Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-12-2012, 02:34 PM   #1
Pentaxian
MSL's Avatar

Join Date: Feb 2012
Location: Greater Toronto Area
Photos: Albums
Posts: 3,398
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
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 43,143
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's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

04-12-2012, 03:05 PM   #3
Veteran Member




Join Date: Dec 2007
Location: Prague
Photos: Gallery
Posts: 1,198
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
Veteran Member
demp10's Avatar

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
Pentaxian
MSL's Avatar

Join Date: Feb 2012
Location: Greater Toronto Area
Photos: Albums
Posts: 3,398
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
Veteran Member
demp10's Avatar

Join Date: Jun 2011
Location: Atlanta
Photos: Albums
Posts: 602
QuoteOriginally posted by elho_cid Quote
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
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
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: 1,623
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
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by dms Quote
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
Senior Moderator
Loyal Site Supporter
Nass's Avatar

Join Date: Aug 2009
Location: The British Isles
Photos: Gallery
Posts: 2,251
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, 10:21 AM   #11
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.
04-13-2012, 11:39 AM   #12
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by newarts Quote
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
Senior Moderator
Loyal Site Supporter
Nass's Avatar

Join Date: Aug 2009
Location: The British Isles
Photos: Gallery
Posts: 2,251
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
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by Nass Quote
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
Senior Moderator
Loyal Site Supporter
Nass's Avatar

Join Date: Aug 2009
Location: The British Isles
Photos: Gallery
Posts: 2,251
QuoteOriginally posted by Nass Quote
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
QuoteOriginally posted by RioRico Quote
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.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, dslr, extension, length, photography, tubes
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
When to use Shake Reduction? Todd Adamson Troubleshooting and Beginner Help 9 11-04-2010 05:36 AM
Do you always have shake reduction ON? gawan Photographic Technique 18 08-01-2010 02:36 PM
Shake Reduction hannsg Troubleshooting and Beginner Help 5 06-11-2010 03:45 PM
Shake reduction on ext tubes ? Transit Pentax DSLR Discussion 17 03-13-2009 05:47 AM
Shake reduction w/K10D and extention tubes joelovotti Pentax SLR Lens Discussion 0 07-01-2007 04:41 PM



All times are GMT -7. The time now is 06:28 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top