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10-03-2012, 02:05 PM   #16
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QuoteOriginally posted by Lowell Goudge Quote
In reading the latter posts here there are a few things not really well explained, although the concepts are touched upon.

Dept of field is actually based upon what is called acceptable sharpness, and it all comes om a point of light still appearing as a point of light on an 8x10 print. DOF is, in fact the product of total enlargement of the lens, through to the print, the bigger you print the less DOF you have

It is also true that there is usually more acceptably sharp behind than in front of the focus plane. It is 2/3 behind 1/3 in front at thenhyperfocal point and beyond, apwith this ratio moving to 50/50 when you get really close

The biggest issue we have today, and I am equally guilty of this, is blowing things up huge. I review my photos on a 22 inch 16x9 format monitor. (it measures 13x19 inches) and significantly bigg than the 8x10 print. I also crop in a lot too. so when I look at shots the normal rules of DOF are useless.

Let's not forget that in discussions about blurry images.
These are all great points. The first point of acceptable sharpness is one I think we all tend to forget about a bit. People often think that the DOF is some magic spot where out of focus becomes perfectly sharp, but in reality there is a transition, and the DOF is really just the limits of where you think things are acceptably sharp and not. That boundary is fuzzy and depends on your own eyes as much as it does the size of the print.

The idea about the print size, is really important but often lost. Most calculators for DOF and literature seem to focus on the size of the sensor or the size of the negative mostly because that is what we are shooting at the moment. However, as you blow the image up to an 8 x 10 or bigger, that DOF appears to decrease even if it is the same image. And, then as you point out with the monitor, that is the biggest culprit. Monitors seem to make everything look a bit worse than they really are when we view them cropped or at 100%. We tend to forget that pixels are rather large and tend to make everything a bit softer than it may really be. It's better to look at your images in a size more like what you might print or view it at rather than 100%. I think we all get a bit too hung up on pixel-peeping at some point.

10-03-2012, 09:20 PM   #17
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All good points and reminders. Thanks.
The part I'm still working on is those pics where everything is probably "acceptably" sharp, but where my main interest is not exactly sharp. More practice, I guess...
10-04-2012, 07:09 AM   #18
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QuoteOriginally posted by mgvh Quote
All good points and reminders. Thanks.
The part I'm still working on is those pics where everything is probably "acceptably" sharp, but where my main interest is not exactly sharp. More practice, I guess...
If your whole image is acceptably sharp but no where is there any point that is perfectly sharp there are many possible issues, one is that the lens is defective (this is rare), one is that the camera is resonding to or generating vibrations that are impacting absolute sharpness, of user issues you could be off on your focus, or shooting at a shutter speed that is too low, causing slight blur.

to try and eliminate some or all of these, take a shot with the internal flash. if it is sharp, then there is nothing wrong with the lens, and it is likely your technique, or focus error
10-04-2012, 08:48 AM   #19
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@Lowell: This thread was instigated because I was just not getting sharp images using LiveView and my manual focus A50 f1.7. I was also getting inconsistent results using Catch-in-focus. The lens is certainly fine and has rendered deliciously sharp images, but I'm trying to standardize my technique to get those consistently. I had tried to eliminate user errors in terms of vibration, shutter speed, etc. by using a tripod. The issue is the best technique for focusing. I kind of knew that CIF was a bit of a gamble whether one catches the focus on the way up or down while focusing. I had hoped, however, that using Live View and magnifying the screen all the way up to 10x would be the best solution, but it wasn't working for me. (It does seem to work best for macro shots, however.)
What is turning out to get me the best and most consistent results is simply using the viewfinder, watching the green focus lamp, and finding the middle of the small range where it indicates it is in focus. And I guess that's where the practice part comes in...

10-04-2012, 08:58 AM   #20
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QuoteOriginally posted by mgvh Quote
@Lowell: This thread was instigated because I was just not getting sharp images using LiveView and my manual focus A50 f1.7. I was also getting inconsistent results using Catch-in-focus. The lens is certainly fine and has rendered deliciously sharp images, but I'm trying to standardize my technique to get those consistently. I had tried to eliminate user errors in terms of vibration, shutter speed, etc. by using a tripod. The issue is the best technique for focusing. I kind of knew that CIF was a bit of a gamble whether one catches the focus on the way up or down while focusing. I had hoped, however, that using Live View and magnifying the screen all the way up to 10x would be the best solution, but it wasn't working for me. (It does seem to work best for macro shots, however.)
What is turning out to get me the best and most consistent results is simply using the viewfinder, watching the green focus lamp, and finding the middle of the small range where it indicates it is in focus. And I guess that's where the practice part comes in...
understood and forgotten through the course of the thread.

What I have found using my collection of 40+ MF lenses is the following, related to focus accuracy and the camera's AF confirmation.

Precision of the AF confirmation is inversely proportional to focal length, for example my tamron 200-500/2.5 is only in focus when the green light confirms it is. my 8mm fisheye is always in focus the system just can;t easily distinguish true focus when lenses have a large depth of field.

With the exception of the 200-500/5.6 which is used on a stock K5, all of my use of MF glass is on 2 bodies my *istD with a Dual split image, and my K10D with a single diagonal split image. I rely on the split image more than confirmation for focus, although I do pay attention to both. you can usually see a perfect split image and move the focusing collar both directions and still have the confirmation light on in the viewfinder.
10-04-2012, 09:56 AM   #21
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Perhaps it is obvious but it is worth to check the Stabilizer

As you are using a tripod I am sure that you have already disabled the Stabilizer of the Camera body or you will have a micro-moved effect due to the solid base.
Check it just in case.
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Last edited by Antanico; 10-04-2012 at 10:25 AM. Reason: Adding screenshot of Kx Menu
10-04-2012, 10:14 AM   #22
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QuoteOriginally posted by mgvh Quote
I see that the focusing screens are not terribly expensive, but I really don't like the idea of messing around inside the camera.
You might consider having this done for you if you are uncomfortable. The split screen that was installed in my K-x when I bought it from another member made it an absolute joy to use for manual lenses.
Something to think about.

The one I used was from focusing screens.com and it was a nikon k3 type
10-04-2012, 12:32 PM   #23
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QuoteOriginally posted by Antanico Quote
As you are using a tripod I am sure that you have already disabled the Stabilizer of the Camera body or you will have a micro-moved effect due to the solid base.
Check it just in case.
Good idea, but switching to the delayed shutter release as I did automatically turns off shake reduction.

10-04-2012, 12:39 PM   #24
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I must say that despite having a focusing screen (a cheap Chinese brand) it is still rather difficult for me to focus manually. It may be because it may need some shims or due to my poor technique - I don't know...

What has really helped me with manual focusing (a true, definite, easily-seen difference) was buying an "lcd viewfinder" - a small gizmo that attaches to the camera that magnifies the Live View screen. I think this is the way to go. The problem with this solution is that:
1) it can't be left on a camera (accidentally pointing it at the sun WILL destroy the LCD)
2) it's awkward to use - the camera is much more difficult to handle and does not balance as well as it does without it
3) the whole live view technique is much slower that catch-in-focus or focus confirmation

The only advantage is that it produces outstanding results .
10-10-2012, 03:00 AM   #25
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QuoteOriginally posted by mgvh Quote
Also, why would the image be so much more overexposed using LiveView? I had to use -.7 EV to make it comparable to the pics using CIF. The lighting did not change.
LiveView meters using the actual image from the sensor. Viewfinder metering works off the image projected onto the focusing screen. The problem arises because the brightness of the focusing screen image usually varies nonlinearly with the lens aperture - a f/4 lens will not necessarily give you an OVF image twice as bright as a f/5.6 lens would.

Probably the best way is to meter a scene using LV until you are happy with it, then switch to OVF and tweak the EV compensation until the exposure matches. Then stick to that offset for that lens/focusing screen combination. An EV offset of +2/3 to +1 is normal.

As for your focusing problem - I'd found the stock screen just about useless for accurate manual focusing. CIF sometimes works but as you'd found, it can also be a bit of a hit-and-miss with some lenses. I also tried a viewfinder magnifier, this helped but wasn't an ideal solution. Fitting the cut-down Canon Ee-S screen from Focusing Screen was the answer, even with slow manual lenses where CIF does not work this screen makes manual focusing easy and accurate - https://www.pentaxforums.com/forums/lens-clubs/71775-mirror-lens-club-41.html#post2127538 - providing that you set things up well using the right shims.
10-10-2012, 10:30 AM   #26
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@kh1234567890: Thanks for the explanation about metering. In the one specific case, LV was overexposing and using the OVF with CIF was getting it right. I think, however, that the issue was that there was a bright glare near the center of the pic that LV was not taking into account. Ie, it seems that LV does a better job of averaging out the scene. BTW, for my AE Metering, I'm using Center-Weighted.
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