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The inadequacy of the MkIII mounting when carrying the folded refractor was too irritating to continue. So I borrowed the crossbars and clamping bars for the MkIV without using the guide rails. I shall make some round spacers to ensure the OTA is guided effortlessly into position when being placed onto the MkIV.
The difference in stability was immediately obvious. Night and day if you will forgive the term in this context. I decided to leave the pier in the most useful position and merely packed the "feet" to bring the pier to perpendicular.
This closer image shows the simplicity of the mounting method. I may increase the dimensions of the crossbars for extra stiffness.
I needed to use some studding [threaded rod] to attach the clamping bars. Loose nuts ensured the clamping bars did not drop too far on the studding. So that the OTA could be mounted without having the clamping bars jammed between the bottom framework rails.
The massive pier and heavy mounting provide formidable stability. It is quite surprising how the large mounting and the OTA both seem to visually shrink each other.
When my 6" f/8 refractor was mounted on the MkIV is was easy to hold a camera up to the eyepiece without causing image shake. Hopefully this will also be true of the folded refractor.
Bu coincidence the single baffle is almost centered on the declination shaft. Making for easy fitting of the OTA to the mounting without lots of adjustment.
The Porsa tubing and reinforced corner joints are proving to be well up to the job of holding the optical components in place.
The 4" & 5" 1/20th wave optical flats came for Steve Dodds in the US. It looks quite alarming, by torchlight, how much dust they collect. Though it seems not to matter. I should probably use my lens blower to "tidy them" occasionally.
An f/12 7" refractor can be a large beast in a straight tube but the optically folded design has shrunk the length by a half.
With the sky clear and the telescope already set up I left it for several hours before I was finally able to point it at Jupiter. It was 36F when I started and it slowly dropped to 32F, 0C. I then spent several hours staring at the planet with a whole range of my Meade 4000 eyepieces: 26, 20, 15, 12.4 and 10mm. Mostly I was swapping back and forth between the 15mm and 12.4mm for 144x & 174x. I tried a yellow No8 filter and the "Fringe Killer" but preferred the view without. The front of the objective dewed over at one point but I added the full length dewshield and it soon cleared again. Tipping the OTA in declination saves climbing ladders.
A white frost descended and the OTA was covered in moisture and then sparkling ice crystals. Slowly, over several ours of exposure, the optical folding mirrors dewed over. Though there was nothing I could do about this but persevere and hope. It occurs to me that only the rear of the OTA needs dew protection. The rear of the objective is unlikely to dew over as it is downward facing. The baffle separates the two sections of the framework at the rear of the shoulder. This section could have a simple cloth shroud fitted using clothes pegs. Or even self adhesive Velcro strip using the cloth for the loops.
By 10.30pm Jupiter was as high as it was likely to reach [37 degrees] that night and the GRS had moved from the limb to not far from central on the planet's disk. [The meridian.] Tantalizing glimpses of fine detail in the belts came and went towards the end but it had been a very long wait. My feet were very cold by this point so I tidied everything away by 10.45pm. [CET] I shall start with my walking boots next time rather than putting them on when it was already too late. With recent experience of clouding over quite early I had no real idea how long I would be standing out there on the lawn.
The full Moon had been following Jupiter upwards but was usefully hidden behind the hedge until quite late. By the time I looked at it briefly, before packing up, the moon was a blinding, rather featureless, misty disk.
The MkIV's drives worked well despite the rust on the worms. Keeping Jupiter in the field of view saved a lot of time searching for it when swapping high powered eyepieces. As was often necessary with the MkIII. In fact the MkIV mounting was so rigid that I could rest my nose against the eyepiece without moving the image or causing any vibration.
Early on I noticed that my wild guess, as to the direction of the Pole Star when setting up the pier, was considerably out. I had to use a length of water pipe as a lever to rotate the massive pier on the ground in the dark. After that Jupiter remained centrally in the field of view with the RA drive running. I shall have to recheck the pier's uprightness in daylight. Despite appearances Jupiter was the perfect height for observing while standing naturally. The beer crate in the top image was for reaching the upper clamping bar. I only rarely imbibe the "amber nectar."
9/4/2016: An hour and half viewing a rather soft Jupiter at 42 degrees local altitude. Image quality was only rather "average" but improved steadily after the first hour. Two belts were clearly visible but it took a while to confirm an orange/tan GRS. The Galilean moons were "woolly" and not even round when I started observing but "shrank" with passing time. As did star images. This strongly suggests that the objective needs plenty of time to cool because Jupiter was on the meridian and did not gain any more altitude over time. The folding mirrors were housed in unheated accommodation in the OTA. While the objective had been kept indoors in a heated room. When I first set up, in the dark, just after 10pm, the sky was rather milky and 'soft' but became steadily darker by 11.30. There was little or no sign of stars twinkling.
I rotated between 20mm, 15mm and 12.5mm Meade 4000 Plossls for most of the time for 108x, 144x & 174x respectively. Magnification seemed not to alter the image quality very much but the 10mm, for 216x, was a step too far. A check through the open star diagonal suggested a slight tweak of the 1st mirror collimation screws to center the 2nd mirror. Once that had been applied all the circles seen through the open focuser were nicely concentric again.
Bu coincidence the single baffle is almost centered on the declination shaft. Making for easy fitting of the OTA to the mounting without lots of adjustment.
The Porsa tubing and reinforced corner joints are proving to be well up to the job of holding the optical components in place.The 4" & 5" 1/20th wave optical flats came for Steve Dodds in the US. It looks quite alarming, by torchlight, how much dust they collect. Though it seems not to matter. I should probably use my lens blower to "tidy them" occasionally.
An f/12 7" refractor can be a large beast in a straight tube but the optically folded design has shrunk the length by a half.
With the sky clear and the telescope already set up I left it for several hours before I was finally able to point it at Jupiter. It was 36F when I started and it slowly dropped to 32F, 0C. I then spent several hours staring at the planet with a whole range of my Meade 4000 eyepieces: 26, 20, 15, 12.4 and 10mm. Mostly I was swapping back and forth between the 15mm and 12.4mm for 144x & 174x. I tried a yellow No8 filter and the "Fringe Killer" but preferred the view without. The front of the objective dewed over at one point but I added the full length dewshield and it soon cleared again. Tipping the OTA in declination saves climbing ladders.
A white frost descended and the OTA was covered in moisture and then sparkling ice crystals. Slowly, over several ours of exposure, the optical folding mirrors dewed over. Though there was nothing I could do about this but persevere and hope. It occurs to me that only the rear of the OTA needs dew protection. The rear of the objective is unlikely to dew over as it is downward facing. The baffle separates the two sections of the framework at the rear of the shoulder. This section could have a simple cloth shroud fitted using clothes pegs. Or even self adhesive Velcro strip using the cloth for the loops.By 10.30pm Jupiter was as high as it was likely to reach [37 degrees] that night and the GRS had moved from the limb to not far from central on the planet's disk. [The meridian.] Tantalizing glimpses of fine detail in the belts came and went towards the end but it had been a very long wait. My feet were very cold by this point so I tidied everything away by 10.45pm. [CET] I shall start with my walking boots next time rather than putting them on when it was already too late. With recent experience of clouding over quite early I had no real idea how long I would be standing out there on the lawn.
The full Moon had been following Jupiter upwards but was usefully hidden behind the hedge until quite late. By the time I looked at it briefly, before packing up, the moon was a blinding, rather featureless, misty disk.The MkIV's drives worked well despite the rust on the worms. Keeping Jupiter in the field of view saved a lot of time searching for it when swapping high powered eyepieces. As was often necessary with the MkIII. In fact the MkIV mounting was so rigid that I could rest my nose against the eyepiece without moving the image or causing any vibration.
Early on I noticed that my wild guess, as to the direction of the Pole Star when setting up the pier, was considerably out. I had to use a length of water pipe as a lever to rotate the massive pier on the ground in the dark. After that Jupiter remained centrally in the field of view with the RA drive running. I shall have to recheck the pier's uprightness in daylight. Despite appearances Jupiter was the perfect height for observing while standing naturally. The beer crate in the top image was for reaching the upper clamping bar. I only rarely imbibe the "amber nectar."
9/4/2016: An hour and half viewing a rather soft Jupiter at 42 degrees local altitude. Image quality was only rather "average" but improved steadily after the first hour. Two belts were clearly visible but it took a while to confirm an orange/tan GRS. The Galilean moons were "woolly" and not even round when I started observing but "shrank" with passing time. As did star images. This strongly suggests that the objective needs plenty of time to cool because Jupiter was on the meridian and did not gain any more altitude over time. The folding mirrors were housed in unheated accommodation in the OTA. While the objective had been kept indoors in a heated room. When I first set up, in the dark, just after 10pm, the sky was rather milky and 'soft' but became steadily darker by 11.30. There was little or no sign of stars twinkling.
I rotated between 20mm, 15mm and 12.5mm Meade 4000 Plossls for most of the time for 108x, 144x & 174x respectively. Magnification seemed not to alter the image quality very much but the 10mm, for 216x, was a step too far. A check through the open star diagonal suggested a slight tweak of the 1st mirror collimation screws to center the 2nd mirror. Once that had been applied all the circles seen through the open focuser were nicely concentric again.
Click on any image for an enlargement.
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2 comments:
I knew you wouldn't be happy until you had arranged things so you have to balance precariously on a stepladder in order to use the instrument! Take care, now, when the view of the heavens takes your breath away...
BW. Andrew
Hi Andrew
I assure you that I had my feet planted firmly on the cold ground for the entire evening. I even removed the objective without leaving the ground. What I do need is more altitude for Jupiter! Only towards the end [and through misty mirrors] was it beginning to reveal itself. I could have saved myself the effort of standing there for the first couple of hours and gone out later! ;-)
Chris
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