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jeffwjz

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About jeffwjz

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  1. Thanks very much for the insights. It's a very good point - that if I were moving to narrowband imaging, e.g. using Ha/OIII/SII pallet, achromatic refractor could actually be a low budget choice. It is a bit disappointing that both luminance and blue channels would be affected - so it looks achromatic is certainly a show stopper for LRGB imaging. I'll probably just focus on finding a apo that suits me.
  2. I'm currently using a newtonian and a very nice mono ccd camera, and am quite satisfied with the experience so far. However I'm still thinking of moving to astrophotography with refractors, for better contrast and supposedly more crystal details. But I was again and again put off by the price for high quality Apos, for the fact that even a "small" 80mm ED will cost more than twice the price of my 150mm Newt, let alone the higher end triplets with larger apertures. Recently I was thinking of the feasibility of using Achromatic refractors for astrophotography. I understand that achromatics are prone to chromatic abberation as colors don't usually focus on one point. However this can be countered by the use of mono cameras, as what I have now. So all I need to do is to refocus for RGB channel and ideally I have have quality monochrome images for each channel at a much lower cost than a Apo (although Lum frames may be affected as it contains information of all channels). I'm not an experienced refractor user so I'm not sure how plausible this idea is. Has anyone had any similar experience or even had a trial on this? Any suggestions will be helpful. If it is a doable idea, are there any suggestions for the "good" achromatics for astrophotography on the market? Thanks in advance.
  3. Hi I'm trying to buy a skywatcher coma corrector which also acts as a x0.9 reducer. If you happen to have one of this spare for sale please let me know! Thanks.
  4. Wonderful advice. Thank you William, I'll put a USB tracing pad in my ebay shopping cart now, sounds like a great idea. Thanks a lot for the tips.
  5. I'm wondering how flats can be taken when there is a need to change focus during a session? Normally I take flats with telescope pointing to a bright wall and a white paper covered on the tube. So imagine if I'm in field and I need to take flats before moving to next filter and refocus, how should I take flat frames? I did stretch the histogram a bit too much to be honest, just personal preference really. Thanks for the advise!
  6. Just to report back, I tried to take some flat frame to experiment the difference, and I'm happy to see the vignetting is mostly gone and the artifacts are greatly diminished. I'm still ramping up with experience of the imaging and processing, I used to think that flat frames are just for removing the image gradients, but now I understand that flats may be even more important to me since it also removes the oddities created by dusts/stains in the optic chain (as for dark and bias, the cooled camera did a good job to control the noise already). Thanks, William, for the nice tips. I did have prepared a folder of dark and bias frames at certain temperature, this proved to be very convenient. One question - if I'm to take mono subframes for different filters, do I need to take flats after each filter? Maybe a silly question, but I still haven't tried imaging through color filter yet, not sure if I need to re-focus for each filter. For comparison with previous image, after flats are included and with a some level/curve adjustment, the image does look way better.
  7. Thanks everyone for the insights. So it looks like the pattern is from dusts in the optical chain (most likely on filter surface?). I'll try to take some flat frames later today and try to clean the filter to check if this will make a difference.
  8. Hi, I am using skywatcher 150PDS with Atik 314L+ mono + IR cut filter. I tool 10*360s frames of M104 and stacked them up using deep sky stacker. However after processing by adjusting levels and curves, I noticed that the stacked image appears to have some weird artifacts in the shape of circles. I'm struggling to understand how they can be generated, or where these patterns come from in the first place. The final stacked image is as below: and I highlighted the artifacts: Does anyone know where potentially these are coming from? I hope the camera is not malfunctioning. Thanks in advance!
  9. Hi, I'm currently using a skywatcher 150PDS on a HEQ5 Pro mount for mono ccd astrophotography. Recently I noticed someone selling a Equinox 80 Apo refractor at a reasonable price and I'm tempted to have one. But before that I'm trying to work out the difference the apo can bring and decide if I really should go for that. The main reason I'm looking at this Equinox 80 is that it will give me a better field of view for certain astro targets. F ratio wise, the Equinox 80 is F6.2, and with a field flattener it will be of a very similar F ratio as my current 150PDS. But because of the size of aperture, 150PDS has almost twice the diameter of Equinox 80, does it mean that I need 4x the guiding time if I'm using Equinox 80 compared to my 150PDS, to have the same luminance? Any advise on this topic? Thanks.
  10. Thanks wimvb, indeed I'm looking to take colour filtered subs as next steps. I'm still doing some research regarding the settings of exposure time and binning etc. for colour subs.
  11. Very nice Easter weather in UK so I can finally have fun with some astrophotography. First image with my recently acquired Atik 314L+ Mono. I took 10 x 360s mono subs of NGC4565 the Needle Galaxy with skywatcher 150pds. I just processed th e image briefly in DSS and PS. Still trying to pick up image processing, any advice on further process is very much appreciated! Thanks.
  12. Thanks Alan for your explanation. This is very helpful!
  13. Hello everyone, I was taking M51 this evening using my new Atik 314L+ Mono camera with a IR/UV block filter. I'm using a Skywatcher 150PDS. I took 10 images and each has an exposure time of 6mins with guiding. I adjust the focus using a Bahtinov mask prior to the session. By looking back the images in DeepSpaceStacker, I noticed that my images are gradually losing focus over the period of the imaging session. Following is my first image and hovered to a star to check focus. Then the next is my 5th image, it's already showing defocusing: Next is the 10th image: As seen on the images, looks to me they are gradually defocusing. I have never encountered such issues before when I was imaging with a DSLR. I'm very confused how this has happened. I have a couple of ideas, but not sure if they are the case 1. The focuser is slipping. This seems possible to me as I didn't have the habit of locking the focuser after Bahtinov (bad practice!). However as I mentioned this behaviour was not shown when I was using a DSLR. But next time I will definitely lock the focuser screw after focusing. 2. The newtonian is not properly cooled down when the imaging started. I left the scope in yard for about 30mins before taking images, and the temperature over the evening dropped from 5degC to 0degC. I'm not sure if focal point would change when scope is not completed cooled, or when temperature changes. Can anyone provide any insights and suggestions about this issue? Could this be caused by some other reasons? Thanks in advance.
  14. Thanks guys. In this case I'll just use eqdir cable then. Looks like the most viable option for me.
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