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11-20-2010, 07:23 PM   #1
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focal lengh question.

I know some lens are specifically built for digital cameras, do these ones experience the crop factor like the older lens on digital bodies (which is not full size), and if they do not have crop factors, then which lens model are these?

If the question is confusing then I can give an example.
DSLR bodies aren't full frame size.

so an older 50mm will look like 75mm

say if I was to buy a camera kit from amazon that includes a 55-300mm

would it look like 55-300 or would it look like 75-450?

11-20-2010, 08:27 PM   #2
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50mm is 50mm is 50mm. The "crop factor" has to do with the sensor size. It's my understanding that a lot of the new lens' built for DSLR bodies won't work on FF bodies due to the optics not being wide enough. Also when entering focal lengths for SR with manual lens' you enter the actual length in mm's. to answer your question the 55-300mm will look like the 75-450mm. Hope this helps.

Last edited by kkoether; 11-20-2010 at 08:29 PM. Reason: Finish answering question
11-20-2010, 08:27 PM   #3
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Focal length is focal length. It is a physical property of the lens and is independent of the camera or sensor

The crop factor is simply the size of the sensor and the "magnification factor" of the ASP-C sensor is just the impact of the change in format and field of view

The digital only lenses have different designs which include rear element coatings to stop reflections from the sensor , optical designs that have the light hit the sensor at high angles to reduce vignetting and some limitations that reduce the image circle because the sensor size does not require as large a projected image as film

That is all
11-20-2010, 09:22 PM   #4
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Yes, focal length is focal length. It is a physical property of the lens and is unrelated to the sensor size.

However, the confusion that the OP is experiencing is very common. It results from the common practice (bad practice, IMHO) of stating focal lengths in 35mm equivalents. That is, how the image would appear on a 35mm film camera or a dslr with a "full-frame" sensor. That is why it is often stated that a 50mm lens "becomes" a 75mm lens on a dslr.

Stating focal lengths in 35mm equivalents is only useful for someone who is familiar and comfortable with 35mm cameras. More and more camera users, especially dslr users have never touched a 35mm camera in their lives, so what is the point of using equivalents?

I have been an amatuer photographer since 1967, when I bought my first "real" camera, a Pentax Spotmatic, so I was very familiar with those lenses. When I got my first dslr, I spent about five minutes thinking about the "crop factor" and then promptly forgot about it.

I simply learned a few new reference points. On my K10D, with its aps-c sensor, a "normal" lens has a focal length of about 33mm. Anything shorter than that is a wide-angle lens. Anything shorter than about 18mm is a super-wide-angle lens. Anything longer than 33mm is a telephoto. The longer the focal length, the greater the telephoto effect. I no longer make comparisons to 35mm cameras. No need to.

My advice to the OP: unless you grew up with 35mm film cameras, ignore any reference to "crop factor", from now on. Without reference to 35mm cameras, the term is meaningless.

An American who finds him/herself in Europe for the first time, may have trouble grasping the distances posted on freeway signs, in kilometers, instead of miles. They may have to think about the fact that 60mph is about 100kph and 200 miles is approximately 320 kilometers. OTOH, a child who grew up in Europe has no need for making any kind of conversion. As far as lenses are concerned, you are that child. Why learn about miles, and how to convert them to kilometers, when no one there uses miles? Simply learn about kilometers. Same for lenses. Learn how various focal lengths perform on YOUR camera, not your father's.

12-05-2010, 01:20 PM   #5
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Everything above is quite true. Here's something to try: Cut a picture from a magazine. On it, draw a 60x45mm rectangle. That's about the size of 645 medium-format (MF) frame. Inside that, draw a 36x24mm rectangle. That's the size of a 135/35mm full-frame (FF) frame. Inside that, draw a 24x18mm rectangle. That's the size of a frame on an 135 half-frame (HF) or APS-C (dSLR) frame. Inside that, draw an 18x12mm rectangle. That's about the size of a 110 or m4/3 system frame. In each case, THE PICTURE HASN"T CHANGED! Perspectives and placements remain the same. It's just that smaller sensors or film frames see less of it.

A 50mm lens is a 50mm lens, no matter what camera it's on. On a 645 camera, it's a bit wide-angle. On a 135/FF camera, it's long-normal. On a 135/FF or APS-C camera, it's a portrait tele. On a 110 or m4/3 camera, it's a long tele. It projects the same image, no matter what body it's on, no matter what size frame receives the projected image. But smaller frams get a smaller slice of the picture. In effect, they crop the image. That's all that crop-factor (I prefer formatfaktor) means. The lens remains the same.
12-05-2010, 01:53 PM   #6
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Thinking about the angle of view may be more helpful.
If you look at the Pentax lens catalogue there are three 35mm lenses listed the two for APS-C sensors (DA35 f2.4 and 35 f2.8 Limited) have an angle of view of 44 degrees. The 645 lens (FA 645 35 f3.5) has a listed angle of view of 90 degrees.
On the large sensor on the Pentax 645 a 35mm lens is very wide, the equivalent if 14mm on an APS-C sensor.
There is a relationship between the focal length of a lens and its target, in other words the sensor or film being used in the camera. The smaller the sensor the longer the focal length and visa versa.
Sorry I have not explained this too well, it was much easier to explain this when there was just film about and people were more familiar with medium format and 35mm cameras.
12-05-2010, 05:14 PM   #7
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QuoteOriginally posted by noblepa Quote

However, the confusion that the OP is experiencing is very common. It results from the common practice (bad practice, IMHO) of stating focal lengths in 35mm equivalents. That is, how the image would appear on a 35mm film camera or a dslr with a "full-frame" sensor. That is why it is often stated that a 50mm lens "becomes" a 75mm lens on a dslr.

Stating focal lengths in 35mm equivalents is only useful for someone who is familiar and comfortable with 35mm cameras.
I guess it's an accommodation to older guys like us who, although we understand the 1.5 factor, doesn't really mean anything to those people who are fairly new to photography.

However, when FF becomes more of a reality to more people, it's GOING to mean something.

And all of my FF lenses are going to represent their lengths in a totally different way, making ASP-C lengths irrelevant.
12-05-2010, 06:02 PM   #8
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QuoteQuote:
More and more camera users, especially dslr users have never touched a 35mm camera in their lives, so what is the point of using equivalents?
You have to relate it to something. A recent poll here showed more than 80% came from film camera background. It's not difficult to get the answer with only a minimal amount of investigation (i.e. google).

12-05-2010, 08:19 PM   #9
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QuoteOriginally posted by Ira Quote
I guess it's an accommodation to older guys like us who, although we understand the 1.5 factor, doesn't really mean anything to those people who are fairly new to photography.

However, when FF becomes more of a reality to more people, it's GOING to mean something.

And all of my FF lenses are going to represent their lengths in a totally different way, making ASP-C lengths irrelevant.
Your first sentence is the whole point of my objection to the use of the term, "crop factor". It seems that the ones asking the questions are not the old codgers, like us, who grew up with 35mm film cameras, but the newbies, who are getting a little bit serious about photography, without ever having used a film camera, let alone 35mm, in their lives.

For the newbies, talking about crop factors is not only meaningless, it is unneccessarily confusing. If you have no 35mm frame of reference, any discussion of crop factor is a major obstruction to understanding.

In the old days, no one ever talked about "crop factor" when discussing the difference between the angle of view of a lens on a medium format camera vs. a 35mm camera. We all seemed to understand, without a lot of math, that a 75 or 80mm lens might be normal on a 6 x 6 film camera, but a short telephoto on a 35mm camera.

BTW, I'm still not convinced that so-called FF (24 x 36mm sensor) dslrs are going to dominate the market in the future. I think that that format will remain a high-end, largely professional format, while the improvements in aps-c sensors will lessen the pressure for FF for the masses. I think that EVIL cameras are probably more of a threat to the dominance of aps-c dslrs, than are FF dslrs.
12-06-2010, 03:22 AM   #10
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QuoteOriginally posted by noblepa Quote
Your first sentence is the whole point of my objection to the use of the term, "crop factor". It seems that the ones asking the questions are not the old codgers, like us, who grew up with 35mm film cameras, but the newbies, who are getting a little bit serious about photography, without ever having used a film camera, let alone 35mm, in their lives.

For the newbies, talking about crop factors is not only meaningless, it is unneccessarily confusing. If you have no 35mm frame of reference, any discussion of crop factor is a major obstruction to understanding.

In the old days, no one ever talked about "crop factor" when discussing the difference between the angle of view of a lens on a medium format camera vs. a 35mm camera. We all seemed to understand, without a lot of math, that a 75 or 80mm lens might be normal on a 6 x 6 film camera, but a short telephoto on a 35mm camera.
I agree with you to an extent, but in the old days, you wouldn't stick a 35mm film lens on a 2 1/4 camera anyway.

I also don't think this is something newbies have trouble understanding, and I don't see the harm in them nailing down the concept. After all, they still SELL film cameras, and understanding the difference in crop factors between film and APS-C digital, using the same lens, is important to know.

Last edited by Ira; 12-07-2010 at 03:52 AM.
12-06-2010, 07:34 PM   #11
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Funnily enough, and I've ranted often enough about crop factors, I've started using crop factor when talking photography with my friend who shoots with a 7D. Apparently, the Canon isn't the same sensor size as Pentax, and so it is handy for us to reference back to 35mm as a common denominator.
12-07-2010, 06:40 AM   #12
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QuoteOriginally posted by Ira Quote
I agree with you to an extent, but in the old days, you wouldn't stick a 35mm film lens on a 2 1/4 camera anyway.

I also don't think this is something newbies have trouble understanding, and I don't see the harm in them nailing down the concept. After all, they still SELL film cameras, and understanding the difference in crop factors between film and APS-C digital, using the same lens, is important to know.
But you easily could stick a medium format lens on a 35mm film camera (or even on an APS-C camera). The crop factor has been sold to consumers as a way of "lengthening" their lenses. Somehow, it amazingly makes you 300mm lenses 450mm lenses. All of this becomes quite confusing if you never really shot film and don't know how lenses behaved on 35mm.
12-07-2010, 09:09 AM   #13
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QuoteOriginally posted by Rondec Quote
But you easily could stick a medium format lens on a 35mm film camera (or even on an APS-C camera).
But nobody ever did that like they're putting full frame lenses on APS-C--so it wasn't a relevant discussion at the time.

Now that so many people are using the older lenses on APS-C, it is.
12-07-2010, 09:19 AM   #14
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A better way to think of it is this:

Put the lens on your camera.

Look through the viewfinder.

Does that field of view work for you?

I have no idea what it was like to use a 50mm on film. I quite like them on digital.

All in all, this only matters if you are familiar with film and want to replace your old gear with equivalent stuff, or you plan on blowing huge wads of cash on FF. Otherwise, learn what each focal length is on ASP-C, because it's going to be around for a while.
12-07-2010, 09:21 AM   #15
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QuoteOriginally posted by Ira Quote
But nobody ever did that like they're putting full frame lenses on APS-C--so it wasn't a relevant discussion at the time.

Now that so many people are using the older lenses on APS-C, it is.
People did do it (hence the adapters Pentax made for their lenses to K mount. In reality it was a dumb thing to do. Medium format lenses don't resolve any where near as well as 35mm lenses as they don't have to to achieve the sharpness. Large format lenses are even worse. A large format lens designed for 4x5 or 8x10 that produces fantastic sharp images on those formats when adapted down to m4/3 (the most common adapter) produces a very soft look and frequently is likely out resolved by the kit lens that came with the camera by a large magnitude
I've played around with MF to 4/3 and apsc a bit, and though the results are interesting (from a macro and homemade tilt shift effect) they are really nothing compared to a good sharp lens. My 45 year old 55 1.8 tak is considerably sharper than my Bronica MC 50 adapted to Digital (the MC 50 is wonderful on the camera it's for though)
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