Reply With QuoteAre you thinking of Aimpoint?
I've not seen a red dot that was parallax free despite what the companies claim.
Ian
Does anybody know of a true reflex gun sight? There was one on the sale in the states a while back. (Few years ago) It would probabley look like a box with a bit of glass at 45 degrees sticking out of it. There would be a lense under this and a mirror at 45 degrees under that. The sight may have a focus as well as brightness control. They have the advantage that you needn't precisely line you eye up behind them. The one I remember projected 2 circles and a cross but in priciple they could project anything.
The more normal red dot sights show this tendancey at various distances but don't seem to be correct for normal air rifle distances to me.
[This message was edited by A John on 09 August, 2003 at 22:05.]
Are you thinking of Aimpoint?
I've not seen a red dot that was parallax free despite what the companies claim.
Ian
I'm not sure what is was called. My best bet is to hope some US readers know about it. If I understand the principle used correctly this type of sight could be engineered to be free of everything.
Armson OEG?
Bushnell Holosight sounds like a modern version of what you descibe
http://www.bushnell.com/productinfo/...holosight.html
But Bushnell state that the dot is set to appear at 50 yards so this is definitely not what he is looking for.
In fact I'd appreciate if anybody can explain properly how a red dot could ever be parallax free. I don't believe it is possible. Assuming an unmagnified sight, the target distance is the real distance as it is not projected on to any focal plane. The dot must apear to be at some distance too. If those 2 distances are not the same then you will get parallax.
See here for some more info.
Damn, link doesn't work properly, try here and click on 'Facts and Figures about red dot sights' in Tools of the Trade.
Ian
[This message was edited by ianc on 10 August, 2003 at 6:19.]
Paralax as i understand it is caused by the fact that any sight is offset from the line of the barrel so they can only intersect at one specific point. I doubt whether any of the focus ring scopes really correct for paralax unless you spend huge amounts of money (?). I've noticed that no body seems to spec the barrel to scope centre distance the scopes are corrected for. As usual I would expect this to be firearm biased. I have noticed that BSA list 2 air rifle scopes but haven't seen them in any shop. Back to red dots where I suspect a simular situation exists.
The red dot sight I am on about does truely project an image of the reticule onto the target. It is a true reflex sight. The company also did a telescope sight and that does work. This focuses the image of 2 circles and a cross to infinity. It does this by using a simple lense. The mirror and the piece of glass simpley reflect the image back into the eye. Do a web search on reflex sights telescope and you will see how they are made (and how to make one). Following on from this the same lense could be made to focus the image to any distance but I do not know if the lack of the need to align the eye would still hold. Some optical principles only work at infinity but sometimes this doesn't matter. A reticule that appeared to be behind the target may even be easier to use. The image would in any case be a hell of a lot sharper. Neither of the above sights seem to use this principle. I think that both are similar to the Cobra.
I have a Cobra sight. The red dot is clearly not on the target. (True of all the sights I have looked at so don't knock it.) This definately does show a tendancy to reduce eye alignment issues at a distance but I wouldn't disagree with the link provided above. (Thanks for that).
...we shooters don't usually call it that. <img src="http://jsramsbottom.co.uk/bbs/e/icon_biggrin.gif" alt="Big Grin" width="15" height="15"><!--graemlin:--> In the land of the lead-hurlers, the conventional term for the perpendicular distance between boreline and line of sight is "sight height" and is an important input to trajectory calculation.
"Parallax error" is properly used by marksmen (that's us <img src="http://jsramsbottom.co.uk/bbs/e/icon_wink.gif" alt="Wink" width="15" height="15"><!--graemlin:--> ) to refer to any mismatch between the apparent "range" R to the reticle image and the actual range to the target T. Whenever these two numbers don't match, then E inches of eye movement behind the sight WILL cause the POI to shift by P inches.
The formula is: P = E(T / R - 1).
Note that P is zero independent of E only when T = R.
All sights that:
1. project a virtual reticle and
2. allow eye movement
...suffer from this effect. So that includes reddots of ALL types and scopes.
Only open sights (because they prevent eye movement) and lasers (because their "reticle" is physically projected onto the target, forcing T = R) are exempt from parallax error.
HTH,
Steve
[This message was edited by pneuguy on 10 August, 2003 at 22:28.]
A John,
Check out the new Aimpoints. Claimed to be free of parallax error. Link below.
http://www.swfa.com/riflescopes/aimpoint/index.html
I am about to buy a couple of Trijicon A.C.O.G. sights which is free of verticle axis parallax. Link below.
http://scopesandmore.itctv.com/s/sco...V=RSR-TRTA01|0
Good luck,
Milo.
Steve
I am allways a bit queezy about formulae like that not that I would care to agrue with you even though I have been hurling lead of one sort or another on and off since 1957. Seem to me though that the effect that you are describing is caused by the feature I have outlined. Don't know how I've managed to stay away from scopes so long.
The sight I am looking for does show zero paralax at infinity (Which means as least as far away as the stars). The intersection of the two axis is there. There used to be a rifle sight version of it. I am mostly interested in what they offer and maybe a purchase. The outfit was called Telrad. I believe the principle was devoloped during one of the world wars and used for a variaty of aiming purposes. They still are in a way - HUDs. They are relatively easy to make so I will probabley do that later this year and see if they do offer any advantage over a conventional red dot. I do agree though that my sort of paralax and yours will not completely go away but I can see other advantages. eg A better range of reticules are easily possible as the sight produces a true image and isn't projected at an angle. They will be sharper too.
Someone suggested a book in one of my posts - Optics for the hunter. (a ? on zoom scope exit pupil size) It would be interesting to see what it has to say on scopes. This aspect also has an effect on your paralax. By the way if you read the post I can see the point in focusing at 10x but not shooting. I'm allways curious about anything I come into contact with so I will buy the book soon. I do agree though that paralax can only be corrected under very specific circumstances. Thanks for the info.
I've seen info on how to set up a scope like that on a US bbs but the possible shifts in eye focus bother me. It seems to me that the usual set up for reticule focus simpley focuses it physically on the back of the eye. There is huge scope for adjustment here. I also get annoyed that the 'default corrections' will generally be for a fire arm not an air rifle. Hence some comments. 50 yards is a long way for our air rifles.
Looking a Milo's sights I don't think that the ruled reticule type will work unless the eye is exactly on the centre line of the sight. The other one claims that this effect is cancelled out. I can't comment. They do not give sufficient details, maybe it's worth looking at the patent. I can sort of imagine a two lense system doing something like that but can't see how to get round the multiple reflections. Coatings might be able to reduce these though.
Aim point are px free. I have one. Secure scope in bench vice aimed at small dot drawn on card any distance you choose away. Ten yards is ok line the two up, fine tune with reticle adjustment. Now move your head around and you will find that both target and dot continue to remain in exact relation to each other. Try this at any range and the same will be found. They are also focus free, with a pin sharp image from six feet to infinity. Parallax is also of no consequance to rifle shooters when magnifications are below 6x
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by HARDRAR:
Parallax is also of no consequance to rifle shooters when magnifications are below 6x[/quote]
Assuming you are making a general comment about scopes here, I would disagree with that statement. I have an ASI 4x40 scope parallaxed to either 100 yards or infinity, which has hideous amounts of parallax error at most airgun ranges. Infact the wide angle TV view provides the eye with a clear image across a wide range of off-centre eye positions allowing the crosshairs to move relative to the target by several inches!
Also have a cheap Nikko 4x32 scope which has a very narrow angle of view which prevents eye position from wandering too far off centre and keeps parallax error to a minimum. <img src="http://jsramsbottom.co.uk/bbs/e/icon_smile.gif" alt="Smile" width="15" height="15"><!--graemlin:-->
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by HARDRAR:
Ten yards is ok line the two up, fine tune with reticle adjustment. Now move your head around and you will find that both target and dot continue to remain in exact relation to each other. Parallax is also of no consequance to rifle shooters when magnifications are below 6x[/quote]
WHat do you mean by 'fine tune with reticle adjustment'? Does the aimpoint have a reticle that can be adjusted for different distances? If so, it is not truly parallax free and is more like an AO scope?
The other comment is plain wrong. If a 4x32 scope is parallaxed for 100y, as is often the case, the parallax error will be just as great as a 10x40 and the exit pupil is even bigger so there is more scope for error.
Rgds,
Ian
tasco made a h.u.d. version, intensity of aiming dot was controlled automaticaly by the amount of ambient light. to shut down unit just replace cover over sight. this puts it in sleep mode. german brand by name of "docter" sells similar unit.
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ianc:
If a 4x32 scope is parallaxed for 100y, as is often the case, the parallax error will be just as great as a 10x40 and the exit pupil is even bigger so there is more scope for error.
Rgds,
Ian[/quote]
Sorry to reply to ym own post, but I'd been thinking about this for a while and then did some searching on the net. Found this site which is very interesting on the whole subject. Look towards the end where you see what Leupold have to say on the matter of parallax and magnification.
Rgds,
Ian
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