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buzz

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Everything posted by buzz

  1. thanks Barry - I had a GM1000 a few years ago but it was not a happy experience and I paid a few hundred more and got the PMX. I'm using SGP and a FLT132 too. How is the Linear in a light breeze? I was always a little concerned with the belt elasticity possibility. The new price is a little high but sometimes trying to be too thrifty is false economy. edit (it is also 12Kg without the extension bar, so I bit higher than budget)
  2. I'm looking to buy a sub 8 kg mount for imaging with short refractors (600mm or less FL) under a £2000 budget. My permanent mount is a PMX. On my shortlist are: iEQ30pro NEQ5 Vixen SX2 Tak EM11 (used) GM8 (bit heavy) Avalon Linear (used) I have a sturdy Berlebach tripod which I will modify to suit and will do extended imaging runs (which is why the Astrotrac is not on the list). Good tracking and guiding performance is essential, as is ASCOM control so I can use SGP or TSX to image with.- (I will use a Polemaster for alignment). I would be interested in others experiences or suggestions many thanks
  3. I'm in the same situation, with London clay in Essex, in a wet corner of the garden. I have a 24x24 x 18" concrete block. It is in an observatory and I have guttered the roof and run it into a water butt. The ground is slowly drying out as far as I can tell. If there is any instability, an unbalanced system will make matters worse. I levelled my pier and mount carefully and ran a T-Point model. The results indicated it was stable, though I do expect to re-run a 'recal' every few months in the case of ground movement. It could be worse, we could be on a fault line, my mate in NZ wants to do astronomy but it is virtually impossible with the continual shocks.
  4. Best - Paramount MX - on a Berlebach Planet or Pier - just delivers Worst - LX200 GPS wedge/forkmount
  5. I have the 10" truss RCT from Altair and it is substantive in my 6x7' shed. I think I might just be able to squeeze in the 12" version though. It would be really great if an owner could measure the overall practical length with a camera on the back and also the approximate balance point too. Now that I have figured how to collimate RCTs, I feel like an upgrade thanks! Chris
  6. The car industry uses a float and a resistive sensor. If you can get a spare tank fuel gauge sender, you can just turn the resistance into voltage and sense with the Arduino? Alternatively, take a pair of welly boots and drill a small hole about 1" up the side wall. When your feet get wet....
  7. I realised my mistake. I was considering the angular field of view from the POV of the sensor, but, since my panel is close to the optics, I have to add the angle to the aperture diameter. So, in summary the panel always is bigger than the aperture. For my 10" RCT I will likely use an A2 panel from ELWirecraft - which is 23x16". I knew the prior analysis did not seem right, I just couldn't think why.
  8. Now I am pier-mounted, I can fix a flat panel to the wall of the obsy, about 150cm distant from the camera. I use a selection of FLs from 180 f/3.4 camera lens to 2000mm f/8 RCT and from the field of view, projected on the wall, I calculated I only need a 24 cm diagonal to fill the sensor with the tiny lens and only 2.5 cm for the big one! Clearly it will not be in focus, so I will need some margin. I know that it is often the case that folks rest a panel up against the optics' / dew shield but this is not the case here. If the image of the flat panel fills the sensor - this should be good,.. right?
  9. 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
  10. Well, after quite a few frustrating sessions trying to use the GoldFocus mask readout as an alternative assessor in an out-of-focus star test, I'm pleased to announce I was able to get the GoldFocus mask to work very well indeed. Jeff worked on an updated instruction manual for dual mirror adjustments. It was not something you would have figured out by random intuition but looking at the procedure, it does make sense. In an hour I was able to collimate both mirrors on a 10"RC with high accuracy. That was also helped with a night of good seeing and changing my locking grub-screws to pointy tipped ones. The original ones were cork-screwing the main mirror by a few microns (laterally) and causing the air to go blue. The great thing is that it achieved this using numerical analysis and one iteration between secondary and primary movements. I could have gone for a second iteration but clouds stopped play. Out of focus stars were even symmetrical donuts but I'm sure that a second iteration would have nailed the last few percent.
  11. Mike - It is sort of like three Bahtinov masks looking at the variation of focus by angle. When all the light focuses at one point, the three focus positions agree, i.e. collimated. For any coma, astigmatism or other abberation, the focus is smeared and the readings for the different orientations of the mask differ. It is virtually impossible to distinguish between small primary or secondary errors with one reading, just like star testing. The focuser part is really useful, since it can directly tell you (after calibration) just how far to move the focuser with one reading. The collimation is intriguing but more elusive at the moment, hence the post.
  12. I had an 1100D, before my son pinched it and it was just fine. The lower pixel count often helps with noise levels too.
  13. Yes Chris - I have one of those too - part of a big evaluation of all the major techniques for collimating a RCT. It is running to 25 pages already. I made a discovery early on with my Altair Astro Truss RC and that was to do all primary adjustments with the OTA vertical. If you don't the mirror sometimes shifts when you loosen an adjuster. Currently a simple HG laser to line up the focuser/secondary and the hall of mirrors on the primary get me very close. I found an excellent reference by Deep Sky Instruments on a particular form of star testing that is very sensitive too. According to the website, the focus mask technique should be able to improve on that, especially in medium seeing conditions. The science is compelling but so far, ahead of my practice. Collimation Procedure
  14. I'm trying to collimate my 10" Truss RCT from Altair using the GoldFocus mask. I'm not having much success and suspect I am doing something wrong. I can get 'good' collimation with classical outside focus star testing but when I use the GoldFocus mask, to try and improve upon it, for some reason the adjustments make things worse. Originally I was using the mask in the same way as the DeepSky Instruments use star testing - adjusting the primary mirror to set a central star and the secondary to balance the appearance of peripheral stars. After getting some advice, I switched over, with little effect. I would be interesting to see if any SGL members have used this clever device to set both mirrors, and how they went about it. regards Chris
  15. Just bought an EOS 60Da - and evaluating bias and dark noise. At ISO400, I measured the bias mean and SD as well as a calibrated 10-minute dark from each. 16-bit figures - no noise reduction options selected. RAW files measured in PixInsight. Camera Mean Bias Bias SD Mean Dark Dark SD Fuji XT1 13.7 2.84 39 170 Eos 60Da 27 8.3 103 235 I think the Fuji does a dark subtract, but it cannot subtract the noise. Having said that, its bias and dark noise seems better. Just trying to work out how best to measure color response...and when the clouds part, a real comparison.
  16. Ian - I just noticed something - on your two screen grabs - the icon next to the GH2 image has a little bayer array - but the one on the XT1 does not - suggesting that DSS does not believe it is a color image. Could that be it? Funny - I had a GH2 too before getting the Fuji...
  17. Ian, I agree - there is something going on here with DSS. For comparison - from RAW - a Jpeg output from Aperture, the JPEG output from PixInsight from the RAW file and finally, PS opening the Pixinsight JPG and doing a 2.2 gamma correction. It is not quite perfect, as I needed to change my color settings in PI, but it is the overall tonality which I'm trying to show here.
  18. I did some work with Ian on one of his FITS files and remembered what I had forgotten from my old photography days. RAW files are linear - i.e. they assume a gamma of 1.0. Each 'stop' has half or twice the tonal resolution of its neighbor, just as it comes off the sensor's A/D converter. Photographic editors (and jpeg conversion) apply a gamma adjustment, normally to 2.2, so they look 'right' on screen. Classical photography (what I call real photography) materials are inherently logarithmic and do the conversion naturally. To prove to myself, I took an exposure from the Fuji and Canon of a blank white wall. The jpegs were a nice mid-grey. I took the RAW files into Pixinsight and output as a TIFF. Reading the TIFFs into Photoshop produces a very dark grey rendering. I then used levels and moved the middle slider to 2.2 (introducing a gamma correction) and lo and behold, my perfect mid-grey returned. regards Chris Woodhouse
  19. Ian - if you bung a RAW file into a dropbox - I can convert it with PI and you can compare results with DSS? Sensors are linear, but exposure is inherently logarithmic. When PS displays images, it applies a gamma correction to give something that the brain can recognize . I can also compare the result from say PI converting and Nebulosity acquiring an image- it should be the same outcome. Which LR are you using? Im using CS6. DNG is free and you can download the latest.
  20. Ian, I think I know what you are experiencing. The RAW file, when it is converted, has no gamma correction. A mid grey on the fuji was 13,000 in 16-bit greyscale and the Canon 60Da, surprisingly, was less at 5000. My first bench comparison is interesting. I averaged 50 biases: The Fuji has a mean bias of 13.7 and StdDev 2.84. The EOS has 27 and 8.3. A calibrated 10-min dark frame, at 20C, for the Fuji had mean 39, StdDev 170 and the EOS, 103 and 235. RAW files are never truly RAW and I suspect the Fuji is doing some kind of dark frame subtraction inside but it does appear that the Fuji is quieter for read noise and thermal noise from the StdDev figures. I want to test the color sensitivity next- My idea is to take an image of my QSI 8-filter wheel against the sky and measure the relative light levels. I have 5 nm SII and Ha in the mix.
  21. Ian - did you try PI? I put a bunch of RAW files into the ImageIntegration tool. It used DCRAW conversion and produced a sensible output as it would with FITS. I didn't see anything unusual in the output.
  22. I just stacked a dozen files in Pixinsight and it worked just fine. I noticed it invoked DCRAW. I'm ordering the Canon tomorrow and I will give them both a good head to head.
  23. I sent an email, guessing his email address and, to my amazement, got a reply. He is in Japan and will mention it to the developers. We shall see... regards Chris
  24. digitalcyanide - For the second book I'm going to do go both upmarket and downmarket - I'm writing a few chapters on portable gear and intend to compare the XT1 and the Eos 60Da too in the context of using with something like an astrotrac or similar. I have to find the links to the noise evaluation process so I can not only compare images, red sensitivity but also dynamic range and noise. Thanks for the Fuji link, worth giving it a try.
  25. The Fuji now also has an electronic shutter - which reduces vibration. I'm using the HS-V5 tethering software. I get it to take a batch of images of a GoldFocus mask and get GoldFocus to autofocus by reading the files as they come into a PC folder. I then switch to camera control and use one of those eBay programmable intervalometers using the standard 2.5mm jack to take long exposures. I also bought the battery grip, that allows for an external supply - but made my own DC-DC module, converting 12V down to the battery voltage. It simply plugs into the end of my PMX Losmandy plate. I'm trying to find a contact in Fuji to whom I can request that the tethering software has a long-exposure intervalometer added.
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