DOF question regarding f2.8 vs. f4.

[canonshooter]

I am just thinking of blurred background with surperior subject IQ and I now shoot a 5DMkIII.  I realize two other factors beyond aperture affect DOF so lets assume:

1. Focal length of 70mm
2. Distance to main subject 8-10 feet.

I am asking because I am considering returning my 24-70mm f2.8  MkII for the new f/4 version with IS.  I have had the f/2.8 for about 10 days and I can't control camera shake consistently with anything below 1/100 of a second.  I rented the Tamron version with VC to compare with the Canon.  The VC worked fair, but to consistently get sharp images I needed 1/60 sec plus.  Just not equal to the Canon H-IS.

I am spoiled with my 70-200mm f/2.8 MkII with IS and I can handhold this lens at 1/30 sec with great results.  Before anyone starts suggesting that I practice or change my technique, consider I am 65 and not that steady of hand.

Thanks for your help, I look forward to your replies.

[canonshooter]

Thanks ScottyP, I didn't understand or agree with Sasen's post either.  Your points are more aligned with my understanding.  So your response leads me to a follow-up question.  Do you think the image quality of the f/4 (with IS) can come close to the 24-70 f/2.8 II?  And if the only thing I am giving up is one f/stop in DOF and light, I am thinking I should go for it for the benefit of IS.  I can always boost ISO on the 5DMkIII to make up for the one stop loss in light (f/2.8 vs f/4).

Thanks again for your help and Merry Christmas.

[ScottyP]

(Kudos to you, B/T/W)  All is speculation of course, but I do know that back before the new 70-200 f/2.8 IS MK 2 came out, it was common sentiment that the f/4 version of 70-200 was sharper than all the f/2.8 versions (both IS and non-IS). 

So presumably a NEW version of the f/4 24-70 might be better than or at least as good as the new f/2.8 24-70. 

Don't know if you can extrapolate anything from that bag of apples and oranges!

If you were to buy used lenses (Craigslist, Photography On The Net, etc.,) you can usually buy a lens, use it indefinitely, then sell it for what you paid (or more?).  I have not done this yet (lazy) but if you did, you might literally have nothing to lose and perhaps something to gain.

With my new FF camera (compared to my crop), I find that a lot of the time I have no desire whatsoever to use aperture wider than f/4.  Too much of the photo is going to be OOF for many shots, and it is more easy to just miss focus completely.   Plus just like you said, the much-improved IQ at high ISO means you can just jump up a stop or 2 or 3 on ISO.

If you go ahead and grab yourself a  Canon 85mm f/1.8 with your savings ($385.00), you retain the option for super-shallow DOF, plus the sharpness and lightness of a prime.  That way you have that capability for very little $$, and yet your walk-around zoom can have IS.

Just my impression, though.  Happy New Year!

[Samsen]

Scotty: Sorry not to escalate an unnecessary war of words that has no benefit for any one but  I could not pass without answering to your statements.

 I am not sure what you mean when you say "IS is invented to compensate for a higher (wider) F number". First of all, a wider aperture is a LOWER F-number, not a higher one. Secondly, I am not sure I understand the point.

The reason that you don't understand is that you don't pay attention or look deep.

Its plain English:

  ap·er·true

/ˈapərˌCHər/

Noun An opening, hole, or gap. A space through which light passes in an optical or photographic instrument, esp. the variable opening by which light enters a camera.

Synonyms opening - hole - orifice - gap - vent - mouth - slot

Now take the word "Aperture" and replace it by Hole.

wider HOLE is a LOWER F-number, not a higher one

Really?!! Is that what you try to tell me and others agree with you. May be The Kudos is to be taken back:)

Please pay attention to what you read and do not Assume...

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Canon claims 4 stops of benefit on its newer IS lenses. The older systems claimed 3 stops but usually provided about 2 stops of benefit. That is more than the 1 to 1.5 stops you cite

Do you only read reviews or actually shoot with the IS lenses too. I only talk of my own hand on experience and firmly believe in what I say as I have learned through experience and not what others say.

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but one does not always WANT a super-narrow DOF

You seem not get it at all. If you have a lens that has wider F (Lower number F), then only you can get a bokeh by choosing that wide hole/aperture, whenever needed. Say F2.8 of first lens. If the second lens has F4 as largest hole, then you CAN NOT get the bokeh. What bokeh is and how DOF is to be handled is a totally different issue that a knowledgeable photographer knows. The second lens simply CAN NOT provide that bokeh because it doesn't have F2.8

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IS is a useful tool for a walk-around lens as much as for telephoto.

Absolutely wrong. Again you rely on what you read and I talk of my own experience.

You simply DO NOT NEED IS for an Ultra Wide angle lens.

If any one tells you the opposite, they want something out of your wallet supported by your lack of understanding.

Let go to extreme of the example:

I can take raser sharp night image with my 11 or 10mm focal lenght lens, handheld  when shutter speed is 1 second.

Same Me, with same breath holding techinque and muscular capabily can not take any sharp image with a 500mm lens when speed is 1/50 even 1/100 sec.

IS is meant to use with tele lenses. As it became popular, its been added to any focal lenght lens just because some ignorant shopper who donot understand physics and at the same time are featureholic simply buy them.

Peace! and Happy New Year to All.

[canonshooter]

Samsen, Both ScottyP and I have a dictionary, an understanding of photography and a nice exchange of ideas.  What we don't need is your intrusion, go away please and thank you.

[ScottyP]

While he has his dictionary out, he should brush up on his spelling.  His shortcomings in that area give an unintended ironic quality to his writing when he is calling people things like "ignorant."