Do you like the VIEW better through a Porro or a Roof prism binocular? (1 Viewer)

[[email protected]]

You're technically incorrect, because there's light loss through any glass element. Also because there are several types of roof prisms; some (like Schmidt-Pechan) have an inefficient mirrored surface, others (like Abbé-König) don't.


No, there's no real difference in that respect. The point of either type of prism is to bounce light around inside them, making the instrument shorter and flipping the image so it's upright. (Straight Keplerian telescopes have inverted images.) The illustration Dennis posted, showing a straight line right through the roof prisms, is inaccurate and misleading. Here's a better one.

If the SP prism is that inefficient why does Swarovski use it in the NL? It can't be that much smaller. Your cut aways are the same just from a different perspective.

"The Porro prism, named for its inventor Ignazio Porro, is a reflective optical prism in the form of a right-angle triangle with two sides of equal length. In binoculars, monoculars, or spotting scopes, it is used in pairs to lengthen the effective focal length of the optical path within a space that is shorter than it would otherwise accommodate. As each turn of the optical path through the prism is 90° the Porro prism does not risk dispersion of the light rays as they pass through it, yielding an image presented to the user that is very natural, bright, and true to the natural colors of the subject. Porro prism optical instruments are easily recognized by their having eyepiece lenses that are not in a straight line with their objective lenses, consequently, they are often physically larger than roof prism models of equal magnification and objective diameters. The classic “broad shouldered” shape of a traditional binocular is a readily identifiable clue to that model being a Porro prism optical system. The roof prism, also called a Dach prism, is a reflective optical prism containing a section where two faces meet at a 90° angle. These two 90° faces resemble the roof of a building, giving this prism type its name. However unlike the Porro prism, which is generally used in identical pairs, the roof prism is used in combination with an auxiliary prism both to lengthen the effective focal length of the optical path within a space that is shorter than it would otherwise accommodate, and to do so in a manner that creates a straight line between the eyepiece and objective lenses of the optic for the result of a sleek and trim exterior shape. The cost of this is that most of the angles the light path must follow through the roof and auxiliary prisms are either very sharp or quite wide, which increases the risk of the light rays dispersing in the process. To overcome this, special coatings such as Phase Coating and Dielectric Coating are used to keep the light rays transiting in proper alignment to one another and thus show the user of the optic a crisp and sharp image in the eyepiece."

 

[[email protected]]

One of the biggest advantages of Porro prisms over roof prisms is field illumination, and it is not talked about much, but it makes a big difference.

"One of the biggest differences between porros and roofs is that roofs lose full illumination very quickly once you move away from dead center. Average porros have a fully illuminated circle 20%-30% of fov. Best porros have a fully illuminated circle 50% of fov. Average roofs have a fully illuminated circle 5%-15%. The Best roofs have a fully illuminated circle 20% of fov or less. So while transmission dead center may appear to vary by only a few %, move 30-40% off axis and transmission might appear to vary easily by 10% or more. You can test this on a deep star field. Set up two equal sized binoculars, one roof and one porro, and observe for deepest stars seen at center and then deepest stars seen at 30%-50%-70% off axis. By 70% out aberrations will come into play, but in the 30%-50% area few aberrations exist in most binoculars and therefore the differences you see will better represent only a loss of illumination.
Deep star maps (M45, Cr399) are available in the Best of Threads on Limiting Magnitude."

"Edz, you are spot on. When first comparing my Leica roofs to my Fujinon 10x50's under very clear dark Austrian skies, I was shocked to see the difference in off-axis illumination between them. It was the most dramatic difference between the two. Second was size. On axis sharpness was comparable, while the Fuji's of course had superior edge of field correction, but that is not an attribute of the prisms."

 

[henry link]

One of the biggest advantages of Porro prisms over roof prisms is field illumination, and it is not talked about much, but it makes a big difference.

"One of the biggest differences between porros and roofs is that roofs lose full illumination very quickly once you move away from dead center. Average porros have a fully illuminated circle 20%-30% of fov. Best porros have a fully illuminated circle 50% of fov. Average roofs have a fully illuminated circle 5%-15%. The Best roofs have a fully illuminated circle 20% of fov or less. So while transmission dead center may appear to vary by only a few %, move 30-40% off axis and transmission might appear to vary easily by 10% or more. You can test this on a deep star field. Set up two equal sized binoculars, one roof and one porro, and observe for deepest stars seen at center and then deepest stars seen at 30%-50%-70% off axis. By 70% out aberrations will come into play, but in the 30%-50% area few aberrations exist in most binoculars and therefore the differences you see will better represent only a loss of illumination.
Deep star maps (M45, Cr399) are available in the Best of Threads on Limiting Magnitude."

"Edz, you are spot on. When first comparing my Leica roofs to my Fujinon 10x50's under very clear dark Austrian skies, I was shocked to see the difference in off-axis illumination between them. It was the most dramatic difference between the two. Second was size. On axis sharpness was comparable, while the Fuji's of course had superior edge of field correction, but that is not an attribute of the prisms."

Dennis, now you’re scrapping the bottom of the barrel to find “advantages” for Porros. This one is not talked about much because it isn’t true. It’s one of several misconceptions promulgated by EdZ on the subject of off-axis vignetting. There are a few variables that affect vignetting, but not one of them is the prism type.

 

[henry link]

Why don’t you explain how prism type affects off-axis vignetting?

 

[henry link]

Are you changing the subject?

 

[albie...]

It's been quite a few years since EdZ has contributed anything about binoculars or anything else for that matter . Not sure if you would get a bite from Edz if you tried to reach out to him . I will say that he provided a wealth of information mostly for cheap to midpriced bins , great for beginners . I was and still am under the assumption that he knew what he was talking about , some pretty in depth reviews and comparisons done by the man .

 

[WJC]

Hi, Gang,

I promised to leave poor Dennis to his machinations. But I’m just way too human and have been pushed over the edge. My goal has consistently been to help others raise their level of optical understanding to be best of my ability, although much of the information is—from my perspective—useless in a practical sense, except for those who need things to talk or worry about. Most of those who are really proficient in the subject wouldn’t touch one of these forums with the proverbial “ten-foot pole,” and we are fortunate to have a few heavy hitters like Holger drop by on occasion. Sadly, to help others in raising that bar, I find myself being consistently at odds with Dennis’s incessant misinformation concerning so many technical aspects of binoculars and observing—not related to size, weight, or ergonomics.

Realities of this matter have been driven home to me by several dozen posts in which Dennis makes some unfounded statement which is swiftly challenged by others. This routine has been going on so long, I find myself forced to reevaluate Birdforum’s place in the pecking order of optical/binocular understanding. Most people, when finding scientifically accurate data to replace their long-held, but erroneous, suppositions will modify their thinking and grow from it. Not so with Dennis. Sadly, in months of peeking into various threads, I’ve come away with the following:

1) Dennis sees himself as the unquestionable source of all knowledge relating to optics and binoculars.

2) Anyone choosing to believe anything not sanctioned by a person Dennis stands behind is “TWISTING” the facts so that, while they may conform to the laws of physics, they don’t conform to Dennis’s 100% accurate OPINIONS.

3) Those with Ph.Ds. in optical engineering or decades on the optical bench—and who are respected by those Ph.Ds.—speak with a harmful agenda because they don’t conform to the “OPINIONS” of the ALLBINOS “ENTHUSIASTS” who Dennis seems to worship because HE “AGREES WITH THEM ... MOST OF THE TIME.”

Thus, it would appear that if you can’t agree with his OPINIONS—no matter how foolish—Dennis will paint a target on your back because he sees differing contributions as twisted, irrelevant, or just plain wrong.

Being a curmudgeon, often what I say is deemed harsh and unkind. But I’m with Mr. Spock in feeling that the needs of the many are more important than the needs of the one and, “None are so blind as those who REFUSE to see.”

“If you can't explain it simply, you don't understand it well enough.” — Albert Einstein

Bill

PS I have little doubt Dennis will, to use HIS words, “twist” all I have said in an effort to defend the consistently indefensible. I care little. The truth is not always popular. However, it is always the truth.

Lee, please be kind. If my words are condemned by the snowflakes among us, just kindly—if you will—ask me to leave. I will make it instantly happen. Just remember, I stood firm for the betterment of the forum and I can never feel bad about that. Also, think of all the times I have waded through the muck but still had the presence of mind to hold my fingers still, which was a noble act, indeed.

 

[tenex]

If the SP prism is that inefficient why does Swarovski use it in the NL? It can't be that much smaller.

Seriously? Of course SP prisms are smaller than the alternatives, that's exactly why most binos today use them.

Your cut aways are the same just from a different perspective.

No it isn't, it shows the correct optical path through a roof prism bino, as yours did not. This is actually not possible to dispute.

"The Porro prism, named for its inventor Ignazio Porro, is a reflective optical prism in the form of a right-angle triangle with two sides of equal length. In binoculars, monoculars, or spotting scopes, it is used in pairs to lengthen the effective focal length of the optical path within a space that is shorter than it would otherwise accommodate. As each turn of the optical path through the prism is 90° the Porro prism does not risk dispersion of the light rays as they pass through it, yielding an image presented to the user that is very natural, bright, and true to the natural colors of the subject. Porro prism optical instruments are easily recognized by their having eyepiece lenses that are not in a straight line with their objective lenses, consequently, they are often physically larger than roof prism models of equal magnification and objective diameters. The classic “broad shouldered” shape of a traditional binocular is a readily identifiable clue to that model being a Porro prism optical system. The roof prism, also called a Dach prism, is a reflective optical prism containing a section where two faces meet at a 90° angle. These two 90° faces resemble the roof of a building, giving this prism type its name. However unlike the Porro prism, which is generally used in identical pairs, the roof prism is used in combination with an auxiliary prism both to lengthen the effective focal length of the optical path within a space that is shorter than it would otherwise accommodate, and to do so in a manner that creates a straight line between the eyepiece and objective lenses of the optic for the result of a sleek and trim exterior shape. The cost of this is that most of the angles the light path must follow through the roof and auxiliary prisms are either very sharp or quite wide, which increases the risk of the light rays dispersing in the process. To overcome this, special coatings such as Phase Coating and Dielectric Coating are used to keep the light rays transiting in proper alignment to one another and thus show the user of the optic a crisp and sharp image in the eyepiece."

This paragraph (Google finds it on celestron.com, as you should have said) is amateur junk, full of falsehoods and clumsy English, the worst indicated in bold above. "Dispersion of light rays" is not relevant here, I have no idea where this writer came up with that. Phase coatings do "realign" light in a sense (which has to be understood in terms of waves not "rays"), but dielectric mirror coatings do not, they just reflect it.

One of the biggest advantages of Porro prisms over roof prisms is field illumination, and it is not talked about much, but it makes a big difference.

It's good that it isn't talked about much, because it's not true. You won't find another (independent) reference to it. (This quote was from Cloudy Nights if anyone cares.) There is no conceivable reason it would be true, so the onus is on you (really meaning this "EdZ" of course) to explain how, not the rest of us to explain why not!

The idea here was to inform a beginner, not confuse and mislead them. Or insult people who know far more than you do, with your miscellaneous second-hand snippets, whose quality you can't even judge.

[Edit: you now seem to have deleted your insulting post to Henry, formerly #65. Which part exactly did you think better of?]

 

[[email protected]]

It's been quite a few years since EdZ has contributed anything about binoculars or anything else for that matter . Not sure if you would get a bite from Edz if you tried to reach out to him . I will say that he provided a wealth of information mostly for cheap to midpriced bins , great for beginners . I was and still am under the assumption that he knew what he was talking about , some pretty in depth reviews and comparisons done by the man .

I wonder what happened to him? He was quite the Icon over at Cloudy Nights. My god the detailed reviews he did! Amazing!

 

[[email protected]]

Seriously? Of course SP prisms are smaller than the alternatives, that's exactly why most binos today use them.

No it isn't, it shows the correct optical path through a roof prism bino, as yours did not. This is actually not possible to dispute.

This paragraph (Google finds it on celestron.com, as you should have said) is amateur junk, full of falsehoods and clumsy English, the worst indicated in bold above. "Dispersion of light rays" is not relevant here, I have no idea where this writer came up with that. Phase coatings do "realign" light in a sense (which has to be understood in terms of waves not "rays"), but dielectric mirror coatings do not, they just reflect it.

It's good that it isn't talked about much, because it's not true. You won't find another (independent) reference to it. (This quote was from Cloudy Nights if anyone cares.) There is no conceivable reason it would be true, so the onus is on you (really meaning this "EdZ" of course) to explain how, not the rest of us to explain why not!

The idea here was to inform a beginner, not confuse and mislead them. Or insult people who know far more than you do, with your miscellaneous second-hand snippets, whose quality you can't even judge.

My point was you said the SP prism was inefficient so do you agree that alpha manufacturers are prioritizing size and ergonomics over optical performance. That is my point. I personally would rather have a bigger, less ergonomic binocular with an AK or Porro prism that performs better than a smaller more ergonomic binocular with an SP prism. The terminology of the quote from Celestron.com is a little confusing, but I disagree that it is amateur junk. It has a lot of relevant information in it pertaining to the advantages of Porro prism binoculars over roof prisms. I believe Edz is correct in his belief that Porro prisms have better field illumination than roofs because I have observed it myself when comparing similar Porro prism binoculars to roof prism binoculars and knowing how thorough he is I am sure he has tested and verified his theory. Everything Edz reports is usually from objective testing and not just his subjective opinion.

 

[CharleyBird]

Errrrrrrrrr, what happened to the post between #64 and #65 ?

 

[CharleyBird]

Hi, Gang,

I promised to leave poor Dennis to his machinations. But I’m just way too human and have been pushed over the edge. My goal has consistently been to help others raise their level of optical understanding to be best of my ability, although much of the information is—from my perspective—useless in a practical sense, except for those who need things to talk or worry about. Most of those who are really proficient in the subject wouldn’t touch one of these forums with the proverbial “ten-foot pole,” and we are fortunate to have a few heavy hitters like Holger drop by on occasion. Sadly, to help others in raising that bar, I find myself being consistently at odds with Dennis’s incessant misinformation concerning so many technical aspects of binoculars and observing—not related to size, weight, or ergonomics.

Realities of this matter have been driven home to me by several dozen posts in which Dennis makes some unfounded statement which is swiftly challenged by others. This routine has been going on so long, I find myself forced to reevaluate Birdforum’s place in the pecking order of optical/binocular understanding. Most people, when finding scientifically accurate data to replace their long-held, but erroneous, suppositions will modify their thinking and grow from it. Not so with Dennis. Sadly, in months of peeking into various threads, I’ve come away with the following:

1) Dennis sees himself as the unquestionable source of all knowledge relating to optics and binoculars.

2) Anyone choosing to believe anything not sanctioned by a person Dennis stands behind is “TWISTING” the facts so that, while they may conform to the laws of physics, they don’t conform to Dennis’s 100% accurate OPINIONS.

3) Those with Ph.Ds. in optical engineering or decades on the optical bench—and who are respected by those Ph.Ds.—speak with a harmful agenda because they don’t conform to the “OPINIONS” of the ALLBINOS “ENTHUSIASTS” who Dennis seems to worship because HE “AGREES WITH THEM ... MOST OF THE TIME.”

Thus, it would appear that if you can’t agree with his OPINIONS—no matter how foolish—Dennis will paint a target on your back because he sees differing contributions as twisted, irrelevant, or just plain wrong.

Being a curmudgeon, often what I say is deemed harsh and unkind. But I’m with Mr. Spock in feeling that the needs of the many are more important than the needs of the one and, “None are so blind as those who REFUSE to see.”

“If you can't explain it simply, you don't understand it well enough.” — Albert Einstein

Bill

PS I have little doubt Dennis will, to use HIS words, “twist” all I have said in an effort to defend the consistently indefensible. I care little. The truth is not always popular. However, it is always the truth.

Lee, please be kind. If my words are condemned by the snowflakes among us, just kindly—if you will—ask me to leave. I will make it instantly happen. Just remember, I stood firm for the betterment of the forum and I can never feel bad about that. Also, think of all the times I have waded through the muck but still had the presence of mind to hold my fingers still, which was a noble act, indeed.

This.
The post I read between #64 and #65 ought to be placed in the 'Warning for a few' as a classic example

 

[henry link]

Errrrrrrrrr, what happened to the post between #64 and #65 ?

Dennis went back and deleted his ad hominem attack, making him appear innocent of any provocation. Not the first time he's done that.

 

[CharleyBird]

There seems a fine line between mere OCD and becoming a spamming wazzock.

 

[Steve]

Gentlemen, different opinions are allowed, personal attacks are not.

I understand that there are a multitude of "personalities" on here, some more forceful in their opinions than others, I also can plainly see that some think they know more than others, I can also see that some flit from binocular to binocular like a hummingbird finding a new favourite every post, but this is
ok isn't it? no need to be offensive, just except that as I said its different strokes for different folks. In the grand scheme of things arguing over optics is not really worth getting wound up over.

So please take a deep breath, realise that your dealing with a Hummingbird or Einstein or any other analogy and all will be cool.

 

[Maljunulo]

Is there a code of conduct or a list of offences which will get your account locked somewhere?

I like it here and don't want to get in trouble.

 

[PYRTLE]

At the very bottom of the page in the dark blue, you will see " Terms and rules ".

As a general guide....( You will usually receive a polite reminder from an Administrator, who can also remove any words or posts that they deem unsuitable. Further offenders may then receive a yellow card [temporary ban from posting] and if one continues with inappropriate behaviour, then a red card / button or lever.

But of course, each case can vary.......

Cheers

 

[Maljunulo]

At the very bottom of the page in the dark blue, you will see " Terms and rules ".

As a general guide....( You will usually receive a polite reminder from an Administrator, who can also remove any words or posts that they deem unsuitable. Further offenders may then receive a yellow card [temporary ban from posting] and if one continues with inappropriate behaviour, then a red card / button or lever.

But of course, each case can vary.......

Cheers

Well, that's pretty straightforward and direct.

Thank you for pointing it out. as I may not have ever found it.

I hope Bill didn't get whacked as a result of that little dust-up. I think his knowledge and experience are very valuable.

 

[tenex]

My point was you said the SP prism was inefficient

No, you said (all) roof prisms were inefficient:

Your technically correct, but the Porro Prism is still more efficient than the roof because there is no light loss through the prism

I just guessed an interpretation of that false and confusing remark that may not have been the one you had in mind.

That is my point. I personally would rather have a bigger, less ergonomic binocular with an AK or Porro prism that performs better than a smaller more ergonomic binocular with an SP prism.

When size isn't a top priority, I agree! As we've both said before. (That's why I like SLC 56s.) But you were criticizing all roof prisms here, not rooting for AKs along with Porros.

The terminology of the quote from Celestron.com is a little confusing, but I disagree that it is amateur junk. It has a lot of relevant information in it pertaining to the advantages of Porro prism binoculars over roof prisms. I believe Edz is correct in his belief that Porro prisms have better field illumination than roofs because I have observed it myself when comparing similar Porro prism binoculars to roof prism binoculars and knowing how thorough he is I am sure he has tested and verified his theory. Everything Edz reports is usually from objective testing and not just his subjective opinion.

You're demonstrating my point that you don't actually know how to judge information at all. If it contains anything remotely true, it's worth citing, regardless of the rest? You can convince yourself that you see what you believe? (Surely you don't claim to have replicated EdZ's limiting-magnitude test yourself? No one else seems to have either. And you don't consider the absence of any plausible reason for that result a problem?) One single person can claim to "test and verify a theory", and it's established? Anything a person you trust says is true? What someone you don't trust says must be wrong? How do you even decide whom you trust? This is completely dysfunctional.

... so where did Birdhenry go? Instead of saving him from Internet junk you've fed him more. Would he like to ask any further questions? (I bet not...)

 

[james holdsworth]

Moderation, IMO, includes recognizing chronic and repetitive abusive posting behaviour and using available tools to eliminate such....without that, we get these sorts of threads for 10 years.