SIGforum.com    Main Page  Hop To Forum Categories  Mason's Rifle Room    Riflescope primer (Added FOV pictures 9/28/2020)
Page 1 2 3 4 5 6 7 8 9 
Go
New
Find
Notify
Tools
Reply
  
Riflescope primer (Added FOV pictures 9/28/2020) Login/Join 
Member
posted Hide Post
This past weekend I shot in the rain-shortened 1000 yard match. I wanted to get some rounds downrange to verify the setup before the state match in a couple of weeks.

As it turned out the elevation was dead on, as expected and windage was a bit off, but that understandable as I did not put the other scope back to "no wind" zero before shooting the two rounds on the tall target, and the wind on Sunday was fairly intense and if the other direction from the settings. Nevertheless, I was in the black in a couple of shots and shooting 10s and Xs until I started shooting for record. After my initial X, one-on, the wind just kept up a crazy dance ahead of the big Texas rainstorm that dumped on us a little later.

I did notice that I could see the reticle quite clearly and I'm very happy with the decision to change the reticle and the selection I made.

Next up, I will be discussing reticles on this thread.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Thanks for all the great info. I have a question.. I'm probably going to purchase a 17HMR if I can ever decide what rifle to buy.. cz, ruger, Savage. etc. Then will come a scope. I'm looking to shoot "whistle pigs", ground squirrels at 100 yds or less. So I'll have to come up wit something.. That's the background.. but the question comes from different types of scopes. I'm told that I need to purchase a specific type.. ie.. a scope for rimless cartridges.

What is the difference between standard scopes and those built for rimless?
 
Posts: 16 | Registered: April 16, 2019Reply With QuoteReport This Post
Member
posted Hide Post
quote:
Originally posted by ID_Bill:
Thanks for all the great info. I have a question.. I'm probably going to purchase a 17HMR if I can ever decide what rifle to buy.. cz, ruger, Savage. etc. Then will come a scope. I'm looking to shoot "whistle pigs", ground squirrels at 100 yds or less. So I'll have to come up wit something.. That's the background.. but the question comes from different types of scopes. I'm told that I need to purchase a specific type.. ie.. a scope for rimless cartridges.

What is the difference between standard scopes and those built for rimless?


I think you mean rimfire and not rimless.

I'll give a longer answer tomorrow when I get to a real computer. There's not much difference but usually scopes for rimfires have their parallax set closer than regular scopes.

More tomorrow.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Yep, rimfire.. not rimless..
I had a brain fart.
 
Posts: 16 | Registered: April 16, 2019Reply With QuoteReport This Post
Member
posted Hide Post
quote:
Originally posted by ID_Bill:
Yep, rimfire.. not rimless..
I had a brain fart.


I get them all the time, don't fret it.

When I bought my first 22LR rifle, I also bought my first scope and it was a Bushnell made for a rimfire. In those days the scope mount designs were varied and this scope use a dovetail mount.

It also had a 3/4 inch tube, no objective bell and 2-7X zoom range, if I remember correctly. (It's long gone, this was almost 45 years ago. I still have the rifle, a Ruger 10/22.)

Nowadays, the rimfire scopes, such as those from Leupold, a one inch tube and are just as good as their centerfire equivalents, but the parallax adjustment is usually at 60 yards instead of the more common 100 to 150 yards of their centerfire brethrens. Of course, if you get a scope with an adjustable objective then you won't have to worry about that.

Recently, I installed my Nightforce NXS 12-42X56 on my Ruger 10/22 and took it to a local rimfire benchrest competition. This is when I discovered 2 things. 1- The minimum focus on the nightforce is way further than I expected and 2- The point of aim shifted by about an inch between 12X and 42X; shocking.

However, for your purposes with a 17HMR, you do not need or want a rimfire scope; you want a normal scope with the parallax set further out than on a rimfire scope, or better yet, you want an adjustable objective.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Thanks for that great information.
"However, for your purposes with a 17HMR, you do not need or want a rimfire scope; you want a normal scope with the parallax set further out than on a rimfire scope, or better yet, you want an adjustable objective."

Do you have any suggestions? I don't want to spend an arm or a leg.. but I'd like a variable that would be on the order of 5-25 or thereabouts with a good light gathering objective that might go for less than $250 at a discount store.

I remember seeing some of what I thought might be decent buys on Leupold and Nikon.. but, can't remember the specs ATM.
 
Posts: 16 | Registered: April 16, 2019Reply With QuoteReport This Post
Member
posted Hide Post
quote:
Originally posted by ID_Bill:
Thanks for that great information.
"However, for your purposes with a 17HMR, you do not need or want a rimfire scope; you want a normal scope with the parallax set further out than on a rimfire scope, or better yet, you want an adjustable objective."

Do you have any suggestions? I don't want to spend an arm or a leg.. but I'd like a variable that would be on the order of 5-25 or thereabouts with a good light gathering objective that might go for less than $250 at a discount store.

I remember seeing some of what I thought might be decent buys on Leupold and Nikon.. but, can't remember the specs ATM.


I would suggest you start your own thread and ask for help in selecting a scope for your purposes. As you might have gathered by my writings, my predilection tends towards long range competition shooting, or target shooting, not hunting at short range.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
posted Hide Post
There are many scopesight options that will permit focusing at close distances for use with rimfire rifles, etc. I have a Leupold “EFR” 6.5-20× scope that can be focused as closely as about 10 yards, and I use it for certain practice. Other current extended focus range sights by Leupold and other manufacturers will also focus about that closely. That, however, may actually not be necessary if the hunter doesn’t anticipate close range shots. If you don’t anticipate shots closer than 50 yards, for example, many other scopesights will be usable. On the other hand, I like to anticipate the other things I might do with a gun and sight combination, so I would be happy with the flexibility that sight gives me on my Ruger 77/22 even if I didn’t have a specific purpose for close focus now.

And yes, I agree with the suggestion about a separate thread. Ironically, these stickied topics seem to get less attention than the new ones.

The one other bit of advice I’ll offer, though, is that if close focus is possible with a side mounted knob rather than an adjustable objective (AO), you will probably find that more suitable for hunting. The AO is usable, but not nearly as fast and convenient as the side focus adjustment. The one I have works fine for target practice, but would not be very good for hunting at different, constantly-changing ranges.




“The most common reaction to a life-or-death situation is to do nothing.”
— Amanda Ripley, The Unthinkable: who survives when disaster strikes and why (New York: Three Rivers Press, 2008)
 
Posts: 42842 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
Member
posted Hide Post
quote:
Originally posted by sigfreund:
There are many scopesight options that will permit focusing at close distances for use with rimfire rifles, etc. I have a Leupold “EFR” 6.5-20× scope that can be focused as closely as about 10 yards, and I use it for certain practice. Other current extended focus range sights by Leupold and other manufacturers will also focus about that closely. That, however, may actually not be necessary if the hunter doesn’t anticipate close range shots. If you don’t anticipate shots closer than 50 yards, for example, many other scopesights will be usable. On the other hand, I like to anticipate the other things I might do with a gun and sight combination, so I would be happy with the flexibility that sight gives me on my Ruger 77/22 even if I didn’t have a specific purpose for close focus now.

And yes, I agree with the suggestion about a separate thread. Ironically, these stickied topics seem to get less attention than the new ones.

The one other bit of advice I’ll offer, though, is that if close focus is possible with a side mounted knob rather than an adjustable objective (AO), you will probably find that more suitable for hunting. The AO is usable, but not nearly as fast and convenient as the side focus adjustment. The one I have works fine for target practice, but would not be very good for hunting at different, constantly-changing ranges.


Speaking of side focus (SF) vs. adjustable objective (AO), (yeah you got me started.) It should be stated that the AO design is simpler and more precise than the SF method. The AO very much functions like a regular telescope or camera lens by actually focusing the objective lens group onto the first focal plane at the front of the erector tube. That's a simple process and it's very precise and you can easily make small focus adjustments. The downside is that the focus is at the front of the riflescope and as sigfreund says that is not easy to reach while hunting but it's great for target or competition shooting at known distances.

The SF method actually involves another lens assembly in front of the first focal plane and that is used to alter the image coming from the objective lens assembly; in other words it's not a pure focus, it's an adjustment behind the objective lens assembly. It is not as crisp as the AO and it involves more lenses. On the other hand, it's very handy and I've really taken to if with my current March scope with the addition of a large focus wheel that allows me to easily fine-tune the focus. It also allows me to change the focus to various distances to look at the mirage at these distances and then snap back to the target line when ready to shoot.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Thanks.. just returned from a trip.. now to try to dig into this....
 
Posts: 16 | Registered: April 16, 2019Reply With QuoteReport This Post
Member
posted Hide Post
While at SHOT 2020, I spent quite a bit of time talking with the chief designed of the March scopes, through an interpreter, of course. Also, he carries documents with him at all times, and he draws really well.

I should point out that before he founded March with other engineers, he was at LOW and designed many scopes with which people here are very familiar.

These guys started their own company to make the scopes they wanted to make, without the constraints imposed my bigger outfits and bean counters.

So over the next several posts here, I'm going to talk about some of the stuff I found out, without going into stuff that may be proprietary.

The first item I want to discuss is the gas used in the scope. As most of you know, high end scopes are sealed against water and air. They are usually filled with nitrogen. (I was a bio-chemistry major back in my university days, 40+ years ago.) As you know nitrogen makes up about 70-some% of the atmosphere. Towards the end of the assembly process, the air in the scope is replaced with nitrogen to prevent fogging and other nasty things and the pressure is equivalent to sea level. The O-rings are inserted and the scope is now sealed with no oxygen or water vapor in it. March does not use nitrogen to fill the scope, they selected argon instead. The reason for that is that argon is a noble gas, completely inert and the argon molecule is twice the diameter of the N2 molecule and so it has less tendency to leak out and over time the argon stays in the scope longer than the nitrogen. Argon makes up about 1% of the atmosphere.

March did not invent argon filled optics, but it seems only very high end optics are argon-filled. Interestingly enough, my triple-pane windows at the house are argon filled. I guess that explains some of the exorbitant cost. They have been installed for over 14 years now and they are still very clear. I know that racing tires are filled with nitrogen now, and that's to replace the air which may have moisture in it. But you do have to keep an eye on the pressure and replenish as needed. Maybe argon-filled tires?

Next up I will discuss the innards of scopes.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
fugitive from reality
Picture of SgtGold
posted Hide Post
quote:
Originally posted by NikonUser:
I know that racing tires are filled with nitrogen now, and that's to replace the air which may have moisture in it. But you do have to keep an eye on the pressure and replenish as needed. Maybe argon-filled tires?


Part of the reason why nitrogen is used in automotive applications is a single gas has a constant expansion rate. Air as we know it is 78% nitrogen, but the remaining gases can vary enough to make expansion under heat and pressure inconsistent.


_____________________________
'I'm pretty fly for a white guy'.

 
Posts: 6752 | Location: Newyorkistan | Registered: March 28, 2007Reply With QuoteReport This Post
Member
posted Hide Post
Probably the singlemost important piece inside a riflescope is the objective lens group. Notice that I say group, not lens. Indeed the big lens in front is part of a doublet, a pair of lenses.

In the March scopes with ED or Super-ED lenses, the lenses made of the material are the two lenses in the objective lens group. I suspect that is the same for other riflescopes.

The reason you want those two lenses to be the ED/Super-ED (low dispersion glass) lenses is because those are the ones that bend the light the most and bending the light is what generates chromatic aberration in a optics. An objective lens of 56mm will bend the light to produce an image of itself that will fit in 26mm or less, whatever the ID of the main tube is at the first focal plane.

The objective lens group receives the light from the objective (target) and scrunches it down to fit on the FFP. If the objective lens group produces a bad image, there's no way it can be improved from there, which is why that lens group is so critical to have as near-perfect as possible.

Now some would think that you want ED/Super-ED glass in all the lenses of a riflescope. In reality, you don't want that, for two reasons.
A) Cost. These lenses cost significantly more than low dispersion glass lenses.
B) Light transmission. Low dispersion glass lenses have the lowest refraction index of optical glass because of the fact the material reduces or eliminates some of the sidebands from the various colors coming through. That's what helps reduce or eliminate CA. So with the low refraction index of the objective lenses, you want to preserve as much as possible the light that does come in and so you use high refraction index glass after the objective lens.

So a high quality high magnification riflescope will have expensive low dispersion glass ($$$$) for the objective lens group and high refraction index ($$$) glass everywhere else.

For scopes that have small objectives compared to the main tube, you will find that they do not have, or need, low dispersion glass in the objective lenses; it would be a waste of expensive glass.

On the other hand, the use of low dispersion glass has allowed the construction of riflescopes with big objective lenses but that remain very short. They bend the light a lot, but the low dispersion glass controls the CA.

For instance at the March booth, we were showing a 4.5-28X52, that is only 12 inches long. That front part is short, but the IQ is superb. There was also a 5-42X56 that's only 14 inches. In comparison, my 5-50X56 with ED glass is 15.7 inches long. The 5-42X56 has Super-ED glass, which allows it to be almost 2 inches shorter and still have as good or better IQ.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Let’s talk about weight.
One of the things that struck me about my March-X 5-50X56 was the fact it was 30 ounces, compared to 38 ounces for my Nightforce NXS 12-42X56. I appreciated the half pound weight saving, as F-TR rifles have a weight limit which includes the scope and the bipod. (Yes, I have a JOYpod, one of the lightest bipods around.) So saving a half pound on the scope meant that it could put that in my barrel.

But why was the March-X lighter than the NXS, with similar dimensions and specs? The obvious first though is that the Nighforce is built tougher that the March-X, that it has thicker wall material and so on. Closer examination shows this to be incorrect, grossly so. The March-X has a 34mm tube compared to the 30mm tube of the NXS. Well, people immediately think that the wall thickness is the same and that the March-X has a wider adjustment range because the tube is 4mm wider. The reality is that the March-X has a tube with walls that are 4mm thick compared to the 2mm walls of the NXS, or indeed, every Nightforce scope as far as I know. The March-X has 4mm thick walls which accounts for the difference in the tube size (34mm, 2mm extra per side). This makes the March-X immensely strong. Stronger than any other scope out there.

I spent quite a bit of time talking optics and the mechanics of a March scope with the chief engineer at SHOT, after hours as we were deluged with visitors. I found out quite a bit more about the scopes and I must say, I am super impressed with March. I think I already mentioned that each and every scope body starts as an ingot of aluminum bar stock and it is machined completely. There is not extrusion or forming or molding of any kind, unlike most other scopes. The 30mm March scopes have 2mm walls like the Nightforces, the 34mm tubes have 4mm tubes, unlike anyone else; but both the 30s and the 34s are completely machine from a billet.

So I asked the chief engineer how is it that my March-X is 8 ounces lighter than my NXS and yet had walls that are twice as thick? How is that even possible? That led to a great discussion which involved drawings on the back of a napkin. The gist of it is that it's all down to engineering. The guy who had done the design was in his element here; I had asked the exact right question, right up his alley and he was proud of his design.
Lenses make up the bulk of the weight, especially ED and Super-ED lenses. Next, the scope body is the single heaviest part, and we know that the March-X scope body is about double the weight of the NXS scope body. Later in my room, I made a quick calculation of the approximate weight of the scope body of the March-X and came up with about 296 grams. If the wall had been 2mm thick, my estimate was 150g.

The total weight of the March-X is 870g. That leaves 574g for the rest. We are talking about a doublet of ED glass at 56mm diameter, a focusing lens in the cone, the erector prism, the 3 zoom lenses with a diameter of about 25mm each, the reticle and the eyepiece assembly. That’s a lot of glass. My estimate is about 350g of glass leaving about 225g for the other inner parts and the knobs and such, about a half pound.

He has designed each and every part that goes in a March riflescope and over-engineered them to make them as strong as possible without unnecessary weight and bulk. So the weight savings were not because of one part, it was the accumulation of weight savings for a hundred plus parts. In a riflescope, there are 150 parts and then were all designed to be as strong as possible and yet light.

To my mind, having light but strong parts on the inside actually enhances the overall strength of the design, where the goal is to keep the zero on the scope. If you understand how a scope works, there is an inner tube that goes up and down and side to side, as you turn the knobs. Opposite of the knobs there are springs or some form of flexible yet firm resistance that pushes the inner tube against the knob, but that can yield to allow the inner tube to be adjusted. A heavier inner tube will exert more force against the knobs and “springs” during recoil or a fall or some type of impact. This helps explain why March scopes are legendary in their holding zero.

Yes, I asked about the “springs”, and he was a little reluctant to discuss them in detail and I understand why; the design is genius. Suffice to say, they don’t take a set. There’s a reason I use scare quotes around the word “spring”.

So when March says that all the parts in their scopes are made in Japan, they are probably made to their exact specifications or they make them themselves like they do for the scope bodies.
It was very educational and also a lot of fun talking with the chief engineer. I felt a bit like a kid in an candy store; ok, a lot like that.

In the meantime, I acquired another March scope, this time a March-X 10-60X56HM, which is very similar to my existing 5-50X56 but this one has Super-ED glass for even better CA control. I have assembled it in its rings and mounted it on a rail. I hope to sight it in on my match F-TR rifle this weekend. I’ll post some pictures soon.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Here is a picture of the new setup

http://img.gg/Y9Pb42t

You can see the Burris XTR Signature Rings, the Tubb level and of course, the March-X 10-60X56HM scope with added zoom lever, large focus wheel and sunshade.


 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
It's been a little while and a lot has transpired since I last posted here. At the risk of repeating myself, I have been working with March scopes on reticles, scope designs, marketing and now testing of scopes.

I recently had a long discussion about the internals of riflescopes and one of the areas where I thought my knowledge was short has to do with the eyepiece. I have learned a great deal, so I thought I would come back here and share some of this newly-acquired knowledge with you. If you already know all that, please correct me when I err.

To catch everybody up and make sure we have it all straight, let me recap in a way that helps me keep things straight in my aging mind.

In a riflescope there are three distinct sections. I call them: 1-The Objective Bell; 2- The Erector Assembly; and 3- The Eyepiece.

1- The Objective Bell; this is the part at the front of the riflescope, starting at the objective lens assembly, usually a doublet (a pair of lens elements), and ending at the front of the erector tube, AKA the First Focal Plane. In an AO scope, there is a ring at the front that you twist to move the doublet lenses away or closer together to focus the desired objective image on the FFP. In a Side Focus scope, there is an extra lens group between the objective lens group and the FFP, right in front of the FFP. This lens group is maneuvered by twisting the side focus knob thus moving it back and forth to focus the desired objective image on the FFP.

The Objective bell has some magnification value due to its focal length and the image it projects is the size of the internal diameter (ID) of the main tube.

2- The Erector Assembly; this is a tube that exists inside the main tube. It will be smaller than the ID of the main tube so as to allow it to move up and down and side to side, thus providing room for the adjustment range. This assembly will have a reticle at the front, if it is a FFP design. The image from the objective bell is focused onto the front of the erector tube (and merged with the FFP reticle if present.) This image then goes through a set of erector lenses that flip and invert the image into a second focal plane that then goes through the zoom lenses built into the tube. The image from that combination is projected at the back of the erector tube onto what we all know as the Second Focal Plane. As I explained in the OP, this is yet another focal plane but since everything occurs within the erector tube as a unit, we just think of its product as the Second Focal Plane, though it should really be called the Rear Focal Plane. In SFP designs, the SFP reticle is located at the rear of the erector tube and is merged into the image emanating from the erector assemble. The Zoom Lenses within the erector tube are the ones providing the boost in magnification, also known as the zoom ratio. This occurs before the SFP.

3- The Eyepiece Assembly; this is the lens group also known as the ocular lens, situated at the rear of the riflescope. This lens group is special in the fact that it is afocal. What this means is that this lens group takes the image from the real of the erector tube, magnifies it but does NOT focus it. It actually transmits the light in parallel waves to the eye of the shooter. The eye will use this parallel waves and focus the image onto the retina at the back of the eye. The diameter of these parallel waves coming from the eyepiece is what we refer to as the "Exit Pupil". The size of this exit pupil is a product of the diameter of the objective lens (you have to start with something) divided by the magnification. This is because as the magnification increases, you are actually looking at a progressively smaller portion of the image coming from the objective lens. As the portion size decreases, the light decreases also and that's why things get progressively darker with magnification.

The eyepiece is designed to present an image usable by the eye at a certain distance, and within a specific range. This is why you see nothing if you're too close or too far. But when you're in the Goldilocks distance, you get a nice image. However, even within that special distance, you can increase or decrease the field of view (FOV) if the image. This is a function of the diameter of the eyepiece lens and the distance from the eye. In the new March scopes, they have increased the diameter of the eyepiece to provide a wider FOV compared to regular eyepieces.

The eyepiece is a marvelous piece of optical engineering and we have various types. There is a big difference between a spotting scope or telescope eyepiece and a riflescope eyepiece. The former is designed to be used from very close up, whereas the latter is made to be used from a specific distance. My Kowa spotting scope has what is known as an LER eyepiece, it is designed to be used from a little further away compared to my 20-60X zoom eyepiece, which is a standard (up close an personal) eyepiece. There are also scout scope that have eyepieces designed to be used from several inches or more. There are also handgun scopes that have eyepieces designed to be used from a couple of feet away.

I am learning about the relationship between eyepiece lens diameter and distance. I was provided some formulae and will come back here to discuss it further when I have had time to play with some riflescopes with wide angle eyepieces.

In the meantime, I have drawn up a very (very) basic drawing showing the various focal points and the role of the eyepiece. I have purposefully avoided going into the details inside the erector tube and decided to stick with just FFP and SFP at the locations where we all understand them to be.

http://img.gg/uFy89Gy




One final thought here. A camera zoom lens can be thought of as two thirds of a riflescope, but without the erector lenses that flip the image. The SFP is located where the camera sensor or film is located. In a prime camera lens (non-zoom), it's really just an objective bell with the FFP being focused on the sensor or film.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
The overall magnification provided by a scope is an amalgam of the three parts described above.

The equation is:
Mag = (Fobj/Feyep)X erector ratio

Fobj is the focal length of the objective bell to the FFP.
Feyep is the focal length of the eyepiece to the SFP.

So for a 200mm objective with a 50mm eyepiece: you have (200/50)=4 and then you have the zoom ratio. For a 3X zoom you have 4-12X.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
posted Hide Post
Thanks for all that. I will have to reread some of it, but I believe I understand most and therefore it was very informative about something that I’ve never delved into.

Regarding the eyepiece, why do most telescopes (not sights) require the viewer’s eye to be very close to the lens when that’s not true of scopesights? Is it because the magnification/zoom lenses are in the eyepiece and not the body of the telescope? (I'm thinking of the spotting scopes I have.)




“The most common reaction to a life-or-death situation is to do nothing.”
— Amanda Ripley, The Unthinkable: who survives when disaster strikes and why (New York: Three Rivers Press, 2008)
 
Posts: 42842 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
Member
posted Hide Post
An excellent question, sigfreund.

The answer is as follows:

Remembering that the sight picture coming from the ocular is afocal, in other words the light rays are parallel, your eye will focus the rays at whatever distance it is from the ocular lens. The problem is that there is a relationship between the size of the ocular lens, the field of view apparent through the ocular, and the distance from the ocular lens. In a telescope, binoculars, or spotting scope, there is no requirement a large minimum eye relief; indeed it is easier for users to mash the lens into the eye socket and the view is instantly maximized for that. You will notice that the size of the ocular lens is very small compared to the ocular lens on a riflescope.

Now, some spotting scopes have an ocular lens that is called an LER (Long Eye Relief) lens. My Kowa has one of those eyepieces (fixed 25X). The ocular lens is quite big compared to the ocular lens of the zoom eyepiece (20-60X), which is not an LER. Kowa also offers a wide angle eyepiece. Just like the LER, it is a fixed power eyepiece (30X) and it uses a wider ocular lens, but it is not meant for LER, just a wider FOV.

March is now adding Wide Angle eyepieces to its new riflescopes. For example the March-FX 5-42X56 sports a wide angle eyepiece that provides for a 20-some% increase in FOV at any magnification. They accomplished this by increasing the diameter of the ocular lens by 15%. That ocular is "massive" and it makes it really easy to get behind the scope and you benefit from a wider FOV at any magnification. So when you're at 5X you get the FOV that other scopes have a 4X. I like to refer to it as the IMAX of riflescopes. The upcoming March-FX 4.5-28X52, for which offgrid and I created the reticles, has a similar WA eyepiece so the PRS shooters will benefit from an IMAX picture at any magnification by being able to spot their shots and conditions even better.

So to recap, the size of the ocular lens is the determining factor here for the FOV coming from that ocular. This is why as you move away from the ocular, the FOV get progressively smaller to the point it disappears.

When you are looking at scout scopes or pistol scopes, you will immediately notice that the FOV is minuscule for the magnification, and these scopes don't come in big magnifications to begin with. They are usually 2X or low numbers. I have a pistol scope somewhere and it's a low magnification and not easy to get properly behind to get a good picture.

I hope this explains it well enough.

This message has been edited. Last edited by: NikonUser,
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Member
posted Hide Post
A few words about riflescope maintenance.

As most people know, modern optics (from 1980 onwards) have coated lenses. These coats are extremely thin, down almost to the molecular level and are used to reduce the reflection of the light at the air-glass boundary. Each coating deals with a small section of the visible light spectrum, so in order to preserve the color fidelity of the image, multiple coatings are used, one for various segments of the spectrum.

Coating, numbers, composition, application, and so on, are all jealousy guarded IP by the coating manufacturers. So I don't know much of anything about them beyond the few pictures and videos I've seem that show some details of that.

However, one question that comes up frequently is how durable are these coatings. That depends, of course but keep in mind that scratching or rubbing the lens hard is not a good idea. Water is a good thing to use to clean the lens of dust and grime but do not let the water sit on the lens. This can have negative effect on the coating if left on for a long time. It's always a good thing to remove all water from the lens such as after a rain or some such. Doesn't have to be done in a hurry, but I would not put away my rifle wet, including the optics.

Isopropyl alcohol is an excellent cleaning fluid and it will remove the water. Just don't drink it. I also like lens tissue to apply the isopropyl alcohol and a clean microfiber cloth to dry everything. A bulb is a great way to blow off the dust from a lens. BTW, dust on the lens will not affect the IQ produced by the scope, but water droplets will.
 
Posts: 3172 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
  Powered by Social Strata Page 1 2 3 4 5 6 7 8 9  
 

SIGforum.com    Main Page  Hop To Forum Categories  Mason's Rifle Room    Riflescope primer (Added FOV pictures 9/28/2020)

© SIGforum 2020