Main optical difference Porros v Roofs (1 Viewer)

There is a difference between porros and roofs that is never mentioned, and is the reason i am sticking with porros. You get far better 3D vision with them
as the objectives are more or less twice as far apart. As magnifying flattens 3D effect you want the objectives as far apart as poss to compensate. Looking at trees and shrubs while spotting birds in them IMHO is more realistic
after all that is why we have two eyes. That said looking long distance or at flat surfaces (buildings eg) there will be no difference but that isn't birdwatching. It will be noticed up to say 100 metres. Not all porros however improve 3D, pocket or reverse porros make matters worse as the objectives are nearer than your eyes to be compact so its sort of a double whammy. I once looked through a pair of Pentax 16x24 reverse porros and there was hardly any 3D effect unless you where looking just feet away as the magnification was 16! naturally they were not very bright either.

Not sure why this is in the opticron forum but anyway here are my thoughts.

The 3D aspect has been mentioned before but I wonder if the effect isn't counter to what nature intended. By this I mean if your ipd is increased with porros your brain is working harder to pull the image together coherently especially at close distances. So a binocular that mimics the ipd of your eye at the objective end will be more comfortable and natural.

Comparing roof to porro of same spec and brand the porro image looks smaller. I wonder if this is an illusion or the roof image looking bigger is an illusion.

Nev

dipped said:

Comparing roof to porro of same spec and brand the porro image looks smaller. I wonder if this is an illusion or the roof image looking bigger is an illusion.

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This might well be an effect of field of view which will tend to be wider in porros than roofs. A wider FOV often gives the illusion of lower power. I tested this by setting up two scopes with 30x eyepeices, one had a narrow FOV and appeared to give a much higher mag than the one with the wide FOV.

I have some problems with porros with objects too close. My eyes get fatigued and confused. I like reverse porros, eith even less 3d!

TDD said:

There is a difference between porros and roofs that is never mentioned, and is the reason i am sticking with porros. You get far better 3D vision with them
as the objectives are more or less twice as far apart. As magnifying flattens 3D effect you want the objectives as far apart as poss to compensate. Looking at trees and shrubs while spotting birds in them IMHO is more realistic
after all that is why we have two eyes. That said looking long distance or at flat surfaces (buildings eg) there will be no difference but that isn't birdwatching. It will be noticed up to say 100 metres. Not all porros however improve 3D, pocket or reverse porros make matters worse as the objectives are nearer than your eyes to be compact so its sort of a double whammy. I once looked through a pair of Pentax 16x24 reverse porros and there was hardly any 3D effect unless you where looking just feet away as the magnification was 16! naturally they were not very bright either.

Click to expand...

Very well put. I tend to go along with your thoughts — there is no way a roof can provide the same satisfying three-dimensional view as a Porro with equivalent optics.

Not long ago there were quite a few discussions, opinions, and preferences on BF about porro vs. roof designs. This has quieted down of late, probably because there are few high quality porros still being marketed by the big four.

My all time favorites are the #804 Swift 8.5x44 ED that went out of production about 2000. Others are still ecstatic about their Nikon 8x32 SE or 8x30 E2. Some still quietly covet their waterproof Swaro 8x30 Habicht's.

Blue skies,
Ed

postcardcv said:

This might well be an effect of field of view which will tend to be wider in porros than roofs. A wider FOV often gives the illusion of lower power. I tested this by setting up two scopes with 30x eyepeices, one had a narrow FOV and appeared to give a much higher mag than the one with the wide FOV.

Click to expand...

Actually the roof has a wider field than the porro! 7.8 to 7.5 degrees so something else is going on. Another effect that I hadn't noticed till I got the roofs is that with the porros I feel I am shorter, the image is at a lower viewpoint, which I guess is explained by the porro design compared to the roofs.

Are the scopes both identical models with the same prism design?

Nev

dipped said:

Actually the roof has a wider field than the porro! 7.8 to 7.5 degrees so something else is going on. Another effect that I hadn't noticed till I got the roofs is that with the porros I feel I am shorter, the image is at a lower viewpoint, which I guess is explained by the porro design compared to the roofs.

Are the scopes both identical models with the same prism design?

Nev

Click to expand...

I have done the scope test a few times though not always with identical scopes. The easist way to test on identical scopes is to compare a 20x fixed against a 20-60x zoom. The zoom will (almost always) have a narrower FOV than then fixed and gives the illusion of being a higher mag. Seems starnge to me that the bins with the smaller FOV seem lower power than the ones with the wider FOV, no doubt someone will be able to explain it.

dipped said:

Not sure why this is in the opticron forum but anyway here are my thoughts.

The 3D aspect has been mentioned before but I wonder if the effect isn't counter to what nature intended. By this I mean if your ipd is increased with porros your brain is working harder to pull the image together coherently especially at close distances. So a binocular that mimics the ipd of your eye at the objective end will be more comfortable and natural.

Comparing roof to porro of same spec and brand the porro image looks smaller. I wonder if this is an illusion or the roof image looking bigger is an illusion.

Nev

Click to expand...

I have noticed this myself. When you look at something through bins its like looking through the end of a pipe. The smaller the apparent field of view the further away from the end of the pipe you feel you are and therefore the further away from the object you feel you are, thus making the object appear smaller .I wonder if this is the reason for the illusion. I check the relative apparent FOV between bins by looking through one eyepiece of each at the same time pointing them to the sky and seeing the relative size of the two circles ,the magnification does not matter when doing this even if they are different, however if the two have different mags it obviously affects the real FOV which is a different thing to the apparent FOV

Don't think you can in any way mimic the naked eye with bins even if the ipd is the same, you couldn't have the objectives between 2 and 7mm in dia like the pupils (I know that may be a silly example) and the eyeballs swivel to try and give you the same field of view with both eyes at changing distance, and objectives can't
(they would be a King's ransom to buy if they had that but you never know what's possible these days).

Doug

Tero said:

I have some problems with porros with objects too close. My eyes get fatigued and confused. I like reverse porros, eith even less 3d!

Click to expand...

If your interest takes you to very close focus (butterflies) reverse porros will be the most comfortable and there is now a pair with close focus 2feet!.

You can ease the discomfort with porros at very close focus by closing up the ipd and moving away from the eyepieces a bit so just the overlaping part of the field can be seen, so temporarily sacrificing FOV for comfort, however nothing can be done for the loss of 3D, by having roofs or reverse porros. It just depends which of the different pros and cons are most important to you.
Perhaps if your interest is equally say butterflies and birds maybe roofs are the best compromise.

By the way at very close focus you will probably find high mag (say 12x) reverse porros will be more uncomfortable than say 8x roofs because the overlap of the fields of the two objectives (even though they are physically closer than the roofs will be less. If you take a ridiculous example say the mag was so high each objective could only take in the physical field the size of a penny and the spacing of the objectives was two pennies there would be no overlap at all and the brain could not cope, so basically its possible to have less 3D AND more dicomfort. Sorry if I am not very clear I know its a bit long winded....Doug

At 2' you're moving into the realm of stereo microscopes, most of which are little more than reverse Porro binoculars with very close focusing capabilities (2 to 3").

Charlie