Thermal Shading: Judging Distances At Night

Kirsch

Kirsch

Active member
I made the following post on a thermal scanner thread. I have talked about this often on PM and other sites. Since the topic is mentioned a lot, I decided to repost this as it's own Topic. I hope this helps.

As for judging distance besides how big they look in the scope another thing to watch is what I call "Thermal Shading". This means you can see subtle heat variations in different parts of the body of the coyote. A coyote loses heat through it's head and lower legs the most. When a coyote is all one color, on most thermals, it is past the shooting distance where you can hold right on your spot. Again, different thermals are different, this is a general statement. I can tell you the animal detail is so sensitive on the Super Hogster that I had to change my yardages a bit coming from a Pulsar XQ38 and then a Flir PTS536.

Here are 4 examples:
#1
coyote.5.jpg


#2
coyote1.jpg


#3
coyote2.jpg


#4
coyote3.jpg


Again, I feel the SH's 12 µm sensor hurts my examples here a little bit. In these 4 images, #1 you see virtually no shading. This coyote is around 400 yards. #2 you can start to see a little shading but it isn't prominent. The yardage on this coyote is around 325 yards. The yardage on #3 is at about 250 yards, and now shading is evident. #4 is about 150 yards. By the time, the coyote is at #4, there is no question it is in range.

How would I shoot these 4 coyotes? With my flat-shooting 22-250 zeroed at 1" high at 100. I would hold on the ears for coyote 1, right on the edge of the back for coyote #2, and hold right on where the brightest spot ends coming up the leg (this looks like the shoulder but it actually isn't) on coyote #3, and 4.

Everyone gets excited when coyotes are coming or we wouldn't hunt coyotes, but let them come. I am probably guilty of not doing this as you see I typically stop coyotes at around the 125 yard mark, Pace off every shot after you start thermal hunting and you will start to get a really good idea of how big a coyote looks in your scope at different distances. If in doubt let the coyote or coyotes continue the approach. The one time to stop a coyote is when they are coming in "hot". It takes them awhile to stop, so stop calling and start yelling or whistling, or bark, etc because often they will run right past. Another exception to letting them come is if they are going to catch your wind. Then stop them before they get there. When a coyote starts taking up a significant portion of your scope, you will know it is time to stop them.
 
Great post! I had several last night that I thought were closer than what they were. This helps give me a better frame of reference for judging those shots.
 
IMO this post is well worth being pinned to the top of the night hunting board so it doesn't get lost in the scroll and the increasing amount of new thermal hunters can easily find it .
 
Originally Posted By: FarmDadIMO this post is well worth being pinned to the top of the night hunting board so it doesn't get lost in the scroll and the increasing amount of new thermal hunters can easily find it .

Agreed! Who do we ask?
 
Another factor to consider in this equation is how much contrast and brightness is dialed in on the scope. Some people, like my hunting buddy, run way more brightness than what I like. That washes the picture out somewhat and makes the shading less discernable.

Below is an example of the same scene with the way the picture looks depending on how the scope is adjusted. The Thermion XP50 should be far better than the Apex XQ50 and would be if adjusted differently. After my buddy actually saw this video, he realized he needed to drop the brightness somewhat and also he is now shooting with the PIP at 8 instead of 16.



 
Originally Posted By: G AndersonKirsch, where does magnification play into this or does it at all? Gene It plays into it some. A high resolution image with a higher base magnification such as a Trijicon MKIII 60 or a Nvision Halo LR, the shading will most likely happen earlier at farther ranges.

However with my last 3 scopes including a Trail XQ38, Flir PTS536, and the Super Hogster, it is pretty spot-on, and actually I would put my Pulsar XP38 scanner in this group also. As I mentioned, the Super Hogster shows it earlier than some of my other scopes, but it still is pretty close.

If you are asking about digital zoom impacting, it is merely enlarging the base image, so if the base image isn't showing much shading, the digitally zoomed image will not either.

The size of the animal will be very different when zooming. This is another reason I rarely ever zoom my thermal scope. With the SH with a base mag of 2.9x and PIP of 5.8x, I am able to shoot to 400 yards pretty effectively, so there is no need to zoom.
 
Originally Posted By: DoubleUpAnother factor to consider in this equation is how much contrast and brightness is dialed in on the scope. Some people, like my hunting buddy, run way more brightness than what I like. That washes the picture out somewhat and makes the shading less discernable. 100% agree. There are things you can do with settings to impact it. This post is just to emphasize get to know your scope. Rangefinders are great. With enough time behind your gun/scope, a thermal coyote hunter can do quite well without one. However, if a person wants to have a rangefinder, it surely can't hurt.
 
DoubleUp .... I analyzed with the magnifying glass the part of the video recorded with the Thermion XP50. I give you a modest suggestion for improving vision, because, IMO, you are not using the Thermion XP50 to its full potential. On the bar with the blue icons, at the bottom of the screen, I don't see the rock symbol, nor the diamond symbol (which distinguishes the Image Detail Boost function in the on position). Try to set these 2 functions and you will surely see an improvement in the definition and contrast of the thermal image.
 
Originally Posted By: nr123Kirsch, thanks for the great info. I still have a hard time judging distance, but that info really helps a lot! It just takes some time. As I typically say, pace off every kill and guess the distance before you do it. See how close you get. Also, let them come as far as they will without winding you. We all get excited but if they get so close that they fill a good portion of your scope, they should be in range.
 
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