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buzz

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Posts posted by buzz

  1. On 16/02/2023 at 11:38, R26 oldtimer said:

    I haven't noticed different guide rates for RA & DEC in the unity app and I am not sure if PHD2 copes with that but, if aggression settings won't do the trick for you, perhaps you could try a different guide algorithm such as the Z FILTER algorithm for DEC.

    Aggression is quite different to guide rate. PHD2 does not care about the guide rate - which is the speed at which the mount corrects the tracking. The calibration routine takes it into account automatically.

    The aggression is the amount. DEC drift is slow and smooth, so kicking it with a high guide rate in alternating directions is not a great plan, regardless of the correction duration. On the Rainbow, I had better DEC RMS error if I turned off the guiding outputs. 

  2. That is a good target for this time of year.  Out of interest, do you know if you can set independant guide rates for RA and DEC? The Rainbow could only have the same rate on both....  but DEC did not like the fast tracking rate and often its RMS was worse than RA, no matter how delicately I set the aggression.

  3. This is really interesting and thanks for sharing the guide log. Have you checked the tracking error with guider outputs disabled?  I had the Rainbow and it was ±25 arc second, which was alright... but it could swing quite quickly at almost 1 arcsec/second, which was hard to keep up with.  Knowing the rate of change is often a clue to the best guide algorithm. PPEC was a bit touch and go with the Rainbow.

     

     

  4. I found my 10 micron's mount clamp was difficult to tighten sufficiently and it also seemed to relax as it got cold. Lovely polished silver knobs but completely useless for gripping tight. 

    When I first started using it I managed to catch a large refractor sliding out. I now always put a safety tether on my scopes - the sort used for stage lighting. It loops round the front of the clamp and through the back of the tube rings, preventing a complete slide out. My Paramounts grip better, but I still do it as an insurance policy.

    • Like 2
  5. When I wrote my book The Astrophotography Manual, I wanted to explain how to collimate an RCT. I gave myself a 5 page budget.  There are many, many alternative possible ways of collimating and in the end, I tried most of them, if only to discount them. The chapter took 25 pages.

    Those techniques that rely on anything other than mirrors are flawed - there is no guarantee that mirrors are centered in housings or center spots are centered. In essence, it takes three passes. The first checks the secondary spacing to ensure the focal length is right (big difference to field curvature), second does basic alignment with tools such a centered laser and hall-of mirrors and lastly, using star test to do the last little bit. There are some other variations that work too but you have to distinguish between folks' suggestions, that just get lucky with one technique compared to a robust method that works in all cases.  I spoke to the astronomer who wrote a positive review for a US collimating tool. Turns out he only used it to adjust the secondary. Rather misses the point as it is the primary that is the PITA.

  6. Thanks for the suggestions - the sharpstar quaduplet looks nice but is a bit short and close to my Tak85 native focal length.

    As already mentioned, I previous had a FLT98  and FLT110 (which I sold to buy the FLT132). I used the Flat 68 from the FLT132 on  my FLT98 but I never found a spacing that gave a good outer field, so I only used it with a reducer making it only 500 mm FL. I sold both to buy the Tak85.

    Nice to hear about the rotolock, has to be better than my original DDG focuser, which wagged around like a puppy tail. Nobody used the StellaMira (or the Orion-badged equivalent)?

     

     

  7. I'm looking for a good performance and value 600-something focal length refractor for deep-sky imaging, which is relatively portable.

    Over the years I have had several WO scopes (FLT98 / FLT110 / Star 71 / ZS 73 ) and still have an FLT132 (feathertouch) and RedCat.  I sold the FLT98 to get a Tak85 - but the Tak106 is too close in focal length and more than I want to spend.

    The FLT132 and Redcat have good optics, most of the others were good to ok optically but their focusers were a mixed bag. I have the new reducer for the FLT132 - but the assembly is a bit of a beast for portable use.

    Both the GT103 and SM104 have similar specs. I am not familiar with either of their focus mechanics or how they compare optically. I'm wary of fancy glass claims as it does not necessarily make for a better image.

    I wondered if anyone had insights into these two? Shame I cannot get Mr Reid to contribute!

     

  8. The major problem lies with how one defines 'beginner'.  Some want to do astrophotography with their iPhone. Remarkable as it is and while some will get some images, it is not the right tool for the job. Some starters will want a full explanation of how to use a photo-editing suite like Photoshop. That is a book in itself.

    The subject depth is an issue with some books that cover a broad church. When you delve, however, there is precious little insight in any of the tricky subjects like guiding, autofocusing and image processing. Publishers restrict page count and it is a tricky decision on what to leave in and what to take out.

    I'm one of the few authors who includes a bibliography and acknowledges the work of others. In the list above, Charles' stands out.

    • Like 1
  9. On 22/04/2020 at 20:32, Louis D said:

    I was wondering why the following books are never recommended on SGL for beginners:

    The Deep-sky Imaging Primer [by Bracken]

    Getting Started: Long Exposure Astrophotography [by Hall]

    Beginner's Guide to DSLR Astrophotography [by Lodriguss]

    The Astrophotography Manual: A Practical and Scientific Approach to Deep Space Imaging [by Woodhouse]

    Is it because Making Every Photon Count is just that much better or the ones I listed are just much too advanced for beginners?

    My book, The Astrophotography Manual, is intentionally not a beginner's book. It is aimed at existing practitioners who want to progress. Astro books go out of date very quickly and some of these are already showing their age. I have just published a new book, aimed at beginners, called "Capturing the Universe" which is bang up to date.

    • Like 1
  10. To polar align - it depends on what reticle they are using. If it is a clock face, like the latest EQ ones, you would set a single orientation with 12 - 6 line vertical, center the reticle (once only) with the two adjusters by rotating RA axis and then just read off the setting from any smartphone app.

  11. Some new news  on their website now. Looks like its electrical interface has developed. I'm guessing if you can control a modem or printer via a HTTP webpage, there is no reason why you couldn't do the same with a mount to align it and point it in the right direction. Full robotic control (via ASCOM say) would be the icing on the cake.

  12. These are the draft instructions. They worked for me and I cannot think of anything particular I would change. I used TSX's jog command to move the star about and their feature of being able to download and save subframes, which speeded up things a lot.

    I stacked 15 images and with reasonable seeing, the readings were quite stable. 

    I only managed one iteration before the clouds came over. I'm hoping for another clear night to complete a second iteration and then image a star cluster as the acid test.

    GoldFocus Plus Off-Axis Cassegrain Collimation Analysis.pdf

    • Like 2
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