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09-04-2014, 07:26 PM   #1
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Manual Telephoto Newbie Problems

I recently purchased a used K mount manual 300mm lens for my k-3.
Despite reading the various posts on using old manual lenses etc I have not been able to get decent shots with it.

I identified it as a 300 mm lens when prompted, on attaching the lens.
I run it in manual mode.
I tried using the green button as an exposure aid.

On some cases I end up with bland shots with very poor contrast.
On other occasions I end up with very limited depth of field.

I would appreciate your advice please.


Michael

09-04-2014, 07:36 PM   #2
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Telling us which lens might help give you better answers. No idea what it should be capable of if we don't know what it is.
QuoteOriginally posted by mekiAus Quote
On some cases I end up with bland shots with very poor contrast.
Older lenses often exhibit lower contrast because the coatings were not as good. Using a hood is a requirement on older glass IMHO. A picture with EXIF intact might let someone give you better information.

QuoteOriginally posted by mekiAus Quote
On other occasions I end up with very limited depth of field.
I've no idea what your experience is but limited DOF and telephotos kinda go together. Do you know how to use a DOF calculator? There is one here: Online Depth of Field Calculator to play with. Input your numbers and it will show you what DOF you should expect. If you are getting results that differ from the calculator then something else might be amiss.
09-04-2014, 07:39 PM   #3
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Well poor contrast could easily be a quirk of the lens itself, but that can be pretty easily be fixed in post but keep fiddling with it. The depth of field you can fix by changing the aperture to something like f8, f11 or smaller to get more stuff in focus.

What lens exactly are you using?
09-04-2014, 08:30 PM   #4
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QuoteOriginally posted by mekiAus Quote
On some cases I end up with bland shots with very poor contrast.
On other occasions I end up with very limited depth of field.
Green button (stop-down) metering on the K-3 is not fully linear at all apertures. It is not as bad as the K10D, but not as good as I had expected based on my tests done with the K-7 and K-50. You may need to adjust a little (or a lot) for narrower apertures.

As noted above, poor contrast may be a characteristic of the lens. It may also be due to veiling flare and/or internal haze/fungus. Limited DOF sort of comes with the territory if the subject is at all close.


Steve


Last edited by stevebrot; 09-05-2014 at 12:47 PM.
09-05-2014, 07:04 AM   #5
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i have not had to attach this chart for a long time, but note. Green button metering is not truely linear on any pentax camera with a manual lens. the attached chart shows the impact of camera body and in some cases focusing screens, on the camera metering system, I do not have a K3, but the following is what i have done and in some cases with the help of other forum members, to map out metering errors with manual lenses.



the process involves finding a uniformly lit concrete block wall or pavement or sidewalk. at each aperture use the green button to meter the scene, and then take the shot . In a photo editor, measure the greyscale value (if possible do a selection on the middle of the screen) and plot the results against F stop,

I used a 50/1.4 because it is a common lens that most people have, but the issue exists for all lenses.

what you will find is that the exposure is really only accurate at F4-5.6 because that is the kit lens native aperture. All other apertures will have errors. The camera reads the native aperture from the aperture coding iin the mount on A lenses and later and compensates to be correct when using modern lenses and open aperture metering.
09-05-2014, 12:38 PM   #6
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QuoteOriginally posted by Lowell Goudge Quote
I do not have a K3, but the following is what i have done and in some cases with the help of other forum members, to map out metering errors with manual lenses.
Lowell, your work from several years back continues to be much appreciated.

The K-3 does not follow this pattern, at least not in M mode*. Neither does the K-50 based on a quick set of tests I did a few months back. My preference for this kind of testing has been to simply record the measured EV with a FA lens in the A position and plot the delta EV (+/-)** for the same lens for stop-down measurements. Measuring the grayscale value just introduces multiple additional variables*** into the analysis.

I actually did a series last week as part of my evaluation of the KatzEye on the K-3. Unfortunately, I tossed the results, though I can redo it this afternoon


Steve

* Meter stop-down linearity differs by mode on many Pentax bodies from the K-7 on with M mode generally being the more linear. In specific regard to the K-3, the metering system is sufficiently different from previous Pentax bodies that a variance from how previous cameras responded is expected.

** In other words, the number of stops over/under the nominally correct value. In practice, I take an open aperture reading at start of sequence and another after doing the stop-down measurements to detect changes in light during the test. There is no reason to do separate open aperture readings for each aperture setting.

*** These include shutter accuracy, aperture stop-down precision, sensor behavior, RAW conversion (either in-camera or out-of-camera), and base image processing. The goal is to evaluate the metering, not the full image processing stack. Blende's tests in the graph above for A-series lenses show this quite nicely. One would expect very similar flat graphs for both the tested A-series lenses except for brightness variations introduced after the exposure settings were determined.

Last edited by stevebrot; 09-05-2014 at 12:46 PM.
09-05-2014, 01:37 PM   #7
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QuoteOriginally posted by stevebrot Quote
Lowell, your work from several years back continues to be much appreciated.

The K-3 does not follow this pattern, at least not in M mode*. Neither does the K-50 based on a quick set of tests I did a few months back. My preference for this kind of testing has been to simply record the measured EV with a FA lens in the A position and plot the delta EV (+/-)** for the same lens for stop-down measurements. Measuring the grayscale value just introduces multiple additional variables*** into the analysis.
while it may do so, i have found it consistent, and not everyone has a suitable FA lens. thats why i use the method i do. but what ever method works is all you need.
QuoteQuote:

I actually did a series last week as part of my evaluation of the KatzEye on the K-3. Unfortunately, I tossed the results, though I can redo it this afternoon {/quote] too bad[quote


Steve

* Meter stop-down linearity differs by mode on many Pentax bodies from the K-7 on with M mode generally being the more linear. In specific regard to the K-3, the metering system is sufficiently different from previous Pentax bodies that a variance from how previous cameras responded is expected.
while i agree in general, as i have both K7 and K5 and yes they are progressively better, until I see the results across the whole aperture range, i will be suspect
QuoteQuote:

** In other words, the number of stops over/under the nominally correct value. In practice, I take an open aperture reading at start of sequence and another after doing the stop-down measurements to detect changes in light during the test. There is no reason to do separate open aperture readings for each aperture setting.
the reason i do the shots is that K lenses don;t have open aperture readings they are stopped down.
QuoteQuote:

*** These include shutter accuracy, aperture stop-down precision, sensor behavior, RAW conversion (either in-camera or out-of-camera), and base image processing. The goal is to evaluate the metering, not the full image processing stack. Blende's tests in the graph above for A-series lenses show this quite nicely. One would expect very similar flat graphs for both the tested A-series lenses except for brightness variations introduced after the exposure settings were determined.
Blende's test shows with an A lens yes, until minimum aperture if the mechanism is designed right you are ok, but, i ran a test with a tamron 28-75/2.8 and found that the aperture progressively has an error, exposure is spot on at F2.8 and rises linearly vs f stop until at F32 it is a little over +1 stop. conversely my sigma 70-200/2.8 is within +/-1 value (out of 256) in greyscale across the entire aperture range. I am a firm believer in testing the equipment, and knowing the real impact.
09-05-2014, 04:35 PM   #8
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QuoteOriginally posted by Lowell Goudge Quote
I am a firm believer in testing the equipment, and knowing the real impact.
Yep...if a particular lens has a lazy or poorly-calibrated aperture mechanism, even the best metering system can't compensate.

I redid the exposure series with the FA 35/2 on the K-3 (stock screen) this afternoon and was surprised to see that the meter response was almost identical to that from the K10D test I did with the same lens in 2009. This does not make me happy. I will be swapping out the stock screen for a KatzEye this afternoon and will be curious as to how things look with the screen I will actually be using most of the time.


Steve

09-06-2014, 05:47 AM   #9
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QuoteOriginally posted by mekiAus Quote
I recently purchased a used K mount manual 300mm lens for my k-3.
Despite reading the various posts on using old manual lenses etc I have not been able to get decent shots with it.

I identified it as a 300 mm lens when prompted, on attaching the lens.
I run it in manual mode.
I tried using the green button as an exposure aid.

On some cases I end up with bland shots with very poor contrast.
On other occasions I end up with very limited depth of field.

I would appreciate your advice please.


Michael
Michael, please post a pic or two with exif. also whether hand held/supported/tripod etc, and how focussed (by eye, any VF aids, live view etc)
09-12-2014, 07:00 AM   #10
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Thank you for your replies and advice.

The lens is the old film camera K mount SMC 300mm F4 described in the database.

I experimented this week based on your feedback, and found that most of my problem was caused by my inexperience - a different camera, (K-3 instead of K10D), everything manual instead of P mode, an old Prime telephoto lens, instead of the two lenses I have been using for many years; and, when I re examined the photos, flare from the sun. Also when I looked at the exif info I noticed that I was taking quite fast shots wide open ... No wonder I had very little depth of field.

Once again thank you for your replies and hints.

Michael
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