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05-09-2012, 07:20 AM - 1 Like   #1
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An article about focus

Since it's such a popular and recurring topic on here, I thought I'd help shed some light on the subject with an article explaining some technicalities.

Are your pictures out of focus?

05-10-2012, 10:03 AM   #2
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lord not again how may threads do we need on this
05-10-2012, 12:19 PM   #3
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QuoteOriginally posted by adwb Quote
lord not again how may threads do we need on this
Did you read the article or just blindly comment? I suggest giving the link a thorough read, as well as other members. I think it would answer the majority of questions related to the "poor" focusing of the Pentax (I think it does rather great given what kind of system it is).

The article is quite technical though. Those with a reactionary attitudes (cough cough ) might prefer some lighter reading.

From the introduction to the article:
"
The point I am trying to make is that the sensor will not be exactly where it is supposed to be, the mirror in an SLR will not come to rest in the perfect position, the autofocus system may be mounted just a wee bit off from the perfect position, it may be slightly out of perfect calibration, the focusing screen may be a little thinner or thicker than the spec, it may be placed slightly off in the camera, the lens mount may be slightly deeper or shallower than the spec, etc.
So, the consequence of mass production in large quantities at reasonable prices is that all these small deviations will pile up on top of each other and can cause the AF system in your camera to be out of focus. There is also a statistically significant probability that even if the autofocus system is working superbly, manual focus on the screen does not match the autofocus system on the camera."
05-10-2012, 12:37 PM   #4
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Thanks GnipGnop. Good article. Thanks for posting.

05-10-2012, 02:13 PM   #5
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QuoteOriginally posted by GnipGnop Quote
Since it's such a popular and recurring topic on here, I thought I'd help shed some light on the subject with an article explaining some technicalities.

Are your pictures out of focus?
Sorry, but this article looks like it's advertising of an overpriced product...

Last edited by Edvinas; 05-10-2012 at 02:19 PM.
05-10-2012, 04:39 PM   #6
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QuoteOriginally posted by Edvinas Quote
Sorry, but this article looks like it's advertising of an overpriced product...
yes I managed to refrain from making the same comment.

This type product including printable home made ones are readily available [mostlyfor free] with a little searching.
and have been around for years it is not new i am sorry to say.

The topic on this and similar types of back/.front focus testers has been covered in depth many times before.

I own and use 4 Pentax bodies and assorted lenses and regularly shoot portraiture a wide open settings and do not have any visible problems with focus even when printed out at A 3plus or greater which I have a lot of orders for.
05-11-2012, 05:56 AM   #7
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To those who think this is just an article advertising a product - you're wrong. The author actually states it started out as a product test, but since his cohort already reviewed it, he thought he would share some insight on why focus in dSLR camera systems is almost always off, and why we should expect it to be that way.

Glad you liked the article!

And yes, I agree that Lens Aligh is an overpriced product.
05-11-2012, 07:39 AM   #8
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QuoteOriginally posted by adwb Quote
This type product including printable home made ones are readily available [mostly for free] with a little searching.
and have been around for years.

The topic on this and similar types of back/.front focus testers has been covered in depth many times before.
Would you mind pointing me to a few free testers and articles. As a neophyte, I can use the help.

05-11-2012, 08:05 AM - 1 Like   #9
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QuoteOriginally posted by Tatume Quote
Would you mind pointing me to a few free testers and articles. As a neophyte, I can use the help.
Tatume, give this article a read. It's about a series of focus exercises you can do to improve your manual focusing techinque. I've used them and they do work. However they are boring. Unfortunately a lot of practice of craft is boring. I play several musical instruments, I've found playing scales is a very good way of getting proficient on any particular instruments. Playing scales is boring. So are focus exercises, but they also work.
boring but effective exercises

NaCl(if you want to get good you have to work at it and work is mostly boring)H2O
05-11-2012, 08:09 AM   #10
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Thanks NaClH2O,

What is the significance of the salt water reference? (As a blue-water boater I'm interested.)

Take care, Tom
05-11-2012, 08:16 AM   #11
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@ Tatume
I've been playing in and around salt water for most of my life. I grew up on Long Island Sound and learned to sail before I ever learned to ride a bike. As they say, I'm currently "between boats". About 10 or so years ago I looked at my nonexsistant bank account and realized I could either continue to own a boat (at that point a Norwegian Folkboat) or I could retire at 65 but not both. sigh. In any event the beach and bay are still where I go when my spirit needs to be recharged. Hence the NaClH2O handle.

NaCl(it's in my blood)H2O
05-11-2012, 08:30 AM   #12
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Hi NaClH2O,

I wish you were closer, I'd take you boating with me. The Folkboats have always interested me, but I don't have a sailboat at present. Anyway, as an active member of the Coast Guard Auxiliary, I can assure you that there are plenty of boating opportunities in your area. People who own boats are always looking for crew. Check in with the Auxiliary, you might be pleased. Here's a place to start: Unit Home

In the article to which you referred me the author says "Do it slow enough that you can watch the focus transition from blur to sharp to blur, but fast enough that the transition to critically sharp "pops" for a moment as you turn." As a player myself, this is a very familiar experience when tuning.

Thanks, Tom
05-11-2012, 10:31 AM   #13
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Tatume,

I had never thought of that but of course you are correct, it is almost exactly! like tuning. As for sailing, my boat is now OP. I've occasionally crewed around the area, I used to live on City Island which at one time was mostly boat yards and yacht clubs. I still crew off and on. But this is enough thread jacking for now.

NaCl( tuning is focusing for the ear....that's a good one!)H2O
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