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Re: [tec-scopes] Re: NGC6357-6334 area and M8-M20

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  • Tim Khan
    It should work fine with a lodestar or ST-i....I prefer the ST-i since its has less noise than the loadstar compared to those that my friends have. The
    Message 1 of 11 , Jun 1, 2012
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      It should work fine with a lodestar or ST-i....I prefer the ST-i since its has less noise than the loadstar compared to those that my friends have. The internal shutter is a mute point when using with MaximDL, I use full calibration for the guider so the shutter is a minor convenience.

      here is my sketch for what I plan to do...since I already have the ST-i lens kit.....

      http://scas.org/tk/ST-i.pdf


      From: daniel_verschatse <antilhue@...>
      To: tec-scopes@yahoogroups.com
      Sent: Wednesday, May 30, 2012 5:10 PM
      Subject: [tec-scopes] Re: NGC6357-6334 area and M8-M20

      Thanks Percy and Tim for the input on finderscope-guiding.
      Baader actually advocates using their Variofinder for guiding which is why I have their "conversion kit" consisting of an extension tube and 1 1/4" clickstop eyepiece holder.
      I can see where a heavier  guide camera like the ST-402 will induce flexure, hence my idea of using an ST-i or Lodestar that weigh less than a typical illuminated eyepiece. Guess I'll have to get a small guide camera and try it out.

      best,


      Daniel


      --- In tec-scopes@yahoogroups.com, Tim Khan <timkhan@...> wrote:
      >
      > Thanks Floyd!
      >
      > Hello Daniel,
      >
      > Yes, it was quite low in the horizon. You'll love the scope visually as well as photographically. I can just imagine seeing the Winter Chilean Milky Way. That has got to be incredible with the Eclipse!
      >
      > A pair of small rings on a slightly longer plate that holds the lens in the front and the camera at the rear will work. This is exactly how I hold my other guider setup that is used with my 180FL and it works without fail (borg 60, helical focuser, Atik 314e). In fact, due to the borg helical focuser there is about as much tilt play that is in the Kowa lens itself. The trick is to actually introduce a some minor misalignment with the guidescope rings and optical train thus introducing a small bending moment which eliminates play.
      >
      >
      > As to the Vario Finder, the problems I see are:
      > 1. Short lever arm of the adjustment screws against the guidescope body itself, there is more potential for differential flexure if a heavier guide camera is used.
      >
      > 2. Then there is the attachment of the finder to a quick release base, again small moment arms.  
      > 3. if a helical focuser is introduced then again the same problem with the small amount of tilt during guiding.
      >
      > I'm going to design a solution and have it machined by Ashley's (precise parts).
      >
      > Tim
      >
      >
      >
      > ________________________________
      >  From: daniel_verschatse <antilhue@...>
      > To: tec-scopes@yahoogroups.com
      > Sent: Tuesday, May 29, 2012 4:12 PM
      > Subject: [tec-scopes] Re: NGC6357-6334 area and M8-M20

      > Congrats, Tim. Great results on objects that must have been pretty low in your Florida sky.
      > Took receipt of my Eclipse at NEAF recently and eager to collect some photons with it.
      > Thanks also for the info on the ST-i lens kit.
      > In this context, has anyone ever tried the Baader Variofinder on the TEC finder base as a "guidescope" with ST-i, Lodestar or similar ?
      >
      > rgds,
      >
      > Daniel
      >
      > --- In tec-scopes@yahoogroups.com, Tim Khan <timkhan@> wrote:
      > >
      > > The T-storms died early Friday and it cleared relatively quick so I was able to take a couple of images directly over the city of Homestead, FL to my south from my backyard. Images are taken with TEC Eclipse (110FL) with FLI-ML16803, actually was a test to check out the ST-i guider (w/ 100mm c mount lens kit and added 2x extender to 200mm). I have to somehow align the two scopes/cameras they were a bit out of
      > > alignment and I had some field rotation.
      > >
      > > Both images are 10 Ha images at 600 secs each:
      > >
      > >
      > > http://scas.org/tk/NGC6357-6334-SH2-10.jpg
      > >
      > > http://scas.org/tk/M8-ic2175-M20-ngc6544.jpg
      > >
      > >
      > > for the Imager's in the group:
      > >
      > > The ST-i with lens kit is a
      > > novel idea; unfortunately SBIG's ST-i lens kit does not allow for any
      > > alignment adjustments. In addition, the Kowa 100mm c-mount lens has a tiny amount
      > > of play/movement. So It looks like I will have to dump their solution
      > > for a more robust solution to guide. The nice thing is I was able to
      > > mount it directly on top of the TEC clam shell ring, by removing the
      > > handle and placing the ST-i camera in its place. SBIG should have just included a pair of small guidescope rings, this would not have cost much more for the kit.
      > >
      >
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
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      >




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    • lmbuck2000
      hi tim -- are you saying that RBI affects your narrow band images beyond 15min subs without greater cooling? is RBI an issue if i am doing one NB image after
      Message 2 of 11 , Jun 1, 2012
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        hi tim -- are you saying that RBI affects your narrow band images beyond 15min subs without greater cooling?

        is RBI an issue if i am doing one NB image after another (same filter) -- what does the ghosting affect other than the next image which is the same as the one i just took (perhaps minor affect if dithering).

        i always do 30min (or more) narrow band subs with both KAI and KAF chips and don't see a problem. my cooling varies from -15C to -30C. maybe i don't know how to recognize RBI!! :-) is it 'obvious' or subtle? i don't do flats and darks right after doing light frames. i thought RBI had the most impact on calibration frames (or when changing filters)

        thanks for some enlightenment...

        Lee

        --- In tec-scopes@yahoogroups.com, Tim Khan <timkhan@...> wrote:
        >
        > Thanks Bernard,
        >
        > I can do about 15 minutes without using Anti RBI flooding using narrowband filters. After 15 minutes, then the shot noise is greater than the read noise. This is the problem with the kodak full frame sensors. Really need a camera that can cool to -90C to slow trap leakage with RBI flooding and take exposures in the 15 - 20 minute range.
      • Tim Khan
        Lee, loaded question not easily explained at once... it all depends on several factors. First, KAI is not really badly effected, there is a buried channel that
        Message 3 of 11 , Jun 1, 2012
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          Lee, loaded question not easily explained at once... it all depends on several factors.

          First, KAI is not really badly effected, there is a buried channel that holds an electric field thus preventing trapped electron hole pairs from surfacing back into the photo site. This is also the reason for reduced red sensitivity in the KAI sensors since red and IR travel deeper (and past the buried channel) before being converted into electron hole pairs.

          On the KAF, particularly the 3200, 16803, 09000, and 6303 are prone to RBI and at the temperatures that you are operating at, it can take hours for the charge to leak out. If you do not use RBI mitigation then you have to be very careful not to expose the sensor to any bright light, otherwise you will have added noise from trap leakage. Same with taking darks, you cannot expose the sensor when you turn it on to any bright sources. 

          So in my case when I do narrowband I do not perform flats until the end of the imaging session. I also take care that there is no bright star in my focus reference filter for which I use blue since it does not penetrate deeply into the senior's epitaxial layer. If you accidentally expose to any bright source and over expose, your only safe bet is to use RBI mitigation. The same goes for darks: I turn on the camera, let it sit for 15 minutes with the cooler off, then turn on the cooler for 10 minutes before taking darks, keeping the cover on, and never opening the shutter.

          With RBI mitigation, I get Read noise = shot noise in about 65 secs. Without RBI mitigation it takes 900 secs. This is for my 16803 operating at -25C.

          to really understand the effects, do a simple test, turn on the camera that has been sitting for a day. Do not expose the sensor to any light what so ever, take a 600 second dark. Then take flat with the clear filter over exposed for 10 seconds (use a flashlight) follow with 2 bias frames to flush the surface charges, then take a 600 sec dark. See what you get.

          Tim


          From: lmbuck2000 <lmbuck2000@...>
          To: tec-scopes@yahoogroups.com
          Sent: Friday, June 1, 2012 1:29 PM
          Subject: [tec-scopes] Re: NGC6357-6334 area and M8-M20

          hi tim -- are you saying that RBI affects your narrow band images beyond 15min subs without greater cooling?

          is RBI an issue if i am doing one NB image after another (same filter) -- what does the ghosting affect other than the next image which is the same as the one i just took (perhaps minor affect if dithering). 

          i always do 30min (or more) narrow band subs with both KAI and KAF chips and don't see a problem.  my cooling varies from -15C to -30C.  maybe i don't know how to recognize RBI!! :-)  is it 'obvious' or subtle?  i don't do flats and darks right after doing light frames.  i thought RBI had the most impact on calibration frames (or when changing filters)

          thanks for some enlightenment...

          Lee

          --- In tec-scopes@yahoogroups.com, Tim Khan <timkhan@...> wrote:
          >
          > Thanks Bernard,
          >
          > I can do about 15 minutes without using Anti RBI flooding using narrowband filters. After 15 minutes, then the shot noise is greater than the read noise. This is the problem with the kodak full frame sensors. Really need a camera that can cool to -90C to slow trap leakage with RBI flooding and take exposures in the 15 - 20 minute range.




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