Do Bigger Objectives Let In More Light?
BY Herschel Smith
3 years, 10 months ago
The answer to the question is yes, regardless of what Brownells says. I believe much of what they say is just wrong.
There are two types of telescopes (and a rifle scope is a telescope): refracting and reflecting. A rifle scope is a refracting telescope. He was misled by the analogy he drew, and the amount of the light let in by the scope is certainly a function of the diameter of the objective lens. If the tube diameter is small, the degree of convexity of the lens must be more extreme, but that’s the point with an objective lens with a different diameter than the tube.
In fact, in theory it’s possible to capture enough light with a very large objective diameter and highly convex lens that it would blind you regardless of the diameter of the tube.
The diameter of the objective lens affects more than just the field of view. It also affects the amount of light captured.
On February 15, 2021 at 9:26 am, Furminator said:
A 30mm tube may transmit more light than a 1 inch, but it is primarily designed to be stronger and allow for greater range of adjustment. All other things being equal, a larger lens may gather or pass more light, but things never are. Everything is a compromise. I put my money on optical engineering, coatings, and glass quality when it comes to being able to see a clear image in poor conditions.
On February 15, 2021 at 9:38 am, Frank Clarke said:
I recall in my earlier days — what else could I have recalled? — when Canon produced a lens for its 35mm SLR line that could deliver f/0.95. The objective lens was wider than the lens’ focal length. Of course, depth of field at wide-open was roughly the thickness of toilet paper, but — holicau! — you could shoot in candlelight!
On February 15, 2021 at 12:08 pm, Fred said:
When I saw the question as the headline I thought this was a daily devotion. The answer in that case is also a resounding yes.
On February 15, 2021 at 1:42 pm, Paul said:
according to the instructor at a Leupold class that I attended, the tube acts like a funnel and therefore a 30mm tube will indeed allow more light to pass thru to your eye than a 1 inch tube regardless of the size of the objective lens. Larger obj lens has to do with increased field of view, not light transmission.
On February 15, 2021 at 7:43 pm, Herschel Smith said:
Okay let’s try this in a different way. It may be that practically speaking, it’s not possible to build a lens that is convex enough to take a 50 mm objective lens and focus the photons of light down to a 1 mm tube diameter (to use a hyperbolic example). I don’t know, I’d have to study it a bit more and pull my physics textbooks out again.
That’s not the point. The scope tube IS NOT A FUNNEL. The tube doesn’t ACT like a funnel. Photons of light are not fluid, and they are certainly not an incompressible fluid. The analogy is not suitable, not for a physics major, and not for a machinist, and not for an “expert” or “instructor” who works for Leupold or any other scope manufacturer.
The amount of light (photons / sec) GATHERED by a scope is a function of the objective lens.
On February 15, 2021 at 10:36 pm, Daniel K Day said:
Wow. It’s disappointing to see Brownells screw up like this.
“The amount of light (photons / sec) GATHERED by a scope is a function of the objective lens.” Disbelievers: Think of it this way. You are in a pitch-dark room and you drill a hole in the wall to let in daylight. Which brightens the room more, a 3″ hole or a 2″ hole?
On February 16, 2021 at 9:37 pm, X said:
A bigger objective is certainly more effective on my spotting scopes. I have a 60mm scope and and 80 mm scope, and the 80mm is much better despite the fact that the 60mm may be of slightly higher manufacturing and lens quality.