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The Setup
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When my new 10" LX200R OTA arrived I spent the first couple of clear
nights messing around with astrophotography issues. On the third, mostly
clear night I undertook a thorough comparison of this new scope with my
trusty old C-11. Here are some photo's of the two scope installed side
by side on a 16" Casady Tandem Bar
with two 8" Casady Saddles. An embarrassment of riches to be sure!
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If anyone is contemplating the same course let me recommend a longer tandem bar.
The 16" just barely worked. The screw head on the front ring of the Meade are
touching the front ring of the C-11 and the Meade dust cap is touching the C-11
so tightly that I had to remove the OTA to take the cap on and off! Never fear
this is not a permanent setup, just a one or two night testing arrangement.
I had to order an extra 25# weight in order to balance both of these OTA's
together on the CGE mount. While I certainly can't recommend this for photographic
stability for casual visual use it works alright.
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Focus and Collimation
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I finished the two-star alignment of my mount on Regulus and it was high enough
up that I decided to use it for my initial testing. The first difference that
I noticed between the two scopes was that in slewing from my first alignment star
to my second alignment star the focus of the C-11 showed no discernible shift
but the LX200R did need to be refocused. The focus lock was not engaged on the
LX200R but then the C-11 has no focus lock. My second observation was that
when viewing the region around Regulus in my 56mm Meade Plossl eyepiece in
both scope the C-11 showed a slightly crisper view and slightly better contrast
than the LX200R.
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I had collimated the LX200R on the previous night but I decided, based on these
initial observations, to recollimate. I spent the next 30-45 minutes fine
tuning the collimation of the LX200R. While I did make some improvement I was
disappointed to find that I could never get my concentrically defocused star
perfectly center both inside and outside focus. When I got it perfectly centered
on one side of focus I would roll to the other side and it would not be centered.
I finally settled on splitting the difference between the two sides of focus.
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Star Test
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I proceeded to star testing the scope using Thomas Back's Primer
as my guide. I should note that the seeing was not spectacular. I would estimate
it to be about Pickering 6.
Normally one would not wish to undertake a serious star test under such conditions
but since my primary concern was a side-by-side comparison I decided to forego
a prolonged wait for ideal conditions. I did not use a diagonal in the testing.
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Starting on the LX200R I centered Regulus at slightly better than 200X and
defocused 5 diffraction rings. This looked promising, the inner most and outer
most rings were of similar thickness and the three intermediate rings were
thin, evenly spaced and quite distinct. Shifting to 5 rings on the other side
of focus was less impressive. The outer ring was still thick and symmetrical
but the inner ring was mushy and blurred into the second and third rings. Next
I moved to the C-11 and repeated the test. The inner and outer rings were
thick and well defined. The three intermediate rings were fairly distinct and
evenly spaced but slightly broken. The whole diffraction pattern had radial
"jaggies" that I did not observe in the LX200R. The pattern was the same on both
sides of focus.
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Next I defocused by just a couple of rings. The LX200R showed a pretty symmetrical
ring with just a little bit of squashing on one side. On the other side of focus,
however, the ring was fuzzy and indistinct. The C-11 made a much better showing
on this test. It displayed a sharp symmetrical ring on both sides of focus.
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I defocused the LX200R by 10 rings or so and on both sides of focus it showed
a fairly nice and symmetrical ring pattern with no real obviously thinner or
brighter rings. The C-11 showed similar results. At this level of defocusing
the radial "jaggies" were less noticeable.
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Next I attempted an in-focus test but with the seeing conditions I could not
get a steady enough airy disk to judge the 7% and 3% energy distribution of
the first and second rings. I evaluated the "snap" of the focus and found
that there was none. Critical focus was mushy in both OTA's.
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Jupiter
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First let me say that you can't got wrong observing Jupiter near opposition with
either one of these instruments. The differences were subtle. Here are a few
observations.
- In 32mm eyepiece C-11 showed darker sky background around the planet.
- In 17mm eyepiece both scopes showed amazing detail in the equatorial bands
including faint swirls in moments of excellent seeing. Maybe a slight edge to
the C-11.
- In 17mm eyepiece the moons appears more sharp and "pin-point" like in the
LX200R.
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Splitting Doubles
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I've never been into splitting doubles so forgive me if I've butchered your
pastime. Again, for comparison purposes I figured it was worthwhile. I slewed
the scope to STF1647 in Virgo. I naively thought that a well known double of
1.3" separation should be no problem. As it was I had to go to about 375X with
seeing conditions that could scarcely handle it but I did manage to split the
pair in both telescopes. The only useful comment I can make is that I thought
the LX200R showed a little better defined separation than the C-11.
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Field Correction
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Clouds were starting to roll in around the south-east and south-west horizons
so I slewed over to Ursa Major for my last test. I wanted to spend some time
inspecting the edges of the field in my 56mm Plossl in both telescopes. Here
I think I could finally see what all the "R" fuss is about. In the LX200R the
stars were pin-point from edge to edge. In the C-11 I could see flaring around
stars close to the edges.
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Conclusions
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I bought the LX200R primarily for astrophotography. If I had bought the scope
as an upgrade for visual use I would have been disappointed with these results.
My biggest concern from these tests is the collimation problem and asymmetrical
focus properties. Further work may be required to resolve these issues.
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I hope that you have found this information helpful. As for me, I intend to
continue debugging photographic issues with my LX200R rig.
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See my
first light image
taken with the LX200R.
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