New member, need your opinion RE:Focus and 70-200 f/4 L

[splitslim]

Hi,

Just came across this forum, and I have to admit that it's the most wealth of information in one spot that I have ever seen. Great job!

I recently purchased a 70-200 f/4L in Croatia while on my honeymoon. I shoot with a RebelXT, and have a question regarding focus with this lens. It could be my eyes, but it seems like this lens has a terrible time focusing properly. Can someone please take a look at a few of my shots and let me know what they think? You can see which lens was used in the EXIF data.

http://splitslim.smugmug.com

The "Roko" gallery was shot with the 70-200 only. You can see what I mean on some of the closeups of my dog (Roko).

http://splitslim.smugmug.com/gallery/1776021/1/88228029

It's almost as if sometimes it's focused, but most of the time it misses the sharpness.

I shoot with Parameter 1 set when shooting LF jpegs, which these shots are. No post-pro.

I really appreciate any opinions/help guidance.

Thanks everyone!

SS

[Curtis N]

I don't really see a focus problem. Some of them lack enough depth-of-field to get the whole subject acceptably sharp.

For example in #8 of the Roko gallery, you were at 70mm and f/7.1 from a distance of maybe 3 or 4 feet. Your DOF in this situation will be maybe an inch or so in front of and behind what it's focused on. The camera focused on the tip of his nose, and the rest of his head is out of focus. It's also possible that you were closer than the lens' minimum focusing distance on this one.

The shallow DOF of long lenses can be blessing or curse.

[Jamie Holladay]

First of all Welcome to POTN
I think Curtis is correct. I did not notice an focal problems either. The only thing that you might want to consider is on #5 change to AI Servo so that you focus follows Roko. Other than that. I see no problems. They all look nice.

[splitslim]

Thank you very much for your replies. I'm still learning all the ins and outs of this DSLR world, and I'm sure I have a lot of learning experiences ahead of me.

I have to agree with you Curtis, I was about 5-6 feet away Roko when I took that shot. Do you then recommend that I stand further back while using this lens, and use the zoom if needed to frame the shot? Also, would it have helped if I was at f/4.0 from that distance?

24zero, do you feel that switching to AI Servo during any action shot is more beneficial then leaving the AF in AI Focus mode? Which technique should I use for the AF during an action shot in regards to focusing via the shutter button? Do I get the subject in focus pressing it down half way, then a full press when I see the shot, or do I just try to half press-full press as quickly as possible?

Thanks again everyone.

SS

[mrkgoo]

Thank you very much for your replies. I'm still learning all the ins and outs of this DSLR world, and I'm sure I have a lot of learning experiences ahead of me.

I have to agree with you Curtis, I was about 5-6 feet away Roko when I took that shot. Do you then recommend that I stand further back while using this lens, and use the zoom if needed to frame the shot? Also, would it have helped if I was at f/4.0 from that distance?

24zero, do you feel that switching to AI Servo during any action shot is more beneficial then leaving the AF in AI Focus mode? Which technique should I use for the AF during an action shot in regards to focusing via the shutter button? Do I get the subject in focus pressing it down half way, then a full press when I see the shot, or do I just try to half press-full press as quickly as possible?

Thanks again everyone.

SS

The depth of field (width of plane of the image that is acceptably in focus) would be the same (or change very little) if standing back and zooming in with the aim of having your subject fill the same amount of the frame. The only thing that will change significantly will be the perspective in regards to teh size of the background (on higher zooms, longer focal length), the back ground will looke more 'compressed', ie. closer to your subject. TO achieve a larger DOF, you need to narrow the aperture (f4 up to f8 or more). This means you will need to lengthen your shutterspeed to achieve the same exposure level, and consequently may require a tripod.

[Jamie Holladay]

24zero, do you feel that switching to AI Servo during any action shot is more beneficial then leaving the AF in AI Focus mode? Which technique should I use for the AF during an action shot in regards to focusing via the shutter button? Do I get the subject in focus pressing it down half way, then a full press when I see the shot, or do I just try to half press-full press as quickly as possible?

Thanks again everyone.

SS

Using AI Servo you Press the button half way down focusing on the subject and follow the subject while holding the button half way down. When you "see" the shot that is when you press the button.

You do know that on the f/4 you have a switch that changes the focal length from 1.3m to infinity or 3m to infiity right? That might help you as well in Single point focusing.

Jamie

[splitslim]

@mrkgoo, so my f/7.1 was too large for the shot that Curtis was mentioning? If I was up around f/8-f/11 I would have had a larger DOF, in turn putting more of the dog in focus during that shot?

@24zero, thank you for clarifying the AI Servo procedure, I tried to find that information in the manual, but it wasn't there. Regarding the switch on the lens, I was under the impression that when selecting 1.3m or 3m, the only real benefit would be the speed of the AF, since it wouldn't have to range between 1.3 and 3. In this instance, the switch was on 1.3m, due to the proximity of the subject. Is this correct?

I have to admit, I'm happy that the lens isn't having a focus issue, I much rather improve my skills surrounding the use of this lens, then have to worry about equipment.

If I could, I would like to ask your opinions on one more issue. If you could be so kind so take a look at my Honeymoon 2k6 - Dubrovnik, Croatia gallery

http://splitslim.smugmug.com/gallery/1776064/1/88230515

...at this shot for example;

http://splitslim.smugmug.com/photos/88230515-L-2.jpg

...what could have I done to improve that haze surrounding the old city? This shot was taken mid-day, under sub-perfect lighting conditions, with my 18-55 kit lens. I admit the ISO was too high at 800 (must have been shooting in P, but why would it select such a high ISO?), but the sky in the background looks horrible, and washed out. I wasn't familliar with using the histogram during this shot, but I have a feeling I should have stopped this shot down 1/2 or more. Would this shot have benefitted from a polarizing filter, or maybe a UV filter?

Thank you all again.

SS

[Jamie Holladay]

In this instance, the switch was on 1.3m, due to the proximity of the subject. Is this correct?

Basically. If the switch is set to 3.m then the lens ignores anything that is from 0m to 3.m and does not try to focus on that. It will focus on anything that is 3.m to infinity. With the switch set at 1.3m it will focus on an object 1.3m to infinity.

...what could have I done to improve that haze surrounding the old city? This shot was taken mid-day, under sub-perfect lighting conditions, with my 18-55 kit lens. I admit the ISO was too high at 800 (must have been shooting in P, but why would it select such a high ISO?), but the sky in the background looks horrible, and washed out. I wasn't familliar with using the histogram during this shot, but I have a feeling I should have stopped this shot down 1/2 or more. Would this shot have benefitted from a polarizing filter, or maybe a UV filter?

Thank you all again.

SS

This is a little out of my my area but I will take a stab at it. I would have taken multiple exposures. exposing the sky properly, the near objects properly and the far objects propery and then created an image in post. You are correct about the ISO, It should have been 100. You could have also tried metering you light, locking it with the "*" and then re-composing.

[mrkgoo]

@mrkgoo, so my f/7.1 was too large for the shot that Curtis was mentioning? If I was up around f/8-f/11 I would have had a larger DOF, in turn putting more of the dog in focus during that shot?

@24zero, thank you for clarifying the AI Servo procedure, I tried to find that information in the manual, but it wasn't there. Regarding the switch on the lens, I was under the impression that when selecting 1.3m or 3m, the only real benefit would be the speed of the AF, since it wouldn't have to range between 1.3 and 3. In this instance, the switch was on 1.3m, due to the proximity of the subject. Is this correct?

I have to admit, I'm happy that the lens isn't having a focus issue, I much rather improve my skills surrounding the use of this lens, then have to worry about equipment.

If I could, I would like to ask your opinions on one more issue. If you could be so kind so take a look at my Honeymoon 2k6 - Dubrovnik, Croatia gallery

http://splitslim.smugmug.com/gallery/1776064/1/88230515

...at this shot for example;

http://splitslim.smugmug.com/photos/88230515-L-2.jpg

...what could have I done to improve that haze surrounding the old city? This shot was taken mid-day, under sub-perfect lighting conditions, with my 18-55 kit lens. I admit the ISO was too high at 800 (must have been shooting in P, but why would it select such a high ISO?), but the sky in the background looks horrible, and washed out. I wasn't familliar with using the histogram during this shot, but I have a feeling I should have stopped this shot down 1/2 or more. Would this shot have benefitted from a polarizing filter, or maybe a UV filter?

Thank you all again.

SS

About your f-value (and keep in mind, I'm a newbie, so the more experinced around here are sure to know more/better), yeah that's the idea. I noticed your aperture was f7.1, so try going with a higher value to achieve greater DOF and have more in acceptable focus. The two major things to affect your DOF are distance to subject (or zoom - in that zooming in has a similar affect DOF-wise, it's like getting closer to your subject - of course, I as I said it has other differing effects on the background/compression) and aperture setting. I'm not sure how equivalent it is, but I equate closing your aperture down to 'squinting'.