Difference in View Size: 8.5x42 and 8x30 (1 Viewer)

[Sequoia Kid]

Strange question, but here we go.

I regularly use a set of 8.5x42s and have recently tried a set of the 8x30 Habichts and noticed a strange thing about the views in them. Other than the slight difference in the magnification I noticed that things looked smaller through the 8x30s compared to 8.5x42s. The FOV

My question is what causes this? My two possible ideas are either the difference in exit pupil, with the smaller view being a symptom the smaller EP in the 30s, or possibly it's a difference between the porros and the roof prisms.

There are some folks around here who know a hell of a lot more than me and I'm hoping to glean some knowledge.

Thank you for any help.

 

[tenex]

Other than the slight difference in the magnification I noticed that things looked smaller through the 8x30s compared to 8.5x42s. The FOV

If you think things look smaller in the Habicht, that's exactly because it's only 8x compared to 8.5. So I'm not sure what "other than that" means, or what you meant to say about FOV? The real field of the two is quite similar, 408 ft vs 399, which means the apparent field of the Habicht will look smaller, again because of the lower magnification. (FOV is ultimately due to eyepiece design, not related to exit pupil, prism type etc.)

 

[Sequoia Kid]

If you think things look smaller in the Habicht, that's exactly because it's only 8x compared to 8.5. So I'm not sure what "other than that" means, or what you meant to say about FOV? The real field of the two is quite similar, 408 ft vs 399, which means the apparent field of the Habicht will look smaller, again because of the lower magnification. (FOV is ultimately due to eyepiece design, not related to exit pupil, prism type etc.)

Yeah, the FOV sentence Didn't get fully written I guess. I was just thinking that the FOV is similar on both, as you say.

I guess it's a matter of the magnification difference, and the apparent FOV as you have mentioned.

 

[tenex]

On second thought, did you really notice a difference in AFOV here? The Habicht has the slightly larger RFOV, the EL's magnification is only modestly larger, and the angular magnification distortion of Swarovision tends to reduce AFOV. That all seems likely to add up to not much.

 

[yarrellii]

I think I remember reading several forum members stating how switching between Porro vs roof binoculars of the same magnification, say 8x vs 8x gave the impression of viewing smaller image through the Porro, as if one was truly 8x but the other slightly less. I have had exactly that experience comparing roof vs Porro of the same magnification in many occasions. My recollection is that magnification remains true to what specification say (within margin of error and with the exception of some binoculars that do have inconsistencies), but there was a reason I just can't remember for that (I'm sure a forum member can chime here, or else a quick search might find the answer). But yes, many users share the same impression... and if you add to this that you were actually comparing an 8,5x roof vs an 8x, then the difference may have felt even bigger.

 

[A2GG]

I have an 8x30 CL and 8x32 Trinovid HD with same true FOV (372ft@1,000yds). When I use the CL for a couple days then go to the Trinovid I notice right away the bigger view (circle) in the Trinovid. The exit pupil is slightly larger (4mm vs 3.75mm) but it makes a noticeable difference when viewing. I'm not sure if this is what you're referring to by "view size" but I think this may contribute to the view looking 'bigger' because the viewing 'circle' appears bigger in a bino with larger EP.

 

[yarrellii]

Here is an old thread, from 2005, about this (which oddly enough references to an even older thread about this):

Porro and roof object size

This is an effort to pick up an interesting thread which was lost when the site went down recently. Someone posted the observation that porro and roof binoculars of the same magnification deliver the rather puzzling effect of presenting the image (object really) different, i.e. in roof...

www.birdforum.net

So apparently, this is an impression being reported by many users.

 

[henry link]

I think eventually a consensus developed (to the extent that is possible on Birdforum!) that attributes most of the size illusion between roofs and Porros to the increased stereopsis of traditional Porros with widely spaced objective lenses. Here's another thread where I experimented with increasing the stereopsis of my eyes alone without any added magnification at all. The difference in apparent object sizes was quite obvious just from changing the stereopsis of the eyes, no binocular needed.

Is "3-D" More Natural in Porros or Roofs?

I understand the allure and entertainment value of increased stereopsis in traditional Porros over inline roofs, but I've wondered whether it is Porros or roofs that come closer to matching the natural stereopsis we experience with no binocular. In other words do we see an exaggerated "3D" with...

www.birdforum.net

In the particular case of the Habicht 8x30 W there is an additional reason for the smaller size of objects in the image. Its magnification is below the 8x spec. Gijs measured it at 7.8x . I measured mine at 7.78x

 

[Sequoia Kid]

Right on, glad to know I'm not imagining things. Interesting to think that it might be because of the greater stereopsis of the porros.

Thank you all for all the information. I'm going to read up on these threads.

 

[tenex]

All this is true, but the OP isn't comparing bins of the same magnification, and didn't specify how distant his view was. The fact that objects at any distance look smaller in his Habicht than his EL is already explained by the nominal 0.5x difference in magnification (which may actually be 0.7x). This effect may be enhanced by stereopsis if these objects were nearby, but he hasn't confirmed that. And stereopsis is not relevant to differences in the overall field of view. So it's still unclear (to me) which effect was supposed to be explained here, and accordingly stereopsis is either not the only factor involved, or not involved at all.

 

[Sequoia Kid]

I think it is very possible that it is the sum of all the parts.

The difference in magnification is one thing, and I did notice that in the view, but it did seem that the view itself was smaller.

It is hard to describe, as it is my perception that we are talking about, but the best way I can describe it is if you had two televisions next to each other, one smaller than the other, that were both showing the same thing. The smaller would show everything the larger was showing but it would be a smaller picture. Reading that over it certainly does sound like I am describing the difference in magnification, but it was more like the circle of the view was more distant from the ocular lenses.

Not sure if that makes sense, but that's what it seemed like. As I said, it is likely the sum of all these parts, but it is interesting to hear that there are others that have noticed a slight difference in the view of the porros.

Thanks again for all the responses.