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07-06-2009, 05:07 PM   #16
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QuoteOriginally posted by Lowell Goudge Quote
somehow I missed that. I have offered to help establish this several times by post a standard for tests. after all no one will have all the different lenses or bodies, but if we extablish the "rules" so to speak, of an exposure test, then we can use this test to "normalize the entire thing.

As far as a test goes, here is what I do.

Select a uniform grey to white surface. My favourites are paved roads, block walls and side walks.

Set exposure to neutral, by this I mean contrast brightness etc all to neutral, and using JPEGs.

Use an ISO that allows you to cover the full range of exposure and then take a shot at each aperture indent (and / or dial position for A lenses)

Using a photo editor, measure the grey scale reading in the central 10% of the frame.

Plot grey scale (linear) vs aperture (log) in a spread sheet.

I have one all set up for this.

I find in neutral contrast one stop is about 45 greyscale (50 with high contrast, 40 with low contrast)

The method works and is repeatable.
Stupid question probably but I am right in assuming you are using the green button to get a base setting at each aperture for the pre A lenses?


Last edited by robbiec; 07-07-2009 at 08:40 AM. Reason: spelling mistake
07-06-2009, 06:15 PM   #17
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QuoteOriginally posted by robbiec Quote
Stupid question probably but I am right in assuming you are using the green button to get a base setting at each apeture for the pre A lenses?
not so stupid, but for me yes, as I only have *istD and K10D (in the shop at present) and newly aquired K7

All have green button.

YOu can also use DOF preview and match needle approach on cameras that don't have green button, Not sure of any other metering methods without green button, but never having owned other than a camera with green button, I am not the best to say
07-07-2009, 08:26 AM   #18
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QuoteOriginally posted by Lowell Goudge Quote
somehow I missed that. I have offered to help establish this several times by post a standard for tests. after all no one will have all the different lenses or bodies, but if we extablish the "rules" so to speak, of an exposure test, then we can use this test to "normalize the entire thing.

As far as a test goes, here is what I do.

Select a uniform grey to white surface. My favourites are paved roads, block walls and side walks.

Set exposure to neutral, by this I mean contrast brightness etc all to neutral, and using JPEGs.

Use an ISO that allows you to cover the full range of exposure and then take a shot at each aperture indent (and / or dial position for A lenses)

Using a photo editor, measure the grey scale reading in the central 10% of the frame.

Plot grey scale (linear) vs aperture (log) in a spread sheet.

I have one all set up for this.

I find in neutral contrast one stop is about 45 greyscale (50 with high contrast, 40 with low contrast)

The method works and is repeatable.
Except for the plot, that is very close to what I have done with each pre-A lens I have used. I use raw files so it is easy to zero out compensation. My trusty old grey card has gotten lots of use. I keep consistent on the exposure by using it as the entire field of view, even if I can't get it in focus. I would be interested in your SS if you are willing to share.
07-07-2009, 12:03 PM   #19
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My pet peeve with reviews (particularly on Amazon) is those who do a review without adaquate time using a lens. Someone who says "I just go this lens yesterday and it is awesome," should wait a while. I don't think you can really say what you think about a lens until you've actually spent some serious time shooting with it.

07-07-2009, 01:38 PM   #20
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QuoteOriginally posted by GeneV Quote
Except for the plot, that is very close to what I have done with each pre-A lens I have used. I use raw files so it is easy to zero out compensation. My trusty old grey card has gotten lots of use. I keep consistent on the exposure by using it as the entire field of view, even if I can't get it in focus. I would be interested in your SS if you are willing to share.
I think you mean this?
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File Type: zip exposure template.zip (5.9 KB, 58 views)
07-07-2009, 01:52 PM   #21
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well you know we only have that many lenses in the Pentax line.
you know you can't go wrong with any of the Ltd's or *s lenses

that leaves you the old / cheapo lenses ... since the price of those is usually low... or they are too rare to find , you know you cant really go wrong with these as well, (especially with the ones you cant find )

In other words I am asking the OP : have you ever seen a reavew in here that does not fit the lens?
07-07-2009, 02:32 PM   #22
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QuoteOriginally posted by redpigeons Quote
well you know we only have that many lenses in the Pentax line.
you know you can't go wrong with any of the Ltd's or *s lenses

that leaves you the old / cheapo lenses ... since the price of those is usually low... or they are too rare to find , you know you cant really go wrong with these as well, (especially with the ones you cant find )

In other words I am asking the OP : have you ever seen a reavew in here that does not fit the lens?
Sent ya a pm.. I am wary of a slinging match breaking out.
07-07-2009, 06:00 PM   #23
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I have done a fair number of reviews...

Hi,
I have done a fair number of reviews (mostly for third-party lenses) and try to be complete adhere to a specific format. Here are my personal guidelines:
  • List the price, but also make note in the body of the message regarding condition and whether new or used.
  • Rate the lens based on the combination of optical qualities, build, and handling characteristics regardless of current market pricing
  • Try to include some notion of what I think the lens is good for and what it is not good for.
  • Give some explanation for the rating as well as factors that might raise/lower the score.
  • Try to fill in details about the lens that are missing from the general description above the first review.
  • Attach one or two example shots that show the strengths/weaknesses of the lens.
  • Try to include pros/cons and general impression for each of the following:
    • Optical performance
    • Build
    • Handling characteristics
Those last two sub-points are often left out of the reviews, but strongly affect the degree of satisfaction a user may experience when actually using the lens. My Jupiter-9 is a good example. It would be unkind to omit the awful truth that the J-9 is a bit ponderous in use, good as the lens may be.

In regards to the dSLR exposure issues, I always mention the exposure issues, but qualify the statement with a reminder that ALL non-A contact lenses suffer from this issue on KxxD and KxxxD bodies and that it is not a problem with or deficiency of the lens per se. As such, I don't factor the exposure problems into the final rating. (I can hear the howls rising up even as I type, but if the potential buyer owns a K-7 this may not be a significant issue to them. As I said...the exposure issue is not a lens problem, but a problem with a limited subset of cameras on which most of these lenses will mount.)

Steve

P.S. In case anyone is curious...I have been an avid photographer since the late 1960s and am approaching 3000 posts to this site at the time of this comment. I guess that makes me and a few others around here some sort of expert! (Tongue firmly planted in cheek!)

07-07-2009, 07:23 PM   #24
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QuoteOriginally posted by stevebrot Quote
In regards to the dSLR exposure issues, I always mention the exposure issues, but qualify the statement with a reminder that ALL non-A contact lenses suffer from this issue on KxxD and KxxxD bodies and that it is not a problem with or deficiency of the lens per se. As such, I don't factor the exposure problems into the final rating. (I can hear the howls rising up even as I type, but if the potential buyer owns a K-7 this may not be a significant issue to them. As I said...the exposure issue is not a lens problem, but a problem with a limited subset of cameras on which most of these lenses will mount.)
here comes the first howl

for exposure issues, I think there are two types, and while one may be a function of camera, specifically K10/20 metering with non A series, the other is very important, specifically exposure drift with aperture. In several of my reviews, I have noted an increasing error in exposure as you stop down, due probably to errors in the aperture control or settings. Reporting this is useful
07-07-2009, 08:16 PM   #25
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QuoteOriginally posted by Lowell Goudge Quote
here comes the first howl

for exposure issues, I think there are two types, and while one may be a function of camera, specifically K10/20 metering with non A series, the other is very important, specifically exposure drift with aperture. In several of my reviews, I have noted an increasing error in exposure as you stop down, due probably to errors in the aperture control or settings. Reporting this is useful
Thanks for qualifying my statement Lowell. There are indeed some lenses that came with non-linear apertures from the factory. Back in the day (as you are aware), the camera magazines tested for such things!

Steve
07-08-2009, 09:45 AM   #26
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C&C welcome, please tell me what you are missing here and/or what could be left out in your opinion: Carl Zeiss Jena Flektogon MC 2.4/35 review

I did try not to be too enthusiastic although this is one of my big fave lenses. I also realized that although I got a ton of lenses I can't really compare this lens to the most obvious Pentax rivals and alternative lenses cause I never used them. This still is good to know for the reader imo.

I see that the quality of the database consists of individuals willing to contribute in the first place and then there's individual information in the text for the readers to pick up or not.

The last thing I am wondering about is the amount of non-PK-mount lenses to be included into the database. OTOH why should there be any limit to that database, the more lenses come up the more sub-categories will be created at a certain point.

A big shoutout to Ole, who I think was the guy that put hard work into the lens database to get it to where it is right now, thanks a lot Ole! (guess it started here: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/163-lens-revie...m-members.html)

Best, Georg (the other)
07-08-2009, 10:13 AM   #27
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QuoteOriginally posted by Lowell Goudge Quote
here comes the first howl

for exposure issues, I think there are two types, and while one may be a function of camera, specifically K10/20 metering with non A series, the other is very important, specifically exposure drift with aperture. In several of my reviews, I have noted an increasing error in exposure as you stop down, due probably to errors in the aperture control or settings. Reporting this is useful
I think I almost understand this, but I have some questions/thinking while typing:

Let's say I have an M50/1.7 and an A50/1.7. To test the M, I put the camera in M mode, point the camera at a block wall, choose an exposure for a baseline, then take a series of shots at the same Ev but different apertures. So f1.7 and 1/2000, f2 and 1/1500, etc., no metering. If I have this right, I already have used this method, just not analyzed the results. I'm not sure why it's necessary to use JPEG - you eliminate converter issues but each camera has different processing even at neutral settings.

Then I put on the A50/1.7, but since it is an A lens, I use the A setting and change the aperture on the camera, because I can. That appears to be the same thing but is using different mechanisms to control the aperture. When you use the aperture ring (and thus M mode so it actually works), the camera just moves the aperture lever between "wide open" and "stopped down", with no intelligence about where "stopped down" is. The aperture ring setting on the lens moves a cam which adjusts the "stopped down" position of the actual blades. When you use the A setting, the camera moves the aperture lever directly.

Lenses without an A position can have errors related to the aperture ring-cam mechanism. With an A position, they can have errors related to that mechanism or the aperture lever mechanism, and would require testing with both. Lenses without aperture rings can only have errors with the aperture lever mechanism. So one important question - has anyone seen exposure errors caused by the aperture lever mechanism? If not, a lot of testing is eliminated.
07-08-2009, 10:31 AM   #28
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QuoteOriginally posted by Lowell Goudge Quote
I think you mean this?
That looks like it.
07-08-2009, 11:52 AM   #29
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QuoteOriginally posted by Just1MoreDave Quote

...Lenses without an A position can have errors related to the aperture ring-cam mechanism. With an A position, they can have errors related to that mechanism or the aperture lever mechanism, and would require testing with both. Lenses without aperture rings can only have errors with the aperture lever mechanism. So one important question - has anyone seen exposure errors caused by the aperture lever mechanism? If not, a lot of testing is eliminated.
Dave,
This has popped into my thoughts several times over the last few weeks. There are so many comments/posts regarding under/overexposure but nobody considers that the aperture is not determined by a mechanical "stop" (like in the old days). Instead it is based on the very limited travel of a lever that couples into the lens diaphragm mechanism. If the lever/mount/lens is even a little out-of-wack, the aperture opening will be something other than what the camera asked for.

Say for instance that one has a Pentax-A 50/1.7 with a slightly bent aperture coupling lever. The taking aperture could be off by 1 or more stops. Or, consider a mount that is loose on or over/under-rotates onto the camera. A few degrees one way or another can make a big difference.

Steve
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