What are the top factors in accurate ranging?

[GatorCountry]

Which should be more accurate (in theory) for range finding in HFT:  a variable 4-16x scope at 16x, or a 6-24x scope at 16x?  Other factors, such as objective size being the same. I.e. should the focus/ranging ability be inherently any more or less accurate at the maximum end of the mechanical zoom range?

The depth of focus decreases at higher magnifications, making it harder to range.  However does this translate in a higher variable power scope, when at less than maximum?  I.e. in theory should there be any degradation due to the variable power mechanism?

Or would other factors be more of a concern, such as image quality in scopes reaching for higher magnification?

[ShakySarge]

I would say that depends on the make and model as well as tube diameter. If they are both 30mm tubes and Hawkes(for example) then the 6-24 at 16 would be more crisp a picture than a 4-16 maxed out at 16. Until you get into higher end optics, the maxed out scope will almost always have degradation in clarity when comparing two of the same make and grade.

That being said, the 6-24 IMO would be the better optic for range finding, whether that be HFT or just in the field. Again, assuming that it would be at 16x

[Scotchmo]

Which should be more accurate (in theory) for range finding in HFT:  a variable 4-16x scope at 16x, or a 6-24x scope at 16x?  Other factors, such as objective size being the same. I.e. should the focus/ranging ability be inherently any more or less accurate at the maximum end of the mechanical zoom range?

The depth of focus decreases at higher magnifications, making it harder to range.  However does this translate in a higher variable power scope, when at less than maximum?  I.e. in theory should there be any degradation due to the variable power mechanism?

Or would other factors be more of a concern, such as image quality in scopes reaching for higher magnification?

"Which should be more accurate (in theory) for range finding in HFT:  a variable 4-16x scope at 16x, or a 6-24x scope at 16x?..."

HFT does not allow focus range finding (AAFTA Hunter Division does allow focus range finding, but it is not HFT)


"The depth of focus decreases at higher magnifications, making it harder to range...."

As the depth of field declines, ranging becomes more precise, so higher magnification is better for that.

ShakySarge said:
"...If they are both 30mm tubes and Hawkes(for example) then the 6-24 at 16 would be more crisp a picture than a 4-16 maxed out at 16..."

Assuming scopes both have the same overall length, objective size, and same glass quality, I would say that the 16x@16x would have a clearer picture than the 24x@16x. For a given scope length, and objective size, the higher magnification scope will require greater lens curvature, increasing the likelihood of optical aberrations. Though that does not mean that one will range any better than the other. The Sidewindwer 4-16 has a shorter length and smaller objective than the Sidewinder 6-24. So in that case, the 6-24@16x might indeed be "more crisp" than the 4-16@16x.

[GatorCountry]

HFT does not allow focus range finding (AAFTA Hunter Division does allow focus range finding, but it is not HFT)

Imprecise wording on my part.  I was referring to AAFTA Hunter Division.  Thanks for clarifying.  More specifically, I'm personally interested in Hunter Piston for local competitions.

"The depth of focus decreases at higher magnifications, making it harder to range...."

As the depth of field declines, ranging becomes more precise, so higher magnification is better for that.

Stated that way, it does make sense as the two would follow.  Could be part of my problem in sorting this out in my mind, I've either mis-heard or understood that relationship.  What I may have been confusing is that (at least at 16x), I've been told that ranging accuracy via repeatable focusing is within a yard or two under 35 yards or so, becoming much greater past that distance, within only 5+ yards.  Which might be bridging beyond theoretical scope mechanics into the reality of the scopes of various price ranges.

Assuming scopes both have the same overall length, objective size, and same glass quality, I would say that the 16x@16x would have a clearer picture than the 24x@16x. For a given scope length, and objective size, the higher magnification scope will require greater lens curvature, increasing the likelihood of optical aberrations. Though that does not mean that one will range any better than the other. The Sidewinder 4-16 has a shorter length and smaller objective than the Sidewinder 6-24. So in that case, the 6-24@16x might indeed be "more crisp" than the 4-16@16x.

Not entirely following the conclusion.  Does this infer that a shorter tube will range better than a longer one?  Or just in relative proportion to the smaller, potentially clearer, objective lens?

[Scotchmo]

HFT does not allow focus range finding (AAFTA Hunter Division does allow focus range finding, but it is not HFT)

Imprecise wording on my part.  I was referring to AAFTA Hunter Division.  Thanks for clarifying.  More specifically, I'm personally interested in Hunter Piston for local competitions.

"The depth of focus decreases at higher magnifications, making it harder to range...."

As the depth of field declines, ranging becomes more precise, so higher magnification is better for that.

Stated that way, it does make sense as the two would follow.  Could be part of my problem in sorting this out in my mind, I've either mis-heard or understood that relationship.  What I may have been confusing is that (at least at 16x), I've been told that ranging accuracy via repeatable focusing is within a yard or two under 35 yards or so, becoming much greater past that distance, within only 5+ yards.  Which might be bridging beyond theoretical scope mechanics into the reality of the scopes of various price ranges.

Assuming scopes both have the same overall length, objective size, and same glass quality, I would say that the 16x@16x would have a clearer picture than the 24x@16x. For a given scope length, and objective size, the higher magnification scope will require greater lens curvature, increasing the likelihood of optical aberrations. Though that does not mean that one will range any better than the other. The Sidewinder 4-16 has a shorter length and smaller objective than the Sidewinder 6-24. So in that case, the 6-24@16x might indeed be "more crisp" than the 4-16@16x.

Not entirely following the conclusion.  Does this infer that a shorter tube will range better than a longer one?  Or just in relative proportion to the smaller, potentially clearer, objective lens?

My last paragraph above did not infer anything about ranging ability. When reading ShakySarge's statement about the 24x@16x being "more crisp" than the 16x@16x, you might get the impression that it's because you are not using the full magnification, when it's really because the 24x scope has a longer physical length, and bigger objective. That was about clarity and not range finding ability.

Something to remember about "focus range finding" - most scope parallax adjustments are not really intended as range finders. However, in most AO scopes, the minimum parallax and clearest focus usually agree (at least at closer distances). And you can make them agree even more if you put your own distance markings on the side-wheel. There might be a few FT specific scopes that market that ability, but in general, they won't because that is not what it's for in most any other non-FT application. So there is no emphasis on it and it's usually hit or miss depending on the scope design. Big objective lenses and more importantly, high magnification in a scope that focuses down to 10 yards seem at odds, but that is what you need.

These days, electronic range finders are readily available for a lot less $$$ than FT specific scopes. Outside of the sport of airgun Field Target, there is no call for expensive, short range scopes, that range find via parallax adjustment. The long standing FT rules have created a perverse outcome where FT people seek and expect scopes to be able to range find.

[dan_house]

What are the top factors in accurate ranging?

Practice.

IMO if you have a crappy scope you know how to use, understand its idiosyncrecies (spelling Im sure) and have been using it forever you'll do better than the shooter that has a big dollar scope he hasnt much time behind.

Quality gear only gets you so far, the rest is on you......

[rsterne]

Given a choice, a large aperture (objective lense) will have a brighter image, and therefore likely more contrast, particularly on a dull day or in shadows.... The pupil of your eye could easily be open as far as 4 mm under such conditions.... and at 16X, to get a 4mm exit pupil, you would need a 64mm objective.... Most scopes are 40 mm, 44 mm, or 50 mm, anything larger you will pay a premium price for.... A 50 mm scope set to 16X will have an exit pupil of only 3.1 mm.... While that is fine for a bright day, it could be struggling to provide the best image in low light situations....

Good glass and great coatings will help with both image sharpness and contrast, of course.... but they can't make up for asking a scope to provide more magnification than it's basic limitations.... The tube diameter has virtually nothing to do with image brightness, but it does make room for more adjustment.... I agree with Scott's summary to buy the largest objective scope, with the best glass and coatings, that you can afford.... I also agree that FT rules have warped our expectations somewhat....

Bob