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Old Jun 19, 2007, 7:22 AM   #11
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Well no sorry I will just state what I know like this recent R lens BS.....


And again will stand and be corrected like about STAR * lenses stuff at the time didn't know....


Without getting all nasty and defesive... like many of you all do when I catch your butts on something. Though I may have questioned is it REALLY 8x cost better IQ than the typical 135mm..... answer was basically no....(And ONLY from a honest amongst you) yes rare, but yes some are into that BS... And again even the ordinary Prime non * 135's were pretty costly (especially if you consider inflation min 3x since 1970) the non stars are dirt cheap at like $35-70 typically now but an A 135 * $14000+ really that difference but for the bragging rights of I have one?

Guess you are into the coolest and deep pockets OK.

Like that there are two different R(icho) lens situations... and some other things. Or there is a concentration of light factor difference between DA and FF lenses. (as well as functionality across all cameras)



I just want to see the relative FACTS out there not win battles or whats cooler than what BS out there :shock:.


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Old Jun 19, 2007, 8:15 AM   #12
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bilybianca wrote:
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Hayward wrote:
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OK I'll give you at one point I didn't know what a * lens was.... have I said any thing since? Did I get nasty and DEFENSIVE about it????
Not since but before...
Gee what did I just admit and even several times before never appreciated say... but can we Mr Roger's style....sweaters on... say DUHHHH?


And only said it ONCE before corrected but for the *135 A..... again wide or long and fast could understand it.... but a pretty normal A 135* $1450+? when far from less 8x IQ 135's same f/ are going for ~$50 again REALLY 20X+ lesser IQ A's? No they weren't
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Old Jun 19, 2007, 9:21 AM   #13
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OK so sue me I'm not a Pentax owner but I find this subject interesting. I did a little looking around the net. Two interesting things.

First thing I found was the same topic being discussed at a few other photo forums. And with many camera makes. This tells me that what ever is going on it is not unique to corvairfan and his equipment.

Second I could only find a couple of "articles" that covered this but the answer was the same. F/2 is F/2 regardless of sensor size. Though Hayward's explanation sounds good it does not hold up. If that where so all of our 35mm slides would be dark in the middle In fact the opposite is true. Those of us who have been shooting for years know that most lenses are in fact brighter in the center. There is no wasted light outside the censor there is wasted image. But the light level is the same.

So what causes this??

My first though was that maybe one lens lacks something and the camera automatically switches to Center Weighted Average metering. This would be the case with many lens cameras combinations, and it would explain a difference in exposure readings. But I don't know the camera and lens in question.

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Old Jun 19, 2007, 10:49 AM   #14
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Well first of all other than saying others don't count just what are you complaining of????

Rather vague

As I have saisd f/2 is f/2 if same coverage area.....

Of course I suppose you also don't believe light isn't particulate fluid matter either do you? Has waves and interference just like waves in a pond do. (Why do you think a polarizer works? ITS ALL about physical/particulate wave interferance)

And light not only particulate even falls in the electromagnetic realm of things.

But yes a FF standard lens at 2.8 is about the same as Digital coverage DA lens is at 3.5.... again the DA no light spillage there is with a FF an lens on a digital and hense the FL x factor... just AE shutter compensation makes it invisible unles you AV it F totF and see what the shutter speeds are. Or deaal with things manually. A DA will be about a half stop faster than a FF lens at same f/


Again just PLAIN (used to be VERY BASIC) High School PHYSICS
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Old Jun 19, 2007, 8:57 PM   #15
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Oy
The f/factor is a product of aperture size and focal length. A lens set at f/2 will provide the same EV across the entire image circle (with some fall off as it reaches the edge) the fact that you are only using a small portion of that will make no difference in exposure. f/2 on a FF lens is the same as f/2 on a DA lens and the same on a medium format lens (if you attach one to your DSLR) and so on. Coverage area does not enter into it.

If anything the light from the unused portion of the image circle would scatter inside the camera and increase the shutter speed, not decrease it and lower the over all contrast of the image. But in reality it is mostly absorbed by the walls of the mirror box.

The guys at Pentax, Nikon, Cannon etc. are pretty smart if their was a light loss when using FF lenses they would have told us.

As I said before I'm not a Pentax user so I did some more research. I was wrong about the camera reverting to Center Weighted metering. But I did find out that "A" lenses only transmit minimum and maximum aperture information to the camera. And not focal length, subject distance and other info more modern lens transfer. So the meter has less info to work with when using these lenses. This should not make a huge difference but it could affect the final reading to some extent. It would be interesting to see comparison shots from the two lenses at the same settings in manual mode ignoring the metering difference.
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Old Jun 19, 2007, 9:03 PM   #16
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As I suggested in my first post of this thread, it's a lot more likely that the difference is due to the kit lens metering at actual aperture since that was it's max at that focal length, and the FA 50, metering at f1.4 and calculating the exposure at f5.6.

. . .or perhaps it's a matter of the actual effective aperture being marginally larger relatively, since it's supposed to be f5.6 at 55mm.

Let's assume that the actual iris opening is the same for both focal lengths (opened up all the way, with the blades fully retracted and not visible). At 55mm, we can calculate the actual opening diameter. Since FL/iris diam = fstop, FL/fstop=iris diam -- so 55/5.6 =9.82 (rounded). When you shorten the FL to 50, 50/9.82 =5.09, or f5.1 which is the effective aperture of the lens at 50mm. My cameras round the aperture values, sometimes not mathematically correctly, so this might still register as f5.6 for exif purposes.

Scott




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Old Jun 19, 2007, 11:39 PM   #17
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Hayward wrote:
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"Of course I suppose you also don't believe light isn't particulate fluid matter either do you? Has waves and interference just like waves in a pond do. (Why do you think a polarizer works? ITS ALL about physical/particulate wave interferance)"


Light is definitely not "particulate fluid matter". For one thing, matter, by definition, takes up space, and has mass. If you accelerate any mass to light speed, it's mass increases proportionally, and almost infinite mass would make my camera very heavy, even after one exposure, since I live in a gravity field. Maybe it's different in FL. . .The polarizer and wave interference things are among those behaviors not consistent with particle theory, BTW. -- and what does "physical/particulate wave interference have to do with your light concentration in a smaller image circle theory anyway. . .?

And just to give you something to pick at, if you even choose to answer this post -- nice double negative in the first sentence -- kinda changes the meaning -- to the opposite of what you seem to have meant. . .

"And light not only particulate even falls in the electromagnetic realm of things."

It's generally accepted that light has both wave and particle like properties, some of these properties can be explained by particle theory but certainly not all. On the other hand, all but the photoelectric effect are explained by wave theory, and there are logical theories that explain the photoelectric effect in terms consistent the wave theory, and eliminating particle theory.

I would say that it would be better (and a lot more accurate) to say that light is electromagnetic energy that in at least one stuation behaves like it is made up of particle-like packets of energy -- at least that's the way IIRC Plancke put it. . .

. . . since we're talking science here afterall. . .

"But yes a FF standard lens at 2.8 is about the same as Digital coverage DA lens is at 3.5.... again the DA no light spillage there is with a FF an lens on a digital and hense the FL x factor... just AE shutter compensation makes it invisible unles you AV it F totF and see what the shutter speeds are. Or deaal with things manually. A DA will be about a half stop faster than a FF lens at same f/"

If this were true, I think that there are a lot of former Pentax optical engineers and marketing people looking for jobs. To understate the max aperture of lenses would, in a world where faster means "better" and better means more expensive, and more expensive (at the same cost) means more profits, would be at least a firing offense, with a serious loss of honor (they take mistakes pretty seriously). If anything, I would think that if a lens doesn't meet its max aperture spec, the error is more likely to be on the "fast" side.

"Again just PLAIN (used to be VERY BASIC) High School PHYSICS"

A pretty snide comment from one who apparently has a loose grasp of the subject.

My .02

Scott
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Old Jun 20, 2007, 7:39 PM   #18
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...

Stop the flames.
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Old Jun 20, 2007, 10:18 PM   #19
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just to add another dimensiuon to the f stop thing
if one were to use a hand held light meter it owuld give f stops and shutter speed for the given situation
it wouldnt ask what lens or camera is used

i have 4 lenses that cover 50mm
and an old weston master II light meter
and a Kodak retina that has a light meter on it and a 50mm lens
i will try to do some experiments today seeing as i am off out now to do some shooting




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Old Jun 21, 2007, 5:08 AM   #20
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NM
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