Gast
Dear forum members,
I’m having a major problem with Efke films. I’ve performed two exposures, occasionally using a 25A red filter, and relied on the TTL automatic exposure settings of an EOS 50E. However, the developed negatives with red filters have too little detail in the shadows (the ‘lower range’), whereas the sky has good detail. Other negatives with no filters have good detail; the film is not underexposed. However, the shadow detail in the problematic negatives is very poor, or rather barely there, so that even with compensation during enlargement, no usable results will be achieved apart from a nice cloudscape.
Hence my question: Should one not use a red filter with Efke films, given that they are supposed to be orthopanchromatic?
Is it worth using copper enhancers to improve detail?
I would be grateful for any answers.
Regards
Thomas G.
cfb_de
Hello Thomas,
Should one avoid using red filters with Efke films, given that they are supposed to be orthopanchromatic?
Yes, you should be careful with red filters and, if necessary, *significantly* adjust the exposure. Efke films are slightly less sensitive to red. But isn’t that also clear from the data sheet (I don’t have one to hand at the moment)?
Is it worth using copper enhancers to preserve detail?
No. You can’t conjure up something where there is nothing.
Best regards,
Franz
MirkoBoeddecker
To what extent did you rely on the automatic settings?
Did you measure through the filter, or did you adjust the correction factor printed on the plus-minus mark?
Otherwise: clearly, if you look at the spectral curve of the sensitivity distribution, it is obvious that the film has less sensitivity in the red range than higher-sensitivity films.
http://www.fotoimpex.de/Technik/efkefilms/...e50/efke50.html
The total speed is the integral under the curve.
By filtering, you block light coming from one side.
That is precisely what leads to its good blue-red differentiation and its ‘distinctive’ look.
Consequently, you need to increase the exposure factor to achieve the same result.
Best regards,
Mirko
Gast
Hello Thomas,
Just a quick note and a very simplified explanation, but correct in principle.
Efke’s 25 and 50 films actually belong to the Ortho/Receptan range. In practice, this means their speed and detail in the shadow range (blue light, spectral range below 400 nm) is excellent; however, their speed peaks very early in the range of evening light and incandescent bulbs (red light, spectral range above 700 nm)! In practical terms, this means that all films with receptan characteristics react at least one stop weaker on average when exposed to red light. So a 50 is effectively only worth 25! It stands to reason that films with receptan characteristics react very problematically to red filters and that this filter is actually counterproductive. However, try using a Superpan film, such as Classicpan 200/400, Macos Cube or R3, with a red filter, and you’ll be amazed; dramatic skies and even an increase in sensitivity (under lamplight and evening red) of up to half a stop (depending on the developer)!
Right, that’s it. Have fun with your photography.
Best regards,
Lothar
Gast
Hello,
Thank you for your replies.
‘Of course’ I didn’t set any correction; I just assumed that the TTL metering would detect the lower light levels. The problem probably also lies in the film’s sensitivity itself, because looking at the curve, the speed must have dropped by at least half. If the automatic exposure control is also being misled by the filter, that would explain the faint negatives.
Unfortunately, these shots are very important to me, and the question arises as to whether using a contrast enhancer might help ‘bring out’ the detail? Does anyone know anything about this?
Regards
Thomas G.
cfb_de
Hi Thomas,
As I mentioned briefly above...
To answer your last question: Yes. I’m a chemist, and photographic chemistry is slowly becoming something of a fourth hobby of mine.
To answer your penultimate question: No. The rule still applies: you can’t make something out of nothing. All that developer business – whether it’s chromium, copper, uranium or any other developer bath – basically only works where there is detail and increases the overall density. Sometimes even whilst maintaining a reasonable amount of contrast. It doesn’t help with underexposure, but rather with underdevelopment, where at least ‘something is there’.
Incidentally, with most developer baths, another issue arises: they generally have a colouring effect. And that can lead to real frustration when using variable contrast papers, as these papers are, after all, also designed to be ‘colour-sensitive’.
Perhaps, to conclude, a simple question: how is an intensifying bath supposed to work if it doesn’t know where on the spotless negative you’d now like to have the slightly less dark shadow?
It’s frustrating, but there’s nothing you can do about it. Even before the wildest hopes and artistically inspired expectations, God has placed the natural science (chemistry) of photography. And the best way to get to grips with its effects is through correct exposure and development. Even if you have to learn that first. I messed up my first Efke with a red filter too. And my first one with a flash as well – that’s actually the next potential area for improvement :-)
Best regards,
Franz
MirkoBoeddecker
Thomas,
You’ve already got the hang of TTL metering, haven’t you?
The density of the filter doesn’t necessarily correspond to the correction factor.
You can test this very easily. Take a reading on a uniform surface (wall) and make a note of the result. Then screw the filter on and take another reading. If it shows a longer exposure time corresponding to the factor, you can carry on taking readings.
If it doesn’t, correct for the remaining difference!
For example: Without filter, f/8 and ISO 250
With filter, it shows: f/8 and ISO 60
Filter factor printed on = 3x
Remaining correction = add one stop (set exposure override to +1 or use ISO 25 instead of ISO 50).
Or: Set external exposure and factor.
Regards,
Mirko
NOTE: As correctly pointed out below by other authors, it should read:
Filter factor printed on = 8x :huh: Exposure time change = 3 stops!
I’d snapped this too quickly and had already ‘converted’ the factor into stops.
Basically, of course, it’s all about the difference between the displayed TTL reading and the printed factor.
But if we’re going to do it, let’s do it properly – and voilà, the conversion table:
Factor 1x ==> No extension
Factor 1.5x ==> 0.5 stops
Factor 2x ==> 1 stop
Factor 3x ==> 1.5 stops
Factor 4x ==> 2 stops
Factor 6x ==> 2.5 stops
Factor 8x ==> 3 stops
etc.
Gast
Hi Mirko,
I think you’ve made a mistake in your calculations in the example. The filter factors are exponential, after all. So if you’ve measured a difference of 2 f-stops, that corresponds to a factor of 4; the filter is marked as factor 3 (= 1.5 f-stops), so you only need to add half a stop.
As for TTL metering, you could also compare the different metering methods against each other; it’s worth considering whether centre-weighted integral metering might not produce a more balanced result with filters.
Regards, Sven.
Gast
Hi everyone,
Sven is right. A filter factor of 2 corresponds to one stop, 4 corresponds to two stops, and 8 corresponds to three stops. This is the base-2 logarithm (e.g. 2 to the power of 3 = 8, meaning the aperture opens by three stops)
The ‘filter compatibility’ of TTL light meters varies enormously. The old Nikkormat light meters, for example, display wildly inaccurate readings with a red filter; the old TTL prism viewfinder for the Hasselblad starts to go haywire even with a medium yellow filter, but its greatest deviation is not, as I had expected, with a medium red filter but with an orange one. To work effectively – though this is just my personal opinion – you simply can’t do without a good additional handheld light meter anyway, not even with a spot meter built into the camera.
Added to this, as mentioned above, is the film’s low sensitivity to red light. Consequently, the aperture must be opened further even under artificial light or at sunset. In the past, this was taken into account by specifying different speeds for daylight and artificial light. Incidentally, the Maco PO 100c data sheet addresses this issue.
The opposite is also true: Technical Pan has an extended red sensitivity; not to mention infrared films.
It is therefore always worth taking a look at the spectral sensitivity curve when using a film you are not yet familiar with.
What do your negatives look like? Is there really so little on them that you can’t get an enlargement? Your exposure time is wrong, but not so far off that no enlargements—at least not decent ones, let alone beautiful ones—should be possible.
You can certainly forget about pushing the film, though; the reasons for that have already been explained by others. But since the film is already ‘ruined’ anyway, you could always give it a go: if I were you, however, I’d rather spend the money on new film and retake the shots.
Regards, CP
Renate
Hello,
Mirko has calculated it CORRECTLY. The filter factors are logarithms to the base 2. In other words, a factor of 1 means 2 to the power of 1, which is 2. The exposure time must be increased by a factor of 2. With a filter factor of 3, this corresponds to 2 to the power of 3, which is 8. The exposure time must be increased eightfold. The term ‘filter factor’ is somewhat misleading, as mathematically speaking it is not really a factor.
The filter factor is best interpreted as the number of exposure stops. So, with a filter factor of 3, the aperture is opened by 3 stops, or the exposure time is extended by 3 stops, or the ISO sensitivity is reduced by 3 stops. It always amounts to the same thing. In any case, the amount of incident light is increased by a factor of 8. The filter factors apply only to daylight.
I have made it a habit to always measure the exposure without a filter and then set the filter factor as a correction. This ensures I always get reliable results. For some films, there are also specially tested correction values, which can be found in the films’ data sheets. These take the film’s ISO sensitivity into account.
Gast
Hello Renate,
No, Mirko is NOT RIGHT in his example. A filter factor of three does NOT correspond to one f-stop.
You can also multiply the time by the factor: e.g. filter factor 3, measured 1/30 sec x 3 = 1/10 sec (so set to 1/8). Here you can clearly see that it results in more than the single stop that Mirko mentions.
Regards, CP
MKL
Hello Renate,
Mirko’s post has nothing to do with calculations. Mirko pointed out that, in TTL metering, the metering sensor may give an incorrect reading. It is entirely possible that a red filter and a neutral density filter with the same density rating will display different values in TTL metering, even though, purely mathematically, this shouldn’t be the case. The spectral sensitivity of the light meter plays a part here.
After all, a red filter does not merely have an extension factor in daylight; it also transmits the red component almost unimpeded. Consequently, whilst a blue filter and a red filter have the specified extension factors in midday light, at dusk the red filter will have a smaller extension factor and the blue filter a larger one.
A TTL measurement therefore makes perfect sense, as it automatically takes different colour temperatures into account; however, you should be familiar with the characteristics of your camera (and the film). That is why I find Mirko’s tip about the white wall extremely practical.
Best regards,
Michael
Gast
So I’ve just measured an orange filter again using the handheld light meter: 4x = 2 f-stops.
Factor 1 is the ‘basic’ light intensity, i.e. the measured value; no adjustment required
Factor 2: double the light intensity = one f-stop
Factor 4: double the light intensity of factor 2, i.e. 2 x 2 or 2 to the power of 2 (I can’t find the key at the moment), so 2 f-stops
Factor 8: double the light intensity of factor 4, i.e. 2 x 2 x 2 or 2 to the power of 3, so 3 f-stops,
all my filters are labelled this way, not just the old ones but the newer ones too; I’d be surprised if there were any where it was different. I’m only mentioning this because two years ago I got really annoyed because I’d overexposed a whole roll of film due to this very mistake.
Regards, Sven.
Gast
Hello Renate,
Just to follow up on your last sentence
I’ve made it a habit to always measure the exposure without a filter and then set the filter factor as a correction. That way, I always get reliable results.
Do you also use filters with a factor of 4 or higher? I’m just asking out of interest – in theory, you shouldn’t be able to get correctly exposed negatives or slides from that point onwards. I usually do the same: I measure with the handheld light meter and then add the filter factor.
Regards, Sven.
MKL
Hello CP,
You seem to be getting a few things mixed up here. An exposure compensation factor of +3 for filters means that you need to achieve an overexposure of three stops (aperture steps) in order to get the same amount of light onto the film as you would without a filter. +3 full stops means either opening the aperture by three full stops (e.g. from f/11 to f/4) or extending the exposure time by 2³ = 8 (e.g. from 1s to 8s) compared to the reading without a filter. All of this, of course, without taking the actual purpose of the filter into account, but only in relation to the influence of the filter density in daylight.
What Mirko meant is that even with a TTL metering using colour filters, although measured through the lens, the values can be incorrect due to the filter’s properties (e.g. red) and must then be corrected again. With a neutral density filter, the TTL measurement is always correct automatically, because all light components are filtered evenly and the light meter therefore measures correctly.
Best regards
Michael
Gast
Hi Michael,
I’m sorry, but what you’re saying is completely wrong. Have a look at Sven’s penultimate post.
I’m guessing that you either never use filters, or that you use TTL and your camera is accurate enough to handle different filters, or that you can live with badly exposed negatives. – A filter factor of 3 means that the film needs three times the amount of light, not three stops more. That would actually be eight times the amount of light, because 2x2x2=8. Example: measured without a filter at 1/500, f/16 gives 8x1/500=1/60 at f/16, or 1/500 at f/5.6 – so exactly THREE stops.
Regards, CP
Gast
Hi Michael,
Just to add one more thing – perhaps this is where the misunderstanding lies: there is no such thing as a filter factor of +3, as you mention; in that case, it wouldn’t be a multiplication (factor) but an addition; only then would the ‘+’ make sense. I’ve never seen such a specification on any filter. If you still don’t believe me, have a look at the introductory pages of any filter catalogue – in my B&W catalogue, at least, it’s described very clearly.
Regards, CP
Gast
Hello everyone,
As the *Little Prince* says: words are the source of all misunderstandings.
I’d therefore like to make just a few practical comments below and leave out terms like ‘factor’ and so on. I only work with filters now and then; at the moment I use Heliopan and Cokin or filter sheets (10 x 10 in large format), but I’ve been doing so for more than twenty years and I only apply the necessary exposure corrections as a reference for aperture or ISO sensitivity, n o t in the area of ‘shutter speed’, as this is where the greatest uncertainty lies, or where errors occur.
A concrete example:
A Heliopan yellow filter states the following: 3x -1.5
A Heliopan yellow-green filter states: 2x -1
A Heliopan red filter states: 4x -2
With Heliopan filters, the first number refers to shutter speed and the second to aperture!
In practice (all of which has been done for years with correctly exposed results), if I take a 400 film as an example, the film speed (adjust the setting on the light meter) drops to 200 ISO when using the yellow-green filter (see above). I should then take my measurement using this ISO value. Alternatively, I can leave the setting at 400 ISO, but in that case I must open the aperture by a full stop after the measurement to compensate for the loss of exposure. If I want to adjust my shutter speed, this means that with this filter – assuming we measured 1/60 at 400 ISO – I must double my shutter speed. In concrete terms, starting from 1/60, this gives 1/30 and then 1/15. The latter would be the required exposure time.
With the red filter mentioned above, the ISO sensitivity on the light meter would need to be set to 100 ISO. Or I could leave the setting at 400 ISO, but then I would have to open the aperture by two full stops to compensate for the loss of exposure. However, if I want to adjust my shutter speed, this means that with this red filter – assuming we measured 1/60 at 400 ASA – I must increase my shutter speed by a factor of 4. In concrete terms, starting from 1/60, this gives 1/30, then 1/15, followed by 1/8 and then 1/4. The final value would be the corresponding required exposure time. The same principle applies to the other Heliopan filters, etc.
Now a word about the light meter. Regardless of whether I measure using the built-in TTL, a handheld light meter, or whether it’s spot or matrix metering, etc., only calibrated, colour-corrected light meters enable correct exposure times (not just when using filters)! Even measuring a red surface compared to a grey surface, using the same light meter, can produce different results even though the lighting conditions etc. are the same, even though, in principle, both surfaces would require the same exposure.
Pentax produced an analogue spot light meter that was very well calibrated; it was distributed by Monochrom at the time and was, of course, correspondingly expensive. Another good light meter with a practical colour calibration/correction is, for example, the Minolta Spotmeter F.
Incidentally, this subject – filters, colour measurement and exposure metering – is a very complex one, and it is best not to read clever books on the matter, but rather to follow the filter manufacturers’ specifications and then test your own films, cameras, light meters etc. yourself, based on the filter specifications (printed on the filters). Many people will then surely wonder why the same filter, under the same conditions, produces a different reading on camera A than on spot meter B, and so on.
So testing it yourself is the best way!
Have fun and best regards,
Lothar
Gast
Hello Lothar,
Thanks for clarifying that. I didn’t know about the markings on Heliopan filters! My B&W filters only show the density factor.
In my opinion, the effect of the filter is also very film-dependent (I’m referring exclusively to films with ‘normal’ colour sensitivity here, i.e. not those with reduced red sensitivity like Efke), even though I was once contradicted on this point by an authoritative source in another forum. The Ilford XP2, which I used as a 35mm film for quite a long time, reacts to filters in a rather peculiar or, let’s say, unpredictable way; Pan F reacts best, followed by APX 100 and FP4 (I haven’t tried filtering other films yet!). I don’t have a physical explanation for this, however, as the spectral sensitivity of the four films is quite similar (perhaps not similar enough?), and other photographers have confirmed these experiences to me.
The filter effect, and thus also the filter factor – which brings us back to that pesky word – depends on the composition of the light. I’ve also toyed with the idea of a ‘colour-calibrated’ spot meter – but the price alone!
Anyone who fancies a go over the Whitsun bank holiday can have a go at ‘Googling’ polarising filters. You’d normally only hear so many contradictory statements – from specialist authors, mind you – in politics, with the difference being that I don’t accuse the specialist authors of deliberately lying.
Best wishes and happy Whitsun
CP
MKL
Hello CP,
Please read through my posts again and tell me where I used the term ‘filter factor’.
Manufacturers provide two pieces of information for filters: a time factor and a value indicating how many EV (aperture stops) are absorbed. If the specifications are 8x EV -3, the exposure must be corrected upwards by 3 stops, i.e. the aperture must be opened by 3 stops or the exposure time increased eightfold. That is what I meant by ‘exposure correction factor’ – perhaps not the right term and misleading in this context.
By the way: there are always misunderstandings in this forum partly because individual replies cannot be clearly assigned to a specific thread – this is handled better in black and white magazine.
Best regards,
Michael
