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Posts posted by robertm

  1. Thanks all.  I have the ASI2600MC so know how good the sensor is.

    I find the sensor in the ASI needs the tilt plate for correct alignment.  QHY quote that their sensor is well adjusted - can anyone quantify that for fast optics i.e. the tilt plate is unnecessary ?

    Edit: By fast I mean f/2 or f/3

  2. 3 minutes ago, gorann said:

    Thanks Robert!

    Yes, getting distances right is the major problem, especially since I move between using an NBX filter (when the moon is out) and no filter for RGB. I often have to accept some long stars in the corners and deal with them in processing. Takes an extra half hour. Using an APS-C camera is really a bit past the limits of this scope so I cannot complain. What has surprised me is how easy it is to focus and how well it keeps focus not only during the night but from night to night. Celestron really got the mirror holding sorted out in this scope.

    It good that yours is working well, I’m finding mine a bit challenging at the moment... one for another thread.

  3. Would be grateful if anyone could help.

    The issue I have is that the handset firmware update only ever gets to no more than 1.00% complete before it fails; usually it's between 0.04 and 0.40%.  Another issue is that I have is that it takes two attempts to retrieve the Hand Controller version as the first fails to connect.

    Not sure what I'm doing wrong here, could be a school boy error who knows.

    I've powered up the handset so it goes into firmware update mode (V1.7 firmware updater on the handset).  The firmware is the latest downloaded SW (03.39.03) as is the PC firmware loader (V3.3).  I've tried all sorts of baud rates, handshakes and buffer/timeout values but the failures always seem to be at random percentages.

    The handset is a V3 which was at V3.27 and I'm using the SW handset to DB9 cable and a Startech FDDI DB9 to USB adaptor plugged directly into a PC USB port (tried a hub and that made no difference).

    Anyone have any ideas ?

    Many thanks


  4. I've been following the Cloudy Nights thread on this and it seems like the original work was done by a guy called Rick Kellogg a few years ago.  He wrote a paper with examples and code in which he expressed a hope that it would be taken up by makers of guide programs; this could be just co-incidence of course but PoleMaster does seem to follow the original work quite closely.

    Here's a link to the original paper: http://www.syracuse-astro.org/pdf/2012_August_R_Kellogg_Electronic_Polar_Alignment_Scope.pdf

    Quite an interesting read I found.


    I'm singing in the rain
    Just singing in the rain
    What a glorious feeling
    I'm h....  sorry it must be the weather  :confused:  :mad:
    • Like 1
  5. I think this is where experience comes in. A lot of lenses look superb for terrestrial but as soon as you look at the bright pinpricks that are stars then that's where you see astigmatism, coma and chromatic aberration rear themselves. The last thing you want is a compromised image before processing even starts (that's my personal opinion).

  6. The main reason for stopping down is to avoid use of the glass around the edge where lens design is most compromised. I'm afraid the trade off is to make the lens a bit slower but that depends what the use is. The 200L II is definitely good for f/3.2 narrowband but for broadband (I.e. luminance) then I suspect the f/4 that has already been mentioned is where the sweet spot is. One thing to note is that at f/4 you are only using 200/4 = 50mm of aperture and that's within a knat's of a 48mm threaded filter. Also if you use a threaded filter then, as well as the f/4 stop, you won't be troubled with awful diffraction spikes.

    I've not used the 70-200 so can't comment.

    One new lens of mine is that Samyang 35mm f/1.4, live view with the A7s is absolutely astonishing. It does need to be stopped down a tad to around f/2 for that sensor size but an APS camera might be able to use it opened up a bit more. I've had a few bad samples (sent back to Amazon) so you need to take a critical look to make sure the aberrations are symmetrical.


  7. An interesting topic, this is exactly what I went through a few years ago.

    My images were taken with Baader 7nm filters and I feel they worked well at f/2.8. I think the shift in band pass was still well within the filter profile. You may also want to consider filter size and how large the sensor is as well as filter to sensor spacing.

    As others have mentioned getting a filter wheel into the equation may be a challenge but I gave up with adding an oag. The light path is so narrow that any prism will affect the image even if you could fit it in.

    An alternative is to go with larger format lenses but demand by people who think they need them has pushed up prices massively over the years.... sigh !

    If you're worried about over sampling then consider dithering and drizzle stacking as that might help. Something else I've done is doubling the image size before stacking, that can work quite well.


  8. If you want to even consider using it wide open then it has to be well collimated (check for centred vignetting).  If it's out, then because it's a professional lens, you can send it back to Canon (UK branch is Enfield I think) free in the first year for adjustment.

    It's very good at f/2.8 with an 8300 sensor equipped camera but I found that f/3.2 produced outstanding images (in narrow band) if you can get it focussed accurately enough; the edge stars will be squiffy if you don't !


    The next is full size unbinned showing how good it is at the edges:


    There are other examples there but it really is a top lens !

    Hope that helps


    • Like 1
  9. I've not seen any problems like this when using Maxim but you could try setting the screen stretch to medium which should show guide stars. If that fails then take a single guider exposure, ensuring that you can see stars, then double click on one of the stars to select it then click track (I know it should automatically do it but doesn't always get the ideal star). I would also change the track box size to something like 32x32 or 64x64 temporarily to make sure the star hasn't already drifted outside the 16x16 box.


  10. Nope you're not the only one ! I had the same problem with a C11 and the orange dovetail but I used a couple of tiny aluminium wedges so it did work eventually. Was a shock when I first tightened the knobs though as it arrived about two days before I was to take it on holiday ! The gap on mine was about a millimeter after fully tightening it down.


  11. Sounds like you're having a wonderful time with that mount Olly and creating more than a bit of jealousy I can tell you :D

    Regarding the Tak. I always used Chucks Temma Driver with Maxim. It's certainly the best thing that happened to the Temma II and makes the Sky controlled telescope look like hard work.



  12. Hi,

    Just seen this. The off center screw does act as the location lug for the secondary to stop it rotating. This secondary collimation has had my attention for a while now but I think I finally cracked it.

    The rotation is very critical and I found the only way of accurately setting it was using a camera and checking for even illumination and equal vignetting in the corners. For fine adjustment I rotated the whole corrector assembly within the confines of the OTA screw holes. Even a millimeter can make a difference ! Start with the threaded secondary holes central in the ota holes (they are a few mm larger in diameter.

    This is a quote from my OAS thread on the subject.

    Have taken a different approach. Using some of the collimating instructions in 'How to build a Dobsonian' I realigned the secondary laterally along the tube length. I then used a camera to accurately set secondary rotation so the centre of the flat was even radially. The secondary was then accurately aligned using a laser and the whole process repeated till perfect both visually and using camera/collimator. Rounded off with a Cheshire as a double check.

    It looks good but it's looked good before. Will see what the results look like tonight on Jupiter and with an image if the cloud gives me a chance.

    PS. The laser is a Hotech and looks to be perfectly adjusted.

    The results did look good but bad weather and guiding has thwarted further checks so far.

    Link to the saga here: Help - How to correctly collimate a Newtonian... with a twist

    Hope that helps


  13. That's really awful - ok I'm just jealous :) It's one of my favourite areas and you've done a wonderful job on the processing too. I like it very much.

    It looks like the Mesu and ODK combination is working very well indeed. Olly, I don't suppose you have room for another observatory down there do you...

  14. Hi Will,

    I have a HS C11 and currently use a SXVF-M25C (same size chip as the QHY8). I view the Atik 450C (presuming the colour version) as more of a complimentary camera to the M25 and would use them for different purposes. The main reason being pixel size - at 7.8u the HS C11 with the M25 gives roughly 2.9 arcsec/pixel over a large area whereas the 450 would give 1.3 arcsec/pixel for narrower fields.

    Another thing of note: the HS is very sensitive to chip misalignment and any misalignment requires collimation. Just make sure the chip can be adjusted for orthogonality. I recently sent my M25 back for just such adjustment and Terry did such a good job that now I don't need to collimate when I fit the camera - you have no idea how much setup time that can save on a camera without liveview.

    Just my two cents.


  15. I have a catalogue from that era. PM me and I can send you some scanned pages but basically the Type B mount was supplied with 8.5-10" AE Equipment Newtonians and Cassegrains. It had 5" setting circles and 6" 192 teeth RA worm wheel powered by a synchronous motor. The mount was adjustable between 0-60 degrees latitude. Drive for dec was by pushing the telescope by hand though some did have the optional declination slow motion via a sprung handle. The axes had 1" diameter solid stainless steel shafts running through sintered bronze bearings (no rollers/balls).

    Hope that helps


  16. Thanks for the kind comments.

    Olly, I was concentrating on the nebula but you're right about the stars. Will try to contain them in PI.

    I'm shunning PS completely at the moment in favour of PI as I grapple with the learning curve - I haven't even got it loaded on my new laptop.


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