DSLR lens focal length / shutter speed rule

[Ungaloob]

Okay, maybe the answer to this is self-evident to everyone but me, but I got to thinking about it last night and I began to wonder if I'd stumbled on something.

Does the same 'inverse of the focal length' rule apply to the minimum handheld shutter speed with DSLRs with APS sized sensors? If I can presumably shoot at 1/50 of a second with a 50mm lens with a 35mm negative size, can I still shoot at that speed with the same 50mm lens with my DSLR's APS sized sensor, or should I go with a minimum of 1/75 of a second to compensate for the longer effective focal length?

When I was shooting a lot of 35mm I nearly always used a tripod, but for some reason since I made the switch to digital I've shot mostly handheld, I guess because of the more run-and-gun, immediate gratification style I've developed. While I've captured shots I never would have gotten with my earlier style, sharpness has greatly suffered.

[PhilMasters]

You lost me on this one. Did you ever figure it out or get an answer?

[Ungaloob]

I never did get an answer. The "inverse of the focal length" rule is so ingrained in me that I still use it even with the smaller sensors, but I've tried to really work on being a lot more careful about managing camera shake by using faster shutter speeds whenever possible, and also by using a tripod more often like I did in the past.

It's interesting with digital, and again this is something that is obvious once you think about it, but you can always speed up the ISO if you need another stop or two of shutter speed. Being sort of an old school film guy, that concept has taken some getting used to for me, but it's a trick that I use all the time now.

[Rufus]

Well now, as I see it, (maybe incorrectly), the focal length hasnt changed, the magnification in real terms hasnt changed either. Only the percieved size has changed due to the crop. Therefore I'd say that the shutter speed remains the same, as it would on a true 35mm body.

Interestingly, and maybe due to me getting older, I find camera shake in low temperatures an issue. Now, living in the middle of the UK, it's never really cold, but temperatures which are quite bearable still create a minute shake which can be problematic. This wasnt true when I was younger, and in those days it used to be much colder!!

[Ungaloob]

I realize that this topic was practically meaningless from the getgo, because we're only talking about half a stop in shutter speeds here, but it's become interesting to me for other reasons.

So you're saying that since the physical properties of the lens aren't changing, then the rule doesn't change? I'm not sure I agree with that, because if you have to enlarge the original recorded image area 1.5 times more than 35mm to get the same size print (say an 8x12), doesn't that translate into lower tolerances for camera shake? I mean, yeah, the lens is producing exactly the same resolution at the film plane, but you're using less of that available resolution to create your image.

Is it related only to the focal length of the lens, or is it more related to how much cropping and enlarging is done to create the final result? If you start with a smaller recorded image area, do you always need higher shutter speeds?

[Rufus]

Well now, I must emphasise that I'm only voicing my thoughts,and not solid facts.
Mind you, if size were the issue, then where would that put the very small (110, etc), formats?
Personally, I'd say that you answered it yourself by saying: " I mean, yeah, the lens is producing exactly the same resolution at the film plane" ............... Now taking this as fact, where does the influence of the crop interfere with the actual shooting process? The printing, yes.... The shot, no.

IMHO

See what I mean Ungi? Of course I may be quite wrong. Maybe. Possibly.

[Ungaloob]

I'm only voicing my thoughts, too. Certianly not facts...

I guess what I meant was that if you have two 8x12 enlargements, one made from a full frame 35mm negative, and the other one made by doubling the same 35mm negative to a 16x24 and then cropping it back down to an 8x12, you'd have two of the same size pictures, but one with half the resolution, right? So any imperfections such as camera shake and whatever else would be doubled.

So if you have an APS size sensor and a 35mm size sensor, to generate the same size print you'd have to blow up the APS sized sensor image 1.5 times more than the full sized one, right? Does that mean your original image would have to be 1.5 times as sharp for it to look as good? And, how is that different from the actual resolution in pixels the sensors produce? There's obviously two things going on here: the physical world; and all the mysterious electronic stuff that happens inside the camera after you push the shutter release button.

[Rufus]

Oh blimey Ungi!! :eek:

I think I need to go and lie down. My brain hurts!!!

[Ungaloob]

Sorry, just trying to have a little fun... :D

[Rufus]

Ah, sorry. Cant answer you at present as I'm in a darkened room, lying down, repeating, "it's ok....you arent mad, (yet)" :D

[Ungaloob]

Happy to have been of service...

Any time your brain needs a good tweak, let me know...

[Rufus]

Huh? Who are you? What day is it?


Who said that?

[Ungaloob]

Get some rest... We can talk about this sometime later on after you've recovered.

[Rufus]

It just struck midnight.

Zzzzzzzzzzzzzzzzzzzz.............................. .....

[pixelkat]

ok now you guys have my head hurting.... LOL NO SERIOUSLY A MIGRAINE >>>UUUGGGGHHHH so much to think about now..... why do you guys do this to me...

[Rufus]

It's fun! We like to confuse people, and we're good at it. :-)

[pixelkat]

oh you sure are - my head was a nightmare... LOL

[Ungaloob]

Ah yes, but it's a new day, and the time has come to get back to the discussion at hand.

It's obvious that whenever shooting, camera stability and the sharpness of the image are critical. We could probably go 'round and 'round about sensor size and all of that, but maybe it's all academic.

I always felt that the lenses were a lot more important than the body, and being a Pentax guy I always treated my K-1000's more like interchangeable film backs in a medium format system than centerpieces of the shooting process. So my new question is this: in this era of high end DSLR bodies that cost anywhere from $3,000 - $8,000 and up, are you really that much better off with them than you are with a lesser body with great glass?

Compare for example the Canon 5D to a Canon 350D. With the same lens stuck on the front, how big of a difference will there be in an 8x12 or an 11x14 print? Or compare the Nikon D200 to a D50 and ask the same thing.

Obviously you'll get a better image with the more expensive cameras, but it's a question of priorities. Given a limited budget, is money better spent on buying the best lenses that can be afforded and going with an entry-level DSLR body, or in intitially throwing as much money as possible at the body and then slowly adding lenses later?

[pixelkat]

i would answer that as the lenses are every bit as important as the body if not more so... I speak from experience... I have a cheap lens on my 350d that produces less then desirable prints and then more expensive lens I found at a pawn shop for a steal in perfect condition that produces exceptional prints from the same camera body.. so in my experience the lens makes the difference........ but ofcourse a better camera body can only help right.. LOL