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40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

 
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  #1  
Old 06-10-2004, 10:22 PM
 
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40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

I am a bit worn out this evening; however I have THE hypothetical question of the year to post. You may or may not be aware of this, however as the light enters into the first lens of the scope and continues on through approximately 10 more, the light rays bend, just like they do when light rays hit a prism or water. This principle affect of light causes bullet impact to shift throughout the day. Hence, the wandering Zero. When the sun is behind you, the bullet will impact a little low; to the right and it will impact a little left, left and the poi will be a little right. This is because of the bending of the light rays as it passes through the lenses of the scope. The question? Does a larger objective and erector tube (larger lenses) magnify or reduce this affect?
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Old 06-11-2004, 06:18 AM
700 700 is offline
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Re: 40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

W

That is a strange proposition. If there is any truth in it, I would love to find out more.

Here is my understanding of the situation.

Glass lenses bend light. This is how they form focussed images. Light beams from the target fall on the objective lens of the scope. Consider that light beams from all parts of the target may fall on all parts of the front of lens. The lens and subsequent lenses bend each light beam from each part of the target so that they coinside to form a focused image at some point. In doing this the lenses act as an analog optical computer.

As the scope is processing light beams reflected from the target, the position of the sun is irrivelant in this matter.

The position of the sun during the day should have no optical effect on how the scope holds zero.

Could your observations be due to parallex error, wind, mirage or athmospheric conditions changing as the sun changes position.

Mirage could be a factor. This is where the air between the target and scope bend the light. I have no experience with shooting through mirage as we do not get much here in Ireland.

Does anybody have any info on this.

Rgds

700
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Old 06-11-2004, 08:39 AM
 
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Re: 40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

700: I am not being a bully in saying this, however, it is true; the position of the sun does affect the bullets poi. In addition to this being true, what happens when you add a pair of shooting or sun glasses to the equation?

But, to STAY ON THE TOPIC, Does a larger objective and erector tube (larger lenses) magnify or reduce this affect?
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Old 06-11-2004, 09:57 AM
700 700 is offline
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Re: 40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

W

I'm just going to sit back and see what I can learn here.

Rgds

700
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Old 06-11-2004, 10:07 AM
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Re: 40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

me thinks a bad coffee, beer or tabacco habit will effect the POI more..
Pete
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Old 06-11-2004, 12:26 PM
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Re: 40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

I will throw in my 2 cents and agree with 700.

The image we see through the scope is a straightline reflection from the target (assume no atmosphere). How the target is lit will affect shadows and the air between the target and the obj of the scope. The target doesn't move.

The obj is still in a straight line however, the image reflection may be distorted/bent by the changes in atmosphere conditions.

So the change in POI is a function of the distortion of the reflection due to the changes in air - temp, wind, etc. If we shot in a vacuum, the POI would not change regardless of the position of the light source (assume that amount of light emitted is the same).

As to the amount of distortion vs obj size, the effect is very small and would contradict due to the differences in lense quality, number of lenses, coatings, internal finish, size and thickness of lenses.

You will not be able to qualify that one obj diameter is better then another. Too many other components play a part.

However, if you assume that our eye can only absorb so much light and the exit diameter of light from the scope is equal or larger then the pupil, then the quality of coatings will play a much larger effect then size of objective.

I have "small" obj scopes that work better in dim light then "big" obj scopes. Same diameter tube so let's assume same diameter erector lenses. The number, quality and coatings of the better "small" scope plays a more important role then size of objective lense.

confused???

Jerry
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Old 06-11-2004, 04:13 PM
 
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Re: 40mm, 42mm, 44mm & 50mm Objective - Optical Question of the Year

Peter: Especially those little tiny cups of coffee... How are you? Hope all is well in Europe...

Jerry... The poi shift from sunlight is for real. Contact David Tubb, he will concur... Try to accept this point as fact, because it is.

I have sent an email to the one person who can probably answer this and am hoping that he will jump on this string. This same person insists that building scopes with the parallax adjustment on the front ocular bell instead of on the side is the best build for similar reasons. Letís see what comes of it.

[ 06-11-2004: Message edited by: W ]
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