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Re: [William-Optics] prime focus

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  • Scott Walker
    I am not sure what type of mount your camera has. I general the adapters for the telescope ends in a male T-thread. You then uses a T to camera adapter. This
    Message 1 of 10 , Mar 17, 2006
      I am not sure what type of mount your camera has. I general the adapters for the telescope ends in a male T-thread. You then uses a T to camera adapter. This adapter is specific to your camera mount. They cost 15 to 20 dollars. Typically the film plain is about 48mm behind the camera mounting surface. Normally a diagonal would not be used. It would likely keep you from being able to focus. Most Barlows are designed to have the focus plain at the eyepiece to Barlow surface. If used with a camera the focus plain will be around 60 to 70mm behind this point due to adapters and the 48mm space in the camera. This should still work but the magnification factor of the Barlow will increase to perhaps x3 for a x2 Barlow. This will depend on the Barlow. The longer the Barlow the less the change. The x3 is the expected value for the Televue x2 Barlow.
      If you want to continue with a astrophotography I would recommend buying the Digital Rebel. I have seen some great results with it and its is also a good general use camera. For slide film it costs about 15 to 20 dollars for 36 shots( film plus process, does not include cost of gas to drop off and pick up film). The Rebel cost about 800 dollars or 50 rolls. If you shot a roll a week you would pay for the Rebel in a year with the money saved. Because of the almost instant feedback from the Rebel you will learn much more quickly. Also digital is much better in low light. 
      Good Luck
      Scott Walker
      ----- Original Message -----
      Sent: Friday, March 17, 2006 5:07 AM
      Subject: Re: [William-Optics] prime focus

      You mentioned the power mate, and I looked at a 5x t ring ready and also a t ring, but I don't know if the t ring would fit my old minolta.  So, would I use this power mate directly through the scope like I used my camera last night, or would I use such a device using prime focus with my diagonal?  I also looked at a teleview eyepiece projection, and was fairly confused on how that worked.  Eventually, I might like to get some magnified bright planet like jupiter which is pretty bright right now in the morning or even something a little more challenging.  I will get the results of my first prime focus astrophotography tonight.  There are alot of articles on focusing, but going directly through the telescope with the fresnel plate on the old minolta, I felt like I could focus very well using the micro focus on the ZenithStar 80.  Hey thanks for all your suggestions.  I am pretty excited about this stuff, I just wish I had the money to get a good mount.

      Scott Walker <sdwalker@...> wrote:
      Taking a picture of the moon when it is full it like taking a picture of a desert on earth in daylight. For daytime shooting in bright sun you can use the "sunny 16 rule" . It says the shutter speed at f/16 is 1/(film speed). So with 200 speed film the shutter speed would be 1/200 of a second at f/16. Your shooting at f/6 so your shutter speed increases by (16/6)^2, or 7 times. So you should shoot at 1/1400 per the formula. I find this produces an image that is a little dark so I normally increase exposure by 1/2 to a full stop ( I believe the reflectivity of the surface is quite low this is why the sunny 16 rule needs modification). When the moon is not near full it is good to further increase the exposure. This is because the sun light is no longer perpendicular to the surface but rather at a smaller angle. This makes the surface less bright. Remember if you use a X2 Barlow you will need to increase the exposure by 2-stops or 4 times. If you need more magification you can use a powermate or use "eyepiece projection".  
      Good luck
      Scott Walker
      ----- Original Message -----
      Sent: Thursday, March 16, 2006 3:32 PM
      Subject: [William-Optics] prime focus

      I am attempting to photograph tonight using a minolta body, 200 ASA
      color fuji film with my Zenith Star 80.  I can only focus the camera
      with the telescope when I go directly into the scope 1.25 adaptor. I
      can't focus using the dialectric diagonal or a barlow 2x.  Do I need
      some type of attachment to be able to increase magnification using a
      barlow and are there any other methods to increase magnification
      using prime focus with a camera body using the ZenithStar 80.

      What I am doing is pretty low tech.  I don't have a good Losmandy,
      but a little Nexstar GOTO scope.  I am usng a 7 x 50 guide scope on
      top of the ZenithStar 80.  The moon will be my first easy target and
      I took meter readings this morning using the 55mm camera lens to get
      some idea of shutter speed.  It will be 1/8 of a second.  I will
      experiment with different speeds and later I will try using a
      shutter cable for longer timed shots guiding as I go.  Since I am
      using film, I will have it processed and put on cd so I can use
      Registax 3.0.  I will try to shoot orion also doing some short shots
      of at 10 seconds.  I think my limit might be 15 seconds, but because
      the mount is Alt Azm tracking will not be correct even with trying
      to aim by hand.

      Any suggestions on magnification using this method would be
      appreciated.  I am also using the red dialectric filter on the 1.25
      Rickie Rainwater


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