First, thanks to all who even bothered to reply. I guess folks on this forum really care and I am simply overwhelmed.

To me the lesson is that I should not assume my camera will behave in a certain way. I will keep tab from now on.

Quension, thanks for your theory on SR. Will keep that in mind too.

As for books, I have The Digital Photography book by Kelby, and Understanding Exposure by Peterson. The latter explains all about ISO, aperture etc. It is definitely not rocket science, but my take is it will take quite a bit of experience to understand how to get one's camera to make use of the elements.

OregonJim, You are right, I did not find a single good book on photography in my local book store. My colleague got the above books for me when he was visiting the US

Hope to be back sooner or later to the forum !

It would be a very good idea to put the camera in manual mode and learn the basics that way. It is the best way to learn both photography and your camera.

[Alfisti]

Wheatfield you're gibbering absolute rubbish, read the OP again and his reply

To the OP, it's a pretty common occurance in my experience, the camera just changes it's mind when metering, nothing you can do about it.

[Wheatfield]

Wheatfield you're gibbering absolute rubbish, read the OP again and his reply

To the OP, it's a pretty common occurance in my experience, the camera just changes it's mind when metering, nothing you can do about it.

Just sounded to me like a return to the basics was in order before he got totally bamboozled by his camera.
Bot honestly, I did have some trouble parsing the OP.

[OregonJim]

First, thanks to all who even bothered to reply. I guess folks on this forum really care and I am simply overwhelmed.

To me the lesson is that I should not assume my camera will behave in a certain way. I will keep tab from now on.

Quension, thanks for your theory on SR. Will keep that in mind too.

As for books, I have The Digital Photography book by Kelby, and Understanding Exposure by Peterson. The latter explains all about ISO, aperture etc. It is definitely not rocket science, but my take is it will take quite a bit of experience to understand how to get one's camera to make use of the elements.

OregonJim, You are right, I did not find a single good book on photography in my local book store. My colleague got the above books for me when he was visiting the US

Hope to be back sooner or later to the forum !

Hi subhrajitb,

"Understanding Exposure" is a great book. If you set your camera to manual mode, and turn off auto-ISO, then the camera should behave as described in the book. The Pentax manual is sometimes confusing and incomplete in describing the camera's other options, so you'll likely have to do a little experimenting on your own. Just ask questions here if you get stuck.

[Quension]

Quension, thanks for your theory on SR. Will keep that in mind too.

Since I mentioned it so obliquely, I should explain a bit.

In order to avoid image blurring from your hands shaking the camera, there's a guideline that the shutter speed should be at least as fast as the reciprocal of the lens focal length (in 35mm equivalent). So if your lens is physically at 40mm, with the crop factor on cameras of this size making that about 60mm equivalent, the shutter speed should be no slower than 1/60".

Pentax DSLRs, when controlling the shutter automatically, will generally try to follow that rule. The camera would rather raise the ISO or open the aperture first, and only slow the shutter speed if it can't do anything else.

Since SR does allow you to use slower shutter speeds in practice, you would think the camera would take that into account when automatically adjusting shutter speed. Apparently Pentax decided the guideline was better than relying on SR (and they're probably right), so that guideline is followed whether SR is on or off. It's not mentioned in the manual, so that's something you have to figure out by watching the camera, or reading about things others have tried on the forums.

Anyway, this probably explains why it increased ISO instead of reducing the shutter speed. There might be some other reason, this is just my best guess right now.

[OregonJim]

So if your lens is physically at 40mm, with the crop factor on cameras of this size making that about 60mm equivalent, the shutter speed should be no slower than 1/60".

I don't want to confuse the topic, but I've heard this guideline mentioned before and it doesn't make sense to me.

If you mount a 40mm lens on a 35mm FF camera, the "rule of thumb" says shutter speed should be no lower than 1/40 second. Ok so far.

If you mount that same 40mm lens on an APS-C camera, the crop factor should have nothing to do with it - it's still 1/40 second. The physics of the lens hasn't changed, there's no "magnification" involved. All you have is a sensor with a smaller field of view.

Am I missing something?

[DAZ]

I don't want to confuse the topic, but I've heard this guideline mentioned before and it doesn't make sense to me.

If you mount a 40mm lens on a 35mm FF camera, the "rule of thumb" says shutter speed should be no lower than 1/40 second. Ok so far.

If you mount that same 40mm lens on an APS-C camera, the crop factor should have nothing to do with it - it's still 1/40 second. The physics of the lens hasn't changed, there's no "magnification" involved. All you have is a sensor with a smaller field of view.

Am I missing something?

Possibly because they is no physics behind it. It is just a coincidence that it works. How well it works depends on how close you look. With digital it is easer to look close so if you use times 1.5 it will looks better.

It has always been dependent on the photographer taking the photo and how much the photographer was willing to except some motion blur. For some 1/focal length was not good enough and others it was. If you use the rule on very long focal lengths it usually doesn’t stand up as well as for very short focal lengths.

It is just a rule of thumb to help guide the photographer.

DAZ

[OregonJim]

Possibly because they is no physics behind it. It is just a coincidence that it works. How well it works depends on how close you look. With digital it is easer to look close so if you use times 1.5 it will looks better.

It has always been dependent on the photographer taking the photo and how much the photographer was willing to except some motion blur. For some 1/focal length was not good enough and others it was. If you use the rule on very long focal lengths it usually doesn’t stand up as well as for very short focal lengths.

It is just a rule of thumb to help guide the photographer.

DAZ

Yes, it is just a guideline. My point was that, if 1/40 is good enough on a FF camera, it will still be good enough on a cropped sensor camera, assuming it's the same photographer. No need to multiply by 1.5.

[Quension]

If you mount a 40mm lens on a 35mm FF camera, the "rule of thumb" says shutter speed should be no lower than 1/40 second. Ok so far.

If you mount that same 40mm lens on an APS-C camera, the crop factor should have nothing to do with it - it's still 1/40 second. The physics of the lens hasn't changed, there's no "magnification" involved. All you have is a sensor with a smaller field of view.

Am I missing something?

Hmm, it's a good question. I can't give a solid answer (I don't understand optics well enough), but as food for thought...

Apparent magnification is based on the field of view. That's why 40mm on APS-C is equivalent to 60mm in the first place. So, if the field of view is narrower, and the magnification is apparently higher, doesn't that mean motion from the camera would also be magnified (or rather: visible sooner)?

Otherwise it seems like P&S cameras wouldn't need SR at all, since their lenses are so very tiny. It also seems like you would get different optical results with a FA lens vs DA lens for the same physical focal length, since there would be a difference in the size of the image projected toward the sensor with no difference in the lens "magnification".

I see the entire guideline as being based around the idea that at a given field of view, that's how long it takes for the motion from your hand to become visible. To me that makes intuitive sense when I look through the camera, but I can't explain the physics of why field of view works that way.

[OregonJim]

Apparent magnification is based on the field of view. That's why 40mm on APS-C is equivalent to 60mm in the first place. So, if the field of view is narrower, and the magnification is apparently higher, doesn't that mean motion from the camera would also be magnified (or rather: visible sooner)?

But there really is no magnification at all. The exact same image circle is projected onto the FF sensor (or film) as on the APS-C sensor. The smaller sensor just captures a smaller field of view.

The "magnification" doesn't happen until you enlarge the image 1.5x to match the image size of the FF image. That is done post capture.

I can't answer your P&S question (interesting point, though). My suspicion is that since the lens is far closer to the sensor than it is in SLRs/DSLRs, that true magnification does occur (wrt (D)SLRs).

[DAZ]

Yes, it is just a guideline. My point was that, if 1/40 is good enough on a FF camera, it will still be good enough on a cropped sensor camera, assuming it's the same photographer. No need to multiply by 1.5.

That’s just it. As you increase the resolution and look close you see motion blur. On 35mm film I would print 4x5 and it would be good. If I had blown it up to 40x50 it may not be OK. When I was using my DS at 6Mp and only printing to 4x5 I thought 1/FL was OK and times 1.5 a little over kill. Now I use a K20D and 1/FLx1.5 with SR is just barely good enough. But I like to crop more and print bigger now. I can do that because I have more resolution but to use this increases resolution I have to be less tolerant of motion blur. So if I was using a FF at 6Mp I may not see motion blur. This is the same as when I was using film and not printing any bigger then 4x5. If I had a FF with 8-10Mp about the same pixel density as my DS (but I could print bigger because I have more pixels to work with) so the amount motion blur I could see would be the same. If I had a FF with 21Mp then 1/FL would probably not be good enough even thou it was good enough for FF 8-10Mp.

Like I said it is just a coincidence that it works OK for 35mm film for most photographers. If you had taken the film into the darkroom and enlarged it large enough you would probably see motion blur if you were close to 1/FL. It is just how much someone could tolerant it. With digital we can all do the same thing just now we pixel peep and can see it. If we used a 6Mp APS-C camera and printed 4x5 like a lot of people did with film then 1/FL would probably be just as good. Those who printed fine grain film and larger prints usually used something bigger the 1/FL. This is like pixel peeping now.

So if you keep the resolution (on the sensor not Mp total) the same and have the same low standard of expectable motion blur then 1/FL for FF and APS-C would work OK.

This is just my opinion, as I have not seen anything other the coincidence explaining 1/FL and how much expectable motion blur the photographer is willing the except. For some this was not good enough.

DAZ

[OregonJim]

As you increase the resolution and look close you see motion blur. On 35mm film I would print 4x5 and it would be good. If I had blown it up to 40x50 it may not be OK. When I was using my DS at 6Mp and only printing to 4x5 I thought 1/FL was OK and times 1.5 a little over kill.
[...]

Ok, increased resolution I can agree with. But sensor size is not the same as resolution (although they tend to increase together).

I'm afraid I've hijacked the thread, so my apologies to the OP. I'll go make trouble somewhere else now...

Gentleman, if you have a 40mm lens you have a 40mm lens regardless of the camera.
On an APS-C you will have the equivalent FOV (field of view) of a 60mm lens on 35mm format but it is still a 40mm lens.

If you have a 40mm lens what makes you believe that the lowest shutter speed you can use is 1/40sec? What are you going to do if there isn't enough light, wait until it gets brighter or send someone for a flashlight.
OregonJim, I think someone was pulling your leg or you are trying to pull others legs.
Either way it's the photographic equivalent of 'the world is flat'.

Spread the word, you can use any shutter speed you like on any lens you like as long as you have the right available light.
That also applies to Aperture and ISO.

[Quension]

The "magnification" doesn't happen until you enlarge the image 1.5x to match the image size of the FF image. That is done post capture.

I see it as being dependent on the field of view at capture time, whether you enlarge it afterward or not. You would normally compare the resulting images at the same size to decide which one is magnified more, yes, but the smaller field of view was always more "magnified" to begin with. At least, that's how our brains see it. Looking at 4x6 images, the one with the smaller captured field of view looks more magnified, even if it was captured with a P&S and you "shrunk" all of the images in resolution terms. If they all had the same output dimensions to begin with, where is the post-capture "magnification"?

DAZ has a very good point about resolution though. That would help explain the physics, since the distance of motion projected for a given field of view should be proportionately larger (so faster) in a physically larger image circle. If a physically larger sensor has the same resolution (and therefore more total pixels and greater physical magnification, in terms of detail), then it would be more sensitive to the motion.

That makes a lot of sense to me: sensor resolution combined with field of view, with both accounting for physical magnification. An FF-sized lens on a APS-C sized sensor doesn't change this relationship, because the smaller sensor sees a smaller field of view as well.

Then the guideline works because of the typical viewing resolution of images at that time. Hmm.

If you have a 40mm lens what makes you believe that the lowest shutter speed you can use is 1/40sec? What are you going to do if there isn't enough light, wait until it gets brighter or send someone for a flashlight.
OregonJim, I think someone was pulling your leg or you are trying to pull others legs.

This sub-discussion is in reference to the guideline for avoiding visible camera shake in your images when taking handheld shots. We were trying to figure out how it makes sense physically.

It was originally relevant to the OP because the camera seems to follow it, or something similar, when auto-adjusting shutter speed. We kinda got sidetracked though

[OregonJim]

If you have a 40mm lens what makes you believe that the lowest shutter speed you can use is 1/40sec? What are you going to do if there isn't enough light, wait until it gets brighter or send someone for a flashlight.
OregonJim, I think someone was pulling your leg or you are trying to pull others legs.
Either way it's the photographic equivalent of 'the world is flat'.

Spread the word, you can use any shutter speed you like on any lens you like as long as you have the right available light.
That also applies to Aperture and ISO.

Ummm, where have you been for the past half-century? It's a well known photographic maxim that, in order to produce a blur-free handheld shot, the shutter speed should be no slower than the reciprocal of the focal length. Any slower and you need a tripod.