Rifle Scopes How does one get most field of view from a scope?
- Thread starter russkim04
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Lots of things, there’s also angular FOV and linear FOV. tube length, magnification, objective size All play a part.
Think of it as looking through a paper towel tube and a toilet paper tube. The longer one has a smaller FOV. The TP tube is shorter and fatter (small tube big objective). now increase magnification and you are effectively making the tube longer thus lowering FOV
At the same magnification, the field of view in a riflescope is predicated by the size of the eyepiece. The objective lens creates an image in the first focal plane that is the size of the internal diameter of the riflescope tube. The erector tube will only look at a portion of that image, further reducing the FOV right there. At that point, as you adjust the magnification by twisting the zoom lenses in the erector tube, the image at the back of the erector tube is has the FOV reduces as the magnification increases. At that point, the image formed at the back of the erector tube, the second focal point, is presented to the eyepiece further reducing that FOV. For the same diameter of eyepiece, you can have larger FOV or longer eye relief.
Some riflescopes come with larger diameter eyepieces presenting a wider FOV at the same magnification and eye relief distance as ordinary eyepieces. For instance, the March-FX 4.5-28X52 HM WA has a larger eyepiece that provides a 25% increase in FOV over the regular size eyepiece, at all magnifications. They also have a 5-42X56 with similar increases and the March Genesis 4-40X52 and 6-60X56 also sport the wide angle eyepieces.
Some riflescopes come with larger diameter eyepieces presenting a wider FOV at the same magnification and eye relief distance as ordinary eyepieces. For instance, the March-FX 4.5-28X52 HM WA has a larger eyepiece that provides a 25% increase in FOV over the regular size eyepiece, at all magnifications. They also have a 5-42X56 with similar increases and the March Genesis 4-40X52 and 6-60X56 also sport the wide angle eyepieces.
Hunting with low side of variable power scope to get maximum field of view. Field being key word
Trade off between weight and size. But remember a rifle scope is not a spotting scope.
March has been introducing their Wide Angle fast focus eyepieces on their new scopes such as the 4.5-28X52, the 5-42X56 and their Genesis series.
I don't know why other makers don't do that.
You can see the difference in FOV in this thread.
Rifle Scopes - New March-FX 4.5-28X52 HM WA
Here is a picture of the new March-FX 4.5-28X52 HM WA scope that was discussed here a while back. I mounted it on FTR Match AR-15 and took it shooting. This copy has the FML-PDK tree-type reticle. As is my wont, I have sunshade, the fast lever, the middle focus wheel and the March flip caps...
www.snipershide.com
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Redfield had one out YEARS ago where the eyepiece looked like a TV screen, much wider than taller. I don't know if it's still made today.
Be careful. I don't think that's what we are discussing here. I had a Japanese Tasco 4X which I bought maybe 40 years ago and it also had a view through the eyepiece that looked like a TV screen; it was rectangular. The reticle died about 10 years ago and I pulled it apart. I had known for a long time that it was not any wider than all the other scopes of similar magnification. What I found was a rectangular cut out and the reticle was a pair of wires pasted on the cutout. One side of the vertical wire had detached.
What the essentially did is obscure the top and bottom of the image along with the sides to make it look like a rectangle and give the impression it was a wide screen scope. In actuality, the scope had a much smaller image, but it was a fun, cheap scope. I probably have it here somewhere in pieces. I'm sure the Redfield is the same way.
Does the larger ocular lense have any effect on the apparent brightness of the image? I'm not schooled in optics, but it seems like a larger lens might result in a slightly dimmer image.March has been introducing their Wide Angle fast focus eyepieces on their new scopes such as the 4.5-28X52, the 5-42X56 and their Genesis series.
I don't know why other makers don't do that.
You can see the difference in FOV in this thread.
Rifle Scopes - New March-FX 4.5-28X52 HM WA
Here is a picture of the new March-FX 4.5-28X52 HM WA scope that was discussed here a while back. I mounted it on FTR Match AR-15 and took it shooting. This copy has the FML-PDK tree-type reticle. As is my wont, I have sunshade, the fast lever, the middle focus wheel and the March flip caps...
Actually that would be the other way around as the scope is transmitting more image to your eye.
The reason the image dims when you increase the magnification is that your are viewing a smaller portion on the image, so instead of getting the light from 20 square feet of target (for example,) you're only getting the light from 3 square feet but viewed closer so that the 3 square feet looks the same size as the 20 square feet image in the reticle. With a wide angle eyepiece, the image will be 4 square feet (and the original would be 25 square feet, not 20.) The bigger the lens the more light goes through it.
WARNING: The area of an image has a square in the equation (Pi* R squared) and I did not computing to come up with these numbers.
The reason the image dims when you increase the magnification is that your are viewing a smaller portion on the image, so instead of getting the light from 20 square feet of target (for example,) you're only getting the light from 3 square feet but viewed closer so that the 3 square feet looks the same size as the 20 square feet image in the reticle. With a wide angle eyepiece, the image will be 4 square feet (and the original would be 25 square feet, not 20.) The bigger the lens the more light goes through it.
WARNING: The area of an image has a square in the equation (Pi* R squared) and I did not computing to come up with these numbers.
I am a big fan of 40x's mag I can see my target clearly , my misses on the ground in front of the target if there is any be hind the target left or right of it and still see the wind flags and grass and trees behind and around that could be blowing and what the mirage is doing , yea you can get a better view of other stuff at lower powers i could turn it down to 10 power and watch people shooting at the 300 yard target , but why . I am unsure of what more I could need to see to make me go to a lower power , heck I've only ever had to go to 30x's one time in two years .
The dimming due to increased magnification I understand pretty well. What I'm wondering about is if the image is ever so slightly dimmed by being projected across the area of the larger ocular lens, regardless of the magnification. For instance, imagine a movie projector placed 1 foot from a screen - the image there would be small, but very bright. Move the projector back 50 feet, and the image would be much larger but not as bright. Besides the obvious exaggeration, is my analogy incorrect?
And interesting question and it shows that you are thinking about. However, I believe your analogy is flawed. In your example, the projector would be equivalent to the target. If the target was 1 foot away, that would be like shooting at a target 1 foot away. And that's not what we are doing.
You have to remember that a riflescope has 3 major parts: the objective lens group that creates the FFP image, the erector assembly that magnifies the FFP image and forms the SFP; and the eyepiece, an afocal lens system that transmits the SFP to your eye, which then focuses the image on your retina.
You have X amount of light coming to the FFP. You have X*Y% light going from the FFP to the SFP depending on the magnification used. You then have (X*Y%)*Z% light sent from the SFP to your eye. The z variable is proportional to the eyepiece. The larger the eyepiece lens, the bigger Z is and I submit that the image from the eyepiece has overall more light in a wide-angle version compared to a normal sized eyepiece.
Great discussion and I am happy to be corrected.
I'm so very much *not* an optics expert..... but doesn't the apparent brightness of the image have more to do with the "exit pupil" size rather than the size of the eyepiece?
similarly, I would have thought that the field of view wouldnt be too reliant on eyepiece size being that usually the image being projected through it is so much smaller (eg 3mm exit pupil, how much difference will it make if the eyepiece is 10mm or 100mm? the eyepiece set for our astronomical telescopes seem to have the lens diameters not much bigger than their exit pupil sizes - or is this more a factor of the way precision ground lenses are made?)
similarly, I would have thought that the field of view wouldnt be too reliant on eyepiece size being that usually the image being projected through it is so much smaller (eg 3mm exit pupil, how much difference will it make if the eyepiece is 10mm or 100mm? the eyepiece set for our astronomical telescopes seem to have the lens diameters not much bigger than their exit pupil sizes - or is this more a factor of the way precision ground lenses are made?)
Well, I'm not the guy to correct anyone when it comes to optical formulas! I honestly don't entirely follow what you are describing, so I'll just take your word for it.
I didn't think it was a very significant issue in any case. I can't imagine March would develop a new feature if it didn't provide a real overall increase in the scope's performance. IMHO, they are one of the most innovative scope-makers in the world and their products are always impressive.
Here is a pictorial that I created to show the difference viewing through a regular eyepiece and a wide angle eyepiece.
I discussed this in detail in this post:
www.snipershide.com
As you can see the target is at the same magnification in both pictures, but the FOV of the 4.5-28X52 is a lot bigger and it's definitely not any darker. Then again, these are Smartphone pictures taken by hand so the quality is iffy, but it does show the concept of a wide angle eyepiece.
I discussed this in detail in this post:
Rifle Scopes - New March-FX 4.5-28X52 HM WA
Here is a picture of the new March-FX 4.5-28X52 HM WA scope that was discussed here a while back. I mounted it on FTR Match AR-15 and took it shooting. This copy has the FML-PDK tree-type reticle. As is my wont, I have sunshade, the fast lever, the middle focus wheel and the March flip caps...
www.snipershide.com
As you can see the target is at the same magnification in both pictures, but the FOV of the 4.5-28X52 is a lot bigger and it's definitely not any darker. Then again, these are Smartphone pictures taken by hand so the quality is iffy, but it does show the concept of a wide angle eyepiece.
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I’m not sure comparing a scope with 10x on the bottom and 4.5x on the bottom is even a remotely Fair comparison even with the wide angle eyepiece. There’s no way to know you are actually at 10x on the 4.5. The markings on the scope can’t be trusted. Plus, the objective is smaller on the 4.5, all the special eyepiece is doing is making up for that deficiency. I’ll submit its a little wider, but it doesn’t make March scopes special. They also probably use their special ocular to overcome the eye relief from a large magnification optic with a small objective.Here is a pictorial that I created to show the difference viewing through a regular eyepiece and a wide angle eyepiece.
View attachment 7466793
I discussed this in detail in this post:
Rifle Scopes - New March-FX 4.5-28X52 HM WA
Here is a picture of the new March-FX 4.5-28X52 HM WA scope that was discussed here a while back. I mounted it on FTR Match AR-15 and took it shooting. This copy has the FML-PDK tree-type reticle. As is my wont, I have sunshade, the fast lever, the middle focus wheel and the March flip caps...
As you can see the target is at the same magnification in both pictures, but the FOV of the 4.5-28X52 is a lot bigger and it's definitely not any darker. Then again, these are Smartphone pictures taken by hand so the quality is iffy, but it does show the concept of a wide angle eyepiece.
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This is exactly why I specified the specific riflescopes and did not make a blanket statement. In the pictures I tried like heck to make sure the apparent magnification was the same for both riflescopes. That is why I show the image through the scopes as well as around the scopes. If you see a sizable magnification difference between the two images, please let me know as I don't see one.
The white circle in the 4.5-28X52 is an artifact I created in PP where I made a circle inside the eyepiece of the 10-60X56 and then layered it on top of the other eyepiece and centered it as best I could. With that, I see that the radius of the eyepiece image is 30-35% larger on the 4.5-28X52 compared to the one on the 10-60X56. Again, this is done by hand and eye, no instruments. But then again, when you're looking through a scope, you're not using instruments, only your Mark 1 eyeball.
That said, I have compared the view through the wide angle eyepieces on the March-FX 5-42X56 and the March-FX 4.5-28X52 with various other scopes set to similar magnifications and I will disagree with your statement that they do not make the March scope special, because to my eye and the folks who did the same comparisons, they do make the March scopes special.
