Help with DoF width-wise

[PopsPhotos]

I wonder why this hasn't changed throughtout history, considering an "f stop" is a dimensionless number.

The number used in camera setup are all reversed. Shutter speed set to 60 is longer than shutter speed set to 125, because shutter speeds are fractions. (Ignoring multi-second timed exposures.) F:4 is a larger hole than f:5.6, because it is a fraction. ASA 100 needs more light than does ASA 200, because it is a fraction.

Now, to f:stops and why they are fractions. The f:stop is based on the focal length of the lens. An f:stop of 1 on a 50mm lens will create a 50mm aperture, while an f:stop of 1 will create an aperture of 100mm on a 100mm lens. Thus, the number of f:2 will create an aperture 1/2 diameter of the focal length of the lens. So, the numbering of f:stops is not "a dimensionless number." It is just that "everything is relative, my son."

Personally, I think George E. invented this numbering scheme just to confuse his competitors.

Pops

[leansoli]

Getting wiser day after day!

No, I don't believe there's a right or wrong to it.

Just that we have to be careful to be completely unambiguous when writing about it in places like this, or people that are new to the whole lens thing can easily read something and come away with the opposite understanding to that which the author had intended.

Got your point. At the time I replied to the thread, I just could think of 'bigger' rather than 'wider'. Thanks for the tip!

...Now, to f:stops and why they are fractions. The f:stop is based on the focal length of the lens. An f:stop of 1 on a 50mm lens will create a 50mm aperture, while an f:stop of 1 will create an aperture of 100mm on a 100mm lens. Thus, the number of f:2 will create an aperture 1/2 diameter of the focal length of the lens. So, the numbering of f:stops is not "a dimensionless number." It is just that "everything is relative, my son."

Personally, I think George E. invented this numbering scheme just to confuse his competitors.
Pops

You can go change this bit of information in wikipedia here!
(In that link, you can read the part of 'dimensionless number' in the last sentence of the very first paragraph. Although later on, the article speaks about halving of the diameter aperture regarding f-stops, but people tend to remember simpler sentences ).

[rpcrowe]

Welcome to the Cambridge in Colour Forum! I have always found our members to be very knowledgeable and happy to answer any question and to troubleshoot any problems.

I agree with Colin and I also did the math. Your depth of field, if you focused on the first row of people at approximately 10 meters would be (very approximately) 5.5 to over 55 meters so the difference between the sides of the group to the center should not be of any consequence. If you focused one row back, you would be focusing at approximately the hyperfocal distance of the lens and thus would have a depth of field of from half that distance to infinity. Again, the differential between center and side subjects should be of no consequence.

I would expect that it is the performance of your lens along with the camera (and digital sensor) not being parallel to the front line of people. I definitely try to keep my camera parallel to any group which I am shooting and I always try to shoot at a smaller than maximum aperture. This is most important when using a consumer grade lens at either end of the zoom range.

Here are some suggestions which might improve general image quality:

I would boost my ISO to get a smaller f/stop. Your 450D should be capable of providing very good quality when shot at ISO 400 and very good to excellent quality if some noise reduction software is used. At ISO 400, you could have used about f/6.3 at 1/80 second. Stopping any lens (especially consumer lenses) down a couple of stops will always improves image quality (especially edge quality).

I always use a lens hood, even when shooting in the shade and even when shooting indoors. The lens hood will protect the lens from flare and will also protect it from physical damage. I mention this because you remarked about tilting the camera down to avoid light flare.

One thing which was not mentioned. Were you using a protective filter over your lens? Lesser quality filters will usually degrade imagery and you will often notice the results at the edges. Additionally, I have seen cheap grade filters which, when mounted on the lens, are not parallel to the focal plane. A cheap filter mounted at a bit of an angle could contribute to edge problems.

When I shoot groups of people several lines deep, I will try to shoot from a higher level which will even out the distance between the rows to the camera.

If I shoot long lines of people, I tend to stage them in a convex curve which will somewhat equalize the distance between the people at the ends of the line and the people in the center to the camera.

The above two techniques will allow for the group to be in better focus and will also prevent any distortion which may be caused by using a wide lens when shooting people in groups. However, there really should be no distortion when shooting with a 28mm lens on a 1.6x camera since the equivalent focal length is 44.8mm which is not very wide.

[leansoli]

Welcome to the Cambridge in Colour Forum! I have always found our members to be very knowledgeable and happy to answer any question and to troubleshoot any problems.

I agree with Colin and I also did the math. Your depth of field, if you focused on the first row of people at approximately 10 meters would be (very approximately) 5.5 to over 55 meters so the difference between the sides of the group to the center should not be of any consequence. If you focused one row back, you would be focusing at approximately the hyperfocal distance of the lens and thus would have a depth of field of from half that distance to infinity. Again, the differential between center and side subjects should be of no consequence.

I would expect that it is the performance of your lens along with the camera (and digital sensor) not being parallel to the front line of people. I definitely try to keep my camera parallel to any group which I am shooting and I always try to shoot at a smaller than maximum aperture. This is most important when using a consumer grade lens at either end of the zoom range.

Here are some suggestions which might improve general image quality:

I would boost my ISO to get a smaller f/stop. Your 450D should be capable of providing very good quality when shot at ISO 400 and very good to excellent quality if some noise reduction software is used. At ISO 400, you could have used about f/6.3 at 1/80 second. Stopping any lens (especially consumer lenses) down a couple of stops will always improves image quality (especially edge quality).

I always use a lens hood, even when shooting in the shade and even when shooting indoors. The lens hood will protect the lens from flare and will also protect it from physical damage. I mention this because you remarked about tilting the camera down to avoid light flare.

One thing which was not mentioned. Were you using a protective filter over your lens? Lesser quality filters will usually degrade imagery and you will often notice the results at the edges. Additionally, I have seen cheap grade filters which, when mounted on the lens, are not parallel to the focal plane. A cheap filter mounted at a bit of an angle could contribute to edge problems.

When I shoot groups of people several lines deep, I will try to shoot from a higher level which will even out the distance between the rows to the camera.

If I shoot long lines of people, I tend to stage them in a convex curve which will somewhat equalize the distance between the people at the ends of the line and the people in the center to the camera.

The above two techniques will allow for the group to be in better focus and will also prevent any distortion which may be caused by using a wide lens when shooting people in groups. However, there really should be no distortion when shooting with a 28mm lens on a 1.6x camera since the equivalent focal length is 44.8mm which is not very wide.

Well, you brought another sort of unknown factor until now. I was indeed at a lower height than the people, yet as you mention, despite being lower than them I had to bend in order to avoid sun flares.

I did mention at some point that I always have a UV filter mainly as protection. With that filter I was able to get sharp shots and it was kind of disregarded in relation with this topic. Of course, I'll check that it is correctly screwed.

Thanks for those two tips on shooting 'wide' and 'deep' groups of people!

I mentioned that I would get a few shots, but summer + speedboat + skis + weekend = busy days xD

[Peter Ryan]

Hey Leandro,

I hope you enjoy the summer days and fun but just make sure your next question is an easy one . OK.

[pwnage101]

I agree with Colin and I also did the math. Your depth of field, if you focused on the first row of people at approximately 10 meters would be (very approximately) 5.5 to over 55 meters so the difference between the sides of the group to the center should not be of any consequence.

This is not entirely true. keep in mind that the focal plane is a plane, not a sphere
Hence, all those in the same row should be in focus, even if the aperture was so large that the depth of field was the size of a [human] head

[rob marshall]

Nothing to do with DOF. It's a lens problem. If you look at the screen-grab below you can see it. The four people on the left seem to be definitely standing on the same focal plane, and yet as you look form right to left you can see the IQ failing quite noticeably. For some reason, it doesn't seem as bad on the right side of the group - did you crop this shot?

I know you didn't ask for it (you get added values here ) I think the group needed some direction. There at least four people not looking at the camera, and why is that guy on the right playing with his camera? There is also a lady hiding behind the older man on the right.A shot like this may be an important record shot of a specific event to some people, so it's worth taking an extras 30 secs to ask people to co-operate more in it's execution.

But ignore what I say. I'm just a control-freak.

[leansoli]

Hey Leandro,
I hope you enjoy the summer days and fun but just make sure your next question is an easy one . OK.

Will do! xD

Nothing to do with DOF. It's a lens problem. If you look at the screen-grab below you can see it. The four people on the left seem to be definitely standing on the same focal plane, and yet as you look form right to left you can see the IQ failing quite noticeably. For some reason, it doesn't seem as bad on the right side of the group - did you crop this shot?

I know you didn't ask for it (you get added values here ) I think the group needed some direction. There at least four people not looking at the camera, and why is that guy on the right playing with his camera? There is also a lady hiding behind the older man on the right.A shot like this may be an important record shot of a specific event to some people, so it's worth taking an extras 30 secs to ask people to co-operate more in it's execution.

But ignore what I say. I'm just a control-freak.

Shot is not cropped, but resized to 2.000px × 1.333px (as I mentioned in some previous post, it was resized and converted to JPEG for uploading purposes.)

About the directions, you are kind of correct. There was another guy with a DSLR who took his shot and then I took mine. BUT! Group knew they had to look at that guy and then look at me, yet some of them didn't do so. About the guy playing w/his camera... nothing to say. He knew we would not use his camera, so I have no idea what he's doing. I didn't get the chance to look at the pic. of the other guy, but I hope it's better than mine :/

[leansoli]

Well, thanks for all the feedback!

I managed to get 2 shots ever since that day (been real busy lately) and I know composition, focal lenght, exposure and pretty much everything is different than the one shot that brought me to this forum, but the lens is the same.

Here they are:
snail
lettuce

It looks like the lens is OK after all. Probably its performance decreases drastically at some point.

On a side note, anyone else is worried about a bicephalous lettuce? :P

Once again, thanks for your time in helping me troubleshoot my problem!

[Dave Humphries]

Well, thanks for all the feedback!

I managed to get 2 shots ever since that day (been real busy lately) and I know composition, focal lenght, exposure and pretty much everything is different than the one shot that brought me to this forum, but the lens is the same.

Here they are:
snail
lettuce

It looks like the lens is OK after all. Probably its performance decreases drastically at some point.

On a side note, anyone else is worried about a bicephalous lettuce? :P

Once again, thanks for your time in helping me troubleshoot my problem!

Hi Leandro,

I can't help feeling niether of those shots is going to show the likely lens problem, you really need to get the camera opposite the brick wall, 'square on' to it (i.e. perpendicular to it both horizontally and vertically). Then shoot (ideally from a tripod) at wide open, then at whole stops down from that and review the sharpness at centre and edges at 1:1, or 100%. Do this at 28mm, 50mm and 80mm.

But I wouldn't blame you if you didn't want to, just shoot at f/8 or f/11 in future; that is almost guaranteed to give better results than f/3.5.

Cheers,

[pwnage101]

On a side note, anyone else is worried about a bicephalous lettuce? :P

I'm actually still wondering how you managed to take a picture without your hands

[meltimtiman]

My apologies if I am wrong with my contribution to this thread. I had the same experience about 2 months ago when I was tasked to shoot a sports event. I used a 10-22mm ultra wide lens on a group shot. What I did was, 1) zoomed in to 16mm, 2) adjusted the ISO to 400, 3) aperture opening was at f/8, 4) moved a little farther leaving enough space for cropping. Output was clean from end to end.

With the Tamron 28-80mm and with a similar event, I would suggest you shoot at 35 to about 60mm, ISO 400 to 800, F/8 to 11, and leave some space for cropping.

[leansoli]

Yes, leaving a bit of space for cropping crossed my mind.

This would be the 'cheap' solution as I don't really like cropping unless necessary. After all, if you crop your shot, you are wasting some of the surface of your sensor.

[meltimtiman]

Hi Leandro,

If you look at most of the reviews on the Tamron 28-80, it is soft at 28mm. Sharpness steps in at 35mm, F/5.6 and best at 50mm. At f/11, it appears sharp at all focal lengths. I dont how this lens behaves since I havent used any Tamron lens. So if you are shooting at 28mm, you need to have space to crop the soft edge or zoom in to at least 35mm where it gets sharp.

Best if you do some research on how this glass behaves. That way, you'll know its parameters and capabilities.

Here are a few sites about the glass
http://www.dyxum.com/reviews/lenses/...asp?IDLens=108
http://www.photographyreview.com/cat...4_3128crx.aspx

[Gingerbaker]

You have a very bad lens at that focal length and/or a very bad UV filter. Even if you used that lens wide open, the lack of acuity across the field is way too high to be acceptable. I think you just proved that you need to treat yourself to a new lens.

[leansoli]

Mel, thanks for those links.

And yeah, I am consindering selling this set and get a newer model with a better lens. Will keep those links in mind for when I decide to buy anything new!

[meltimtiman]

Leandro, just like everyone here, it is always our pleasure to help a little and give some suggestions to improve our craft. And just like in a practical shooting competition, its a combination of the shooter, the equipment, and the ammo. If one is not performing well, I wont hit my target, I delay my shot, or I jam the gun.

I borrow and test 3rd party lenses (Tamron, Tokina, Sigma) of friends everytime I needed to buy another lens but at the end of the day, I would always go for the Canon glass (since my camera is a Canon) or I wont buy at all. I also do some research on the internet how a particular glass performs and behaves. Would suggest you look at this link when the time comes you want to buy a new glass: http://www.photozone.de/ I dont know about the rest of us here but I find their evaluations, analyses, and recommendations quite independent and transparent. Just my 2 cents worth.

Regards from Manila, Philippines.

Mel

[LeoLeo]

Hi Leandro,

You may take a look here
http://www.photozone.de/canon-eos/15...report--review

On canon APSC is arround 45mm, and is not so expensive.

Leo
PS: For zoom lenses, I'm planing to get Canon EF 24-105mm f/4L IS USM, but is hurting my wallet deeply.