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About jefrs

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    West Berkshire, England

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  1. The 130SLT is not a bad telescope but the best thing about it is the mirror, The focuser wants to be taken apart, cleaned and serviced; some soft grease used, and the tension adjusted so it moves smoothly. The nylon bars on the slide may want packing with tape to reduce slop. The focussing is rack and pinion, and quite coarse, but by adding a long lever to one of the knobs, such as a battery crocodile clip can move it in small doses. Have the lock screw just touching whilst focussing to reduce slop, nip it lightly once in position. The problem with 'back focus' (which means something else
  2. First of all StarSense is an alignment tool. There are Celestron and SkyWatcher flavours. It connects by the ST4 port to the mount, it does not /need/ a laptop. It does have a USB port but that is /only/ for firmware update. With the firmware updated and its camera focussed (which is a royal pain) it can align and calibrate the mount in 15-30 seconds. Seriously, it can be that fast but it does have to be focussed. As such is it a very valuable tool for aligning the mount. The only way I could focus it was a boring iterative process of screwing the lens in an out a little at a time to find maxi
  3. Chinon (Japan) could make exceptional lenses to rival or exceed Asahi Pentax. Very good glass that will probably exceed Olympus and Nikon. I have a pair of 8x40 wide angle 9°. Chinon produced the first production autofocus camera lenses. Chinon got bought out by Kodak Japan. You should be able to compensate vision on one of the eyepieces. You may want to use a monopod or video head tripod when looking up for long.
  4. That is incorrect. It does have a 4:3 aspect but not why it is called 4/3-inch, It dates back to steam powered TV cameras and the internal diameter of the tube (valve) used in them. It is just a name. Rather like incorrectly calling full frame DSLR full frame when they're the same size as compact film. Image circle diameter of 4/3 is 21.6mm, less than an inch. Something to note though is a smaller sensor does not receive less light than a large one. When they are pulled into focus, all the light from the lens (telescope) is focussed upon it. What is important is the photoreceptor (pixel)
  5. The name "4/3" comes from the size of a TV camera tube, now pretty much obsolete. The image sensor of Four Thirds and MFT measures 18 mm × 13.5 mm (22.5 mm diagonal), with an imaging area of 17.3 mm × 13.0 mm (21.6 mm diagonal), comparable to the frame size of 110 film. (wiki). Micro Four Thirds (MFT or M43) is actually the lens fitting, the sensor is "4/3". The image circle diameter is almost exactly half that of a full frame camera, so the crop factor is X2, which effectively doubles the length of the lens, or telescope. The pixel size of the 16MP sensors is 3.75µ (slightly larger than m
  6. If you are considering 4/3 sensors then you might consider getting a Lumix G7 which may go for as little as £200 used, if you don't want to spring £1,000. Pixel size is more important than pixel count in low light. The 16MP sensor has 3.75µ pixels. The Panasonic designed Live-MOS is biased to sweep stray electrons off, unlike Sony CMOS sensors. And it is mounted on a heat sink to keep the temperature stable. The powerful processor has features to further reduce noise as it is designed to shoot movie indefinitely without overheating. Shutter speed down to 1 minute and built in interv
  7. There is the word 'stiction' that aptly describes the problem, yes it is a real word for a real problem - "the friction which tends to prevent stationary surfaces from being set in motion"
  8. Break it down to first principles. You have OTA focal length divided by eyepiece focal length giving the magnification of the telescope. Then your compact will add some magnification factor. For a camera that is the focal length of the lens (not full frame equivalent) divided by the sensor diagonal, aka image circle diameter. Multiply them together. Personally I have never managed to get a compact camera to focus on the eyepiece image, I'm told it has to be set at infinity.
  9. Simple answer (I hope) is divide focal length by the image diameter circle (the diagonal) of the camera sensor. Full frame is 43.3mm and this is the proper length of a prime lens to give 1:1 image although we normally use 50mm or 45mm. For micro four thirds the image circle diameter is 21.6mm so its 'prime' lens is 20-25mm thereabouts, and APS is somewhat variable, nominal 35mm. A typical guide camera might be a 1.2/3 sensor of 7.66mm diagonal. These give the equivalent eyepiece focal lengths when used on prime focus. Magnification is OTA focal length divided by eyepiece focal length. A
  10. Something I'm always trying to get my head around too. Also complicated by the eyepiece because they can vary in field of view as well as focal length, obviously a long eyepiece will give you a wider FoV than a short one. A camera will also change the FoV, sensor size (crop factor), whether on prime focus or eyepiece projector. This calculator may help https://astronomy.tools/calculators/field_of_view/
  11. The SLT mounts are not strong but with some proper servicing can support and move heavier weights than they were designed for. The bearings need cleaning and a good grease like Castrol used and then set up so they rotate smoothly with a very small end float. If set too tight they bind. The Stifnuts are poor, use Loctite, or they adjust themselves. The Alt clutch can be tightened but must still clutch. The motors like some attention, the muck they put in the gearboxes is not good. Plastic cogs need silicone grease, on the teeth not in a pool on the case floor. The gearboxes are like repairing a
  12. You will find various illuminator adapters here - http://www.astrokraken.fr/accessories-for-skywatcher-star-adventurer-mount-a184487612 ça plane pour moi I don't have a 3D printer and unlikely to get one. A lens hood can be simply made for the illuminator from a black plastic 35mm film can.
  13. Yes! Once I got the camera refocused it's quite amazing. I set up Thursday night 07/05/20. Of course by the time it dot dark there was solid high thin cloud. I could just visually see Arcturus but little else. So I experimented. There's a LED street lamp over our back room before our patios. Despite that and the cloud and high hedge and fence it still did an Auto Align in under a minute. Adding a star to the calibration makes it want to do another Auto Align. So we did that three or four times. Despite only seeing a few stars, now focused, it competed successfully every time, quickly too. I
  14. An older thread but a good one. My StarSense was not seeing stars. I have a lot of light pollution, LED street lamps. Auto align kept failing. I read this thread and spent the night adjusting the StarSense camera focus as described above - thank you people. I found the focus point to be quite critical. I found the focus point between 15 and 24 half turns out and then narrowed it down to to around number 20. Meaning these cameras are not all the same. I then started going in quarter turns in and out and then 1/8 turns until I got maximum star count. Whereupon I lost count of turns a
  15. Using two cables to the computer may well be true with the older Hand Controller and the 'Celestron Programming Cable' with USB/Serial adaptor. The instructions seem to have been written for this older system (pic). With the USB Starsense HC the data is fed through to the camera on the RJ12 cable. I did a little experiment when I had to replace the motor board (which has its own update process) - I updated the camera with the NexStar+ Telcon serial HC attached, this did require the camera USB cable to be used, all devices were updated. The updates are reinstalled if they are already the latest
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