Fixed Parallax @ 35 yard Scopes?

[Darth Laidler]

Mine seems to be fine, except for really close distances.

However, when i soom mine in the x9 mag, it seems to blur in the middle

But thats probably 'cos it was a fairly cheap one

[supersonic]

This is not so simple as it first appears.

Some 'scopes have excellent depth of focus, i.e. what the previous posters mean when they talk about "parallax" but which actually describes the ability to maintain both near and far objects tolerably well focussed.

This is a useful quality, however such a 'scope will still suffer more or less severe parallax errors whilst still giving a sharp image. Unless the distant image and the crosshairs are in EXACTLY the same focal plane, then small off-centre movements of the eye will result in the crosshairs apparently moving compared with the target image. This utterly destroys any accuracy potential, unless the shooter can place his eye exactly in the optical centre of the light path from the eyepiece, every time

It is quite easy to make a 'scope which appears to have a great depth of field, by using simple tricks like inserting a small aperture inside the tube, a bit like stopping down a camera lens. It also sharpens up the image, but it also cuts out a lot of light, which will not be noticed in good daylight.

More honest 'scopes acknowlege such trickery and simply use small objective lenses and lowish magnification to give enormous depth of focus, e.g. 1.5-5x20 or 2-7x32 designs. They are also usually much better quality for the same price, but seemingly undesirable compared with bigger 44 and 50mm objective 'scopes using cheaper glass and coatings to no benefit.

You can buy "focus free" binoculars which use the same tricks, but as anyone who has used a good pair of e.g. 7x50 binoculars will agree, they actually have pretty limited depth of focus and have to be adjusted at almost every range, even well beyond 100 yards. The larger the objective lens, for a given magnification, the smaller the depth of focus, unless "stopping down" tricks are used which negate the light gathering benefits of the large objective. Basic laws of physics.

So to summarise:

For good depth of focus, choose small objectives and low magnification, but realise that true parallax error will be substantial, when used at anything other than the "parallaxed" range

For accuracy, choose larger objectives and higher magnification with an adjustable objective, and accept the need to re-focus the objective to suit the range and so eliminate parallax error.

For true simplicity, accuracy and optical quality, choose a fixed mag. fixed focus 'scope e.g. 6x40 or 7x50, parallaxed at your usual range, e.g. 30 yards for airguns, 100 plus for centrefire. Zoom and PA adjustments will always move the zero, by how much and how repeatably depends on the precision, tolerances and cost of the mechanisms involved. Zoom mechs. require extra lenses which must degrade quality and/or increase price.

How many zoom'scopes end up just being used at one magnification every time ?

[Skoll]

How many zoom'scopes end up just being used at one magnification every time ?

Interesting point.
I tend to use my 3-9x40 at 4x, although I have used 3, 6 and 9 depending on exactly what I'm trying to do.

I decided to give up on my fixed PX scope, because usually I shoot at between 10 and 20 yards in my garden - not good for the 35 yard PX - so I ordered myself one of the JSR 3-9x40 PX IR scopes to replace it.

Does everything my old scope did better - then does a load more on top, all for a decent price.
Perfect - very eager to see it arrive.

[niceguygaz]

I can see it's easy to get a bit carried away with all the bells and whistles of modern scopes, which can be fun , but sometimes it's best to keep it simple.

I may have a look at some low mag fixed scopes just for hunting and keep the big adjustables for fun.

[Garry]

For true simplicity, accuracy and optical quality, choose a fixed mag. fixed focus 'scope e.g. 6x40 or 7x50, parallaxed at your usual range, e.g. 30 yards for airguns, 100 plus for centrefire.

Would the JSR 6 x 32 PX Mini fulfill this criteria?

Am I right in thinking that a scope set for px at 30 yards would be aimed higher or lower via milldots at other distances? Or would the px have to be set again?

I understand that a scope hitting bullseyes at 30 yards means aiming higher or lower at other distances, but I don't understand how a px control comes into it.

My limited experience only involves using open sights as a frame of reference for this subject.

Thanks
Garry

[Garry]

Quick bump for the above questions, ta.