Technical Discussions: Re: number of exposures

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Re: number of exposures
Posted by: Zeki Cosku Gokce , E-mail: photographer21@yahoo.com, on November 27, 2003 at 06:05 :
In Reply to: Re: number of exposures posted by : Juan J. Amado , E-mail: fotexsa@cwpanama.net, on November 26, 2003 at 19:08 :
----------- Start Original Message -----------
: : I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.
: : I would appriciate all the help
: : Regards
: Zeki:
: As you may infer from the formula for geometric unsharpness: Ug=Fd/D, (where Ug is geometric unsharpness, F is focal size of the source, d is the distance from the source-side of the object to the film-side of the object, and D is the distance from the source to the source-side of the object) as you reach the borders of the film in a pipe shot situation, two thing will take place simultaneously: the thikness of the material will increase and the source to object distance will decrease. Both of these factors conspire to increase the geometric unsharpness and make the details near the border of the film blurry. Add to this the effect created by the lessened angle of incidence of the radiation beam in that same area, and distotion of the image will also come in to play.
: Without getting too technical (although the formulas are straight forward, and most of the math is just geometry and algebra), I would suggest, as a general rule of thumb, to incrase the distance from the source to the surface of the pipe, and to go to a 4 shot configuration. For extreme cases, it may be necessary to segment the pipe into even more parts.
------------ End Original Message ------------
Dear Juan
Thank you for your prompt response. I am trying to write some code that will do various calculations for RT personnel. In my filed it is not practical to increase the source to surface distance, and for thick schedule pipes some times it is needed for more then 4 shots. My foremen thinks that there is a formula that will tell you how many shot you need minimum (it was on his level II exam). Are you aware of any?
regards
Zeki

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----------- Start Original Message ----------- : : : I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe. : : : I would appriciate all the help : : : Regards : : Zeki: : : As you may infer from the formula for geometric unsharpness: Ug=Fd/D, (where Ug is geometric unsharpness, F is focal size of the source, d is the distance from the source-side of the object to the film-side of the object, and D is the distance from the source to the source-side of the object) as you reach the borders of the film in a pipe shot situation, two thing will take place simultaneously: the thikness of the material will increase and the source to object distance will decrease. Both of these factors conspire to increase the geometric unsharpness and make the details near the border of the film blurry. Add to this the effect created by the lessened angle of incidence of the radiation beam in that same area, and distotion of the image will also come in to play. : : Without getting too technical (although the formulas are straight forward, and most of the math is just geometry and algebra), I would suggest, as a general rule of thumb, to incrase the distance from the source to the surface of the pipe, and to go to a 4 shot configuration. For extreme cases, it may be necessary to segment the pipe into even more parts. : Dear Juan : Thank you for your prompt response. I am trying to write some code that will do various calculations for RT personnel. In my filed it is not practical to increase the source to surface distance, and for thick schedule pipes some times it is needed for more then 4 shots. My foremen thinks that there is a formula that will tell you how many shot you need minimum (it was on his level II exam). Are you aware of any? : regards : Zeki ------------ End Original Message ------------

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