Do extension tubes affect shutter speed rule?

[TimmyG]

Does anyone know if I put an extension tube on my 50mm lens, do I have to adjust how long I keep the shutter open for while shooting hand held? For example, the rule of thumb for 50mm is 1/50 of a second or faster. Would I need faster (or slower) shutter speeds with the extension tube? If so, is there a rule of thumb? Thanks, I haven't done enough experimenting to find out for myself.

[Scottes]

You're increasing the focal length so yes you'd want a faster shutter. 50mm + 20mm tube = 70mm so 1/75th or whatever.

Don't use that addition when computing DoF or anything like that, though...

[DaveG]

Does anyone know if I put an extension tube on my 50mm lens, do I have to adjust how long I keep the shutter open for while shooting hand held? For example, the rule of thumb for 50mm is 1/50 of a second or faster. Would I need faster (or slower) shutter speeds with the extension tube? If so, is there a rule of thumb? Thanks, I haven't done enough experimenting to find out for myself.\

The use of an extension tube DOES NOT increase the focal length of the lens. The lens's focal length stays the same but you can focus closer. Now a teleconverter (or extender as Canon calls it) will increase the focal length of your lens, but as I say an extension tube won't.

On one level then the 1/focal length rule doesn't change, but it's moot in any case. When you use a macro lens or an extension tube you are focusing so close that your limited depth of field is going to be the problem even when you stop down a lot. And you ARE going to want to stop down a lot! Therefore the aperture is going to be small, you'll have to take a little bellows extension factor into account (the meter in your camera will take care of this so don't worry) and all of this will result in a very slow shutterspeed.

That means that you should be using a tripod and then all the hand holding rules go out the window.

[DaveG]

You're increasing the focal length so yes you'd want a faster shutter. 50mm + 20mm tube = 70mm so 1/75th or whatever.

Don't use that addition when computing DoF or anything like that, though...

Sorry you're wrong. The extension tube does NOT increase the focal length of the lens. A 50mm lens + a 20mm tube is still a 50 mm lens that will focus closer.

[Scottes]

Yes, I said it wrong. "Focal length" is the wrong term - tubes will make the lens longer.

A 50mm lens with a 20mm tube is 70mm long. Thus any shake at the front element will be increased by about 40%. So if you shake the camera body back and forth .5 degrees, the front element will be moving about .87mm back and forth at 50mm, or 1.22mm at 70mm.

[TimmyG]

Thanks for the info... it sounds like I should set my shutter speed to 1/70 or faster using a 50mm lens with a 20mm extension tube.

Of course all this assumes that I can't use a tripod and can afford the poor depth of field I'm left with.

I have managed to snap off a few great macros w/o a tripod but usually need to be outside where there's better lighting. Unfortunately the built-in flash practically doesn't work at all for macros. Anyone know how most external flashes fair for macro work?

[Scottes]

The flash really depends on how close you are. I usually do more like close-up stuff - long lenses with tubes and diopters. I can still be a foot or two away and the flash is OK. I have a 420EX and usually use a diffuser like a Sto-Fen OmniBounce or a Lumiquest Pocket Bounce when I get too close. The OmniBounce sends diffused lght in all directions so some goes towards the subject. With the Pocket Bounce I can angle the flash and aim the bounce towards the subject. But with a 50mm you're going to be a lot closer than I get - you'd probably want an external flash on a bracket arm of some sort, preferably one you can aim downwards.

What type of subjects are you shooting? If it's inanimate then you can use practically any type of lighting. For true macro work inside I have some halogens diffused in a variety of ways.

[DaveG]

Yes, I said it wrong. "Focal length" is the wrong term - tubes will make the lens longer.

A 50mm lens with a 20mm tube is 70mm long. Thus any shake at the front element will be increased by about 40%. So if you shake the camera body back and forth .5 degrees, the front element will be moving about .87mm back and forth at 50mm, or 1.22mm at 70mm.

No, a 50 mm lens is not physically 50mm long, nor will it be 70mm long in physical size nor focal length when you add the extension tube. You would still use the 1/focal length rule for a lens with an extension tube.

I have a 100 mm Canon macro lens. It allows me to do focus down to 1:1 basically by having a huge focus range, sort of like having a built in extension tube. I would not change the 1/focal length rule when I was using this lens. Except that the macro work that I'd use it for tosses the rule out the window. I'm going to stop it down, and I'm going to use f16 and I've lost some light due to the bellows factor. So there it is parked on my tripod. I guess my new rule would be: You don't handhold for macro work.

But once again the extension tube does NOT increase the focal length, ever. I think that you might be mixing an extension tube up with a teleconverter (extender) and with a TC you would change the focal length, and subsequently the minimum hand held shutterspeed.

[Scottes]

But once again the extension tube does NOT increase the focal length, ever.

Yes, you said that, and I corrected myself. We're off focal length.

If you stick 20mm of something in between the lens and the sensor you're making *something* longer, aren't you? And the font element is further way from the sensor, isn't it? So if the camera body shakes then that front element is moving more now that it's longer, isn't it? And you still don't think that the increased motion will be transferred to the resulting image?

By what you're saying I could stick a meter of extension tubes on my lens and not have to worry about increasing camera shake. That's a wee bit far-fetched.

[DaveG]

But once again the extension tube does NOT increase the focal length, ever.

Yes, you said that, and I corrected myself. We're off focal length.

If you stick 20mm of something in between the lens and the sensor you're making *something* longer, aren't you? And the font element is further way from the sensor, isn't it? So if the camera body shakes then that front element is moving more now that it's longer, isn't it? And you still don't think that the increased motion will be transferred to the resulting image?

By what you're saying I could stick a meter of extension tubes on my lens and not have to worry about increasing camera shake. That's a wee bit far-fetched.

I have a 300mm f2.8 that's about half a meter long. A 500mm mirror lens is about a third the size. Should the rule apply to the physical size of the lens as well as the focal length?

You have NOT changed the focal length with your extension tube, but you have changed the magnification. THAT is going to require a re-write of the rule which is what I've been saying all along. You should throw out the rule for all kinds of reasons when it comes to macro work.

But you said "A 50mm lens with a 20mm tube is 70mm long." and I disagree. The problem is the use of mm. The mm for the lens is focal length, while the mm for the extension tube is physical size. They are not apples and apples. The combination of the two has NOTHING to do with 70mm.

[Scottes]

You have NOT changed the focal length with your extension tube, but you have changed the magnification.

So if the image is magnified then the shake is magnified, so a higher shutter speed should be used to combat this extra shake.


So, back to the original question:

Would I need faster (or slower) shutter speeds with the extension tube? If so, is there a rule of thumb?

Yes, you'd need a faster shutter speed. In retrospect, I'd go much faster than I originally thought. In one test I ran a while back I used a 100-400mm lens set at 300mm, and tested with and without tubes without moving the camera, which stayed 12.5' from the subject. With a 36mm tube the image was 27% wider and taller than the image without the tube.

My original post on this: http://photography-on-the.net/forum/showthread.php?t=28037&highlight=tube+300mm

Some other (unposted) tests using shorter lenses also showed that the magnification was much greater than my flawed Lens Length + Tube Length formula would suggest.


So as to rule of thumb, well, more experimentation is needed, really. But if I were to just guess right now I'd take the focal length of the lens, add triple the length of the tube used, and make that my shutter speed. So 50mm lens + 12mm tube is 50 + 36 = 86, so I'd go for 1/100th.


As DaveG has pointed out this does become moot when doing things closer to 1:1. You're so close to the subject that DoF is drastically reduced, so to gain DoF you'll probably be stopped down so much that you'll be using a shutter speed much slower than this. It *is* possible to do 1:1 handheld - it's just not very easy since you need a *lot* of light to get much DoF.

[nosquare2003]

Regarding the physical size of a 50mm lens, it will be nearly 50mm if it consists of only one glass. (Some distance is required from the camera body to the film/sensor.) As the lens are made up by a group of glasses and they can move along, the physical lens size is different from 50mm. I'm not good at science and anyone please correct me if I'm wrong.