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Posts posted by oymd

  1. 23 minutes ago, vlaiv said:

    First part is correct - not all encoders are of equal precision - in fact, one of main specs of encoder is its resolution (number of data bits it produces). Encoder precision is directly related to encoder price.


    I can't say if encoders on CEM25EC are less precise than those on CEM120EC - that is up to manufacturer to decide (which ones they will use) and to publish or not relevant information.


    well, it would make sense that with higher end mounts the encoders would also be higher spec...no?

    i think I read somewhere that the encoders used by AP are the top end ones...

    I think they are called “Reninshaw” 

    pretty sure I got that name wrong...



  2. On 29/03/2020 at 20:42, Mike Read said:

    Evening all,

    Im still learning, started in Jan 2020 and typical with UK weather, the last few days have been clear enough for me to burn some candles. So, my kit: Evostar 80ED Ds-pro, EQ6R, ASI533, Optolong L pro filter and Senso Sesto 2 focuser. I run this from a Dell 3070 micro running CCDCiel, Carter’s du field and PHD2.

    Here are my images from this week: M3, Atlas and M47. I’ve spent today trying to learn PixInsight - these are the results from 4 hrs playing. A big thank you to AlexAstro, with out his document I would be still seeing b&w images.

    As a note, M3 & M47 contains darks and bias, no flats as they totally messed the colour. Atlas is a single 120second image.

    I hope you enjoy my excitement with my journey start...




    Very nice Mike

    i too like the M3  Much better than my first attempt last week  

     Can you share your subs duration etc? Were you guiding?

    I’ve also started imaging just a week or so ago, with a 294MC Pro. Haven’t tried Pixinsight yet, but would like to give it a go. Can you point me towards AlexAstro’s guide?

  3. On 01/04/2020 at 17:25, vlaiv said:

    Both have positive and negative ....

    Encoders can't compensate for dynamic things nor for other types of errors. Poor polar alignment can't be corrected with encoders. Sudden displacement of telescope tube (wind, kick or whatever) - won't be compensated by encoders. Encoders can't correct for atmospheric refraction - you need elaborate sky model for that.

    Guiders have quirks - need to be calibrated, are always dynamic and depend on seeing and other factors. If not configured properly can hurt more then help (chasing the seeing, over corrections - causing oscillations, etc ...)

    One thing is certain - guiding is more cost effective way of doing it (arguably - will depend on justifying some expenses on other tasks as well - such as imaging, for example use of computer), and more people opt to do it that way.

    I think encoders are good thing - if done properly. One of the problems associated with encoders is that it is really hard to get good precision on encoders. You want your encoders to have rather good resolution. For example, I would say that resolution of encoders needs to be around 0.1-0.2" to get really good results (just imagine DEC axis - you want your DEC error to be rather low - and that is dictated by precision in DEC encoder, because DEC is for the most part stationary).

    Now if we want to have that much precision - we need encoders that divide circle in 10 * 60 * 60 * 360 = 12,960,000 steps. That is 23.6 bits of precision, so you need something like 24 bit precision encoder.

    You can also see how tricky this is if you for example imagine that your encoder has 10cm diameter. Circumference of it will be 31.415.... cm = 314.159... millimeters = 314159.265um = 314,159,265.358... nm - you need single "tick" on such encoder to be 24nm wide. You can't even use photons to read such a tick because regular photon is about x20 larger in wavelength.

    Now you can see why encoders are very expensive for that sort of resolution, not to mention level of craftsmanship needed to make perfect circle and avoid what we combat all the time - imperfection in manufacturing of round things (periodic error).

    In the end - I think maybe best design for a mount would be to accept periodic error of worm gear - minimize backlash by using spring or magnetic loaded automatic tension system on worm and have encoders on worm shaft rather than main shaft. This way all other imperfections would be minimized (motor imperfections, gear system imperfections, belt system imperfections) and motion of worm would be properly timed and smooth enough so guiding would take care of worm period error with ease as it is smooth changing. Because mounts have at least 120+ teeth on worm gear - that is about 7-8 bits less precision needed - 16bit encoders are readily available at reasonable cost.



    If I got that right, are you suggesting that not all encoders are equal in their precision?

    that is, encoders on say an IOptron CEM25P EC would be less precise than the ones on a CEM120EC, which would be less precise than those on Astrophysics and Paramount mounts etc?

    the more expensive mounts would have a higher number of clicks/counts etc?

  4. 5 hours ago, Merlin66 said:

    I regularly use the C11 for spectroscopy...

    I've fitted a JMI focus motor to get "best" focus...

    The mirror slop/flop is generally caused by the grease on the baffle being "thinned out" by the mirror always sitting in roughly the same position...

    Wind the focuser through full travel (about thirty turns) each way  every month or so to re-spread the grease on the baffle. This helps. And always approach final focus from the same direction.

    I don't find the slop/flop to be an issue. (The Celestron focuser design is MUCH better than the Meade SCT's , which I had for many years!)


    Many thanks for that.

    Can you please explain what you mean by: "always approach final focus from the same direction"?

    I do not get that?

    Also, do you know which direction does the mirror mover with clockwise and anticlockwise rotations?

    Would like to know which direction moves the mirror backwards?

    Many thanks


  5. 5 minutes ago, johninderby said:

    Or you could replace the stock focuser with a FeatherTouch microfocuser. Works really well but rather expensive. ££££


    Never liked that option.

    It sticks out of the OTA so far back, and makes packing the OTA in the carry bag a nightmare. Possibly on a permanent setup, but not when I need to pack the C11 after every session.

  6. 6 minutes ago, Captain Magenta said:

    if you're planning on that focuser upgrade, I'd go for the Revelation one, which is identical in all respects except for the Revelation Astro branding on it, and the price. I got one myself for my 6" Intes, and it's sitting in front of me right now. I'm very happy with it.




    That looks very smart!

    Are they identical!? wow...one goes for £140 & the other for £90??!!

    So, do you move your primary mirror all the way back, and rely on the crayford to achieve focus?

    Did you try imaging etc?

  7. 3 minutes ago, Davey-T said:

    Clockwise I think, maybe if you look down the front you can see which way it's moving.


    Many thanks, will give it a try tonight.

    Do you know if adding the Crayford Focuser might be detrimental to imaging? I remember I read somewhere that it will significantly lengthen the FL of the scope beyong F10?

    I plan to use the F6.3 reducer as well, so hope this will work?

    Even if I do not fix the mirror flop issue, I would rather bypass the focus knob, as it is not fine enough for subtle adjustments to focus.

  8. 5 minutes ago, Davey-T said:

    Not tried it but I don't think you will be able to achieve focus with the mirror wound right back and it may still flop.

    You could jig it up to see if focus is achievable before buying focuser although it is a nice mod in it's own right.


    Thanks Dave

    What do you mean by "You could jig it up to see if focus is achievable before buying focuser"

    Sorry, did not get that?

  9. Good morning everyone

    I am hoping for some advice regarding my devious plan...

    I have acquired a C11 XLT OTA a couple of months ago, and only stated using it regularly over the past few days. Focusing on it is really hard, but achievable. I have noticed that whenever I slew to a target at a HIGHER altitude, the stars get slightly out of focus, and I need to refocus?

    Is this what is called "Mirror Flop", which is inherent to the design of the SCTs, fixed with the lockable mirror in the newer Edge HD models?

    Would getting a Dual-Speed 2" Crayford Focuser for SCT Telescopes, like this one over come this problem, and also help with imaging when I attach a ZWO camera?




    My thinking is that I would drop the mirror using the focus knob all the way to the back of the SCT, so it cannot sag anymore, and achieve focus with the Crayford focuser?

    Is that achievable, or is it being done already routinely, and I am just late to the party?

    Many thanks


  10. Evening everyone...

    Following on from my previous thread....I took some time tonight, and avoided going outside to work on the data I acquired over the first night of trying AP.


    Mount: Ioptron CEM25P

    Scope: Sky-Watcher 80ED

    Camera: ZWO ASI 294MC Pro charger was blown, so could not cool the sensor)

    NO GUIDING, yet...

    No filters

    No calibration frames.


    Acquisition with Astrophotography Tool

    Stacking with DeepSkyStacker

    Very light processing in GIMP, just color levels stretch


    Please be gentle....I am fully aware they are very newbie pics, especially the Cat's Eye Nebula. Did not recognise how small it is!!!

    Please advise what are those 2 beautiful galaxies? I forgot what the target was.


    I am over the moon!!




    10 subs x 10 seconds + 6 subs x 15 seconds




    M57 The Ring Nebula

    13 subs x 15 seconds






    Cat's Eye Nebula embarrassing, I know...

    25 subs x 20 seconds




    A Beautiful Galaxy. Please advise what this is? I forgot what I chose that night!!

    5 subs x 20 seconds





    4 subs x 15 seconds



    • Like 2

  11. 46 minutes ago, Marvin Jenkins said:

    As our friends across the pond say “knocked it out the park” well done. Nice spiral arms in the face on. You have done really well.

    How did you find gimp? We are at opposites and equals right now. I have four imaging sessions under my belt but will be delving into processing this weekend.

    You have one session imaging but have already processed your first image, big like from me. 👍👍👍


    Thanks Marv

    I followed Vlad's guide, and there has been virtually NO processing involved. Just playing with COLOR LEVELS:

    Here's what I did:

    Stacked etc in DSS.

    Opened the FIT file in Gimp, then went to Color/Levels, and just did a BASIC STRETCH.

    Moved the 3 sliders around: BLACK, WHITE & GRAY levels.

    And that's it!

    Vlad advised on creating another layer and doing a DENOISE, but did not manage to do that, as found it too complicated.

    Exported the final image as PNG and a JPEG, and that's it.

    • Like 1

  12. With a heavy heart, I am putting up my CEM25P for sale.

    The virus crisis we are in has hurt me financially, and I need to make some sad, but sensible choices.

    I have also bought in January an AZ-EQ6 Pro, and I could not argue with the wife when she said that my new lovely toy has to go


    It is an extremely well made piece of engineering, very light and sturdy. DEAD silent, and quicker that the AZ-EQ6 Pro, carried my ED80mm with gear with ease, but I would not attempt to put my C11 XLT on it, so the AZ-EQ6 Pro will have to do.

    I bought it here on the forums last month:

    The Mount and tripod are exactly like you see in the pics, but happy to provide some more pics if required.

    The original owner is an experienced imager, he bought it from Altair Astro, and upon using it just a few times, was very impressed, and opted to buy the higher capacity CEM40.

    The only difference from the pics in the thread is that my 6 year old coloured some areas of the tripod box, as it stayed boxed for a few weeks in the living room.

    The mount had literally 3 nights of use, 1st was a couple of weeks ago and I used it for visual, 2nd was last Sunday night and 3rd was last Monday night. Later 2 were for imaging UNGUIDED with a ZWO ASI294MC Pro, and I have linked the pics I took here as well.

    I am offering it for £600. With the current virus outbreak, not sure what shipping costs would be, but happy to discuss with any preopective buyer.

    Best regards



    • Like 1
    • Sad 1

  13. So, here's M81 & M82 again

    I went out Monday night, and the power supply died, so was limited to do imaging at 4 degrees C.

    Following Vlad's immense advice and help, I took many more subs:

    50 Light, 20 seconds each

    30 Darks, 20 seconds each

    Still can't get my head around DARK FLATS, and FLATS, so none of those...YET...!


    Stacked in DSS, and then I used GIMP to do some light processing, all myself.


    I think it looks better?

    Super excited!

    M81 & M82 4C using Kappa Sigma option.jpg

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