Sunday, June 18, 2017

bigger jupiter, saturn's coming

finally able to take advantage of larger aperture
for a higher magnification jupiter
Jupiter 5/28/17
still a bit mushy, but showing some promise

meanwhile saturn reached opposition this week
coming up on prime viewing season
here's a wide field with a few moons:
Saturn and Moons 5/14/17
a bit closer on another night:


Saturn 6/14/17

will get to higher magnification when it rises earlier in the evening

Imaging notes:
The larger f/8 scope allowed me to use a 2x Barlow on jupiter, increasing the magnification by a factor of 2 compared to my old system (C8).  
Several other issues were critical to getting the system to work:
1. internal thermal tube currents are a major problem with the new big scope, it takes hours to cool down.  a "cat cooler" made a huge difference.
2. dark subtraction.  this makes sense as i'm trying to minimize expsosure shooting at ~30% max histogram.  the love/hate issue with my ASA DDM 60 mount continues.  the issue here is that most mounts move around so much that the subtle grid pattern in the camera is dithered out.  my mount tracks so well that the planet sits dead center even at very high magnification, so the pattern becomes evident in processing.  this is actually a good problem to have.  for example last night i took a series of images of jupiter at this focal length over the course of an hour and didn't have to budge the mount, even though the pointing model was made with a much lighter scope 6 months ago.  
3. diagonal: didn't test that rigorously, but shooting through the diagonal didn't seem to make that much difference.  
4. made a bit of progress working on LD compensation in win jupos which is necessary with jupiter so far from opposition, you can still see a darker section at the limb on the left (might be processing artifact in part).  
5. more on the mount: the mount is very sensitive to weight changes, the act of switching from eyepiece to camera with barlow felt like this classic scene from raiders of the lost ark. the key is to balance the mount with the camera, not eyepiece.  forget about binoviewers.  

image details (jupiter):
Meade LX850 12" f/8
televue 2x Barlow
FocalLength~4100mm
Resolution~0.19"
ZWO ASI120MC/ASI120MM-S
ZWO RGB filters
4x2 minute captures for each filter R G B
captures with firecapture @ ~140 fps
exposure 3-4 ms per frame
stacked in autostakkert, combined in WinJupos, sharpened in registax 6
5/28/17 (2017-05-28-0446_7)
Eastbluff, CA

Sunday, June 4, 2017

Jupter's out, IR test and a new scope

the bright star in the east after dark (which is pretty late these days)
is in fact Jupiter. 
seeing has been lousy this season, but i finally gave it a try on a night of mediocre seeing and got this:
Jupiter 4/11/2017

ran a few tests with an infrared (IR) pass filter to see if it would yield a sharper image.  In theory the redder the light (longer wavelength), the less it is distorted by atmospheric seeing, so images should be sharper, but...
the optical resolution limit of a telescope is defined by the wavelength of the light: longer wavelength reduces the theoretical limit of the telescope.  furthermore, the IR pass filter typically allows less light than a standard red filter.  therefore, exposures may need to be longer (leading to more atmospheric motion) and/or higher noise.  
so in practice is the IR image sharper than the others?
here's a blink comparing red to infrared (no contest comparing to blue and green):
red vs infrared
clearly sharper, but perhaps a bit more noise.  

However, for the combined image, it was difficult to appreciate any difference:
here's RGB vs IRGB (substituting IR for red):
RGB vs IRGB
the difference is very subtle, with perhaps a bit more detail in the short blue stripe just above the middle white band.  

lastly, i used IR as the luminance channel which changed the colors dramatically, but probably a bit too far from the RGB:
RGB vs IR-IRGB

this, i think, is my first successful image with a new (used) larger scope
which i picked up on astromart almost a year ago
in order to catch saturn's hexagon,
explaining a year of poor seeing.
the new scope is pretty friggin' big and a PITA to haul around in the dark at 2 AM so i hope it works out

new scope specs
Meade LX850 12" f/8 ACF OTA + Feathertouch focuser
2438mm
0.38"
56 lb (25.4 kg) tube weight
UHTC coating
primary 12" (305 mm)
secondary 4.72" (120 mm) / 41%

image details:
ZWO ASI120MC/ASI120MM-S
ZWO RGB filters, Baader IR pass "685" nm
2x90 second captures for each filter R G B IR
captures with firecapture @ ~140 fps
stacked in autostakkert, combined in WinJupos, sharpened in registax 6

Southern California
4/11/17