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[Largo]

AF points and DOF.

Last night I picked up a 50mm f/1.8. A surprisingly sweet lens for the money.

My question, when I shoot wide open for a shallower depth of field, can the AF points effect that? In other words if I am going for only the face to be in focus, but the AF points are focusing on more than just the face will those points also be in focus, despite shooting wide open and blow my shallow DOF? I know I can use just the center AF point only, but I'm just curious about it. And will fool around with it today. I hope this is not a stupid question. I've been playing around with my AF points to improve my focus and play with DOF on my Sigma 70-300mm that only opens up to f/4.

Also, while we're on the topic of DOF. Tell me if I'm thinking correctly. In an unchanging light situtation say in a studio. I can use a range of settings that will let in the same of amount of light for the exposure I'm after, while giving me varying depth of field options yes/no? Also I know that physical distance and lens focal length have an effect on depth of field as well.

 

[GAD]

Congrats on the 50! I have the 50mm f/1.4 and it's one of my favorites. The 50 f/1.8 is the best darn value Canon has in a lens.

Re: The focus points. I'd say it probably depends on the camera, but on my cameras, if two spots light, then those spots are in the same focus plane and will be in focus. My cameras have 45 focus points though, so they have a lot more granularity than the Rebel or 20D.

Now if your camera is lighting multiple points that are not in the focal plane of the lens at the aperture you're set at, I'd say there's something wrong. I'm interested to see what your tests come up with.

Oh and I hereby decree that there are no stupid questions in this forum.

I shoot probably 60% of all my shots with the center-point-only. When shooting with a 1.8 aperture, the DOF is pretty small. The longer the lens the smaller it is of course. Imagine the 85mm f/1.2L or 135mm f/2L! I've taken shots where only the pupil is in focus! It's cool if that's what you want, but I have shots from the wedding today where the bride is in focus and the groom is not. Depending on who paid that could be a problem!

With a 1.8 lens, there's no such thing as "good enough" when focusing!

As for the last question, we need to clarify a bit. In a studio, *using flash*, then yes - you can use the aperture to alter depth of field because the flash is so fast that shutter speed has no effect on exposure. Without flash though, your aperture is tied to your shutter speed as usual.

This was one of the hardest things for me to grasp, but it's why most cameras sync to 1/60th when the flash is on - it pretty much doesn't matter.

Back to your question - in "normal" situations (no flash), where the light is constant, I would use aperture priority (Av in Canon-ese) and let the camera figure out what the shutter should be. I do this a lot when I want a certain effect, or want to make sure a broad range is in focus.

As an example of how the shutter doesn't matter, I shot the entire wedding today at 1/60th, f/8 with the flash. I had knocked the setting (which you're not supposed to be able to do on my camera - grr) and all the formals were at 1/40th f/7.6. I noticed after the formals (Check your settings often!), and to say the least I was horrified that they were all bad. They're all fine because the aperture was still good!

Sorry if I'm rambling. I'm beat.

GAD

 

[Largo]

Yes! I've learned that lesson about checking your settings. Luckily the pics were only important to me. Thank goodness your photos are all fine. What a scare! I've also hiked quite aways from the van with no CF cards!

Wasn't thinking about the flash. That makes sense. I've got some experimenting to do when I set up my studio. I've been looking at equipment. I have some specks on building your own ring light, I'm excited about that.

As for my camera. Something maybe wrong. I'm going to go over my manual tonight. Sometimes it will focus on the points I choose and sometimes all the AF points will flash when I set the focus reguardless of what AF points I've choosen. Could be that I am doing something wrong. I've got one pic where I set the middle AF point and only Bartlett's nose was in focus like I wanted. Then I snapped another shot, again selecting only the middle AF point and his whole face was in focus. Nothing changed./???

Yeah, I'm really liking the 50 f/1.8. Actually bought it on the fly. My next purchase will be the 85 f/1.8 and either the 70-200 f/2.8L or the 135 f/2L to follow. I haven't quite decided between those two. And still shooting for the 85 f/1.2 ahhhh goose bumps!

What do you think of the tilt lenses? I'm thinking they might make for some cool and crazy portraits, especialy animal.

By the way, I'm trying out a new B&W conversion, its suppose to really perserve the tones. I'll post some shots when I'm done, let me know what you think ok.

Thanks

 

[GAD]

"I've also hiked quite aways from the van with no CF cards!"

Heh - only time that's ever happened to me was this last Christmas. Always have a backup.

I ended up shooting the entire night with my S-80

Studio huh? What are you looking at for lights? I'm jealous - I wish I had the room.

"I've got one pic where I set the middle AF point and only Bartlett's nose was in focus like I wanted. Then I snapped another shot, again selecting only the middle AF point and his whole face was in focus. Nothing changed./???"

In order for the DOF to change, the aperture had to change. Check the EXIF in the pics and see if it did. What mode were you in?

"Yeah, I'm really liking the 50 f/1.8. Actually bought it on the fly. My next purchase will be the 85 f/1.8 and either the 70-200 f/2.8L or the 135 f/2L to follow. I haven't quite decided between those two. And still shooting for the 85 f/1.2 ahhhh goose bumps!"

I have the 70-200 f/2.8L and the 135 f/2L. By far the 135 is more fun because of the absolutely beautiful images it produces. Of course by far the 70-200 is more useful.

The 70-200 takes magnificent images in the hands of someone strong enough to hod it up.

The 135 produces magical shots though.

I just got the 85mm f/1.2L for the wedding I did. Good fun, but I got into troule because I thought it was magic.

The "you can hand hold to the recirocal of the focal length" rule still applies, and you can not, in fact, hold an 85mm lens at 1/15th and get sharp shots even if it is at f/1.2.

Lesson learned - again.

The DOF is SO thin at f/1.2 that it's trouble if you're not prepared. I have a quite a few shots where the bride's face is in focus but the groom's is not. Ah well. That's why I carried two cameras.

BTW if you're interested, the Quantum T5D was a miracle machine. Expensive, but a phenominal flash.

GAD

 

[Largo]

The 85mm f/1.2L and the 135mm f/2L are in a class all their own aren't they. Sweet. Lucky you.

I shot in Av mode. The Exif info was the same. Its got to be something I'm doing wrong when I'm selecting the AF points.

LOL Yes Studio! I am excited! I actually will have two rooms to choose from. Either the spare bedroom upstairs (the step son is moving out), or the dinning room thats not used for a dinning room or anything else but my computer desk.

Haven't decided on exactly what lights I will start with. But will probably start with the Ailen Bees line of equipment until I learn what I'm doing and whats important to me. I will definately go homemade on somethings too.

Never heard of the Quantum T5D, thank you.

 

[GAD]

"I shot in Av mode. The Exif info was the same. Its got to be something I'm doing wrong when I'm selecting the AF points. "

Earlier you said that the nose was in focus in one and the whole face was in the other. Assuming the same orientation, physics wins and the DOF didn't change... something isn't right somewhere. If you want to post or email the examples maybe we could figure it out together.

If you have Canon EOS Viewer, it can show you what the focus spots were when the picture was taken, but I've heard rumblings that it can't always be trusted (always good for me, but I don't use it much).

I've been "this close" to getting a set of Alien Bees of White lightnings forever, but I don't have the room. I got two Quantum T5Ds for the wedding, so I may play with them. They're nice and small and super portable. They don't have real modeling lights though, which is the only real disadbantage to me so far. They do strobe for a few seconds at 60Hz to act like modeling lights, but it's not the same.

The Quantum: http://www.qtm.com/QFlash/?res_set=yes&res=1280&resh=1024

GAD

 

[Largo]

Something is definately screwy somewhere. I'm going over my manual and I will take some more shots tomorrow and post them if I can't figure it out. I'll look for the EOS Viewer thank you.

 

[Largo]

Gad I sent you an email.