Why is crop factor shown as 1.5X and not 0.6666666X ?

Because its only .66 recurring of the image which is remaining after the Pentax has cropped the image when compared to what you see on 35mm film using the same lens. A teaser for those in the know )

The sign of the devil is hard to market?
--
John
Iowa, USA

The knowing the difference in sensor size doesn't help much in the field. Knowing what lens to use to get an equivalent 35mm field of view does.

--

Verbage is not a word, but a mangling of verbiage - differing in both print and meaning. It replaces more cumbersome words such as copy and text.

This is true, so to get an image equiv from the old standard prime 50mm lens you would need one 50 x 0.66 = 33mm. So its back to that 0.66x multiple again )

Dividing by .66666666etc is the same thing as multiplying by 1.5. Multiplying by 1.5 is easier.

east(I can do the second operation in my head)saltwater

ozbrit said:

This is true, so to get an image equiv from the old standard prime
50mm lens you would need one 50 x 0.66 = 33mm. So its back to
that 0.66x multiple again )

Click to expand...

Yes, but as the manual states dividing by 1.5 gives you the same result without involving a repeating decimal

--

Verbage is not a word, but a mangling of verbiage - differing in both print and meaning. It replaces more cumbersome words such as copy and text.

but I'm not dividing by 0.66 I'm multiplying it because thats what you need to do in order to find the equivalent lens to get the same result on digital as you would have had on film. I wonder if its plan by the industry to hoodwink buyers into thinking they're getting more for their money instead of the reverse. How often do we see people suggesting that their 50mm lens has magically re-invented itself as a modest 75mm telephoto when used on a digital SLR? Well it hasn't because its still a 50mm lens but the downside is your digi camera will only record 66.666% of the image like a 75mm would have. But unlike a 50mm a real 75mm lens would also bring the subject matter closer.

So why has the industry adopted 1.5x and not 0.66x crop?

ozbrit said:

Because its only .66 recurring of the image which is remaining
after the Pentax has cropped the image when compared to what you
see on 35mm film using the same lens. A teaser for those in the
know )

Click to expand...

Might consider also, then, why are zoom lenses labelled by how much they change focal length towards telephoto(eg 3X), and not how much they change towards wideangle(0.33 recurring)?

Makes no difference, calculation-wise. Except that we have associated the zooming with increasing magnification (then prefer saying "3 times longer"), whereas we've got an association of traditional cropping with reducing an image size (and so prefer the reinforcement of saying "1.5 times smaller" and not "0.66 times the original", which is slightly more abstract perhaps).

Maybe in a general way, also, there's a small aesthetic point of view whereby higher factors look nicer as 10x, 100x, 10000x, 10^20x rather than 0.1x, 0.01x, 0.0001x, 1x10^(-20)x

My 2c worth, for what it's worth [probably considerably less than 2c lol]

--

oceangreen ~ typically based on emerald green with a slightly dramatic tone of deep black and a misty accent of barley

Well, i never shot film, so i don't really care about finding the equivalent lens that will give me the same field of view as a 50mm lens in film.

For me, knowing that 12mm is super wide, 18 is wide and 35 normal, 50 short tele and 200 long tele is just the normal way to think.

But, when i want to know what is the longest exposition time i'll be allowed to set on a 85mm lens to avoid shaking blur (on a Ds), i know it's 85x1.5 = 1/147s
So for me 1.5 is more logical than 0.6666

--
http://www.popopow.com/

Yes some of us are a bit stuck in the film age. A 12mm would be a fish eye and a 28mm a decent wide-angle before distortion sets in. Am quite intrigued by the your calculation as to what shutter speed you set your camera by to avoid "shake blur". so its 85x1.5 = 1/147sec. Or should that be 1/127sec? )

A handy formula to remember thanks, but not sure whether it has any relevance to crop factors.

ozbrit said:

How often do
we see people suggesting that their 50mm lens has magically
re-invented itself as a modest 75mm telephoto when used on a
digital SLR? Well it hasn't because its still a 50mm lens but the
downside is your digi camera will only record 66.666% of the image
like a 75mm would have. But unlike a 50mm a real 75mm lens would
also bring the subject matter closer.

Click to expand...

You stand in a particular place and take a photo. The 50mm lens (with sensor crop) delivers a particular angle of view. A 75mm lens (without sensor crop) gives the same angle of view.

The perspective (geometry) is the same, the framing is the same. Only the physical size of the aperture is different, for a given f-stop.

In what way is the subject brought "closer"?

RP

sory, i miss taped it, it's 1/127. i think it's relevent to crop factor, it would be 1/85 in full frame. But maybe i'm wrong.
--
http://www.popopow.com/

How I understand it, tele(scopic)photo lenses give a narrower field of view and can bring distant subject matter towards you so it will fill the frame.

Conversely wide-angle lenses will set everything back so you can fit a whole landscape into that same size frame.

Which takes us back to why I believe that a 50mm lens can't become a 75mm lens just because a digital camera is removing the sides, top and bottom off of your images to fit it in a frame that is now only 66.6% the size it used to be on film.

I'm only just getting to grips with all this and up to recently I accepted what I'd been reading about how we've all gained by our digital cameras effectively making our lenses more telephoto by a factor of 1.5x. Maybe I'm getting all this wrong (just when I thought I'd got my head around it) but when I compare pics of the same subject taken with with the same 50mm lens on both film and digital I can see basically the same thing only the digital pic has cropped out the central part of the image. But then If I take the same photo with a 200mm telephoto lens I can see the distant detail much clearer than if i removed the central portion of the 50mm image and blew it up to the same size.

There are two issues here: one is about geometry and angles, and the other is about magnification.

1) geometry and perspective

A telephoto lens captures a narrow angle of the scene in front of you. A wideangle lens captures a wider angle of the same scene in front of you (hence the name). The differences arise from what the angle is. A zoom lens varies this angle.

Varying the angle (when shooting from the same position) has the same effect as taking a picture at the widest angle and cropping bits off it - you see less and less of the scene in front of you as you zoom in (or as you cut bits off the picture).

The difference between a large and small sensor, placed behind the same lens, is that the small sensor catches only some of the projected light, not all. This is just like zooming, or like cropping.

2) magnification

The one problem with taking a (say) 6 megapixel image printout, taking scissors and cutting it down to 0.666x the size, is that your scissors would cut away some of that detail. What is left would be fewer megapixels' worth.

Zooming in instead (or, equally, using a specially designed smaller sensor) means that your (say) 6 megapixels covered this narrower angle of view in the first place. So you don't have to crop away any detail.

RP

ozbrit said:

Because its only .66 recurring of the image which is remaining
after the Pentax has cropped the image when compared to what you
see on 35mm film using the same lens. A teaser for those in the
know )

Click to expand...

It's more like 1.53 actually.

--
Rob

popopow said:

sory, i miss taped it, it's 1/127. i think it's relevent to crop
factor, it would be 1/85 in full frame. But maybe i'm wrong.
--
http://www.popopow.com/

Click to expand...

I think you're right, but with modifications. I use 1/350th with a 300mm (450mm on my D), which is about what I used to be able to get away with on a 500mm in film. I can't handhold 1/350, though, on my 500mm, which is the equivalent of 750mm. These days, I need 1/750 or faster for that, but that's creeping age.

To get extra steadiness, I use shooting techniques for breathing and shutter control that I learned at Parris Island. Nothing special: deep breath, let half out, squeeze gently enough so that you don't know when the release comes (on a rifle it is, or was 40+ years ago, called trigger break, which is just about instantly followed by firing: if you don't know it's coming, you don't flinch or otherwise move, so added to no body movement from breathing, you've got excellent target control). It takes a bit of practice to get it right a high percentage of the time (to me, that's now about 60%: to younger people in better shape, it should be closer to 90%), but you can often squeeze 20%, maybe a bit more, off shutter time, and that can sometimes help get a shot you'd otherwise lose.
--
Charlie Self
http://www.charlieselfonline.com

I wanted to ask about angle of view and compression associated to lens focal lengths- If you have a 35mm on a digital slr it crops to approx. 50mm- but will it also have the same compression as a normal 50mm on a full Frame?? My thoughts are- We will never have a true perspective, angle of view and compression associated to that focal length until we get FF?- Am I right?
I am leaning towards Pentax because of their terrific line up of stellar primes.

anthony kucharczyk said:

I wanted to ask about angle of view and compression associated to
lens focal lengths- If you have a 35mm on a digital slr it crops to
approx. 50mm- but will it also have the same compression as a
normal 50mm on a full Frame?? My thoughts are- We will never have a
true perspective, angle of view and compression associated to that
focal length until we get FF?- Am I right?

Click to expand...

My understanding (and experience) is that we do have the same perspective with 50mm on APS-C as with 75mm on "full frame".

To take a more extreme example, if you take a panasonic FZ-50 at the actual focal length of 15mm (approx 2x zoom) you get the same perspective you get at 70mm in the 35mm world.

However the depth of field would be very different.

ozbrit wrote:
...

ozbrit said:

Which takes us back to why I believe that a 50mm lens can't become
a 75mm lens just because a digital camera is removing the sides,
top and bottom off of your images to fit it in a frame that is now
only 66.6% the size it used to be on film.

Click to expand...

...

Focal length is a real number... it's independent of the format (35mm, APS-C, 645, etc). So, you are correct that a 50mm can't become a 75mm lens.

However, some characteristics ARE dependent on format. One of the most important ones is angle of view. Basing everything on 35mm-centric terms (IMO) makes it convenient to compare views offered on different formats... P&S, dSLRs, etc.

However, I never really used anything but my Pentax DS... so, to me, the real focal length of a lens already conveys to me the view I'll get with my 1.5x crop factor camera. DOF is another thing that gets a bit different... however, I am VERY familiar with what f/1.4 looks like with my 50mm... I have no real idea what it looks like on 35mm film. Mathematically, I believe the effective DOF is thinner but it doesn't really matter to me that much.

--
pog



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