Mirage and it's effect

[Tim N]

Hi All,
Must have too much time on my hands
I was thinking about how shooters talk about using mirage as an indicator for "what's going on"down range, even some say they watch it more than the flags.(Maybe only crazy people give me advice?)
My question: what is the depth of mirage seen through a scope?
If my scope is focused at 1000yd and mirage is visible from 900 to 1000yds, only a guess, thats only 10% of the equation and so not a big factor.
Any thoughts?

[AlanF]

Tim,

I've often heard it said that you should focus short of the target to see what's happening closer to you, and that focussing on the target only gives you the mirage at the target. I think this is wrong. Sure, focussing short will change the appearance of the mirage, and often accentuate it and make it more readable, but if you're still reading it against the target as a background (or something else near the target), then it can only be giving you the total mirage effect from shooter to target. Of course, if you look at a closer object, e.g. a mound midway between you and the target, then the mirage will indicate what is happening between you and that mound. Again, shortening the focus is likely to help.

In my opinion, the flags are the main game, and when I go to a new range, I'll only believe the mirage after its proven itself to be reliable. Sometimes mirage can be used simply to indicate that there has been some sort of change, and you need to have good look at the flags to see what it is!

Alan

[DaveMc]

Tim, Very few people know what is truly going on in the image. I am certainly no expert but do listen carefully to someone that knows a lot about optics and imagery. According to him Alan is once again on the right path. Even though we are focused at the target and only have a small depth of focus you are still looking through the whole range of mirage. A simple way to demonstrate this is barrel mirage. The image in scope indeed goes very hazy but you can blow it away with a quick puff.

I guess the mirage we are looking through but out of focus has an effect but the image is dominated by the "in focus stuff". For Raton we specifically designed some scope/eyepiece combinations for coaches that had a huge depth of field. These gave remarkable mirage images and you could clearly see the change in near mirage and confusion when both ends of the field were at odds. It is much harder to determine/differentiate in a rifle scope.

Whenever there is mirage I use it heavily as my main indicator but also always do a flag check (after all mirage can disappear quickly). For best input you need all the indicators you can - not just focusing on 1 flag but all the way down the range as well as trees/grass and mirage. It takes training and time to develop a routine to quickly check all in a sequence and remember what was going on in previous shots or make a whole new call. A type of memory training I guess - and time on the mound is the best way to get it. - Not just when you are shooting but watch the other shooters as well.

[johnk]

I once had the opportunity to look through one of the big Unertl spotting scopes while shooting Match rifle at Lower Light. Set at 1100 metres, that scope gave sharp focus from the 1000 metre mound forward but the mirage looked no different in effect than through my rifle or spotting scopes. It just made it look like liquid snot - what a superb bit of glass.

[bruce moulds]

using a spotting scope, I have moved the focus back and forward, and found this.
at the target end, the mirage was running one way, and back closer it was going the other way. this says that the scope focused on the target is not telling the brain the total story - kind of like a politician's lying by omission.
using both scopes at the same time can have merit.
the flags tell the story, but can be later telling it than mirage.
if the flags have not shifted, but the mirage is altered, something has changed - time to reappraise, even if it is only to wait.
individual ranges have differing habits and requirements.
keep safe,
bruce.

[DaveMc]

High quality glass certainly makes the images clearer but does not necessarily give the best mirage image (depending on scope specifications - focal length, objective diameter (f ratios) etc. Some of the best mirage images I have seen have come from converted bushnell and kowa spotting scopes with relatively large f ratios and high quality eyepieces.

BUT not only do images differ greatly with different "F ratios" (ratio of focal length to objective diameter) and glass quality, power etc but peoples opinions on what they like to see do too. Some TR shooters used to 15-20 power, huge depths of field will not appreciate the "intense" high powered, shorter focal length images from some other scopes. Conversely F classers used to mirage images magnified at 30-50 power might not like the image seen through the lower power spotting scopes. It can be completely personal preference and what you are used to interpreting.

I am often told there is a general push from scope manufacturers to shorten the focal length to satisfy the market. Large diameter, high quality objectives (fluoride coated) with short focal lengths (for compactness) can present fantastically clear images but possibly at the sacrifice of focal length.

It would be an interesting survey (especially amongst coaches) as to personal preference.

For me it is around 32 power with long focal length and good quality glass. My current scope can be set at the 300-400 yard line and clearly see the target lines and also in focus grass back to 7-800 yards when sitting at 1000.

Bruce (interesting discussion)- of course it is also feasible for wind to be moving in opposite directions at each end of the range. A fish tailing head/tailwind will often show this in mirage as the change moves down the course. Some ranges get "back eddies" behind the tree line (or other obstructions) as well that come and go quickly and have to be watched carefully. "dust devils" and other swirling winds can all cause this effect. BUT the often discussed issue of a focal point behind or in front of the target when using the target as your backdrop for mirage. Can this reverse the image and give you a false indication?? ????

[johnk]

BUT the often discussed issue of a focal point behind or in front of the target when using the target as your backdrop for mirage. Can this reverse the image and give you a false indication?? ????

I wondered that too. It should be readily demonstrated.

[bruce moulds]

I have heard of focal point behind the target offering opposite mirage readings, but have never chased that line of thought, preferring instead to focus on my side of the target.
it has proven beneficial on some occasions to shoot using a spotter and the rifle scope, but other times it makes no difference.
it is a bit of a pain running an extra scope, and would be more so with a dual port action.
I am sure a long depth of focus would be an advantage in this issue, although moving a narrow depth of focus up and down the range can be quite interesting at times.
keep safe,
bruce.