I decided to start a new thread on this subject, which has been under discussion in the thread "First Look at 7x42 EDG" in the Nikon subforum. I hope Surveyor will copy and paste his recent measurements from there.
The main question under discussion has been whether binoculars with internal focusing lenses are able to maintain constant magnification at any distance or show an increase in magnification at close distances like binoculars that adjust focus by varying the distance between the objective and eyepiece. Surveyor and Edz at Cloudy Nights Binocular Forum have measured increases in magnification at close distance for some binoculars using focusing lenses. I've measured other models with constant magnification. I'm hoping somebody will come forward with some knowledge about how these focusing lens systems are designed.
In the meantime here are the results of some magnification measurements I made yesterday comparing two binoculars with focusing lenses (the Zeiss FLs) to six Porros with moving eyepieces. I picked the six Porros for their close focusing ability. First measurement is closest focus for the right barrel of each binocular (combination of close focus setting and maximum positive diopter compensation) and second measurement is 80', the distance limit of my backyard test set-up.
Zeiss 8x42 FL: 7.91x at 77", 7.89x at 80'
Zeiss 8x56 FL: 8.07x at 94", 8.08x at 80'
Nikon 8x30 EII: 8.34x at 77", 8.03x at 80'
Nikon 10x35 EII: 10.49x at 112", 10.10x at 80'
Nikon 8x32 SE: 8.44x at 83", 8.08x at 80'
Zeiss 8x30B (Porro): 8.29x at 107", 8.14x at 80'
Swarovski 8x30 Habicht: 8.33x at 87", 8.06x at 80'
CZJ 8x50 Octarem: 8.37x at 146", 8.14 at 80'
Notice that most of the measurements (except the 8x42 FL) are above specified magnification. Magnification at infinity focus would be a little less than 80' in the Porros, but probably not much, maybe 0.02-0.04x. There are only about 2-3 diopters of focus change between 80' and infinity, but over 20 diopters between 80' and the closest focus. So, for reasons I don't understand I think all my figures are probably a little high, maybe about 0.5%. I don't really expect accuracy much better than 1%.
Henry;
I made some rough readings and I am now thinking that even the internal focusing lenses may exhibit some enlargement of magnification. The infinity measurements are iffy at best, done very quickly and hap-hazardly. The close up measurements should be pretty good
The two binos tested, Monarch 8x36 and Leica 8x32 BA, yielded the following approximate results. When time and conditions permit the procedures will be repeated to get a mean error range and check or verify the infinity readings.
------------------Monarch 8x36 (Lt/Rt)---------------8x32BA (Lt/Rt)
Infinity------------7.89x/7.91x-------------------------7.782x/7.791x
Close up-----------8.23x/8.17x—3.366m avg.----------8.176x/8.205x—3.391m avg.
------------------------/8.11x—2.763m----------------------/7.971x—3.364m???
----------------------------------------------------- 8.173x/-----------3.378m
Close up results-----.07x/.09x----------------------------.06x/failed (0.4x)
95% confidence < 0.1x
These rough observations seem to suggest that there may be as much as 0.2-0.25% per diopter change of at least some of these types of binocular.
Note: another factor found. The Monarch had to be refocused between barrel observations.
Have a good day.
Ron
Henry;
I agree fully with your statment "Notice that most of the measurements (except the 8x42 FL) are above specified magnification. Magnification at infinity focus would be a little less than 80' in the Porros, but probably not much, maybe 0.02-0.04x. There are only about 2-3 diopters of focus change between 80' and infinity, but over 20 diopters between 80' and the closest focus. So, for reasons I don't understand I think all my figures are probably a little high, maybe about 0.5%. I don't really expect accuracy much better than 1%.
I will do some checking, I have never checked at around 25m. It seems we are pretty much together at the close end and differ at the long end. I just used the photo method there and may it prove to be worthless.
BTW, for the sake of consistancy, which tube are you measuring. I will drop back to that for future reference.
Have a good day.
Ron
Henry;
I found these old photos of my collimator results before Monarchs went back to Nikon. There is too much camera movement and focus blur to be considered good enough to measure from, but they indicate I have a problem with my camera method, or at least a difference I need to account for.
The blue lines are a 6 arc minute grid (the grid is in 10th's of a degree). This grid is printed on paper and not an etched reticle. I still have a lot of work to do since I never used this for absolute power but just to compare one tube against the other.
These seem to indicate a left tube of 8.21x and right of 8.19x, much closer to the close up readings. Keep in mind that the actual bino to grid distance is only about 500mm though the focus and focusing elements are at infinity.
More study due, get back to you later.
Have a good day.
Ron