When speaking of a scopes ability to work in the darker conditions, I hear that some gather light and some people say transmitt light. Which is it?
Butch

both - one refers to the amount of light the optics allow through from one end to the other, the other term means how much light will hit the front end of the scope (i.e. bigger front, more light can hit it)

Transmit is the correct term to use.

Transmittion of light is the amount of the light gathered at the objective that gets to the users eye. So both are correct but essentially mean two different things.

The size of the objective will determine how much light the scope is capable of gathering. The rest of the optics in line, the quality of the glass and the coatings will determine how much of that light is transmitted to your eye.

Ken....

Technically, a scope does not have the ability to "gather" light. It can only transmit what is there.

quote:

Originally posted by Bobby Tomek:
Technically, a scope does not have the ability to "gather" light. It can only transmit what is there.

Good point Bobby. I've been doing amature astronomy for several years and the words gather or collect are used in normal conversation. You will also see "telescope" defined as an instrument that gathers and focuses light. Technically however, it's your eye or a camera that actually gathers the photons.

Ken....

I always wondered how a scope could gather the light? Does it have little hands to reach out and pull it in? Packy

quote:

Originally posted by Bobby Tomek:
Technically, a scope does not have the ability to "gather" light. It can only transmit what is there.

+1

"Gathering" light is EXACTLY what any optical telescope does. A 10x50 scope doesn't transmit a 50mm shaft of light does it, No it gathers the 50mm of light at the objective and "gathers" it into a 5mm exit pupil.

You can try and mistakenly parse the interpetation of the word "gathering" but if you will read just about any of the technical literature about telescopes you'll see "light gathering" used to describe just about any telescope or binoculars.

a couple quick examples:

Optical telescopes » Light gathering and resolution
The most important of all the powers of an optical telescope is its light-gathering power. This capacity is strictly a function of the diameter of the clear objective—that is, the aperture—of the telescope. Comparisons of different-sized apertures for their light-gathering power are calculated by the ratio of their diameters squared; for example, a 25-centimetre objective will collect four times the light of a 12.5-centimetre objective [(25 × 25) ÷ (12.5 × 12.5)] = 4. The advantage of collecting more light with a larger-aperture telescope is that one can observe fainter stars, nebulas, and very distant galaxies.

from: http://www.britannica.com/EBch...ering-and-resolution

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.


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


etc. etc. etc.

do a Google search for "light gathering" and you can find hundreds of references to how telescopes etc. and how they "gather" light.

There are a couple of rifle scope references that try and refute "light gathering", they are simply incorrect. You can try and reinterpet the word "gather" and "gathering" but you are wasting your time. We all know what it really means and that's just how the real scientists refer to it - they even have formula's for it! .....................................DJ

Yep, if it came from google or wikipedia, it MUST be true...

Seriously, though, there is plenty of false information available on the net. Just because you can reference it doesn't make it valid.

I've worked with optics on a daily basis for more than a quarter-century, and I've yet to see a single camera lens or rifle/pistol scope that had the ability to "gather" anything. There is no mechanical action associated with a scope or lens that enpowers it to "gather" light. It's really pretty simple, actually.

The quality of the glass and coatings, among a few other factors, will determine how much of the available light it can transmit.

"Gathering" is an inartful term, but most people interpret it as the amount of light that strikes the objective lens. More light strikes the objective lens of a 50mm scope than a 40 mm scope, so people commonly say that the larger scope "gathers" more light. Not exactly, but it is working with more light.

"Transmission" refers to the efficiency with which the optical instrument gets the light from the objective to the eye of the beholder. Lenses cannot be 100% efficient, thus each lens disperses or "absorbs" some of the light. Optical efficiencies of above 90% can be achieved in some very high quality instruments. Realisticly, the difference in an "average" 86% transmission efficiency (typical with single-coated lenses) and a stellar 92% transmission efficiency (achievable with multi-giga-turbo coated lenses with Shell Techroline additive) is virtually impossible for the human eye to detect. Incidentally, not that it makes any real difference, but variable scopes can never be as efficient in light transmission as fixed scopes due to the extra, light-robbing lens.

The amount of light the instrument is working with and the efficiency with which it transmits is are important. But so long as those two factors are in the "acceptable" range, it is far more important for the image to be flat, not distorted, without color shift, and of high resolution -- all factors having nothing to do with either "gathering" or "transmission".

By the way, just because a scope has a piece of glass in front that is 50mm in diameter doesn't mean that its effective objective diameter is 50mm. Lots of the cheaper scopes put the big lens up front for show but due to the design and placement of the internal lenses, the only light that is transmitted might come from just the center 44mm or whatever of the lens. Caveat emptor!

To go a bit further on what Stonecreek mentioned: You can take a pair of 3-9x40 scopes (lets take, for example, BSA and a Conquest), put them side-by-side and take a look downrange through both late in the day.

At first glance, the images may look similarly bright, but when you get to the brass tacks -- and what's really important -- it's the ability of the glass to resolve detail under poor lighting conditions that ultimately separates the wheat from the chaffe. Set up some optical grids and see just how much of the detail you can see, and you'll quickly realize why the price difference between the 2 exists.

There are no miracle or magical parts in the more-refined and higher-priced optics. While construction will be a bit more sound that what is used in cheaper scopes, the primary difference will be in how finely-polished the lenses are and the quality of the applied coatings (I won't get into tracking and adjustments here).

Another benefit of these scopes is that under harsh conditions such as a backlit subject against a western horizon, the better scopes will show minimal lens flare. You'll likely lose the entire sight picture with a cheapie.

quote:

Originally posted by Bobby Tomek:
Yep, if it came from google or wikipedia, it MUST be true...

Seriously, though, there is plenty of false information available on the net. Just because you can reference it doesn't make it valid.

I've worked with optics on a daily basis for more than a quarter-century, and I've yet to see a single camera lens or rifle/pistol scope that had the ability to "gather" anything. There is no mechanical action associated with a scope or lens that enpowers it to "gather" light. It's really pretty simple, actually.

The quality of the glass and coatings, among a few other factors, will determine how much of the available light it can transmit.

Yes, there is plenty of BS on the internet but frankly if in deciding BS from truth I think that most people are going to lean towards the Encyclopedia Britannica than a guy named Bobby Tormek that posts on AR.....................................DJ

quote:

Originally posted by Bobby Tomek:
To go a bit further on what Stonecreek mentioned: You can take a pair of 3-9x40 scopes (lets take, for example, BSA and a Conquest), put them side-by-side and take a look downrange through both late in the day.

At first glance, the images may look similarly bright, but when you get to the brass tacks -- and what's really important -- it's the ability of the glass to resolve detail under poor lighting conditions that ultimately separates the wheat from the chaffe. Set up some optical grids and see just how much of the detail you can see, and you'll quickly realize why the price difference between the 2 exists.

There are no miracle or magical parts in the more-refined and higher-priced optics. While construction will be a bit more sound that what is used in cheaper scopes, the primary difference will be in how finely-polished the lenses are and the quality of the applied coatings (I won't get into tracking and adjustments here).

Another benefit of these scopes is that under harsh conditions such as a backlit subject against a western horizon, the better scopes will show minimal lens flare. You'll likely lose the entire sight picture with a cheapie.

I completely agree that there's a big difference between the final image between a good scope and a bad one. A brightly lit unresolved blob is still an unresolved blob, resolution can be critical...........................................DJ

djpaintless wrote:

quote:

...than a guy named Bobby Tormek that posts on...

I hope so. I have no idea who that would be as I couldn't find that name in the entire Accuratereloading.com roll.

---

DJ-

From previous discussions, I know you are an intelligent and articulate individual. But as to your comments here, it almost seems as if you are part of the generation/culture wanting to change everything to what is easy and acceptable instead of what is precisely correct.

I really don't think that is so and will give you the benefit of the doubt.

I guess I am old school and a stickler for precision no matter what it may entail.

Heck, I also despise incorrect changes of the English language. For example, the word "couple" comes to mind. When referring to two people, couple is considered singular -- a unit, if you will. Thus, like English teachers used to teach, the following sentence is, has been and always will be (in my books, at least) correct: The couple is planning to reside in Albany.

But now, thanks to a few follies who decided to rewrite the world, publish a manual and call it gospel, "couple are" is supposedly the correct version. And folks are picking up on it and going with the flow.

While we are at it, let's re-write history, too. Heck, the Holocaust is just someone's imagination, right?

And the Alamo never happened, either. It's easier to say that than explaining to children the TRUTH and having to answer questions -- not to mention possibly offending someone.

But back on topic: Using logic and common sense, one can see clearly see how a scope has no given abilities to "gather" light.

It's plain and simple. And it doesn't take a degree in science or a set of encyclopedias to understand that, either.

But hey, I digress and maybe will change, too. And this evening, I am going to put my scopes outside while there is still good light. I will let them "gather" as much as they can. Then, once it is dark, I can use this "gathered" light to dramatically increase my odds of shooting a hog after midnight...

My thoughts on why "gather" is being used so often:

Years ago, "gather" was used -- albeit somewhat incorrectly -- to describe a certain facet of optics. It was repeated and repeated and undoubtedly even written in the various journals. Folks picked up on it, and it stuck.

"Gather light" is here to stay, no matter what anyone writes or wishes and no matter if it is technically correct or not.

It is much like the term headspace, which is used INCORRECTLY and REPEATEDLY and even appears as such in gun rags. It's even been defined incorrectly in reloading manuals.

But that's another topic altogether...

All of this brings me back to your Britannica reference: So what if something is in print? Does that automatically make it right???

quote:

Originally posted by Bobby Tomek:
djpaintless wrote:

quote:

...than a guy named Bobby Tormek that posts on...

I hope so. I have no idea who that would be as I couldn't find that name in the entire Accuratereloading.com roll.

Oh well I guess if there was a "Tormek" he would be a pretty sharp guy:

http://www.tormek.com/en/



---

But as to your comments here, it almost seems as if you are part of the generation/culture wanting to change everything to what is easy and acceptable instead of what is precisely correct.

It's actually the exact opposite, you are trying to parse the word "gather" which when looked up in the dictionary has several alternate definitions.
I use the term "gathering" because it is the commonly used scientific term! But again don't take "djpaintles" or "Bobby TOMEK" as the final word on the subject. Use the internet as a tool to find more authoritative information from reliable and trusted sources on the subject. You WILL find that the vast majority of serious literature on the subject refers the the "Light Gathering" ability of telescopes.

When "logic and common sense" disagree with documented scientific literature I usually go with the scientific literature. There are plenty of things that defy logic and common sense, quantum theory, relativity, women, and I guess for some the simple concept of Light Gathering in telescopes. ..........................DJ