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WFTF Range Finding on dark lanes and targets  

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Cloud9AG
(@cloud9ag)
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2019-05-04 10:59:25  

At the recent Cajun Spring Classic, I struggled hitting targets at 35-55 yards on dark lanes shooting WFTF Springer.  With my Sightron 10-50x60 set at 50x, I could focus clearly on the target faceplate and feel like I accurately ranged it 95% of the time, but I only hit like 20% of those targets on Belle Terre.  There wasn't any wind that morning, and I was nice and stable with a gun shooting well.  I even checked my guns 25 yard and 55 yard clicks after the match ; they were both within my own error, so I don't believe the rifle was shooting differently that day.  

Any advice on hitting targets in the dark?

Jeff Cloud


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DonC
 DonC
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2019-05-04 12:00:10  

At 50X the target will appear darker than at 35 or 40X. You could check the distance at 2 different magnifications and see if they concur.


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Cloud9AG
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2019-05-04 12:14:50  
Posted by: DonC

At 50X the target will appear darker than at 35 or 40X. You could check the distance at 2 different magnifications and see if they concur.

I actually noticed the target was brighter at lower magnification, and I did check my ranging and they did agree.  It's almost like a dark target is just ranging differently because of my eyes or something, which is causing me to miss.

Jeff Cloud


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Rochester Field Target
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2019-05-04 12:35:52  

This seemed to be a hot topic this year.

Ranging dark targets will typically range differently than bright targets.

For example, a 55 yard target in dark conditions like last weekend will show > 55 on your scope. On my scope I would expect it to range 60 on the wheel, but be a 55 yard target. I would suggest setting up targets to range during daylight and dark conditions and see for yourself how your scope behaves.

Sean McD


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Cloud9AG
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2019-05-04 12:53:47  
Posted by: Rochester Field Target

This seemed to be a hot topic this year.

Ranging dark targets will typically range differently than bright targets.

For example, a 55 yard target in dark conditions like last weekend will show > 55 on your scope. On my scope I would expect it to range 60 on the wheel, but be a 55 yard target. I would suggest setting up targets to range during daylight and dark conditions and see for yourself how your scope behaves.

That is my plan, but it is hard to do when working 6 days a week lately.  I think it would be best to do it at dusk, but I would only get 10-15 minutes each day.

Jeff Cloud


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thomasair
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2019-05-04 15:29:14  

Try to range something other than the faceplate. Something shiny or light colored like a swivel or where the string attaches.  You can also use anything nearby that may have some light on it.  


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Cloud9AG
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2019-05-04 15:44:18  
Posted by: thomasair

Try to range something other than the faceplate. Something shiny or light colored like a swivel or where the string attaches.  You can also use anything nearby that may have some light on it.  

I was doing that during the match, Mike.  I could very clearly see the swivels, and the rivets in the eyes, and the paint chips, and everything.  This is the frustrating thing for me.  I felt extremely confident that I was ranging appropriately, and my gun was shooting well, but I was missing almost all of the longer targets.  I haven't been able to triage the problem yet, so I'm asking questions in areas where I have doubts (dark targets).  As an aside, all 3 of my shooting group (WFTF Springers) all had the same problems with long, dark targets.

Jeff Cloud


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GLPalinkas
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2019-05-04 19:16:12  

I found the same issues using my Hawke Sidewinder ED 10-50. Shooting Open PCP, I range at 40x. I range pretty consistently except I missed more than my usual share of targets past 45 yards at this year's Cajun Classic. I usually don't miss full size Kill Zones at 50 yards with no wind but the last day I missed 2 that cost me 2nd place. Something strange happens on those dark far targets. Has to be ranging issues. 


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thomasair
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2019-05-04 20:38:11  

I thought I might have been having ranging issues on day 1 when I shot on Lagniappe.  I missed one long shot on about every other lane or so.  I actually felt like I was shooting well...so I figured it must be due to me ranging poorly.  I could often see the shot I hit...and really wasn’t off...which really didn’t point to range.   I had no clue where the miss would go.  I thought about it that evening and recalled that the paper targets I was sighting in that morning were pretty shot up and that I had a hard time even finding about 1/3 of my shots at 55y.  I just chalked it up to pellets maybe landing in holes that were already there at the time.  

On Sunday morning I got up and decided to open a new tin of pellets and actually weigh out enough for the day plus some sight in.  When I got to the range...I first used the pellets from Saturday and shot at the painted plate at 55y.  15-20 shots produced a group about 1.25” high.  I shot the pellets from the fresh tin next and 15-20 produced a group around 1/4” high.  I was not holding for wind.  That was what I was expecting.  Sunday went well.  I saw most of my shots, too.  

I rather doubt that it was the weighing that made the difference, because I have specifically tested that previously and did not find it to make a very large difference on the pellets I typically shoot.  It did make a difference in vertical at 55y...but not 1”.  More like 1/4”.   So I could only reasonably conclude that I damaged my initial tin of pellets somehow or another along the trip. I had already loaded them into my soft pouch before we left Colorado...so maybe I squashed them or something in the car.  Who knows?

Initially diagnosing my Saturday difficulty  as ranging trouble seemed sensible...but it didn’t appear to be the real cause since I had no trouble on the even darker lanes of Belle Terre on Sunday.  I have also had trouble before on long targets on courses that had no lack of sunshine.  

I guess that’s the real trouble with FT.  It’s hard to really nail down problems while on the course.  Sometimes it takes days to figure out what went wrong.  It’s easy to go real deep down a hole chasing a problem that may actually not have existed.

Shooting a spring gun...you have a whole lot more variables to manage than us pcp folks.  

Your trouble could have been ranging...or possibly some other multitude of coincidences.  

I know nothing about shooting spring guns...other than you pretty much to adapt on the fly as they change.  I’m only parroting what I have heard from guys like Brad and Steve.

I feel your pain...and I hope you get to the bottom of this.  

Mike 

 

 


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thomasair
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2019-05-04 20:46:46  

One thing I forgot to mention.  If there is a stick, blades of grass, or weeds that are in the scopes  field of view nearer to me when I’m ranging..,I will come up short.  I guess my eye is drawn to the stick or whatever and it tries to blend the two ranges.

You might try setting up an experiment like that and see if that affects you like it does me.  I’m very careful to find positions in the shooting box that avoid things like that since I have figured that out.  

Mike  


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TerryVanpool
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2019-05-04 21:25:15  

Marie Laveau

 

Charter Member of "The Over the Hill Gang"


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Kidpellet
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2019-05-06 06:03:15  

Try putting a target with multiple fonts and font sizes out at 55 yards in the sun. Then find a large cardboard box to cover the target and give you whatever degree of darkness you want. Range the target in the sun then in the shade. Pay attention to how the different fonts come into focus, or don't come into focus. Also don't trust the focus without the "head bob" to confirm the paralax is correct.

That's my 2 cents anyway

Ray Barnett


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Hector J Medina G
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2019-05-06 11:20:34  
Posted by: Cloud9AG
Posted by: thomasair

Try to range something other than the faceplate. Something shiny or light colored like a swivel or where the string attaches.  You can also use anything nearby that may have some light on it.  

I was doing that during the match, Mike.  I could very clearly see the swivels, and the rivets in the eyes, and the paint chips, and everything.  This is the frustrating thing for me.  I felt extremely confident that I was ranging appropriately, and my gun was shooting well, but I was missing almost all of the longer targets.  I haven't been able to triage the problem yet, so I'm asking questions in areas where I have doubts (dark targets).  As an aside, all 3 of my shooting group (WFTF Springers) all had the same problems with long, dark targets.

Jeff and Mike;

We tend to forget that the last lens and stop in the optical train between target and retina is our own crystalline and iris.

The iris will work as s pin-hole condenser (lens) when subject to bright light, the crystalline adopts different curvatures when told by the retina that the intensity of the ambient light has reached a certain level. On top of that, the cones (high intensity receptors that react well to colors), and the rods (low intensity sensors that respond badly to colors) react differently, so that when the target is dark, the central area of your vision field does not respond as well as when the target is brightly lit.

We are all different (even the color of your eyes, that changes over time, will change this), so we each need to come up with a way out of this quandary and the best way is to experiment by/on yourself.

One possibility is to try to use your peripheral vision to focus on dark lanes, but that is not easy because we aren't used to it. It is not impossible, but it takes some practice.

Another is to have several ranging marks, but between that and the temperature changes and other factors, it can get complicated.

IMHO, the best course of action is to keep notes and learn from them what happens to YOU.

In my case, my scope yardage markers were specifically setup during overcast days (not hard in Maryland). So it was evenly lit, but not "bright sunlight". I know from experience that in very bright sunlight, the distance I measure with my scope will be up to 3 yards long, while in very dark lanes or days, the distance measured with my scope will range up to 3 yards short (I use 29X in my Sightron SIII) I try to remember to adjust for that.

Because the way the scope's lenses are made and the materials most used in scopes, the "daytime" color vision will always disagree with the "night vision" B&W. Perhaps as more and more ED glass is available and aspheric lenses become more prevalent, we will have better tools at accessible prices, but until then we need to learn and adapt.

JMHO

 

 

 

 

 

 

HM


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GLPalinkas
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2019-05-06 17:26:04  
Posted by: Hector J Medina G
....... In my case, my scope yardage markers were specifically setup during overcast days (not hard in Maryland). So it was evenly lit, but not "bright sunlight". I know from experience that in very bright sunlight, I will range up to 3 yards short, while in very dark lanes or days, I will range up to 3 yards long (I use 29X in my Sightron SIII) I try to remember to adjust for that.

Because the way the scope's lenses are made and the materials most used in scopes, the "daytime" color vision will always disagree with the "night vision" B&W. Perhaps as more and more ED glass is available and aspheric lenses become more prevalent, we will have better tools at accessible prices, but until then we need to learn and adapt.

JMHO

HM

Hector, The dark lanes were one thing. The biggest thing to me was that if you did miss-range the target, you could not see where it was hitting because almost all targets had reducers, unpainted reducers, so silver like the color of a later-in-the-match Kill Zone. I couldn't tell where I was hitting most of the time so couldn't rule in or out a ranging error. 
That's my excuse and I'm sticking to it...LOL

Gary
Venice, FL


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Cloud9AG
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2019-05-06 21:45:12  

Now that's a great idea.  And I can try it during the day. 

Jeff Cloud


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Cloud9AG
(@cloud9ag)
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2019-05-06 21:49:17  

Hector,

Yes i expect that my eyes were the biggest contributing factor, but I just wasn't aware how they affected my ranging.  I need to practice ranging at dusk and maybe also as described by kidpellet. If you range +/- 3 yards different then I could easily miss the target being off that many clicks. 

Do you range at 29x to try and get a brighter sight picture and replicate your overcast days used when setting up your scope?

Thanks for the good ideas in those last posts. 

Jeff Cloud


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thomasair
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2019-05-07 07:56:51  

Rays idea seems like a good one.  You might even put 2 setups side by side.

Here is some data about a 55y full kz and misranging.  The data is based on 2 clicks per yard at 55...which is pretty common.

You can see that misranging by 1-2 yards is not a huge deal.  3-4y is getting tougher...and past that the kz is getting much narrower...so your wind estimation is now very critical.   Couple this info with the fact that no rifle/shooter combo shoots a group at 55y that is the size of one pellet....and you can see how the effects get more severe. 

In the case of a 6y misrange where the kz is 100 percent smaller...a shooter with a weak hold and/or an inaccurate gun can still knock the target down occasionally.  A shooter with a perfect hold/rifle will never knock it down, but his percentages and allowance for wind error will be much greater at the misranges of 5y and less.

Range error percentage at 55y

1 yard=2 percent smaller 

2yards=7 percent smaller 

3yards=17 percent smaller 

4yards=33 percent smaller 

5yards=64 percent smaller

6yards=100 percent smaller

 

Mike


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Hector J Medina G
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2019-05-07 09:49:28  
Posted by: GLPalinkas

Hector, The dark lanes were one thing. The biggest thing to me was that if you did miss-range the target, you could not see where it was hitting because almost all targets had reducers, unpainted reducers, so silver like the color of a later-in-the-match Kill Zone. I couldn't tell where I was hitting most of the time so couldn't rule in or out a ranging error. 
That's my excuse and I'm sticking to it...LOL

Gary
Venice, FL

Gary;

Right now, we're discussing in the WFTF world a few things, ONE of them is to standardize colors for targets (they were already described, but no specification had/has been given). Of course you surely know that in  WFTF matches, generally, there are no "reducers", there are reduced size KZ's, but the whole faceplate is, usually, one piece.

IMHO reducers, in general, are a bad idea. They require much maintenance to really work well. I've seen reducers that wobble with the wind, reducers that swing like a bell, reducers that are not really circular KZ's once they get smacked by 20.8 ft-lbs PCP's at 10 yards (do the numbers with the AAFTA tolerance for MV), reducers that are like belleville washers, reducers that look like wave spring washers, and reducers that change the KZ position every time the target gets hit, whether it goes down or not. So, IN GENERAL, and I repeat IMHO, the are truly a bad idea.

Of course you can go to the length of adding two screws, then star washers, then paint them (in WFTC's it is illegal to place a reducer BEHIND the faceplate), or outright weld them, but as I said, they take much work to work.

To ME, reducers also point to the peculiar American habit of using tiny KZ's at short ranges. Some people like them, some not so much. It all depends if your emphasis of the game is on the gun or on the marksmanship. I used to hate them, now I just think they are bad ideas. LOL!

When you standardize to just three KZ sizes, reducers become a moot point.

Anyway, back to paints and colors: In Poland, the WFTF description of "light blue"  was interpreted by the Poles as Ocean Blue, not "light" in any way, and the misses during the cloudy days before the storm hit us, and especially the lip hits, were darned hard to detect. So I understand what you are talking about, it's frustrating and it can unsettle you enough to start missing shots out of lack of concentration. To see if this is the case, I usually go to the sight in-range after the match, and take a few shots, if they are dead on, it means I was not concentrating. My wife taught me a mantra: "The ONLY shot that matters is the next one". It helps me to stay in the present, forget the past and don't fret about the future. Which, in itself, is also a valuable lifestyle.

There are really good paints (the ones used to paint grass sports fields) that resist very well the pellets hits without a huge chip flying off, and there is a pale blue, so that is a good option. There is also the fact that the colors chosen were, in part, chosen to make the contrast between faceplate and kz, as relevant to the "color-challenged"  eyesight persons as it is for the majority of us, so, again, from the world of field sports (hockey among others), we get paints that are flexible and color valid for 99% shooters (there is a very specific type of color-blindness that is extremely rare, and that goes against all the other types, so correcting for one of the more common -about 1 in 8 persons are afflicted with at least one type-, will make it worse for the other two groups).

Unpainted reducers is not something that is covered in the AAFTA handbook, at least not in any way I can think of, but it is something that IMHO, should have been forewarned by the MD's. I am sure it was with the good intention of providing an extra " twist" and challenge the shooters, but it has been the source of problems in the past and if the Nationals are going to be held under the same "style", they should let us know well in advance. 

Thanks for the heads up! as this is really something so out of the ordinary as to warrant a request to AAFTA for revision PRIOR to the Nationals.

Keep well and shoot straight!

 

 

 

 

HM


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Hector J Medina G
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2019-05-07 10:10:55  
Posted by: Cloud9AG

Hector,

Yes i expect that my eyes were the biggest contributing factor, but I just wasn't aware how they affected my ranging.  I need to practice ranging at dusk and maybe also as described by kidpellet. If you range +/- 3 yards different then I could easily miss the target being off that many clicks. 

Do you range at 29x to try and get a brighter sight picture and replicate your overcast days used when setting up your scope?

Thanks for the good ideas in those last posts. 

Hello Jeff!

I use my scope at 29X because at that magnification, the MOA marks in the reticle become 1/2 Mrads. If you use the "bracketing" system as sanity check for your focus rangefinding, it helps to have to do the minimum of maths. HOPEFULLY, we will soon get a FFP from SIGHTRON (or somebody else) at useful FT magnifications that also gives us aspheric lenses made of HD glass.

SIGHTRON SIII FT scopes will only darken at beyond 43-45X. So if you want to use the magnification to make the amount of light detected by the eye more or less uniform, you would have to test and see where the border lies for you. SOME scopes have Irises in a sort of front lenscap, but those are not useful unless you want to increase your DOF substantially.
I have also tried two polarizing lenses that rotate in relation to each other to control the amount of light, but that is also very unrepeatable.

It was brought to my attention that my post about the ranging errors with different lighting levels seemed to be reversed, so I have corrected my post. Please do note the correction and do your own tests.

Keep well and shoot straight!

 

 

 

 

 

HM


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DonC
 DonC
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2019-05-07 12:43:18  

Hector,

Schmidt and Bender now has a First Focal Plane 10-50. They say it is not temperature sensitive like their first offering. I own their first offering and it is temperature sensitive. But the solution works perfect...….it's a adjustable pointer that allows you to calibrate for current temperatures. Then the scope ranges perfect. This adjustable pointer is made specifically for the Schmidt and Bender. I bought it from U.K. Maestro. He sells all kinds of adjustable pointers for various applications.

Anyhow, I agree that Sightron should offer FFP scopes. It seems like the Discovery brand are getting a lot of "good press and video coverage". Does anyone have a Discovery scope they use in competition?


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Cloud9AG
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2019-05-07 13:24:24  
Posted by: DonC

Hector,

Schmidt and Bender now has a First Focal Plane 10-50. They say it is not temperature sensitive like their first offering. I own their first offering and it is temperature sensitive. But the solution works perfect...….it's a adjustable pointer that allows you to calibrate for current temperatures. Then the scope ranges perfect. This adjustable pointer is made specifically for the Schmidt and Bender. I bought it from U.K. Maestro. He sells all kinds of adjustable pointers for various applications.

Anyhow, I agree that Sightron should offer FFP scopes. It seems like the Discovery brand are getting a lot of "good press and video coverage". Does anyone have a Discovery scope they use in competition?

holy crap!  $4000!!!

Jeff Cloud


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Scotchmo
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2019-05-07 14:03:13  
Posted by: thomasair

...a shooter with a weak hold and/or an inaccurate gun can still knock the target down occasionally.  A shooter with a perfect hold/rifle will never knock it down...

Mike

That's one of those instances where it's "better to be lucky than good".


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Scotchmo
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2019-05-07 14:08:23  
Posted by: Hector J Medina G
...

It was brought to my attention that my post about the ranging errors with different lighting levels seemed to be reversed, so I have corrected my post....

Thank you. From the earlier posts, I thought my eyes/scope might be different. Your corrected post agrees with what I've been seeing.

In the 50-55yd range, I'll focus range about 3 yards short under overcast skies. For closer distances it's not that bad. So it could be a % difference (about 5% ?).

I've read of others getting a ranging change with temperature. Maybe it's the infrared spectrum affecting focus ranging, and not just ambient temperature.

If it's ambient light that is affecting it, than maybe a low cost light meter or temperature gauge could be used to gauge the amount of correction. If it's the reflected light from the target, than a more expensive spotmeter.

In the past, I have used a temperature gauge to correct for known POI shifts, but I have not yet used one to adjust for ranging.


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Kidpellet
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2019-05-07 19:07:12  

I don't know fellas, I'm still new at this and still figuring out little things.

There's a lot of info coming through my scope and im still learning how to interpret it all.

The more patient I am with it the better I understand what I'm seeing.

It takes me an incredible amount of time to set my scope up and trust how what I'm seeing. (like 3 years now)

As far as the un painted reducers and dark targets go, I could see them fairly well and I found that at that particular venue a few seconds can make a lot of difference in lighting.

Under those trees it's pretty shaded but the sun is always shining through the leaves differently.

A little bit of light shines on the target for just long enough to aid in ranging and it could make all the difference. 

By the way, I am not using the most incredible scope anyone has ever seen lol.

The only problem I had was the rivets on the paddle, or lack of........lol

Ray Barnett


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Hector J Medina G
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2019-05-08 10:51:29  
Posted by: DonC

Hector,

Schmidt and Bender now has a First Focal Plane 10-50. They say it is not temperature sensitive like their first offering. I own their first offering and it is temperature sensitive. But the solution works perfect...….it's a adjustable pointer that allows you to calibrate for current temperatures. Then the scope ranges perfect. This adjustable pointer is made specifically for the Schmidt and Bender. I bought it from U.K. Maestro. He sells all kinds of adjustable pointers for various applications.

Anyhow, I agree that Sightron should offer FFP scopes. It seems like the Discovery brand are getting a lot of "good press and video coverage". Does anyone have a Discovery scope they use in competition?

Don;

SIGHTRON is a somewhat conservative company. It took some time to get them to put a usable reticle into their FT series and, for the last two years, we have been working on something that may offer a big advantage, but all changes are expensive, specially in the optics field.

FFP need a special geometry for the reticle, thin enough at 50X would be lost at 10X, and just thin enough at 10X is overpowering at 50X.

Additionally, current tolerances for the curvature of glass implies that you cannot RELIABLY make a FFP that goes beyond the 24X without substantial reject costs.

I have used Discovery scopes in "local"  competitions, mostly as Hunter/Piston division/class. The  Dragunov style reticle is a REALLY easy way to " "bracket".

If you look for the October 13, 2018 shoot results from BCSA:

http://www.bcsportsmen.org/ft/scores18.html  

You will see what I mean.

That shoot was the test of the VT-3 prototype, and it works real well, again, in AAFTA "Hunter-Piston". Where no focus ranging makes too much sense at 16X and, specially in ranges where there are targets that are INSIDE bushes that are UNDER trees, during a month of overcast skies. In that shoot, my sidewheel was completely blind, no marks.

Of course, it was a help that the National Champion of the Class had an "off"  day, but the scope performed exactly as designed.

At present, I am working with Discovery on refining some internal aspects of their VT-T that should make it more adaptable to FT shooting for open and WFTF. Specially the reticle is an asset for those of us that do not click.

Sadly, Discovery Optics is not widely known in the FT world, and it is not yet a trusted product. But the glass is good, and the tracking is reliable and consistent.
Everyone to whom I have given a 4-16X50  to test and compare say that it is a better scope than the AEON's and about on par with the Mid grades Opti-San's or Athlons. At about ½ the price.

If you want to test a 4-16X50, let me know.

Keep well and shoot straight!

 

 

 

 

 

HM


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Hector J Medina G
(@hector-j-medina-g)
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2019-05-08 10:57:49  
Posted by: Cloud9AG

Holy crap!  $4000!!!

Yup! as much as I like quality optics, it is on these occasions where I cannot but think badly of the current WFTF leadership that still clings to the prohibition of scopes equipped with laser rangefinding. There are now on the market some scopes that are perfectly suitable for airgun use at less than $500.

🤨

Ah, well . . . 

Keep well and shoot straight!

 

 

 

HM


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Hector J Medina G
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2019-05-08 11:06:39  
Posted by: Scotchmo
Posted by: Hector J Medina G
...

It was brought to my attention that my post about the ranging errors with different lighting levels seemed to be reversed, so I have corrected my post....

Thank you. From the earlier posts, I thought my eyes/scope might be different. Your corrected post agrees with what I've been seeing.

In the 50-55yd range, I'll focus range about 3 yards short under overcast skies. For closer distances it's not that bad. So it could be a % difference (about 5% ?).

I've read of others getting a ranging change with temperature. Maybe it's the infrared spectrum affecting focus ranging, and not just ambient temperature.

If it's ambient light that is affecting it, than maybe a low cost light meter or temperature gauge could be used to gauge the amount of correction. If it's the reflected light from the target, than a more expensive spotmeter.

In the past, I have used a temperature gauge to correct for known POI shifts, but I have not yet used one to adjust for ranging.

Sorry for the mix-up Scott.

Since light meters are not rifle mounted and if they were, they are not in the list of  "approved"  devices, being spotted spotting the light with the spotmeter would, for sure, either get you a penalty point(s), or an outright DQ.

I THINK that in SIGHTRON scopes the temperature issue is more a POA problem than one of ranging. I have not tested extensively other brands.

What does happen in the SIII FT is that the ranges will change with the intensity of light. That much is for sure. And I do know that in my case, it is somewhat linear but at around 6% all through the scale.

One more thing to keep track of.

😉

 

 

 

 

HM


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dan_house
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Posts: 78
2019-05-09 11:30:33  

Hector said:

"we have been working on something that may offer a big advantage,"

soooooo just tell me now, how much and who do I send the check to?

for me, the reticle is as important as range finding accuracy. IF you cant put a correct POA on the target, accurate ranging isnt that helpful.....

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On the Lunatic Fringe of American Airgunning
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drputz
(@drputz)
Joined: 1 year ago
Posts: 4
2019-05-14 15:35:41  
You might be overlooking some of the optical issues on ranging on dark days.  Optical ranging is similar to SLR/digital SLR photography and relies on being able to judge “circles of confusion”.  These are points of reflected light that turn into circles that the eye can detect as out of focus. The larger the circle, the easier to detect out of focus. There is a depth of field where an image is in acceptable focus, ala the circle of confusion is small enough we can't tell.  However, there is only ONE plane or focus point where the parallax is correct. 
 
On bright days with high power magnification, this depth of field can be rather narrow.  On lower magnification and/or darker days, this depth of field can grow quite wide – hence the handicap for US HFT folks at 16x.   Not only does the depth of field grow wider, our perception of the acceptable size of the circle of confusion grows larger.  Basically we are not as precise on the focus since there is less light to discern the focus circles.  This is one of the reasons why larger scope objectives are better.
 
If you follow the A-Team setup of the scope and use either the “front of the depth of field” or some other point in the center of the depth of field, you may be ranging wrong when the depth of field widens.  This in itself can cause errors, but I think that there is another issue at play.  When you are ranging wrong, your parallax will also be wrong.  With the larger and longer scopes, the focal length gets long – this gives us the precise focus we need.  However, when we are off, even by a smaller amount, the parallax can be off significantly.  The parallax error could be combined with the ranging/holdover/click and cause us to be off significantly.  Hence missing a shot due to the combined errors.
 
I found this out on the last match – my shooting partner also used the A-Team method to set up ranging, but went back and forth on the focus until he found the center of the depth of field, where I used the front part.  He ranged better than I, and scored better as well.  Lesson learned, but the hard way (as usual).
 
Dan

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GLPalinkas
(@glpalinkas)
Joined: 1 year ago
Posts: 75
2019-05-14 19:12:28  
Posted by: drputz
You might be overlooking some of the optical issues on ranging on dark days.  Optical ranging is similar to SLR/digital SLR photography and relies on being able to judge “circles of confusion”......
 
  With the larger and longer scopes, the focal length gets long – this gives us the precise focus we need.  However, when we are off, even by a smaller amount, the parallax can be off significantly.  The parallax error could be combined with the ranging/holdover/click and cause us to be off significantly.  Hence missing a shot due to the combined errors.
 
Dan

Good explanation Dan. I guess we both need more practice but I can tell you some of the targets at the Cajun were definitely darker than the ones I shot at NOA last year. Although, I have missed that far target in lane 1 (usually on the fallen tree) every single time I have shot at it. 0 for 4. LOL


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