Shake reduction and extension tubes

**MSL** · 04-12-2012, 02:34 PM

When using extension tubes should I adjust the focal length I input into the camera to better reflect the longer length of the lens+tubes that I'm shooting with?

Adam · 04-12-2012, 02:52 PM

Assuming you're on a tripod, you should turn SR off in that case. Otherwise yup, you can adjust it if you want it to be more effective.

elho_cid · 04-12-2012, 03:05 PM

Adam: quick but wrong answer.

tubes do not significantly change the angle of view, which means the focal length and the number you enter to the SR remains the same. It is not like a teleconvertor.

but Adam is correct that at close up or macro distances the SR is not effective. Better not rely on it and use a tripod or short shutter speed.

demp10 · 04-12-2012, 03:09 PM

Extension tubes are used to enable close focusing. As a result the DOF will be very shallow and perfect focus is a must. The use of a tripod is almost mandatory and as it was mentioned, SR must be off when using a tripod. If you try to shoot handheld as close distances with extension tubes, SR is the least of the issues.

If you must shoot handheld, use a flash and CIF, then focus or move the camera slowly back and forth until the subject is in focus at which point the CIF will trigger the camera and flash. This way you eliminate the need for shake compensation and you are in focus using 1/180 speed and a reasonable F-stop (e.g. F8~F16) for good DOF.

**MSL** · 04-12-2012, 03:11 PM

Nope, no tripod, no flash. Trying to shoot handheld with a SuperTak 55/2 attached to a full set of M42 tubes (68 mm extension) attached to a full set of K-tubes (about 50 mm), for a macro of 2:1. Got pretty close to being in focus this afternoon on a bunch of juvenile red ants, and did get a couple of pics from the neighbors pine tree.

Typed this as the above replies were being entered. Sure I'm doing it all wrong - but it is quick and fun (well gets me out of the house for a few moments now and then)

demp10 · 04-12-2012, 03:14 PM - **1 Like**

Originally posted by elho_cid

tubes do not significantly change the angle of view, which means the focal length and the number you enter to the SR remains the same. It is not like a teleconvertor.

The stated focal length of a lens is measured when it is focused to infinity. As the lens is focused to a closer distance the focal length increases by the amount of the lens extension. When using extension tubes and especially bellows, the effective focal length can be significant.

RioRico · 04-12-2012, 04:13 PM

The user manuals say that SR is not effective with close focusing, but they don't say how close is too close. I assume a cutoff of about 3x-5x the focal length, which give 1:3-1:5 magnification. Shooting closer, I use a fast shutter or a tripod rather than SR.

NOTE: I haven't tested that 3x-5x guideline with LONG lenses that purport to be macro. My 500/8 and 1000/10 mirrors both have a close-focus of 1.5m, well within macro range, but I don't know for sure if 1.5m is too close or SR with those. Time for a test, eh?

I also haven't tested SR vs FL with lenses on just slight extension. I'll put a 6mm tube behind a 200mm lens to pull the focus in a bit. I just leave SR at 200mm. Works for me!

**dms** · 04-12-2012, 06:44 PM

If adding extension you are in fact changing the focal length, so for example adding 50 mm extension to a 100 mm lens is increasing it focal length by 50%. So the lens is now a 150 mm lens!

RioRico · 04-12-2012, 07:16 PM

Originally posted by dms

If adding extension you are in fact changing the focal length, so for example adding 50 mm extension to a 100 mm lens is increasing it focal length by 50%. So the lens is now a 150 mm lens!

Incorrect. Focal length is a property of the lens, not the mount. A 50mm lens on 300mm extension is still a 50mm lens; we've only changed the magnification. An optical rule: no unreversed lens can focus closer than its focal length. That 50mm lens on 300mm of tubes can still focus no closer than 50mm.

Nass · 04-13-2012, 03:33 AM

I've never gotten my head around SR settings with extensions. I think there is confusion between actual and effective. Ie, Rio, isn't that kind of like saying the f stop is a property of only the lens, so always stays the same regardless of extension.... When we all know it's actually the effective f stop relative to cam of a lens that matters. Ie a 50mm lens on 150mm of bellows set at 2.8 on the lens isn't actually a f/2.8 exposure, it's more like f/11.

Now to me when you magnify something a lot say 10:1, any shake causes a huge shift in what the sensor sees. Much like a long long tele, a small wobble and the image shifts all over the place. So the value the cam needs to know is not the actual mm value of any lens but the extent of image wobble on the sensor if you move it a little bit. Which if you have a wide angle lens is very little but if you have a tele is a lot. Ie if I have a 28 on a cam and rotate the cam 1 degree the image shifts relatively little, but if I have a 28 on 150mm of bellows and rotate the cam 1 degree I'm looking at something very different.

*still unclear*

newarts · 04-13-2012, 10:21 AM

In optics f-number arises as the ratio of the distance from an aperture and the diameter of the aperture.

For exposure, the ratio of aperture area to the square of distance from the aperture is proportional to relative brightness of an image ( proportional to the inverse of f-stop squared.)

Similarly, the size of an aperture's diffraction spot is proportional to the distance from the aperture divided by aperture diameter ie f-number.

Most of the time, the distance from the the aperture to the image is close to the lens' focal length. So focal.length/aperture.diameter is used to describe a lens and is only strictly valid when the lens is focused near infinity.

Shake reduction corrections are based rotation of the camera (like shaking your head "yes" or "no") in which case the distance the image sweeps across the sensor is proportional to the actual length from lens to sensor, Therefore enter the lens' focal length plus the extension length. For hand-held macros it'll help for side to side and up & down shaking, but not in-out movement which is the biggest problem for macros.

Dave

RioRico · 04-13-2012, 11:39 AM

Originally posted by newarts

Shake reduction corrections are based rotation of the camera (like shaking your head "yes" or "no") in which case the distance the image sweeps across the sensor is proportional to the actual length from lens to sensor, Therefore enter the lens' focal length plus the extension length. For hand-held macros it'll help for side to side and up & down shaking, but not in-out movement which is the biggest problem for macros.

And that's likely why the manuals say that SR is ineffective close-up. At a significant distance, any front-back movement is a tiny fraction of that distance, while up-down or back-forth movement can sweep a substantial (pixel-wise) arc across the view. Close in, any front-back motion makes a substantial (pixel-wise) change, which SR can't handle. At least, that's how I understand it.

Nass · 04-13-2012, 11:58 AM

Yeah that makes quite a lot of sense fellas =). I've actually always thought that the concept of SR with M42 is a bit curious myself, as in - how can one compute an accurate compensation for view movement across a sensor using a whatevermm lens if it's not factored how far away this lens is actually focusing. Again going on the principle that a one degree wobble 100ft away on a 800mm lens causes a lot more 'pixel movement on the sensor' than the same one focused say 10ft away... maybe I'm getting my knickers in a twist here

RioRico · 04-13-2012, 12:19 PM

Originally posted by Nass

maybe I'm getting my knickers in a twist here

Indeed.

I think we can establish a rule here: If you add enough extension to need changing the focal length number for the SR'bot, the working distance will be too close for SR to be effective. Use flash or other external light, and/or a fast shutter, and/or a tripod or other immobilization. SR has its limits.

Nass · 04-13-2012, 12:41 PM

Originally posted by Nass

Yeah that makes quite a lot of sense fellas =). I've actually always thought that the concept of SR with M42 is a bit curious myself, as in - how can one compute an accurate compensation for view movement across a sensor using a whatevermm lens if it's not factored how far away this lens is actually focusing. Again going on the principle that a one degree wobble 100ft away on a 800mm lens causes a lot more 'pixel movement on the sensor' than the same one focused say 10ft away... maybe I'm getting my knickers in a twist here

Originally posted by RioRico

Indeed. I think we can establish a rule here: If you add enough extension to need changing the focal length number for the SR'bot, the working distance will be too close for SR to be effective. Use flash or other external light, and/or a fast shutter, and/or a tripod or other immobilization. SR has its limits.

Still confused. Because that particular post actually had nothing to do with extension, just a lens focused at different points.

04-12-2012, 02:34 PM	#1
MSL Site Supporter Join Date: Feb 2012 Location: Greater Toronto Area Photos: Gallery \| Albums Posts: 4,749	Shake reduction and extension tubes When using extension tubes should I adjust the focal length I input into the camera to better reflect the longer length of the lens+tubes that I'm shooting with?

04-12-2012, 02:52 PM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Assuming you're on a tripod, you should turn SR off in that case. Otherwise yup, you can adjust it if you want it to be more effective. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

04-13-2012, 10:21 AM	#11
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	In optics f-number arises as the ratio of the distance from an aperture and the diameter of the aperture. For exposure, the ratio of aperture area to the square of distance from the aperture is proportional to relative brightness of an image ( proportional to the inverse of f-stop squared.) Similarly, the size of an aperture's diffraction spot is proportional to the distance from the aperture divided by aperture diameter ie f-number. Most of the time, the distance from the the aperture to the image is close to the lens' focal length. So focal.length/aperture.diameter is used to describe a lens and is only strictly valid when the lens is focused near infinity. Shake reduction corrections are based rotation of the camera (like shaking your head "yes" or "no") in which case the distance the image sweeps across the sensor is proportional to the actual length from lens to sensor, Therefore enter the lens' focal length plus the extension length. For hand-held macros it'll help for side to side and up & down shaking, but not in-out movement which is the biggest problem for macros. Dave Last edited by newarts; 04-13-2012 at 10:28 AM.

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04-12-2012, 03:05 PM	#3
elho_cid Veteran Member Join Date: Dec 2007 Location: Prague Photos: Gallery Posts: 1,199	Adam: quick but wrong answer. tubes do not significantly change the angle of view, which means the focal length and the number you enter to the SR remains the same. It is not like a teleconvertor. but Adam is correct that at close up or macro distances the SR is not effective. Better not rely on it and use a tripod or short shutter speed.

04-12-2012, 03:09 PM	#4
demp10 Veteran Member Join Date: Jun 2011 Location: Atlanta Photos: Albums Posts: 602	Extension tubes are used to enable close focusing. As a result the DOF will be very shallow and perfect focus is a must. The use of a tripod is almost mandatory and as it was mentioned, SR must be off when using a tripod. If you try to shoot handheld as close distances with extension tubes, SR is the least of the issues. If you must shoot handheld, use a flash and CIF, then focus or move the camera slowly back and forth until the subject is in focus at which point the CIF will trigger the camera and flash. This way you eliminate the need for shake compensation and you are in focus using 1/180 speed and a reasonable F-stop (e.g. F8~F16) for good DOF.

04-12-2012, 03:11 PM	#5
MSL Site Supporter Join Date: Feb 2012 Location: Greater Toronto Area Photos: Gallery \| Albums Posts: 4,749 Original Poster	Nope, no tripod, no flash. Trying to shoot handheld with a SuperTak 55/2 attached to a full set of M42 tubes (68 mm extension) attached to a full set of K-tubes (about 50 mm), for a macro of 2:1. Got pretty close to being in focus this afternoon on a bunch of juvenile red ants, and did get a couple of pics from the neighbors pine tree. Typed this as the above replies were being entered. Sure I'm doing it all wrong - but it is quick and fun (well gets me out of the house for a few moments now and then)

04-12-2012, 03:14 PM - 1 Like	#6
demp10 Veteran Member Join Date: Jun 2011 Location: Atlanta Photos: Albums Posts: 602	Originally posted by elho_cid tubes do not significantly change the angle of view, which means the focal length and the number you enter to the SR remains the same. It is not like a teleconvertor. The stated focal length of a lens is measured when it is focused to infinity. As the lens is focused to a closer distance the focal length increases by the amount of the lens extension. When using extension tubes and especially bellows, the effective focal length can be significant.

04-12-2012, 04:13 PM	#7
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	The user manuals say that SR is not effective with close focusing, but they don't say how close is too close. I assume a cutoff of about 3x-5x the focal length, which give 1:3-1:5 magnification. Shooting closer, I use a fast shutter or a tripod rather than SR. NOTE: I haven't tested that 3x-5x guideline with LONG lenses that purport to be macro. My 500/8 and 1000/10 mirrors both have a close-focus of 1.5m, well within macro range, but I don't know for sure if 1.5m is too close or SR with those. Time for a test, eh? I also haven't tested SR vs FL with lenses on just slight extension. I'll put a 6mm tube behind a 200mm lens to pull the focus in a bit. I just leave SR at 200mm. Works for me!

04-12-2012, 06:44 PM	#8
dms Site Supporter Join Date: Aug 2011 Location: New York, NY Photos: Gallery Posts: 2,192	If adding extension you are in fact changing the focal length, so for example adding 50 mm extension to a 100 mm lens is increasing it focal length by 50%. So the lens is now a 150 mm lens!

04-12-2012, 07:16 PM	#9
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Originally posted by dms If adding extension you are in fact changing the focal length, so for example adding 50 mm extension to a 100 mm lens is increasing it focal length by 50%. So the lens is now a 150 mm lens! Incorrect. Focal length is a property of the lens, not the mount. A 50mm lens on 300mm extension is still a 50mm lens; we've only changed the magnification. An optical rule: no unreversed lens can focus closer than its focal length. That 50mm lens on 300mm of tubes can still focus no closer than 50mm.

04-13-2012, 03:33 AM	#10
Nass Veteran Member Join Date: Aug 2009 Location: The British Isles Photos: Gallery Posts: 2,402	I've never gotten my head around SR settings with extensions. I think there is confusion between actual and effective. Ie, Rio, isn't that kind of like saying the f stop is a property of only the lens, so always stays the same regardless of extension.... When we all know it's actually the effective f stop relative to cam of a lens that matters. Ie a 50mm lens on 150mm of bellows set at 2.8 on the lens isn't actually a f/2.8 exposure, it's more like f/11. Now to me when you magnify something a lot say 10:1, any shake causes a huge shift in what the sensor sees. Much like a long long tele, a small wobble and the image shifts all over the place. So the value the cam needs to know is not the actual mm value of any lens but the extent of image wobble on the sensor if you move it a little bit. Which if you have a wide angle lens is very little but if you have a tele is a lot. Ie if I have a 28 on a cam and rotate the cam 1 degree the image shifts relatively little, but if I have a 28 on 150mm of bellows and rotate the cam 1 degree I'm looking at something very different. still unclear

04-13-2012, 11:39 AM	#12
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Originally posted by newarts Shake reduction corrections are based rotation of the camera (like shaking your head "yes" or "no") in which case the distance the image sweeps across the sensor is proportional to the actual length from lens to sensor, Therefore enter the lens' focal length plus the extension length. For hand-held macros it'll help for side to side and up & down shaking, but not in-out movement which is the biggest problem for macros. And that's likely why the manuals say that SR is ineffective close-up. At a significant distance, any front-back movement is a tiny fraction of that distance, while up-down or back-forth movement can sweep a substantial (pixel-wise) arc across the view. Close in, any front-back motion makes a substantial (pixel-wise) change, which SR can't handle. At least, that's how I understand it.

04-13-2012, 11:58 AM	#13
Nass Veteran Member Join Date: Aug 2009 Location: The British Isles Photos: Gallery Posts: 2,402	Yeah that makes quite a lot of sense fellas =). I've actually always thought that the concept of SR with M42 is a bit curious myself, as in - how can one compute an accurate compensation for view movement across a sensor using a whatevermm lens if it's not factored how far away this lens is actually focusing. Again going on the principle that a one degree wobble 100ft away on a 800mm lens causes a lot more 'pixel movement on the sensor' than the same one focused say 10ft away... maybe I'm getting my knickers in a twist here

04-13-2012, 12:19 PM	#14
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Originally posted by Nass maybe I'm getting my knickers in a twist here Indeed. I think we can establish a rule here: If you add enough extension to need changing the focal length number for the SR'bot, the working distance will be too close for SR to be effective. Use flash or other external light, and/or a fast shutter, and/or a tripod or other immobilization. SR has its limits.

04-13-2012, 12:41 PM	#15
Nass Veteran Member Join Date: Aug 2009 Location: The British Isles Photos: Gallery Posts: 2,402	Originally posted by Nass Yeah that makes quite a lot of sense fellas =). I've actually always thought that the concept of SR with M42 is a bit curious myself, as in - how can one compute an accurate compensation for view movement across a sensor using a whatevermm lens if it's not factored how far away this lens is actually focusing. Again going on the principle that a one degree wobble 100ft away on a 800mm lens causes a lot more 'pixel movement on the sensor' than the same one focused say 10ft away... maybe I'm getting my knickers in a twist here Originally posted by RioRico Indeed. I think we can establish a rule here: If you add enough extension to need changing the focal length number for the SR'bot, the working distance will be too close for SR to be effective. Use flash or other external light, and/or a fast shutter, and/or a tripod or other immobilization. SR has its limits. Still confused. Because that particular post actually had nothing to do with extension, just a lens focused at different points.