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About cfinn

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  1. I use and can recommend the Baader LRGB set. They are completely parfocal with my Esprit 120, which is a real time saver as I still focus manually with a Bahtinov mask. Can’t comment on SHO yet as I don’t have a set, but I am planning on getting the new ultra narrowband 3.5/4nm filters when they are released. Baader claim they will also be parfocal, which would be fantastic.
  2. Hi Bogdan, No problem. Good to know you have better results with the extra counterweight. The physics suggests this should be the case but nice to hear it works in reality. Charles
  3. I use an EvoGuide 50ED with ASI 120MM Mini riding on top and it works great. To attach it I have a 15” universal dovetail and use a pair of Losmandy female to Vixen female clamps. I’m including a photo below so you can see what this looks like. It’s very rigid, which you want to minimise differential flexure, but comes with the disadvantage of adding more weight. Note that I also have a Pegasus Pocket Powerbox Advance attached using a pair of additional clamps. All of this together with the imaging camera, filter wheel etc gives a total weight of nearly 17kg, necessitating the use of the count
  4. Welcome to SGL! Your findings make a lot of sense. The chart I made based on your setup/location was assuming the use of the ASI 294MC as you say, which has an effective bandpass of roughly 100nm since every pixel essentially has either a red, green or blue filter over it. Using the mono variant with a luminance filter effectively increases the bandwidth to 300nm and you benefit from higher QE as well, so for broadband targets (galaxies, reflection nebulae) you can get to the same SNR in less than 1/3 of the time. For these kinds of targets I don't think there is benefit to be had using a ligh
  5. Just ran another calculation to back this up (as if further proof were needed!). The chart below shows the integration time necessary to reach increasing levels of signal to noise ratio on a target having surface brightness of 25 mag per square arcsecond in Los Angeles (Bortle 8/9). This is with a RASA at f/2 and specs to match the camera in the description (ZWO ASI 294MC Pro). The dashed vertical line shows the integration time of 49.2 hours, which suggests a SNR of roughly 5 should have been reached on IFN of that surface brightness. If you want SNR of 10 you would have to go for 150 hours!
  6. I quite agree. My suspicion is that it gets lost in processing all too often, due to the fact that it is usually very spread out and could be mistaken for background in background calibration.
  7. Here is the discovery paper in 1976 by Sandage et al. In the abstract it states the brightest portions are ~25 mag per square arc second in the V band. Note that these are the brightest portions only. Much of it extends to much fainter surface brightness. I am not completely surprised by this, otherwise there would not be reports of detecting the IFN visually. It is also a question of signal to noise ratio. My calculations above are for a SNR of 5, which is quite small. I suspect many detect the IFN but then lose the signal in processing what with background calibration, removing light po
  8. Absolutely, I would agree with that. If capturing the IFN is your primary goal then the RASA definitely seems to be the best choice.
  9. The more I think about it, if you want to go this deep for not an extortionate amount of money then a RASA/HyperStar or a fast Newtonian are your best/only options. You could use a small refractor with a focal reducer, but then I don't think you can get to f4 or below without problems, plus you start to under sample and lose detail. You could also trade focal ratio for big aperture and large pixels (e.g. CDK, RC), but then you have a very long focal length and would need a very large corrected field and a large sensor to maintain a decent image scale, so things start getting expensive quickly.
  10. Seeing some amazing images of the IFN (integrated flux nebula) in the deep sky imaging section of the forum, I thought it would be interesting to run some calculations to see just how difficult this is to do. The IFN is a component of the interstellar medium at high galactic latitudes that is illuminated by the integrated light of our galaxy. It is incredibly faint, with the brightest sections having a surface brightness of just 24.5 magnitudes per square arc second at visual wavelengths. Let's suppose that we are in a Bortle 5 area, with a sky brightness of 20 magnitudes per square arc s
  11. In this article they acknowledge they weren’t halo free and have put in significant R&D time to develop new coatings which supposedly are (nearly) halo free. The proof will be in the pudding...
  12. No idea. And no idea on price either. They say a “moderate increase in price” compared to previous version, so still considerably cheaper than the high end brands I would imagine.
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