August 28, 2014, 07:11:50 AM

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Messages - PhotoCat

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31
Thanks all for your help! So I went back to test the lens again just to be sure.
Lens set to f2.8 and with a subject 16 ft away in live view x10 in the centre.

It is definitely not a large DOF issue because the critical focus point is reasonably sharp on the
subject. I can easily centre the focus without a doubt.

The problem arises when I try to pull focus by turning the ring in one direction
but I passed the critical focus point a little bit then I
tried to turn the ring in the reverse direction to re-obtain critical focus.

The more I do this the more I find the distance readout (during critical focus) all over the place
from 4ft to 5ft to 6 ft to 8ft to 10ft.


i.e.
hit focus in one direction (readout 6ft) -> passed focus a little (may be half an inch rotation on the ring) -> reverse rotation ->
hit focus again in reverse direction (readout 8ft)  -> passed focus a little  -> reverse rotation -> hit focus again (readout 9ft) etc


So far, I think Logan's theory makes most sense: (also Jim)  (Many thanks!)

"sounds like backlash to me. can you rotate the focus ring without moving the lens elements, if so, by how much? a helicoid(?) and a ballscrew are basically the same thing, i wonder if you could tighten something up inside the lens to fix it, maybe machine some new pins or whatever rides in the helicoid (i know its not really a helicoid but ive seen it called that i think?)"

Yes, I can rotate the focus ring a little (about 1/4 inch on the ring) but the lens element is not changed. (verified
by live view)  This happens at the onset when I reverse the focus ring rotation after achieving critical focus.


Hysteresis is a term used in Electrical Engineering...  but the wiki explanation seems appropriate:

http://en.wikipedia.org/wiki/Hysteresis

"Hysteresis is the dependence of the output of a system not only on its current input, but also on its history of past inputs. The dependence arises because the history affects the value of an internal state. To predict its future outputs, either its internal state or its history must be known.[1] If a given input alternately increases and decreases, a typical mark of hysteresis is that the output forms a loop as in the figure."


My 1st  copy was much worst in "backlash" (much larger "play").   This makes me wonder if this is a
common problem to this lens.  Has anyone else seen this problem b4 on this lens?

32
.
Did you buy a lens to make pictures or to measure distances?

A repeatable distance readout is vy important to me for this manual focused lens. I lot of time I need to preset focus on the hyperfocal distance or on a particular distance and live view maybe too troublesome to use for every shot.
The absolute distance reading on the lens is not vy important but consistency is.

I have a workaround already, which is to "reset" the lens to infinity every time I focus but I am just
wondering if this copy is a lemon or it is a normal behaviour for this lens.

Tks Jim for pointing out backlash. Just wondering if it is normal for this lens. Tks!

33
After reading all the rave reviews on this lens, I ordered one myself from B&H.
It is indeed quite a sharp lens even close to the edge at f2.8. My copy is vy sharp on the left
edge and just a little soft on the right edge. At f2.8 on a 5D2, I am happy with it.

However, upon further inspection, I have noticed that there is a funny "hysteresis" on the manual
focus ring. Let me explain: I used live view 10x to establish critical focus on a subject about 15 feet away.
After I turned the focus ring clockwise to achieve critical focus, I noted down the distance scale reading e.g. 10ft.
With the same subject,  I turned the focus ring anti-clockwise to achieve critical focus once again. The distance scale reading is now 4ft! 
I would have expected the distance scale reading to be the same whether I turned the focus ring clockwise or anticlockwise but I was wrong!

Well, that was my first copy of the Rokinon 14mm! B&H was great to give me an exchange.

After more than 2 weeks, I finally got my replacement and I tested the focus ring once again.
It is much better than the 1st lens but there is still some hysteresis on the focus ring.
e.g. anticlockwise to read 10ft and clockwise to read 7ft.

I have also noticed that the reading would become more consistent if I first turn it all the way to infinity and than
turn it clockwise only to achieve critical focus.  However, if I passed the critical focusing point and tried to turn the ring anticlockwise to back track the focus, this hysteresis effect is noticeable again.

So my question is: should I send it back again or live with it?  Is it normal for this Rokinon 14mm lens?
Anyone has similar experience to share?

Any help would be appreciated!

34
EOS Bodies / Re: What do you hope-for MOST from Canon in 2014
« on: July 01, 2014, 05:25:40 PM »
No question a EF 85 1.4 IS   :)

but I will settle for a EF 85 2.0 IS...

35
EOS Bodies / Re: New Sensor Tech in EOS 7D Mark II [CR2]
« on: June 19, 2014, 09:56:46 AM »
I would be happy if this new sensor addresses the shadow noise problem at low ISO settings like 100 & 160.

36
Wow, I want this camera! This is what I need to shoot my cat catching mice!  :)

37
Lenses / Re: 100mm L not for portraits?
« on: January 29, 2014, 10:24:10 AM »
In the old days, manual focus lenses had DOF markings for different apertures, nice and useful.

In the olden days, some Canon bodies even had a helper mode "adepth" for this - af at spot one, af at spot two & it calculates the required f-stop... alas, newer cameras have you-dont-wanna-know how many creative zone programs, but this has been lost along the way.

mm... new magic lantern feature request?  :)

38
Booyah Yahoo Yippee Hooray Awesome FINALLY ABOUT TIME!!!!!!!!!!!!!!!!!!!!

God I've wanted a sharp wide-open, auto-focusing 50mm 1.4 that isn't over $1k for sooo long.

My copy of the Canon 50 1.4 is sharp in the centre wide-open and I used to believe it wasn't based on many reviews on the web. I went thought 3-4 copies b4 I found a sharp one with my 5d2! I think 50/1.4's bad reputation is mostly focusing related. One can easily test its real optical sharpness under live-view with manual focusing.


39
Testing if YN 600EX-RT Transmitter would work with a 5DMKII on HSS at 1/8000S  is a bonus too. Thanks!

40
OK, I managed to mug a homeless man sleeping in a dumpster and removed from his person a scratched up Windows XP installation disk.  Knowing that I must have been close, I searched his adjacent shopping cart and found an ancient piece of crap Windows XP thinkpad hidden under some flea-infested blankets and a tattered copy of Atlas Shrugged by Ayn Rand that he seems to have used as toilet paper.  I then tried to leave him a license for six months of Adobe Creative Cloud in recompense, but he looked more insulted than he did after I mugged him.

Updater ran just fine on it.

Is there anything in particular that anyone would like me to try out with it?  I have a 5D3 and a 600EX-RT.

Well done pedant!

Please try Radio High Speed Syn at 1/8000S and see if this combo can overpower the sun LOL! Pls try it at full power and also in eTTL.  Thanks!

41
Software & Accessories / Re: My DIY " Muti-Flashes portable rig"
« on: October 22, 2013, 10:12:39 AM »
Awesome! Love to see more out of the box DIY ideas like this! Keep it up Surapon! Thanks for sharing!

42
Hello all,

Can u store more than 3 user defined picture styles in 5D mk ii?
Read from Magic Lantern forum somewhere that this is not possible/dangerous for now.
Any workaround other than carrying a laptop to upload the picture style files to camera?
I suppose I can do it in post with raw capture but if I can get the effect I want in jpg, I save a lot of
post processing time :)
PS: I shoot raw+jpg all the time.
Thanks! John

43
This is a followup to my initial posting.
So I got another brand new 600-ex-rt and tested it again versus my old 580exii.
Same problem... i.e. 600 recycles slightly faster with freshly charged batteries.
This seemed good at the beginning but when I repeated the test with batteries charged 2 days ago,
the 580exii became slightly faster.

This is a bit puzzling so I checked out the spec of the eneloop AA battery. It said 0.025ohms for internal resistance.
Then I tested my 2-3 years old eneloop AA's; surely enough, they have degraded to a range of 0.080-0.120ohms.

Ah... my eneloop AA batteries are old and have higher internal resistance!

So this seems to be telling me that for recycling time alone, the 600ex-rt works well with batteries with low internal resistance but
it doesn't work so well compared to the 580ex-ii with older batteries with increased internal resistance.

Is anyone seeing the same thing?  I start questioning if 600ex-rt beats 580exii hands down in all categories.

44
Unfortunately I have to open up this thread again.

I finally discovered that my 600 is vy voltage sensitive with regard to recycling time.
Freshly charged Eneloop AA batteries give a recycling time of 2.4S and it beats my 580exii.
However, when I use eneloops
charged just 2 days ago gives > 3.2S and it is worse than my 580exii (2.8S), using the same 4 cells.

Also Click mentioned he achieved 2.5S with partly used eneloops!

I think this is unacceptable and I am going to exchange my 600ex-rt.

Thank you all for your help! John

45
Those numbers are for each of my three lights fired in ETTL at a piece of paper on the wall, with white balance drawn from the white panel on my WhiBal card using the tool in LR5; I should have specified.  If you want I can try each of them at different power settings.

Jim

oic... thanks Jim for all the help! I think I have a bigger problem than that now...
My 600 is vy voltage sensitive with regard to recycling time.
Freshly charged Eneloop AA batteries give a recycling time of 2.4S when an eneloop
charged just 2 days ago gives > 3.2S!  I think this is unacceptable and I am going to exchange my 600ex-rt.
Probably the color temp thing is related.

Thanks all for helping out! John

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