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Posts Tagged ‘Takahashi’

Barnard’s Loop

March 7, 2016 1 comment

When I was a kid, Barnard’s Loop was something that I saw on star charts, but it seemed so hopelessly dim, I never expected to actually see it.  And even when I started CCD imaging, it was still a somewhat elusive object: too large to capture unless you used a wide-angle lens, and even then you wouldn’t get decent resolution.  But the combination of a full-frame sensor and a very fast telephoto lens turns out to frame it nicely.

This image obviously has more in it than Barnard’s Loop.  M42/43, the Flame Nebula, the Horsehead Nebula, and M78 all sit nestled within the Loop.  But more interestingly for me, you can start to see the overall Orion Molecular Cloud complex in there: all the dim tendrils that connect each of these objects, some glowing, some blocking the view of the glow.  I regret stopping the lens down to f/2.8 now, as perhaps I would have captured more of the overall cloud that way.  I’d go back and retake the shot if I weren’t having so much fun with this new lens on other targets (and if I hadn’t spent five hours processing this one).  But I’ll consider this a success, as it’s another childhood dream accomplished.

Barnards_Loop_FINAL_50 percent

(This image is reduced to 25% of full size, as the 6D’s output is over 20 megapixels.)

Image data:

  • Exposures: 81×2 min at ISO800 – total exposure time:  2h 42m
  • Telescope: Samyang 135 mm f/2 lens at f/2.8 (reviewed here)
  • Camera: Canon 6D (modified) with Astronomik CLS clip-in filter
  • Mount: Takahashi EM200
  • Guiding: Orion Starshoot, guided using PHD2
  • Conditions:  fair transparency, calm winds
  • Processing: DeepSkyStacker -> PixInsight -> Photoshop
  • Date: Feb 28, 2016

 

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Making an adapter box for a Takahashi EM-200 mount

April 13, 2015 Leave a comment

As much as I admire Takahashi for their dedication to quality products, some of their design choices can be frustrating.  Worse, the cost to accomplish even standard tasks with their equipment — connecting a camera to a scope, controlling a mount, etc. — are steep.  I recently acquired an EM-200 Temma 2 mount, and before I could autoguide it or connect it to my computer, I had to overcome the non-standard cabling.

While the rest of the world has standardized their autoguiding connections with the same RJ-12 cable and jack (though not always the same pinouts) as SBIG’s now-ancient ST4, Tak for some reason decided to go their own way.  The Tak connection on the Temma 2 is known as a mini-DIN-6.  A quick search on the internet revealed that this is the same connection used on the old PS/2 keyboard and mouse cables.  I had some of those laying around the house, so I my plan was to use one of those.  Alas, this was not to be, as you’ll see in a minute.

Communicating with your mount on a deeper level than “speed up” and “slow down” usually requires what’s known as a serial port.  Serial ports on mounts are a little less standardized.  No modern computer has a direct serial (also loosely known as RS-232) connection, so you typically need a USB-to-serial adapter.  The output of this is what’s known as a DB9 connector, which you then have to adapt to whatever your mount requires.  For the EM-200, it’s a mini-DIN-4 connection.  Again, a little internet research reveals that mini-DIN-4 is also the standard for S-Video cables.  Aha, I have one of those lying around too!

Which brings us to an important point:  you cannot use S-Video or mouse/keyboard cables for these connections.  Why?  The pins on the connector do not always reflect the wires in the cable.  S-Video cables have two pins tied common, since the standard has two pins serving as ground.  Thus, there are only three wires in the cable, and we four separate wires for four separate pins.  It’s a similar story with the mouse cables:  only four of the six wires are used.  (Perhaps all six are used for PS/2 type keyboards?  I only had a mouse on hand.)  In fact, the DB9 serial cable I had actually turned out to only be connecting four of the pins when I opened it up.

So I needed one cable for autoguiding that was:  RJ-12 Socket <———->mini-DIN-6

I also needed a cable for serial communications that was:  USB<———->DB9<———–>mini-DIN-4

So it’s off to DigiKey to order some parts, since mini-DIN connectors are not something Radio Shack stocks in store.    I ordered:

  • 839-1091-ND “CBL ASSY MINI DIN MALE R/A 4POS”
  • 839-1093-ND “CBL ASSY MINI DIN MALE R/A 6POS”

The DB9 connector I did have around the house (from Radio Shack, and commonly available).  I also ordered a USB-to-serial adapter from ebay that has the FTDI chipset, as I heard that is the best choice, and I got an RJ-12 jack from Home Depot for $1.99 that has convenient punch-down connections on the back.  Finally, I bought a project box from Radio Shack to house it all.

Thankfully, Takahashi has published the pinouts for their cables, so this was a straightforward project.  I’ve reorganized them here in table format with schematics of the connectors.

The autoguide cable

Autoguide

The serial cableSerial

Now there is only the matter of assembling it all. These steps look easy, but it’s fairly tedious and can take a couple of hours.  First, cut a hole in the project box to fit the RJ-12 socket:IMG_1840

Now cut holes in the box to accommodate the cables (provide strain relief via knots or glue if needed), and strip the ends of each wire:

IMG_1841

Using the tables above, solder the wires to each connector as appropriate.  Double check the connections with a multimeter. Epoxy the RJ-12 jack to the box lid:

IMG_1842The final adapter box has a USB cable coming from one end, and the autoguiding and serial connections coming out the other:

IMG_1844And here it is attached to the tripod, ready for use:

IMG_1843

Vignetting measurements for every scope I’ve owned

June 22, 2014 3 comments

In my recent review of the WO Star 71, I stated that the measured light falloff from center to corner of an APS-C sensor was 3-4%.  That got me thinking… how does that compare to other scopes?

I’ve owned and imaged with many telescopes over the past few years, thanks to the active used market for scopes.  That means I’ve taken flats with all of them, so on my hard drive, I have measurements to quantify vignetting for all of them.  Since that might be useful to people, and since there might be some lessons to be learned, I spent the morning going back through my files calculating vignetting.

Methodology

  • UPDATED:  Only FITS files were used, with raw ADU counts.  (Previous methodology was unable to account for differences in file types due to gamma curve applied by FITSLiberatoror and Photoshop’s RAW import routine).  Camera-scope pairing where I had only CR2 files have now been excluded.
  • I used a 51×51 pixel average, measured in the center of the image, and in each corner.  I averaged the corners, then compared that to the center.
  • I tried to use flats where the peak value was still in the linear range of the sensor (the middle 20-80% of full well capacity).
  • Where the data were variable, I looked at multiple flats from different days and took an average.
  • All flats were taken using a t-shirt over the objective end of the telescope.
  • This is not a bench test; these are values taken from flats used in practical (read: sometimes imperfect) situations.  There could have been a wrinkle in the fabric or non-orthogonality (sensor not perpendicular to the optical axis) in the system, though I tried to exclude any flats like this in the set used for consideration.

Results

  Light falloff from center to corner for:
Telescope KAF-8300

(18 x 13.5 mm)

Full frame (STL-11000)

(36 x 24 mm)

Takahashi FSQ-106ED at native f/5.0 11%
Takahashi FSQ-106ED at f/3.65 with 0.73x Reducer QE 35%
Televue NP101 at native f/5.4 20% 45%
Televue NP101 at f/4.3 with NPR-2073 0.8x reducer 35%
Borg 77EDII at f/4.3 with 7704 reducer 18%
Orion EON 120 at native f/7.5 22%
AstroTech AT8RC at native f/8 with AT2FF flattener * *
William Optics Star 71 at native f/4.9 12%

So have you ever looked at your flats?  I mean really looked at your flats?  I skimmed through four years of my own, and I was very surprised by some of these results.

With faster focal ratios, it gets challenging to fully illuminate the larger sensors.  The effect of mechanical vignetting on the NP101 is apparent on the full frame STL-11000M, and this is exactly what Televue addressed in creating their “is” series scopes, so I’m guessing an NP101is would perform much better here.

I’ve shown the light fall-off between the center and the worst corner I could find.  When the vignetting gets significant, the slightest bit of tilt between the sensor and the objective is revealed, so one corner or side was usually a few percent worse than the best.

It’s also clear that the Takahashi lives up to its stellar reputation.  At the native f/5, it easily covers the full frame sensor.  At a crazy f/3.65, it’s probably pushing the limit of acceptable vignetting for the full frame chip.

The new WO Star 71 holds up very well in terms of vignetting, at least with the ST-8300 chip.  I previously tested it with an APS-C DSLR, but those data are not comparable to the FITS data here.

I’ve long since sold the Orion EON120, but I was surprised it didn’t perform better due to its higher focal ratio.  I didn’t have good data on this scope with reducers.

Finally, the AT8RC is an interesting case, and I’ve excluded the data because it was harder to make sense of.  I’ve always taken it as gospel that the AT2FF was the flattener to use with this scope.  Taking a good look at my own flats, I saw two things:  1) it looks like there is a bit of a “ring” shape in the brightness, which may be introduced by the flattener’s  (which was, after all, designed for refractors) interaction with the RC optics;  2) there seems to be some non-orthogonality in my system that is making one side brighter than the other.  Or maybe the mirror need to be re-aligned a little.  In some cases one corner was slightly brighter than the center.  Either way, this made it harder to state a simple center-to-corner ratio, so I’ve left the data out.

Lessons Learned

This was an exercise I should have done a long time ago.  I took away several important lessons from it:

  • Look at your flats.  Why put all of the effort into taking good lights, then undermine it by introducing gradients due to poor flat fielding?  I got more careful over time, but some of my early flats left me shaking my head, thinking, “rookie.”   Some days I was taking flats where the peak value was uncomfortably high or low, which experience has since taught me to avoid.
  • It gets harder to maintain even illumination with faster focal ratios.
  • There really is a difference with quality scopes.  The Tak easily upholds it reputation here, which makes me feel better about its price.
  • With smaller sensors (I’m looking at you, Sony 694’s), you can save a lot of money by buying a scope that would be otherwise less acceptable for larger sensors.
  • Conversely, when you buy a larger sensor, you need to support it with better optics.
  • With significant vignetting, non-orthogonality is exaggerated in the flat.

Call for Data

Does this represent your experience with your scopes?  Am I crazy?  Have I missed something here?  I’d love to hear what other people have found looking at their own flats.

 

Testing out the Takahashi FSQ 0.73 focal reducer on the Virgo Cluster

May 31, 2014 3 comments

I recently purchased the 0.73 focal reducer “QE”for my Tak 106ED. It promises to turn it from a speedy f/5 to a ridiculous f/3.7 while still filling a full frame sensor. In fact, with the full frame sensor of the STL-11000M, we’re looking at a field of view of 5.3 x 3.5 degrees.

Of course any new purchase like this causes days of clouds and rain, but that’s been the case for about six months anyway. It gave me time to order the insanely priced adapter required to mate it with the STL camera. Once I had a clear night, I seized it, even though it was a full moon. Because of this, the image you’ll see below is far from optimal. Consider it a test image more than a aesthetic image (though the effect is still pretty cool). I fought a valiant battle with gradients in PixInsight, but for the most part they got the best of me.

Wide Field of the Virgo Cluster of Galaxies

Wide Field of the Virgo Cluster of Galaxies

Even after cropping a little, that’s a WIIIIDE field. Looking in detail at the extreme corners, the left side showed a little distortion, but that could potentially be due to some non-orthogonality in the connections.

Extreme corners of the image

Extreme corners of the image

Overall, the image is very sharp, and it’s a pleasure to capture a field that would normally require a mosaic. I look forward to the beginning of narrowband season to really give this new system a try.

NGC 6888 Narrowband (plus some PixelMath)

September 29, 2013 Leave a comment

Finally, some color images!  (Or at least false color.)

This is one panel from my earlier Crescent Nebula 4-panel H-alpha mosaic, with OIII and SII data added.  The first version is in a slightly modified “Hubble” narrowband palette (R=70% SII+30% H-alpha, G=100% H-alpha, B=100% OIII).

NGC 6888 in Hubble Palette

NGC 6888 in Hubble Palette

Image data:
Exposures: 13 x 1200s Ha, 16 x 1200s SII, 18 x 1200s OIII (Total exposure time: 15 hours, 40 minutes)
Software: guiding by PHD, stacking in DeepSkyStacker
Processing: PixInsight 1.8
Telescope: Takahashi FSQ-106ED (530 mm f/5)
Camera: SBIG STL-11000M with Astrodon 6nm narrowband filters, 2×2 binned
Mount: CGEM
September 16, 17, and 28 2013

PixInsight allows you to easily blend and mix images or color channels to create alternate palettes, so let’s use this image as a simple example.  Consider the following simple PixelMath parameters.

PixelMath

PixelMath refers to the color channels in an RGB image as [0], [1], and [2] respectively.  So this tells PixInsight to create a new image with the:

  • red channel composed of the original green channel
  • green channel composed of 70% of the original red channel + 30% of the original green channel
  • blue channel unchanged

The result is a false color image with a different flavor.

NGC 6888 Red-Green Reversed

NGC 6888 Red-Green Reversed

M16 and NGC 6604 H-alpha widefield

September 7, 2013 Leave a comment

I don’t usually post monochromatic images, but this is a nice example of how wide the view is with the STL-11000M through the FSQ-106ED (530 mm focal length).  Not only does the Eagle Nebula, M16, fit in the field, but the entire area of nebulosity around NGC 6604 fits as well.  It makes me wish I lived further south so I could spend more time on the Sagittarius/Serpens area of the sky.  It was all I could do to capture 3h 20 min of exposure time from here in NJ.

M16 and NGC6604 H-alpha

M16 and NGC6604 H-alpha

Image data:
Exposures:  10 x 1200s Ha
Software:  guiding by PHD, stacking in DeepSkyStacker
Processing:  PixInsight, Photoshop CS3
Telescope:  Takahashi FSQ-106ED
Camera:  SBIG STL-11000M with Astrodon 6nm narrowband filters, 2×2 binned
Mount:  CGEM
September 3-5, 2013

 

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