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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 06 Jan 2018 (Saturday) 21:44
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All Manual lens - Trying to understand EV and Light Meter App

 
56_kruiser
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Jan 06, 2018 21:44 |  #1

I purchased a Bower 8mm lens which is manual. The T2i that I have does no reading from the lens. What I see in the display when I turn the camera on, for example is:

Exposure time show: say 1/10
F stop does not show: F00
ISO Shows: say 200

So lets say I set the lens manually to 8mm, then on the camera I set ISO to 200. Then with teh camera in manual mode, as I turn the dial to increase time for shutter, it does show a dash under the minus 2 to +2 for exposure gauge.

I am presuming that when that dash gets under the 0 that is 'proper exposure time'. Would that be right? Would that be the case even though teh camera has no idea what F-Stop I have it set at?

I presumed no, but am finding it to not be that far off.

So, I thought I'd experiment with an app on my phone called Light Meter which has relatively good reviews. I can set the ISO setting on it, then point the phone camera at whatever I'm shooting, press a measure button, and it will tell me the exposure time for each Fstop. (Picture attached).

What I don't know about or understand, is that it also shows an EV number. I don't know what to do with or about that, if anything.

Interested in your feedback on this.



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kf095
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Jan 06, 2018 22:26 |  #2

I'm using real exposure meter for years. It looks similar to this picture. But it is made in Japan (accurate :) ).
This is how I read it.
ISO is set to 100.
At f1.4 it is close to 1/15, 5.6 is close to one second, f22 will take close to 15 seconds.
Baby it is dark out where!

EV is in use by masochists :) The GUI you have on the screen... as well. Switch to liveview measured by spot. At the bottom it will show ISO, shutter speed and APERTURE.


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Wilt
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Post edited 4 months ago by Wilt.
     
Jan 06, 2018 22:30 |  #3

You need not consider the EV value being displayed.

If you were making multiple measurements, comparing EV values is easier than trying to remember combinations of f/stop and shutter speed, and then calculating differences of light intensity.


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JeffreyG
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Jan 07, 2018 08:10 |  #4

56_kruiser wrote in post #18535264 (external link)
I am presuming that when that dash gets under the 0 that is 'proper exposure time'. Would that be right? Would that be the case even though teh camera has no idea what F-Stop I have it set at?

I presumed no, but am finding it to not be that far off.

The camera is telling you what it meters to be a proper exposure for the manual aperture setting that the lens is set at at the time you meter.

With a normal electronic lens, the camera needs to know the aperture setting because it does all metering and focusing with the aperture wide open, and then moved the aperture to the setting you have picked to take the photo. So if you elect f/8 while using a lens with a maximum aperture of f/2.8, the camera knows that the final image will be three stops darker than what it sees while metering, and it recommends a metered solution based on that knowledge.


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56_kruiser
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Jan 07, 2018 11:10 |  #5

JeffreyG wrote in post #18535463 (external link)
The camera is telling you what it meters to be a proper exposure for the manual aperture setting that the lens is set at at the time you meter.

With a normal electronic lens, the camera needs to know the aperture setting because it does all metering and focusing with the aperture wide open, and then moved the aperture to the setting you have picked to take the photo. So if you elect f/8 while using a lens with a maximum aperture of f/2.8, the camera knows that the final image will be three stops darker than what it sees while metering, and it recommends a metered solution based on that knowledge.

That all makes sense to me. But, I am thinking that this Bower lens (external link) does not interface for readings to the Canon, basing that mainly on the fact that F/Stop shows as F00. Am I wrong on that?


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JeffreyG
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Jan 07, 2018 11:17 |  #6

56_kruiser wrote in post #18535571 (external link)
That all makes sense to me. But, I am thinking that this Bower lens (external link) does not interface for readings to the Canon, basing that mainly on the fact that F/Stop shows as F00. Am I wrong on that?

You are correct, the camera does not know the aperture. But so long as you meter and shoot with the aperture manually set to a single aperture, the camera doesn't need to know what the aperture is.

When you center the needle at 1/100 and ISO100 for example, the camera is telling you: "1/100, ISO 100 and whatever aperture I'm looking through is a correct exposure for this scene." The camera doesn't really need to know what aperture it is looking through so long as the aperture will not change between metering and the shot.


My personal stuff:http://www.flickr.com/​photos/jngirbach/sets/ (external link)
I use a Canon 5DIII and a Sony A7rIII

  
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56_kruiser
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Jan 07, 2018 11:31 |  #7

kf095 wrote in post #18535278 (external link)
I'm using real exposure meter for years. It looks similar to this picture. But it is made in Japan (accurate :) ).
This is how I read it.
ISO is set to 100.
At f1.4 it is close to 1/15, 5.6 is close to one second, f22 will take close to 15 seconds.
Baby it is dark out where!

EV is in use by masochists :) The GUI you have on the screen... as well. Switch to liveview measured by spot. At the bottom it will show ISO, shutter speed and APERTURE.

I tried your suggestion for Live mode. It seems to not work whatsoever near accurate, at least with this Bower lens (again, maybe the camera is not gettinga ny readings from it at all?).

I'll show a couple pictures below:

When using live mode, in order to get the dialed speed on the -2 to +2 meter to be at 0, or center, it sets the speed to 1/250th, and the picture would be black. (I'm doing this inside).


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Then when I change out of live view, this is what is displayed:



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Shouldn't both be in synch? In any event, the settings used in live mode don't work.

FYI...when not using live mode, if I dial the speed to get the pointer to the zero point, it sets it to 2.5 seconds, and I get a relatively decent picture.

I had downloaded the app because I thought I would need a light meter and was going to toy with that before buying a light meter. It gives readings for time about the same as the camera.

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Wilt
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Post edited 4 months ago by Wilt.
     
Jan 07, 2018 14:12 as a reply to  @ 56_kruiser's post |  #8

I have a Tamron f/2.5 SP Adaptall mount lens from the days of film SLRs.
For that lens I have an

A. Adaptall-EOS mount adapter with no electrical contacts and no chip
B. Adaptall-EOS mount adapter with electrical contacts and with chip.

If I set up a gray card in fixed artificial illumination and aim a handheld Minolta spotmeter at it, it reads ISO 400, 1/30 f/2.0 + 0.9EV... the same reading as my Minolta Autometer Vf incident meter.

Combination A (above) is like using your Bower manual lens


  1. If I put 'A' onto a Canon 40D or a Canon 7DII, both in Av mode, the needle always centers on the scale because that indicates zero Exposure Compensation has been set. One would assume that when the Tamron lens is set to f/4, a reading of 1/15 would result (equivalent exposure to 1/30 f/2.8). The 40D reads 1/13; The 7DII reads 1/10.
  2. If I put 'A' onto a Canon 40D or a Canon 7DII, both in M mode, One would assume that when the Tamron lens is set to f/4, a reading of 1/15 should result (equivalent exposure to 1/30 f/2.8). The 40D reads 1/10; The 7DII reads 1/10.

Combination B

  1. If I put 'B' onto a Canon 40D or a Canon 7DII, both in Av mode, the needle always centers on the scale because that indicates zero Exposure Compensation has been set. One would assume that when the Tamron lens is set to f/4, a reading of 1/15 would result (equivalent exposure to 1/30 f/2.8). The 40D reads 1/13; The 7DII reads 1/10.
  2. If I put 'B' onto a Canon 40D or a Canon 7DII, both in M mode, One would assume that when the Tamron lens is set to f/4, a reading of 1/15 should result (equivalent exposure to 1/30 f/2.8). The 40D reads 1" f/4; The 7DII reads 0"5 f/4.


Because of tested behaviors seen with Combo B at other aperture settings, I do not trust stopped-down readings from any Canon dSLR (10 year old ones or 2 year old ones!) used with chipped or non-chipped adapters, for any adapted lenses (Tamron, Olympus OM, or otherwise). I use handheld meters and transfer the readings to the Canon dSLR in M mode, and ignore the camera meter. Use of a chipped adapter only provides in-viewfinder focus confirmation.

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Post edited 4 months ago by Wilt. (5 edits in all)
     
Jan 07, 2018 15:04 |  #9

I just shot two series with my Tamron 90mm f/2.5 lens, in Av mode, using the Tarmon-EOS mount adapter with electrical contacts, this time using my 7DII to avoid the possibility that my testing was invalid because newer cameras did not behave like 10-15 year old bodies!


  1. In the first series (shots 1-6), I set the aperture value in camera to max f/stop f/2.5, and let the camera adjust the shutter speed to suit the declining amount of light as I stopped down the lens...
    f/2.5, f/4, f/5.6, f/8, f/11, f/16
  2. In the first series (shots 7-12), I set the aperture value in camera to the actual f/stop f/2.5, f/4, f/5.6, f/8, f/11, f/16, and let the camera adjust the shutter speed to suit the declining amount of light as I stopped down the lens...f/2.5, f/4, f/5.6, f/8, f/11, f/16


In interrogating the density of the 18% gray card using LR, I discovered that the camera overexposed the wide-open shots by +1.02EV, and I had to adjust Exposure slider in order the get eyedropper values of 50-50-50, as I would expect the 'midtone' value to record. I applied that same correction across all shots. Where one should get UNIFORM density of the 18% tonality patch in all shots, the density actually varied based upon the chosen f/stop...in most cases overexposure but in one case of each (at f/16) the shots were underexposed! This illustrates the inability to adjust uniformly for correct exposure as measured by the camera when using manual adapted lenses.

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/adaptedlensmeter_zpsoh2m5ifv.jpg

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Jan 08, 2018 09:02 |  #10

56_kruiser wrote in post #18535589 (external link)
I tried your suggestion for Live mode. It seems to not work whatsoever near accurate, at least with this Bower lens (again, maybe the camera is not gettinga ny readings from it at all?).

I'll show a couple pictures below:

When using live mode, in order to get the dialed speed on the -2 to +2 meter to be at 0, or center, it sets the speed to 1/250th, and the picture would be black. (I'm doing this inside).

thumbnail
Hosted photo: posted by 56_kruiser in
./showthread.php?p=185​35589&i=i205559250
forum: General Photography Talk


Then when I change out of live view, this is what is displayed:

thumbnail
Hosted photo: posted by 56_kruiser in
./showthread.php?p=185​35589&i=i180156967
forum: General Photography Talk


Shouldn't both be in synch? In any event, the settings used in live mode don't work.

FYI...when not using live mode, if I dial the speed to get the pointer to the zero point, it sets it to 2.5 seconds, and I get a relatively decent picture.

I had downloaded the app because I thought I would need a light meter and was going to toy with that before buying a light meter. It gives readings for time about the same as the camera.


I don't know what is happening when you are in Lv mode, I suspect you have something odd set up, but it is obvious from the fact that you have a completely black screen that the exposure is way under despite the meter being centered. The results showing on the info mode show that you are indeed at a minimum 2 stops underexposed, just what one would suspect. I would do a full reset of all of the camera settings, and see if that helps. I'm not a great user of LV, it's simply not useful for most of my photography.

One of the great advantages of Canon bodies, which it seems is absent on many other brands, is the fact that you can simply use Aperture Priority autoexposure mode with manual lenses with no electrical contacts. If you set the camera to Av and then simply select any of the manual aperture settings directly on the lens, the camera although displaying ƒ/0.0 will still adjust the shutter speed to achieve a correct exposure. You can even set exposure compensation, and bracketing if you need to. In fact Program mode will still work, I'm not sure about Green Box, but there is a possibility that it might too. The exposure automation knows that it can't adjust the aperture, so it simply adjusts the shutter, and possibly the ISO if that is also set to auto, or you have the safety override on.

When it comes to the lightmeter app on your phone I would set it to incident mode, just tap the circular bit in the top right of the screen. the center part will just white when in incident mode. This uses the forward facing camera's exposure metering system to provide an incident reading

For an incident reading you have to have the meter at the subject location, or if outside in the same light, to make a correct measurement. You can tap the measure button to lock the reading, which is useful. With the ISO set to the value you will be using the outside scale is the Aperture value, and the inside value is the shutter speed. The dots give you the one third stop settings. Reading off is simple, Pick an aperture and read off the adjacent shutter speed. Or pick the shutter speed, and read the aperture value. I really like incident meters, especially the ones with the analogue scale readouts like this app has. They are very useful since it allows you to see every possible choice of aperture and shutter speed the current light level and ISO allows for.

On my Samsung Galaxy Note 3 I have checked this app against my 50D and it matches the exposure to within 1/3 EV across a range of light levels against my grey target.

You don't really need the EV setting these days. In the past there were some cameras that allowed you to set the EV value, then simply change one control to adjust the shutter speed and aperture together to maintain a constant exposure. The EV scale is based on EV0 being an exposure of 1s @ ƒ/1. Each unit of EV is one stop of exposure. It is independent of ISO, so if you change the ISO the EV value will change. The one time that EV is still commonly used is in camera specifications. You will find that for your camera Canon specify minimum and maximum EV values for both the AF system, and the exposure metering. I know for example that the 5DIII has AF specified to work over a range of -2EV to 18EV @ ISO100 and 23°C. Now you can pretty much stop worrying about EV.:-)

Alan


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56_kruiser
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Jan 08, 2018 14:18 |  #11

Everyone...I am really appreciating the input. I am reading things that points me mto needs of some learning and will be going down that path.

All good and appreciated input.

If my practicing and testing reveal anything interesting, I'll post it here.

RE: Live mode: I've read that a lot of people really like it. I too have not found it something that I typically like. One thing that is helpful, when the time and need permits, is to put it into livie mode and zoom in with the button on the back of the camera and get a more accurate focus.


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All Manual lens - Trying to understand EV and Light Meter App
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