Airplane!

An airplane heading for SJC while imaging the M81/M82 mosaic. This is a single 60 second frame through the V filter.

NGC 1502

NGC 1502 on December 3, 2004. A 10 minute exposure (20x30s) through a V filter using the 80ED. The camera was cooled to -15°C.

I also imaged it with an I filter. I still have to perform photometry.

The Double Cluster in Perseus

NGC 869 and NGC 884. Mosaic of two images taken on December 3, 2004 through a V filter with the 80ED telescope. One of 57x30s and the other of 31x30s. The camera was cooled to -15°C.

Click the image to see the full mosaic.

Equipment

Telescopes

• Oberwerk 10.5x70mm Ultra Series binoculars. I selected 10.5x instead of the more common 15x because I assumed this would allow me to use it without tripod. It also has a larger exit pupil distance. However, although these are great binoculars, I regret not buying the 15x variant instead. It's too heavy to not use with a tripod anyway, I find the 10.5x magnification too low and, more importantly, the exit pupil diameter of the 10.5x variant is too big. Since 2010 I use it with an Orion binocular mount on the Orion XHD Paragon Plus tripod I originally bought for the 80ED. Its weight is really pushing the limits, especially when viewing near zenith, because of the poor design of the binocular attachment on that mount. This binocular mount is far from perfect, but it does make observing with the binoculars more convenient;
  
• My main telescope is a 254mm f/10 Meade UHTC LX200GPS. It has the standard electrical focuser and primary mirror lock. A nice feature of this telescope is the upgradable firmware (older versions and history can be found here). To reduce the slewing noise and load on the gears, I use a maximum slewing speed of only 1 degree per second;
  
• For wide field imaging, I have an 80mm f/7.5 Orion 80ED. I usually mount it on top of the main telescope;
  
• 7x50 binoculars of an unknown brand bought mid-nineties. The optics were never properly aligned, but I wasn't actively observing in this period anyway. In 2001 I picked up the observing again but when I bought the LX200GPS, a GOTO telescope, I stopped using it again. I replaced it in 2008 with 10.5x70mm binoculars;
  
• 115mm f/9 Newton telescope bought in 1981 through Gerard Keijzers from N.J.R.S for a 10% reduced price from Ganymedes in Amstelveen, The Netherlands. I still remember my excitement when Gerard helped me setting up this telescope and I viewed through its 20mm eyepiece for the first time. It has a aluminum OTA and equatorial mount on a wooden tripod.
  It's a decent telescope but it has its flaws. The equatorial mount is inadequate for the OTA. The slightest breeze or touch causes the OTA to wobble and it takes several seconds to dampen. Also its 30mm finder is of very poor quality and I rarely used it. The telescope is rebranded as "Vesta", but I think it is a predecessor of the now discontinued Celestron Firstscope 4.5" Newton on a CG-3 mount (model 31044) with .965 inch Huygens 20mm (magnification 45x) and 6mm (magnification 150x) eyepieces. Later I also added a Huygens Mittenzwey 9mm (magnification 100x) and a Symmetrical Ramsden 4mm (magnification 225x). The ones I used most were the 20mm and the 9mm eyepieces. From my old drawings it is clear that my eyes and the telescope optics once were pretty good. I did see the casinni division and a cloud belt on Saturn with it for example. Nowadays the mirrors are very much in need for a recoating;
  
• 40mm refractor. I was really my brother's, but I used it for many years instead. It had a cardboard OTA, wooden ALT-AZ mount and probably because of the heavy use by me its achromatic doublet developed an air bubble between its crown and flint lenses which made it a poor performer. I also ruined the single Huygens eyepiece at one point, but continued to use it. In addition I ruined most of the negatives of my family's pictures in my Sun spot viewing sessions (usually at sunset), but I don't think anyone but me ever realized that.
  

Cameras

• SBIG ST-7XE NABG CCD camera. This is a dual CCD camera with a full-frame NABG 765x510 (9x9μm) pixel Kodak KAF-0401E imaging CCD and a full-frame ABG 192 x 164 (13.75x16μm) pixel TC-211 CCD tracking CCD. Mine can cool up to -40°C from abient without using the water cooling. I usually set it to -35°C. In San Jose, CA, this means that the CCD temperature is around -25°C (-13F) on a "cold" winter night, and around -15°C (5F) during summer.
  
• SBIG CFW8A color filter wheel. This automatic filter wheel has room for 5 1.25 inch filters, which is 5 too few, because besides the standard R, G, B and clear filters (and an empty slot), I also own Bessel V and I filters for photometry and narrowband H-alpha, OIII and SII filters.
  
• SBIG AO-7 Adaptive Optics. This is a high speed tip-tilt mirror system. My laptop limits it to 30 corrections a second. I usually use it at 7Hz - 15Hz.
  
• Philips ToUCam Pro webcam for planetary imaging;
  
• Meade Superwedge. Instead of the standard knobs, I use replacements from Scopestuff so I don't have to use tools.
  
• Meade f/6.3 and f/3.3 focal reducers.
  
• Cable (Radioshack)
  
• Jumpstarter (Walmart). I never even tried to use the telescope with internal batteries. From the start, I used a 12V 17AH battery.
  
• 25ft serial cable for connecting the telescope to the laptop (Radioshack).
  
• Springy Thingy (parts from Home Depot)
  
• Pizza pan. I found it a pain to try to put the telescope on its tipod for ALT-AZ. As I didn't want to spend $95 on a scopesaver table, I bought a $2.95 pizza pan instead, drilled an off-center hole in it and marked the outline of the telescope base on it.
  
• Dew shield (Orion)
  
• Quick Rigel finder
  
• Collimation thumbscrews (Scopestuff)
  
• Balancing kits and weights (Scopestuff)
  
• Dew heater. I bought the convenient Dew Buster. To recover the costs, I made all the heaters (telescope, finder and eyepiece) myself.
  Case (JMI).
  
• 350 Watt inverter (Walmart).
  
• The next thing I will buy is the ASO optical cleaning kit. After almost one year of use, the corrector of the SCT is dirtier than my car's wind-shield.
  

I generally use this equipment in the following combination:

• Telescope - focuser - camera
  This combination fits through the forks and results in a f/10 system. The image scale is 1.028"/pixel??? in 1x1 binning mode and field of view is 10'x9'.
  
• f/6.3 reducer - focuser - camera
  
• Focuser, F/3.3 reducer, 15mm spacer, camera
  
• Focuser, F/3.3 reducer, 30mm spacer, camera
  This results in a F3.3 system.
  
• Telescope - focuser - AO-7 - camera
  F/11.3???
  
• Telescope - Focuser - f/6.3 reducer - AO-7 - camera
  This results in a f/7 (1774mm) system. The image scale is 1.04"/pixel in 1x1 binning mode and the field of view is 13.3'x8.8'. 1.033avg-1.030+1.035??
  
• Telescope - Focuser - f/6.3 reducer - 15mm spacer - AO-7 - camera
  

The image scales were determined using actual images. I used the formula:
focal length [mm] = 205 * pixel size [micrometers] / image scale ["/pixel]
to compute the effective focal length.

My reasons for not using other combinations,are:

• Telescope - AO-7 - camera.
  This combination fits through the forks, but without microfocuser it is pretty useless.
  
• Telescope - f/6.3 reducer - focuser - AO-7 - camera
  This results in a f/4.9 (1253mm) system. The image scale is 2.098"/pixel??? and the field of view is 26.7'x 17.8'. This combination results in off center vignetting with a brightness difference of about 30%. For this reason, I will not use this combination anymore.
  

Problems

Although the LX200GPS is an incredibly value for the money, it does have a few problems.

• The fork mount is heavy. swing
  
• The OTA of my telescope is not mounted parallel to the fork arms. When I put it in polar home position and rotate the telescope back and forth in RA, I will never find position (by adjusting the declination) where the stars move around a center.
  
• The optical axis is not aligned with the mechanical axis of my optics. When I use the f/3.3 reducer or the f/6.3 reducer with a big spacer, the vignetting is off center. Coma is visible in one corner when I use the f/3.3 reducer.
  

Hardware Issues

A list of issues encountered:

• The OTA of my telescope is not mounted parallel to the fork arms. When I put it in polar home position and rotate the telescope back and forth in RA, I will never find position (by adjusting the declination) where the stars move around a center.
  
• The optical axis is not aligned with the mechanical axis of my optics. When I use the f/3.3 reducer or the f/6.3 reducer with a big spacer, the vignetting is off center. Coma is visible in one corner when I use the f/3.3 reducer.
  

• Internal reflection caused by the visual back.
  
• Telescope didn't fit in the JMI case.
  
• The handy microfocuser mounting thumbscrews that were included with the JMI case ruined the original visual back and many of my images.
  

Planetary Nebula M76

M76 on October 30, 2004. Four 30 minutes exposures combined for a total exposure of 2 hours.

Equipment used: 254mm SCT @ f/6.1, ST-7XE @ -15C, AO7 @ 7.5Hz (RMS wander 0.1x0.1, activation level 10%, bump 0.30s, dither 3), 656.3/4.5 nm H-alpha filter. Location: San Jose, CA.

The Moon

The Moon. This image is a mosaic of 8 frames captured on September 6th, 2004 around 1am PST. Each frame was exposed 0.2 seconds through a 656.3/4.5 nm H-alpha filter.

Equipment used: 254mm SCT @ f/6.1, ST-7XE @ -15C. Location: San Jose, CA.

Click the image to see the full 1650x1650 mosaic.

Crab Nebula (M1)

2004-09-05: 40 minute exposure (4x600s) through H-alpha filter. Camera cooled to -15°C.

Minor Planet (1316) Kasan

Asteroid 1316 Kasan was discovered on November 17, 1933 by the Russian astronomer Grigoriy Nikolaevich Neujmin (1886-1946). He is credited with the discovery of 74 asteroids, including 951 Gaspra and 762 Pulcova. He also discovered or co-discovered the periodic comets 25D/Neujmin, 28P/Neujmin, 42P/Neujmin, 57P/du Toit-Neujmin-Delporte and 58P/Jackson-Neujmin.

This movie was created from 11 images, each having an exposure of 2 minutes, taken over a 35 minute timespan on the night of 2004-08-19 (around 11PM PST). Each image was taken through an infrared filter. 1316 Kasan is marked at the start of the sequence and can be seen moving towards the West (North is up and East is to the left). At the time the images were taken, the asteroid distance from the earth was almost 1 AU, and its distance from the Sun was 1.8 AU.

The bright star on the upper-left of this movie is magnitude 9 SAO 71737 in the constellation Cygnus. The star immediately east of the asteroid is of magnitude 12.5. Because the images were not obtained using a V filter, but using an I filter, the differential photometric magnitude of 16.2 for the asteroid is not accurate (but it is still close to the expected magnitude of 15.8).

The center of the images as reported by the telescope was RA 21h 48m 48s, DEC +38d 14' 19''. A plate solution found RA 21 48m 43.78s, DEC +38d 13' 30.7''. The image scale is 2.35 arcsecs/pixel (the whole image is about 15' x 10'). During the 35 minute sequence, the asteroid moved almost 21 arcseconds.

The animation is noisy because I did not have matching bias/dark frames, nor did I have flat frames. I downscaled other bias/dark frames, and used strong dead/hot pixel removal to reduce the remaining noise.

PEC training using a CCD camera

TODO

The Bubble Nebula Revisited

NGC 7635 on June 25, 2004. My first SII Ha OIII image attempt.

2004-06-25:

The Bubble Nebula

NGC7635 on June 4, 2004. A combination of eight 20 minutes exposures through a 656.3/4.5 nm H-alpha filter for a total exposure time of more than 2.5 hours. The ST-7XE camera was cooled to -20C.

The Cocoon Nebula

IC5146 on May 29, 2004. A star-forming region of glowing hydrogen at an approximate distance of 3000 light years, surrounded by a sparse star cluster. The hydrogen is lit by the type B0 star of magnitude 9.6 in the center of the nebula.

This is an 80 minute exposure, consisting of four 20 minutes individual exposures, through a 656.3/4.5 nm H-alpha filter. The ST-7XE camera was cooled to -20C.

NGC 6888

NGC 6888 on May 29,2004. This is a mosaic of two 100 minute exposures, each consisting of five 20 minutes individual exposures (2x5x1200s) through a 656.3/4.5 nm H-alpha filter. The ST-7XE camera was cooled to -20°C.

Dumb Focuser Thumbscrews

Last night I realized that much of the flexure in the optical train I have been noticing many times before is really caused by the focuser. It is never snug to the back of the telescope. So today I took a closer look and noticed something I should have noticed a year ago. The damage to the optical back is not caused by over tightening, but by the focuser thumbscrews that were included in the JMI case itself! Comparing them to the original ones that came with the telescope, it is obvious that these replacements have a flat head instead of a round one, and they do not properly fit in the optical back.

So I filed them. And indeed now the focuser connects well. Moving forward, this should reduce the elongated stars I have been seeing in so many of my images.

Planetary Nebula M57 Revisited

My first image using my new AO-7. Not perfect yet, but sure an improvement on my previous image.

2003-04-08: 4 minute exposure (2x120s). Camera cooled to -10-20°C.

Imaging bright objects

How I take images depends on the object in question. I usually use a webcam for bright objects inside our solar system, and a sensitive cooled camera for everything else.

The reason is that even though the webcam is much less sensitive than my main camera and has a much smaller dynamic range (brightness levels), it can take up to 25 frames a second, whereas the main camera is limited to one 0.1 second frame each second. To minimize the effects of seeing (air turbulence), I can therefore use the technique of "lucky imaging" with the webcam. This is a technique with exposure times short enough so that the changes in the atmosphere during the exposure are minimal. From these images (a movie really), I select the frames least affected by the atmosphere and combine them into a single image by shifting and adding the short exposures. This yields a much higher resolution than would be possible with a single, longer exposure and allows me to reach the diffraction limit of my telescope, about 0.5 arc seconds (one arc second is the apparent size of a dime about 3.7 kilometers away). By adding hundreds of individual frames like this, the effective dynamic range of the webcam increases, reducing the effects of noise, and I can apply advanced image processing techniques to further increase the resolution of the final image.

Because the exposures are short, I can also use the simpler ALT-AZ setup for the telescope, which is less sensitive to disturbances and vibrations by the wind. During the exposures, the telescope is passively tracking the object to counter the effects of the rotation of the Earth. The Earth's rotation moves objects with a speed of up to 15 arc seconds each second out of view or, with the image scale generally used for these images, between 30-60 pixels each second. The telescope mount can counter the effects of this rotation, but with my telescope, the remaining tracking errors have an eight minute periodic component of 21 arc seconds in them. With the built-in software of the telescope mount I reduced that to an eight minute periodic error of 7 arc seconds peak to peak (in polar mode; I never measured it in ALT-AZ mode but it sure is much higher).

But, because the individual exposures are very short, this remaining periodic tracking error in an 8 minute time period does not lead to image smearing.


Another benefit of the webcam for these kinds of objects is that, unlike my main camera, it is not a monochrome but a color camera. The 640x480 pixel CCD contains a Bayer filter (50% of the pixels have a green filter, 25% have a red filter and 25% have a blue filter). Although this means that each RGB pixel has at least two interpolated color components, it does have the benefit that the colors are shot at the same time. The only post processing required is relative shifting of the color channels, as the Earth's atmosphere refracts light at a slightly different angle for each color, which amounts up to several pixels on the image scale used.

The maximum number of frames that can be combined using this method is limited to a few thousand. Only a certain percentage, like 10%, of the frames can be used to maximize the resolution of the result. My wish to use an ALT-AZ setup for these kind of images also limits the total exposure time because of the effects of field-rotation in this mode. In addition, the imaged objects themselves rotate too, which leads to smearing if the movies are longer than about 10 minutes.

Saturn

Saturn on March 8, 2004.

Jupiter

Planet Jupiter floating in space on March 8, 2004. A combination of 662 frames taken with a ToUCam Pro webcam through the 254mm SCT. A total exposure time of 44 seconds.

Please note how this exposure is expressed in seconds, while most others of this blog are expressed in minutes or even hours. Jupiter's apparent brightness is extremely high compared to objects outside our solar system. In fact, only the Sun, Moon, Venus and Mars can reach a higher apparent brightness.

I clearly improved my technique compared to my first attempt of this planet with this telescope.

Eye Opener II

On several occasions when using the SCT visually, I noticed a significant glare around bright objects (e.g. planets). This is caused by internal reflections in the optical system. I also ran into this problem during imaging several time. For example the January 21 raw frames of M109 are completely ruined by the reflections of the light of a nearby star.
I found that the standard visual back of the SCT is a major cause of this. Flocking it is however not an option as this increases vignetting. To test this theory, I took some flats on December 26, 2003. Indeed, with the standard visual back my replacement f/3.3 focal reducer has an ADU drop of 7% across the field when used with the ST-7XE camera. But, after flocking the inside of this original visual back, this increased to 12%.
I figured that although an Eye Opener II would theoretically not have any benefits with my 1.25 inch eye pieces, nor with my cameras, it may actually lead to a reduction of the reflections. So I bought one, and found that it was actually even more reflective than the original visual back. Indeed, it is slightly worse than the original visual back in regard to the glare.
However, after flocking the inside of the Eye Opener II, it is actually much better than the original visual back. When using the camera with the f/3.3 focal reducer flocking the Eye Opener II doesn't have any negative effects (the 7% ADU drop remains). However, the glare is very significantly reduced when using it visually with bright objects.

So, for my purposes the Eye Opener II isn't beneficial because it reduces vignetting, but it is only because I have more room to add some flocking to suppress the reflections.

Determining Declination Backlash Using a CCD Camera

By using a 4mm eyepiece, speed 3 (8x sidereal) in ALT-AZ mode I found that my DEC axis backlash can be compensated by entering a value of 30 . This is the value I have been using until now. But, most of the time

• The telescope is used in a completely different configuration while imaging (heavy camera, counter weights, etc);
  
• I am using polar mode, not ALT-AZ;
  
• I am using a guiding speed of 66% sidereal (sidereal is 15 arcsec/sec, so I am guiding at 10 arcsec/sec), not 8x sidereal while imaging;
  
• For any speed other than guiding speed, the UP/DOWN buttons behave different. For guiding speed UP/DOWN moves the Declination axis only, but for any other speed, this moves the telescope Altitude. In ALT-AZ mode, Dec movements cause both axis to move, while in Polar mode, an Altitude movement causes both axis to move.
  

So, for a proper backlash compensation, the amount of backlash should really be determined in the same configuration as that will be used for imaging.

A more accurate approach to determine the DEC backlash compensation in polar mode is:

1. Set up the telescope with the camera attached as usual (but not with focal reducer for increased accuracy).
   
2. Turn off tracking (SETTINGS - TELESCOPE - ...).
   
3. Point the telescope to east.
   
4. Set the guiding speed to 66% (or whatever what you usually use).
   
5. Select guiding speed (MODE - 1)
   
6. Take an image of 60 second, while doing that, do the following:
   
   
   
   1. Press UP key for 10 seconds.
      
   2. Wait 10 seconds
      
   3. Press DOWN key for 10 seconds
      
   4. Wait 10 seconds
      
   5. Press UP key for 10 seconds
      
   
   
7. TODO
   

This is how I came to use the value 100 instead.

Of course, backlash is only a problem if the the guiding direction is changed, so, with a proper polar alignment and an AO7 all this is not really a problem. Also, as long as the direction is not change, the issue of retrograde motion also doesn't appear (this is the problem of a drive, usually the Dec drive, to move a bit in the opposite direction selected by the keypad, before resuming in the correct direction).

On the night of 2004-02-07 I set out to improve my DEC backlash correction using the Single Axis Mount Dynamics command of CCDOps. The telescope was mounted in polar mode.

TODO

No backlash compensation Backlash 8s, Y [-7.87,34.56]	Backlash compensation 25 Backlash 6s, Y [-7.33,48.56]
Backlash compensation 50 Backlash 4.5s, Y [-10.57,45.69]	Backlash compensation 75 Backlash 2.5s, Y [-33.86,33.80]
Backlash compensation 100 Backlash 1.5s, Y [-25.32,38.82]	Backlash compensation 150

Galaxy M109 in Ursa Major

The aurora in this image is the result of a reflection in the optical system caused by a star just outside the field of view. After taking this image I have been flocking the inside of the AO-7 adapter ring, which was a major contributor to this problem.

For this image, I have used a longer exposure time for the blue filter than for the other two, to compensate for the lower sensitivity of the main CCD for this color.

This is the first image I used my newly built light box for to do flat field correction.

2004-01-21: Luminance 50 minute exposure (5x600s). R and G binned 2x2 10 minutes (1x600s), B binned 2x2 16 minutes (1x960s). Camera cooled to -20°C.