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11-24-2010, 04:16 AM   #1
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Effectiveness of SR in K-5 vs. K-7

Do you good folks who have owned or do own both, have a sense as to whether these cameras have comparable SR effectiveness? Is one better than the other, and if so which one? And if there's a difference could you quantify it?


i've owned the K-7 for 15 months now and with my unit at least i've found that the SR has always been a bit less effective than i'd wish for. With an 85mm lens mounted 1/25s - 1/30s is borderline for clear shots even braced on a monopod.

11-24-2010, 07:43 AM   #2
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oooh, you did it. one of my pet peeves. here we go.

1. the 1/f-length rule is wrong
2. sr effectivness depends on the user too.

i shot at 85mm with my k20 and got sharp pictures well bellow that (more like 1/8). it is not easy, because my 85mm is 1.4 so rather heavy, so there was a difference to my zenitar . anyway, keep in mind that, according to that rule of thumb (which is wrong), 85mm on aps-c would mean 1/125 or so, so you're getting two stops already according to that, it's arguable how sharp you will get at that speed, without sr, in the same conditions, though (and that is important)

now why is the rule "wrong" (and this is arguable, make no mistake). if you shoot the same subject, from the same distance, and only swap the lens, it is quite valid, but than again, if you do that you're not using the lens right. the logical way to use a lens is imho this way: look at the scene, decide what kind of perspective you want (imagine the shot in your mind, frame it, etc), based on this chose the distance you need to shoot from (which determines the perspective, yes, the distance _alone_ does), and last chose your focal length that will give you the right framing. if you just stand still and swap lenses, what's the point? you will only have one focal length which gives you what you _want_ from you standing position, if you're lucky that is, so all the other shots are mistakes, for the lack of a better word.

how does this relate? well, if you think about it, it's hard to determine effectivness of sr if you don't take this into account. the distance to your subject is _essential_ for the shutter speed you can handhold. try this experiment, if possible with a constant aperture zoom lens: chose a framing, and a very confortable position for you to shoot/handhold, frame with the wide end, see how low can you go (shutter), now zoom in, but frame the same way (so you will have to step back, and your perspective will change), see how low you can go. you might be surprised .

imho, and based on my own experiments, there's hardly any practical use for the 1/f-length rule, it is rather more like, the photographer has his own lowest shutter speed he can handhold with a certain kit (depends on weigth, balance on the body, etc, so it does depend on the lens), if it's a zoom, it will be the same for the entire range of that zoom, for the typical subject that photographer shoots with that zoom (read: focus distance)

hope this helps somewhat, though it doesn't answer your question directly (didn't own a k-7, sorry, and the k-5 is too new to me to compare to the k20, but i'm quite happy with the later)
11-24-2010, 08:30 AM   #3
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I have them both. Not messured anything but to my idea: K-5 kicks in SR much more faster, with K-7 it is a little bit more waiting. or ending up with a picture that says: not stabilized or not finished. And to my idea also better stabilisation.

Then again, no testing at all, just the feeling I have till now.
11-24-2010, 02:23 PM   #4
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One thing to consider is the crop factor. The "rule of thumb" was based on 35mm focal lengths. So you should convert that 85mm lens to the 135mm-equivalent length, or about 128mm. Instead of avoiding shooting slower than 1/85s (~0.012s), you really should be avoiding shutter speeds slower than 1/128s (0.008s). The 1/30s (~.033s) is about 4X slower than the converted "rule of thumb" guideline for that lens. This fits in with Pentax's SR claim of 4 stops.

- Jason

11-24-2010, 02:35 PM   #5
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Inferno, isn't 1/30 only 2 stops slower than 1/125? one half of 1/125 (or 2 times length of shutter) is equal one stop, right? that would be 1/60 - same rule to apply to go another stop, which takes you to 1/30.
11-24-2010, 02:36 PM   #6
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so 3-4 stops, even by the 'general' rule, should be able to take you from the 'minimum' of 1/125 to anywhere from 1/20 to 1/8.

I agree with Nanok's sentiment that the 1/focal length is only a general guide, for some it is more and some less, and your own stability can change depending on size/balance of the lens as well.

To the OP: I haven't seen any quantifiable difference between the two - it works great in both cameras (I no longer have the K7). Since it is not a rigid system (i.e. it WILL gain you exactly four stops on command), as a general rule I just find it is great to have. I used a GF1 for awhile early this year, but couldn't get over not being able to shoot at the shutter speeds I had become accustomed to with any of the Pentax cameras I have used.

Last edited by pxpaulx; 11-24-2010 at 02:41 PM.
11-24-2010, 06:33 PM   #7
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pxpaulx is correct, 4 times is only two stops as already stated (it's powers of two..). so to get the stops difference you basically need to do a log in base 2 of the ratio of the shutter speeds or iso speeds (a bit different for apertures, i have a hunch you don't want to know )

i also agree that not having the sr is.. confusing
11-24-2010, 07:24 PM   #8
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Why not actually test SR yourself? Shoot with it off and look at what percentage of blurred photos you have at a given focal length and then look at photos with it on. It really isn't hard. I find that three stops is a good rule of thumb for me, personally on the K7.

11-25-2010, 06:58 PM   #9
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o thank you folks for all your input. --So the K-5 despite a quieter shutter than the K-7 (which presumably means less mirror shake) doesn't provide any better SR?

Yeps, like everyone else with a K-7 i'm looking hard at the K-5. i know already it'll have IQ that fits my night time shooting better so now am trying to figure out if i can expect any more effective SR for the hand held dark street stuff. Together that's the large part of what i use a camera for.

As for the SR i generally find my Canon A650 has better shake reduction. It just has terrible IQ for night work. With the A650 i can count on abt 3 stops (abt 40-50% hit rate for clear shots) with a cut off at 1/5s below which it's all blurry.

My K-7 gives me 2 stops with a 50% hit rate for clear shots, without caffeine in my system. It seems to have for me a hard cutoff around 1/10s below which all shots are blurry whatever lens i use.

... the nature of shooting on the street means i don't want to dawdle, and don't get to reshoot stuff very often. i do find that with the K-7 on a monopod i get abt 15% clear shots down to 1/15s. By then with the 85mm i'm shooting at f1.4 and can barely see anything in the viewfinder so misfocus is a bigger problem.

i'm also finding i don't want to use zooms older than F lenses for night work: the A zooms don't communicate focal length to the camera so i have to set one value for them, smack in the middle of the zoom ratio being the best compromise, and both extremes of their zoom ranges are less well handled by the SR.
11-25-2010, 08:10 PM   #10
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Let me add some entertainment. 2 shots, one handheld with the Rokinon 85mm wide open, one tripod shot with the F 35-135mm.

Apologies for the large sizes.

Rokinon 85mm, f1.4, 1/25s, -1.3EV, ISO200

F 35-135mm, f10, 30s, +1.7EV, ISO100

--Both with K-7 tho, despite this being the K-5 forum.

Last edited by conradj; 11-25-2010 at 08:18 PM. Reason: Camera:
11-26-2010, 05:20 PM   #11

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If I'm very careful, I have gotten some reasonably sharp shots (though not razor sharp) handheld at 300mm at 1/25 of a second, 6 feet away from the target, using the in-body SR in the K-5.

Last edited by Cannikin; 11-26-2010 at 05:44 PM.
11-26-2010, 07:33 PM   #12
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Well I'll leave the number crunching to others, but the other night was adjusting AF for my F*300 lens. I was focussing about 20 ft away indoors, and ALL my shots were sharp enough to judge FF/ BF. I was a bit shocked when I looked at the shutter speed and found I'd been shooting at 1/8th.

And no, I'm not one of the freakishly steady handed people either
11-27-2010, 06:07 AM   #13
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Wow, no way i could do that with my particular K-7. i'm wobblier than jello, but also always suspect my camera of having gremlins in the SR bits, wielding tiny tuning forks that go ting! at bad moments.

Used to get clear handheld shots with my Sony DSC-R1 down to abt 1/25s, not much worse than i get from the K-7. The R1 doesn't have mirror or focal plane shutter, but also doesn't have SR at all. Also terrible, noise ridden IQ on night time long exposures plus mandatory dark frame exposures for anything 1s and longer, tho in daylight can shoot at ISO400 without any issue.

The R1 did have a nice user interface for B mode which i miss; up to its 3min. max it showed a digital count up, and you pressed once to start and again to stop. But then it'd do an equal length dark frame shot.

Last edited by conradj; 11-27-2010 at 06:17 AM.

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