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Monday, 23 January 2012

Comments

Thanks very much for this. This goes to MJ's "sufficiency" criteria. I still own 4/3's gear (not m4/3) and I understand that such equipment may not meet more exacting standards, whatever those are, but 20 inches wide is about as large as I would ever want, not because of esthetic reasons, but purely because of limited home wall space. I don't have that many places in my house that I can stand back far enough for anything larger. I don't know who those galleries are selling those murals to, but it's not to anyone I know.

Carl: Thank you for your micro 4/3 insights. It is relevant to a pro like myself who is dying to get back to the days of a lightweight SLR such as the Pentax H, Olympus OM or Nikon FM (2) series of cameras, just to name a few brands, but the ones that I owned prior to going digital.
I'm currently using a Nikon D700. Most of my work is documentary type and enlargements are frequently the equivalent of 24-28" at 300 dpi when cropped. What are your thoughts on how your prints made with the micro 4/3 format compare with a full frame sensor (now pretty dated on both the D700 and similar Canon) or with the APS sized sensors of the same pixel density of the micro 4/3? Best, Barry

Carl, I had similar experiences with this lens. Even today I had a couple of pictures, handheld at 1/200 sec. which where sharp in focus, but with a visible blurring.
It is obviously that at certain (handheld) exposure times the stabilizer caused blurring. But as you write, it is optically a amazingly good lens.

This echoes my experience (with full frame sensor), and my conclusion: the allure of stabilization, whether in lens or camera, has made us photographers lazy. I too come from a background of exclusively using a 4x5 view camera where, of course, I always used a tripod and paid meticulous attention to focusing with an 8X loupe. With digital, and everything that comes with it, it is too easy to handhold, rely on the electronics (H/W and S/W), to obtain "sharp" images. Additionally, and unfortunately, most of us view the majority of photography on-line, not beautifully made prints. And as we also know on-line is not as demanding as making prints. I too have discovered that prints made this way fall down miserably. And so the conclusion I have come to, the same that you have, is that there is no free lunch. The fundamentals still count.

The increase in resolution is likely one of the big reasons for the rumored IS improvements (5 axis) for the new Olympus m43 16mp camera coming. 12mp mated to the quite good IS in my E5 (with the very sharp 50-200) seems just right for tack sharp hand-held landscapes like you display, only requiring the tripod when the light goes down. I find I can print at 13x19 no problem, but our print-peeping standards may differ. Looking forward to your future findings, especially since I have a GH2 now too. Have you tested the 100-300 Panasonic?

What are your feelings about the in body stabilization of the Olympus cameras?

I would be interested to hear your impressions of how Olympus compares to the lens stabilization of the Panasonics.

The rumor is the OM-D has 5 axis stabilization in body, so you can go back in time to get that shot you missed.

QUOTE This time I put the camera on a tripod and turned off the stabilization (Panasonic—and everyone else who offers some form of anti-shake--instructs us to turn it off when using a tripod). UNQUOTE

I very recently tested my NEX 5n with the 18-55 kit lens using a very heavy tripod and a USAF type lpm chart to see if it was true that the Optical Steady Shot should better be turned off when using the camera on a tripod.

Stabilization on or off did not make any difference at all, at least not on my computer screen with maximum blow-up without showing individual pixels.

Perhaps the recommendation to turn off stabilization when working with a tripod is a new urban legend.

Anyway, the 18-55 lens is very good, even compared fixed focus Leica lenses!

Pierce, thanks for the confirmation. I should post a snap of the G3/45-200 mounted on my Ries J-100 tripod...

Martin, I've gotten some very crisp results with the 45-200 handheld with IS on, but the weather this past week has made it difficult for me to set up and execute the couple of tests I'd like to do, tripod and not, IS and not, etc.

Graham, these are "user reports" that I do when I think I've run into something others will find interesting. I'm not a professional reviewer and generally have no access to anything but my own equipment so I can't speak to differences with the Oly in-body stabilization. I have had a chance to examine some 24.4 MP Sony RAW files sent by a friend and the difference is clear, a well-made file will hold up at 20x30 according a test strip print I made. But if 20" is enough, then we're back to the "sufficiency" model. What's clear to me is that the m-4/3s gear is performing "above its payscale."

Stabilization is relatively new and I'm sure not yet mature. We're bound to see improvements in new models.

The "higher expectations factor" Carl suggests falls straight out of the definition of circle of confusion. Larger prints, closer viewing distances, higher magnifications (smaller sensor), or greater visual acuity are result in smaller values for CoC, and thus a lower tolerance for camera shake to maintain apparent sharpness.

Commendably Pentax gives the user the option of a "fast" auto-ISO setting that maintains higher shutter speeds, along with normal (1/EFL) and "slow" settings. Other manufacturers would do well to follow their example.

Very nice article with some good points, although I do have a nitpick. I think that you are, at times, confusing resolution with dimensions. For instance, you stated a 20-inch image is a 1.5x the resolution of a 13-inch image when, in fact, it's about double (depending on the aspect ratios) as area is the determining factor, not length.

My theory about image stabilization, based on nothing more than some intuition about how physical systems work, is that there may be cases were deliberately "jiggling" the camera subtly may improve sharpness, if you have IS on.

My thinking is that there are probably some frequencies of motion where the IS is very very good, and others where it is quite bad, and there MAY be frequencies at which it's actually worse than nothing. By using more "typical" neophyte jiggle, you might be better results.

I like to think that one of the things us old geezers can do pretty well is hold the stupid camera fairly still -- this may be hurting us when IS is in play.

Ctein wrote something about this a while back, another piece on IS apparently ADDING blurriness', which is when I actually thought this through -- now I'm just paraphrasing my memory of of what I think I thought then ;)

Great write-up esp. re: uprezzing factor for digital original files. I've also found 1.75x to be a practical upper bound.

Question: what does the 'RA' in RA-4 (or -2 possibly) stand for? (what I assume you were referencing in your comment: "darkroom RA enlargements from Hasselblad negatives.") Bonus question: what does 'SM' stand for (those pre-made plug-in boxes)? I'm not being coy, I don't know and have never run across an acronym expansion for these.

Geoff,
As far as I know "RA-4" doesn't stand for anything, it's just a Kodak appellation for the process, like a model number or car or camera name.

Ctein will know.

Mike

Very nice article and true to my experiences. I don't own a 4/3 camera but have used a variety of 12MP APS-C sized Nikon cameras (presently it is a D5000 and most often a 16-85 lens). And vitually ALWAYS with a tripod. With careful exposures, bracketing, image stacking and stitching, I have presented in several shows prints that are up to 3 by 5 feet in size. Yes, I feel they need to be viewed at a proper distance and not pixel peeped from 6 inches, but I have been totally pleased with viewer feedback. Now my local Nikon dealer has 5 up on his walls and they look very sharp indeed. I am amazed at what can be done to achieve very good large prints from small sensors, and it all harks back to solid technique. Though it may not be pertinent to the discussion, I'm glad I started life as a photographer when all the decisions regarding focus, exposure, aperture, etc. were all set manually.

Some interesting, almost painterly, landscapes there. I like those.

Incidentally, if your Lumix has an iAuto-ISO mode, you might find that that differs from Auto-ISO by an iexpectation that the lens will be stabilised; my GH2 keeps the shutter speed around 1/125th (fair assumption with anything up to an old 50mm prime) but will drop a stop or two in iAuto.

'RA' means 'rapid access'. This label was coined because the new color-print process was twice as fast as its predecessor EP-2; 4.5 minutes dry-to-dry vs. 10 minutes. Kodak also used the RA name for a wide variety of b/w graphic-arts films and processes.

Your post got me thinking: one advantage of a lighter camera + lens is an inherently lower center of gravity when on a tripod. This means that it should be much more stable compared to a larger, heavier camera + lens on a similar set of legs.

It also never ceases to amaze me how much more "still" I can hand hold a smaller, lighter camera. I just bought an S95 which was on runout special and I'm amazed how much stabler I am with that compared with say, my GF1 or K-5.

Pak

Thanks Mark!

Mike

Having recently acquired a Panasonic Micro 4/3 camera, I find this all interesting. But after going head to head with some 35mm (new) 400 TMY, I opted for film and silver gelatine prints. I find this new version of TMY astonishingly sharp and quite fine-grained, as well. I sure hope Kodak hangs in there because some of their most recent films (e.g. new Portra 160) show just how good film can be.

Chuck, I was using the term "up-res" to mean digital enlargement by interpolation, and 1.5X and 1.75X are the factors of linear enlargement, achieved through up-interpolation of the file, that I find usually or sometimes manage good results. As you point out, the resolution by pixel-count indeed increases with area, not linear measure.

Mark, thanks for answering on RA. C-41 was the process used at the time to develop the negatives for RA printing, E-6 was the chromogenic transparency film process (predecessor was E3--don't know what happened to 4 and 5, like camera models), and I think Kodachrome 25/64/200 was process K-14.

Tim, thanks for the tip about iAuto ISO setting, I'll see what it might change about shutter speed selections.

Andrew, my thought from the outset has been that if stabilization can "fight" the tripod it's logical that it could sometimes fight a very safe, high, shutter, speed. I might get to experiment with this soon since the weather forecasts for the rest of this week are promising. First thing I want to do is shoot a lot of frames on a very sturdy tripod with and without IS to see if I can identify an IS error, as Christer mentions doing without uncovering any differences.

Maybe image stabilization will be completely replaced by excellent high ISO one of these days. I've set the max ISO on my GH2 at 3200

1. Not every company does recommend turning IS off on a tripod, I don't think. You have to check the instructions for every single product to be sure, though.

2. In my own testing, the Nikon 70-200/2.8 VR really didn't like IS being on when mounted on a tripod (and the instructions reflected this).

Thanks Carl for this very useful contribution!

What about the relative impact of diffraction and noise on the quality of a a good sized final print, as compared to the use of a slower speed?

The amount of camera shake changes with every exposure, depending lots of unknown variables. As a result I think of this rule in a statistical sense, i.e. use a shutter speed that is roughly the reciprocal of the focal length of the lens in use and X of every 10 shots you take will be acceptably sharp.

The obvious corollary to thinking about is this way is to make more exposures when operating handheld, then select for sharpness. You can think of this as bracketing for camera shake, except that it is never that clean as statistics/probability never guarantee that you can take enough exposures to get one as sharp as you expect.

I have been pretty successful with this technique, I can usually take enough to get one that is noticeably sharper than average. The further you are from the rule, the more exposures you need to take in order to increase your chances to get lucky.

Dear Carl,

My “data point” fits with yours very nicely. My large standard print size is a 15" x 20" image area, just squeaking into your “large” territory. And back in the Paleolith,ummm, film era, I was sufficiently satisfied with the quality I could eke out of 6 x 7 cm format that I never quite felt impelled to buy a view camera. So, I'm like one notch below you in fussiness.

At that slightly lower level, I have had a very good success rate taking my 12 Mpx Olympus Pen photographs up to 15" x 20" image area. Kind of surprised me. When I decided that I wanted my standard size to be a 17 x 22" print instead of an 11 x 14" print, I figured I'd have to discard a lot of what was in my portfolio. Instead, I found that 85-90% of them went to the larger size just fine.

Of course, I am a stickler for technical accuracy, like you, to begin with. Those 11 x 14's had, for the most part, pixel-perfect clarity; the photographic subject had to be something truly extraordinary for me to even consider printing anything less (which I did at times).

I want to make an important observation, here. What you're discussing is fundamentally about pixel counts, not format. Based on what I've seen and printed from even smaller formats, a 12 megapixel 4/3 camera isn't operating anywhere close to the physical limit (or even the current technological limit) of what a digital sensor/camera/lens combination can do. There is room for very substantial improvement in all aspects of image quality without going to a substantially larger format. The NEX-7, which does not have a significantly larger sensor, demonstrates that–– amazing what 3 or 4 more years of development can do.

And, yeah, I think that 50-200 mm lens is a lot better than many of the online reviews I've read suggest. This photograph was made at or near the 200 mm limit:

http://ctein.com/Boston_Hotel_Roof.jpg

It simply wouldn't work as a 17 x 22 print if I couldn't get good clean edges and decent clarity.

~~~~~~

Dear Andrew,

Good memory! Here's the article:

http://theonlinephotographer.typepad.com/the_online_photographer/2010/04/oddities-of-image-stabilization.html

Ties very nicely into Carl's article; it's even talking about the same lens! Déjà vu, all over again.

~~~~~~

Dear Chuck,

An entirely incorrect nitpick. Almost no characteristic of the image scales with area, with the exception of the manufacturer's hype. That includes (but is not at all limited to) image resolution and camera shake.

Linear dimensions, not areal ones, are the proper ones to use when discussing the relative merits of different formats. Carl had it dead right.

pax \ Ctein
[ Please excuse any word-salad. MacSpeech in training! ]
======================================
-- Ctein's Online Gallery http://ctein.com 
-- Digital Restorations http://photo-repair.com 
======================================

The caveat is that there is no margin of error.

I get the impression that for many photography is increasingly, even predominantly, an exercise in doing more with less. "I shot this at 1/4 second handheld!" "This huge print was from a [insert humble camera of your choice]!" Yes it can be done, but what's the point? Does a typical viewer care how economical you've been with means?

A working pro isn't likely to leave things to chance and rely on all their ducks being in a row. A margin of error is required to ensure results ... assuming of course that consistent and reliable results are the aim.

This isn't to disparage Carl's efforts (who I'm sure knows his stuff) but to flag the fact that if "there is no margin of error" maybe the means aren't really adequate for the task. It's not the occasional success but the typical performance that's important, at least for me.

Thom Hogan has an interesting article on lens stabilisation that may be pertinent.

Further to the above, the Panasonic 45-200 is labelled "Mega O.I.S", for which Panasonic claims a sample frequency of 4kHz (that page pertains to compacts, but I cannot find any that refer to the sample frequency of Mega O.I.S in the context of m4/3 lenses).

Great column Carl, thanks!

Is there any way we can get a Bill Pierce column on TOP once in a while, too? That would be swell...

Re: E3 vs E4 transparencies...E3 had a reversal step that used visible light to do the reversing, E4 & E6 used a chemical. I never heard of an E5 process.

"My theory about image stabilization, based on nothing more than some intuition about how physical systems work, is that there may be cases were deliberately "jiggling" the camera subtly may improve sharpness, if you have IS on."

It's a process called "dithering" where you introduce noise in a system to improve its response. THe Wikipedia page is a pretty good explanation.

I think there is another factor in print size, the software used in resizing digital files. I've had printed 12MP Olympus M4/3 images to 30X40" (that's 100 pixels/inch) and the results are quite amazing. But I uploaded a file to Meridian and they did the sizing. I just looked at it with a 8X Agfalupe and all you see is what looks like fine film grain. There is no sign that it's not from a film negative. Anybody got a explanation for that? Looks like dithering again!

Eh, Carl, at a 19 x 13 print using a Pana G3 you are running at 4592 pixels at 19 inch....4592/19 = about 250 ppi......to most of us that is tack sharp......I run 4000/19 using a GF1 = about 210 ppi and that is sufficient as well. But I also printed a 8200 pixel file (2500 ppi x 3,25 inch)on 19 inch.....(coming from a GSW690 Provia 100F using a V750 scanner) and that gives 440 ppi resolution. Now even to the naked eye this is visible. Just a more solid colour representation and more natural sharpness in all small details. NOt that I hate my GF1 now, but for work where I need critical sharpness (large objects with lots of detail) I like the GSW690 and its cousin the GX680 better. On the other hand, objects without much detail are ideal for shoting with a GF1. Mr. Gianni Galassi blows up GF1 shots to 70 x 70 inch pictures for an exhibition in Venice (Italy that is http://giannigalassi.typepad.com/).

Greetings, Ed (http://blogger.xs4all.nl/stomoxys)

And to be clear:

Image sharpness depends on more then a few factors:

a) ppi count of the sensor used (FIXED)
b) lp/mm of the lens used (FIXED)
c) aperture of the lens in relation to the absolute pixelsize (ADJUSTABLE)
d) contrast in the picture (FIXED)
e) aa-filter or not to aa-filter (FIXED)
f) noise reduction needed and used (ADJUSTABLE)
g) sharpening amount and algoritm used (for instance octave sharpening versus unsharp masking) (ADJUSTABLE)
h) often forgotten, but mentioned to me by the excelent book of Uwe Steinmuller (Fine Art Printing etc.) the MICROCONTRAST in the picture, especially gently enhancing microcontrast can make a lot of difference to very detailed pictures. (ADJUSTABLE)
i) Shutter time (ADJUSTABLE)
j) Tripod or no tripod (ADJUSTABLE)
k) IS or no IS (ADJUSTABLE)
l) Fringing (and CA) (ADJUSTABLE)
m) The ISO value of the sensor (ADJUSTABLE)
n) The noise behavior of the sensor used (FIXED)
o) Using RAW or using .jpg's and trusting in camera sharpening and noise reduction algorithms. (ADJUSTABLE)
p) Some that you will add (ADJUSTABLE)
q) Some that you will add (FIXED)

Non of these will address the physical limits of the ppi value, but not having them right means that you do not reach those limits. Having them right means you can get away with breaking (or at least bending) them a little.

For instance you should take account of the fact that an incorrect exposure can ruin image sharpness just as much as shaking hands can, due to noise reduction algorithms eating image detail. That a tripod gives freedom of exposure, and can elliminate the need to use fast shuttertimes or high iso values. If all the adjustables are just right you get optimal image sharpness.

And if you are not satisfied with that, the only option is to change something in the camere/lens/imaging algoritm chain, or simply improve you image manipulation skills. For instance look what happens to te overall image sharpness when you only use a noise reduction algorithm on the dark parts of picture via a mask. Keep thinking, keep experimenting, keep tweaking untill everything is just right.

Greetings, Ed

Please Smart people: At the risk of sounding dumb here, using the "new" rules of thumb what would be the minimum handheld speed for say a 25mm non stablized lens on a micro 4/3's.?

Carl, you say you "gave up on a fairly pricey wide angle lens because I couldn't stand the never-really-sharp corners".

Which lens was that? Did you own it for a while?

I've been shooting indoors a lot with my X100 - no flash. I'm happy with ISO 3200 most of the time, but I dare not shoot at less than 1/60 hand held, since I use arms extended at least as often as I use the OVF/EVF. The camera has no IS; fixed lens is 23mm (35mm equiv.)

Maybe age is a variable. Am I holding the camera as steady is I did when I was young or middle aged?

Carl, just a nit -- but E4 was the predecessor process to E6.

I believe Ektachrome Infrared was E4, and that kept the process available in a specialty niche long after the general 1976 cut-over to E6.

Dunno what happened to E5; or to previous numbers.

I suspect one thing we're seeing here in comments is the difference between the assignment photographer who goes out on an assignment for a client with an absolute necessity of coming back with first-rate images of the assigned subject between his teeth (or they'll be disgraced in front of the client and never work in this town again), and the artist who needs to create an adequate number of new first-rate images each year. (Or between people who take the attitudes of those positions, regardless of what their actual profession is. I tend to think like an assignment photographer, though I haven't made a significant part of my income from that since college.)

I dunno, I thought this was pretty obvious stuff. If you need critical detail resolution, camera shake must be minimized. For this type of highly detailed landscape work, a sturdy tripod, proper focus, good selection of focus zone, etc, are all musts.

BTW, I've found that the sweet point of image up-rezzing interpolation is almost always to multiples of the square root of 2 (1.414x). Multiply pixels by 1.414x in H and V using Bicubic Smoother and then resharpening nets double the pixel density and retains the best perceptual sharpness in my experience. It's how I make larger prints from the E-1, turning the E-1's 5Mpixel output in to 10Mpixel files.

Most people put way too much faith into image stabilization and then complain that their lenses aren't sharp. My sharpest lens is a sturdy tripod... ;-)

I do very sharp 15x20" prints from my E5 and E-P3. Also, better than those I did from my Hasseblad negatives during the 80th using a zig aligned 105mm APO Nikkor. In order to get top sharpness I:

- use high quality lenses (Olympus HG and SHG and 2 leica M tele)
- use a tripod
- turn off the IS
- focus manually using the 10x on screen image provided in the E5 and E-P3.

Clearly not a technique for horse races, but landscape results are just amazing.

I used to live in Woodbury. The "Willow" photo brought back nice memories. Thank you for posting it.

Just a random FYI, Kodak did have an E4 process for transparencies, but I don't recall and E-5.

IIRC, E-3 required a manual reversal be exposure to light, and E-4 eliminated this, and was a total chemical reversal process. But that might have been the difference between E-4 an E-6.

In any case, I remember hand developing transparency film with E3 and E4.

Regarding IS on tripods, Canon recommends turning it off on some lenses, but on some of their L lenses the lens, in theory at least, detects the lack of motion and turns IS off automatically.

I remember very well that back in the 70's there was a saying 'the best lens is a tripod' and it seems to be true in our modern age too.

Dear Ed,

"...at a 19 x 13 print using a Pana G3 you are running at 4592 pixels at 19 inch....4592/19 = about 250 ppi..."

Don't confuse pixel count with resolution. For an assortment of tedious technical reasons, a Bayer array camera delivers actual resolution which is about 70% of the pixel pitch (depends on the camera, depends on the signal processing, depends on the kind of fine detail, depends on the phase of the moon...).

So, in your example, you're really getting about 180 ppi of real spatial detail, not 250.

Now, that's 3-4 lp/mm, which falls in the (lower) range of what convinces us a print is "sharp," so it ain't garbage. But it's not anywhere close to the limits of what we can see, which is why when you put it up against a much higher-resolving print you can readily see the difference.

pax / Ctein

"Great column Carl, thanks!

Is there any way we can get a Bill Pierce column on TOP once in a while, too? That would be swell..."

What a great idea! We'll just have to see what Pierce thinks about it.

Not one for technical perfection, I print A1's from my Oly 12mpix Pens all the time. Just add some grain, upres with Alien Skin 3, and print to textured paper... oh, it helps if your photo wasn't very sharp to begin with, that's usually not a problem for me.

Christer -- I think some newer cameras automatically detect whether the camera is on a tripod/table/stable surface, and automatically turn off shake reduction. I know my Pentax K-5 does so; earlier Pentax cameras had a prominent on/off switch for the sensor shake reduction feature, which the K-5 lacks. To explicitely turn it off, you have to go digging in the menus, but supposedly it shouldn't be necessary because the camera is smart enough to know when it is on a tripod. Perhaps your NEX is similar in this regard.

"What about the relative impact of diffraction and noise on the quality of a a good sized final print, as compared to the use of a slower speed?"

Jean-Louis, there's no simple answer to that. Diffraction will certainly reduce definition and it sets in early with a small sensor. Noise can be obtrusive in a picture with large areas of smooth tone, but can actually enhance the impression of "sharpness" in a picture without large smooth areas. Etc. Everything counts, and there's no single balance of factors that can apply to all pictures.

An alternative theory of what is happening is put forward by Andrew Alexander in his review of the Panasonic 14-42mm f/3.5-5.6 ASPH MEGA OIS LUMIX G VARIO lens published on SLR Gear Review. He tested it on a Panasonic G3 and found that at 42mm, at some (higher) shutter speeds the IS system reduced the sharpness of the images. His theory is that the particular design of MFT shutters causes vibrations which lead the IS system to react badly.

“Our theory is that, in common with other Micro Four Thirds cameras we've tested, the Lumix G3's shutter produces vibration that can cause blurring even at very high shutter speeds. The issue with Micro Four Thirds shutters (at least in cameras we've seen to date) is that the shutter has to snap closed before the exposure, and then open again for the exposure itself. This is in contrast to conventional focal plane shutters, which only have to move across the frame once per exposure. When a Micro Four Thirds shutter snaps closed to start the exposure, it can set off vibrations that affect the exposure. Because these vibrations can be at a fairly high frequency, they can cause blurring even at higher shutter speeds than one would expect. We've found that these vibrations can sometimes interact unfavorably with an IS system, with the IS system trying to correct for camera movement that isn't actually happening.”
see the IS test section of
http://www.slrgear.com/reviews/showproduct.php/product/1336/cat/69

The closing and then opening for exposure of the shutter is the reason for Olympus to have an "Anti-Shock" setting in the menu. The setting closes the shutter and then after a user set time interval (I use 1 sec.) it takes the exposure. This of course only works well when the camera is on a tripod. IBIS has to be turned off when a tripod is used. Otherwise the camera makes a faint buzzing noise trying to stabilize the image, and blurry pictures result.

I see that there is a more thorough investigation of the Four Thirds shutter-induced vibration at
http://www.imaging-resource.com/PRODS/EP1/EP1BLUR.HTM

Roy Feldman's question: using the "new" rules of thumb what would be the minimum handheld speed for say a 25mm non stablized lens on a micro 4/3's.?

Carl said: It's pretty commonly understood that for sub-35mm sensor sizes this rule has to be modified by the "crop factor" of the sensor size.

Crop factor of 2 for FourThirds sensor 25 x 2 = 50 (i.e. a FourThirds 25mm lens is 50mm in 35mm equivalent terms) so the minimum handheld speed is 1/50th.

If you already think of your lenses in terms of "35mm equivalent focal length" then the old rule still applies to the "35mm equivalent focal length" of your new lenses.

As another poster pointed out this is all probabilistic (perhaps 80% of the time you get a decent shot) but you need to check out how "shaky" you are with a given camera. Take a repeated set of shots of decide which are acceptable. Same goes for IS on.

Should the IS for a camera/lens be on or off on a tripod depends on how the IS system is designed.

All IS systems will depend on a target frequency spectrum for shake (with an upper bound limited by how fast you can vibrate a lens element or sensor). For handheld systems'll be tuned for "typical human shake" rather than say "boat roll" or "vehicle motion". If you have an IS stabilized system (like binoculars or camera or video system) on a vehicle then the shake spectrum (frequency and amplitude) changes and you design for that use. You can see this in IS binoculars optimized for terrestrial (e,g, Canon) or nautical (e.g. Nikon and Fujinon) uses.

When the camera is on a tripod you can see this spectrum changing in a couple of directions. Wind induced modes can be quite high frequency (the tripod buzzes). Or the tripod being more massive can move much more slowly. Even (as mentioned here before) the ground can be shaking (especially in urban areas). It all depends on the tripod (large/small, heavy/light, stiffness, etc) and the environmental conditions.

Usually the designers of the IS system know what's optimum on a tripod. Heed their advice. But if you are going to measure it there are a lot of variables to vary before you come to a conclusion.

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