I thank you for the clarification, I always read your posts with great interest and have learn a lot (for example, to be wary of advertising bloating specs). However, there's two things that escape me.
- It is a proven fact that sometimes manufactures cheat in the advertising, bloating the performance of their devices, but then... why would anyone in their own mind advertise a product being worse than it is in reality. Why would you say your product has a 6,4º FOV when in reality it has 7,1º? (Yes, I know that in a few cases the brands err for good, and declare worse performance, but I guess this is quite scarce).
- On the other hand, just like Rob, as a lay person I'm a bit confused about your explanation of FOV being a simple division of objective mm and magnification.
I thought this was actually exit pupil in millimeters. But maybe I'm missing something or there's a technical explanation to it.
Furthermore, how is it possible then, that there exist binoculars with the same format and very different FOV. Without leaving the 7x50 and the very same brand.
Nikon 7x50 Aculon: 6,4º (advertised)
Nikon 7x50 IF SP WP: 7,3º (advertised, tested by Allbinos at 7,24º)
Nikon 7x50 WX: 10,7º (advertised, Allbinos tested the 10x50 WX and it was in accordance with the brand specs)
Then if we check other formats, there are varying (and pretty different, sometimes extreme) FOV for any given format. Maybe I'm misinterpreting some information or mixing different concepts.
Thanks for your kindness and your willingness to see things from other angles. Many people refuse to do so.
“It is the mark of an educated mind to be able to entertain a thought without accepting it.” — Aristotle
Considering differing advertising specs from empirical specs.
1) Uncaught human errors. Why would an optical giant like Fujinon advertise their best 7x50 binocular as having an apparent field of 7.5-degrees instead of the actual 52.5-degree? ‘Seems to me that the missing 45 degrees would make a big difference to buyers.
2) The only reason I can see for the downgrading the field of view—instead of using the tried and true “7.14 degrees” that has been used for years is that they stopped down the field to make what WAS presented to the eyes optically superior. The Swift Ultra Lite, Celestron Ultima, and the Adlerblick Fernglasser (all the same basic binocular) have a narrower field of view than possible. However, the image presented to the eyes competes well with some binoculars costing a great deal more. What is more important to the consumer with dollars to spend?
You may take an unmounted objective lens and hold it in front of you and tilt it at huge angles. You will note that being ... glass, light still passes through. You will also note that you can see objects on the other side. Further, an image can be formed. Will that image be garbage? Absolutely! Some people base their ideas concerning the size of the Field of View solely on the size of the objective lens. I’ve even seen that promoted by the source of all knowledge and wisdom ... Wikipedia!
That is massively oversimplified! An objective lens with the capacity to form a useless 90-degree FOV has to be restricted by field stops and a practical optical system. The primary field stop with others potentially in the ocular—as well as the DESIGN of that ocular. In optics, one size does not fit all. The engineer has control over that which is mathematically possible but optically foolish. Math doesn’t care what the image looks like; the engineer does.
3) My comment about FOV calculations was based on approximations. Those observers interested in stacking BBs will find the information in the following of interest: https://www.optics-trade.eu/blog/field-of-view-calculations/
But, when you are done, please determine—in a practical sense—which doctrine is most useful TO THE AVERAGE OBSERVER. Another helpful website might be: https://www.birdwatching.com/optics/binoculars5_fov.html
I don’t need time-wasting mathematical gyrations; I can measure FOV directly with my collimator. (See Attached)
Finally, I just try to make things easily understandable. Pontification may be great for ego-stroking but it falls short in useful communication. There are two kinds of light. Reasonable glows that illuminate and obfuscative glares that obscure. I will forever be taken to task for the route I have chosen. However, you’re worth it. :cat:
I hope this has been helpful.
“The first principle is that you must not fool yourself and you are the easiest person to fool.” — Dr. Richard Feynman