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yelvertoft
07-02-06, 11:09
Having covered fully manual exposure, exposure compensation and aperture priority, it’s time to round off this set with an article on shutter priority mode.

Ok, you’ve got your first camera that goes beyond “point and shoot”. There’s a lot of buttons and dials on it that you really would like to know about but feel a little intimidated in case you break your new toy or get stuck. Your pictures seem ok when you stick to “Program” mode so you stick with what your comfortable with. Why should you change? Read on……

A lot of users, when they get their first ‘serious’ camera find themselves in the situation described above, there is nothing wrong with using Program mode, but you’re going to find it a lot more difficult to get the picture you see in your mind’s eye if you don’t understand the settings the camera is choosing for you.

Let’s discuss shutter speed priority mode, more commonly referred to simply as shutter priority. This mode of operation is usually marked on the camera’s mode dial as Tv. Tv stands for Time Value.

What is the shutter speed? Put in its simplest form, it’s the amount of time that the film/sensor exposed to the light. All SLR cameras have shutters (or curtains) to block the light from the film or sensor. These shutters are opened for a given amount of time to expose the film/sensor to the light. In many compact digital cameras the sensor is exposed to the light all the time, but the sensor is not in “capture” mode. In this case, the shutter speed is the amount of time the sensor is actively capturing/recording the light falling on it.

Shutter speeds are typically measured in fractions of a second ½, ¼, 1/8, 1/16, 1/32…… etc. down to speeds as fast as 1/8000th of a second on some models. The speed is normally displayed on modern cameras just as 125 instead of 1/125th (for example), so a bigger number means a faster shutter speed. Long exposures, measured in whole seconds, are usually displayed with a “ suffix, so 8 seconds would be shown as 8”, whereas 1/8th of a second would simply be 8.

Why do you need to change the shutter speed? Because it affects many things, most notably, it can have the effect of freezing the movement of the subject (or movement of the camera). A faster shutter speed is capturing a shorter period of time, a slower shutter speed is capturing a longer period of time. Remember, each time the shutter speed is halved, the amount of light getting through to the film/sensor is halved. To compensate for this either the sensitivity (ISO speed) needs to be increased or the aperture needs to be opened up.

So what effect does changing the shutter speed have on the movement of the subject or camera? Any relative movement between the subject and camera whilst the shutter is open will cause some blurring. This is not always a bad thing, this effect can be used to emphasise any movement of the subject. It can tell the viewer that the subject is moving, impart a sense of speed to a moving subject. Likewise, this subject blur can ruin a shot where the intended image needs to be sharp.

Use the shutter speed to vary the effect of freezing a moment in time. A longer shutter speed is often used to blur moving water, giving a smooth flowing effect. Another example may be a picture of a slalom canoeist where the exact opposite effect is desired. A high shutter speed could be used to freeze the movement of the water, enabling the viewer to see the dramatic shapes of the water splashes.

It all depends on the desired effect. Using shutter priority mode allows you to control the sense of movement in the picture you want.

Unless a tripod or other support is used, for 35mm film, the rule of thumb always used to be that a shutter speed of less than 1/focal length of the lens was needed to prevent blur due to camera shake. For example, if a 50mm lens was used with the camera hand-held, it was inadvisable to use a shutter speed of less than 1/50th of a second. This rule is still useful to know, but it should be adapted if used with today’s digital sensors – if your camera has a “crop factor” of 1.5x then the 50mm lens becomes an effective 75mm lens and it is inadvisable to use a shutter speed of less than 1/75th if blur due to camera shake is to be avoided. With practice, there’s a bit of leeway in this rule, and if you are using a lens/camera with image stabilisation then there’s considerable latitude to go slower than the rule suggests.

Right, now having outlined the basic effects of changing the shutter speed, how do you put this into practice? When you switch your camera to Tv mode, you have control over the shutter speed. You can set the shutter to a large number (slow speed), providing less movement “freeze”, or a small number (fast speed), providing more movement “freeze”. The camera will then automatically set the aperture to a value that it considers will give the correct exposure, providing the lens aperture and ISO speed can cope with the shutter speed you have chosen given the amount of light available.

I hope this helps to demystify the Tv mode on your camera and gives a greater understanding of the effect of shutter speed even if you are using Program mode.

Regards,

Duncan.

6eor6e6
12-02-06, 01:25
Thanks Duncan this gives me a track to go down on a issue that I had with a pic I posted yesterday I was advised thankfully that the pic lacked sharpness, this thread is just the sort of advise an ameture like me needs to come across. The suns making its way through some overcast as I write so I may go back and try a couple of things if I get improvement I shall post.
Thanks again George

Dr.Manjeet Singh
02-05-06, 13:50
Ducan-thanks for the info but can you let me know how to control the shutter speed in a T.D.1-i havent the faints idea-there is no such thing any called Tv on my camera.Regards.:confused:

Don Hoey
02-05-06, 15:06
Ducan-thanks for the info but can you let me know how to control the shutter speed in a T.D.1-i havent the faints idea-there is no such thing any called Tv on my camera.Regards.:confused:

Hi Manjeet,

I have been having some problems with my connection so I am posting a few links to your Kowa TDI while I have them.

TDI features http://www.kowa-usa.com/sporting_optics/product_ss_td1_ft.php
Digital Camera features http://www.kowa-usa.com/sporting_optics/product_ss_td1_dc.php
Outer view and nomenclature http://www.kowa-usa.com/sporting_optics/product_ss_td1_nm.php
Specifications http://www.kowa-usa.com/sporting_optics/product_ss_td1_sp.php

There is not a lot of help here in trying to understand what controls you have. I will see if I can find a link somewhere to the operating instructions.

Don

Don Hoey
02-05-06, 16:21
Manjeet,

I have had no luck trying for a manual for the TDI.

Looking at the images of the scope I am unable to see if there are any controls for the camera.

If there are non then it is working in fixed program mode. If there are camera controls then a description of them would be helpful in answering your question.

Don

tallurianil
02-05-06, 20:25
Hi Manjeet:

I tried looking up the nomenclature for a TD-1. Apparently it doesn't have a manual override for the shutter, hence it may not be possible for you to have a control on the shutter, unless, the Setup has some features.

Hope the attached link will help some of our fellow members to review and provide their inputs.

http://www.buytelescopes.com/product.asp?m=&pid=10173&display=desc

Hope this helps.

Wheeler
03-05-06, 01:13
Duncan, I'll happily stand corrected, but since the crop factor is the result of a smaller effective lens circle rather than an actual lengthening of the focal length, isn't taking the crop into account when working out the shutter speed unnecessary?

Dr.Manjeet Singh
03-05-06, 07:38
Thank you all waiting for more info.Regards and Thank you again.

yelvertoft
06-05-06, 17:03
Duncan, I'll happily stand corrected, but since the crop factor is the result of a smaller effective lens circle rather than an actual lengthening of the focal length, isn't taking the crop into account when working out the shutter speed unnecessary?

Hi Wheeler,

The crop factor is an effective magnification, as you say, due to the smaller section of the image being projected onto the sensor. This magnification will still affect the extent of blurring caused by camera shake. It makes sense to me to take this into account and the owners manual for my camera also mentions this factor should be taken into account to avoid shake.

There are no hard and fast rules here. If you are happy with the results you get at slower shutter speeds then go ahead and use them. This article was written to try and give people basic advice, a primer. The result you will get will depend very much on what kind of subject you are taking.

Regards,

Duncan

John
07-05-06, 17:21
Duncan, I'll happily stand corrected, but since the crop factor is the result of a smaller effective lens circle rather than an actual lengthening of the focal length, isn't taking the crop into account when working out the shutter speed unnecessary?

Because of the smaller effective lens circle the image (and therefore the blur) has to be enlarged proportionally more and that is why the effective focal length has to be used when working out the shutter speed. That's how I see it anyway.

John

Wheeler
08-05-06, 08:32
John, the physical (??) image produced at the back of the camera isn't enlarged by the crop factor, infact it isn't changed at all from one you'd get at the same focal lengths with 35mm. You're simply looking at less of the lens circle than you are with 35mm. Any movement induced by shake at 300mm will be the same on 35mm as it is on digital.

Since we're looking at a smaller portion of the resultant image, it's important that it's sharp, there's no point effectively enlarging something that isn't, but if I took the effective crop into consideration when taking photos I'd get a hell of a lot of frozen propellor blades taking ground to air shots at 1/640.

John
08-05-06, 13:31
John, the physical (??) image produced at the back of the camera isn't enlarged by the crop factor, infact it isn't changed at all from one you'd get at the same focal lengths with 35mm. You're simply looking at less of the lens circle than you are with 35mm. Any movement induced by shake at 300mm will be the same on 35mm as it is on digital.

Since we're looking at a smaller portion of the resultant image, it's important that it's sharp, there's no point effectively enlarging something that isn't, but if I took the effective crop into consideration when taking photos I'd get a hell of a lot of frozen propellor blades taking ground to air shots at 1/640.

Yes I agree with you about the frozen prop. blades but my point about enlarging blur (due to camera shake) is, I believe still valid. To illustrate my point imagine a sensor measureing 1 mm x 1.5 mm and try blowing that up to A4. Blur due to camera shake would be magnified enormously.

John

Wheeler
08-05-06, 13:40
John, I think the blur you're referring to in your example (and in the way you've interpreted camera shake) is wholly a factor of resolution rather than cancelling the effects of movement.

John
08-05-06, 19:14
John, I think the blur you're referring to in your example (and in the way you've interpreted camera shake) is wholly a factor of resolution rather than cancelling the effects of movement.

Wheeler, you have raised some doubts in my mind. I need to think about it. I will be back, eventually!

Wheeler
08-05-06, 22:50
John, as I said earlier, I'll happily be proved wrong, it's just that I've not found this to be the case in practice. I regularly get away (only a fool tries to kid people that a hefty dollop of luck's not involved) with shutter speeds considerably lower than the 1/FL guidance suggests. If the crop factor really did come into play in this calculation then luck would be playing an even bigger part.

yelvertoft
09-05-06, 13:05
John, as I said earlier, I'll happily be proved wrong, it's just that I've not found this to be the case in practice. I regularly get away (only a fool tries to kid people that a hefty dollop of luck's not involved) with shutter speeds considerably lower than the 1/FL guidance suggests. If the crop factor really did come into play in this calculation then luck would be playing an even bigger part.

Not really, it's just that some people are much better at hand-holding than others.

John
09-05-06, 19:27
Hello Wheelr, as promised I am back. This is how I see it although, like you, I stand to be corrected.

Suppose you take two pictures with the same focal length and from the same spot, one on 35 mm film, the other on a digital camera with a sensor measuring 15 mm x 22.5 mm. Providing that the same level of camera shake is common to both shots then the blur on both images will be identical. To obtain a 10 in x 8 in print the film image would need to be enlarged 8 times. However, the digital image would need to be enlarged about 12 times and the blur would, be magnifide 50 % more. Hence the need for a faster shutter speed to reduce the blur. There may be an exception to this which I have yet to think through. If when taking the digital picture you moved further away from the subject so that the field of view was the same in both cases, then the final blur on the print would be the same in both cases (Ithink) and there would be no need to increase shutter speed. The answer to the question thus depends on your standpoint (ha ha). I would be interested in your comments.

By the way I think it would need a hell of a lot of camera shake to equate to the blur produced by a revolving propeller blade.

John

Don Hoey
09-05-06, 19:54
I'll agree with that John, so I also agree with Duncans initial statement.

Ever one to chuck a rock into the pool, I think sensor resolution will also have an impact. ie D2Hs 4mp and D2X 12mp on the same sensor size.

Don

Alex Paul
12-11-06, 23:23
Duncan very informative and extremely well written.....Alex

yelvertoft
28-11-07, 20:38
I found these two pictures whilst having a tidy up. Thought they did a reasonable job of explaining the different effects of slow and fast shutter speeds. Fast shutter on the left, slow shutter on the right.

Duncan