20mm objectives

[DefendersOfValda]

Why do so many scopes use 20mm objectives now.


1) less light is getting in
2) bad for low light situations
3) bad for dusk or dawn hunting when game animals are most active
4) diffraction error is worsened creating less sharp image

Besides cost, and some 20mm scopes are still pricey, what advantage is there?

[M1NM]

Size. Glass has gotten better over the years. It is acceptable for most uses. A new 20 will let in as much light as an old 30. Of course with the better glass a new 30 will let in more light than a new 20.

[Horrendo Revolver]

Glass quality is just as important as objective size.

[goodlookin1]

It's all about the exit pupil and magnification level, and light transmission.

Most people's pupils cannot get larger than 7mm is the darkest of environments. Therefore if you have a scope that has a 30mm obj and is only a max 4x, you have an exit pupil of 7.5mm and during daytime conditions, the size of your pupil will only be able to utilize 3mm-5mm of that 7.5mm light pipe.

The answer is because it's pointless: If you can use it, why spend more in glass, materials and bigger size that a 20mm will let you do with zero detriment to sight picture and smaller size?

The only time this matters is when you get into the higher magnification levels. IMO, going below 4mm-3mm exit pupil is when your eye will begin to discern MASSIVE sight quality differences and discernibly less light coming through the scope. That's because the exit pupil is much smaller than your pupil is, thereby not giving your eye as much light as could be accepted.

Unless it's is a very bright day, you'll find a 20x scope with a 50mm obj will look very dim. I personally like to keep 5-20x scopes at or under 17x...

Finally, glass quality will help a little in light transmission but does much more towards crisp resolution and contrast than it does light transmission.

Hope this helps...

[Merc1138]

Why do so many scopes use 20mm objectives now.


1) less light is getting in
2) bad for low light situations
3) bad for dusk or dawn hunting when game animals are most active
4) diffraction error is worsened creating less sharp image

Besides cost, and some 20mm scopes are still pricey, what advantage is there?

1) Yes? Kinda...
2) No.
3) No.
4) Get better glass.

Exit pupil = objective lens diameter / magnification. Like goodlookin1 said, having an exit pupil that is uselessly large would be pointless.

https://en.wikipedia.org/wiki/Exit_pupil

[DefendersOfValda]

For the record, re glass quality....

Im looking at Leupolds, which I favor. And possibly Night Force scopes.

Im buying up all wishlist heavy metal first before glass, because Dip****s in Sacramento wont make glass illegal in the next few years. I really don't want to be swapping scopes between them, would like a scope for each rifle.

Im not going for BSA type crap(which i do have some of). Nor can I afford to fit all my arms with $2-3000 Swarovski or Trijicon scopes.

Maybe, I am dense, and I read the posts a few times. Still not clear why have a 20mm objective when a 50mm let's in more light.

I can't wrap my brain around exit pupil importance, when the exiting cone shape and size is determined by the backend viewing lenses, not the objectives.

[MongooseV8]

Weight is also a factor. Less lense=less weight.

[JMP]

I think it is for folks that don't want to carry around more than they need. If you have a scope with low magnification and don't need a large objective, you may opt for such a smaller scope.

[berg]

I was just comparing my Nikon M223 1-4x20 scope to a Hi-Lux 1-4x24 scope and was surprised to find the Nikon had a wider field of view at 1x (by at least 8 feet at 60 yards). There was also a slight edge in brightness to the Nikon.

I tested this by looking for detail in distant shadows. As said above I don't think there's any draw back to a 20mm objective as long as the glass is good quality.

[Merc1138]

I was just comparing my Nikon M223 1-4x20 scope to a Hi-Lux 1-4x24 scope and was surprised to find the Nikon had a wider field of view at 1x (by at least 8 feet at 60 yards). There was also a slight edge in brightness to the Nikon.

I tested this by looking for detail in distant shadows. As said above I don't think there's any draw back to a 20mm objective as long as the glass is good quality.

The nikon might be closer to 1x than the hi-lux(1 to anything variables aren't a true 1x with very few expensive exceptions), but that's not really an objective lens diameter thing.