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02-16-2011, 09:26 PM   #631
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That is an interesting formula...and if I had a K5 I would perhaps try it, although I am poor at math in the worst of ways. I do however understand Cats.....like those posted on this page...and old as I am, my eyes are still/ 20/20.

BTW-Al informed me that is not a cat, but a wolf...he said his snout "fell off".....Interesting...I guess I know wolves too!
Regards

02-16-2011, 09:40 PM - 1 Like   #632
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QuoteOriginally posted by qtopplings Quote
Rupert, no one is trying to convince you that a faulty camera is acceptable
Well, I won't say "no one". I've been following this thread a little bit, although you aren't, there a few people that's been questioning if the prosumers are expecting too much; or saying no camera is perfect; or saying no manufacturing process is perfect.

While it's too much to expect a perfect camera, it's not too much to expect a camera to perform to specifications or at least the same or better than old camera models.

I was happy to hear the news a while back that there’s going to be a firmware fix in 2 weeks, but judging from proper working focus on some cameras, I think it might be a hardware problem (unless the working focus is cause by a not 100% functioning focus system to detect light temperature or whatever that + does). If it’s hardware issue, the only thing the firmware is going to do is workaround the problem, which can be very kludgy.
02-16-2011, 10:06 PM   #633
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Looking at some of the recent posts, I think it is best we all take a step back and cool our heels.
Both sides of the discussion have the right to put their views.
Without any sarcastic comments.
I have been involved in the discussion as well.
But there is no need for some of the remarks made at members of a different view.
Address the issue in an orderly fashion, but don't attack those that disagree.

Thanks.
02-16-2011, 10:24 PM   #634
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I find the "ignore" function on this forum really useful - I have one person currently in my ignore list, and there's 1-2 candidates that I may add in the future as well.

I like to read different opinions, and I have learnt a lot from reading many posts. But I find it difficult to read some people's posts - so it's best if they are hidden from me.

02-16-2011, 10:49 PM   #635
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QuoteOriginally posted by Christine Tham Quote
I find the "ignore" function on this forum really useful - I have one person currently in my ignore list, and there's 1-2 candidates that I may add in the future as well.

I like to read different opinions, and I have learnt a lot from reading many posts. But I find it difficult to read some people's posts - so it's best if they are hidden from me.
doesn't it put the later posts out of context for you. if they are referring to members that you have ignored ?....
02-16-2011, 10:54 PM   #636
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QuoteOriginally posted by Tommot1965 Quote
doesn't it put the later posts out of context for you. if they are referring to members that you have ignored ?....
Not really. I haven't seen replies to this person's posts. Maybe he's on their ignore list too?

Hint: the person is not Rupert. Rupert may be a One Note Johnny, but as far as I can tell he is a *polite* One Note Johnny
02-16-2011, 11:14 PM   #637
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QuoteOriginally posted by Christine Tham Quote
Not really. I haven't seen replies to this person's posts. Maybe he's on their ignore list too?

Hint: the person is not Rupert. Rupert may be a One Note Johnny, but as far as I can tell he is a *polite* One Note Johnny
at least I know its not me that on your list...

The ignore list is good advice though, I may look at that option to..it will certainly keep me out of hot water with the Mods...I got two forum infringements last week
02-17-2011, 12:09 AM   #638
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QuoteOriginally posted by mtngal Quote
... If someone could tell me what EV a picture would be that was taken with f5.6, a shutter speed of 1/25, and Ev of -.3 and an ISO of 16,000 (2.5 something, like 2.59278175)
...
The formula looks good and plugging those in it gives me the same 2.29278175. Be sure to check f=1 t=1s ISO 100, should give you EV 0 (and match with how things are defined).

02-17-2011, 02:38 AM   #639
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Calculating EV

QuoteOriginally posted by mtngal Quote
I think I've come up with an excel "spreadsheet", actually a form, where you can plug in any aperture, any shutter speed and any ISO and it will give you the EV for the picture. At least, I think it works - Excel's format for logarithms is different than how you usually see it written. If someone could tell me what EV a picture would be that was taken with f5.6, a shutter speed of 1/25, and Ev of -.3 and an ISO of 16,000 (2.5 something, like 2.59278175) I could verify if I have the formula working right. My days of doing math like this are long gone (and I never went all that much beyond this even when I was in school too many years ago).

I've been wondering about this whole issue and if what I sometimes see is the low-light front focus or just a lens that isn't adjusted right (I've been struggling with that and what's possibly a faulty lens issue also). And I've taken pictures with other lenses, in what I consider low light where I haven't had the issue so I wanted something where I could just put in all the figures, rather than trying to figure out from a chart and trying to compute how many stops different ISO (fill in the blank) was from ISO 100.

If someone can verify whether my example is correct, I'd appreciate it. By the way, the picture in my example was, in fact, front focused. But it was also taken with one of my problem lenses so at this point I'm not convinced either way. If I know my formula is correct, I'll be able to figure out if the ones that are not front focused are really low enough light or if I have simply a lens problem.

If anyone is interested, the formula I am working with is: =LOG(((Av*Av)/Tv),2)-LOG((ISO/100),2)-Ev . Excel's format for logs is to put the number then a comma and then the base, so I would assume that would be an appropriate formula for log2(aperture squared/shutter speed)-log2(ISO/100)-Ev. That is, assuming I managed to understand the formula for EV correctly, as I said, my math skills are very, very rusty.
It's been done by "blende8" in a thread called https://www.pentaxforums.com/forums/pentax-dslr-discussion/131738-calculating...ure-value.html. A link is below for the file.

Formula used is "=((2*LOG10(C2)-LOG10(1/C3))-LOG10(C4/100))/LOG10(2)"

QuoteOriginally posted by blende8 Quote
Well, seems like Zip Files do not work.

Here's the direct link to the Excel file:
http://www-user.uni-bremen.de/~wie/EV.xls
Also, here is a chart for EV values which may be helpful.

To understand how to read it;

Start with an EV, then slide to the right and pick an fStop, then slide up and pick a shutter speed and finally, slide to the left and and you see the needed ISO, also you could go in reverse to find what EV you are shooting in. (The green and red values show 2 example calculations).
Attached Images
 

Last edited by betaPhoto; 02-17-2011 at 08:37 AM.
02-17-2011, 03:47 AM   #640
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Thanks for the link to the blende8's formula (I had missed that thread entirely) - his formula is different than mine but seems to come up with the same answer. It looks (if I understood what I read about logarithms) that he used base 10 and however you convert base 2 to base 10 is well beyond anything I remember. I just looked up in Excel's help menu how to use the log function and that told me how to do the formula using base 2, which is how it was written on Wikipedia. I can handle things like that, but that's the extent of my abilities.

I've looked at a couple of charts but none of them (including the one above) mention 16000. And my eyes glaze over whenever I need to try to remember numbers or figure things in my head.

Thanks again for the information about the my formula and Blende8's excel form - that's going to help a lot in trying to evaluate what's going on with me and my photo stuff.
02-17-2011, 05:07 AM   #641
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QuoteOriginally posted by mtngal Quote
...his formula is different than mine but seems to come up with the same answer.
That's because you can transform one formula into the other by simple algebra. Just as "x + x" and "2x" look different but are equivalent.

QuoteOriginally posted by mtngal Quote
It looks (if I understood what I read about logarithms) that he used base 10 and however you convert base 2 to base 10 is well beyond anything I remember.
You don't have to have access to log2(X) (LOG(X,2) in Excel) in order to calculate the logarithm regarding basis 2. You can simply take any log (basis 10, e, whatever) and calculate log(X)/log(2).
02-17-2011, 05:40 AM   #642
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so ... mid February, no fix for this or the flash issue ... well that sucks
02-17-2011, 07:34 AM   #643
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QuoteOriginally posted by Christine Tham Quote
Not really. I haven't seen replies to this person's posts. Maybe he's on their ignore list too?

Hint: the person is not Rupert. Rupert may be a One Note Johnny, but as far as I can tell he is a *polite* One Note Johnny
Honestly, I have a couple of notes.....listen again! I do appreciate that you think I am polite......I try to be, but do sometimes fail.

Just my personal opinion on "Ignore".....I have and will never use it. I want to hear it all, the Good, the Bad, the Ugly. The only way I can really learn the attitude and worth of a discussion is to hear it All. Alligator hide helps a lot, but we are all adults, sort of, and should be able to take it all without taking it personal.

Now, I do admit that for most of my life I have placed Mrs Rupert on my "Ignore" list, and only with some wisdom I have gained in my older age have I discovered how costly that can be. When I ignore her rambling it invariably leads to massive expense for me.....like when I wasn't listening to her about that Big Shopping Spree she planned at Christmas for herself. Yep, old habits die hard, and I damn sure should have been listening. I had been saving that lens money for a long time.......
Best Regards
02-17-2011, 07:45 AM   #644
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QuoteOriginally posted by Christine Tham Quote
I find the "ignore" function on this forum really useful - I have one person currently in my ignore list, and there's 1-2 candidates that I may add in the future as well.

I like to read different opinions, and I have learnt a lot from reading many posts. But I find it difficult to read some people's posts - so it's best if they are hidden from me.
But you still can't help reading there posts eh?
02-17-2011, 09:45 AM   #645
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QuoteOriginally posted by Christine Tham Quote
Agree.

The eyes are typically low contrast with no well defined sharp edges, so the AF sensor will probably focus on something else - I only mentioned the spoon because in the photo that object is brighter than the face and has sharp edges so would register very strongly on the phase detect.
I don't know if anybody is interested in this.

Normally, what a phase AF does, is this:

it takes the two 1-D images from the two sides (left/right or top/down) of an AF sensor's line sensor. It ends up with two curves ci(x) from each sensor. The curves would have large values for bright regions and low values for dark regions (normally, ci is defined such that Integral_x ci(x) dx = 0 but it doesn't matter here).

Now, it computes the so-called cross correlation function between both curves, where one curve is shifted against the other curve by a so-called phase p: Integral_x c1(x)*c2(x-p) dx

In a quick optimization, it detemines p such that this is maximized. (Actually, this isn't fundamentally different from what a contrast AF system does. Which is why I sometimes don't differentiate between phase and contrast AF, much to people's surprise normally )

This value of p is then used to determine the necessary lens shift to aquire focus.

The important point is this:

Whatever p maximizes Integral_x c1(x)*c2(x-p) dx is taken.

So, you cannot say the AF sensor focussed on feature x. It's not as simple as this. To further complicate things, a vendor can experiment with functions, e.g., replace them by ci^2 etc. Unmatched contrast edges make a correlation function small which is why they matter. But all contrast variations within an AF sensor's area contribute to the phase decision to a smaller or larger amount. It's not feature x like pupil or spoon.


Sidenote:

In the presence of noise, the computed value of p starts to be noisy too up to the point where it becomes a random value. An AF module has to decide how much light it receives (in order to take longer captures with its AF sensor) and if it can trust the value of p. Both are sources for mistakes being made by the firmware of the AF module if it is autonomous.

Last edited by falconeye; 02-17-2011 at 09:54 AM.
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