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Author Topic: Scope DOF considerations.  (Read 292 times))

Offline Cableaddict

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Scope DOF considerations.
« on: May 05, 2021, 02:07:49 PM »
I'm posting this in the hunting gate, as it pertains more to application than to scope quality, etc. 

I'm considering a new scope, for pesting and short-range (typically sub 50 yards)  small game hunting.  I've done all the research and considered all the factors, and have decided that I like a fairly high magnification, as long as the eye relief and FOV are decent.  So I'm looking at two fixed prismatic (short eye reliefe / wide FOV) scopes,  10x30 and 12x50.    I really don't want to discuss the benefits of lower power in this thread, even though that argument can be made.  I like to go for head shots even at distance, plus the scopes in question have very wide FOV, which offsets the negatives.

--------------------------------

My main concern is depth of field,  and the need to constantly re-adjust for focus & parallax error.  The 10x30 will be better in this regard,  but I can't find any hard data on just HOW much of a difference there will be.  I typically pest as close as 7 yards,  which of course exacerbates the problem.

I'd love to get the 12x50 for 2 reasons:  Better light gathering at dusk & dawn,  and (due to the smaller focus window) it also works well as a range finder.
But again, I'm not clear on just how much more of a PITA it will be when quickly switching target distances.  (I've only even used my 3-9x32 bug buster)

The 10x30 is a bit marginal in both light gathering and exit pupil size,  but probably good enough, would have a wider focus range (but again, how MUCH wider?)  and costs a lot less $$$.

---------------------------

One possible way to go:   Get offset iron sights, and use them for anything closer than 20 yards, then enjoy the light gathering on the 12x50.
(Or just make the physical adjustments when close-pesting.)

Another way to go:  Get the 10x30, and then get some kind of lighting system to aid in dusk / dawn shooting.


Any and all thoughts would be much appreciated.
« Last Edit: May 05, 2021, 02:22:09 PM by Cableaddict »
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Offline KevinJBrown

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Re: Scope DOF considerations.
« Reply #1 on: May 05, 2021, 02:24:20 PM »
Lots of things going on. Probably the biggest thing that you haven't mentioned and still the most important is the quality of the glass.

But, assuming the glass is equal, can you get these scopes to look through in the conditions you are talking about shooting in? IMO 10X is plenty of magnification at sub 50 yards unless you are hunting really small critters.

Another advantage of the 30 mm scope is it would mount closer to barrel CL.
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Offline Cableaddict

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Re: Scope DOF considerations.
« Reply #2 on: May 05, 2021, 03:01:55 PM »
Another advantage of the 30 mm scope is it would mount closer to barrel CL.


That's a good point.  Close-range shooting benefits greatly from a lower scope-center.

Again, using offset iron sights for sub-20 yards would help, but I'm not crazy about that idea.

---------------------------------

Hmmm....  thinking on it more,   this may not actually be a significant factor with a bullpup: 
Due to the high cheek area, one has to mount the scope extra-high, anyway.   So, would the bore center - to - occular center really be much different, between the two scopes?  I suspect that they would be the same, with the 50mm simply requiring shorter rings. 

-  But I'm not sure, I can't quite wrap my head around this.   
« Last Edit: May 05, 2021, 03:18:29 PM by Cableaddict »
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Offline JimD

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Re: Scope DOF considerations.
« Reply #3 on: May 05, 2021, 05:40:51 PM »
I agree lower mounts reduce the necessary hold over at close range but I would play some with a trajectory calculator if you haven't already to see how much difference it actually makes.  I like medium rings and would use lows if I could but I was surprised recently at the relatively small difference high rings would make.  They actually allowed a longer zero range for my limit of +- 0.25 inch shift in POI.  But they did make things a little worse at really short range. 

I have a Hawke Vantage 2-7 on my Prod.  It adjusts parallax at the objective lens.  I have a Primary Arms 4-14 on my Avenger and it adjusts on the side near the elevation and windage knobs.  The side adjustment is more convenient but not hugely IMHO.  An advantage of the objective location is more leverage.  But you can put a big wheel on the side adjustment knob and add more leverage.  You did not mention which style you are considering but I think how you make the adjustment is also something to consider.
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Offline Cableaddict

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Re: Scope DOF considerations.
« Reply #4 on: May 05, 2021, 07:02:34 PM »
I agree lower mounts reduce the necessary hold over at close range but I would play some with a trajectory calculator if you haven't already to see how much difference it actually makes.   

Good point, so I just did.  It does make a huge difference if you need to shoot as close as 7 yards.  (See below.)  But again,  I think that with a bullpup, you are going to mount the scope as low as you can and still be comfortable when using the available "cheek rest area."  - And so, the CENTER of a 30mm scope may end up at the same distance-from-bore as the center of the 50mm.

The left numbers are for my 32mm bug buster, with a 21 yard zero,  mounted as low on my bullpup as I can stand. 
The right numbers would be for a 50mm scope, mounted with its bottom at the same height as the bottom of the bug buster.  (But again, why would you ever do that? )
« Last Edit: May 05, 2021, 07:13:56 PM by Cableaddict »
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Offline Cableaddict

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Re: Scope DOF considerations.
« Reply #5 on: May 06, 2021, 02:46:30 PM »
So can no one comment on the "useable" DOF differences between two scope in these two size ranges?

That's what I'm asking about.
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Offline mobilehomer

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Re: Scope DOF considerations.
« Reply #6 on: May 06, 2021, 03:23:39 PM »
Generally speaking, the higher the magnification, the shallower the DOF. I don't believe there will be much difference between 10 and 12 power. However, the 10 X 30 will have a 3 mm exit pupil. The 12 X 50 will have a 4.17 mm exit pupil. The 12 X 50 will have a MUCH brighter view at dawn and dusk than the 10 x 30.
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Offline KevinJBrown

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Re: Scope DOF considerations.
« Reply #7 on: May 06, 2021, 04:52:57 PM »
So can no one comment on the "useable" DOF differences between two scope in these two size ranges?

That's what I'm asking about.
Useable includes the quality of the optics, and the intended use. Your intended use is hunting. So without specifics of the scopes, you're asking a question people can't answer. Without those specifics, the easiest way for you to answer the question for yourself is to get at least one of the two scopes and see what your results are. You are talking about hunting, not putting an image on a screen or media (which is when depth of focus is really important).

What type of game are you shooting at 7 yards? Birds and mammals look HUGE through a 10X magnification. I can pick which hair I'm shooting at. I really don't like to take shots that close. My scope doesn't focus that close, so I'm looking at a somewhat blurry image, but it really doesn't matter. I can turn my magnification down, miss by a bunch in my opinion, and still be well within a squirrel or rabbits or birds vitals (or headshot).
« Last Edit: May 06, 2021, 04:58:59 PM by KevinJBrown »
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Offline Back_Roads

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Re: Scope DOF considerations.
« Reply #8 on: May 09, 2021, 10:03:28 PM »
 Here might be a good option I have some of their older style that just had rails for added sights etc.
https://www.opticsplanet.com/ncstar-gen3-uss-3-9x40mm-p4-sniper-riflescope-w-red-micro-dot-optic.html
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Offline Cableaddict

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Re: Scope DOF considerations.
« Reply #9 on: May 09, 2021, 11:26:35 PM »
Here might be a good option I have some of their older style that just had rails for added sights etc.
https://www.opticsplanet.com/ncstar-gen3-uss-3-9x40mm-p4-sniper-riflescope-w-red-micro-dot-optic.html


That's an intersting design. The scope is a bit too cheap for what I want (And not prismatic, either)  but I love that they made a combination scope.

Someone should do that but with the red dot on the bottom, since it would obviously be used for short range and thus needs to be as close to the barrel as possible.

I think we are going to see a lot of interesting developments in scope / sight technology in the very near future. 
Heck, we're probably not far away from a mini camera mounted to the barrel,  wirelessly transmitting to a heads-up display goggles. No ocular at all. 
-  And automatic hold-over and focus adjustments, to boot.   


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Offline JungleShooter

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Re: Scope DOF considerations.
« Reply #10 on: May 10, 2021, 12:18:06 PM »
DoF is affected by several factors.

🔶(1) 
You'll find that the DoF is much shallower at closer ranges, i.e., you might have to move the parallax turret a lot to adjust your focus from 10 to 11 yards, but not at all from 40 to 41y.


🔶(2)
The larger the aperture, i.e., the objective lens, the shallower the DoF, and the more you'll need to adjust the parallax.


🔶(3)
For that reason (and to reduce mirage if you ever shoot that far), some companies are offering objective lens reducers, that are really overpriced washers: discs with hole in them that scew in where the sun shades screws in.

▪They reduce the objective lens diameter and thus increase the DoF.

▪They also reduce the brightness of the image, but hey, when it gets darker you just take out the reducer beats buying two scopes and switching between them.... 😄

▪They also reduce the exit pupil which reduces the "eye box" that hard to define "box" that your eye has to be in for it to perceive a full scope image without darkened edges.

▪These are called whatever: objective lens reducer, aperture reducer, mirage caps, March calls theirs a "modifier disk."
One guy that makes them:
http://www.kreativ-solutions.com/mirage-caps.html

▪DIY: I supposed you could just buy a UV photographic filter of the right size, and paint part of it using spray paint and a stencil; or just tape the stencil on the filter, then you can switch them out as desired.
Or you could drill a hole in a spare scope cap. 😊


🔶 (4)
I hear you! Taking rushed close shots gets a bit complicated with having to mess with parallax and holdover.
The offset iron sights are are good idea. For a similar application I'm just pricing laser sights for those close range rushed shots.

Of course, if you went with a variable magnification scope you could just dial down the magnificaton to 3x or 2x and that quarry at 7y might still be pretty much in foucs even though you had the scope focused at 30y.


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Offline Cableaddict

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Re: Scope DOF considerations.
« Reply #11 on: May 12, 2021, 12:38:07 PM »
Bumping this.

I REALLY need some opinions here, folks.   I can't believe no one has weighed in on my specific question.

I did find out that the 12x50 has it's center just a hair higher off the bore than the 10x30,  so that's a consideration, but the difference apears to be less than 1/4",  so not a HUGE factor.

So again:

10x30 or 12 x 50?   (remember, they both have an extremely wide FOV, so that's no a factor, just DOF adjustments.)

Help a brother out !    :D
« Last Edit: May 12, 2021, 12:40:30 PM by Cableaddict »
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Offline KevinJBrown

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Re: Scope DOF considerations.
« Reply #12 on: May 12, 2021, 01:13:20 PM »
Can you give us the specific scopes you are considering? Also the specific range you will be focusing at? Help us out please.
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Offline mobilehomer

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Re: Scope DOF considerations.
« Reply #13 on: May 12, 2021, 04:52:38 PM »
One more time, read this, my post #6, I think it DOES answer you.

Generally speaking, the higher the magnification, the shallower the DOF. I don't believe there will be much difference between 10 and 12 power. However, the 10 X 30 will have a 3 mm exit pupil. The 12 X 50 will have a 4.17 mm exit pupil. The 12 X 50 will have a MUCH brighter view at dawn and dusk than the 10 x 30.
« Last Edit: May 12, 2021, 04:54:42 PM by mobilehomer »
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Offline Cableaddict

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Re: Scope DOF considerations.
« Reply #14 on: May 12, 2021, 09:12:58 PM »
One more time, read this, my post #6, I think it DOES answer you.

Generally speaking, the higher the magnification, the shallower the DOF. I don't believe there will be much difference between 10 and 12 power. However, the 10 X 30 will have a 3 mm exit pupil. The 12 X 50 will have a 4.17 mm exit pupil. The 12 X 50 will have a MUCH brighter view at dawn and dusk than the 10 x 30.


Thanks,   but that's the stuff I already knew. 
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Re: Scope DOF considerations.
« Reply #15 on: May 12, 2021, 09:15:33 PM »
Can you give us the specific scopes you are considering? Also the specific range you will be focusing at? Help us out please.


Kevin, both things are right in the second paragraph of my first post.

The actual brand of scope doesn't matter, which is why I didn't mention it.  (MTC SWAT, most likely)
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