why do I need adj. objective for fixed known distances...

K

kennisondan

Guest
will a front objective adjust scope with the distances on it work or is it not advisable.??
I will not be range finding as a noob BR shooter, correct? so why a sidewheel adjust, etc.
also if he min. marking of the scope a leupy 6-20 is 50Y I imagine that is a big problem for 25 meters ?
I have heard of twisting the bell of the scope or something along that line I would not hazard to do unless really confident in it.. to get it to focus closer..

what say you ..
help a noobie out.
I am more excited about BR than I have been about anything in a long long time.. thanks in advance.

dk
 
At higher magnifications, there is less depth of focus, so just like you would focus a spotting scope for different distances so that the image of what you are looking at is sharp, you will need to focus either the front of the scope, or do the same thing by using a third knob that is located opposite the scopes windage adjustment. That is one reason. The other reason is to, at the same time, eliminate parallax. If you line up your rifle so that the reticle is on your desired target, and without touching the rifle, move your eye from side to side (or up and down), within the range of motion that you can still see what you are aiming at, and the intersection of the cross hairs appears to move, even the slightest amount, when neither the rifle or the target are moving, you have parallax. This means that where you are pointing the rifle will depend on the location of your eye. The target and reticle are focused in different internal planes within the scope. For precise shooting, this is not a desirable condition, and if a scope that has front or side focus is in good repair, and has been properly adjusted to the shooter's vision, the same point of adjustment where the target image, will also be the point where parallax is eliminated. What scope are you using?
 
Hi Boyd : I was thinking of using a leupold 6-20x that has the yardage parallax adjust on the front.. can I get rid of the parallax with that ? when I adjust to my vision that is meant with the rear loosened for seeing the crosshairs clearly then tightened down ?
I would love to use this scope but will buy one if Ihave to.. I have a side objective cheaper scope in 8-32 both a hawke and a low cost model leapers or sightron. I was just reasoning that without having to range find, a 20 x max magnification and the front parallax adjust might be ok.. however the lowest if 50 yds on that adjustment so I am worried about that on the leupy.
dan kennison
thanks
 
I guess that I lose points for not noticing that you posted on the airgun forum. (I saw your post on a list of new ones from all of this site's forums.)Now I see what you are getting at. Some airgun matches are at unknown ranges and a large diameter side focus knob is used as a rangefinder. If your scope will focus (at the front or side) for the shortest distance that you will be shooting, I don't see that there would be a problem. As far as adjusting the eyepiece, there has been lots posted (some of which I disagree with) so you might want to search this site for more information. Putting it as briefly, a properly adjusted eyepiece should make it possible to see a sharp reticle,the sharpest target image, and have no parallax. The problem is that because of the fine eyepiece adjustment threads that some scopes have, the depth of focus of eyepieces, and the eye's ability to almost immediately compensate, one may be slightly off on the first attempt to focus the eyepiece, even if you follow the directions perfectly. In this case, a little trial error, using very small adjustments, and working back and forth between the front or side focus, and the eyepiece will be needed. I have had some disagreement on this point, but I know that I am on solid ground, both in theory and actual experience.
 
thanks mr. Allen : concise and well put answer. I will not be able to use it for 25meters airgun distance since it will not focus under 50yds. I am pretty sure that there would be induced error in attempting to use it without having it worked on. I will use the technique you pointed out to fine tune my other closer focusing scopes to be sure I have it as good as I can get it. The explanation makes good sense, as the eye is quick adjusting, so I will relax look unfocused in the distance and look through again.
much appreciated.
dan kennison
 
fifty foot adapter ... it was commonly available for that scope from the maker.
 
I just spoke with someone about the 50 foot adapter (on a matter unrelated to airguns). Unlike what I had assumed, it is not a lens, but reduces opening of the objective, which increases depth of focus. It is a flat piece of aluminum with a hole in the middle that is significantly smaller than the scope's objective, that screws into the front of the scope. Although this method may produce serviceable target image sharpness, I wonder if it would allow for elimination of all parallax.
 
Boyd Allen, I have a 50 ft Leupold adapter it is in fact a lens that screws in to the front objective. The one have is from at least 20 or more years ago and was made to fit M8 (Fixed power) series. It is possible these are no longer made.
 
Correction: After reading blades' post, I downloaded the latest Leupold catalog, to do a little research on what the 50' adapter looks like. It seems that I was misinformed. It is a lens, in a mount that is designed to screw into the front of the objective bell of the scope. The fellow that I spoke with must have been thinking of something else.
 
Don't go with that (apreture) ... I know some feel its good enough, but its really better to use the right tool for the job, which is the adpter lense.
 
trying to determine if the one I have found will fit my vari x III 6.5-20.. I am unsure of the MM of the front objective.
thanks
dk
 
I will have the adapter shortly and should be able to check it out and report just for the sake of closure and to help others should they press their leupolds from old into service. thanks to each and every responder.. I am just a newbie but this is an exciting aspect of shooting for me as I might be able to do it much better and much longer than my physical abilities will allow other shooting... I am quite excited over this prospect and am pricing for rests and bags ... etc.
dk
 
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