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jimwc6491

doubler

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Anyone

 

is it possible to use a 2X dobler when doing prime focuses? or will there be a problem with focus between the doubler and the camera? to increase magnification.

 

Yes you can.  You have 2 options here.

 

1) Use a 2x barlow.  This will move your focus point further.

2) Use a 2x Powermate.  Your focus point should be relatively the same.

 

Hope this helps,

 

Guylain

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When I use either of my 2X or 4X Powermates, I need to insert a 3" extension between the focuser and the Powermate to achieve focus.

 

Hey Rick, even with a PowerMate?  I always thought a PowerMate was telecentric and as a result the focal point would not change that much.

 

Guylain

 

 

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Guylain & Rick

 

Thanks

 

I have a "OPT" 2" 2X Barlow.

I also have a 35mm and a 50mm extension, and if my conversion is correct this gives me 3.3438"

my usual setup is the 35mm between the camera and the focuser.

Ill mount the camera to the Barlow and just move the 35mm to the bottom of the Barlow and add the 50mm.

Ill find out how well it works the next time I'm under the stars.

Star Party coming up at the Grand Canyon Caverns this weekend.

 

 

 

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Jim,

 

I am not saying that you will need an extension piece when using a barlow.  However, with my 5" refractor and 2X or 4X Powermate I do need an extension.

 

The easiest way to test is to aim at the moon and look through the viewfinder while manually racking the focuser.  You will be able to tell pretty quickly whether you can focus or if you need an extension.

 

Good Luck,

 

 

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Rick

 

Thanks

 

at least I have them if I need them. using a 2X Barlow will halve the ISO so I will have to take a longer shot or increase the ISO correct or both. I'm sure ill get it sorted out during my setup phase.

now I just hope the clouds stay away for this weekend.

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To be technically correct:  

ISO is a Camera Setting which controls the Camera Hardware application of Gain when reading the DSLR Sensor and converting the photons collected into digital data.

 

The 2x Barlow has the effect of "doubling" the Focal Length.  This in turn doubles the Focal Ratio.  It is the larger Focal Ratio which dictates that you will need Longer Exposure Time in order to capture the same amount of Light.

 

You'll want to work to extend your Exposure Time until you are limited by either your Tracking or the Light Pollution overtakes your Image, rather than raising the ISO above either 400 or 800 (Canon DSLRs reach "Unity Gain" somewhere near these values).  Raising the ISO simply Multiplies BOTH the Signal AND the Noise, while Longer Exposures actually capture More Signal.

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s3igell

 

I knew the terminology was not quite correct. but I thank you for setting me straight.

I was not sure what the ISO should be set at for optimum exposure.

 

 

thanks Again   

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