# Question about proper exposure with a manual lens



## Novelectro (May 18, 2016)

Hi All,

First post so hopefully I am in the right place.  I'm still learning a lot and am pretty new - but I figured this question wasn't completely basic, so here goes.

I'm into nightsky photography and I recently picked up a Rokinon 16mm f2.0 lens for my canon 70d.  It appears that it's one of the best nightsky lenses for aps-c cameras and I'm really excited to use it.  It's a manual lens and so understand my I need to adjust focus and aperture via the lens itself and not my camera.

What I'm confused about right now is that my camera doesn't seem to tell me the appropriate exposure at all prior to taking a picture.  Basically if I set my shutter speed to what my camera says is zero/in the middle/ perfectly exposed - the photo image when I view it is significantly underexposed.  In order for me to expose properly where the histogram is in the middle - I actually need to take the picture at somewhere around +2 or +3.  This doesn't seem right to me, but then again I'm still very much a novice.

I bought the lens used, so most importantly I want to make sure that I didn't get hosed by a faulty lens (or maybe there is even something wrong with my camera? But I don't seem to have this problem with my kit lens).

Thanks in advance to anyone who has some suggestions!


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## runnah (May 18, 2016)

sounds like something going on with your camera. I have a few manual Rokinon lenses for my video camera and since they are manual there is no lens to camera communication. 

What metering mode are you in? Does it only happen for night photography?


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## Novelectro (May 18, 2016)

I'm on center weighted average but tried another mode as well and didn't seem to make a difference.  I just switched back to my kit lens and that still appears to be measuring alright.  If I'm in the middle then the histogram on the taken picture looks roughly where it should be.

I haven't taken any night shots yet.  This is just taking the first few test shots in my kitchen and wondering why I need to get it to +3 to get an appropriately exposed photo.


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## jcdeboever (May 18, 2016)

I don't have a Canon but the older Pre- AI, AI, and AIS glass will not meter on my Nikon D3300. I go by the sunny 16 rule. In your case with nighttime stuff, a notepad may be in order. Mobile light meter app may be useful as well.

Sent from my XT1254 using Tapatalk


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## gsgary (May 18, 2016)

It should work in manual and aperture priority exposure mode


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## Novelectro (May 18, 2016)

jcdeboever said:


> I don't have a Canon but the older Pre- AI, AI, and AIS glass will not meter on my Nikon D3300. I go by the sunny 16 rule. In your case with nighttime stuff, a notepad may be in order. Mobile light meter app may be useful as well.
> 
> Sent from my XT1254 using Tapatalk



Thanks for the suggestion.  While I don't really want to give up and accept that the only conclusion is a workaround (at least until I get the impression that my issue is known and accepted by many), do you have any recommendations for an app?  I tried downloading "myLightmeter" but it doesn't work very well.  Seems to be like 4 or 5 clicks underexposed.

Man this is frustrating.  Just wanted to hit the ground running with the lens.


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## jcdeboever (May 18, 2016)

I have used light meter and it is generally spot on when comparing to digital. One thing to keep in mind though, if you have auto ISO set in camera, this may throw things off as light changes rapidly and this may be why your stuff isn't right.  

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## Novelectro (May 18, 2016)

gsgary said:


> It should work in manual and aperture priority exposure mode



Good point about Aperture priority.  Just tried that and it appears to be much closer.  Still not perfect and maybe a touch underexposed but that's probably just me nitpicking (I still don't know enough to say whether or not something "should" or "shouldn't" be anything.  I'm basically 3 months into learning photography from YouTube and Google).

Manual is very clearly off though.  Like not even close and I definitely don't plan on using Aperture priority for the bulk of what I want to do with this lens.


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## Novelectro (May 18, 2016)

jcdeboever said:


> I have used light meter and it is generally spot on when comparing to digital. One thing to keep in mind though, if you have auto ISO set in camera, this may throw things off as light changes rapidly and this may be why your stuff isn't right.
> 
> Sent from my XT1254 using Tapatalk



Nope I'm set to 100.  Now I'm really wondering what's going on.


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## gsgary (May 18, 2016)

Novelectro said:


> gsgary said:
> 
> 
> > It should work in manual and aperture priority exposure mode
> ...


Manual should be closer than aperture priority if you are reading the meter properly you can't just go by the meter you have to learn to evaluate the scene

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## jcdeboever (May 18, 2016)

Novelectro said:


> jcdeboever said:
> 
> 
> > I have used light meter and it is generally spot on when comparing to digital. One thing to keep in mind though, if you have auto ISO set in camera, this may throw things off as light changes rapidly and this may be why your stuff isn't right.
> ...


Have you tried a total reset? I once was having issues similar to that and I apparently changed something in the menu and couldn't figure out. Reset and was back on track. Now I am totally familiar with the menu and developed pretty good pre-check skills. 

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## jcdeboever (May 18, 2016)

Novelectro said:


> jcdeboever said:
> 
> 
> > I have used light meter and it is generally spot on when comparing to digital. One thing to keep in mind though, if you have auto ISO set in camera, this may throw things off as light changes rapidly and this may be why your stuff isn't right.
> ...


I'm not familiar with that app, some are apparently better than others. Relax, you'll get er sorted. gsgary is familiar with your Canon stuff. 

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## Novelectro (May 18, 2016)

I just tested something...looking at the same subject with the same focus and making no changes at all, set to aperture priority and the camera selected 40 as the shutter speed and I took a picture.  It was slightly underexposed but definitely right in the ballpark.

Immediately after I switched to manual, the camera was set to 250 shutter speed and indicated that it was exposed correctly (of course it was very dark).


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## Novelectro (May 18, 2016)

A total reset doesn't sound like a bad idea.  I'll figure out how to do that and report back.



gsgary said:


> Novelectro said:
> 
> 
> > gsgary said:
> ...



I'm sure you are right about that.  But you're saying that there could be a discrepancy as large as what I'm indicating?  That seems far fetched but maybe not.


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## wfooshee (May 18, 2016)

That lens does not communicate electronically with the camera, and metering must be done stopped down. If you can't do stopped-down metering with your camera, then you have some arithmetic to do. Meter at _f_:2, which is wide open, then adjust your reading for what you want to set your aperture to. If you want _f_:8, for example, then whatever it meters for your shutter speed when it's wide open, you need to lengthen by 4 stops, since _f_:8 is four stops under _f_:2.


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## KmH (May 19, 2016)

*A Stop*

A stop of exposure is a fundamental photography concept.
A 'stop' is a doubling (2x) or a halving (0.5x) of the amount of light that reaches the recording media, be it film or an electronic sensor.
Since exposure is a triad of adjustments (shutter speed, ISO, lens aperture) you can change 1, 2 or all 3 of the triad settings.

If you want 1 more stop of exposure (brighter) you can adjust just one of the 3 by 1 more stop.
Or, you can change 2 of the 3 by 1/2 more stop each for a net gain of 1 stop of exposure.
Or, you can adjust all 3 by 1/3 more stop for a net gain of 1 stop of exposure.

You can also change the triad of settings and have no change in the exposure.
If you change 1 of the 3 settings by 1 stop more exposure and change a 2nd setting by 1 stop less exposure the net change is zero.

Suppose you subtracted a stop of shutter speed to help stop subject motion, you could add a stop of lens aperture to keep the exposure the same. However, adding a stop of aperture will also affect the total DoF by a small amount. So, if you don't want the DoF to change you would add a stop of ISO instead, however, adding a stop of ISO will increase by some amount the image noise in the photo.

*Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.*
Most DSLR cameras let you change that to 1/2 stop or 1 stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.


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## gsgary (May 19, 2016)

Novelectro said:


> I just tested something...looking at the same subject with the same focus and making no changes at all, set to aperture priority and the camera selected 40 as the shutter speed and I took a picture.  It was slightly underexposed but definitely right in the ballpark.
> 
> Immediately after I switched to manual, the camera was set to 250 shutter speed and indicated that it was exposed correctly (of course it was very dark).



When you tested it in Aperture priority was the compensation set to zero, you could have easily taken a reading from a different position, it needs to be on a tripod so it meters off the same spot


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## petrochemist (May 19, 2016)

Cameras generally do not meter down to the low light levels used for night skies.
Even if the did they would try to make the image average to 18% grey - not what you want!

It's usually best to put the camera in manual mode & set the shutter speed yourself. Anything longer than about 30 seconds (with your camera & lens) will start to show movement of the stars due to the earth's rotation. The '500 rule' gives the maximum to avoid star movement.

The quality of your skies (basically light pollution) will often have a significant effect on how many stars you can see - round here (semi rural England) 'sky glow' is a significant nuance for astronomy.


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## Novelectro (May 19, 2016)

gsgary said:


> Novelectro said:
> 
> 
> > I just tested something...looking at the same subject with the same focus and making no changes at all, set to aperture priority and the camera selected 40 as the shutter speed and I took a picture.  It was slightly underexposed but definitely right in the ballpark.
> ...



This was in the exact same spot, aiming at the exact same place, where aperture priority was indicating that "40" appropriate and then immediately switching over to manual, which thought that 250 should be dead centered on the meter.


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## Novelectro (May 19, 2016)

petrochemist said:


> Cameras generally do not meter down to the low light levels used for night skies.
> Even if the did they would try to make the image average to 18% grey - not what you want!
> 
> It's usually best to put the camera in manual mode & set the shutter speed yourself. Anything longer than about 30 seconds (with your camera & lens) will start to show movement of the stars due to the earth's rotation. The '500 rule' gives the maximum to avoid star movement.
> ...



I'm not even attempting to take night sky photos yet.  I'm just sitting on my couch aiming at furniture and the meter is dead center when it's way way way underexposed, and when I just try to expose it properly through trial and error, I have to go up to +3 until my histogram is telling me that I am in the right spot.


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## gsgary (May 19, 2016)

Novelectro said:


> gsgary said:
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> 
> > Novelectro said:
> ...


In your post you said you were using +3 compensation this would account for the difference 

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## Novelectro (May 19, 2016)

wfooshee said:


> That lens does not communicate electronically with the camera, and metering must be done stopped down. If you can't do stopped-down metering with your camera, then you have some arithmetic to do. Meter at _f_:2, which is wide open, then adjust your reading for what you want to set your aperture to. If you want _f_:8, for example, then whatever it meters for your shutter speed when it's wide open, you need to lengthen by 4 stops, since _f_:8 is four stops under _f_:2.



I think you're right that the only way of dealing with this is via math/formula.  It doesn't seem like this is something that can be "fixed".  When you say that I should meter from f2 to know how to meter when I'm stopped down - I am somewhat confused.  I don't get correctly metered at f2 either.  I'm "guessing" as to where my shutter speed should be whether the lens is wide open or not.


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## wfooshee (May 20, 2016)

Stopped-down metering means that you have the aperture set where you want it for the picture, and you'll see that the viewfinder is darker than it usually is. I'm not a Canon user, but my brother is, and he's telling me that the camera will show 00 as the aperture rather than the actual setting, because it's getting no information from the lens. Set the aperture on the lens (with the aperture ring, not the camera dial - the camera cannot control the lens's aperture) to its largest aperture (smallest number) to compose and focus, because that's where you get the brightest viewfinder. Then set the aperture on the lens that you want to use and then meter the scene. You'll see the viewfinder darken as you turn the aperture ring on the lens. You should be able to meter in Av or M modes, but you may not be able to use evaluative mode on the meter; just spot or center-weighted.

The term "stopped-down metering" is opposed to auto-aperture metering, which is how we're all used to using the camera. The lens stays wide open, no matter what the aperture is set to, until the shutter is triggered, and at that point the lens automatically stops down to the selected aperture to take the picture. The meter knows this will happen and compensates automatically. It knows that the lens wide open might be _f_:2 or _f_:5.6, whatever it happens to be, and when you have the camera set for say, _f_:11, the camera reads the light through the wide open lens and computes what it will need to be when the lens stops down. By the way, this automatic aperture capability, where the camera meters wide open and the viewfinder operates wide open, and the lens stops down just for the instant when the shutter fires, is what the term "AUTO" means when you see it on a lens. That tells you that the lens is capable of automatically stopping down to the selected aperture for the shutter to fire, but remains wide open for metering and viewing. We take that for granted, but it has not always been the case! With your lens, it's _not_ the case.

You set the aperture ring to maximum aperture to focus and compose, then set it to the desired aperture for metering and shooting. Use a metering mode other than evaluative.


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## Novelectro (May 20, 2016)

Thanks for explaining that, wfooshee.  I think that the other problem though is that I can't really see anything at f2 anyway (when metered at what is supposedly a perfectly exposed picture).  I still don't really get it, even if the lens can't electronically communicate with the camera, it seems like the camera should still understand roughly where the meter should be.


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## Vtec44 (May 20, 2016)

What about shooting with live view or a using a light meter?


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## Novelectro (May 20, 2016)

Vtec44 said:


> What about shooting with live view or a using a light meter?



I am shooting with live view.  Going to mess around with some light meter apps.


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## gsgary (May 20, 2016)

Novelectro said:


> Vtec44 said:
> 
> 
> > What about shooting with live view or a using a light meter?
> ...


Do you know how to use a lightmeter 

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## Novelectro (May 20, 2016)

gsgary said:


> Novelectro said:
> 
> 
> > Vtec44 said:
> ...



No I don't.  The one I downloaded "myLightMeter" looks relatively self explanatory?


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## Novelectro (May 20, 2016)

So I realized today that I don't have this issue with taking photos through the viewfinder.  The metering seems to be roughly where it's supposed to be.  The problem only exists when shooting in live view.  

So at least Ive made some progress.  Any ideas as to why the live view metering is acting so differently?  I think it's something that I can live with, but I like to take a lot of shots from really low angles - it's nice to be able to compose my shots from the live view screen since I can angle it up when the camera is only a few inches off the ground.

Appreciate everyone's contributions btw.


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## john.margetts (May 20, 2016)

Your camera probably came with  a soft rubber 'plate' to go over 
the viewfinder. This stops the meter responding to light entering the camera through the viewfinder when your eye is not blocking it. Try it.


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## wfooshee (May 20, 2016)

The camera's actual metering system is totally bypassed in Live View because the mirror is up and no light gets into the top of the camera. the metering system lives around the pentprism at the top. The camera "meters" during Live View by trying to examine what it sees on the sensor itself and making a best guess. it's not really metering the light, it's reading the signal strength of the sensor pixels.

Basically, Live View is _not_ for photography, it's for video. You can use it in photography for critical focus, by switching to Live View, zooming it in and focusing, but then you should switch out of Live View and use the camera as a reflex camera so all of its systems are in play. Also, keep in mind that a Live View image does _not_ represent the exposure the camera will actually make. While in Live View, the camera plays with the gain as needed to present a usable picture on the LCD screen. If you have it set for 30 second at _f_:2 and you're outdoors on a sunny day, you're going to get an all-white blown-out image for your photograph, but the Live View will show you a scene you can see. Similarly, if you set it to 1/500 at _f_:16 at night on the beach, Live View will show you a scene you can look at, but the camera will produce a black, seemingly unexposed image.

Live View is a television, not a viewfinder. Don't use it for a viewfinder.


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## Novelectro (May 21, 2016)

wfooshee said:


> The camera's actual metering system is totally bypassed in Live View because the mirror is up and no light gets into the top of the camera. the metering system lives around the pentprism at the top. The camera "meters" during Live View by trying to examine what it sees on the sensor itself and making a best guess. it's not really metering the light, it's reading the signal strength of the sensor pixels.
> 
> Basically, Live View is _not_ for photography, it's for video. You can use it in photography for critical focus, by switching to Live View, zooming it in and focusing, but then you should switch out of Live View and use the camera as a reflex camera so all of its systems are in play. Also, keep in mind that a Live View image does _not_ represent the exposure the camera will actually make. While in Live View, the camera plays with the gain as needed to present a usable picture on the LCD screen. If you have it set for 30 second at _f_:2 and you're outdoors on a sunny day, you're going to get an all-white blown-out image for your photograph, but the Live View will show you a scene you can see. Similarly, if you set it to 1/500 at _f_:16 at night on the beach, Live View will show you a scene you can look at, but the camera will produce a black, seemingly unexposed image.
> 
> Live View is a television, not a viewfinder. Don't use it for a viewfinder.



Awesome.  Thanks very much for this post.  Really helpful.


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