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Why Such Incredible Depth of Field On My Fuji 7x50? (1 Viewer)

pwjp2011

Active member
Before I ask the question I am about to ask I want to mention that I am quite familiar with f-stops and iris size. I am a long time amateur photographer and have used Canon EOS when there was no digital. So I get the whole thing about iris size relating to depth of field.

So here is my question - why do my military surplus Fuji 7x50 have such incredible depth of field? My friend whom is a big time hunter brought over a pair of older Pentax 7x35 (metal with black leather) and a Leica 8x42 that was about 5 years old I guess (though I really like those Leicas :) ). We were playing in the yard with them and with the 7x50s I didnt have to adjust them at all to stay sharp while with the Pentax and Leica you had to tweak them at times.

Anyway what I was surprised was that my $120 Fuji's had better depth of field than either. I understand that newer binocs have better lens coatings and all that. My 7x50s have a giant exit pupil (you can see in the dark never mind at twilight) so they shouldnt have such incredible depth of field.

Anyone want to explain it to me?
 
I strongly suspect (but cannot prove) that the Fuji has a much longer focal length and therefore larger focal ratio. So deeper dof.

Best,
Jerry
 
At f4 a 7x35mm binocular would use a 20mm eyepiece. A 7x50 binocular would use a much larger eyepiece of about 28.5mm.

I suspect that both your 7x binoculars are Porro prisms but you don't say so. If one is a Porro and the other is a Roof maybe it looked like there was a difference? Close objects in a Porro prism typically look smaller than if seen with a roof prism.

The Leica 8x42 is always going to be at a disadvantage in a comparison with your two 7 power binoculars when it comes to DOF.

My experience comparing my Leica 8x42 Ultravid with my Leica 7x42 Trinovid clearly shows that the 7x42 has a deeper DOF. I did this by looking into the heavy foliage on the branches of a large Silver Maple tree which has a trunk about 20 feet off my deck. The 7x42 is by far the better binocular to use in following small birds through this tree.

Bob
 
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At f4 a 7x35mm binocular would use a 20mm eyepiece. A 7x50 binocular would use a much larger eyepiece of about 28.5mm.

I suspect that both your 7x binoculars are Porro prisms but you don't say so. If one is a Porro and the other is a Roof maybe it looked like there was a difference? Close objects in a Porro prism typically look smaller than if seen with a roof prism.

The Leica 8x42 is always going to be at a disadvantage in a comparison with your two 7 power binoculars when it comes to DOF.

My experience comparing my Leica 8x42 Ultravid with my Leica 7x42 Trinovid clearly shows that the 7x42 has a deeper DOF. I did this by looking into the heavy foliage on the branches of a large Silver Maple tree which has a trunk about 20 feet off my deck. The 7x42 is by far the better binocular to use in following small birds through this tree.

Bob

Thanks for the reply. So what does the size of the eye piece have to do with dept of field?

Yes the 7x50 and 7x35 are porro prism binoculars. You have to excuse any ignorance on my part. Till recently I didnt know there were two different kinds of binoculars. The 8x42 was a roof. Have to say I really liked the Leica, really sharp picture and it was built like a tank.
 
Thanks for the reply. So what does the size of the eye piece have to do with dept of field?

Yes the 7x50 and 7x35 are porro prism binoculars. You have to excuse any ignorance on my part. Till recently I didnt know there were two different kinds of binoculars. The 8x42 was a roof. Have to say I really liked the Leica, really sharp picture and it was built like a tank.

Hi again and Welcome to Bird Forum!

I don't really know if it has anything to do with it. The 7x50mm binocular does have a longer focal length than the 7x35mm which is why it requires an eyepiece with a longer focal length. If you put the shorter eyepiece of the 7x35 on the 7x50 it would become a 10x50.

The consensus here is that all binoculars of the same power will have the same depth of field and the lower the of power the binocular the longer the depth of field will be at short distances.

The depth of field will become more shallow as the distance of the object you are viewing gets further from the binocular. If you are going to test your two 7 power binoculars DOF against each other you will have to do it on the same object and try to determine if one has greater DOF than the other.

That is why I used a tree near my house to test the DOFs of my 7x42 and 8x42 binoculars.

Now, for this purpose, it is probably better to use a tree that has dropped its foliage. What you do is focus both binoculars on, say, a knothole in a branch in the middle of the tree and then try to determine how much of the tree branches are in focus in front of the knothole branch and behind it. (I could clearly see a difference when I did this with my 7x42 and 8x42. The 7x42 had deeper DOF.)

Theoretically both 7 power binoculars should show the same DOF. Give it a try!

Bob
 
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I don't know how similar those older milspec 7x50 Fujinon are to the FMTSX 7X50 Fujinon, but the latter certainly has the greatest depth of field I've ever seen in a binocular. The IF focusers are virtually redundant for the massive majority of viewing. Regardless of the exit pupil, They're also the largest eye pieces I've seen on a binocular. They're monstrous jewel like things of beauty.

DOF obviously goes well beyond mere format, because I have other zeiss roof bins of 7x42 and 8x56 and the Fujinon blow them both away regarding depth of field. The Fuji are massively superior in this regard. The big porro fuji objectives are quite a distance apart too.
 
I don't know how similar those older milspec 7x50 Fujinon are to the FMTSX 7X50 Fujinon, but the latter certainly has the greatest depth of field I've ever seen in a binocular. The IF focusers are virtually redundant for the massive majority of viewing. Regardless of the exit pupil, They're also the largest eye pieces I've seen on a binocular. They're monstrous jewel like things of beauty.

DOF obviously goes well beyond mere format, because I have other zeiss roof bins of 7x42 and 8x56 and the Fujinon blow them both away regarding depth of field. The Fuji are massively superior in this regard. The big porro fuji objectives are quite a distance apart too.

Yes, I would agree with that Rathaus, my Fuji FMTR-SX probably has the best depth of all my binoculars, but I have a vintage Swift Storm King MK11 7x50 IF, which was top of the Swift range back then, a big heavy beast, similar specs to the Nikon Tropical, and it actually comes pretty close to the Fuji for DOF, actually runs it close for everything.
 
Yes, I would agree with that Rathaus, my Fuji FMTR-SX probably has the best depth of all my binoculars, but I have a vintage Swift Storm King MK11 7x50 IF, which was top of the Swift range back then, a big heavy beast, similar specs to the Nikon Tropical, and it actually comes pretty close to the Fuji for DOF, actually runs it close for everything.

Yes that doesn't surprise me about the vintage Swifts you mention. I've been astonished at the image quality of a 20-30yo Audubon I snapped up off eBay, so I don't doubt what you say about the 7x50.
 
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