Why do you need to factor in sensor crop when using the 1/(focal length) handholding

I just read in another thread to factor in sensor crop when using the 1/(focal length) hand holding rule. Why do you need to do that? I understand that whether you're using APS or full frame, (x)mm will ALWAYS be (x)mm. The camera just uses less of the projected image and that's where you get the crop. So, why would you need to factor in sensor crop when using that hand holding rule? If you were using a 5D MK II and were planning to crop it down to APS-C format, would you have to factor in the 1.6x there too?

Since the image on the Crop sensor is smaller then image on the FF sensor, when you print (or present on screen with the same, specified dimension) both of them at the same paper, the cropped image has to be enlarged more then FF image.
More enlargement shows more of the displacement caused by the camera shake.

When you crop down FF image and enlarge it to the same size as the uncropped image, results will be the same: cropped final picture will show more imperfections then the FF one.

Also, don't forget that 1/FL*CF is only the guide line: actual results depend on couple of other, non photographic factors.

If you are only using crop sensor camera, then this really has no reference for you, but if you are comparing the field of view to a FF camera or 35mm camera, then you will use that 1.6x crop factor to assess how to create a similar FOV.

Simple, If the image is amplified (cropped) then your shake is also amplified. Always good to throw in a fudge factor anyways.

So if you were to crop a full frame picture into a 1.6 crop format and enlarge it to the same size, you SHOULD take that into consideration when hand holding?

What does your own experience tell you about your own ability to handhold lenses? Go by that!

edmyloo wrote in post #12035355
So if you were to crop a full frame picture into a 1.6 crop format and enlarge it to the same size, you SHOULD take that into consideration when hand holding?

Or any other factor you care to use.

Do keep in mind that this is just a guide. How still each person can hold a camera/lens depends on many variables. Find out for yourself what works and what doesn't.

Haha, alright! I generally use the 1/(focal length) rule and don't factor in the 1.6 crop and it's been working for. Just wanted some clarification about something I read I guess.

The 1/focal length rule is a suggestion. It is most useful for those starting out, but it is also useful to pros as well as a general reference point. It also saves you from having to memorize a ton of info for each lens you have....

For instance, I know that I can only use my lenses effectively at the inverse of the focal length - 1/3rd stop. So instead of memorizing (literally) the 15 different minimum shutter speeds I need to know for all my lenses, + the 15 others I need with my other camera, or about 30 total shutter speeds I can just memorize 3 things....

The rule, the crop factor for when using my 7d, and that after setting shutter speed to 1/focal length I can roll it one more click to the left.

I don't even have to remember IS if I don't want.... Just set my focal speed, then roll up to 6 clicks for my 50-500, or up to 9 clicks for my 70-200.

edmyloo wrote in post #12035409
Haha, alright! I generally use the 1/(focal length) rule and don't factor in the 1.6 crop and it's been working for. Just wanted some clarification about something I read I guess.

Yeah, definitely use what works for you. A lot of people do that and are fine. 1.6 is only 2/3rds stop. I bet a LOT of people are steady enough to use 1/FL - 2/3rds stop on Full Frame after they have a little practice. So it makes sense that with a little practice a lot of people just use the unmodified rule on crop.

edmyloo wrote in post #12035023
If you were using a 5D MK II and were planning to crop it down to APS-C format, would you have to factor in the 1.6x there too?

That's a really good point. That is the way the guideline would work; if you're cropping then you would be seeing the camera shake more so you would want to give yourself a bit of extra safety margin. But as stated, it's just a guide and you should see what works for you.

I find that when I factor in the conversion factor, I need a little less compensation than this for a shorter focal length. Thus, I can hold my 35f2 at 1/40 or 1/50. For the 85, I need at least 1/125, but it is much better to have 1/160. I need to brace myself if using the 85 at 1/100. Some people may have steadier hands.
IS helps and I don't hesitate to use 1/15 or 1/10 with a short zoom and IS.
Action matters. A speed of 1/400 may not be enough for the 85 when photographing runners. A higher shutter speed is better for this.