Focal length and crop factor

[William W]

From your last answer, I am a little dumfounded as to what it is you are asking: or if you just wish to argue points using empirical mathematics to disprove a “Rule of Thumb”. A Rule of Thumb is “a guideline”.

But I shall address your last post individually: and then perhaps I shall leave it at that.

I totally agree, but look at it on the screen of your computer at 100% magnification. Don't do it while printed at full frame crop, whereas your entire demonstration is based on that.

The word “Print” is a metaphor.
Use the Screen if you wish, but ensure the resolution of the screen is adequate.

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Better yet, compare the image shift to the fixed elements in your picture. Don't compare it to the image size.

The image size is important and so is the viewing distance – if you do not understand these points then you will fail to grasp this is all about what we “see” the “perception of blur or movement” – if you look at a 24” x 20” at 3” Viewing Distance you will see a lot more mess than viewing the same picture in a 5 x 3½ at 6ft viewing distance – the postcard size print will look very sharp by comparison.

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A lot of changes may occur between computer and print (cropping, resizing up or down, sharpening or blurring etc.).

Yes, there are a lot of post production changes we can make, but we are not discussing that.

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The rule was established when little or no crop was done between taking the photo and printing.

Incorrect.
Pictures have been cropped in printing or cut after printing, to various sizes, since the birth of Photography.
Certainly in the 1950's to 1970's we cropped and enlarged in printing, all the time, it was commonplace: the printing labs had cardboard cropping matts onto which the negs were stuck.

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Nowadays you can do a lot of post process that could change the perceived blur.

Yes, but we are not discussing that.

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When I use burst mode to avoid camera shake, I compare my pictures at 100% magnification on my monitor, I choose the sharpest one and afterwards I continue my workflow. I don't carry on with my post processing and printing for all the pictures within that series and choose the best one from the prints. I am pretty sure you do the same.

There are a couple of points here.
Firstly: when faced with a slow Tv (Shutter Speed) and hand holding the technique of shooting a burst of three – I do use.
Invariably I will find that the middle shot is the sharpest, the middle shot is usually the one with the least camera shake – not necessarily the one which eliminates camera shake, however.

The second point is: you have misinterpreted my answer and assumed and then applied it as my workflow – of course I do not select the best images by printing all of them – as already clarified the word “print” was used as a metaphor.

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So let's NOT compare print perceived blur and then "establish" how optics work.

NO. I did NOT do what you suggest.

I did not compare prints to establish how optics work.
If you re read my previous you will not that I established the perceived blur we will see, is predicated on the viewing of a “standard print” at a “standard viewing distance” and takes into consideration of the resolving power of the human eye (and thus also the Circle of Confusion for any given camera format).

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Because one lens angle shift doesn't care about the print size. A 1 (one) degree lens angle shift translates into the same pixel shift amount, no matter the sensor size !

No it does not.
Firstly, as you pointed out previously, there is a difference – even by your pixel example.
And secondly, there is a difference in the spread of that blur, when the two images (the complete “Full Frame Crop” images) are viewed at the SAME Viewing Distance.
And thirdly, the Shutter Speed makes the counter difference – and that is why we need to apply the SPEED of the 1° camera movement – and not just how far the camera moves – but how far the camera moves over TIME.

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I shall re-summarise:

This “Rule of Thumb” is only a STARTING POINT as a GUIDELINE to SUGGEST what shutter speed to use.
It suggests that with your 135 format camera you need to use 1/50s when using a 50mm lens and with the APS-C camera you need to use 1/80s with the same lens – there is NOT much difference in those two shutter speeds.
The “rule” guarantees nothing.
The rule is predicted on: Optics; The ability of the Human Eye’s resolving power; The average SPEED of the average person’s ability to NOT hold a camera steady; The CoC of the format; and assumes the fact that if we compare always, the Full Frame Images from any camera and look at those images at the same viewing distance.
And that is what this Rule of Thumb is all about – it is merely a Guideline suggesting a shutter speed to arrest perceivable movement when looking at like prints (or computer images) and again I stress that this is 1/Focal length Rule is a “Rule of Thumb” as a guide for taking pictures and was developed around the 135 CAMERA FORMAT, but it can be adapted to other formats.
And - since the advent of Digital and the popularity of APS-C cameras this Guideline has been adapted to APS-C cameras:
And the rule gives this guideline . . . if we hand hold a 200mm lens on a 30D, it is a good idea to use about 1/320s but if I put the same 200mm lens on a 5DmkII I could use 1/200s, as the slowest shutter speed to arrest camera shake . . .
But that does not mean if we use 1/320s or 1/200s there will be not any shake – there are many, many other factors, including how much coffee I had and how tired I am . . .
It is just a guideline.

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In conclusion if you are happy with using whatever shutter speed, when you are hand holding either of your cameras, and applying techniques, like shooting a spread; or using Post Production Sharpening Tools in order to get sharp looking images - that is fine.
BUT: The OP’s question was about clarifying a guide as to a starting point for a shutter speed to make sharp photographs, that’s all.
I understood your question to be about what guideline to use as a starting point for a shutter speed when hand holding an APS-C camera.
I believe I have given you that guideline and also the historic background; the basic empirical mathematics upon which the original 1/Focal Length Rule of Thumb was predicated.
If you wish to argue; accept what I have written or not - that’s fine too.
At the moment, it is neither possible nor reasonable for me to explain these three matters any more clearly, than I have.

May your light be with you, too.

WW

[Colin Southern]

This “Rule of Thumb” is only a STARTING POINT as a GUIDELINE to SUGGEST what shutter speed to use.

I agree, and might also add that it's also been said that to (practically) eliminate camera shake, one needs a shutter-speed that's in the order of 5 times the 1/focal length rule.

[William W]

Yes one has to know "the limits".

To pull a good shot that is better than "OK" at 16 x 20 Display Print: for me to be "safe" I would like to use something in the order of 1/400s to 1/500s when using a 50mm lens on my 5D's.
With my 135mm lens I want about 1/1000s for top quality work when making pictures of irretrievable opportunities.
. . . Or forget all this Hand Holding stuff and learn how to use a Big Sturdy Tripod. . . hey Colin!


. . . then of course there are “the limits” to learn about Subject Movement and what Shutter Speeds are required to arrest those little buggers. . . Like the B&G “Standing Still” at the Altar – but they are actually moving . . .

WW

[Colin Southern]

. . . then of course there are “the limits” to learn about Subject Movement and what Shutter Speeds are required to arrest those little buggers. . . Like the B&G “Standing Still” at the Altar – but they are actually moving . . .

Oh Bill - didn't they teach you that all you need to do is just use a flash! It freezes all motion

[William W]

yep, so does IS . . .

. . . love your work: cute pooch.
Like kids, you gotta get down low with them to make the visual connection

135/2L ? ? ? . . . didn't know you were into Primes, or is it your zoom, and just happened to be at 135?

[Colin Southern]

yep, so does IS . . .

. . . love your work: cute pooch.
Like kids, you gotta get down low with them to make the visual connection

135/2L ? ? ? . . . didn't know you were into Primes, or is it your zoom, and just happened to be at 135?

Hey Bill,

I've got 14/2.8L, 85/1.2L, TS-E90/3.5, and 135/2L Primes - in the studio shooting distances are a bit more predictable, so it's about 50/50 with the135/2L & 70-200/2.8L II.

This was the final "cute pooch" shot ...

[William W]

Nice!

Aside question if I may – OP please excuse me. But this is perfect timing -

Re your 90: How often or do you it at all, for Portraiture.

I was actually driving over to buy one today, but got caught up and didn’t make it.

I believe I have decided that the 90 is what I want and that I will get more use from a 90 and its movements, than if I buy the TS-E 45

(Referencing: I am asking about wanting a flexible use lens for Portrait Studies only).

Other Details:
Using 5D’s.
I have plenty of space – Shooting Distances are not an issue.
The other lenses which I use for Portraiture: 24L; 35L; 50/1.4; 85/1.8; 100/2.8M; 135L 300/4 (can get 300/2.8 and 400/2.8 if needed)

Comments please?

WW

[Colin Southern]

Hi Bill,

Personally, I'd never use it for portraiture because it doesn't have AF (so AF confirmation is as close as you'll get to anything in the camera helping you). In reality, I think it's great for product shots, but apart from that, not a lot of use for me. I can see how it could be used for portraiture, but it wouldn't suit my style at all.

On the plus side, it's ideal for photographing photos (minimum focusing distance is really nice) (and even nicer with a 12mm extension tube on it).

Does that help?

[William W]

ha! ha!

Thanks, Well it does help - as I thought that was going to be your answer: "I don’t use it for Portraiture . . ."

But I also anticipated you knew how I would . . . so as it has been on my mind today I just asked anyway. Those two lenses aren't used much for Portraitiure - the 45 gets a run a lot with some specialist Wedding Fellas who are really into it.

Hmmm?

Thanks, I’ve been through all the pros and cons six times - the 90 is better than the 45, so the 90 it is . . . and lots of very patient Sitters.

regards

[benm]

Those being said, I am still trying to figure out WHY are we multiplying the focal length by the crop factor in the empiric rule of thumb time=1/focal, since there's NO magnification involved ?

But there IS magnification. It does not occur in-camera but on the screen. When viewed on the screen the crop sensor is enlarged more to fill the screen because the crop sensor is smaller than the full frame sensor. The image on either sensor is identical in size; the full frame sensor just shows more around the edges.

Why the word "crop" ever came into play is a mystery. In the days of film no one ever called 35mm film "crop" when comparing to 220 film or 4x5, etc.

[Colin Southern]

Why the word "crop" ever came into play is a mystery

Because - in a 35mm system - part of the image circle is cropped on an APS-C/H sensor sized camera?

[William W]

Why the word "crop" ever came into play is a mystery. In the days of film no one ever called 35mm film "crop" when comparing to 220 film or 4x5, etc.

and . . .

Because - in a 35mm system - part of the image circle is cropped on an APS-C/H sensor sized camera?

. . . and because, going way back into the 1970's when 6x6; 6x7; 6x9 and 5x4 cameras were being used alongside 35mm cameras. All those cameras were:

a) Being used by a smaller and a more select group of people, because they could afford them.
and
b) The conversations, between that smaller group of camera users, were much more selective than the now all common chat on the internet.

So what happens is: common parlance; shorthand words and the dilution of meaning increases with the size of the group conversing and the speed at which those conversations develop.
Hence the language "develops": ad hoc.

I teach Photography.
Have a guess how many 22 to 28 year old "ADVANCED" Students of Photography, from a class of 20 people, know why Post Production Programs term two of the processes "Dodge" and "Burn".

The pollution and divergent nature of language is not limited to Photography and misinformation is rampant generally.
I am not whinging -just noting it.

The CiC tutorials and this site generally are of an extremely high order of information; and as a bonus the forums are quite friendly, interactive and accepting, due in large part to the all the Moderators’ and Administrators' efforts.

I refer to the CiC tutorials, often, as a general reference for students.

WW