So I've been reading up a lot on normals, true normals and otherwise. I get that on the old full-frame 35mm format, 50mm is the true normal focal length - as such, there was a proliferation of old primes in this focal length with many variations in speed among all manufacturers.

However, on an APS-C sensor, there is the 1.5x magnification crop, which means the old "true" normal of 50mm suddenly becomes a medium telephoto of 75mm.

Stop me if I'm wrong.

By this calculation, if the true normal is still 50mm (meaning the focal length equivalent to normal human eyesight, the normal FOV), then 50mm/1.5 = 33.33mm. So the true normal on an APS-C DSLR should be somewhere in the vicinity of a 33mm lens. Sounds simple enough.

However, I got the opportunity to play with both a 31mm and a 35mm (I've yet to find a true 33mm lens in K-mount) and I've found the results slightly wider than expected. By this I mean the image I see in the viewfinder is slightly closer (a slight amount of zoom/magnification) when compared to the actual image taken by the sensor - and closer compared to the actual FOV of my own eyes.

To do this, I simply focus on an object at a fixed distance away, then raise the viewfinder to my eye. By pure optical judgement, the image I see through the "new normal" is wider than what I see in the viewfinder (taking the viewfinder's magnification into consideration.)

When I put on a 50mm lens, the results are more on the telephoto end of the range. The object seems slightly closer than with my own eyes.

So I tried a little experiment. I mounted the camera on a tripod, slapped on the kit lens (18-55/3.5-5.6) and took a large series of photos, zooming the lens in every step of the way. What I found was interesting.

At 33mm, (I tried to get it as close to 33.3333, but the EXIF data won't show me tenths of focal lengths. Oh well.) the equivalent FOV was not 50mm, and it certainly wasn't "normal" by my eye's standards. I zoomed through to 50mm and the telephoto effect was still there, close enough to the zoom factor of a 50mm prime (using the SMCP-A 50/2 as a baseline.)

The interesting thing I found, is that the focal length that BEST matched what I was seeing with my own eyes was 45mm. Calculating for the magnification factor, that's 67.5mm. A highly unconventional focal length, to say the least.

I am aware that this process isn't entirely scientific, as I am simply using my own eyes to judge what "looks normal" by optical comparison.

I have no really specific questions. Just opening the floor up to discussion on "normal" focal lengths, I guess.

I think you got it right, the true normal is 43mm because its exactly the diagonal length of 35mm film. That probably makes a 28mm the normal for our DSLRs.

Pentax is the only SLR manufacturer that creates a 43mm lens, I think. This they claim to be the true normal lens in a full-frame 35mm camera.

The normal "normal" lens (in the old film/full frame sense) is a sliding issue. Some thinks its actually the 55mm (so the SMC Pentax 55/1.8) or even 58mm (anyone remember Minolta's Rokkor MC 58/1.4 & 58/1.7?). I have used both (Minolta & Pentax; I still have a 55/1.8) and I tend to think its a correct assumption. I can shoot with the 55/1.8 on a film cam with both eyes open and not get dizzy because of differing magnifications.

55mm in the digital paradigm is 36.667 (55/1.5).

@Roger: That would be fine if the 45mm equivalent I was viewing was AFTER the magnification. When I use my 28mm lens, it still comes out too wide (to my eyes, and the photo itself.

@Francis: But the 43mm "true normal" will become a medium telephoto with a focal length of 64.5, am I right? After the magnification factor? Making the old 43mm too long for normal.

For clarification, I mean "normal" in the sense that the magnification as you look through the viewfinder matches the dimensions you see in real life. So when you raise the viewfinder to and from your eyes, the images you see will not shift in terms of magnification. Neither image will be "bigger" or "smaller" than the other.

The primary reason I want this is so I can teach myself to visualize the FOV of my camera - so I can "frame" shots without looking through the viewfinder. Not only will this make it an ideal walkaround lens for street photography, but it will also make taking pictures "stealthily" a heckuvalot easier. I've just gotten the hang of mental distance measurement (only because all my primes are manual focus!) so now I just need to tune myself to the lens' FOV.

The normal "normal" lens (in the old film/full frame sense) is a sliding issue. Some thinks its actually the 55mm (so the SMC Pentax 55/1.8) or even 58mm (anyone remember Minolta's Rokkor MC 58/1.4 & 58/1.7?). I have used both (Minolta & Pentax; I still have a 55/1.8) and I tend to think its a correct assumption. I can shoot with the 55/1.8 on a film cam with both eyes open and not get dizzy because of differing magnifications.

55mm in the digital paradigm is 36.667 (55/1.5).

Oh. I thought, at first, you meant 55mm on a DSLR. So once again, a 35mm would be best, eh?

I can't seem to shoot with both eyes open, though. The hump of the pentaprism gets in the way. :P

I think the viewfinder image magnification plays a role. I recently got a couple of K-mount film cameras; one has 0.82x magnification and the other one 0.88x. The larger VF throws a slightly bigger image and looks closer to normal than the other one, though it still looks smaller than real life. The strange thing is that when I get close to the subject, around 3 feet or less, the VF image is now bigger than real life.

I believe Sir Roger is correct. The viewfinder plays a part.

Here is my "hula". 100% unproven speculation! :Grin:

Suppose the true normal lens is the 50mm, then the angle of view of the human eye would be Diagonal 46.8 degrees, Vertical 27 degrees, and Horizontal 39.6 degrees. Given that the digital Pentax has a 1.5 multiplier effect, the closest to the 50mm you can get is the 35mm (with an effective 52.5mm field of view). The resulting field of view will be slightly narrower than the supposed true field of view, but very close nonetheless. When a lens is coupled with the K10D, the frame coverage is cut by 5% (Therefore, you only see 95% of the whole field of view.) Plus, the K10D has a 0.95x viewfinder magnification when a 50mm f/1.4 set at infinity focus is attached. (I think) this VF magnification shrinks when you use a wider focal length (such as with the 35mm lens in our case). Also, the magnification increases when you focus at closer distances. So in effect, it is very complicated to really see exactly what the naked eye sees when looking through a the viewfinder.

I think the viewfinder image magnification plays a role. I recently got a couple of K-mount film cameras; one has 0.82x magnification and the other one 0.88x. The larger VF throws a slightly bigger image and looks closer to normal than the other one, though it still looks smaller than real life. The strange thing is that when I get close to the subject, around 3 feet or less, the VF image is now bigger than real life.

Yeah, especially with the little diminutive Pentax MX which has the biggest magnification of 0.97x in all of the K-mount Pentax cameras! That has been my benchmark for most of my equipment. The Pentax K2 has 0.88x and it is where the SMC Pentax 55/1.8 looks "normal".

Wow, wish i could find one of those. I asked my suki to text me immediately when a LX, MX or K2 becomes available but the best he could find was a P3N, which is pretty basic.

The MX? There's a good one sitting in Dado's in Hidalgo (his estante is in the same row as Acel's <I finally got that right> first one if you're coming from Quiapo church).

Yup yup! I was about to say that as well. We saw it last week. :)

I think it was going for... 5K? Or was that the K2/KX?

I believe Sir Roger is correct. The viewfinder plays a part.

Here is my "hula". 100% unproven speculation! :Grin:

Suppose the true normal lens is the 50mm, then the angle of view of the human eye would be Diagonal 46.8 degrees, Vertical 27 degrees, and Horizontal 39.6 degrees. Given that the digital Pentax has a 1.5 multiplier effect, the closest to the 50mm you can get is the 35mm (with an effective 52.5mm field of view). The resulting field of view will be slightly narrower than the supposed true field of view, but very close nonetheless. When a lens is coupled with the K10D, the frame coverage is cut by 5% (Therefore, you only see 95% of the whole field of view.) Plus, the K10D has a 0.95x viewfinder magnification when a 50mm f/1.4 set at infinity focus is attached. (I think) this VF magnification shrinks when you use a wider focal length (such as with the 35mm lens in our case). Also, the magnification increases when you focus at closer distances. So in effect, it is very complicated to really see exactly what the naked eye sees when looking through a the viewfinder.

The magnification of the VF! Of course! That would explain a lot - especially why my supposedly focal lengths and FOVs would change dramatically between a close up and a MLS with the same lens! Darn it. I guess there's no real way to compensate for that, in that case. In order to get a "true" normal at all lengths... I'll really have to use a zoom. In which case, I guess the 18-55 kit lens does its job with that.

The only problem, then, is that I can no longer safely shoot from the hip at all distances. :(

Yup yup! I was about to say that as well. We saw it last week. :)

I think it was going for... 5K? Or was that the K2/KX?

A lot less I think, the K2 was ridiculously priced at P5k with a damaged VF! :Thinking:

The MX was somewhere in the P3k++ range, I'm confused because what I was interested in was the lens attached to it not the body (I already have one) so I was bargaining if I can get the lens only (Dado wants to sell off his bodies so it has to be a set) or how much if I bought the lens with one of the P30Ns or the MEs (so I got a litany of prices...).

A lot less I think, the K2 was ridiculously priced at P5k with a damaged VF! :Thinking:

The MX was somewhere in the P3k++ range, I'm confused because what I was interested in was the lens attached to it not the body (I already have one) so I was bargaining if I can get the lens only (Dado wants to sell off his bodies so it has to be a set) or how much if I bought the lens with one of the P30Ns or the MEs (so I got a litany of prices...).

Ah, yeah. That's right. That's Dado's stall pala? Who is the woman who's always manning it? It's so hard to get any of the stalls to sell off lenses only. What's nice, though, is that there seems to be a resurgence of K-mount lenses everywhere. What's not so nice, as we've all mentioned, is the ridiculous price increases we're having to deal with these days. :(

since we're talking about normal lenses, on 35mm and/or digital, just thought of sharing a shootout done by a fellow pentaxian.. http://www.pbase.com/carpents/nls

since we're talking about normal lenses, on 35mm and/or digital, just thought of sharing a shootout done by a fellow pentaxian.. http://www.pbase.com/carpents/nls

TFS! Interesting site...I guess if you can't have a SMCP A 50/1.2 your next best choice is the SMC Takumar 50/1.4.

That means you really have to get a M42/Screwmount adaptor. :Grin:

TFS! Interesting site...I guess if you can't have a SMCP A 50/1.2 your next best choice is the SMC Takumar 50/1.4.

That means you really have to get a M42/Screwmount adaptor. :Grin:

dont count on it! getting hooked with the K mount na.. dont want to enter the M42 mounts.. :D

dont count on it! getting hooked with the K mount na.. dont want to enter the M42 mounts.. :D

Do I smell pancakes cooking? Or an all-'rounder? Hehe! :D

Do I smell pancakes cooking? Or an all-'rounder? Hehe! :D

i wish i can get pancakes.. with some bacon and eggs! hehhe

*hmmm.. why not create a post your FULL pentax gear thread.. :) *

dont count on it! getting hooked with the K mount na.. dont want to enter the M42 mounts.. :D

haaayyyy, salamat naman...

i wish i can get pancakes.. with some bacon and eggs! hehhe

*hmmm.. why not create a post your FULL pentax gear thread.. :) *

I'll wait for January haha! Still undecided with this friggin' LBA. :D

haaayyyy, salamat naman...

For every one person not struck by MFLM, 5 others that are, are sure to be on the way... haha! :D

i wish i can get pancakes.. with some bacon and eggs! hehhe

*hmmm.. why not create a post your FULL pentax gear thread.. :) *

That was my breakfast today ... :Grin:

Hey! Why don't you start it?

I was just thinking about this today, brought on by an old essay of Mike Johnston's (again). He posted an photo he made and asked readers to guess what focal length was used to shoot it with. Of course, typical for Mike, it was a 50mm on a Leica. (Summicron? I don't remember.)

The point is, the focal length was "distinctive" due to the compression of the background, the depth and all the elements combined. As we all know, wide angle shots tend to increase the effects of DOF, and telephotos, conversely, tend to compress it.

So going back to the original idea: what hocus-pocus goes on with the 1.5x multiplier when you mount FF lenses on a cropped APS-C sensor camera? The focal length is simple. 50mm x 1.5 = 75mm. But what happens to the DOF? Ceteris Paribus, (i.e., the opening on both lenses is fixed at, say, f/2), what will the DOF and "element compression" in the frame look like when you shoot a 50mm on an APS-C and a 75mm on a FF (film, for instance) camera?

In other words, since I'm using a 50mm as my "normal" right now (which is really a medium telephoto) until I can afford the 31 Ltd., am I getting the same look as if I had used it on a FF camera, only "cropped in" to 75mm?

Not sure if it has been mentioned (skipped a page or two), but the issue of "normal" FOV isn't as simple as crop factor as the perspective differences between "true" negative focal length and sensor-equivalent focal length is different.

a 28mm lens vs a 17.5mm lens will not yield the same perspective and "compression" factor due to the overall scene.

This is more prevalent with wide than tele lenses.

Not to mention that even during film days, the focal length markers aren't indicative of their actual focal lengths... Old magazine reviews always mention their "true" focal lengths as part of the reviewed specs.

It hasn't been mentioned, but yeah - that's what I was going for. The perspective of a 50 is always going to be different from a 75, so even when you use the former on a 1.5x APS-C sensor, it won't LOOK like a 75, right? It'll have the same framing but a different angle of view, a different perspective? Sort of like taking a 50 and then CROPPING it to the frame size of a 75. So in the example I gave, the two images won't look alike. The scene will be more "compressed" in the 75mm on the full-frame sensor/film?

I'm not sure I understand your last point, though, David. What do you mean that the focal length markers weren't accurate? On zooms, you mean? And what were these "true" focal lengths?

(i.e., zooming to 50 in a 28-70 won't have the same focal length/AOV/perspective as a true 50mm prime?)

Michael: Pretty much in zooms... Most of the old magazines I have around always has this line:

"Actual Focal Range: 27-72 " for example, for a lens that says 28-70 on the barrel...

IMO, we have to factor in the definition of "normal". we're assuming that "normal" focal length is the same with what our own eyes can see. but there are differences in each person's eyes' focal lengths. i remember the man i saw on ripley's believe it or not who has a telephoto vision that sees a 1-ft diameter plate from more than a mile away, and the one who can see the individual pixels on a tv he's watching from 5 (?) meters - telemacro. then there's the one who can direct his eyeballs away from each other, seeing a very wide-angle view. i think the normal 50mm is the average, and each individual may have slightly wide or telephoto vision.
i believe mine is medium-wide, a 36mm lens comparison somehow proved it. how about yours? :)

My "lens" are defective... must've been dropped before hehehe

IMO, we have to factor in the definition of "normal". we're assuming that "normal" focal length is the same with what our own eyes can see. but there are differences in each person's eyes' focal lengths. i remember the man i saw on ripley's believe it or not who has a telephoto vision that sees a 1-ft diameter plate from more than a mile away, and the one who can see the individual pixels on a tv he's watching from 5 (?) meters - telemacro. then there's the one who can direct his eyeballs away from each other, seeing a very wide-angle view. i think the normal 50mm is the average, and each individual may have slightly wide or telephoto vision.
i believe mine is medium-wide, a 36mm lens comparison somehow proved it. how about yours? :)

I downloaded the 1986 Canon FD Lens Work months ago, but didn't get to read it thoroughly till yesterday. Here's some quotes from the book, which may be of interest:

"Why is the 50mm lens referred to as the 'standard' lens? Aside from the fact that in the past a 50mm lens has customarily accompanied 35mm SLR cameras on purchase, there are several other reasons. One theory is that this lens' focal length is closest to the 43.2mm diagonal of the 35mm camera's 24x36 frame. Another is that its field of coverage (40 degrees horizontally, 46 degrees diagonally) is roughly equal to what one human eye can view with relative clarity. There is much disagreement on this point; some argue that the unaided eye covers only 35 degrees, some even say 28 degrees. Still another theory is that at a normal shooting distance, the 50mm lens' perspective is closer to what one senses as being 'normal' than that of any of the other interchangeable lenses. Here again, others disagree, favoring 85 or even 100mm lenses. Simply, the 50mm standard lens gives an 'honest' image, which is extremely close to what the unaided eye sees. Combine this with the fact that this lens is often successful in creating the same image of the scene that the photographer has in mind, and it's easy to see that the 50mm lens is a good basic lens."

"Take a look at the diagrams below showing the standard lens construction. As you can see, the front and rear lens groups are symmetrical. Symmetrical lens construction is a feature of standard lenses which is not found in wide-angle or telephoto lenses. This construction allows the large maximum apertures and excellent color reproduction offered by standard lenses. Because of these qualities, standard lenses are regarded as a starting point from which to build a lens system including wide-angle and telephoto lenses."

"This lens (FD 50mm f/1.4) is now being used for optical measurements at various public institutions and is also the standard which determines color balance for the rest of the almost 60 lenses in the FD lens series. Perhaps instead of 'standard', a more accurate name would be 'reference' lens."

Its interesting that the reference for 'normal' is human vision. Optha folks would probably need to verify this (hearsay...I think I picked it up either in Discovery or Nat Geo) but the optic nerves dedicated to hi-res human vision are all clumped up that what we see as 'clear' is limited to a very narrow FOV. Lo-res optic nerves which covers the rest of our FOV also known asl peripheral vision. In real life things are fluid since our eyeballs are in constant motion and anything in our periphery which warrants attention gets focused on by a twitch of a nerve instantly viewed by our hi-res vision.

It is a given that peripheral vision may not be the same for everyone (or our hi-res vision for that matter). Health and nutrition issues factoring as well as disabilities. I have/had my opinion on what is a 'normal' lens but age does strange things to one's opinion.

:Grin: