Calculating distance through scope

[Roper]

I was watching a show on Wild TV and the fella was describing how to calculate object distance through your scope.
His scope of course had minute graduations marked on the vertical lower crosshair.

He said if you knew the measurement of a particular animal (for instance a whitetail) to be 20 inches (on average) from bottom of chest to top of shoulders then you measure that same area through the scope - how many minutes/graduations. Lets say it measures 6 graduations.

So you take the standard 20 in. and divide by the 6 minutes = 3.33. Multiply that by 100 and the distance is 333. I assume feet.
But I don't know how the scope power factors into the formula. If your scope is set at power 3, or set to power 7 - it would make a difference. Do you simply multiply the 333 by the scope setting?

ie: if the scope is dialed to power 3 then the distance is 333 x 3 = 999 ft. ?

Does this make any sense or am I just confusing everyone - including myself.

[Crash2000]

I found an easier way....buy a range finder. LOL

[trimmer21]

Judging distance accurately takes experience and practice. Some scopes have range finders on them,but,most are prohibitively expensive and only work on stationary targets. Range finders are indispensable for ranging trees,fence lines,stumps,anything that's stationary. Then,when game appears,you know what distance they're at in relation to those objects that you've previously established the distance.. That's where the range dots on a lower vertical reticle comes in handy.

[welsh]

But I don't know how the scope power factors into the formula. If your scope is set at power 3, or set to power 7 - it would make a difference. Do you simply multiply the 333 by the scope setting?

ie: if the scope is dialed to power 3 then the distance is 333 x 3 = 999 ft. ?

Nope.

This is actually a very accurate method of range estimation. The military has used it for years and army binos have a marked reticle for this purpose. The scope will be marked in mils (milliradians) and the basic rule is that one mil subtends one meter at a range of one kilometer.

Assuming a fixed magnification scope, the reticle will be marked according to that magnification level, and all you have to do is compare the size of the known target with the reticle markings and do the basic math -- no compensation for the scope power is required.

With a variable power scope, the reticle will be marked according to one of the magnification settings. If you change the magnification, you have to compensate. If the magnification doubles, then you have to double your calculated distance. Supposing a 3-9x scope, you do the math at 3x and come up with 200 yards ... but if the scope was dialed to 6x then the same sight picture would actually be 400 yards.

Clear as mud, I hope....

This might help:
http://www.bushnell.com/getmedia/e62...e.pdf?ext=.pdf

Google "mil dot reticle" and you'll get a zillion articles on this, I think.

[skypilot]

Yep. Mildot reticles or similar(EBR). Or you can simply buy a scope with the Mildot reticle, etc. in the FFP(first focal plane) and the reticle zooms with the magnification so you're good at all power settings.

I have used one for many decades and I kept notes on all usual field measurements. Rounds hay bales for example 5' x5'(big ones), round hay ring 36" tall, rural mailbox 7x7x18", car tag/license plate 6x12, fence post 48," harrow disc blades 16", etc.

If you have MRAD/MRAD reticle AND turrets AND FFP, ranging is done at any magnification and dialing or holdover is easy. Just take the 5' dia. hale bale the yote is standing by and it takes up the spacing in the reticle of 3 mils. So...a 5 ft bail is 1.524 meters x 1000 divided by 3 mils= 508 meters. OR 5 ft dia in yards is 1.6 then x 1000 then divided by the 3 mils =533 yds.

My SFP second focal plane scope is calibrated at 12 power(6-24x56mm)so all reticle measurements have to be taken at 12 power.

As mentioned there are numerous articles available, plus many people use the mildot and of course all scopes ship with good instructions on proper use, measurement, ranging, etc.

The trick is knowing the dimensions of common items like car tire diameters, farm equipment, fencing, anything likely to be encountered that can give you a quick range or one can simply use the animal, I use 11-12" on a yote for calcs, some use from feet to shoulder measurement.

[Roper]

Welsh - Skypilot - nice - I knew I would get accurate answers on this site.
Thanks

[line052]

Nailed it, and brought many memories of range estimation guides we had to learn in my early days before the CF got RF's. Hydro poles, memorizing people sizes at different ranges, associating vehicles and size relation to ranges, houses, barns all used to contribute to range profile…it’s a wonder how we hit anything at times. Wouldn’t know what to do without my range finder now…lol Then add in wind profiles as present thru bino’s at different ranges…especially valleys where the wind always presented challenges.

Yep. Mildot reticles or similar(EBR). Or you can simply buy a scope with the Mildot reticle, etc. in the FFP(first focal plane) and the reticle zooms with the magnification so you're good at all power settings.

I have used one for many decades and I kept notes on all usual field measurements. Rounds hay bales for example 5' x5'(big ones), round hay ring 36" tall, rural mailbox 7x7x18", car tag/license plate 6x12, fence post 48," harrow disc blades 16", etc.

If you have MRAD/MRAD reticle AND turrets AND FFP, ranging is done at any magnification and dialing or holdover is easy. Just take the 5' dia. hale bale the yote is standing by and it takes up the spacing in the reticle of 3 mils. So...a 5 ft bail is 1.524 meters x 1000 divided by 3 mils= 508 meters. OR 5 ft dia in yards is 1.6 then x 1000 then divided by the 3 mils =533 yds.

My SFP second focal plane scope is calibrated at 12 power(6-24x56mm)so all reticle measurements have to be taken at 12 power.

As mentioned there are numerous articles available, plus many people use the mildot and of course all scopes ship with good instructions on proper use, measurement, ranging, etc.

The trick is knowing the dimensions of common items like car tire diameters, farm equipment, fencing, anything likely to be encountered that can give you a quick range or one can simply use the animal, I use 11-12" on a yote for calcs, some use from feet to shoulder measurement.

[skypilot]

Line052, Amen on the RF. I still carry the old laser rangefinder for redundancy because I haven't the luxury of a second set of calibrated eyes on most outings.

I was always old school with Second Focal Plane, MOA turrets and mil dot for a few reasons, however I now use and recommend First Focal Plane reticles, matching turrets and the hash mark style EBR reticles are easier to get the overall height and lead.

Much less math too with the FFP/MRAD, and keeping everything in division by 10 makes it extremely simple and quick in the field.

[rippin_355]

It can also be done if your scope is marked in MOA, the math will just be different. First focal plane scopes were more popular in Europe but are gaining ground in North America. I love mine! You don't need a FFP you can range with a SFP on max power or where ever that particular scope is set for the elevation marks.

Yep. Mildot reticles or similar(EBR). Or you can simply buy a scope with the Mildot reticle, etc. in the FFP(first focal plane) and the reticle zooms with the magnification so you're good at all power settings.

I have used one for many decades and I kept notes on all usual field measurements. Rounds hay bales for example 5' x5'(big ones), round hay ring 36" tall, rural mailbox 7x7x18", car tag/license plate 6x12, fence post 48," harrow disc blades 16", etc.

If you have MRAD/MRAD reticle AND turrets AND FFP, ranging is done at any magnification and dialing or holdover is easy. Just take the 5' dia. hale bale the yote is standing by and it takes up the spacing in the reticle of 3 mils. So...a 5 ft bail is 1.524 meters x 1000 divided by 3 mils= 508 meters. OR 5 ft dia in yards is 1.6 then x 1000 then divided by the 3 mils =533 yds.

My SFP second focal plane scope is calibrated at 12 power(6-24x56mm)so all reticle measurements have to be taken at 12 power.

As mentioned there are numerous articles available, plus many people use the mildot and of course all scopes ship with good instructions on proper use, measurement, ranging, etc.

The trick is knowing the dimensions of common items like car tire diameters, farm equipment, fencing, anything likely to be encountered that can give you a quick range or one can simply use the animal, I use 11-12" on a yote for calcs, some use from feet to shoulder measurement.

[urbansherpa]

I used to do a lot of mountaineering and hiking. Here is a trick I learned years ago.

Stick your arm out in front of you and point your index finger at an object. Close one eye. Now, without moving your finger, 'switch' eyes. Estimate how many feet/yards/meters your finger moved. Multiply by ten and you have the approximate distance from you to the object.

Example: I'm sitting in my treestand and point at a buck across the field with my left eye closed. Now I open my left eye and close my right. My finger has moved about 20 yards. The deer is about 200 yards away!

The reason for this is because when you point your finger straight out ahead of you, it is ten times the distance of your interpupillary distance (distance between your pupils).

Not as accurate as a laser rangefinder, but better than guessing (and lighter and cheaper!)