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Light loss with canon 814


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#1 jon lawrence

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Posted 09 May 2007 - 01:23 PM

The time has come where I need to caliberate my sekonic l508 and canon 814az. I have shot a few rolls with my 814 so I'm pretty confident that the internal light meter is accurate.
My question is how much light does the viewfinder eat up? I've read that with most split prism cameras its normaly about 1/3 of an f-stop however I was talking to someone at the widescreen centre in London and they said that due to the camera's etremely bright viewfinder its eating up around 1 and 1/2 stops.

Also, I was wondering how much the difference in light loss there is between a 150 and 160 degree shutter angle. I know the diference between 180 and 160 is about 1/3 of a stop so I'm guessing it isn't a great deal.

Any help would be much appreciated.
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#2 Terry Mester

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Posted 21 May 2007 - 12:58 AM

My question is how much light does the viewfinder eat up? I've read that with most split prism cameras its normaly about 1/3 of an f-stop however I was talking to someone at the widescreen centre in London and they said that due to the camera's etremely bright viewfinder its eating up around 1 and 1/2 stops. ... Also, I was wondering how much the difference in light loss there is between a 150 and 160 degree shutter angle. I know the diference between 180 and 160 is about 1/3 of a stop so I'm guessing it isn't a great deal.


I don't know why none of the DPs have offered you some advice -- hint hint Jonathan :blink:. You need to know the specific ISO Speed of the Film, and whether you are shooting at 18 or 24 f/s? At 18f/s each 10 Degrees amounts to 1/648 of a Second of Exposure Time, and at 24f/s it amounts to 1/864 Second. You can find data sheets for Kodak Films on their Website kodak.com. I personally wouldn't want to use a 'prism-fed' Viewfinder Camera. Not only are you losing light to the Viewfinder, but the light lost is not evenly balanced between the R,G&B Light Waves. This alters the colour and contrast of the image. I don't understand why manufacturers chose to use prism Viewfinders. My Sankyo uses a mirror to feed the Viewfinder, and it works perfectly well.
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#3 Anthony Schilling

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Posted 21 May 2007 - 07:31 PM

The only way to tell for sure is to run some tests, or comparisons with the internal meter. The 814xls 1/58th at 24fps, or 1/38th at 220 shutter. Last time I used it with my Sekonic, it was at least a stop if I remember. 1.5 sounds possible.
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#4 jon lawrence

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Posted 22 May 2007 - 04:34 AM

Thanks alot for your help. I know at the end of the day I'll have to run some tests- I was wanted to get a little background knowledge before I tried- film doesn't come cheap.
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#5 jon lawrence

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Posted 22 May 2007 - 10:40 AM

And.. Mr Mester- What are you hint hinting at? Is my question that ridiculous?
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#6 Mark Dunn

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Posted 22 May 2007 - 01:01 PM

Sorry Terry, but the light loss has nothing to do with the ISO. I don't see why the partially-silvered mirror in a prism finder shouldn't transmit all colours equally
And your Sankyo must be unique in having a mirror shutter. All the rest have a prism, like most super-8 cameras. Unless you're confusing partially-silvered with spinning or guillotine.
A stop and a half seems a lot to lose.
The difference between 150 and 160deg. is 16/15, or a factor of 1.066, rather less than a sixth of a stop.
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#7 Terry Mester

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Posted 23 May 2007 - 04:25 PM

And.. Mr Mester- What are you hint hinting at? Is my question that ridiculous?

I wasn't referring to you Jon. This was a good question. I was referring to Jonathan Bowerbank who is a Director of Photography (DP) and a S8 user. Sorry about the confusion.

Sorry Terry, but the light loss has nothing to do with the ISO. I don't see why the partially-silvered mirror in a prism finder shouldn't transmit all colours equally
And your Sankyo must be unique in having a mirror shutter. All the rest have a prism, like most super-8 cameras. Unless you're confusing partially-silvered with spinning or guillotine.

Mark, you're twisting up everything I said :o . I didn't say that ISO affects light loss. Higher Speed Films will suffer more from light loss than Lower Speeds, and this is a consideration with regard to any need to change Aperture size. Since the Higher ISOs are Negative Film it's not as big a problem. Also, I didn't say that my Sanko has a "mirror shutter". It has a mirror to feed the Viewfinder. The mirror does not come into contact with the light being focused onto the Film. If a Camera has a prism in front of the Film Gate, then you cannot expect that the Red, Green and Blue Light Waves will be equally divided between the Film Gate and the Viewfinder. Thus, the colour and contrast of the image is affected just as with the Optical Printer. Ideally, the only thing that you want to come between the Light image and the Film is the Camera Lens.
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#8 Mark Dunn

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Posted 24 May 2007 - 04:32 AM

IIRC fast films don't suffer more from light loss. If anything, being of inherently lower contrast they have greater latitude.
I maintain that the beamsplitter in most super-8 cameras is in the form of a prism with partial reflection off the 45 degree surface. Anyway, even with your viewfinder mirror, most of the light has to pass through the glass- why doesn't that affect the colour, if a prism does?
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#9 Terry Mester

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Posted 24 May 2007 - 06:23 PM

I maintain that the beamsplitter in most super-8 cameras is in the form of a prism with partial reflection off the 45 degree surface. Anyway, even with your viewfinder mirror, most of the light has to pass through the glass- why doesn't that affect the colour, if a prism does?


As I stated, the Mirror does not affect the Light going through the Aperture. The Mirror is located below the light path -- in front of the Aperture. The Frame of Light provided to the Mirror would be minutely off of the Frame for the Film Gate. The best I can figure as to how it works is that the Mirror is in front of the Aperture the same distance as the Film Gate is behind the Aperture. This accommodates changes to the Frame image from the Zoom. The Light from the Mirror would then have to go through a fixed side Aperture before it reaches a second mirror to then be reflected to the Viewfinder Eyepiece. There is nothing in my Sankyo which comes between the Lens and the Film Gate except for the Filter (if it's in). My Argus has a separate Viewfinder on top of the Camera -- there is no mirror in the diaphragm. There is simply no reason for a Camera to use a prism for the Viewfinder. If you don't believe what I say about the colour being affected by the prism, then try filming the same scene with both a prism and non-prism Cameras, and compare the developed Films. It would be better to do this test without using the Filter.
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#10 S8 Booster

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Posted 25 May 2007 - 02:14 AM

the simpler cams use 1 beamsplitter in the light path while the advanced oned use 2: one for the viewfinder and 1 for the lightmetering ensuring a bright viewfinder AND bullet proof exposures at the cost of some light loss.

ecample Nikon R10 & R8:Posted Image

the only cameras as far as i know to use mirror shutters and thus give no light loss in the film path are Beaulieu 2000 to 9000 series and Fujica ZC1000.

the Beaulieu is plagued with poor original lenses in low light condition though (severe vignetting) and possibly a design problem with the goulitine shutter which - it seems allow for uneven light distribution over the film path unlike rotating disc shutters.

cams with mirror shutters have a flickering view in the viewfinder while shooting.

beaulieus read exposure data via a beamsplitter in the viewfinder path and this requires big compromises in readings because the no shoot reading is quite a bit higher than the one it reads while shooting which makes the film be incorrectly exposed in shoot mode unless it is compensated for or if the the exposure control is locked prior to shoot.

the reason for the inacurate beaulieu auto exposure control is the flickering light appearing in the viewfinder while shooting and since the light metering cell use the same flickering licht fior measuring inaccuracy and compromises are unavoidable.

true beamspiltter cams have none of these problems at the cost of some light loss.

shoot....
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#11 Terry Mester

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Posted 26 May 2007 - 05:16 PM

the simpler cams use 1 beamsplitter in the light path while the advanced oned use 2: one for the viewfinder and 1 for the lightmetering ensuring a bright viewfinder AND bullet proof exposures at the cost of some light loss.


Thanks for this additional information on different prism (beamsplitter) Cameras. I must state that I'm completely appalled that some Cameras actually had two prisms in front of the Film Gate in order to feed the Light Meter. The difference between a Camera without a prism and with one prism is the exact same difference as looking through one window and three windows (with one at a 45 degree angle). The Camera's Lens itself constitutes the first window. The light is horribly degraded by going through three glass windows. Now I understand why so many former S8 users considered the S8 format to be "too grainy". They obviously had a prism-type Camera. I don't know if the designers at Sankyo were some type of geniuses, but their 45 degree angle mirror-fed Viewfinder is a fantastic design. Now, this is not the same thing as a 'mirror shutter' -- the Sankyo simply uses a mirror at a 45 degree angle. The framed image to the Viewfinder would only be slightly off the framed image to the Aperture Plate in the Film Gate, and the amount of light going to the Viewfinder is equivalent to the amount of light for the Film Gate. I don't know if there's a prism in the Viewfinder light path to feed the Light Meter. My Sankyo Viewfinder would be so bright that it has a White Filter to dampen the light so that you're not deceived into thinking there is enough light in low-light conditions. Those of you with prism-type Cameras would be flabbergasted by the quality of image my Sankyo provides indoors with only a few hundred watts of incandescent light. Now I know how lucky I am to have come across my Sankyo. The guy was going to sell it to me six years ago for only $30 Canadian dollars, but I paid him $40 because it was such a good Camera.

It is possible to remove the prism from a Camera, and still be able to use the Camera. You would need to attach a Scope on top of the Camera to use as a Viewfinder, and you would no longer be able to use the Auto Aperture. You would preferably want the Scope to be on a pivot in order to maintain convergence with the Lens for changing depths of field. You would also want to create a data chart of the widths of field (by angle) for the different positions on the Zoom Dial. Designers of 'things' often come up with some dumb and bird-brained ideas, and the guillotine shutter and the prism-fed viewfinder are two examples. Assuming that Sankyo didn't have a patent on their mirror-fed viewfinder, the other manufacturers were dumb to have not used it.

Does anyone know if any of the Arriflex and Aaton professional Cameras use prism-fed Viewfinders?
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#12 jacob thomas

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Posted 26 May 2007 - 06:32 PM

I don't understand how you can keep this up Terry. What evidence do you have to suggest this is the way your camera is designed? How about you share it and prove everyone wrong.

Why would a manufacturer make a camera as you describe it doesn't have the advantages of true reflex viewing (i.e. parallax error despite being ttl), and the lens would have to be bigger to cover a larger image circle to include this fantastical mirror. The prism fed viewer is a great system good enough for most super 8 cameras including nearly all the high end ones (not the beaulieus obviously), not to mention 16mm bolexes and canons.

Furthermore you are wrong about beamsplitters effecting grain, grain is inherent in super 8 and is primarily exacerbated by underexposure not beamsplitters.
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#13 Terry Mester

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Posted 26 May 2007 - 08:32 PM

I don't understand how you can keep this up Terry. What evidence do you have to suggest this is the way your camera is designed? How about you share it and prove everyone wrong.


Jacob, how am I to share it? Do you want me to mail you my Camera? It's so difficult to see inside the diaphragm through the Lens that I wouldn't even be able to take a picture. I would need to remove the Lens to take a picture, and I'm not about to risk breaking my Lens. There must be other users on this Website who have a Sankyo of similar design -- I know that Matthew Buick has one, and they can look inside their Lens to see if it has the same setup. If they can verify this design, will you then believe?

Why would a manufacturer make a camera as you describe it doesn't have the advantages of true reflex viewing (i.e. parallax error despite being ttl), and the lens would have to be bigger to cover a larger image circle to include this fantastical mirror.


:lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:
It's just a regular mirror. Nothing fantastic about it! Just a fantastic idea.
You are correct that there would be small parallax error, but it is vertical -- not horizontal. This means that the horizontal center of the Viewfinder and Film Gate images are aligned. The Lens is 35mm.

Furthermore you are wrong about beamsplitters effecting grain, grain is inherent in super 8 and is primarily exacerbated by underexposure not beamsplitters.


No, I'm not wrong. "Graininess", as I explain in my Photography Article, is caused by insufficient light resulting in fewer developed Dyes in the Film Emulsion. The reflection / loss of light off of the surface of the two glass panes of a prism beamsplitter adds to under-exposure -- increasing graininess. This isn't complicated. If you're using the Auto Aperture, the light feeding the Light Sensor is not the same light exposing the Film, and thus you cannot completely rely (100%) that the Aperture will be set to the correct size. You're simply not guaranteed that the light is divided 50/50 between the Film Gate and the Viewfinder / Light Sensor. The Light Sensor would basically be getting 25% of the light. Furthermore, those multiple disc-type Apertures are not as good as a completely round hole type Aperture, but this isn't related to the prism. If as you say, a prism doesn't contribute to graininess, then are you stating that to look through three glass windows is no different than looking through one window?
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#14 S8 Booster

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Posted 27 May 2007 - 06:57 AM

grain is more or less generated by incorrect exposure either by incorrect camera exposurecontrol or user error.
cameras like Canons 814/1014 XLS which has the most advanced and efficient exposure control system ever designed for ANY motion picture film camera allways exposes the film on the "high" side to supress grain in auto mode - and it does.

all my main stay cameras has bright viewfinders in low light either it is the Canon, the Nikon R10 or the Beaulieu 5008 MS.


shoot......
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#15 Anthony Schilling

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Posted 27 May 2007 - 12:09 PM

I don't understand how you can keep this up Terry. What evidence do you have to suggest this is the way your camera is designed? How about you share it and prove everyone wrong.

This is the same cat that recommends shooting tungston films in daylight without the filter, because the filter adds grain or something.
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#16 Alessandro Machi

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Posted 27 May 2007 - 01:29 PM

The loss of light is actually a good thing when shooting outdoors in bright environments, so overall it's probably an identical trade off. When shooting outdoors in bright environments, the light being siphoned off is a good thing, when shooting in ultra low light situations the loss of some light could be a bad thing.

Correctly metering when there is enough available light should make the grainiess issue a moot point and the Kodak negative stocks make having enough light much easier to do than it used to be.
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#17 Terry Mester

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Posted 27 May 2007 - 09:34 PM

This is the same cat that recommends shooting tungston films in daylight without the filter, because the filter adds grain or something.


Anthony, I did not generically "recommend" tungsten outdoors, but Kodak doesn't provide S8 users an outdoor Reversal stock. I was only referring to a very contained outdoor setting like your backyard. You were the one complaining about K40A colour problems, and you were unfairly comparing K40 (with a Filter) to E100D and Velvia 50D (without Filters). I tried to explain to you the optical problems with using a Filter -- which are the same as a glass plate Prism. I said, if you can remember, that some light reflects off of the surface of the Filter (as it does with glass), and that reflected light will not be equally balanced between Red, Green & Blue. Thus, the reduced light (caused by the Filter / Prism) decreases exposure, and the combined colour (RG&B) and contrast is also affected. Blue Light Waves refract more than Red and Green, and since Blue is brighter your contrast is affected.

The loss of light is actually a good thing when shooting outdoors in bright environments, so overall it's probably an identical trade off. When shooting outdoors in bright environments, the light being siphoned off is a good thing, when shooting in ultra low light situations the loss of some light could be a bad thing.


Alessandro, are you primarily talking about the Negative Stocks, or are you including Reversal? Since there's no S8 IP Stock, it's really necessary to look at the Negative to assess it properly as regards graininess. A telecined Video copy is not a good way to judge the Film itself. When I talk about graininess I'm really only thinking of Reversal Stocks which, in the case of 40,50,64 ISO, need a lot of light for proper exposure. I'm also really only thinking of graininess when it comes to viewing the Stock via Projection -- not Video. I would never assess a Film based upon how it looks on Video. Jon's original concerns regarding the Prism are not a big problem with Negative Films. My concerns about a Prism would be the effect on colour accuracy.
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#18 jacob thomas

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Posted 27 May 2007 - 09:46 PM

No, I'm not wrong. "Graininess", as I explain in my Photography Article, is caused by insufficient light resulting in fewer developed Dyes in the Film Emulsion. The reflection / loss of light off of the surface of the two glass panes of a prism beamsplitter adds to under-exposure -- increasing graininess. This isn't complicated. If you're using the Auto Aperture, the light feeding the Light Sensor is not the same light exposing the Film, and thus you cannot completely rely (100%) that the Aperture will be set to the correct size. You're simply not guaranteed that the light is divided 50/50 between the Film Gate and the Viewfinder / Light Sensor. The Light Sensor would basically be getting 25% of the light. Furthermore, those multiple disc-type Apertures are not as good as a completely round hole type Aperture, but this isn't related to the prism. If as you say, a prism doesn't contribute to graininess, then are you stating that to look through three glass windows is no different than looking through one window?


Thanks for the explanation.

However, you are confusing a number of factors. The prism does not effect graininess! You are right looking through one window rather than three is a good thing, the more glass generally the less sharpness. Softness (or the lack of sharpness) is not graininess.
Furthermore the lightmeters behind these prisms are calibrated to take into account the fact that they are not receiving all the light.
And one more thing in a camera such as the canon 1014xl-s (and all other prism viewer cameras with ttl metering that I am aware of) there is only one prism between the lens and the gate; that prism splits off a percentage of light to the viewfinder and meter. The second prism is in this light path to split off the light for the lightmeter from that going to the viewfinder (i.e. this second prism has no effect on the light reaching the film).
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#19 Mark Dunn

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Posted 28 May 2007 - 05:23 AM

There's no arguing with someone with such, er, novel ideas about everything from optics to photochemistry.
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#20 S8 Booster

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Posted 28 May 2007 - 07:11 AM

still may add that the light loss in the 2.nd light metering prim steals much less light than the viewfinder one as it does not need to be calibrated for the human eye but rather just distributing a very small amount of light to the very sensitive light cell and the exposure system are calibrated thereafter.

2 square presicion prisms wont add any destortion to the image as they will not be curved like the optical elements in the light path.

a little light loss thatr is all....

shoot.......
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