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07-24-2013, 11:13 AM   #16
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QuoteOriginally posted by stevebrot Quote
Hi Boris,
With the J-9 you have the choice of using M-mode with the green button and getting reasonably accurate metering or using Av mode and getting fairly inaccurate metering (the degree of inaccuracy is dependent on aperture, tends toward gross underexposure at wider apertures, and is not a simple bias). I would suggest M-mode.

The flow in M-mode:
  • Frame your shot and focus
  • Stop the lens down to the shooting aperture. This is requires some forethought with pre-set aperture lenses like the J-9.
  • Press the green button to meter (camera will set the shutter speed)
  • Press the shutter release

I took my J-9 for a spin today. And I can confirm what Steve is saying. I consistently get slightly better exposure in M-mode (using the approach described by Steve) than in A-mode. Both modes give me an underexposed image and this improves a bit as I close down. A few of my shots came out at the limit of K-5 ability (shutter speed 1/8000). If Boris had overexposure he must have reached that limit (even more probable if ISO was higher than 100)


QuoteOriginally posted by stevebrot Quote
A few other points:
  • With all lenses lacking the "A" contacts you will be limited to center-weighted average metering. You will not have spot or matrix metering.
  • Your J-9 will benefit immensely from having a hood attached
  • With the J-9, lower contrast and less sharpness are the rule when shooting wide-open
  • In M-mode you will not be able to use exposure compensation. Instead...shoot, chimp, adjust shutter speed/aperture, shoot again. Once you determine the appropriate exposure for your subject you don't need to re-meter until either the light changes or you choose a different subject.
small correction. you can use exposure compensation, but you have to re-meter (press the green button) again after you dial in the exposure compensation, otherwise it will have no effect. You can instead change the shutter speed directly of course.


QuoteOriginally posted by stevebrot Quote
Now...having said all the right things, I have to ask a silly question. When your Jupiter-9 is mounted to the camera does the display show F-- as the aperture? If so, everything is great. If not, we have a problem.
Never happened to me.

07-24-2013, 01:18 PM - 1 Like   #17
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QuoteOriginally posted by vanyagor Quote
small correction. you can use exposure compensation, but you have to re-meter (press the green button) again after you dial in the exposure compensation, otherwise it will have no effect. You can instead change the shutter speed directly of course.
Cool! This is an improvement over the older model cameras where exposure compensation is not available in M-mode with non-A-contact lenses.

QuoteOriginally posted by vanyagor Quote
Never happened to me.
Me neither, until I experienced some weird metering a year or so ago and noticed an aperture value in the display. It happens very, very rarely and will usually clear up by backing the lens out of the adapter a bit and reseating. I have my theories as to what is going on, but have no way to really test my hypothesis.

As for the M vs. Av mode metering, Pentax changed the stop-down meter algorithm several years ago to provide a more linear response. The improvement was implemented with the debut of the K-7 and only applies (for fairly obvious reasons) to M mode. The distinction is in the camera manual for the current bodies, but is not very clearly stated.


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07-24-2013, 02:28 PM   #18
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QuoteOriginally posted by 6BQ5 Quote
Do full frame lenses overwhelm APS sensors?
I'd just be delighted to be given a chance for my FF lenses to overwhelm a Pentax FF DSLR.

Sorry I couldn't stop my fingers from saying that.
07-24-2013, 03:24 PM   #19
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QuoteOriginally posted by kh1234567890 Quote
In my experience fast (f/1.4) full frame lenses on APS sensors can give this sort of hazy flare when used wide open :
That is likely due to the FF (Pentax) lenses not having the proper coatings for digital sensors. The APS-c size sensor is seeing exactly what that portion of a FF sensor would be seeing.

07-24-2013, 03:45 PM   #20
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QuoteOriginally posted by Parallax Quote
That is likely due to the FF (Pentax) lenses not having the proper coatings for digital sensors
Well, Last week I took 2 shots of same scene and f/- with the K-01 with equally hooded lenses and the sun was just outside the frame.
The first was the 35 year old kit lens SMC Pentax -M 1:2 50mm , the second was the 6 year old kit lens the SMC Pentax -DA 18 ~ 55mm AL

The old -M lens was much better, in flare resistance than the DA.
I posted them on this forum, here are then links again.
The -M lens
https://app.box.com/s/izcv2q8akxhdh1ajxwuk

the DA lens
https://app.box.com/s/xnir6j5sp99sdf05g6vs
07-24-2013, 03:51 PM - 1 Like   #21
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QuoteOriginally posted by Parallax Quote
That is likely due to the FF (Pentax) lenses not having the proper coatings for digital sensors. The APS-c size sensor is seeing exactly what that portion of a FF sensor would be seeing.
Coatings have little to do with this effect since it disappears when you stop the lens down from f/1.4 to say f/1.8 either using the lens aperture diaphragm or with a reducer ring 'hood', as was used in this shot.




Several explanations have been proposed - e.g. stray light from area outside the APS sensor being reflected around inside the sensor box or that digital sensors are not happy with light at a significant angle from normal incidence and then exhibit this sort of hazy blooming. This could be a plausible explanation, since as far as I can gather it does not happen when shooting film.

We'll see when/if Pentax ever come up with a FF body

Last edited by kh1234567890; 07-24-2013 at 03:58 PM.
07-24-2013, 09:38 PM   #22
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I had a chance to capture some pictures with my Jupiter-9 during my lunch time walk today. There were two setups and I cycled through all the aperture settings from f/2 to f/16. In the first setup I used center weighted metering only and in the second setup I did both center weighted and spot metering. All of the pictures were taken in Av mode. I didn't read through Steve's post about using M mode vs. Av mode before my walk.

Question: why would the camera calculate a different exposure between the two modes? Doesn't the same amount of light hit the same sensor?

Before I go nuts posting pictures let me make a couple of observations. The camera seemed to underexpose at large apertures. f/8 was the ideal aperture. Spot metering shifted all the exposures to be faster and therefore all the shots are underexposed.

Here is a shot my first setup taken with my iPhone. I am taking a picture of a small stump on the left and my K-30 on a tripod is on the right. The wind was blowing too hard for flower shots. Stumps don't tend to sway in the wind much.



I forgot to take my measuring tape with me but according to the lens I was 2.5 meters away.

I focused once wide open and then snapped one photo at each aperture. It would be crazy for me to post everything here so I'll pick a few. There was no post processing done to these JPGs. I used Silky Pix to simply develop the shots as-is.

Here's a picture at f/2.



Soft, hazy, and underexposed. Shutter speed is 1/4000 at ISO 100. Center weighted metering as stated before. Skip on to f/8 and the picture looks a little overexposed.



The shutter speed was 1/125 at ISO 200.

Next I took a closer focus shot of a bird house I found on the premises which I placed on a stone flower bed.



The distance now to my focus point is 0.9 meter according to the lens. Remember, in this setup I took both center weighted and spot. Here's center weighted at f/2.



Once again the picture is soft, hazy, and underexposed. Shutter speed is 1/4000 at ISO 100. Now let's go up to f/8.



It's a little bright so maybe a tad overexposed but I like it. Details seem more vivid and contrast is tasty. Shutter speed was 1/250 at ISO 400.

Then I switched over to spot metering. Much more underexposed! Here's the same birdhouse at f/2 with spot metering.



Shutter speed is 1/6000 at ISO 100. Jumping ahead to f/8...



Shutter speed is 1/250 at ISO 200.

You may notice that I played around a bit with the sensitivity and this was on purpose. The shutter speeds were getting to be under 1/50 and slower at the smaller apertures. I was afraid of a smeared background from the wind blowing the lavender in the background. There was also a shadow cast on the birdhouse from a tree that was behind me. Oddly enough the shadow never appeared in any of the shots.

So, what can I extract from this experiment? I still think there is too much light bouncing around the sensor cavity. Maybe the light is bouncing back from the sensor to the rear element and back again? This double whammy of light makes the sensor think that there is even more light so the shutter speed goes up and up and up. At f/8 the total light is much less so maybe there is less reflection and the metering system doesn't freak out. Or, is the metering function expecting a different sensitivity curve from the lens?

It'll be a few days before I can return to this spot to try some other combinations of metering.
07-25-2013, 07:54 AM   #23
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Good Morning Boris,

On your tests, you are changing too many parameters at the same time. If you are wanting to test the difference between spot and averaging metering, then that should be the only change made. The birdhouse series is a good exercise at depth of field (just look at the background), however with all the parameter changes you are muddling the waters on metering. The stump photo set, also demonstrates depth of field, where wide open the rock wall in the shade is fuzzy (out of focus) while stopped down to f8, the rocks in the background are much sharper and in focus. In doing this, you are confusing the difference in the images as being soft, but in reality being caused by the change in aperture forcing a different treatment due to the difference in the depth of field.

Anyway on metering, consider this scenario - shooting the full moon at night:
  • Averaging - You go out and shoot the moon with metering set on averaging. You are going to meter the entire scene - i.e., black with a bright white spot, and thus the moon (the bright spot) will be way overexposed. It will be just a bright white blob.
  • Spot - Again shooting the moon with spot, you put your metering point (center) over the moon and it will meter the light off the moon, and expose correcty. You really do not care about the rest of the scene.

So lets address the rock wall set of images. The wall photo set has two different lighting conditions - the foreground in the sun and the rock wall which is in the shade.
  • Averaging - In averaging you are going to average across the sunny foreground and the shady background. What you get is somewhat unknown, since it will depend on how you frame it. But it will be the average of the two - not specifically set for either the objects in the sunny foreground nor the shady background.
  • Spot - This will depend on where you put the center spot metering point - if you put it on the stump - the sunny foreground it will meter for the sunny side and the shady wall will be very dark. If you put the center spot metering point on the shady rock wall, it will meter for the shady wall, and the sunny foreground will be very blown out (over exposed).
In these examples, maintain a constant set of parameters - don't go changing apertures across shots, this will just add an additional dimension that needs to be evaluated in terms of what is going on with the exposure.



07-26-2013, 07:39 PM   #24
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QuoteOriginally posted by Parallax Quote
That is likely due to the FF (Pentax) lenses not having the proper coatings for digital sensors.
They do the same thing on film, though it has little to do with brand.


Steve
07-26-2013, 07:50 PM   #25
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QuoteOriginally posted by 6BQ5 Quote
Question: why would the camera calculate a different exposure between the two modes? Doesn't the same amount of light hit the same sensor?
Yes, the same amount of light hits the sensor, but the exposure settings (the numbers) are the result a mathematical conversion on the raw sensor output. Why this is needed is not clear to me, but it creates an issue for stop-down metering. This is the case for brands other than Pentax too. Pentax response was to provide a different conversion for stop-down metering in M-mode only. The manual for your camera has this information, though it is not real obvious. The key is the table that shows the capabilities for various lenses by type.


Steve
07-26-2013, 08:19 PM   #26
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Here is something to try. Use M and don't meter. Just use "Sunny 16" - Here's a brief table. The 16 is the aperture. The shutter speed is the inverse of the ISO

Bright sun behind you - f/16 @ 1/ISO
e.g ISO 400, f/16 @ 1/400
Side lit. f/11 @ 1/ISO
Back lit f/5.6 @ 1/ISO (for the subject, not the scene)
Back lit to cheat f/8 @ 1/ISO

Set your LCD to display the histogram and keep it barely clear of the right (bright) side until you get the hang of this.

My two M lenses on K10d work just fine with this un-meter.

Good luck - it's all a learning curve for everyone.
07-27-2013, 11:22 AM   #27
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QuoteOriginally posted by Canada_Rockies Quote
Set your LCD to display the histogram and keep it barely clear of the right (bright) side until you get the hang of this.
Shoot/chimp the histogram/adjust/shoot again

Works great!


Steve
07-27-2013, 12:05 PM - 1 Like   #28
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QuoteOriginally posted by stevebrot Quote
The key is the table that shows the capabilities for various lenses by type.
...I just checked the K-30 manual and I pointed to the wrong section. The pertinent information is on page 259, "Using the Aperture Ring". From the table in regards to Av mode and M/P lenses (includes adapted M42), "The shutter speed changes in relation to the open aperture but an exposure deviation may occur." The manual for the K-5 is a little more blunt and reads, "...an exposure error may occur."

Either way, the exposure mode behavior for non-A lenses on K-7 and newer bodies can be summarized as:

M-mode:
  • Accurate exposure for all lenses
  • Stop-down metering for aperture ring off "A" position (or lacking such)
Av-mode:
  • Accurate exposure for aperture ring in "A" position
  • No stop-down for metering or exposure for K-mount lenses with aperture ring off "A" position (wide-open only)
  • Deviant metering for aperture ring off "A" position (or lacking), includes manual aperture lens
Modes other than Av or M
  • Full functionality with aperture ring in "A" position
  • Defaults to Av with aperture ring off "A" position

Steve
07-27-2013, 08:08 PM   #29
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One thing that we all forgot to ask...

...Are you using the stock Pentax focus screen or have you upgraded to a replacement with split-image/microprism focus aide? The aftermarket screens with focus aids pretty much hose the spot metering on Pentax dSLRs.


Steve
07-27-2013, 08:18 PM   #30
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Spot metering with screens with central focus aids has nothing to do with the camera and everything to do with the blackout in the screen. That's why I use an LL-60 instead of one with central focusing aids.
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