How bad are the 20mm scopes at dusk compared to the larger objectives in reality.

I read that people complain about them as far as light gathering goes, yet they seem to be the most universally accepted scopes for larger rifles. Surely they are "adequate" at these times of the day, otherwise no one would be mounting them on there guns and leupold and other companies would not offer them if they did not sell.

Soooo..."Is the truth out there"

fire away with your theories and opinions.

Paul,

The 20 mm objective scopes do not work as well as larger objective scopes in the dark.

See this thread:

http://www.serveroptions.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=1;t=005047

for more on scope size.

jim dodd

objective/mag SHOULD equal >7mm for max light transmission.

so, a 42mm bell, at 6 power, means 7x.. 42/6=7 which is why fixed 6s are soo bright!!

for 20 (close to 21) it will get "darker" after 3x.. 20/3 = 6.666666m

jeffe

In the real world do they stop you shooting game ??

I the real world, if you can't where is cross hairs are on the animal you won't know where to shoot. Something larger than 20 mm will give you more shooting time.

What Jeffe said about light gathering is right on target, in the real world!

Rusty
We band of brothers!

The average human cannot take advantage of more than 5mm of exit pupil in hunting situations. The average human eye dilates to about 7mm in the dark. How well can one see in the dark and is it then legal to shoot game? A 1-4x20mm Leupold has 5mm of exit pupil at 4X and more than the human eye can use at 1X. So to make the blanket statement that smaller objectives don't work as well in the dark as larger ones is not correct. It depends on the shooters eyes, the exit pupil provided by the scope and the quality of the optics in the scope.

The operative word is transmission not "gathering". Show me a lens or lens system that "gathers" light!

I bought a VariX-III 1.5-5x20 earlier this year from Premier Reticle. Had it customized with a USMC Mildot Reticle, and 1/2 moa per click target turrets.

The heavy outerposts of the reticle are great in near dark conditions, and the mildots themselves add to the visibility of the reticle center portion. At power settings of 3X or lower, I can see as well as with my larger 40mm and 50mm scopes, in my unscientific, side by side lowlight comparisons. This is in heavy NC vegetation. In more open country, dry grass, or some snowcover (I'm thinking typical central/eastern MT here) it should be even better in low light.

MM

In the very real world using my 1.5-5X24 Trijicon, and in last September's black dark before the full moon rose, I could not find a leopard in the scope when the PH's flashlight went on . Three nights later under the same conditions I was able to see the leopard with the 3-9X40 Trijicon on another rifle, and make the shot.

So for this experiment the 24 mm objective in the low-power scope was not enough, but the 40 mm objective of the higher-power scope was more than enough.

I have an article coming in African Hunter describing this hunt, and with some commentary on rifle scopes for leopard. As Jerry Pournelle says "I do these things and write about them so you don't have to".

jim dodd

Thanks for the opinons, still a lot people choose to mount these 20mm scopes is it all for looks/ruggedness. I only own two at the minute and there both 2.5x compact leupolds. One is on a 45/70 the other on my 602 conversion. I have used both under a spotlight (1,000,000 candle power Lightforce 240 blitz) and they seemed to work fine in that application, but then again that spotlight produces a fair bit of light.

PC- You still jacking those Roo's at night with your 585 Nyati? heck 20 mm aught to be good enough when you unleash those 15 illion candlepower headlights! How can you find the bodies? They must fly 100 yrds or so.? I thought you only used the roo bars on the toyota at 100 mph.?-Rob

For those who have difficulty seeing in reduced light it might be a good idea to start with the eyes. Its been long known that vitamin A deficiency will cause loss of night vision. They gave it to figter pilots in WWII. Other nutrients are involved also, check it out.

Rob,

I have not used my .585 under the spotlight since September, I am still recovering...

I actually missed a fox with my .585 that I whistled in to about 50 yards, I must have flinched, cause it was shooting right the next day as I whopped 11 grassy's with it.

Rob, I have a spotlight mounted through the roof of my land cruiser, which has a handle that comes through to the cabin. so we can turn the light a full 360 degree's. I remove the revision mirrors on the drivers & passenger side and have rifles rests made up out of 1" square tubing with foam lagging over the top for a rest, one for my hunting mate and one for me. Systym works well. However when spotlighting with the .585 I actually get out of the ute and shoot over the bonnet in the standing bech rest type position, I have fired my .416 rigby from the ute window a few times and that is an experience.

.585 scope is off at the minuet as I have ordered 2 sets of Talley QD's 1 set for the .585 and another for the .416.

Just wanting infromation on 20mm scopes as I am thinking about standardiseing my serious rifles with 1-4 leupolds and 2.5x comapcts on the kickers.

Rob when are you making it to Oz ??

Mete thanks for the tips on the vitamins, all of us shooters should probably look into that.

Hunting in Norway at nights with a full moon and snow on the ground, or early in the morning, most hunters, myself included, find that a large objektive lens is much better. Exit pupil only tells you how bright a scope is at a certain magnification. When shooting in the dark you want at least 8x magnification to actually see the game, wich means you need at least 40mm objective lens for the scope to be bright enough at that setting. I have a 2,5-10 x 56 scope for shooting in low light. In theory it should be brightest at the 8x setting, but I can actually see much better when its cranced up to 10x.

A 4x magnification scope with a 20mm objective lens is close to useless in the dark, in my opinion. For a low power scope I like a 1,5-6 x 42, since less magnification is annoying (I get a wonderfull view of my barrel, but thats not really interesting when all I want to see is a deer or a moose behind the reticle) and at the 6x setting its usefull at low light.
Tron

Hunting in Africa for DG with .375 and .416, had a 1.5x5 Leupold 20mm obj lens on both. For the Leopard, the 20 mm scope worked OK, even at the last light, but then there was a profile outlined on the sky.
jackfish--indicates that 20mm scopes should be adequate in light gathering with larger objective lens scopes, but I'm not so sure. To add to my problem, I tend to have a bit of night blindness, my optometrist indicates that my cones have shut down, at my age that is not all .
Hunting brown bear and returning to camp floating down a river, had a deep dusk shot at a good size brownie, but couldn't see him in my 20mm scope. The guide could see OK with his binocular, but the shot was not possible, at least for me, with the 20mm tube. So have to agree with trb on this.

Some scope manufacturers indicate that they have large obj lens scopes which are fail proof on the 50 BMG rifles, are they correct on this as I would like to have at least one large obj lens scope (30-40MM) which could take the hammering of 40-50 cal big bores. That way the durability and light gathering problem might be improved.

from http://www.mta.ca/~rhawkes/courses/3001/lightgathering.html :

Telescopes: Light Gathering

The amount of light which is gathered by the telescope will be proportional (in the ideal case) to the square of the diameter of the objective lens or mirror (this is simply because the light collected will depend on the area of the objective lens or mirror). For example, small department store telescopes often have an objective about 5 cm in diameter. A modest amateur astronomer telescope is often about 20 cm diameter. The latter instrument would collect 4x4 or 16 times as much light. This corresponds, on the astronomical magnitude scale, to a difference of about 3 magnitudes (2.5x2.5x2.5 is approximately 16). So, to calculate the light gathering of a telescope one simply calculates the area of the objective. Of course in actual cases the optics will never collect all of this light - e.g. there is some fraction which is lost due to the obstruction of the telescope, and also there is some loss due to incomplete reflection at mirrors or transmission through lenses.

In the ideal case one can calculate the limiting magnitude for a telescope of some diameter D (in mm) using the following relationship:

m = 2.7 + 5 log D

From http://www.astronomynotes.com/telescop/s6.htm :

Powers of a Telescope

There are three features of a telescope that enable them to extend the power of our vision: a telescope's superior light-gathering ability enables us to see faint objects, a telescope's superior resolving power enables us to see even the tiniest of details, and the magnification power enables us to enlarge tiny images. Department stores and camera shops which do not know anything about telescopes, loudly proclaim their telescope's magnifying power. Magnification is the least important power of a telescope. Amateur and professional astronomers know that the light-gathering power and resolving power are the most important. These two abilities depend critically on the objective, so they make sure the optics of the objective are excellent.

Light-Gathering Power

The ability of a telescope to collect a lot more light than the human eye, its light-gathering power, is probably its most important feature. The telescope acts as a "light bucket", collecting all of the photons that come down on it from a far away object. Just as a bigger bucket catches more rain water, a bigger objective collects more light in a given time interval. This makes faint images brighter. This is why the pupils of your eyes enlarge at night so that more light reaches the retinas.

Very far away, faint objects can be seen only with BIG objective telescopes. Making faint images brighter is critical if the light is going to be dispersed to make a spectrum.

The area of the objective is the determining factor. Since most telescope objectives are circular, the area = p � (diameter of objective)2/4, where the value of p is approximately 3.1416. For example: a 40-centimeter mirror has four times the light-gathering power as a 20-centimeter mirror [( p402/4) / ( p202/4) = (40/20)2 = 4].

from http://www.twcac.org/Tutorials/powers%20of%20a%20telescope.htm :



Gathering light is like catching rain in a bucket. A large diameter telescope (large aperture) gathers more light and has a brighter image than does a smaller telescope of the same focal length.

[ 01-02-2003, 20:51: Message edited by: BFaucett ]

BF,

thanks for that it was a good read, I take it all your rifles wear big Euro scopes 56mm and up...

Yes BFaucett,

the 20mm scopes certainly do look better on rifles, particularly the bigger ones.

I actually thought you might have those astronomy telescopes mounted on yours

The leupold 2.5x compact is also a good scope, I have found in the last 12 months that I shoot better on low magnification.