Thanks for the explanation Chosun. So are you saying that all 8x42's have the same depth of field? There must be some odd illusions going on with my eyes and brain then as I've always thought I've been able to see quite a bit of variation in different 8x42's.
I don't know why I perceive such a good DOF with these then especially as they are a flat field design, my understanding is that field curvature creates more of an impression of increased DOF.
I thought stereopsis was a completely different thing related to the 3d effect of porros? I'm not saying the SF's have that.
MO, (and All),
Well, that's the theory
..... :cat:
All of those factors I mentioned go into our perception of the view .... and there's a few others too ! Our eyes will all see different things to each other, but my guess is any perceptual effects you are seeing are largely due to the wide focused Fov of the SF and the feeling of an 'immersive view' that this gives.
You have it right with the field curvature understanding, though it's a separate issue from pincushion or barrel distortion which is related to angular magnification distortion. Heaps of people get this screwed up.
With field curvature, you can refocus the edges of the view to be sharp (those with younger eyes can use their focal accommodation to achieve all or part of this depending on the design). There may or may not be straight lines depending on the design of the distortion too (barrel distortion as in looking at the surface of a sphere, or pincushion distortion as in looking into a bowl).
It should be noted that both these things (field curvature and barrel/pincushion distortions) are not necessarily linear - one, or both could have compound curves -ie. a changing rate with respect to angle that may be either increasing, or decreasing, positive and/or negative directions and may contain inflection points too - the so called mustache distortion profile. The SF has such a distortion profile. It has very little field curvature, and so appears sharp nearly to the edge. Note too that a particular distortion profile may not necessarily be symmetrical about the horizontal and vertical axes, so there may be differences in what is seen between left / right, and up and down (most notably evidenced in the foreground view).
Also, our eyes focal accommodation (which affects the depth of field seen from the binocular + eye system as a whole) not only changes with respect to ageing, but also physiological condition (tiredness, health, etc), and lighting /brightness.
Complicating all of this, our individual eyes have their own curvature, and pincushion/barrel distortion profiles too. Those with larger barrel distortion are more likely to experience the 'globe effect' or 'rolling ball' in flat field designs that are on the low side (high coefficient) of the circle of condition. This affects maybe less than ~10% of people ...... I thoroughly recommend doing the tests on Holger Merlitz's site to test your individual situation, and recording the results there. The more results Holger has recorded, the more valuable the research. I think the number was up over 50 participants last time I looked.
http://www.holgermerlitz.de/globe/test_distortion.html
Further complications to all of this occur if you wear glasses which introduce their own set of distortion profiles to add to the system .....
The Petzval curve of the eye /image plane nexus, visual acuity /peripheral vision, all play roles, as do a whole host of neural processing factors too.
Is it any wonder there is so much opinion and disagreement in what is being seen! :cat:
Apart from the dof test I mentioned, I would also recommend a quick map of a bin's distortion profile. This was first suggested to me by Henry Link, and goes something like this:-
* Turn your bins around and look through the objective end (this eliminates most eye distortion variables to the equation)
* Find a small round object (like a screw head) about 2~4m away to focus on.
* Focus on it in the centre of the view.
* Gradually move it to the side of the field of view taking note of any changes of shape of the circle, and the amount - (i)elongation vertically, or (ii)squashing horizontally, or (iii)any out of focus.
* Because you are looking reversed, (i) is barrel distortion, (ii) is pincushion, and (iii) is field curvature if it can be refocused, or astigmatism etc if it can't.
* By paying careful attention to the way the shape changes, and the amount, you will be able to tell if the distortion profile is more linear or mustache like, subtle or wild. If the circle remains a circle then the optical design meets the circle of condition criteria.
There you have it. Quick. Easy. and in concert with the dof test, eliminates ~up to or more than 95%
of BS and misunderstandings not to mention posts around here ! o
If you want to improve on that then you are into the photographic realms (of grid paper etc) that Henry has posted many times before. This requires careful setup. If you want to photograph brightness levels and colour casts then that really does require meticulous set up, standardization and calibration to eliminate additional variables.
Personally, I find that bins with heavy pincushion distortion seem to give me a quasi 3D like impression which many people mistake for increased dof. It is not of course.
There is some debate as to whether Leica has hit upon a 'secret sauce' with it's NoctiVid. It seems that a combination of precisely designed and matched field/ petzval curvature and mild, gently increasing pincushion distortion toward the edges gives the 'illusion' of greater 3D effect and greater dof. It is all 'perceptual', and while not everyone sees it, most folk agree that it is a pleasing view.
You are correct in your understanding - the 3D effect (stereopsis), most usually seen from horizontally offset Porro-I designs is completely separate from dof.
Hope this helps everybody
Chosun :gh:
