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Old Nov 26, 2003, 8:20 AM   #1
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Default Minolta A1 vs. Nikon 5700: Operation Issues

Hi Folks,

I posted a comparison between Minolta A1 and Nikon Coolpix 5700 in the Nikon Talk Forum. The first three posts are
http://forums.dpreview.com/forums/re...essage=6769052
http://forums.dpreview.com/forums/re...essage=6769142
http://forums.dpreview.com/forums/re...essage=6769107

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Old Nov 26, 2003, 9:57 AM   #2
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With any camera you should be using manual focus to shoot a CRT. The CRT image is a pulsating light source and it's not surprising that some autofocus systems cannot handle a CRT. You should also be using a tripod to carefully align the camera straight at the screen and use a shutter speed 1/2 the refresh rate or slower.
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Old Nov 26, 2003, 11:33 AM   #3
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i posted a image i shot with an A1 right after your first post using AF and now i'll do it again

http://www.pbase.com/image/23645958

now i read all your threads and replicated most of your situations. regretfully i feel that there must be some operational issue that may not be executed in the same way because i had little AF issues with my screen and i used AF. also you should reword the line-

Quote:
(7) Auto Focusing:

This is the department that 5700 cannot beat!
Quote:
In any rate, A1's AF system beats that of the 5700 miles.
sort of contradicts.

operational awareness is the key to use of both cameras. juast as when i switched from nikon SLRS to the canon 1Ds DSLR the relearning curve went vertical and my first 500 or so shots were definate examples of how vertical the learning was learning :shock:.

you have to treat and learn each camera before a true comparison can be made.
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Old Nov 26, 2003, 10:05 PM   #4
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Quote:
Originally Posted by browntimdc
With any camera you should be using manual focus to shoot a CRT. The CRT image is a pulsating light source and it's not surprising that some autofocus systems cannot handle a CRT. You should also be using a tripod to carefully align the camera straight at the screen and use a shutter speed 1/2 the refresh rate or slower.
The following is my response to your post on DPreview:

I have 20+ years experience in shooting various CRT and LCD tubes, screens and monitor with many different type of cameras, AF, MF, film and digital, and I am fully aware of this fact. The Minolta A1 is the only high-end camera that fails frequently. Please see my first post here http://forums.dpreview.com/... .../read.asp?forum=1007&message=6769052

> You should also be using a tripod to carefully align the camera
> straight at the screen and

This is a quote from post regarding the use of tripods:

A Minolta A1 is place about 60cm from a CRT monitor.
Right behind the A1 is a Coolpix 4500 in movie mode
for shooting A1's monitor. Both cameras were on sturdy
tripods.


Since I only test AF capability of A1 and 5700, whether the camera is aligned so that the viewing line is perpendicular to the screen is not an issue. After all, the AF sensor only picks up a very small area for focusing rather than the whole screen.

> use a shutter speed 1/2 the refresh rate or slower.


This is not for focusing; this is only good for shooting. When doing AF, the shutter speed is irrelevant.

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Old Nov 26, 2003, 10:33 PM   #5
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shene

This has nothing to do with AF! What it all means is the sampling rate on the A1's frame readout CCD is just out of sync with the display rate on your monitor (sjms has already proven this out) or how persistent a display is.

If your monitor has the capability to accept different rates, just change it to a different frequency and as you'll find out each camera's AF will be more adept to one scan rate than another and this has more to do with Nyquist...

Exception like this are not indicative of how good an AF system is... I have never seen any reviewer testing a camera AF using a CRT have you?
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Old Nov 26, 2003, 10:36 PM   #6
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Quote:
Originally Posted by sjms
i posted a image i shot with an A1 right after your first post using AF and now i'll do it again

http://www.pbase.com/image/23645958

now i read all your threads and replicated most of your situations. regretfully i feel that there must be some operational issue that may not be executed in the same way because i had little AF issues with my screen and i used AF.
The following is my original writing:
Quote:
I suspect that A1's AF system must have something unusual that I don't quite understand. Also note the position of the focusing cross jumps quite randomly around its initial position even though the camera is fixed on a tripod. This could mean that the CRT screen flickering may be the cause of this random move and the unusually high AF failure. But, I really don't know if it is the case and further investigation is needed.
And, in another post, I stated that "I am not sure if it is a general problem or a problem of my own A1". So, if you don't have the problem, congratulations. Maybe my copy is a defect one. However, your example cannot be used to indicate my finding is wrong. Moreover, I also stated clearly that future investigation is needed. I am a rigorously trained scientist who is fully aware of the fact that one cannot "prove-by-example." But, since I only have one A1 in hand for evaluation/review purpose, I derive my results from my only sample unless you think the two movies I recorded are cheating.

Quote:
Originally Posted by sjms
also you should reword the line-

Quote:
(7) Auto Focusing:

This is the department that 5700 cannot beat!
Quote:
In any rate, A1's AF system beats that of the 5700 miles.
sort of contradicts.
The first quote says that the 5700 cannot beat the A1's AF system, while the second quote says A1's AF system is better than that of the 5700. Either my English writing is poor or you did not read my post correctly.


Quote:
Originally Posted by sjms
operational awareness is the key to use of both cameras. juast as when i switched from nikon SLRS to the canon 1Ds DSLR the relearning curve went vertical and my first 500 or so shots were definate examples of how vertical the learning was learning.
You may consider I am an extremely fast learner. In my previous 20+ years pro-life, I shot so many completely different camera systems such as the medium format Hasselblad, Mamiya and Bronica, and 135 system like Nikon, Minolta and Canon. In fact, in additional to me Nikon system, I must use whatever the assignment manager handed to me for a particular assignment. This system may be totally different from what I have. This Minolta A1 thing, frankly speaking, only needs a few days to master its operational aspects that I reported in my posts. How to get the best images with various settings is, of course, another story. I also made it very clear that the image quality issues will be reported in the future.

Quote:
Originally Posted by sjms
you have to treat and learn each camera before a true comparison can be made.
Do you mean I am not quality to post the operational issues? :shock: Which parts of my posts are incompetent? I really would like to know in order to improve.

CK
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Old Nov 26, 2003, 11:14 PM   #7
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Quote:
Originally Posted by NHL
This has nothing to do with AF! What it all means is the sampling rate on the A1's frame readout CCD is just out of sync with the display rate on your monitor (sjms has already proven this out) or how persistent a display is.
Yes, I suspect this may be the case for some time. Note that when I say AF, I use a more technical meaning which includes AF CCD array operations, comparison algorithms, lens barrel movement, etc rather than locking on something because the latter is a consequence of the former. (So, I view it as a AF system.) The AF system also failed frequently when using studio and/or macro fluorescent lights which do not allow frequency change. The AF system dedicates a portion of the CCD for contrast comparison. It is likely that the sampling rate is too high or the sample reading time is too short that may miss the monitor scanning frequency which is about 60-90hz. Studio and macro fluorescent lights are usually in about the same range. My copy of A1 failed with all of my monitors (all of the them being high-end graphic gears with price tags ranging from $800 in the low-end to $2,000- in the high end).

This is the reason that I suspect Minolta must have something strange in their A1 AF system. How could a company allow their AF system to fail in the most commonly used monitors, especially those high-end ones that always run in the highest frequency? I checked the same thing with D1X, D100, 1Ds, F5, F100, N80 and many Coolpix systems, and they were all successful in locking on the subject. I haven't try Maxxum cameras because I could not find one. IMO, strictly speaking, it is an AF system design problem because it fails in a common scenario. This I may force me to dump some of my favorite fluorescent lights, although some more research has to be done to absolutely make sure it is the case. I wish I could know A1's AF algorithm and their design sketch. But, it is unlikely I can get it.

Quote:
Originally Posted by NHL
Exception like this are not indicative of how good an AF system is... I have never seen any reviewer testing a camera AF using a CRT have you?
No, I did not use this CRT thing as a negative nor positive factor about A1's AF system. As a scientist, I am fully aware of the fact that one cannot prove or disprove something by a single example. Indeed, I personally rated A1's AF system very highly. Do you need quotes from what I said? Why I choose shooting CRT? This is simple. As I mentioned in one of my posts, I made $$$ from shooting CRT tubes, screens, TV and monitors for magazines and books in my early pro years. If you know a type of shooting well, you will naturally pick it as a test target, although the results may not be valued significantly in the final conclusion or decision. It is simply a natural instinct of a profession.

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Old Nov 27, 2003, 12:42 AM   #8
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first of all reading is part of the game. i must have read your statement on the 5700 5 times and still i missed it. for that i apologize. Duh!

as an avionics tech for 17 yrs and photographer for 27 yrs we look at things similarly but different. i shoot the crt and lcd screens on the flt decks for our traing department regularly on ground and in flight using in the past thr D7Hi and now the A1. i worked systems on the most modern commercial aircraft in the world and was trained by Boeing boys themselves and some of their simpler systems have humbled me on numerous occasions and then have put a few of Boeing engineers back on their seats too.

as a professional i will defer any further comment on this subject and let you work to your end.
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Old Nov 27, 2003, 8:16 AM   #9
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Quote:
This is the reason that I suspect Minolta must have something strange in their A1 AF system. How could a company allow their AF system to fail in the most commonly used monitors, especially those high-end ones that always run in the highest frequency?
There's nothing strange about this: The AF system in the Dimages are no different than in the CP5700 or any other EVF cameras based on a video contrasting system. This the same version of the CCD used on the CP5700, D7 series, E20 and F717 cameras:
http://www.sony.co.jp/~semicon/engli...1/a6803214.pdf

Check page 15 or 35 of the above datasheet for details, that's just the available sampling rates... How many time a camera sample the different AF frames (no camera can focus with just 1 frame) depends only on each camera software algorithm and how fast or slow the camera will achieve their focus, ie they all have to do with aliasing (hence -> "the position of the focusing cross jumps...") and frames rate, and unrelated to prices, pro/high-end or cheap toys! :lol:

To refresh your memory SLR (or dSLR) cameras used phase detectors after their beam splitters which are absent in EVF based cameras. The phase detectors not only can tell if the subject is in focus but also if a subject is near or far (ie the focusing mechanism will be directed to go one way). With a video AF based on contrast the mechanism is at least twice as slow since this system inherently has to hunt back and forth to determine the direction of focus! That is of course if a subject is static which it is clearly not the case with a CRT and this special circumstance is nowhere indicative of how good or bad a video AF system is @ certain frequencies or scan rates!

... and then of course we have the Ultrasound AF system used in Polaroid camera, and the various infrared system used on mostly point and shoot camera with the various range finders... 8)

But then this is just a hobby for me... I made zero $$$, and so far its just a money pit! :P :P :P
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Old Nov 28, 2003, 2:20 AM   #10
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Quote:
Originally Posted by NHL
There's nothing strange about this: The AF system in the Dimages are no different than in the CP5700 or any other EVF cameras based on a video contrasting system. This the same version of the CCD used on the CP5700, D7 series, E20 and F717 cameras:
http://www.sony.co.jp/~semicon/engli...1/a6803214.pdf
Yes, how could I forget this document especially that I have a printed copy! Thank you for reminding me.

Quote:
Originally Posted by NHL
Check page 15 or 35 of the above datasheet for details, that's just the available sampling rates... How many time a camera sample the different AF frames (no camera can focus with just 1 frame) depends only on each camera software algorithm and how fast or slow the camera will achieve their focus, ie they all have to do with aliasing (hence -> "the position of the focusing cross jumps...") and frames rate, and unrelated to prices, pro/high-end or cheap toys! :lol:
This is what I said. I suspect that Minolta's AF algorithm must have something strange/unusual. I have been working on image processing/acquisition problems on and off for sometime now. AF systems, whether they are contract detection and phase detection, they work the same way as in many image/signal processing systems. Hardware aside, the key component is the algorithm that computes the result. This is something I'd like to know. Maybe I should talk to a image/signal processing researcher at my University who knows the internals of contrast detection well in order to find out the details.


Quote:
Originally Posted by NHL
But then this is just a hobby for me... I made zero $$$, and so far its just a money pit!
This is no more my $$$ making skills because I have found better ways that can integrate my research and photography together and support my previous $$$ making hobby.

CK
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