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07-22-2015, 07:35 AM   #121
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QuoteOriginally posted by Rondec Quote
If I post something about my FA 77, I am unlikely to say that it is a 115mm equivalent, because that doesn't mean anything to me.
Calling it an FA 77 f1.8 is always correct. What causes a backlash is when someone calls it a 115mm f1.8 FF equivalent. You can call it a 115mm f2.7 equivalent when it is mounted on an APS-C body, but you can't mix equivalent focal length without also converting aperture. Mixed equivalence is what some manufacturers use to advertise their products, especially bridge cams. A Sony RX10 has an 8.8-73.3mm f2.8 lens. It is 24-200mm f7.6 equivalent lens. It is definitely not a 24-200mm f2.8, which would be a huge and expensive lens. This was Tony Northrup's original point:

Focal length divided by f-number = iris diameter in mm.
Equivalent focal length divided by iris diameter in mm = equivalent f-number

For a 100mm f4 lens:
100mm / 4 = 25mm iris diameter

Mounted on m4/3:
200mm equivalent FL / 25mm = f/8 equivalent aperture

---------- Post added 2015-07-22 at 10:55 ----------

QuoteOriginally posted by aleonx3 Quote
To reference a parallel example, I use a 31mm f1.8 on a (future) Pentax FF with similar pixel density (assumption) as k-3. The resulting image cropped to APS-C size as if it is taken from the k-3, both images should be identical if both taken from the same distance from subject. Although the exposure could be slightly different due to metering of a bigger/smaller scene from the two cameras. DOF remains the same since subject distances are the same (?), though I am not sure.
There is one consideration you have not mentioned. DOF is not a fixed number, it is dependent on viewing distance and magnification. If you view both images from the same distance, and keep the cropped image proportionately smaller, you will observe the same DOF. But that is not normally what we do. We view or print both at the same size. The crop image is magnified compared to the FF image, which makes noise and aberrations more visible, and makes details that appeared to be in focus on the FF image look more blurred on the enlarged crop, i.e. shallower DOF on the cropped image.


Last edited by audiobomber; 07-22-2015 at 08:01 AM.
07-22-2015, 08:04 AM   #122
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QuoteOriginally posted by cfraz Quote
Many APS-C folks do exactly that while putting down m4/3 gear. Not that many of them use the word equivalence*. But the very ideas embodied in equivalence are often used to prove APS-C is "better" than m4/3. And were you hiding under a rock when the Q came out? The vitriol directed at that camera, by APS-C users in large part, was incredible. And many of the arguments were based in equivalence concepts. All miss-uses of the concept, in my view. Equivalence does not imbue a "better than" attribute on one format vs. another. It can provide useful information to make rational choice of one vs. another for a specific purpose. People are just so self-centered that they believe their "specific purpose" is or ought to be everyone's.

*It's such a misunderstood concept and so the word has become encumbered with all sorts of false meaning and emotional baggage. But many defend their choice of gear using the very ideas behind equivalence, yet will say in the same breath that equivalence is invalid.
I don't remember this hatred of the Q and haven't really seen APS-C users putting down four thirds gear (admittedly I don't really look at those threads much). To me, every sensor size is a bit of a compromise and if someone likes what they shoot with then who am I to bash it?

Some people quote DXO Mark scores so much that you would think that those were the sole important factor when it comes to shooting, just as some people believe sensor size is the most important thing. If you just have a full frame with a Sony sensor, you should be in the best shape possible. But obviously that isn't true. Micro four thirds cameras test a little lower, Canon cameras test a little lower, but they are still good cameras and the nice thing is that even if their lenses are a little slower, they are nice and sharp and are quite small in size.
07-22-2015, 08:14 AM   #123
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QuoteOriginally posted by Ratcheteer Quote
and the easiest way to stop all this f-stop confusion when it comes to camera's with sensors smaller than full frame is
Actually, the easiest way is for a person to to learn how each of his/her lenses renders on his/her camera(s), regardless of sensor size, and think of "equivalence" as just another word in the dictionary.

Last edited by Parallax; 07-22-2015 at 08:20 AM.
07-22-2015, 08:18 AM   #124
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QuoteOriginally posted by audiobomber Quote
Calling it an FA 77 f1.8 is always correct. What causes a backlash is when someone calls it a 115mm f1.8 FF equivalent. You can call it a 115mm f2.7 equivalent when it is mounted on an APS-C body, but you can't mix equivalent focal length without also converting aperture.
To be honest, I think this terminology (in bold) should also be scrapped. It is (apparently) confusing from an exposure sense and people will always complain about it, no matter how careful you are in explaining what you mean by the f2.7 equivalence. There's something ingrained about f-stops that I don't think you can beat out of people without using a very large textbook.

I think the best bet might be to confuse people with more numbers so they don't even know what to ask, start including the iris diameter in mm (and inches), pupil magnification (this would be nice in any case), the fields of view in degrees for width, height, and diagonal (also include a radian conversion) for the body it's intended for, and also throw in the standard binocular version of field of view (how wide in ft the image is at 1,000 yards, also convert to metric).

QuoteOriginally posted by audiobomber Quote
Mixed equivalence is what some manufacturers use to advertise their products, especially bridge cams. A Sony RX10 has an 8.8-73.3mm f2.8 lens. It is 24-200mm f7.6 equivalent lens. It is definitely not a 24-200mm f2.8, which would be a huge and expensive lens.
We had someone flogging the superzoom nikon p900 as having a 24-2000mm, f2.8-6.5 lens. Despite direct questions about the actual focal length of the lens, he kept claiming it really was a 2000mm/f6.5 lens. Awesome how they managed to defy physics.

---------- Post added 07-22-15 at 11:20 AM ----------

QuoteOriginally posted by Parallax Quote
Actually, the easiest way is for a person to to learn how each of his/her lenses render on his/her camera(s), regardless of sensor size, and think of "equivalence" as just another word in the dictionary.
Many aps-c users ask about what happens to their lenses if they get a FF camera. For pentax folks, I've often suggested they pick up a cheapo k1000 or other k-mount film camera. A practical hands on demo can go a long way.

07-22-2015, 11:21 AM   #125
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QuoteOriginally posted by Parallax Quote
Actually, the easiest way is for a person to to learn how each of his/her lenses renders on his/her camera(s), regardless of sensor size
still does not solve the ignorance problem of people who only use crop cameras with crop lens, but then again ignorance sells

12-60mm f2.8-f4 sounds more attractive on a 4/3rds lens than printing the 35mm equivalent on it ( 24-120mm f5.6-f8 )
07-22-2015, 11:31 AM   #126
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QuoteOriginally posted by Ratcheteer Quote
still does not solve the ignorance problem of people who only use crop cameras with crop lens,
????
I guess I don't understand how learning to use something doesn't solve the "ignorance" problem; nor do I understand why anyone who uses only cameras with sensors smaller than 24x36 would have any need to understand equivalence.
07-22-2015, 11:37 AM   #127
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QuoteOriginally posted by Parallax Quote
Actually, the easiest way is for a person to to learn how each of his/her lenses renders on his/her camera(s), regardless of sensor size, and think of "equivalence" as just another word in the dictionary.
Sounds like the 'most expensive' way to me.

---------- Post added 07-22-15 at 11:41 AM ----------

QuoteOriginally posted by Parallax Quote
????
I guess I don't understand how learning to use something doesn't solve the "ignorance" problem; nor do I understand why anyone who uses only cameras with sensors smaller than 24x36 would have any need to understand equivalence.
I want to take a picture of wildlife with my K-5. The moose only comes out after sunset, and he comes out at a distance from which I would have to crop to 400mm to get the shot I want. I try with my DA 55-300mm and am disappointed that I need ISO 3200.

Should I switch to my Tamron 70-200 F/2.8? Would I be better off with a Tamron + T/C? How many megapixels of each of the three would I get? Which would have the best SNR? How much better?
07-22-2015, 11:58 AM   #128
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QuoteOriginally posted by ElJamoquio Quote
I want to take a picture of wildlife with my K-5. The moose only comes out after sunset, and he comes out at a distance from which I would have to crop to 400mm to get the shot I want. I try with my DA 55-300mm and am disappointed that I need ISO 3200.

Should I switch to my Tamron 70-200 F/2.8? Would I be better off with a Tamron + T/C? How many megapixels of each of the three would I get? Which would have the best SNR? How much better?
That has nothing to do with DOF equivalence between formats (the subject of the thread). It has to do with knowing what results each of those lenses, or lens/TC combination give you on your camera.
Call me a radical, but I think knowing how your equipment works is far more beneficial than obsessing over charts, graphs, and mathematical formulas,.


Last edited by Parallax; 07-22-2015 at 12:11 PM.
07-22-2015, 12:08 PM   #129
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QuoteOriginally posted by audiobomber Quote
There is one consideration you have not mentioned. DOF is not a fixed number, it is dependent on viewing distance and magnification. If you view both images from the same distance, and keep the cropped image proportionately smaller, you will observe the same DOF. But that is not normally what we do. We view or print both at the same size. The crop image is magnified compared to the FF image, which makes noise and aberrations more visible, and makes details that appeared to be in focus on the FF image look more blurred on the enlarged crop, i.e. shallower DOF on the cropped image.
Thanks for this confirmation....

As for the lens specification claimed by camera makers on bridge cameras, they are fine as long as they don't infer to "equivalent" focal length for full frame camera. And as long as that specification is universally understood by people that the lens specification only applies to that sensor's image circle.
07-22-2015, 12:09 PM   #130
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QuoteOriginally posted by Parallax Quote
That has nothing to do with DOF equivalence between formats (the subject of the thread).
If you say so. I can figure out which will have more DOF or less in my head in less than the time it takes me to switch lenses. I can also figure out, again in my head in that same time, which will have a better SNR.
07-22-2015, 12:13 PM - 1 Like   #131
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QuoteOriginally posted by ElJamoquio Quote
Sounds like the 'most expensive' way to me.

---------- Post added 07-22-15 at 11:41 AM ----------



I want to take a picture of wildlife with my K-5. The moose only comes out after sunset, and he comes out at a distance from which I would have to crop to 400mm to get the shot I want. I try with my DA 55-300mm and am disappointed that I need ISO 3200.

Should I switch to my Tamron 70-200 F/2.8? Would I be better off with a Tamron + T/C? How many megapixels of each of the three would I get? Which would have the best SNR? How much better?
With wildlife photography you will use the longest/fastest lens that you can afford and wield. End of story. Has nothing to do with equivalence.

As to whether or not you should use a full frame camera, probably not, because you'll probably be cropping your D800 past APS-C levels. Once again, not an equivalence thing, just common sense. If you aren't using the outer one half of your sensor, why pay for it?
07-22-2015, 12:19 PM   #132
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QuoteOriginally posted by ElJamoquio Quote
I can figure out which will have more DOF or less in my head in less than the time it takes me to switch lenses.
So can I. Again, knowing which lens will have more or less DOF on your camera has nothing to do with equivalence between formats. It's because you understand basic optical physics. i.e. longer focal lengths have shallower DOF than shorter ones at the same subject distance, and that the more you enlarge a photo, the greater the visible noise on digital or grain on film.
07-22-2015, 12:39 PM   #133
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QuoteOriginally posted by alamo5000 Quote
Most of the people who have been here a while get it with some exceptions. Then we get someone who posts something and it turns into a 15 page thread...

I just don't participate in those threads for the most part.
No kidding. In one thread on the DOF markings on legacy MF lens one poster kept insisting you had to apply to crop equivalency factor to the scale. I didn't bother to argue. You can find photos of people using the same lens on a crop vs FF Nikon or Canon and demonstrating the DOF is the same between sensor size.

Maybe they don't believe the results because it is not Pentax gear even though you could use Pentax K or screwmount lenses with adapters. Perhaps when the Pentax FF camera is out someone will post similar tests.
07-22-2015, 12:47 PM   #134
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The "equivalent" in comparing lenses from cameras with different sized sensors means field of view, and field of view only. If manufacturers said that in their ads, nobody would be confused.
07-22-2015, 12:58 PM - 1 Like   #135
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QuoteOriginally posted by ElJamoquio Quote
If you say so. I can figure out which will have more DOF or less in my head in less than the time it takes me to switch lenses. I can also figure out, again in my head in that same time, which will have a better SNR.
Is the iso on your camera better at 100 or 400? I tried to figure it out with equivalence but couldn't come up with an answer. /sarc
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