• BirdForum is the net's largest birding community, dedicated to wild birds and birding, and is absolutely FREE!

    You are most welcome to register for an account, which allows you to take part in lively discussions in the forum, post your pictures in the gallery and more.

10x32 v 10x42 image size (1 Viewer)

Sancho

Well-known member
I have IS 10x42 and 10x32. Tonight is a full moon, with clear skies here, and the moon rose at about 6pm. I took both binos out to look. Firstly and more obviously, the image through the 10x42 was noticeably brighter and sharper. This is not a criticism of the 10x32, which is no slouch. But the image through the smaller bino seemed...smaller. At first I though this was an illusion, so I checked by holding a barrel of each to each eye to compare. The image of the moon through the 10x32 was definitly 20 per cent smaller than through the 10x42. I'm not ocncerned, I love both binos. But I thought 10x should be 10x no matter what the objectives are. It seems the IS 10x32 are really the IS 8x32 of my dreams. This is good news, but I am confused.
 

Pinewood

New York correspondent
United States
Hello Sancho,

Occasionally, the specification is not an accurate description of the binocular. I have a 6.5x32 which is really a 6.4x32.

Stay safe,
Arthur
 

Sancho

Well-known member
Thank you Arthur!!! In this case, the Canon specifications are way off the mark. At least in my two units.
 

kabsetz

Well-known member
Sancho,

Not to doubt your observations, but I'd suggest (if you did not already) to do the same test of one barrel of each binocular to each eye also with eyes reversed. At least for me, my two eyes give my brain a distinctly different-sized image, both with and without glasses.

One way to test magnification differences is to put a booster behind an eyepiece and check the field width of the booster (any binocular or monocular will do as a booster). Larger magnifications will give a narrower field for the booster, so if distance is kept exactly the same it is a simple and quick way to see if the magnifications are same or different. If you have a tape measure as a target, you will get two figures that let you calculate the relative magnification difference.

I would not be surprised if there is some real difference in magnification, but 20% I find quite unlikely.

- Kimmo
 

Sancho

Well-known member
Sancho,

Not to doubt your observations, but I'd suggest (if you did not already) to do the same test of one barrel of each binocular to each eye also with eyes reversed. At least for me, my two eyes give my brain a distinctly different-sized image, both with and without glasses.

One way to test magnification differences is to put a booster behind an eyepiece and check the field width of the booster (any binocular or monocular will do as a booster). Larger magnifications will give a narrower field for the booster, so if distance is kept exactly the same it is a simple and quick way to see if the magnifications are same or different. If you have a tape measure as a target, you will get two figures that let you calculate the relative magnification difference.

I would not be surprised if there is some real difference in magnification, but 20% I find quite unlikely.

- Kimmo
Thanks Kimmo, I'll give it a try!
 

Sancho

Well-known member
Okay I tried every combination of barrel-to-eye, and the booster test with a tape measure. I'm getting a difference of 15-18%. I tried to take photos of the moon, through the binos, using all four barrels, but couldn't get my phone 'lined up' and gave up. Has anyone else out there got IS 10x42 and 10x32? If so, could you check? None of this is important but it passes the time.
 

Binastro

Well-known member
Hi Sancho,

Just count bricks on a wall allowing for mortar.
At say 50 metres or more.
Use left eye, then right eye.
Unaided eye and binocular at the same time.

However, if wearing glasses with different eye prescriptions a difference of 15% is possible.

A difference is also possible if one is comparing views at close distance.

I wonder if using the 10x42 with a reversed 10x32 behind it should give 1x magnification.
Although, again, having to focus may affect result.

Measuring exit pupils may not help if either binocular vignets.

Regards,
B.
 

henry link

Well-known member
Sorry to be so late with this, but I just got around to measuring the magnification of my Canon 10x32. I used the simple method of photographing a linear target at about 150 meters with a DSLR set at 55mm and infinity focus, then photographing the same target through the binoculars using the same camera and settings and then measuring the difference in the size of the target in the two photos. I found the magnification across the center 5ยบ of apparent field to be within 1% of exactly 10x at that distance.

Henry
 
Last edited:

Binastro

Well-known member
Thanks Henry,

I have found that Leica, Zeiss and Russian binoculars usually have accurate magnifications and field sizes.

Bushnell had a habit of overestimating magnification by 15% on some binoculars.
This allowed for large stated real FOVs but small AFOVs.

For example the 4x21 is actually 3.5x21.
5x25 is actually 4.4x25.

The Celestron 8x30 is from memory about 6.5x27.

The Canon 10x42 L IS was reputedly originally 10x38 but later models nearer 42mm aperture.

It is worth checking specs.

Many of the extra wide angle binoculars overstate the field by up to 10%.

Magnification usually changes across the field anyway.

Regards,
B.
 

kabsetz

Well-known member
Henry,

Could you measure the objective spacing on your 10x32?

I just re-measured the true aperture of my 10x42 L IS as just over 41 mm and the exit pupil diameter as between 4.1-4.15 mm. This would mean a magnification of 10x +-1,5%.

For measuring, I used a rectangular card held in front of the objective, measuring what is the width of the card where you go from seeing the faintest of light on both sides of the card simultaneously to only seeing light on one side or the other as one moves the card from side to side.

For the exit pupil, same method but holding an electronic digital calliper over the exit pupil, checking what is the width that no longer shows light on both sides when viewed by one eye from arm's length.

Quick and dirty but amazingly precise.

- Kimmo
 

Binastro

Well-known member
The only slight extra error is the width of the eye pupil.

Perhaps also tiny head movements and persistence of vision.

Regards,
B.
 

Sancho

Well-known member
Thanks Henry. I'll try to replicate that test through all four barrels (on 10x32 and 10x42). Smaller bino has no tripod mount so some duct tape will be involved. Not sure how to ensure the camera lens is at exactly the same distance from the oculars, but I'll figure something out. Meanwhile the moon's image (not full anymore) through the 10x32 sits comfortably inside the 10x42 version, with a healthy margin, no matter which eye or barrel I use. I wish I had some way of showing this to you more expert folk. I'm not complaining, I like both binos, I'm just mildly amused. I don't know if there's such a thing as sample variation in particular models, that could cause two binos of the same model to vary in magnification, somehow I doubt it.
 

Binastro

Well-known member
The Canon 10x32 and 10x42 may focus in different ways.

They may correct different observers eyesight in different ways.

Two observers with different eye prescriptions may see different magnifications.

The variable here seems to be eyesight rather than the neutral magnification of 10x in each binocular.

Regards,
B.
 

Sancho

Well-known member
The Canon 10x32 and 10x42 may focus in different ways.

They may correct different observers eyesight in different ways.

Two observers with different eye prescriptions may see different magnifications.

The variable here seems to be eyesight rather than the neutral magnification of 10x in each binocular.

Regards,
B.
Thank you Binastro! I don't know anyone here foolish enough to stand out in the cold looking at the moon through four different barrels with each eye, just to compare. So if it is just my eyes, I'll stop torturing the binoculars.
 

PeterPS

MEMBER
Thank you Binastro! I don't know anyone here foolish enough to stand out in the cold looking at the moon through four different barrels with each eye, just to compare. So if it is just my eyes, I'll stop torturing the binoculars.
Hi Sancho,
The difference in the apparent sizes of the two images might be due to the scaling effect illusion: if your IPD is smaller than the distance between the objective lenses of the 10x32, which is 69mm as measured by Henry, then there will be a scaling effect in the 10x32, the question is if their effect is less than that via the 10x42 (what is the objective separation for the latter?).
Peter
 

Binastro

Well-known member
Hi Peter,

The separation of the objectives on my Canon 10x42 is 70mm using a ruler, which probably isn't of high accuracy.

I don't want to use calipers as I'd scratch the front glass surface.

Regards,
B.
 

Sancho

Well-known member
Hi Sancho,
The difference in the apparent sizes of the two images might be due to the scaling effect illusion: if your IPD is smaller than the distance between the objective lenses of the 10x32, which is 69mm as measured by Henry, then there will be a scaling effect in the 10x32, the question is if their effect is less than that via the 10x42 (what is the objective separation for the latter?).
Peter
Hi Peter! No, it's not on account of the IPD, because the real (?) difference is most obvious when I hold only one barrel of each binocular to each eye, and 'merge' the images of the moon into one (which makes one moon-image fit comfortably inside the other, instead of both being the same '10x' size). As Binastro says, this could well be my eyeballs and frazzled brain, rather than the glass involved.
 

PeterPS

MEMBER
Hi Peter! No, it's not on account of the IPD, because the real (?) difference is most obvious when I hold only one barrel of each binocular to each eye, and 'merge' the images of the moon into one (which makes one moon-image fit comfortably inside the other, instead of both being the same '10x' size). As Binastro says, this could well be my eyeballs and frazzled brain, rather than the glass involved.
Hi Sancho,
If you noticed the same size difference after repeating the above test for all four combinations of eyes and barrels, then I am unsure that the explanation is (a difference between) your eyes. The mystery remains unsolved....
Cheers, Peter
 

Binastro

Well-known member
I was suggesting that as the objective/eyepiece distance changes or apparently changes when correcting eyesight these two binoculars are giving different magnifications compared to the neutral position.

This is either when wearing glasses or not wearing glasses.

Does one use a positive focus element and the other a negative element?
Or are the separations of elements and design of the optics different in the two binoculars?

Regards,
B.
 

Users who are viewing this thread

Top