What's the most important factor in light-gathering?

T

thaddeus

New member
What's the most important factor in light-gathering?

Is it mainly do to the width of the objective?

Quality of scope or glass?

For example, comparing a midline quality scope like a Redline with a 40mm objective, with a nicer scope like a Leupold with a 20mm objective...which one is giong to have the best light gathering abilities? (both on the same low power, like 3X for example)


Are there other factors involved with objective width and quality of glass?
Clarity? Contrast?
What about Field of View? Does quality affect FOV, or only objective width?

How about speed of aquisition, on a snap shot? Is quality all that matters, or is the larger objective going to give the quicker aquisition due to larger FOV and more light?

thanks!
thaddeus
 
I am not an optics expert, but I consult with them about my scope purchases... ;)... I have been discussing the advantages of larger objectives in terms of light gathering with a couple people recently. Though opinions of professional/experiences shooters is mixed, and actually seems to favor the larger objectives, assuming that they are significantly better than the smaller ones, the reps form the companies seem to disagree.

In fact, The Leupold National rep told me last week that the 50 mm objectives offer only an 8-10% over the 40mm objectives in their high end scopes. That 8% advantage, he says, would be important only uner precise cirucmstances.. he mentioned hunting before sunrise or after sunset in the South East U.S. as examples of when it would matter.
One disadvantage of the larger objective is also the need for higher mounts, which can affect the way your head rests on the gun and will affect the deviation of the Point of impact versus the Crosshairs with range.
 
Yo thad, whassup

Me again, just trying to get sleepy before bedtime.

Think of light gathering as if you were catching rain in a funnel - the bigger the big end is, the more light you gather.

Also the lower the power of the scope (bigger field of view) the more available light there is to gather. The field of view is affected more by the magnification of the scope than the size of the objective. But given the same magnification, the larger objective also adds a little field of view. The quality of the lens then determines how well you use the light you have gathered. But even quality can't create light that isn't there so the 40mm objective is always going to gather more light than the same power scope with the 20mm objective. The scope would have to be pretty poor quality to not put that light to use.

Quality of glass will definately affect clarity and contrast but not field of view which is determined by a combination of power and objective lens size.

For snap shooting, assuming almost any serviceable quality scope is used, field of view is everything. The field of view is increased when the magnification is decreased and it is increased further (a little) with larger objectives. Snap shooting is done at close range so the quality of the glass is less important than it would be for long range precision shooting.

Mikey
 
not sure if this applies to rifle scopes, but it applies to binoculars and spotting scopes.

Lens coatings. The more they're coated, the better they'll be. There are four basic levels of coating: 1) Coated--when at least one side of one lens is coated with one coating. 2)multicoated--when at least one lens is coated with more than one layer of coating. 3) fully coated -- when every lens is coated at least once. 4) fully multicoated -- when every lens has more than one coating.

Fully multi coated optics usually equal good light transmission. The coatings serve to reduce reflection, thus allowing more light to pass through the glass. Some manufacturers are very specific in their coating procedures and explicitly state that every glass-to-air lens surface is multi coated. This is supposedly the best.

But, as usual for me, this is mostly knowledge obtained from reading, not using.

Spencer Stewart
 
I have a zoom lens on my camera. It's coupled to the built-in light meter. I noticed that as I zoom to higher magnification, I have to open the shutter wider to keep the same amount of light for the exposure/speed setting.

For the higher settings on a scope sight, there is effectively less light coming through. The larger the diameter of the objective lens the more light comes through, but you'll always have more light at lower magnification.

Rob's comment about the relatively small advantage of the larger objective lens is well taken. Unless early-morning or late-evening shots are very important, there is a weight penalty as well as the possible height-to-centerline problem...

If you're taking really long shots on small targets, and need the 14X to 24X scopes, the very large objective lenses are a must. For the more "usual" sort of, say, deer-hunting, a 40mm objective lens is typically quite sufficient.

FWIW, Art
 
Thaddeus,
I'd rank them, in descending order, thus...
1) Quality of glass, including coatings.
2)Quality of construction. It doesn't matter how good the materials are, poor work can make 'em trash.
3) Size of objective lens.
As I recall, you'd stated an extreme of 300 yd. You didn't say if'n 'twas ground squirrels or revenoors, but assuming a deer sized target, any good scope in the 2-3X to 8-10X range, with approximately a 40mm objective should suit you well. As an example, my pet .308 has a 2-8X Bushnell (an older one) and performs well at the ranges that round is suited to. Unfortunately, my perfect scope is not yet made...:0 2X to 50X, perfect clarity, and will cancel out any blurring from mirage... You might slip over to the go go varmint go board and talk scopes there for a while, and a lot of info.

------------------
Shoot carefully... swifter...
 
Thad, Swifter is right in saying that poor construction can make even good materials worthless. But that is seldom the case. A good quality instrument will be good all the way through; a piece of junk will be junk all the way through. No one is going to spend money on superb lenses and then put them in a scope tube made of high quality aluminum foil.

There are some things to look for, and the others have covered them well. I'll just add two things.

1. You basically get what you pay for.

2. Don't overlook used scopes of good quality. Unlike a gun, most of the big problems in a used scope are readily apparent. Also unlike a gun, no one ever wore out a scope by looking through it. Dealers long ago found that a scope didn't increase the sale price of a gun to any extent, so they take the scopes off and sell them separately at (usually) reasonable prices.

Jim

[This message has been edited by Jim Keenan (edited April 25, 1999).]
 
OK... one thing I haven't heard mention is is the exit pupil of the scope. This is found my dividing the objective lens millimeter diameter by its magnification (ie a 7x35 would have a Exit Puple of 5mm).

The pupil of the human eye in daylight measures about 3mm. There for you are seeing all the available light through the scope. However, at night, when the eye's pupil measures 6 or 7 mm, if you are using the same scope you will be loosing some of your "seeing" ability.

Though I'd just through this in.


------------------
Schmit, GySgt, USMC(Ret)
NRA Life, Lodge 1201-UOSSS
"Si vis Pacem Para Bellum"
 
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