September 20, 2014, 04:18:22 PM

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Messages - PhotoCat

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EOS Bodies - For Stills / Re: Quick and Dirty AFMA
« on: August 09, 2014, 10:23:45 PM »
or use Magic Lantern Dot-Tune AFMA  8). I have had excellent & repeatable results

You've had better success than me, I found dot tune to be somewhat unreliable.

I also thought dot-tune had reliability issues for some lenses I have, as it kept hunting left and right (increasing)
for the AFMA value.  I finally discovered that one must enter an initial value of AFMA for the lens in question.
Just give it a value like +2. After that, dot-tune behaved itself very well and always converged on a repeatable value +/- 1.  Body was 5D2.

I found it critical that the initial live view manual focusing be as precise as possible using 10x digital magnification. Otherwise dot-tune may not converge.

EOS Bodies - For Stills / Re: Quick and Dirty AFMA
« on: August 09, 2014, 07:02:59 PM »
the end result is the same as u would do it all by hand.
The advantage is that dot-tune will give u the AFMA number much much faster and repeatable in an almost
automated way. Credit goes to Horshack for his algorithm and A1ex's of Magic Lantern for the implementation.

EOS Bodies - For Stills / Re: Quick and Dirty AFMA
« on: August 09, 2014, 06:43:03 PM »
or use Magic Lantern Dot-Tune AFMA  8). I have had excellent & repeatable results.
In all fairness, Dot-Tune also relies on how accurately the focus is set during live view.
Just google it.

EOS Bodies - For Stills / Re: D810 vs. 3D
« on: August 02, 2014, 03:00:25 PM »

If you want to address Canon, it is better you contact Canon directly instead of using this forum.

Well, I think the OP just wanted to rant and pls just let him. It will be therapeutic for him whether or not
Canon is listening. In the end, there is no sure way to influence Canon's product roadmap anyway.

Lenses / Re: New Canon L Primes, but Not Until 2015 [CR2)
« on: July 29, 2014, 12:38:05 PM »

I hope the non-L 85/2.0 IS is still coming this year!  ::)

I'll take one of those too!

An 85 IS sounds great, but I really hope it's faster than f/2!

A 135 IS would be interesting too.

An 85 f2.0 IS in hand is worth two 85 f1.4 IS in 2015 LOL!

Lenses / Re: New Canon L Primes, but Not Until 2015 [CR2)
« on: July 28, 2014, 09:51:28 PM »
I hope the non-L 85/2.0 IS is still coming this year!  ::)

Lenses / Re: What Lenses are missing from Canon's range
« on: July 19, 2014, 08:58:20 AM »
85 f1.4, 85 f2.0 IS, 135 f2.0 IS,  EF 50- 135 f2.8 portrait zoom.

Software & Accessories / Re: To filter or not to filter
« on: July 14, 2014, 06:52:02 PM »
I use UV or 1A or 1B filters all the time when I am shooting casually.
But when I am really serious about image quality under backlit situation, e.g. a wedding, I would
take all filters off b4 I shoot. Same for studio shoots with hair lights on or brightly lit background.
Really cut down on flare. Whenever filters are off my lens, I use a lens hood to protect it.

if the OP wants to complain that he can wants MORE mp, let him.
nikon has better DR and more MP.
you can't argue with that.

U r right! I praised the Canon for jpg skin tone but I failed to point out that my friend's
D800E model pics are consistently sharper than mine  :(   He could turn a full length shot
into a head and shoulder shot without any problems when blown up to 100% view on a 25 inch monitor!
Well, I just have to walk closer and do a real head and shoulder shot!

Not only did u leave your loyal wife but u have also chosen to depart from your kind mom-in-law who
cooks for your every morning, washes & irons your clothes everyday and does all kinds of
house chores for u, without making any complaints.

Magic Lantern I mean! 

I am sorry, from now on, u will have to do all kinds of house chores yourself, as your new love D800E
is an orphan and she doesn't know how to do even basic house chores like boiling water LOL!

Excellent reply unfocused!! It would be hard to believe u r not a woman LOL!
Truth be told, as far as skin tone (out of in-camera jpg) is concerned,
I have not seen a Nikon to be able to match my old 5D2 :)

When my friend with a D800E shoots models side by side with me, the models have
always preferred the 5D2 jpg on the back of the camera!

I think Canon definitely has a successful secret formula on in-camera jpg rendering.
To me, it is even more obvious in high ISO skin tone rendering.

However, I must admit that with proper RAW processing & skill, Nikon's skin tone can match
Canon but that is a lot of extra work. I would rather get it right in camera.

I have one of these lenses.
The focusing ring is very smooth and there is no backlash.  I think you would feel backlash when twisting the focus ring back and forth.
It is true that there is variability with the position of the distance scale in relation to the actual focus.  My first lens was about 1cm off along the distance scale.  The focus ring seized and I got a new one under warranty - this one is spot on.

Tks Frodo for the info. Good to know there r good copies out of the box...

if it is plain backlash, you should be able to get repeatablility by always coming at it from the same way. the focus scale may line up better one way than the other, if so, use that direction. does that make sense?

Yes, it makes perfect sense. Good point. Thanks again Logan for the tips! I will try that. As I had mentioned b4, the distance readout is much more
consistent if I first "reset" the lens to infinity and then turn it clockwise only. So I have to try again by resetting the lens for the other end (short end) of the scale and then turn it counter-clockwise only. 
Compare the 2 and see which one gives me a better reading and consistency.

if you focus from 9' then 10', and it is actually 10', then always focus short first before using the focus scale.

I found that I can't just go from 9' to 10' to obtain more consistency. I had to go all the way to 0.28m first (the min focus distance)  and then turn it anticlockwise only, in order to obtain better focusing consistency.  It is more work starting from 0.28m then from infinity because of the large rotation distance of the ring at short distances.

Well, this workaround works for now but I am not so sure if it will work in a year's time because some screws
might get more lose.  Just don't know...    Same question again: should I exchange it or should I live with it??

Thanks again for everyone who has contributed!

Will this help ??

Wow! Thanks a lot Sama! This is vy informative. This fix is less intrusive than other fixes I have
seen on youtube. (open up the lens and add a shim etc)

If I had an old or 2nd hand lens, I would do this right away for sure.
But this is a brand new lens... and I have a chance to exchange another one too...

So my question is:  Do all brand new Rokinon/Samyang 14mm lenses have this problem?
If so, I will live with it for now and fix it later when I feel more comfortable messing with it.

If not, (i.e. there are many "good copies" out there directly out of the box), I would try to
exchange it once again and hope for good luck.

What do u think I should do?  Live with it and fix it later?  Or roll the dice and try another exchange,
hoping for a good copy?  Anyone has a good copy right out of the box?

I am so surprised that this lens is so poorly calibrated, yet the optical quality is not bad at all...
My 2nd copy is vy sharp on the left edge & centre but a little soft on the right edge about 10% of the frame.
Not bad for a $350ish lens!

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.

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:

"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?

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