[osv]

I think you misunderstood my post. I am not saying the sensor size has no influence on the field of view you get with the same focal lenght, I was just saying that the OP just wanted to know about possible advantages or disadvantages of useing lenses designed for ff on a crop camera.

that's what i gave him, disadvantages with putting ff glass on a crop sensor... 1)the focal length is wrong, 2)the aperture numbers are wrong, 3)the point of visible diffraction doesn't match the aperture number, etc.

[GUB]

that's what i gave him, disadvantages with putting ff glass on a crop sensor... 1)the focal length is wrong, 2)the aperture numbers are wrong, 3)the point of visible diffraction doesn't match the aperture number, etc.

How is a FA 50mm wrong if a DA 50mm is right. Read the original post.

[othar]

that's what i gave him, disadvantages with putting ff glass on a crop sensor... 1)the focal length is wrong, 2)the aperture numbers are wrong, 3)the point of visible diffraction doesn't match the aperture number, etc.

But it is the same for lenses designed for crop, therefore no disadvantage for ff designes on a crop camera.

Concerning your individual points:
1)I think you made a semantic error but I know what you mean (FOV is different for the same focal length when compared on different sensor sizes.) -> This is only important if you change between ff and crop cameras. If your first and only camera is an aps-c camera you don't have any expectations of how a certain focal length should look like anyway.
2)concerning DOF and out of focus rendering when comparing ff and crop cameras, you are correct. But regarding exposure f1.4 is f1.4 no matter what sensor size.
3)I don't know much about diffraction so I don't agree or disagree with your statement as such, but again this is only important when comparing different sensor sized cameras and not when comparing different lenses on 1 aps-c camera.

[osv]

How is a FA 50mm wrong if a DA 50mm is right. Read the original post.

wrong... you need to read the link i posted.

---------- Post added 07-07-16 at 08:41 AM ----------

But it is the same for lenses designed for crop, therefore no disadvantage for ff designes on a crop camera.
Concerning your individual points:
1)I think you made a semantic error but I know what you mean (FOV is different for the same focal length when compared on different sensor sizes.)

i agree that the lens itself doesn't change, but the effect is not the same, as you admitted, the fov is different, and i'm here to tell you that the aperture numbers on the aperture ring are therefore also effectively wrong.

you claim no disadvantage, then admit that there is a difference, and argue semantics about what the word "disadvantage" really means.

if you want to claim that everything being wrong is not a disadvantage, you are certainly welcome to your opinion... i do agree that with ff lenses on crop, we get used to everything being wrong, but my point is, lets not lose sight of what the truth really is.

2)concerning DOF and out of focus rendering when comparing ff and crop cameras, you are correct. But regarding exposure f1.4 is f1.4 no matter what sensor size.

that's another contradiction, and it's not correct because the total light falling on different sensor sizes is different... you can't have it both ways... "Saying "f/2 = f/2 = f/2" is like saying "50mm = 50mm = 50mm". Just as the effect of 50mm is not the same on different formats, the effect of f/2 is not the same on different formats... Total Light = Exposure x Effective Sensor Area, and it is the total amount of light falling on the sensor, as opposed to the exposure, which is the relevant measure."

that's why the aperture numbers are wrong.

[ScooterMaxi Jim]

that's what i gave him, disadvantages with putting ff glass on a crop sensor... 1)the focal length is wrong, 2)the aperture numbers are wrong, 3)the point of visible diffraction doesn't match the aperture number, etc.

Not only is this factually wrong, you're missing the point of the thread and what the OP is asking.

Focal length doesn't change, aperture is a function of light intensity on the film (sensor) plane, and the diffraction, etc. remains the same for the particular point on the surface.

Yes, issues related to perception of diffusion and circle of confusion change significantly as greater magnification of the image area are taken into account. However, nothing in the physical relationship between the lens and crop surface area are changed within that full frame section. It's a challenging thought, but diffusion builds as you stop down. A perfectly sharp lens wide open will show some diffusion even when stopped down slightly; the ability to perceive the diffusion effect is related the amount of magnification involved - roughly f/8 for FF and f/5.6 for crop.

The basic answer is that a 50mm FF is also a 50mm crop lens. You only see an equivalence rating on the point and shoot cameras, equating to full frame field of view.

[Lowell Goudge]

One thing I find curious about pentax camera and lenses as a beginner in photography is that many people use FF lenses on their crop sensor bodies. And, I believe there is no disadvantages of FF lens on crop-body because the image coming through the lens is perfectly covering the sensor and there is no problems on picture image. In fact, because FF lenses are shooting bigger images than the sensor itself to the sensor, the corner contrast and sharpness issues we see from APS-C lenses on APS-C body is not present on the FF lens on APS-C body. Does this make sense? and is there any disadvantages of using FF lens on crop bodies? I think this could help me making right choices for lens purchases. Thanks!

actually there are potential issues with FF lenses on crop sensor bodies, largely due to potential for reduced contrast due to an excessive amount of light entering the mirror box area. light in the mirror box area, which is not hitting the sensor, needs to be absorbed or it will result in images that are foggy, may have odd reflections, or greatly reduced contrast.

additionally, and again not fully appreciated, is that lens hoods for full frame lenses ARE NOT optimized for the field of view of a cropped sensor. as a result, light outside of the field of view can enter the lens and lead to flair, especially if it is a bright light or the sun specifically.

so while FF lenses may have some benefits, you need to be ware that there are also drawbacks

[ScooterMaxi Jim]

Lowell raises a couple of technically correct points here, but the impact is not significant nor often perceived in practice. The extent of mirror box light reflection on a modern camera is very low even for bright scenes, but bringing in the added light from FF optics could reduce contrast a bit (or having the larger mirror box that correspondingly reduces reflections slightly); and getting the FoV just right for hoods can help - especially in critical light angle situations. (This is why zooms with hoods tend to be much less effective.) Generally, we are talking about very small factors in either event. When you see the old 50s paired against the DA 50, the only significant factor you will tend to notice is increased contrast and saturation mostly related to coatings technology. The contrast progression from Tak to A-series to DA (and points in between) is quite evident.

[othar]

that's another contradiction, and it's not correct because the total light falling on different sensor sizes is different... you can't have it both ways... "Saying "f/2 = f/2 = f/2" is like saying "50mm = 50mm = 50mm". Just as the effect of 50mm is not the same on different formats, the effect of f/2 is not the same on different formats... Total Light = Exposure x Effective Sensor Area, and it is the total amount of light falling on the sensor, as opposed to the exposure, which is the relevant measure."

Are you trolling or are you really that obstinate?
Yes the total light falling on different sensor sizes is different, but the amount of light per square millimeter is the same and for a correct exposure thats the important part. And for the last time the OP is not interessted in different formats he is just interessted in aps-c sensor size.

Let`s please stop now even if you don't agree with me, I have the feeling you are misreading every sentence I write, if on purpose or some other reason I can`t tell.

[osv]

Not only is this factually wrong, you're missing the point of the thread and what the OP is asking.

no, it's you who are confused and wrong, despite all the factual link information that's been posted.

Focal length doesn't change,

correct, no one ever claimed otherwise... what you fail to understand is that it's the effective focal length(aka angle of view) that was proven to change with sensor size... at least othar got that part right, i'm kind of shocked that you don't know better.

don't tell us how p&s cameras have an equivalence rating, then turn around and claim that there is no such thing as an equivalence rating for aps-c cameras... the same exact principles apply in both cases.

aperture is a function of light intensity on the film (sensor) plane, and the diffraction, etc. remains the same for the particular point on the surface.

totally wrong, you are confusing aperture with exposure... "Aperture is the size of the opening in the lens." Aperture in Photography Defined | explora it's a physical measurement of size, period.

aperture size is like focal length, it can't be changed, but like focal length, the effect of aperture size is altered with sensor size, which you yourself admitted with your correct post on the sensor-sized differences in the onset of diffraction(wrt aperture numbers on the aperture ring).

The basic answer is that a 50mm FF is also a 50mm crop lens. You only see an equivalence rating on the point and shoot cameras, equating to full frame field of view.

once again you contradict yourself... a 50mm ff lens on ff is also a 50mm lens on p&s cameras, so why do the manufacturers put equivalence ratings on p&s lenses... hint: it's to prevent people like we have in this thread from getting confused, lol

[GUB]

no, it's you who are confused and wrong, despite all the factual link information that's been posted.



correct, no one ever claimed otherwise... what you fail to understand is that it's the effective focal length(aka angle of view) that was proven to change with sensor size... at least othar got that part right, i'm kind of shocked that you don't know better.

don't tell us how p&s cameras have an equivalence rating, then turn around and claim that there is no such thing as an equivalence rating for aps-c cameras... the same exact principles apply in both cases.



totally wrong, you are confusing aperture with exposure... "Aperture is the size of the opening in the lens." Aperture in Photography Defined | explora it's a physical measurement of size, period.

aperture size is like focal length, it can't be changed, but like focal length, the effect of aperture size is altered with sensor size, which you yourself admitted with your correct post on the sensor-sized differences in the onset of diffraction(wrt aperture numbers on the aperture ring).



once again you contradict yourself... a 50mm ff lens on ff is also a 50mm lens on p&s cameras, so why do the manufacturers put equivalence ratings on p&s lenses... hint: it's to prevent people like we have in this thread from getting confused, lol

Look I have been following this thread with interest because I have been musing like the OP. I have a K30 and I can see a point in the future when I may go FF. So when I buy a lens for the K30 does it make sense for that lens to have forward compatibility with FF. So should I decide to get a 50mm prime then if I get a FA50 instead of a DA50mm am I compromising my K30 imagery. This has absolutely nothing to do with equivalence.

[osv]

Are you trolling me here or are you really that obstinate?

i don't think you are trolling, but at this point i'm convinced that english must be a second language for you.

Yes the total light falling on different sensor sizes is different,

why do you keeping failing to understand the implications of that? stop pretending that sensor size doesn't matter... i'll explain it once again, per the link: " Total Light = Exposure · Effective Sensor Area. The same total amount of light will fall on the sensor for equivalent photos but, for different formats, this will necessarily result in a different exposure on each format, since the same total light distributed over sensors with different areas will result in a lower density of light on the larger sensor."

your claim that "the amount of light per square millimeter is the same" is disingenous, it's not the same with equivalence, because the differences in sensor sizes must be compensated for with differences in exposure.

sure a 50-watt bulb puts out the same amount of light regardless of what size of sensor takes the pic, but that doesn't mean that sensors of different sizes will use the same camera settings to capture the same pic... quite the opposite in fact.

[clackers]

25mm f/1.4 on mFT (4/3) is equivalent to 31mm f/1.8 on 1.6x (Canon APS-C), 33mm f/1.9 on 1.5x (APS-C for everyone else), and 50mm f/2.8 on FF (FX), where "equivalent to" means:"

As usual, Osv laps up that Joseph James post, which is scripture for the Equivalence fanatics.

Osv of course would hate you to point out that if you take that 50mm FX lens and reduce its aperture to make it 'equivalent' to the 25mm on mFT, the pictures are now two stops too dark.

So much for equivalence!

[BrianR]

Look I have been following this thread with interest because I have been musing like the OP. I have a K30 and I can see a point in the future when I may go FF. So when I buy a lens for the K30 does it make sense for that lens to have forward compatibility with FF. So should I decide to get a 50mm prime then if I get a FA50 instead of a DA50mm am I compromising my K30 imagery. This has absolutely nothing to do with equivalence.

So you want to compare an FA50 on a k30 to a DA50 on a k30? Sorry, that's all about equivalence. However, the crop factor from a k30 to a k30 is 1, so it's pretty straightforward

[osv]

Look I have been following this thread with interest because I have been musing like the OP. I have a K30 and I can see a point in the future when I may go FF. So when I buy a lens for the K30 does it make sense for that lens to have forward compatibility with FF. So should I decide to get a 50mm prime then if I get a FA50 instead of a DA50mm am I compromising my K30 imagery. This has absolutely nothing to do with equivalence.

the o.p. didn't mention any specific focal length, so he clearly wasn't asking for a comparison between specific 50mm lenses, like you are doing... stop trying to confuse the intent of the thread with misinterpretations of what it's about.

---------- Post added 07-07-16 at 04:29 PM ----------

So you want to compare an FA50 on a k30 to a DA50 on a k30? Sorry, that's all about equivalence. However, the crop factor from a k30 to a k30 is 1, so it's pretty straightforward

he did state: "I can see a point in the future when I may go FF"

so if equivalence doesn't matter, why did pentax rate the lens for aps-c use? even sony has both a fast 50 and a slow 50 for ff, it's not like a slow 50 should cut into the sales of fast 50's.

[Adam]

Look I have been following this thread with interest because I have been musing like the OP. I have a K30 and I can see a point in the future when I may go FF. So when I buy a lens for the K30 does it make sense for that lens to have forward compatibility with FF. So should I decide to get a 50mm prime then if I get a FA50 instead of a DA50mm am I compromising my K30 imagery. This has absolutely nothing to do with equivalence.

The DA 50mm is practically a full frame lens, for what it's worth. Just a bit more vignetting wide-open than with the FA.