IPD Discussion (was 8x32FL. Super-sweet? Semi-sweet?) (1 Viewer)

Recently there was some debate (I forget which post) about the size of the FL sweet spot, especially the 8x32. I've had my 8x32 for about a month now and am willing to say that the "super-sweet" spot is in fact fairly small, but that it is surrounded by a large "semi-sweet" donut, an area just a tiny bit less sharp.

As a result, I find that IPD on the Zeiss is more critical than on my other 8x32's. I was having fits trying to get both barrels super-sweet and then realized I generally had the IPD set a bit too wide. Narrowing it lined up the super-sweet spots and now these things rock. I notice that, like porros, it helps to narrow the IPD for closer distances--something that most roofs don't need except at minimum distances.

Any of this sound familiar? I'm curious about how others see this. If the FL's weren't so doggone sharp I doubt I'd ever have picked up on it.

Mark

Hello Mark,

Either this is a very personal thing, or I am not as critical as you are. I set the IPD and it works for me.
Yes, it an extraordinary binocular.

Happy bird watching,
Arthur Pinewood :hi:

Very good observation,..I am quite pleased with the sharpness that I can achieve with the FL 8x32,In fact I found it sharper than the Nikon SE,or as sharp,and to give such wide field without distortion and keeping the image quality so constant through the FOV is amazing.....You are right about the size of the sweet spot,But the sweet spot is VERY sharp,and the DOF is great for a 8x ,so usually i can carry either of my eyes to reach extra sharp images without any stress ,pretty much all around the ,WIDE,field of view..I found the FL extremely comfortable to hold and to look through.

Hi Manuel, I liked the FL8x32 I tried at the Amish shoe shop. I hope you don't mind me asking but I notice you have your Zeiss FL 8x32 for sale and if you like it why would you sell it? I guess some people just like to check out all the different optics out there.
Regards,Steve

I measure my idp with a tape measure,which is 67mm and then use the tape measure to set all my bins at the correct idp.I note the markings,and never deviate from those settings.That takes one mistake out of the formula...

mayoayo said:

But the sweet spot is VERY sharp,and the DOF is great for a 8x ,so usually i can carry either of my eyes to reach extra sharp images without any stress.

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mayoayo,

I seem not to have a "dominant" eye, which I think is what you're getting at. The idea that one eye can supply the brain with a sharp image for both eyes when the other eye doesn't have it. In my case it just felt like the diopter was misadjusted, but no amount of fiddling with the diopter had any effect--well, I should say it made things worse both + and -. So the IPD was the cure.

As an eyeglass wearer with astigmatism, I also realize that my 8x32 SE and 8x32 FL are possibly both better optical instruments than my glasses are, especially since my current pair are no-line bifocals which are complex "asphericals" of some sort in their own right. So I've reached the point, with these two bins at least, where I have trouble determining where the tiniest faults lie. All I can say is "I know what I like."

Which means I've topped out and probably wouldn't see much improvement no matter what bin was involved. Hey, maybe that's the cure for binoholism: get old and lose your eyesight. New EL's? Who needs 'em?

Mark

I ususally use my right eye to look through my scope,but I dont know if it is really a dominant eye,..In the case of binoculars,like my pentax sp,for instance,..yes,IPD being correct at a given distance helps to get the sweet spot aligned and to create sharper images ,..the FL is no different,but i find it more forgiving in that regard,due to the excellent DOF

mayoayo said:

I ususally use my right eye to look through my scope,but I dont know if it is really a dominant eye,..In the case of binoculars,like my pentax sp,for instance,..yes,IPD being correct at a given distance helps to get the sweet spot aligned and to create sharper images ,..the FL is no different,but i find it more forgiving in that regard,due to the excellent DOF

Click to expand...

There's an easy test for determining which eye is dominant.

Look for a spot on the wall in your room. It could be the ceiling, though it's less strain on the neck if it's not too high.

I have plenty of spots on my wall from thumb tack holes. If you've just plastered your walls, make a good sized round dot on the wall with a pencil. (if you're married, do this experiment when your wife is out of the house and keep an eraser handy just in case she comes home early

Then with pencil in hand, sit down in a chair, and with either hand, hold the pencil up in front of you so that it's parallel to the wall (i.e., the pencil is straight up).

Find the hole/spot on the wall and while focusing your eyes on the pencil, line up the pencil just below the spot in the background.

(if you focus on the spot while doing this, you will see a double image of the pencil; if you can't avoid doing that, pick one of the "pencils" to line up the spot with)

Close your left eye. With your right eye, notice where the pencil is in relation to spot, and then do the same thing with your right eye.

Close your right eye and look at the spot with with your left eye and and see if the pencil lines up with the spot or "jumps" away from it.

Blink your eyes back and forth if you are having trouble determining which eye is making the pencil "jump" from under the spot.

The view that keeps the pencil lined up with the spot is your dominant eye.

Mark,
Well, sure, you need to set your IPD right. Whether you attribute some unusual criticality to the FL's optics, your eyes' astigmatism, an eye dominance issue, etc, is a moot point. But if there is something strange and akilter in the mix, it's probably better to set it by feel, rather than from a measurement of your actual eye separation.

Sometimes I will think I have discovered some kind of new and magic way to get a better view, but find it doesn't hold up under a few days of trial. I have been on jags of IPD criticality myself. I have rigged IPD-locks for some of my binoculars. But with my 8x42 FL at least, it seems like a quick and dirty adjustment by feel, looking at infinity, is all that is needed, if they get changed through abuse or sharing the view with my beady-eyed wife, who doesn't carry her binocular fully half the time, because she is normal, and knows she can always cop a quick view, what a deal.

So there's no need to worry about this IPD thing, is what I have finally concluded, after laborious measurement, experimentation, and trial and error. In fact I can quickly set the IPD repeatably within a maximum full range of 1.0mm, and with a standard deviation of only 0.5mm. This, at a 90% confidence level. Nope I am definitely not uptight about it.
Ron

"There's an easy test for determining which eye is dominant."

Just point your finger like you are going to shoot something at a distance, close one eye at a time the eye that is lined up is the one.

ronh said:

Mark,
Well, sure, you need to set your IPD right. Whether you attribute some unusual criticality to the FL's optics, your eyes' astigmatism, an eye dominance issue, etc, is a moot point. But if there is something strange and akilter in the mix, it's probably better to set it by feel, rather than from a measurement of your actual eye separation.

Sometimes I will think I have discovered some kind of new and magic way to get a better view, but find it doesn't hold up under a few days of trial. I have been on jags of IPD criticality myself. I have rigged IPD-locks for some of my binoculars. But with my 8x42 FL at least, it seems like a quick and dirty adjustment by feel, looking at infinity, is all that is needed, if they get changed through abuse or sharing the view with my beady-eyed wife, who doesn't carry her binocular fully half the time, because she is normal, and knows she can always cop a quick view, what a deal.

So there's no need to worry about this IPD thing, is what I have finally concluded, after laborious measurement, experimentation, and trial and error. In fact I can quickly set the IPD repeatably within a maximum full range of 1.0mm, and with a standard deviation of only 0.5mm. This, at a 90% confidence level. Nope I am definitely not uptight about it.
Ron

Click to expand...

Hello RonH,

I just read your post with interest. I, too, have taken a critical view of IPD for quiet some time.

Seems to me to be an important subject that is largely ignored or deemed of no consequence. Then, again, may be much ado about nothing. I can not convince myself though.

I have been doing IPD tests for many years. These tests started in the mid 80’s and continue today. The methodology has remained the same but some of the techniques and equipment have changed.

The basic test consists of having the subject adjust binoculars to their IPD after I have spread them to maximum IPD setting. I then do the same procedure but I set the binoculars to minimum IPD and then have the tested party set them to their IPD. I then measure the IPD setting of the binoculars and record the setting. Both tests are repeated at least three times. I then measure the subjects IPD using a commercial pupilometer at infinity setting and record that figure. I will also, occasionally, record data for close range IPD’s.

Experience has shown the largest factors on the above tests come from the difference in sizes of the exit pupil of the binoculars and the pupil diameter of the test subject at the time of the test. For instance, a larger error will be found when using a 6 mm exit pupil and the subject’s pupil diameter is 2.5 mm versus measuring a 4 mm exit pupil with inside lighting and pupil diameter is 3-3.5 mm. It appears that the test subjects almost always quit adjusting the binocular as soon as the eye pupil is completely within the boundaries of the exit pupils. This does not mean they are centered, they usually are not as suggested by the test results. Tests suggest the best accuracy is when the exit pupils and pupil diameter match.

Before continuing with the test results, a note about measuring IPD by ruler and pupilometer. I have researched the subject on the web and with my personal ophthalmologist and refractionist. Research papers on the web suggest measurements by ruler are usually off by about 2 mm or more, while pupilometer results average less than 1 mm. Both of the professionals mentioned measure my eyes once a year and we run this test for both our benefits. Both usually measure my IPD with a ruler at 66 or 67 mm. Using their pupilometer, my pupilometer and having measured my IPD with “close range photogrammetry” and having instrument persons measure my IPD by surveying means, I am confident my average infinity IPD is 63.83 mm. My pupilometer only reads to the closest 0.5 mm and always shows either 63.5 or 64 mm. My ophthalmologists pupilometer indicates to 0.1 mm and is always within +/- 0.2 mm of 63.8. Keeping the eye still during measurements is very hard to do.

I have attached a brief test result using a 4 mm exit pupil with average indoor store lighting for 11 test subjects. It indicates that coming from wide IPD the average error was 3.7% and coming from the narrow IPD position, the error was about 1%. The first time I did this test (without the aid of the pupilometer) was in the mid 80’s and using 7x50 porro (7 mm exit pupil) at an outdoor archery tournament with 32 volunteer test subjects, the results were about a 5% error. At that time I was measuring IPD with a ruler, I expect now that the results were conservative.

It may pay for some to take several pairs of binos with varying exit pupils and set their IPD by your customary means and the measure the actual settings and record them and average them. You may find a larger than desirable spread which would indicate you may need to get a better idea of your actual IPD.

Why is this important? I have an unconfirmed theory (actually, more of a question/supposition) that the wrong IPD may be responsible for a lot of the CA complaints posted. Consider that if your IPD is off 5% you would be off center 1.6 mm for a half IPD setting of 32 mm. That is 6.1 degrees off axis AFOV if your eye relief is 15 mm. Your eyes are starting 10% off axis even before you start scanning your FOV, this may be enough to see CA even at the center field.

This is the reason I always set the IPD on my binos with a gauge.

I have had lingering questions on this subject for many years.

Ron

Most, if not all, (to the best of my knowledge) porro prism binoculars have an IPD gauge. I've always liked them for this reason. You can preset them to your best IPD and then tweak them to get the best view. I don't know my exact IPD but I do know it is somewhere around 68-69. I think that is another reason that the Nikon SE's and EII's and the Swift Audubon's are so easy to use. With roof prisms one has to initially hunt and seek the closest, most comfortable IPD.
Bob

mooreorless said:

Just point your finger like you are going to shoot something at a distance, close one eye at a time the eye that is lined up is the one.

Click to expand...

Neat test and it works. I've always naturally used my left eye with my microscope and spotting scope--and now I know why. Is it possible some end up using the non-dominant eye? What difference would it make?

Ron's measurements are also interesting. If I read it right 15 of 22 IPD adjustments were wide of the mark, exactly what I had done.

Mark

Kammerdiner said:

Is it possible some end up using the non-dominant eye? What difference would it make?

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Sometimes, yes.

It means you either use your worse eye (the vision is worse so it becomes non-dominant) or you have to close the dominant eye.

I have a couple of examples as I'm left eye dominant (my right eye has a lot more uncorrected astigmatism than the left and my vision wasn't corrected as a kid so I think my brain selected the better eye) but right handed (and left footed ... go figure).

People who make rifles assume you are going to be right handed and then assume you are right eye dominant too so you can look down the open sights. So I have to close the left eye to shoot otherwise I just don't see the sights well.

The same is true of small cameras that put the viewfinder on the left side expecting you to use your right eye (and have your nose out to the left of the camera) and your right hand for a button push.

I couldn't figure out "what a dumb this design was because it always gets nose prints on the LCD" when putting my left eye up to the viewfinder. It wasn't until I though about it that these folks wanted me to use my non-dominant eye and not smoosh my nose into the LCD .

Oh no we are getting off topic again, easy to do. Maybe we should move IPD/Dominant eye down to here.
http://www.birdforum.net/showthread.php?t=156974

mooreorless said:

Oh no we are getting off topic again, easy to do. Maybe we should move IPD/Dominant eye down to here.
http://www.birdforum.net/showthread.php?t=156974

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Steve,

That "schoolmarmish knuckle rapping" about the thread taking a knuckleballer's winding path tells me that you have been spending too much time on that other bin forum.

But if you need to squawk, the FAA's hijack notification frequency is "7500". I kid you not!

Back on, ur.. I mean, off topic... generally, I find that my IPD setting is more critical with roofs, particularly midsized roofs, than it is with porros.

With high quality porros such as the 8x32 SE or 8x30 EII I can't detect any discernible degradation of the image or significant increase in CA if my IPD is a bit off.

OTOH, with a roof, once the IPD is set correctly, I can "set and forget" whereas with porros, I have to reset the IPD at close focus if I want to avoid crossing my eyes and seeing overlapping barrel shadows.

The factor that negates that general rule of thumb has already been mentioned, the size of the sweet spot.

The Celestron 8x32 Ultima (the original Jap. porro) had such a small (but very sharp) sweet spot that my IPD on those porros was critical at any distance.

So I find that the size of the sweet spot and more generally the binocular type (roof vs. porro) both affect the how fastidious I must be with my IPD setting.

Bringing this back to the OP, I think the relatively "smallish" sweet spot on the 8x32 FL would drive me batty.

Not so much because I had to be more critical about the IPD setting, but because I would see the "fuzzy edges" when my eyes darted ahead while panning.

The way to avoid that is to turn your head with the bins rather than let your eyes wander, but that's not easy for me or my cousin Dion (I kid you not), because...

Oh well, we're the type of guys who will never settle down
We wander off topic when the mods are not around

They call us the wanderers, yeah the wanderers
We roam around around around...

After rereading Oleaf's thread I guess this "off/topic wouldn't really fit in there. Interesting topic IPD settings etc.

With "help" from Surveyor I reread the start of this thread and the only one getting off topic is me.:eek!:B

brocknroller said:

…Bringing this back to the OP, I think the relatively "smallish" sweet spot on the 8x32 FL would drive me batty.

Not so much because I had to be more critical about the IPD setting, but because I would see the "fuzzy edges" when my eyes darted ahead while panning.
...

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Hail B'rock, son of Grilka,

I do not perceive the 8x32 FL's sweet spot as smallish, although the very edge is certainly fuzzy. I find that this binocular possesses a quite useful image across a very large part of the field, but I am not prepared, this evening, to be more specific.

Happy bird watching,
Arthur Pinewood

Pinewood said:

Hail B'rock, son of Grilka,

I do not perceive the 8x32 FL's sweet spot as smallish, although the very edge is certainly fuzzy. I find that this binocular possesses a quite useful image across a very large part of the field, but I am not prepared, this evening, to be more specific.

Happy bird watching,
Arthur Pinewood

Click to expand...

I find it just as user friendly as my 8x32 SE's

Surveyor said:

Hello RonH,

I just read your post with interest. I, too, have taken a critical view of IPD for quiet some time.

Seems to me to be an important subject that is largely ignored or deemed of no consequence. Then, again, may be much ado about nothing. I can not convince myself though....

Why is this important? I have an unconfirmed theory (actually, more of a question/supposition) that the wrong IPD may be responsible for a lot of the CA complaints posted. Consider that if your IPD is off 5% you would be off center 1.6 mm for a half IPD setting of 32 mm. That is 6.1 degrees off axis AFOV if your eye relief is 15 mm. Your eyes are starting 10% off axis even before you start scanning your FOV, this may be enough to see CA even at the center field.

This is the reason I always set the IPD on my binos with a gauge.

I have had lingering questions on this subject for many years.

Ron

Click to expand...

Ron,

Really interesting. With my two 8x32s--SE and EL--I have slightly different experiences. For me, the SE is quite forgiving, but the EL is extremely sensitive to proper IPD setting. I can't go so far as to set IPD with a gauge, because in the field I often fold bins down for close viewing and then spread them again. I have found that CA is obviously affected by improper IPD setting in the EL. In fact I am convinced that in the EL, the entire quality of the image is affected by only slightly maladjusted IPD, though I am at a loss to quantify it.