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Messages - neuroanatomist

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7306
Lenses / Re: 600mm lens - tripod
« on: April 19, 2013, 06:58:10 PM »
The 4 section one I believe is a little smaller for portability.  That was the only reason but I may have to rethink.

I considered that, in looking at the RRS TVC-33 vs. the -34L.  While the 4-section is 1.5" shorter, I decided that 1.5" wasn't enough - 25.5" (TVC-34L + leveling base) was still too long to be 'portable'.  I did get a RRS TQC-14 + BH-30 as a travel tripod (it can still hold my 600 II), with the head on it's 20.5" long and when in its quiver bag, the whole thing still fits inside my Pelican Storm im2500 carry-on hard case - that's my definition of 'portable'.  The TVC-33S would still not be quite short enough, and would have me hunching over during use (I'm 5'7"), whereas the -33 gives me a few inches extra for use on a slope.

7307
Lenses / Re: 24-105 &/or 24-70
« on: April 19, 2013, 02:08:46 PM »
Interesting, Ive always heard it sucked at 24.
Has a lot of distortion at 24, but it gets softer at the long end. Different kinds of flaws.

Yep...and while you can correct for distortion at the cost of some loss of corner sharpness, you can't correct for lost detail.

7308
Third Party Manufacturers / Re: FoCal or LensAlign - Which is better?
« on: April 19, 2013, 01:32:14 PM »
I'm just getting into AFMA, we're referring to Reikan FoCal correct?

http://www.reikan.co.uk/focalweb/

Correct.

7309
So $9000 worth of gear means you're able to take good night shots...go figure...#sarcasm

I can take good pics of small birds with >$20,000 worth of gear.  :P

7310

As for the execution of AFMA, nothing physical is shifted in the camera. It's an electronic correction factor - if the AF system would prompt the lens to move the focus elements a distance of x, the AFMA value modifies that command to x+n.
If its only an electronic correction, couldn't the manufacturers make some software that's kinda "idiot proof" for people like me who find AFMA a bit too tedious and complex? e.g. I shoot some text using the center focus point, with the camera connected to a computer and the software analyses if Af is accurate or not and makes AF adjustments accordingly? ... does that make sense?

Camera manufacturers could, but they haven't. Reikan did, it's called FoCal.  Worth every penny (or pence, in this case).

7311
Lenses / Re: New Sigma 18-35: What does f/2.7 DOF equivalent mean?
« on: April 19, 2013, 12:13:47 PM »
Yes. For equivalent framing, you're further away on APS-C meaning the DoF is deeper.  Basically, the 'crop factor' applies to DoF, too.

7312
Lenses / Re: 24-105 &/or 24-70
« on: April 19, 2013, 12:12:18 PM »
I have both, may sell the 24-105L.  I suspect that a 'walkaround' shot from the 24-70 II at 70mm cropped would equal or beat the IQ of the 24-105 at 105mm (which is where the lens is weakest). 

Actually, the utility I can see for the 24-105 is for portraits in a studio-type setting.  While a 70mm image can be cropped, the perspective is not going to be the same as a shot at 105mm.  The shot at 105mm will be a much more appropriate perspective for a tight portrait.  In a studio setting, there's plenty of light and the background is controlled - so f/4 is fine.

7313
Third Party Manufacturers / Re: FoCal or LensAlign - Which is better?
« on: April 19, 2013, 10:15:04 AM »
FoCal over LensAlign, IMO.  After using FoCal for a few months, I sold my LensAlign Pro.

I've not tried FocusTune, but FoCal has been around longer and is likely more refined (plus the Pro version offers many other tests).

7314
Canon General / Re: Why I don't like DxO Mark Scores
« on: April 19, 2013, 08:30:31 AM »

7315
The OP's point seems to be that if the fundamental problem corrected by AFMA is one in the camera body, the lens shouldn't matter.  While I offered a couple of possible reasons the lens does matter, whether or not those reasons are correct, it's an empirical fact that the lens does matter.  Different lenses (including different copies of the same type of lens) require different AFMA values to achieve optimal focus, zoom lenses require different AFMA values at different points in the zoom range to achieve optimal focus.  In fact, subject distance - something not determined by camera or lens - also affects the needed AFMA value.

As for the execution of AFMA, nothing physical is shifted in the camera. It's an electronic correction factor - if the AF system would prompt the lens to move the focus elements a distance of x, the AFMA value modifies that command to x+n.

7316
I believe the lens plays a role - I'm not sure it's really a closed loop with the AF sensor. Roger Cicala's data showing more accurate focusing with the more recent lenses/bodies was supported by the finding of rotational encoders on the USM lens motors.  So, with older lenses (pre-2000) we had a basically open loop where the AF sensor determined magnitude and direction of the move and that was transmitted to the lens (look-move) - if the motor moved a ratio slightly off 1:1 from the instructions, AFMA would compensate.  The newer lenses+bodies apparently have a closed loop where the encoder reports movement (look-move-confirm).  But there may be tolerances in the encoder (e.g. detecting movement as other than a 1:1 ratio) for which AFMA could correct.  I'm not positive the loop is closed with the AF sensor, i.e., look-move-confirm-look.

Certainly, a misalignment of the AF sensor with the image sensor is one factor that AFMA corrects.  I can personally attest to that - at one point, I dropped my 5DII to the pavement.  :o  The camera was perfectly functional, but the sensor alignment changed such that all of my AFMA values (for ~8 lenses) shifted 10 units negative relative to the initial values.

7317
Lenses / Re: 600mm lens - tripod
« on: April 18, 2013, 10:20:05 PM »
That's a 'classic' setup for a supertele lens, will work fine.  You might consider a leveling base, which means less fussing with the legs to get the platform level (not needed for a ballhead outside of shooting panos, but better for tracking with a gimbal). 

Personally, for my 600 II, I went with the Really Right Stuff TVC-33, PG-02 LLR gimbal, and the leveling base (with clamp, so I can easily swap on my BH-55 ballhead).  I also replaced the Canon foot on the lens with the RRS LCF-53.

7318
EOS Bodies / Re: 21mp Sensor in the 7D Mark II? [CR1]
« on: April 18, 2013, 08:00:31 PM »
18 MP. 21 MP. 24 MP. Even 15 MP.  Frankly, I don't especially care.  If it does a full stop or more better in terms of high ISO noise performance for RAW images vs. the 7D, a 7DII will be interesting to me. If not, no interest.

7319
Lenses / Re: Why aren't zoom lenses faster than 2.8?
« on: April 18, 2013, 06:04:49 PM »
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

7320
That setup will work very well for single-row panos. You'd need something more elaborate (and RRS has them) for multi-row panos.

For a tripod, I'd go with the Versa 2 series, but 23 vs. 24 vs. 24L will depend on your height and your needs for travel (4 sections means shorter collapsed length).

For the head, you might also consider the Acratech GP - it functions as a standard ballhead, but it's designed so that it can also be used upside down to function as a panning base. 

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