TriX Loc: Raleigh, NC

Gene51 and Clapperboard are correct. This discussion recurs periodically along with the same misinformation obtained in the "video". Let's examine the facts.

1) the FL of a lens does not change depending on the body it's attached to - it's a function of the lens and is independent of the body it is attached to. The field of view changes on a crop camera as compared to a FF

2) the aperture does not change. The same amount of light is transmitted by the lens regardless of the body it is mounted to. As proof, notice that the exposure, as measured by either an external or in-camera light meter does not change If a given lens is moved from a FF to a crop body (or vice-versa)

3) the type body has zero effect on the ISO since the light transmission does not change.

4) the DOF is best determined by your DOF calculator, but you must consider that to fill the frame with the same percentage of the image, you would need to move closer with the FF by the "crop factor" or choose a longer lens.

Consider an 85 mm lens at f5.6 on a crop body with a subject distance of 15 feet. The effective field of view on a 1.5 crop body is the equivalent of ~ 127mm on a FF. The DOF (on my DOF calculator) is 13.4-l6.5 ft or 3.1 ft.

Now consider the same lens on a FF at f5.6. To fill the frame with the same subject size/percentage (and this is the critical point), you would need to move in to 10 feet. The DOF is then 9.6-11.1 ft. or 1.5 ft.

If you chose the equivalent 127mm lens on the FF and stayed at 15', the DOF is 14.1-15.5 ft or ~1.4 ft. (your DOF calculator may be slightly different)

rehess Loc: South Bend, Indiana, USA

An engineer should recognize an overly simplistic explanation.

Usually when you compare an APS-C camera to an FF camera, you are confounding two variables, overall sensor size and individual pixel size. The Canon 5DS, a FF camera which has very crowded/small pixels, has limited ISO range, apparently because noise in those crowded elements looks more like noise in APS-C crowded elements than like noise in normally spacious FF elements. Similarly, the Nikon D500, an APS-C camera with very good noise characteristics, has elements which are less crowded than typical for APS-C cameras.

Plus, two sensors of exactly the same size characteristics will behave differently depending on who made them and when. Every so often, a clever engineer will find a way of improving things, and for the moment only her/his company will benefit. Also, a company may put a sensor with more clever engineering / more manufacturing effort into an upscale camera, while the same company may put a less capable sensor into a different product with lower list price.

TriX Loc: Raleigh, NC

But the lumens per square meter (lux) is the same. Given a specific intensity of light, even though the smaller sensor captures less total light, it is also smaller in terms of area. You can prove this to yourself if you have both a crop and a FF body. Put the same lens on each, measure a specific subject with the same illumination, and see if the readings are different. Note also that light meters do not have different exposure scales for FF or crop (or MF or 4x5 or 8x10).

lautenk2

Not quite. You're right except for the part where you say the video is opposite of the other posters here.
To calculate equivalent exposure, the aperture is not adjusted by the crop factor.
To calculate equivalent depth-of-field, the aperture is adjusted by the crop factor.
So its not opposite because equiv exposure and equiv DOF are two different things. The video was certainly more detailed, but I don't see where the other posters are wrong about equiv exposure.

Fascinating to me how each element of these conversions is simple enough on its own, but when your finger is on the shutter button you have to consider them all simultaneously. That's a lot of stuff to keep in mind at the same time, the very definition of complicated.

Tracy B. Loc: Indiana

Working in Engineering I recognize bullies too.
I only stated my profession because I was telling someone how And why I like details. I don't need that to be thrown in my face because I happen to disagree with you.

rehess Loc: South Bend, Indiana, USA

Actually, during much of my career, my job title was "Software Engineer", and I worked with people whose job title was "Electrical Engineer". My profession always required that I be completely on top of details, and to examine what others told me. I was not throwing any thing in your face. I was disappointed that someone self-identifying as an "engineer" didn't look past the presentation.

Now that we got that out of the way, instead of attacking me personally, please address the technical aspects that you have been repeatedly ignoring.

Tracy B. Loc: Indiana

You have no idea how much I have researched. Just because my conclusion is not what yours is, does not mean I have not "examined" other resources! Do not include me in anymore of your posts. If you were "completely on top of details" maybe you could see you are the one attacking me!!!!

rehess Loc: South Bend, Indiana, USA

And you have no idea how much research I have done. I have responded to your "facts". You are the one who has steadfastly refused to address facts.

burkphoto Loc: High Point, NC

The actual focal length of the lens is still 300mm. Aperture is still f/2.8.

The same projected image is just "cropped" tighter due to the smaller sensor sitting in the center of it. This IMPROVES *performance consistency across the recorded image*. It DIMINISHES overall MTF performance for multiple, combined reasons I won't get into here.

The FIELD OF VIEW of a 300mm full frame lens mounted on a DX body is equivalent to a 450mm lens used on full frame digital or 35mm full frame film.

Depth of Field changes as well, due to the 1.5X magnification.

At 300mm, 50 feet, f/5.6 yields 2.85 feet of DOF on the D610.

On the D7100, at the same 50 feet, with the same 300mm lens and f/5.6 aperture, you would get 1.86 feet of DOF.

But a 450mm lens at 50 feet, f/5.6, on the D610, would have a DOF of 1.26 feet.

Source: Depth of Field Calc app on my iPhone.

jmvaugh Loc: Albuquerque

I’m a retired engineer and I viewed the entire video, read the whole article, and then read all the posts in this thread. My goodness, what a muddled mess!
I think I just take some aspirin for my DOF/focal length/crop factor headache and go play with my camera to relax.🙁

burkphoto Loc: High Point, NC

Different bodies CAN be calibrated a little differently. Out of 100 bodies of the same model, a few will be "fast" and a few will be "slow". But most perform the same way. Mixing two different formats may yield slightly different results. It's really just like the old T/stop vs f/stop thing... Different lenses may have different T/stops (a measure of absolute light transmission) at the same f/stop setting. And cameras and lenses put together are systems. Inevitably, multiple bodies may need to be calibrated to each other, and to hand-held meters, if you use them. In my own experience working with slide films and JPEGs, I've ALWAYS found that to be true. With raw digital capture and negative films, it usually isn't a factor.

Hsch39 Loc: Northbrook, Illinois

I just checked http://www.dofmaster.com/doftable.html with 300mm lens at 50 feet - f/5.6 with Canon 7D vs Canon 5D Mark IV. APS vs FF. Same DOF 49'-2" to 51".

burkphoto Loc: High Point, NC

It varies slightly with brand and model comparison. And it’s also just a rough estimate. Actual DOF varies with print size. The quoted figures from most calculators are based on 8x10 prints, where the available pixels are cropped the least.

TriX Loc: Raleigh, NC

Maybe my calculator (DOF Master) is different, but I'm showing 1.78' for the 7D (CoC =.019mm) and 2.82' for the 5D (CoC= .03mm). Both the DOF and CoC are different by a factor of 1.5, exactly as I would expect since the circle of confusion is a factor in DOF calculation.

Clapperboard

Tracy B Forgive me, I don't need to watch some half baked ill informed video. The argument against my points are disagreeing with the most famous scientists the world has known. There are established 'Laws of Physics' that I am surprised you don't appear to know as an engineer. GCE students in the UK would know better than to accept the 'theories' expounded by this man. That I believe is probably the equivalent of sixth grade students in the USA.
Whilst it is true you don't need to understand the behaviour of light and lenses in order to design bridges it is usual that the courses training students for such careers normally include such basic training. And it really is BASIC TRAINING.
Yes, fifteen and sixteen year old students know better than to spout the bunkum this man keeps repeating.
Cheers Tracy B and good luck in your photography and your career.