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jefrs

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Posts posted by jefrs

  1. Do not buy cheap and nasty.  Or something that needs three more parts of equal expense to make it work.

    For simple astrophotography with camera and lens, the Sky Watcher Star-Adventurer with a hefty photographic tripod (Manfrotto 055XPROB or similar). . With that you get the wedge, the motor, the mount, polar finder, and counter weight.  And it is relatively light and portable.  About £330 quid plus about £150 for new tripod. Eats batteries and wants a power supply.

    Latest version comes with wifi. I cannot think why you would need that on this.  It can be guided but not really needed because its motor is good and it's only got one axis to control.

    It is simple. It works.

    • Like 1
  2. On 23/05/2020 at 22:54, JOC said:

    I haven't waded through tbe rest of the answers, but my telecope has a focal length og 1200mm.  I always assumed that if I put my dslr into the focusser with no other Eye piece in place that it was like stcking a 1200mm lens onto the DSLR

    That is exactly right. It's a 1200mm lens on your camera, any camera.

    We focus an image circle diameter of  the diagonal of the sensor.  It has nothing to do with pixel pitch, it's an optical image size. With crop sensor cameras we often refer to equivalent length to full frame. On a MFT with a x2 crop factor the 1200mm lens will be /equivalent/ to 2400mm on full frame. It's properly called field of view.  I hate using "equivalent focal length", it's a poor term.  The image circle diameter is smaller thus reducing the field of view. In other words, the moon looks bigger.

  3. The StarSense is brilliant for alignment, once its initial set up is done.  I found mine needed focussing to solve maximum number of stars. Which meant moving the focus in and out in ever decreasing little turns whilst running alignment over and over again. After the initial Auto-align it then needs calibration - do read the instructions. Calibration aligns the camera to the OTA. It is not a guider, it is a goto alignment tool.

    It is a Celestron device, there are Celestron and SkyWatcher flavours, they are not interchangeable.  

    Once set up operation is very simple, you just push the button. Full alignment may only take a few minutes. A lot easier and less painful than squinting at a red dot or finder scope and then trying to put the star in the middle of the eyepiece (what is an eyepiece?). It will also polar align to aid you setting the manual polar alignment screws. 

    If StarSense is run by wifi it will get lat/lon and time from the computer.

  4. A Power Tank battery that seems on its way out may be recharged with a Noco Genius G3500 which is a small intelligent charger for motorcycles. It is a 3.5A charger but has a 1A setting for small batteries as used on motorcycles, and in the Power Tank. To charge the Power Tank connect to the red and black screw terminals with the Power Tank set to OFF.  The G3500 will indicate when the battery is fully charged.

    Small lead acid should not be charged at more than 1A rate. Use the 1A AGM battery setting. Do not use any 3.5A setting. The G3500 is far more 'intelligent' than an optimiser. It also has a recovery mode that may bring a lead acid back from dead.  Please note I use the word 'may' here and above, if the battery is completely dead it will not work; I have recovered a deeply discharged but fairly new motorbike battery that has continued to work perfectly.  A charged lead acid 'in storage' should last up to six months without any current drain; I have a reminder set up for every two months to check all lead acid and lithium batteries, and recharge as required.  Lead acid batteries do not like being on continuous charge (small current), nor being recharged too often; but they do like being fully charged (full current) when they are recharged; leave them on an intelligent charger for 24h.

    If the Power Tank battery is dead it will not recharge.  It is a fairly standard burglar alarm type leisure battery, replacements can be obtained from the usual suspects online.

    Perhaps keep the Power Tank in the car plugged into a lighter socket so that it charges whenever the car is running, as the car's own battery does. Not into an always-on socket that may drain the car's battery.

  5. I have StarSense from my 130SLT on which it is very good and takes only a few minutes, and which I have just fitted to AVX and waiting for clear sky to test.

    Reading the StarSense manual the sequence is to AutoAlign first (no I do not know why as it is going to need Auto-aligning again after polar align is shifted) then Polar Align upon which StarSense will give instructions on how far to Manually move the mount up or down, left or right, to align Polaris. Note - Manually using the big screws, not the motor controls.

    The StarSense has to be calibrated to your OTA, it does not know where your OTA is pointed. To aid doing this I first align RACI crosshairs to the centre of the OTA, which can be done in daylight. This process is described in the StarSense manual - StarSense will move to a star and tell you to align the OTA centre to the star and save the position. (my OTA will be loaded with a camera and I cannot use a red dot, RACI is easier)

    The StarSense /must/ be focussed. Which is not a lot of fun as there is no camera output. So you have to run alignment and iteratively move the focus in ever decreasing turns back and forth to gain maximum star numbers during plate solving. This can take all night but once done is done. When done StarSense will align very quickly, a few minutes.  If it takes longer it needs focussing.

    Once the first Auto-alignment is done StarSense needs to ba calibrated per the manual. StarSense will also plate solve during the night to aid GoTo alignment.  It is a GoTo aid and will allow you to hit the mark accurately. StarSense also likes additional calibration points, and to know which areas it should not try to use (like the side of the house). What it is not is a star guider. It takes the hard work out of aligning a computerised mount.

    StarSense is very easy to use in practice, you just hit the button to align. Once it has been set up, that's is. It is worth having; the mount will not work without alignment, StarSense does that for you. But you must read and understand the manual first, and the manual is written backwards and sideways.

  6. Rotate the OTA in rings so you can access the eyepieces. I have a RACI for alignment calibration of a StarSense which is all pretty heavy so I position to counter balance the camera i.e. along the top of the Newt.  The AVX mount doesn't seem to mind the slight sideways imbalance.

    Why are EQ mounts always shown with the telescope facing Polaris? They're never used like that. Rotate the Newt in its rings  to where it is in viewing position.

    I also use Micro Four Thirds (MFT) cameras. The G9 is not small, it is heavier than the half-brick GH4 whereas the E-M5ii is small and light, which itself is heavier than the DMC-G7 (I've been acquiring them for years). What we can do is fit a not cheap but worth it clip-in CLS filter (STC Astro Nightscape) to knock out most but not all of the annoying terrestrial lighting.  (I'm Bortal 4/5 but with a problematic (cof) 'shielded' streetlamp).  The usual T2 to MFT adaptor is probably loo long, the depth of a DSLR light box, so a thin one is needed on the focusser. If the focusser is swung below the OTA the weight of the camera can drag it out making focussing a pain.

    Unlike Canon we don't have BackyardEOS but can cable tether to either Panalympus apps, but they're far from ideal for astro. So we have to rely on the cameras, which are excellent and have built in interval timers to 1 minute exposure. Using them on wifi makes them get hot and is a bit of a waste of milk because so many functions are missing from the fondle slab app. They will also focus-peak on e.g. the moon, which helps. NR needs playing with to stop it removing faint stars.  Olympus will get a hot battery, use their power supply, but Panasonic have effective heat sinks.  The G9 eats more battery than the GH4 which has the best heat sink, but then a used G7 may be had cheaply and is very light.

  7. A CLS-CCD filter is for a modified camera with no IR filter, or an astro eyepiece camera. They can be fitted to an eyepiece and some Barlow, or the T-adaptor for the DSLR.

    I have an Astronomik  CLS-CCD on a T7C guide cam, eyepiece screw-on. It made a significant improvement. The sensor lacks filters and the firmware of a DSLR. Using that filter with an unmodified DSLR produces rubbish results, a lot of colour shift.

    A DSLR needs to be set up for astro and night photography. They will get rid of a lot of the rubbish which an astro cam relies on a laptop app to do. The auto WB usually works. A lot of the NR needs to be reduced (or it will remove faint stars). The contrast and sharpness needs to be fiddled with. Any auto exposure will be way off.  AF won't work on stars unless you have a Panasonic, new Olympus or Pentax.

    I have the STC Clip Astro Nightscape Filter clipped into my Olympus E-M5ii. It did not make a significant difference however we are Bortal 5 going Bortal 4 but with a LED streetlamp nearby.  LED lighting is difficult to filter out. For more Bortal you may well want the heavier Multispectra filter cf (scroll down) https://shop.stcoptics.com/product/clip-olympus/

    But, big but, clip-in filters are expensive, they are good where you are using a camera lens, they also shield an otherwise open sensor mounted prime on a telescope. They're also camera specific, the Olympus clip-in will not fit my Panasonic, nevermind. You may want to save the money and spend it on an astro camera for a telescope; then you also want filters.  I do mount the Olympus on the telescope or with lenses.

  8. 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 to photographers) aka 'flange focal distance' means the camera needs to be moved in or out from the the eyepiece/Barlow. Typically the sensor needs to be at the distance your eye would be.  This may be done with extension tubes, an eyepiece projector, longer or shorter camera adapters, or even a focussing eyepiece adapter. A DSLR has a mirror box, a mirrorless camera does not, an eyepiece camera (ZWO etc) can be moved on its stop ring. This distance is not super critical as then the whole lot is focussed on the telescope.  Experiment.

    The 130SLT eyepiece adapter may even be fitted on the underside of the plate, allowing a Barlow or nosepiece T2 adapter to drop further inwards, saving that the clamp screws are too long and would have to be replaced with shorter ones or grub screws. I've tried this with the screws out, loose, it kinda works.

    An Olympus E-M5ii can for example achieve prime focus mounted directly on the 1.1/4 eyepiece adapter of the 130STL with a thin T2-MFT adapter; most MFT adapters have an extension tube to allow for the missing mirror box when adapting a camera lens.  A different length tube may be needed to mount it onto a Barlow. Tubes and adapters are available in different lengths.

    The NexStar 130SLT does not have powerful motors and cannot support much weight on the nose of the OTA, a suitable tube ring may be used at the back end to counter balance the additional mass.

  9. 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 maximum stars, it took all night.

    It can be operated by software, Celestron provide apps for laptop (USB) or fondle slab (WiFi). If USB then that is the one on the StarSense handset. I do not know about the StarWatcher version. The iPad app has poor controls, very jerky, but that may be the WiFi. The Celestron laptop app "CPWI" is very good.

    It does not star guide as such but during the course of a night it will occasionally go into plate solving mode and realign/recalibrate. Thus StarSense should be left connected during the course of the night. It aligns by plate solving. Thus it maintains accurate tracking, but it does not guide the mount on a star, you would need an additional star guider for that. 

    I have tried to get images out of it but to no avail, its USB port does not transmit image data. Its ST4 port is only for guiding the mount. If it did have a proper camera output that would be a great boon for focussing; there's a missed trick here. But using it as a guide camera might interfere with its auto-recalibration routine; it's a one-purpose device.

  10. 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.

  11. On 24/05/2020 at 12:44, Adam J said:

    People always get this wrong and say it's 4/3 of an inch diagonal...which it can be in some cases but it's actually the aspect ratio. 

    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) size. A larger sensor can have larger pixels but on the down side they become slower to transfer data, harder to keep cool, and are noisier.

  12. On 24/05/2020 at 10:47, spikkyboy said:

    Can somebody tell me what a 4/3 sensor is and what the pros and cons of that would be? Thanks

    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 most APS). but the 20MP sensors have smaller pixels.

    For example - The £700 ZWO ASI294MC Colour 4/3"  has a Sony 4/3 11MP CMOS sensor with 4.63µ pixels. The earliest MFT cameras were about 12MP.

    The MFT cameras have a Live-MOS which unlike a CMOS is biased, this reduces electronic noise. Some are made by Panasonic and some by Sony, but to Panasonic design. It is not unusual for a rival to manufacture parts.

    Being mirrorless MFT cameras only have a live view, which can be boosted for faint objects to aid focussing. Or dimmed right down for the moon.

    Recent MFT cameras will wifi to iOS apps on fondle slabs to control and view images However some of the functions are then missing and probably not suitable for astro. Both makes will shutter to 1 minute and have intervalometers, Lumix ASCOM  drivers are available to wifi to laptop, however in my feeble efforts these appear clunky, the wifi keeps falling over.  iPads only have a single wifi, so you cannot get GPS and time from the interweb when connected to the camera. The higher end cameras can be tethered to a laptop by manufacturer or third party applications. What you get in a MFT camera is a very good sensor and a powerful processor that can interval shoot long exposures to JPEG+RAW and optionally compile to movie, and do its own dark framing better than most software.

    • Like 1
  13. 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 intervalometer.  ASCOM drivers are available.

    • Like 1
  14. 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.

    • Like 1
  15. 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 common misconception is that a larger sensor will see more light than a small one. Both see all the light gathered through the lens/OTA iris (or aperture if closed down). The sensor is at the image focal point and sees all the light. A 130mm reflector is 130mm iris. If 650mm focal length then 650/130 = f/5.

  16. 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 clock, and reassembly is a metal puzzle, so if you're not confident, leave it alone. The motors seem to like a drop of Servisol Super 10, an electrical lube. The drive cog onto the platen does need a small amount of play, not forcing the two cogs tight together as it is doubtful the platen is perfectly circular; this does mean some backlash has to be tolerated.  The tripod can be adequately braced to reduce vibration with some bungee cord around the legs under the tray.

  17. On 30/04/2020 at 15:25, The Admiral said:

    Glad my redundant StarSense is working out for you ☺

    Ian

    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 cannot bend down to use the red dot without pain.

    Thank you once again.

    • Like 1
  18. 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 and simply went back and forth, I had marked the focus housing. Seeing conditions were variable so I was getting between say 65 and 87 stars at the same place on repeats. Tightening the lock ring moved the focus so the last adjustments were made with the ring locked each time.

    As I got near to optimum focus the StarSense would 'solve' and complete alignment, which had to be blown away and resume the Manual Align. 

    Once completed I got Auto Align to run complete successfully in about one minute. Quite amazing considering the street lighting, houses and trees in the way. Finding a target is not spot-on but it is nearby.

    Once again thank you to everyone who posted on this thread - if StarSense Auto Align is not solving, refocus the camera even though it is long winded and boring. I actually had more problems with the dog prancing about and trying to eat large planter pots, which makes a change from destroying lens bags and my gloves.

  19. On 19/03/2020 at 23:17, noah4x4 said:

    Not entirely true. I refer you to the earlier posts above that mention the comprehensive guidance I offered in 2017.

    1. The Starsense camera has never had a  firmware update  (e.g. since 2014).

    2. If it ever needed an update, you will need a second cable from Starsense camera to PC in addition to that from HC to PC. That is, unless using WiFi to update.

    3. If you connect only a single cable to HC, then CFM will falsely report "Starsense camera updated". That is because it is up to date  (since 2014). But if there was ever a camera update required, I am not sure what it would report! 

    4. You definitely need two cables according to Celestron. I know that because I too reported that it didn't given the false "camera updated" message and I got rebuked. Celestron Support was apparently referring people to my pinned guidance note  in Cloudy Nights as their own manual was pants! 

    4. The Starsense HC had major bug fixes in 2018 and notable updates for Evolution and some GEM mounts in 2019. It is desirable to update to embrace these.

     

    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 ones. Then repeated with the USB StarSense HC, with one USB cable, and again with two USB cables. With one USB cable to the StarSense HC all devices were seen and updated. One or two USB cables made no difference. You can observe the updating in progress on the CFM - latest updates are reinstalled.

    fyi the supplied camera to mount RJ12 cable is far too long, a 50cm RJ12 cable is adequate (usual online vendors)

    StarSense_Connection_Diagram.jpg

  20. Celestron mount with StarSense AutoAlign USB handset on Windows 10. The StartSense Camera does not need to be connected to the computer by its USB, indeed the computer and CFM will not see it. I do not know why the camera has an USB port, the computer does not recognise it.

    If you connect the handset by USB before turning on the telescope, the  handset will light up but you will not connect to CFM. 

    Connect Camera and handset to the telescope in usual manner, switch on whilst holding down button 7 and the Celestron key together so handset shows 'BOOTLOADER', then connect handset USB to computer.

    Start CFM, it should now see both handset and camera, in the info box.  Wait for its preamble to complete then hit 'update'. Go and have a cuppa whilst it does its thing. Switch off telescope and disconnect from computer.

    Sorted.

  21. I have acquired a number of old camera lenses over the years and adapted to modern digital cameras. However long ones can also be adapted as telescopes.

    The M42 lens thread is M42x1mm, as used by Praktica et al. When we speak of a camera lens with a M42 thread, this is the one it will have. The T2 (or T) thread we are familiar with on telescopes is the M42x0.75mm, also known as the Taisei (the inventor) or Tamron thread. Both are ISO-metric threads, they are not interchangeable. M42x1 to DSLR camera adaptors are readily available, these lenses were mostly for 35mm compact film SLR  thus back focus should accommodate a mirror box however using a shorter adaptor will increase focus-turn range at infinity (some old lenses are not right at infinity on full turn).

    To adapt a M42 camera lens as a telescope to astro cameras or eyepieces we need to convert to T2. The TS-Optics Adapter M42x1 female to T2 male aka "russian adaptor" is available from 365 Astronomy in the UK without the silly shipping charges from abroad. https://www.365astronomy.com/TS-M42x1-female-to-T2-male-adapter-for-Russian-Objectives.html 

    We may need to further reduce from T2 to C mount (CCTV camera) but these adaptors are more readily available.

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