DoF, Focusing, Shutter Speed, what went wrong?

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harkins
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DoF, Focusing, Shutter Speed, what went wrong?

Post by harkins »

Wondering if anyone can suggest what's been going wrong with a few of my photos recently?

The problem that seems to be recurring is varying degrees of sharpness/focus on those 3/4 angle type shots. In the example below, I have the tail in reasonably good focus but the pointy end is less so. So I'm looking at shutter speed, depth of field, focusing and wondering if it's down to one of those or maybe a combination. This one has an aperture of 5.6 and shutter speed of 1/1000
ImageMcDonnell Douglas F-15D Eagle 'Baz' , Israeli Air Force by Phil Childs, on Flickr

This one seems better and the main difference is aperture, being 7.1
ImageMcDonnell Douglas F-15D Eagle 'Baz' , Israeli Air Force by Phil Childs, on Flickr

Can 5.6 versus 7.1 make that much difference over a distance of just a few meters when the object itself is several hundred meters away? Or is my camera set up badly? I know I'm not a great photographer by any stretch and I make many stupid errors and some very poor or ill-thought decisions with settings, but this issue seems so marginal.

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Wrexham Mackem
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by Wrexham Mackem »

I'm not sure what lens you have Phil, but my first thought when I see f5.6 is that is a bit too close to wide open, which invariably is of lesser quality than the lens stopped down to f8 or thereabouts - which on most lenses is the sweet spot.

Depth of field - yes, definitely it will have an effect too.

So your second shot at 7.1 is showing improvement for two reasons, it having greater depth of field and being shot with the lens stopped significantly down from wide open.

If light gets low I find it less detrimental to image quality to up the ISO in order to avoid the aperture getting too wide.

All just my experience of course.
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Brevet Cable
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by Brevet Cable »

DOFMaster ( http://www.dofmaster.com/dofjs.html ) will give you an idea of the DOF for numerous body-lens combinations depending on how far away the object is.
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harkins
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by harkins »

Thanks Nigel. I think that is definitely the problem then. I guess I should maybe shoot in manual but leave the ISO in auto. I tend to favour using the shutter speed (TV) for jets as I like to try and avoid blurry images but this very often with longer focal lengths forces the aperture wide open. I'm also often wary of higher ISO due to noise. I suppose something has to give somewhere. My lens is an old Canon 100-400mm. I'd love to change it for the MkII as I believe it's much much better but, it's a lot of dosh. I'll certainly try and avoid F5.6 from now and and try to keep at F8.

Also need to concentrate more as well. Apart from the settings talked about above, I'm forever mucking about with IS and having that set inappropriately too. And that's not to mention the time I waited hours for a B-1B to return and ran out of space on the card after about 3 shots! Maybe I should just find another hobby :dunno:

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harkins
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by harkins »

Brevet Cable wrote:DOFMaster ( http://www.dofmaster.com/dofjs.html ) will give you an idea of the DOF for numerous body-lens combinations depending on how far away the object is.

That was interesting and slightly confusing as it suggests that I had a lot of slack even at f/5.6. Maybe it's more about the quality of my lens/glass. It's quite old and zooms are often criticised for being soft at the top and bottom ends of zoom and aperture. The answer is possibly to sell a kidney and buy a full frame camera and a 400mm prime lens!

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Wrexham Mackem
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by Wrexham Mackem »

I'm still using the mark one too. I must get round to an upgrade. But, no lens is at its best wide open. The mark two may well be better than the mark one, but still best aim for f7.1 or f8.

I use aperture priority at f8 when shooting fast jets, keeping an eye on the shutter speed and adjusting the ISO if need be. Shutter priority for props and rotors. IS on or off as I see fit, Mode 2 unless there's little movement in the subject, and if I was lucky enough to have the latest version of the lens Mode 3. We have all have been caught out with a settings from time to time, despite years of experience and practice. Its an occupational hazard :smile:
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Col. Chibani
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by Col. Chibani »

Other ideas:
  • which Focus Point setting did you use ? Single / Multiple, Centered, Auto, ...
  • which Focus Point(s) were used on each photo ? Are they positioned on the tail / center / nose of the a/c ? (if you can retrieve this information from your files)
You may also have a back/front focus issue that moves the depth of field zone relatively to the Focus Point targeted by the camera.

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harkins
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by harkins »

Col. Chibani wrote:Other ideas:
  • which Focus Point setting did you use ? Single / Multiple, Centered, Auto, ...
  • which Focus Point(s) were used on each photo ? Are they positioned on the tail / center / nose of the a/c ? (if you can retrieve this information from your files)
You may also have a back/front focus issue that moves the depth of field zone relatively to the Focus Point targeted by the camera.

That's not something that I'd thought about and didn't know how to do. Having now learnt how to get the focus point information (using Canon Digital Photo Professional) I've got an image showing the focus points and specific focus point used.

So this image (the top one) has was taken at 1/1000 sec, f/5.6, ISO 250, 330mm focal length, AF Point Expansion (8) and from an approximate distance of 250m. The aircraft was descending and moving away as it came in to land. It was late afternoon with the sun pretty low. Looks as if the focus point is on the wing tip or drop tank.

Image

Col. Chibani wrote:You may also have a back/front focus issue that moves the depth of field zone relatively to the Focus Point targeted by the camera.

I'm afraid that I don't really understand this bit and it sounds both potentially serious and complicated.

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Col. Chibani
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by Col. Chibani »

Hello Harkins.

For the focus point, I use a single, centered point and strive to place it on the a/c center or even better on the cockpit to be sure that it is on focus (it is like having the focus on the eye when doing portrait photography).
A little re-composing may be needed in post-production.

harkins wrote:
Col. Chibani wrote:You may also have a back/front focus issue that moves the depth of field zone relatively to the Focus Point targeted by the camera.


I'm afraid that I don't really understand this bit and it sounds both potentially serious and complicated.

Front or back focus is the fact that some camera/lens combinations make systematic focus error. This error can depend on distance and/or focal length.
In your case, if you experience front focus, it means that the actual focus point is ahead of the point selected by the camera. Consequently, only a small part of the DoF covers the a/c, aggravating the fact that the focus point is not positionned on the a/c centerline.
Some cameras and lens offers the possibility to compensate for this but this requires an accurate calibration procedure.

Hope this helps.

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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by nighthawk999 »

"but this requires an accurate calibration procedure" All of my DSLR -owning friends,who have much more experience than me,have said if you have to ask how to do the calibration,then leave well alone!If you know someone that knows how to carry it out,all well and good,but otherwise I'd leave it alone.

Well done for getting the screen shot showing the focus point.Perhaps,when the EOS Magazine forum is up and running again..it's been offline for a while following some DDOS attacks..you might consider joining,and seeing if the chaps on there can point you in the right direction?

They're a friendly bunch,and I'm sure the aviation enthusiasts among them would be willing to help.If you pm me,I'll send you the link to one on Flickr in particular who takes brilliant airshow images.He's a nice guy and will help you if he can once the forum is up again.

But as Wrexham has already said,using f7.1 or f8 would have helped to get more of the plane in sharper focus.

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alanp
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by alanp »

I'm in the f8 club too. I went through exactly the the same issues you are experiencing with my 100-400. Softish looking shots even at high shutter speeds, so up the ISO and shutter speed but no better. I eventually noticed that shots at f8 were consistently good, even when the shutter speed was getting low. I switched to AV and f8 and haven't looked back since. The lens although an old design can actually perform really well in its sweet spot - and it is a spot - f9 is okay but anything else and off it goes again. There's a link on the left (in the PC version of the site) that will take you to my Flickr, you can gauge for yourself.

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GeorgeP
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by GeorgeP »

I have noticed a similar problem with some of my images but I'm not convinced that the problem can be explained by lack of depth of field (DoF). At two hundred metres camera-to-subject distance and with an airshow standard 300mm focal length on a crop sensor camera, the DoF is almost identical at f/5.6 as it is at f/8. I believe there's something else causing the problem but I'm happy to be corrected by anyone who knows more about physics and optics than I do.

FWIW, I have ground-to-air shots of aircraft from this year's Oshkosh that show the same problem as your first image. Images of the same aircraft after landing and taxying parallel to the show axis were taken at roughly half the distance, approx. the same angle, SAME f-stop, SLOWER shutter speed and are tack sharp along the entire length of the aircraft.

Out of interest, were the original two F-15 images full-frame or cropped and is the image with the focus points a full-frame image, or a crop? If none are full-frame, would you please post an image of each straight out of the camera. I'd be interested to see where they were in the original frame.
Cheers,

George

Melbourne, Australia.

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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by alanp »

I don’t think it’s a depth-of-field issue. It’s down to optical sharpness. The lens is optimised for maximum sharpness at f8.

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harkins
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Re: DoF, Focusing, Shutter Speed, what went wrong?

Post by harkins »

Thanks for all the feedback gents. Some really interesting points and plenty to think about. I'll definitely try and stay at the f8 aperture now as there does look to be an improvement in the shots with that aperture. However, having looked at Brevet's link, the DoF at the figures I input make almost no difference. So I'm with George there. And I'm certainly with nighthawk regarding calibrating. I'm certain that would result in me completely cocking everything up for good!

I'm also wondering about IS. I've a tendency to leave that at various settings which doesn't help. But I've also been told before that when shooting 1/1000sec, IS isn't worth using and can cause more harm than good.

George, the originals are cropped a bit to get the aircraft in the centre of the frame and slightly edited in LR5 with the usual tweaks to exposure, shadows, sharpening and noise reduction.The way image with the focus points is a screen capture from the Canon software and it is of the original CR2 file. I may have lost a millimetre around the edge when using the snipping tool.

And yes Alan, f8 looks like the best solution for me. It'll be a while now before I get the chance to try it out though. I'll spend the meantime trying to make the best of what I took this year with this varied focusing on different parts of the jet.

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