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Help a noob understand the exposure conundrum
Hi everyone, first post!
Been a lurker and generally familiar, although far from competent with 6x6. I love analogue, so have ventured into LF.
I have a 'no budget' set up, scratched together off eBay and diy:
Kodak specialist 3 rail camera
Ross of London telemetric 6.8 300mm
Elgeet no.3 universal shutter
DIY brass lens to shutter converter
Weston exposure meter.
Home made film holder (camera is a half plate)
Conundrum is: Weston is "accurate" for my Mamiya 330, ie if I do what it tells me I get decent negs.
When I meter for the big Kodak I have to allow 8 stops more exposure (!) to get a decent neg.
Why?
Cheers, Rob
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
TimberwolfII
Conundrum is: Weston is "accurate" for my Mamiya 330, ie if I do what it tells me I get decent negs.
When I meter for the big Kodak I have to allow 8 stops more exposure (!) to get a decent neg.
Why?
Hi Rob, and Welcome Aboard.
That is a really odd situation.
Commonly, old shutters slow down, so you need to use a setting for a faster speed than you really want.
If you expose at the nominal marked shutter speed, negs will be OVER-exposed.
I can't envision a shutter problem that would cause under-exposure.
- Leigh
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Re: Help a noob understand the exposure conundrum
Start with the basics:
In sunny conditions, set lens shutter at f/16 and expose the film at 1/ISO. So if the film is ISO 100, expose for 1/100s. This should tell you if the shutter is operating properly at that setting.
Reduce the aperture and correspondingly increase the shutter speed.
Alternatively, down load the iphone app shutter speed and test your shutter that way.
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Re: Help a noob understand the exposure conundrum
Eight stops is too much for a simple problem!
What film?
Close-up photography? If so, exposure needed to be added to compensate for long bellows extension.
Is you lens marked with modern f/stop system?
Try an exposure that you time with a lens cap rather than the shutter -- a second long exposure or more. That will eliminate shutter problems.
Test your shutter by firing a known good one at the same time -- at times around 1/4 sec or slower.
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Re: Help a noob understand the exposure conundrum
Eight stops--do you know if your shutter is the more modern system of f-stops (i.e. the British,) or the old U.S. (Uniform System) from around 1900? On both systems, f16 is the same. On the U.S. system, I think f8 is actually f11 in modern system. As for your question, the film is the same speed so exposure should be the same. Oh, the Mamiya will definitely have the modern f-stop system. There might be several exposure scales on your meter too--a bit confusing.
Kent in SD
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Vaughn
Eight stops is too much for a simple problem!
What film?
Close-up photography? If so, exposure needed to be added to compensate for long bellows extension.
Is you lens marked with modern f/stop system?
Started with a portrait, subject got bored, ended with a tree! At about 2m distance both. Same light etc.
Ok, more info:
HP5 rated at 200
Light meter set at asa 200, gives an indication of no.11 off a grey card, which cos I want the lens wide open (6.8) equates to 1/250-1/500. Via lots of trial and error I get a decent neg off the camera set at 1 sec 6.8. (Eights stops more than indicated?) Lens is 1912 so f stops are a bit funky but all there. Shutter sounds like about a second, faster speed is under exposed 4 sec bulb exposure over.
The lens is physically about the same as the Mamiya 250 mm I have, in my head I'm wondering if so much light goes in through the hole in the lens and illuminates a 6x6 then the intensity of similar light through a similar hole hitting a 5x7 INCH neg area will be so much less intense?
I can maybe just shift all the numbers along and go from there, but that's not very scientific and I'm trying to understand what's happening.
I got into LF to really dial down into the theory, analogue stops me at first hurdle!:rolleyes::)
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Re: Help a noob understand the exposure conundrum
If the shutter wasn't meant for that lens, the f-stop calibration is useless. This is compounded by the difference in f-stop units historically.
Could your lens have an iris or studio shutter that's stopped down even though your separate shutter is wide open? Or waterhouse stop needing to be removed?
If the film stays the same, exposure for one camera and film size will be the same for another camera and film size. (assuming you doing normal photos not closeups)
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Re: Help a noob understand the exposure conundrum
No -- there is no fundamental difference in lenses/formats that should cause a one stop difference, let alone 8.
You are losing light due to the extension of the bellows past the focal length of the lens. Set up the camera the same way, measure the bellows and run this equation and see what factor you would need to increase your exposure: http://www.cookseytalbottgallery.com...mpensation.php also:http://www.largeformatphotography.in...ws-factor.html
Also you might want to measure your aperature and run the equation to make sure you lens in marked with the proper modern f/stop system.
https://en.wikipedia.org/wiki/F-number
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Re: Help a noob understand the exposure conundrum
At 2 meters, the bellows extension wouldn't be much of a factor, and would be the same on the medium format C330 at the same distances. In daylight with HP5 at f/6.8, 1 second is way too much exposure. As you're new to LF processing, I'd suspect development first.
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Re: Help a noob understand the exposure conundrum
It could be the film is loaded facing the wrong way.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
jp
If the shutter wasn't meant for that lens, the f-stop calibration is useless. This is compounded by the difference in f-stop units historically.
Could your lens have an iris or studio shutter that's stopped down even though your separate shutter is wide open? Or waterhouse stop needing to be removed?
The lens has its iris which is wide open at 6.8. The shutter also is wide open, at 1.9.
The lens focuses at what looks like around 14" (no tape measure till morning) which is way bigger than the Mamiya can open out to. I only mentioned the Mamiya cos the 6x6 must be approx 1/8th the size of the 5x7. It isn't the same lens, one is Mamiya the other on the LF is the wray
I'll measure and run the formulas in the morning.
It's not development. I can run a decent neg, it's something about the camera/lens/shutter combo.
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Re: Help a noob understand the exposure conundrum
The U. S. system of marking apertures was invented to simplify [?] exposure calculations. The numbers double for each halving the exposure. U.S. 1 + f/4, U.S. 2 = f/5.6, U.S. 4 = f/8, U.S. 8 = f/11, U. S. 16 = f/16, U.S. 32 = f/22, U. S. 64 = f/32, U.S. 128 = f/32, and U.S. 256 = f/64.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
jp
It could be the film is loaded facing the wrong way.
Could be ........Ilford hp5, grooves in top right corner with film held in right hand has the emulsion facing me? Correct?
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Jim Jones
The U. S. system of marking apertures was invented to simplify [?] exposure calculations. The numbers double for each halving the exposure. U.S. 1 + f/4, U.S. 2 = f/5.6, U.S. 4 = f/8, U.S. 8 = f/11, U. S. 16 = f/16, U.S. 32 = f/22, U. S. 64 = f/32, U.S. 128 = f/32, and U.S. 256 = f/64.
The shutter is wide open, showing 1.9. As the English lens only opens to 6.8, this should be the limiting factor?
I started by going with what the Weston said -1/250th at 6.8 and got virtually nothing on the neg. only when I increased it in steps up to 1 sec did I get good density. Development was held the same - rodinal 1:50 at 20 degrees c for five minutes. All I did all through the 'tests' was increase the exposure time from 1/250th to 1 sec.
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Re: Help a noob understand the exposure conundrum
Is it a Telemetric or Telecentric? A shutter like that marked 1.9 would probably have contained a short oscilloscope lens. It's possible that the clear area of the shutter wide open is smaller than the clear area of your lens wide open. There is also the possibility of mechanical vignetting I suppose. When you look through the front glass of the lens when it is on the shutter and measure the opening you see in mm and divide that into 300 what do you get?
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Re: Help a noob understand the exposure conundrum
Also Rodinal 1 to 50 for 5 minutes for HP5 sounds kind of short. I think my time is 12 minutes.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Chauncey Walden
Also Rodinal 1 to 50 for 5 minutes for HP5 sounds kind of short. I think my time is 12 minutes.
Oops 1:25, my mistake. 4.75mins - off the Massive development chart. Yes 1:50 would be 10-13 mins.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Chauncey Walden
Is it a Telemetric or Telecentric? A shutter like that marked 1.9 would probably have contained a short oscilloscope lens. It's possible that the clear area of the shutter wide open is smaller than the clear area of your lens wide open. There is also the possibility of mechanical vignetting I suppose. When you look through the front glass of the lens when it is on the shutter and measure the opening you see in mm and divide that into 300 what do you get?
1.9 is the shutter iris. The lens has a 6.8 iris. I'll measure in the morning. I just get the 5x7 covered, no real room for movements.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Chauncey Walden
It's possible that the clear area of the shutter wide open is smaller than the clear area of your lens wide open.
I second this. Just looking a an image of the shutter, the opening looks quite small for a 300mm f6.8 lens. For example, the 300mm f5.6 Symmar-S takes a Copal No. 3. Just a guess.
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Re: Help a noob understand the exposure conundrum
Good point, Frank. The OP says he has a #3 Elgeet shutter. Its an Ilex #3 Universal rebadged for Elgeet, who made the lens that was originally in it. Most likely taken from an oscilloscope camera.
Normal Ilex 3s open to 35 mm. Many 'scope camera Ilex 3s for f/1.9 lenses have restricted apertures, open to around 30 mm.
OP, a shutter's aperture scale ia for the lens intended to be mounted in it. From all other lenses' points of view, totally arbitrary and incorrect numbers. Oh, and by the way, when you took y'r shots the shutter's diaphragm should have been wide open. Was it?
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
TimberwolfII
Could be ........Ilford hp5, grooves in top right corner with film held in right hand has the emulsion facing me? Correct?
Correct.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Dan Fromm
Good point, Frank. The OP says he has a #3 Elgeet shutter. Its an Ilex #3 Universal rebadged for Elgeet, who made the lens that was originally in it. Most likely taken from an oscilloscope camera.
Normal Ilex 3s open to 35 mm. Many 'scope camera Ilex 3s for f/1.9 lenses have restricted apertures, open to around 30 mm.
OP, a shutter's aperture scale ia for the lens intended to be mounted in it. From all other lenses' points of view, totally arbitrary and incorrect numbers. Oh, and by the way, when you took y'r shots the shutter's diaphragm should have been wide open. Was it?
Awake early for a Sunday and had tape measure out. The aperture in the Ross lens is 25mm at 6.8 on the dial - wide open; the shutter is 26mm at 1.9 - wide open. Both were wide open when making all the shots, I only changed the one variable whilst searching for the neg density - shutter speed. Also no bellows extension, I left it where it was focused when I brought it in - near as makes no odds 300mm lens iris to ground glass.
So, is my lense with a circa 30mm dia overall and an iris that opens to 25mm able to transmit less light that a massive aero Ekta say which is physically five times bigger? Or do they go to 2.8, 1.9 etc and have a greater aperture to focal length ratio?
Still not much idea as to where my 8 stops of light has gone!! Lots of head scratching from all you kind folk for which I'm very grateful! :)
Is it because I have a dinky little lense with a dinky little hole that only lets in a glimmer of light for that big ol 5x7, and just live with it darn it!? :)
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Re: Help a noob understand the exposure conundrum
A picture of your camera and lens might be worth a thousand words. Did you ever look inside the camera to make sure there is not a color gel inside or a filter on the back of the lens? Is your subject 14 inches or your bellows length 14inches when focused? Is it possible your medium format camera shutter is off by a couple of stops too?
Try a different lens or have your lens tested, meter with a phone App to compare meter results. Does your meter have low light and daylight settings (like the leica meters) ?
You have to eliminate one variable at a time.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
TimberwolfII
Also no bellows extension, I left it where it was focused when I brought it in - near as makes no odds 300mm lens iris to ground glass.
Arrgh!
Ross didn't make a "Telemetric." They made a telephoto lens called Telecentric.
300/6.8 = 44, not the 25 you measured.
You have a telephoto lens. The rear nodal point, from which extension is measured, is far in front of the diaphragm.
You have a telephoto lens. It has considerable pupillary magnification. The f/ number is calculated as focal length/diameter of the entrance pupil. Measure the entrance pupil, not the diaphragm.
There are books on LF photography. The two most commonly recommended here are Leslie Stroebel's View Camera Technique and Steve Simmons' Understanding the View Camera. Both available used at low prices from on-line booksellers, e.g., abebooks.com, alibris.com, amazon.com, bn.com, ... Buy one and study it. You'll learn more that way than from short random answers to random questions.
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1 Attachment(s)
Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
esearing
A picture of your camera and lens might be worth a thousand words. Did you ever look inside the camera to make sure there is not a color gel inside or a filter on the back of the lens? Is your subject 14 inches or your bellows length 14inches when focused? Is it possible your medium format camera shutter is off by a couple of stops too?
Try a different lens or have your lens tested, meter with a phone App to compare meter results. Does your meter have low light and daylight settings (like the leica meters) ?
You have to eliminate one variable at a time.
The Kodak is just the usual two stages with a bellows, no gels etc, nowt on the lens eitherAttachment 169173
This is it picked up and brought inside, haven't moved bellows etc.
Yes maybe the MF is off too, they are all the same vintage, but both MF shutters would have aged identically. But the MF and LF would still be eight stops different relative to each other. The MF works fine when set to the readings of the Weston light meter, whereas the LF MASSIVELY under exposes.
Yes the Weston has a bright/dark flip up screen, but imho the light meter and Mamiya aren't at fault I've used them fine for two decades....
It's just this darn new fangled large format! :)
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Dan Fromm
Arrgh!
Ross didn't make a "Telemetric." They made a telephoto lens called Telecentric.
300/6.8 = 44, not the 25 you measured.
You have a telephoto lens. The rear nodal point, from which extension is measured, is far in front of the diaphragm.
You have a telephoto lens. It has considerable pupillary magnification. The f/ number is calculated as focal length/diameter of the entrance pupil. Measure the entrance pupil, not the diaphragm.
There are books on LF photography. The two most commonly recommended here are Leslie Stroebel's View Camera Technique and Steve Simmons' Using the View Camera. Both available used at low prices from on-line booksellers, e.g., abebooks.com, alibris.com, amazon.com, bn.com, ... Buy one and study it. You'll learn more that way than from short random answers to random questions.
Ok, entrance pupil is 50mm. I will look up "pupillary magnification" sounds painful.
So, 300/50 is 6, seeing as its all actually in imperial that would work out about right for f6.8.
I have lots of books and an internet, but it's much more companiable chatting to you guys. Try and find 'real' folk ready to talk about this stuff!!! Even 'photographers' just glaze over. My son just said "just take the picture with your iPhone!" Philistine.
Anyhow, it's not doing what it's supposed to! Where's my light gone!?
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Re: Help a noob understand the exposure conundrum
Wiki says
"The pupil magnification of an optical system is the ratio of the diameter of the exit pupil to the diameter of the entrance pupil. The pupil magnification is used in calculations of the effective f-number, which affects a number of important elements related to optics, such as exposure, diffraction, and depth of field. For all symmetric lenses, and for many conventional photographic lenses, the pupils appear the same size and so the pupil magnification is approximately 1."
Which for my lens is 50mm entrance 25mm exit. Does this effect what light hits the ground glass relative to the aperture setting then?
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
TimberwolfII
Which for my lens is 50mm entrance 25mm exit. Does this effect what light hits the ground glass relative to the aperture setting then?
No. The f/ number is all you need to know. Buy a book. Read a book.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
TimberwolfII
I have lots of books and an internet.
it's not doing what it's supposed to! Where's my light gone!?
Books don't tell you how to trouble shoot, they tell you theory and protocol, what happens when theory and protocol don't work?
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Re: Help a noob understand the exposure conundrum
I checked and an Ilex 3 has a max iris of 34.6mm. A Copal 2, for example, has a max iris of 30mm, and a Copal 3 has a max iris of 45mm. Still, eight stops light loss is a lot.
Maybe the OP could measure the diameter of the rear element of his lens.
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3 Attachment(s)
Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
faberryman
Maybe the OP could measure the diameter of the rear element of his lens.
Iris at max opening = now I look very closely the iris opens up to maybe 30mm - it's in the centre of the lens half way down so hard to gauge with the optics
Attachment 169175
There is a mask near the rear element that is 25mm dia.
Attachment 169176
You can just see a glint of its edge above, its close to the rear element, but is NOT the iris.
Rear element is 50mm dia
Sheesh, plenty of crud in that lense! :rolleyes:
Attachment 169177
34.6mm of shutter aperture. Plenty of holes for light to tumble in!
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Re: Help a noob understand the exposure conundrum
Well if the rear lens element is 50mm, and the shutter opening is 34.6mm, then I would think that you are suffering light loss, though hard to say if it is eight stops.
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Re: Help a noob understand the exposure conundrum
I think, as someone else mentioned, that you are loading the film backwards. Are you sure you have the emulsion side facing the lens on your homemade holder? Looking through the lens at the film in the holder the notch should be in the upper right corner.
Exposure on LF is exactly the same as MF and 35mm. Exposure doesn't change with format.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
faberryman
Well if the rear lens element is 50mm, and the shutter opening is 34.6mm, then I would think that you are suffering light loss, though hard to say if it is eight stops worth.
As the picture above shows the light actually has to get through a 25mm hole [I]after[I]the lens aperture, which is part of the lense design, maybe that's an issue?
All I can say about the emulsion is: grooves in top right corner held in the right hand makes the emulsion face towards you, left hand holds the carrier facing upwards and the right hand holds the film with emulsion also facing upwards. Slot the two together and voila!
I'm still not clear how an amount of light going through a hole of say 25mm and hitting say 36 square centimetres (6x6) has the same intensity per unit area as the same amount of light going through a 25mm hole and dispersing itself over 234 square centimetres (13x18cm or 5x8")?
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Dan Fromm
Buy one and study it. You'll learn more that way than from short random answers to random questions.
Quote:
Originally Posted by
TimberwolfII
Books don't tell you how to trouble shoot, they tell you theory and protocol, what happens when theory and protocol don't work?
I hold with Dan on this one, I have to say. Books will teach you to ask correctly, to look correctly for questions. You start to be cocky on people who give their time to help. I want to be helped as I say, not as you want to help me is selfish and childish.
You cannot learn to cook just asking your nose how it smells.
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Re: Help a noob understand the exposure conundrum
I'm really really not trying to be cocky; I've been shooting b&w on and off for thirty years 35mm then MF. I have books and I use them. I'm trying to improve my craft. Because LF facilitates craft it was my next move. I've never come across this phenomenon where the kit seems to be doing something weird. I thought it might be something peculiar to LF so I came here.
But in four pages of dialogue there doesn't seem to be an answer. I have responded as thoughtfully and thoroughly as I know. I can't go to a book and find the answer to this, I've tried. I thought that was the purpose of a forum and a community, to ask respectfully of ones peers?
It wasn't a 'random' question.
Maybe I just go and ask elsewhere.
Newbies may seem childish because of their ignorance, we all have to start somewhere.
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Re: Help a noob understand the exposure conundrum
You could always just meter, add eight stops, and expose. If that consistently works for you, then you have solved your problem.
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Re: Help a noob understand the exposure conundrum
Thanks Faberryman. Looks like I'm gonna have to.
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Re: Help a noob understand the exposure conundrum
Why dance around the problem?
If the shutter has an iris in it always leave that iris fully open. That iris is not used in the operation of the lens and the aperture numbers engraved on it are irrelevant.
Measure the entrance pupil of the lens with the lens iris fully open. The entrance pupil size is the diameter of the aperture as seen through the front glass of the lens. Measure this appearance. This can be tricky, avoid parallax error.
Measure the actual focal length of the lens. It's not the distance between the front and rear standards of your view camera if the lens is a telephoto. It's not the focal length engraved on the lens if the lens has some missing or extra glass and you don't know about it. There are a number of ways of measuring focal length. Study. Pick the one most convenient.
Divide the focal length you measured by the entrance pupil you measured and the number you get is the maximum relative aperture, or f-stop, of the lens. That's optical law and it hasn't been repealed. Compare the number you got with the number engraved on the lens. If there is a difference then the f-stop markings of the lens needs recalibration.
Check the shutter speeds for obvious errors.
Emulsion side of the film? Hold the film in portrait orientation, short edges top and bottom, long edges left and right. If the film is notched in the top edge and the notches are toward the right corner the the emulsion is facing you.
The rest is just the usual subject brightness, film speed, f-stop, shutter speed equation.
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Re: Help a noob understand the exposure conundrum
If the 8 stop underexposure would be due to an iris issue, then the iris would have to be quite tiny. 8 stops is a difference in light intensity of roughly 1:500 (1:512 in fact), so an iris that is even only half the diameter it should be, would not amount to this effect (that would only make for an underexposure of 2 stops, not 8).
Exposing through the wrong side of the film generally makes for an underexposure of 3 to 5 stops, in my experience.
If you were to add a very significantly smaller iris to film loaded the wrong way round, one would get in the neighborhood of the observed 8 stop underexposure. Either of these effects separately would in my opinion not result in this huge issue.
Aperture and focal length in principle have nothing to do with film format; think of he image as a cone of light casting a circular image, part of which you capture and the size of that part depends on the film format chosen. The light cone doesn't change in brightness depending if you capture only a small or a large part of it. Hence, it doesn't make a difference if you measure for 8x10" or 35mm; if a measurement says e.g. 1/100 @ f/5.6, then that isn't dependent on film format.
Something odd certainly seems to be going on and I can't really come up with a good hypothesis on what's going on, apart from that it looks like a pretty significant error somewhere in the process.
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Re: Help a noob understand the exposure conundrum
Maris, koraks, the OP seems to have hung a 300 mm telephoto lens in front of an Ilex #3. This puts the lens' rear node a good distance in front of the lens' diaphragm and farther in front of the shutter's aperture. It might act as a stop.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Maris Rusis
Why dance around the problem?
If the shutter has an iris in it always leave that iris fully open. That iris is not used in the operation of the lens and the aperture numbers engraved on it are irrelevant.
Measure the entrance pupil of the lens with the lens iris fully open. The entrance pupil size is the diameter of the aperture as seen through the front glass of the lens. Measure this appearance. This can be tricky, avoid parallax error.
Measure the actual focal length of the lens. It's not the distance between the front and rear standards of your view camera if the lens is a telephoto. It's not the focal length engraved on the lens if the lens has some missing or extra glass and you don't know about it. There are a number of ways of measuring focal length. Study. Pick the one most convenient.
Divide the focal length you measured by the entrance pupil you measured and the number you get is the maximum relative aperture, or f-stop, of the lens. That's optical law and it hasn't been repealed. Compare the number you got with the number engraved on the lens. If there is a difference then the f-stop markings of the lens needs recalibration.
Check the shutter speeds for obvious errors.
Emulsion side of the film? Hold the film in portrait orientation, short edges top and bottom, long edges left and right. If the film is notched in the top edge and the notches are toward the right corner the the emulsion is facing you.
The rest is just the usual subject brightness, film speed, f-stop, shutter speed equation.
Thank you for the comprehensive answer it is appreciated.
I'll do the math and see whether the lens is doing what it should. I will study.
I believe I am putting the film in correctly, but obviously I will be very conscious to be aware when loading.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
koraks
Aperture and focal length in principle have nothing to do with film format; think of he image as a cone of light casting a circular image, part of which you capture and the size of that part depends on the film format chosen. The light cone doesn't change in brightness depending if you capture only a small or a large part of it. Hence, it doesn't make a difference if you measure for 8x10" or 35mm; if a measurement says e.g. 1/100 @ f/5.6, then that isn't dependent on film format.
.
Now I understand why the light intensity doesn't change between formats. Thank you koraks succinctly and clearly described.
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1 Attachment(s)
Re: Help a noob understand the exposure conundrum
Attachment 169234
This is the lens/adapter/shutter configuration. The lens has the mount thread just behind the iris, about a third the way along the barrel, hence the long adapter otherwise the lense would clash the shutter.
Sorry bout the dark image, it's early morning and I don't want to disturb my significant other turning on lights...:)
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Dan Fromm
Maris, koraks, the OP seems to have hung a 300 mm telephoto lens in front of an Ilex #3. This puts the lens' rear node a good distance in front of the lens' diaphragm and farther in front of the shutter's aperture. It might act as a stop.
I understand, but how could that amount to an 8 stop difference? 2 or 3 stops, sure, and maybe even 4. But 8? Even quite far from the nodal point, the iris would have to be quite tiny to get even close to 8 stops!
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Re: Help a noob understand the exposure conundrum
Right. The eight stop difference is huge, and the reason I though the OP was shooting through the film base (although I'm not even sure that would give you eight stops).
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
koraks
I understand, but how could that amount to an 8 stop difference? 2 or 3 stops, sure, and maybe even 4. But 8? Even quite far from the nodal point, the iris would have to be quite tiny to get even close to 8 stops!
Fair question. I too have trouble with 8 stops.
Here's a test for the OP. Hold the lens/shutter at arm's length with the shutter open and its and the lens' diaphragms both fully open. Looking through the lens from the rear, slowly close the lens' diaphragm until the blades just become visible from the rear. What's the marked aperture at that point?
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Re: Help a noob understand the exposure conundrum
Immediately. I can see them start to move off max 6.8. I can see them past the 'mask' near the rear element. It's like an uninterrupted tunnel, all the projections - lens iris, mask, shutter iris all look the same diameter.
I'm hoping I can get time to contact print the under-ok-over negs in next couple of days so I can post them with accompanying data. Maybe they will shed some light, if you'll excuse the pun.
Rob
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Re: Help a noob understand the exposure conundrum
Ok, lets go back to check the film base way round. Maybe I can put it to bed yes I've put it in right or no I've screwed up. I've looked at the negs and I know the subject was looking to MY left when I took one of the images. My brain is hurting trying to juggle which way the notches/emulsion/head direction is cos everything turns upside down and back to front.
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Re: Help a noob understand the exposure conundrum
Quote:
Originally Posted by
Greg Davis
If your subject on the negative is looking the same direction as in real life with her head at the top of the image, the notches should be in the top left while held vertical.
Only if he loaded the film with the notches at the bottom of the holder, or put the holder in the camera from the bottom.