo.

Next, check which gives the best FOV and deepest magnitude using various combinations of the 1.25" diagonal, the HighPoint 0.5x focal reducer (HP05) and the Celestron f/6.3 and Meade f/3.3 reducers. One goal too is to see which allow getting to high altitude stars, since "straight through" with the Meade or Celestron reducers will not. Can perhaps the 1.25" diagonal and HP0.5x reducer do not much worse than the Meade f/3.3? The answer is NO. The FOV is much smaller using just the HP 0.5x reducer.

Config #1

1.25" Diagonal + HP05

Menu wheel on upper right, vid out on bottom

Config #2

1.25" Diagonal + f/6.3 + HP05

menu wheel on upper right.

Required 4.8 revs CCW on focus knob to get Watec in focus, after pulling off 2" diagonal + Orion Q70 eyepiece visually in focus.

Config #3

Straight through: f/6.3 + HP05

Menu wheel on the lower left, vid out on top

Config #4

Straight through: f/3.3 + HP05 + longnose adapter

Menu wheel on the lower left. Required endless CCW turning of mirror focus knob, probably very near end of travel

Config #5

Straight through: f/3.3 + longnose adapter. Menu wheel on the lower left.

Config #1

C2A chart for video above: 1.25" Diagonal + HP05

Config #2

f/6.3 + diagonal + HP05. The dimensions are identical to that of the straight-through f/3.3 setup I favor

Config #3

Straight through, f/6.3+HP05

15'40" x 12'22"

Config #4

C2A for Straight through: f/3.3 + HP05 + longnose adapter in table above


Config #5

C2A for Straight through: f/3.3 + long nose

I rotated the camera for config 3-5 to have video out on the Watec on top as I looked at the back. Just an experiment. This is opposite from the convention which allows "horizon" view to reproduce in C2A.

So: Conclusions....

If star is above 75 degrees altitude, then use Config #2 = 1.25" Diagonal + f/6.3 + HP0.5x. Put camera on always with Vidout on top, menu wheel in lower left, just like in straight through. Then to produce C2A chart, just need to make in 'horizon' mode, and then in Photshop flip horizontal only. Cannot try to adjust in C2A because must be in Field mode to do that, and this changes orientation in hard to figure ways. Don't do it. Just flip it in Photoshop. So, should know before you prepare for observation what configuration you'll use so you can just prepare one set of charts and avoid confusion. If star is below 75deg altitude, just use config #5 as before = f/3.3 alone, with camera menu wheel on lower left.

I don't see any change in mag limit between config 2 and 5; given that config #2 was out of focus, and also lower in the sky when done. Would be good to reproduce in drier conditions higher overhead to verify mag limit. If config #2 is superior, that would simplify things. Also, Derek points out that the coma reversal in Config 4 could be helped by reversing the order of the HP05 and the nosepiece; try it.