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Shutter Blur on K7

flossie
Posted 22/07/2010 - 09:04 Link
There seems to be a bit of a storm brewing on the Other Forum after one of the regulars there did some serious research into the shutter blur at 1/100th sec issue.

Read the details here - follow link for the White Paper for full explanation.

As I understand it, what they are saying is that there is some mechanical vibration, which peaks in its effect around the 1/100th sec region, but its impact is dependent on both lens length and how well the body is being held. This could go someway towards explaining why the infamous k/x 1/100th "blur" affects some people and not others, although they did not look into any camera other than the K7 and brief test with the K20.

Anyway, may be a storm in a teacup, or alternatively it could be very damaging for Pentax, especially when they have new models on the way (allegidly). They were given the report early, but have yet to respond.
Still shooting in the dark (literally and metaphorically)...
johnriley
Posted 22/07/2010 - 09:21 Link
I've done a very quick scan of this and they seem to be discussing a phenomenon that they have described as shutter blur. They do stress that this is not something that is pecular to Pentax cameras, although they used a Pentax to demonstrate it.

The hypothesis is that the movement of the shutter causes an equal and opposite movement in the camera body that causes blur. The effects of this are seen most obviously at ultra wide angles (10-12mm) and 1/100 sec or so shutter speed. The faster the shutter travel, the bigger the effect. Therefore, the K7 will show the effect more than the K20D as the shutter traverses the sensor gate more strongly.

This effect is independent of other vibration effects, which are insignificant.

Turning SR off does not improve this.

Logically, the movement of the shutter must cause an equal and opposite movement of the camera, but traditionally it has been accepted that focal plane shutters are virtually vibration free. Leaf shutters must also create a vibration, but this has always been considered effectively zero.

My suspicion is that we can now measure so much, so accurately, that we are finding new defects to worry about. Cameras are precision objects, up to a point, but not totally 100% efficient.

This seems a bit like the front and back focusing issue - something else to worry about that has never been seen as a problem in the past.

For the shutter vibration, a sturdy tripod apparently cures it totally, for the front and back focusing I guess it's always been there but masked by DOF and the fact that we waited hours/days/weeks to see the images anyway and just assumed any out of focus ones were our fault!

This is all the ultimate version of fellow photographers who when asked "What sort of pictures do you take?" would usually say, "Well, I'm doing a test film at the moment..."

Less worry and more fun sound good to me!
Best regards, John
alfpics
Posted 22/07/2010 - 12:08 Link
I think you are probably right, John: another issue that we now see as a potential problem that didn't worry us in the past pre-digital and ability to pixel-peep etc!

However I did find it a very interesting article which I guess could lead to further improvements in the stride for 'better and better'. I guess one of us could actually try to repeat the effect on a real picture and then print it up at different sizes and see how it shows up (or not) in reality!

Andy
Andy
Algernon
Posted 22/07/2010 - 15:03 Link
I had noticed shake problems with the 12-24mm and started to use it without shake reduction. It could have been just the SR hadn't settled. I'll have to see what shutter speed I used if I can find the shots.

Shake has always been a problem I noticed it years ago on a Koni-Omega 6x7 which had a leaf shutter and should have been a lot sharper. I stripped it down and disconnected everything connected to the shutter release apart from the shutter itself. The camera was a lot better for it and by far the sharpest lens I've ever had (still got it). I also removed all the other frames from the viewfinder apart from the standard frame. (I might have blacked them out.... I just remember using some black electrical tape).

With regard to focusing on film cameras numerous magazine articles were written in the past about how to check your cameras focusing accuracy. Polysales and Fishwicks used to sell magnifiers with built in fresnel/ground glass to check for focusing errors.

When the US mag Modern Photography (now merged with Popular Photography) tested a camera they tested everything including focusing accuracy (across the frame)and also stripped it down to the last nut and bolt

AP and the BJP were also equipped with optical collimation equipment which took readings directly from the film plane including focusing errors and lens curvature. This is how the are able to quote the exact focal length and aperture of the lens.

Some lenses such as the Pentax 43mm Ltd. have shown up to 140 lpmm in film resolution tests something that just wouldn't be possible if the camera wasn't focused exactly.
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
johnriley
Posted 22/07/2010 - 15:24 Link
Film flatness is another source of error - expecially when "kinks" occur in the film as it winds its way around the transport mechanism.
Best regards, John
Algernon
Posted 22/07/2010 - 17:29 Link
johnriley wrote:
Film flatness is another source of error - expecially when "kinks" occur in the film as it winds its way around the transport mechanism.

I think it was CZ who used a vacuum in the Contax to keep the film flat. CZ also claim the highest resolution ever recorded on film with the Cosina made Carl Zeiss ZM-Biogon 25mm ƒ/2.8 at 400 lpmm link

Or on the CZ site

Looks quite sharp on this photo

Digital is capable of a maximum of 87.5 lpmm according to Bob Atkins so does that mean film is sharper than digital
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
polchraine
Posted 22/07/2010 - 19:55 Link
Algernon wrote:
Carl Zeiss ZM-Biogon 25mm ƒ/2.8 at 400 lpmm

Digital is capable of a maximum of 87.5 lpmm according to Bob Atkins so does that mean film is sharper than digital

I was told - many years back even pre *istD, that to match good quality film with digital that it would require a pixel count of around 35 to 40 Mp - so yes film is sharper but how long before digital catches it?
.
K20D, *istD, MZ-S, Super-A, ME Super, MX
DA* 16-50, DA* 50-135, DA* 300,
DA 50-200, FA 24-90, FA 20-35,
M 400-600, A 50 f1.4, A 28 f2.8, A 70-210, M 35-80, M 50 f1.7
A x2S teleconverter and a few others ...
Mongoose
Posted 22/07/2010 - 20:20 Link
Surely it depends on the grain size of the film?

I'd be willing to believe that good quality ISO 100 film is better than digital, but how far does it maintain its advantage when compared with a camera like the K-x which is basically just hitting its stride at ISO 1600?
you don't have to be mad to post here



but it does help
johnriley
Posted 22/07/2010 - 22:13 Link
Digital has already overtaken film in most respects. I wouldn't even agree that film is sharper, unless we were talking about Kodak Technical Pan with special processing and a camera mounted on a very solid tripod.

16 ISO if I remember correctly, or thereabouts.
Best regards, John
Algernon
Posted 23/07/2010 - 08:47 Link
I don't think they quoted a film speed for TP-135? There was another called TPS-135, but I think it was TP I used to used for testing lenses about 30 years ago. Pan F was also very good.

Film is very sharp and it's amazing what detail it picks up. I used to use a Peak 20x microfilm viewer to look at it. Unfortunately printing paper isn't very sharp and lots of the detail on the film never makes it onto the print. In fact the highest resolution I've ever managed to transfer onto a print was about 90 lpmm of a negative (taken with a Pentax-A f/1.7) that had over 140 lpmm on it. 90 lpmm is very close to what digital is capable of. No idea how much of that finishes up on paper.

The only good thing about film nowdays is that you can still achieve higher quality quite cheaply by using bigger negatives. Not possible with digital unless your a mega-corporation with loads of cash
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
Pentaxophile
Posted 17/09/2010 - 12:40 Link
I have noticed this effect on my K-7... definite motion blur at 1/60-1/125 and thereabouts, using my 10-20 and 16-45mm. I have tested with the focus fixed, 2 sec timer engaged, SR off, and camera set down on a window ledge etc. Every time I check, the shot at 1/80 (ish) is softer than the one at 1/25, and much softer than the one at 1/320.

It's hard to avoid shooting at these speeds I'm half in a mind to send it back, but when very slow or very fast shutter speeds are selected, the iq is terrific and it's a lovely camera. I took a night shot at 25 secs, and it blew my mind!
[link=https://500px.com/will_brealey/[/link]
Edited by Pentaxophile: 17/09/2010 - 12:41
MattMatic
Posted 17/09/2010 - 14:41 Link
Interesting read...
I've had some odd occasions of blur that shouldn't be there. I think I'll go back and examine the meta data in the light of those experiments
Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)
Don
Posted 17/09/2010 - 15:20 Link
possible there is a (not so)sweet spot where the SR and shutter speed collide?

if so, turn the sr off until you need it.... with a wide angle you should not need sr until you are well below 1/15 sec
Fired many shots. Didn't kill anything.
Edited by Don: 17/09/2010 - 15:22
Pentaxophile
Posted 17/09/2010 - 16:02 Link
SR isn't implicated Don. According to Faulk, it's a shutter vibration which is masked by high or low shutter speeds but is more visible at moderate speeds around 1/80.
[link=https://500px.com/will_brealey/[/link]
Pentaxophile
Posted 17/09/2010 - 17:17 Link
16mm, SR turned off, camera placed on concrete windowsill, 2 second timer engaged, and pre-focussed using Live-view.

Comment Image


OK, maybe its not *horrific* but it is disheartening to see in such an expensive piece of kit. There are many factors that cause slight motion blur, but it's a bit annoying when your £700 camera consistently delivers blur at normal shutter speeds. It's even more annoying when your camera is superb in every other important respect and you don't really want to send it back. I was out yesterday taking pictures, and tried to avoid 1/80-1/200, but constantly tweaking ISO and aperture as an avoidance measure isn't really much fun.
[link=https://500px.com/will_brealey/[/link]
Edited by Pentaxophile: 17/09/2010 - 17:19

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