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04-19-2010, 05:48 PM   #1
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Image Stabilization and Focal Length

I am shooting pictures with my DA 55-300 and I am noticing that there is blur at shutter speeds in the 1/30s and even 1/50s. This is with IS enabled.

If I read other posts correctly, to get clear pictures you need to increase the shutter speed if the focal length increases.

So my question is, what should I set my shutter speeds (no action shots) to if I have my focal length at say 55mm, 100mm, 200mm, or 300mm? How much of a difference will image stabilization make if enabled?

If I have action shots (ie kids running) I will have to set my shutter speed much faster, what are reasonable shutter speeds for this sort of thing if I am at 300mm?

I hope I have the concept down, if you could help with the particulars I would appreciate it.

I am sure there is some sort of mathematical formula...perhaps if you shared it that would be great also!

04-19-2010, 05:55 PM   #2
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There is really no formula, trevorgrout.

The rule of thumb is that the minimal shutter speed in second is the reciprocal of the 35mm-format focal length.

For APS-C sensor DSLRs, it means: the minimal shutter speed is the reciprocal of 1.5 X focal length.

For example: 1/500sec for a lens of 300mm focal length.

In general, Pentax DSLR with sensor-based shake reduction gives you 2 more stops. So for a 300mm lens, the lowest shutter speed is 1/125 sec. (2 stops lower than 1/500).

Then of course it is based on your techniques and on how stable you are. I can do 1/25 sec for a 250 mm lens if I have something to brace onto, but that's before I have any beer.....

Note that this is about the person operating the camera, not about the movement of the people/things being photographed. That is a totally different discussion. Hint: SR doesn't help.

Last edited by SOldBear; 04-19-2010 at 06:01 PM.
04-19-2010, 07:13 PM   #3
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think of it like holding a big stick that extends outward for as long as your subject.

Jerky movements when the subject is close to you are quick and small in comparison to the jerky movements seen while at 300mm, which are slower and larger. You need to compensate a little more to keep the image still when at 300mm because the smallest movements at the origin are magnified the longer the stick becomes.

the inverse rule works great, but its just a rule of thumb. Shake isn't really affected by your subject moving, just the point of origin, which is why i think in camera stabilization is a little better.

You don't always need a fast shutter speed with kids. If you want to be creative, try following your kids/subject with your camera at a slower shutter speed. You will have a clear subject, and an interesting result to the background.
04-20-2010, 04:44 AM   #4
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Basically, when you are shooting at 300 mm every movement you make is magnified. We think of SR in terms of "stops improvement." The formula is that without SR you should be able to shoot completely steady at 1/focal length *1.5. So, for shooting at 100mm, your shutter speed should be (at a minimum) 1/150 second without SR to get a steady shot. One stop improvement would be half that at 1/75 second, another stop at 1/30 second and so on.

On the K7, I find that I get three to four stops improvement (occasionally more). The most important thing however, has nothing to do with SR. Work on good camera control. Arms in at your sides, relaxed, slow your breathing, and gently push the shutter button. These are things that will make you a more steady shooter and improve your photos significantly.

04-20-2010, 05:54 AM   #5
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QuoteOriginally posted by trevorgrout Quote
I am shooting pictures with my DA 55-300 and I am noticing that there is blur at shutter speeds in the 1/30s and even 1/50s. This is with IS enabled.
If I read other posts correctly, to get clear pictures you need to increase the shutter speed if the focal length increases.
So my question is, what should I set my shutter speeds (no action shots) to if I have my focal length at say 55mm, 100mm, 200mm, or 300mm? How much of a difference will image stabilization make if enabled?
a lot depends upon 3 things,
- technique, good technique can help reduce blurr substantially even without Image stabilization
- enlargement of the image. The old rule of thumb was 1/focal length to get an acceptably sharp image on an 8 x 10 print. WIth the crop factor for an ASP-C sensor, this drops down to about a 4 x 6 print, or conversly to print at 8 x 10 inch it needs to be 1 /( focal length x 1.5) the 1.5 is the crop factor. Unfortunately today we all tend to pixel peep and look at our shots at extreme magnifications and demand perfection when sitting 8-12 inches away from an image that might scale up to something in the 40 x 60 inch or more range. I am just as guilty aws the rest in this respect. as I sit here in front of my 22 inch wide screen 1920 x 1050 pixel monitor.
- whether the subject is stationary or moving. Image stabilization eliminates camera shake, but moving subjects will still be blurred due to their motion.
QuoteQuote:
If I have action shots (ie kids running) I will have to set my shutter speed much faster, what are reasonable shutter speeds for this sort of thing if I am at 300mm?
I hope I have the concept down, if you could help with the particulars I would appreciate it.
if kids are running you need to consider 2 things, first a shutter peed in the 1/300 up to 1/500 range may be necessary, and second, you should turn shake reduction OFF. SR is meant for stationary subjects, it does not know how to interpret correctly camera motion to track moving objects.
QuoteQuote:
I am sure there is some sort of mathematical formula...perhaps if you shared it that would be great also!
Hope this helps
04-20-2010, 06:43 AM   #6
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Shake reduction is a wonderful thing but it has its limits. Everyone is going to get different results as to how steady they can hold the camera. I find a monopod gets me the best results whenever I am using a long lens. With my 70-300, I will have far more keepers with the SR off using a monopod or tripod for sports shots than hand held with SR on. For any action shots, I consider 1/250 the minimum. Even at that speed, some motion blur may show up. I have had shots come out ok at slower speeds but not consistantly. For freezing action, I will go for the fastest shutter I can get in the lighting conditions.
04-20-2010, 07:17 AM   #7
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Original Poster
Thanks guys for the comments.

I guess I am guilty of pixel peeping and that is affecting my judgment of how sharp a picture is. I also appreciate the comments on action shots.

It makes sense that I should just turn off SR for action shots. This probably a good thing because it takes SR a few moments to kick in anyways. I will also try to improve my camera holding technique also.

So if I do have 300mm and without IS enabled, I should set my shutter speed to 1/450s.
If I have IS enabled can I safely lower the shutter speed to 1/100s?? I believe that is around 2-3 stops? I have the KX.

I really appreciate the replies from everyone.
04-20-2010, 07:40 AM   #8
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Take some test photos and see. The question is sort of a combination -- how shaky are you in the beginning and how good is the SR at compensating. I can shoot at 300 mm and 1/10 second and have pretty sharp photos, but I am pretty steady to begin with.

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