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03-15-2013, 09:08 PM   #1
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Calculating exposure value?

If I set my k-01 to iso 100 and compare the f stop and recommended shutter speed to this chart

Exposure value - Wikipedia, the free encyclopedia

Am I somewhat accurately calculating the EV?

03-15-2013, 09:24 PM   #2
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Yes, that sounds right for EV(100) based on your cameras meter. You can use the chart or do the calculation.

EV 0 = 1 second at f/1.0

Note that EV is merely an abstraction of camera settings. When constrained by ISO meter setting, it becomes an indication of light intensity. Hence EV(100) for ISO 100.

Out of curiosity, why are you wanting to calculate EV?


Steve
03-15-2013, 09:45 PM   #3
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I just bought the camera and am having all kinds of trouble with AF. Well, maybe not all kinds. Shooting indoor at further distances (20-30 feet out past where the AF assist light can help). I bought the camera with the primary purpose of getting a camera with better low light performance than my ist-ds and jumped on this one despite knowing it would have some limitations due to the current price. The high iso and shake reduction are a dream compared to the ds. The low light AF, not so much of a dream. I have basically discovered, the camera does have worse performance that a dslr (even my old ist-ds but only under those specific conditions), the light in the room was dimmer than I thought, my lenses are not terribly fast and this camera hates slow glass, I don't know how to use the camera (I am getting the camera to work better as I learn its quirks and learn to get the setting right) etc.

Knowing the EV lets me know the actual light available to the camera in a particular shooting situation so I can determine how much of the problem is low light and how much is other things. I have lots of manual glass so I can overcome the problem with that (and the high iso performance and shake reduction will allow good capture in lower light which my ist-ds wouldn't). It basically solves my low light problem though I might have to manual focus at times when the ist-ds could auto focus. I just want to learn to use AF as well as it is capable, and also learn to use MF glass with it.

I did tell a littel about the problem in this thread

https://www.pentaxforums.com/forums/pentax-k-01/216790-k-01-vs-dslr.html

But that started out as a comparison between it and a dslr before I bought it.

Thanks for the info by the way.
03-15-2013, 09:57 PM   #4
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I guess a reasonable rule of thumb would be that if the light is dim to you, it will be dim to the camera as well and when the camera can't "see", it truly cannot focus accurately either. AF assist can help, but there are limits.


Steve

P.S. A lot of people (mostly Canon and Nikon users) will claim that their AF system will lock focus in available darkness, but focus lock and accurate focus are two different things


Last edited by stevebrot; 03-15-2013 at 10:35 PM.
03-15-2013, 10:41 PM   #5
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QuoteOriginally posted by stevebrot Quote
I guess a reasonable rule of thumb would be that if the light is dim to you, it will be dim to the camera as well and when the camera can't "see", it truly cannot focus accurately either. AF assist can help, but there are limits.


Steve

P.S. A lot of people (mostly Canon and Nikon users) will claim that their AF system will lock focus in available darkness, but focus lock and accurate focus are two different things
It didn't seem dim to me (I guess I just got used to it or can see in lower light just fine or something). Testing did show that the light was infact dim compared to normal lighting (I read EV 5-7 is typical indoor lighting).
03-16-2013, 05:05 AM   #6
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Here's a thought for you, if you get hold of an Sangamo Weston Light Meter Weston Master or similar (should be cheap enough these days, there's one on eBay just now starting bid 20) it shows light readings in EVs. Have a look at my review on the link below.

https://www.pentaxforums.com/accessoryreviews/showproduct.php?product=1223&cat=136

Hope this helps.
03-18-2013, 03:16 AM   #7
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QuoteOriginally posted by Ponosby Britt Quote
As does a Gossen Digisix
Aye, I think most of the light meters probably show an EV values, at least a light meter is easier to use than a chart, especially at all different ISO settings.
03-18-2013, 04:50 AM   #8
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I think I might actually have a light meter somewhere that came with some film stuff I got (for the lenses). Out of curiosity, do some film camera bodies have a light meter built in? I have several film bodies that I have got along with lenses.

03-18-2013, 05:35 AM   #9
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QuoteOriginally posted by ripit Quote
do some film camera bodies have a light meter built in
Most SLRs did, some of the really early ones didn't.
03-18-2013, 06:06 AM   #10
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Hi Ripit
I did a comparison between the ist ds and the k-01, with the same kit lens at 35 mm on both, in the basement here with lights off on a box with white printing.

Focus assist lights enabled:
At 6 metre, the k-01 could focus with its green light about 4 out of 5 times.
The ambient light level was below { iso 12800, 30 sec and f/4 }
The ist ds,could not focus until I moved to in to about 1.5 metre.

Focus Assist lights disabled: (I had to move to brighter light than above)
The ist ds can focus consistently at about 2 metre in light { iso 200 1.5 sec f/4 } .
Th k-01 was not able to focus at all in this light with its assist light disabled.
03-18-2013, 03:30 PM   #11
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QuoteOriginally posted by wombat2go Quote
Hi Ripit
I did a comparison between the ist ds and the k-01, with the same kit lens at 35 mm on both, in the basement here with lights off on a box with white printing.

Focus assist lights enabled:
At 6 metre, the k-01 could focus with its green light about 4 out of 5 times.
The ambient light level was below { iso 12800, 30 sec and f/4 }
The ist ds,could not focus until I moved to in to about 1.5 metre.

Focus Assist lights disabled: (I had to move to brighter light than above)
The ist ds can focus consistently at about 2 metre in light { iso 200 1.5 sec f/4 } .
Th k-01 was not able to focus at all in this light with its assist light disabled.

In room light (maybe 4-5 ev at first which is a bit low and then 5-6 when I added a light bulb)m it was fine in random conditions, when it was close enough for the focus assist light to work. At 20-25 feet is where I had problems. WIth lenses at f5.6, it was almost non functional and at ones in the 4.? there wer some problems. Even the 40mm 2.8 had some problems before I added the bulb and it was 4-5 ev. As far as problems, I mean will not focus at all. I did learn that the AF seems to have some weirdness to it. it didn't seem to like dark objects at all (less light reflected?). When outside the range of the af light, it did better focusing on a white wall, ceiling and door than it did on a brown couch with lots of edges and shapes, different lighting from shadows etc. I always thought a white wall was a serious challenge for contrast focus. I'm kind of thinking once I get used to the camera (learn what kind of objects the AF likes to lock on), things will be a bit better.

I have several film slr bodies so I'll check for light meters.
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