Field of View

O

Optix1

Inactive
Gentlemen:

I know how maddening it can be to see someone pop in from nowhere and start pontificating, especially when he has a small number of posts. Thus, with this ONE under my belt, I should probably keep quiet; especially considering the post died almost 2,000 days ago. However, in one of his posts, back in 2010 (just stumbled on by me) thesheepdog said:

“The advantage-though minor-that a 50mm objective has is a WIDER FIELD OF VIEW …”

And, seeing no further entry on that subject, I thought I might like to pipe up. Please let me offer a snippet from an upcoming book on binoculars:

“It’s a common misconception that a binocular’s field of view is determined by the size of its objective lens.

Field of view, however, is a property of magnification, the size and position of the field stop (an orifice just in front of the field lens of the eyepiece), or perhaps the type of eyepiece used. The size of the objective lens has nothing to do with it. All other things being equal, field of view decreases as magnification increases. The objective should be thought of as a lens—not a window.

A good example could be found in comparing Nikon’s diminutive 6x15 with a Celestron 25x100. Although the Nikon has objectives the size of the tip of your finger, it has a field of view 4 times greater than a 25x100, with its 4-inch objectives!”

Optix1 (Chief Opticalman, USN-Ret.)

PS If someone has already addressed this, please just ignore the post. I’ll understand … I have kids.
 
Field of view for scopes and binoculars is one of the specs that manufacturers publish. As far as I know, they're pretty honest about that one. Checking the specs is the only way for a consumer to predict field of view.
 
Hi SSA:

Some are honest, but there are MANY mistakes. One such, by Fujinon, will be in my book. In one of their ads they say the “apparent field of view” of the 7x50 FMT is 7.5 degrees. It is not. 7.5 degrees is the REAL field of view; the APPARENT field is 52.5 degrees. With optical realities being such a mystery to the average consumer, many importers are too free with their unopposed advertising.

As the founder of one of America’s biggest optical importers (now defunct) is purported to have said to a gathering to his sales staff:

“Telescopes are not to look through; they’re to sell.”

Although having spent 45 years in many disciplines of the optics industry, I was overflowing with misleading Blarney around my 10th year. Thus, I will most certainly not win any friends with my book, but I intend to march through these misconceptions (some going back generations) like Patton on his way to Bastogne.

Cheers,

Optix1
 
I am not an Optix expert, nor have I played one on TV so can't answer Art's question. :)

However I can tell you I will trade a lower scope mount set up for quick target acquisition with a good cheek weld over a few more feet of FOV any day on my hunting rifles.

Now if I was a long range shooter (I call 300 yds plus) where I had a lot of time and a great rest, I might change my mind.
 
Question: For scopes of equal magnification, is the FOV of a 50mm lens greater than for a 40mm?
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It can go either way, and is often listed exactly the same for two scopes the same make and model.

I will trade a lower scope mount set up for quick target acquisition with a good cheek weld over a few more feet of FOV
Click to expand...

No trade involved there. The widest FOV's are with 20 and 24 mm scopes that go down to around 1x.
 
All that is answered in my first post. But, remember, a lot of those things relate to mechanical, and not optical, considerations. For example, the lens designer can change the FOV by altering the size and position of the field stop.

Again referring to binos, some people claim they can see dirt specks on the objective lens. They cannot. When they THINK they are seeing the objective, they are really seeing the VIRTUAL image formed at the focal plane, the field stop. In scopes, that would be the reticle.
 
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