Nerd alert! Got a Stouffer 21-step wedge and want to share some interesting things I've been learning

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jonmon6691

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Strips_overview.jpg


A note about the graphs, the x-axis is just in terms of pixels along the strip, so its essentially increasing exposure from 0 to 2000 because that's how the strip is set up, and each point is the value of the strip pixel at that point along it. I just picked a line through each strip near the middle. The values are computed by taking log(pixel / darkest_pixel_anywhere) where darkest_pixel_anywhere is a constant found by looking for the maximum black pixel value out of all three scans. So 0 on the scale is sort of artificial but at least well-defined.

Development time: This was the most surprising result, but with my setup, I'm getting much more range from my RC paper by developing for another minute longer than Ilford's recommended time of 1m. This is super noticeable in-person and I will for sure being doing 2 test strips at the start of each printing session, 1m and 2m from now on, to check how long I should be developing for. I've noticed this gap get smaller or go away on some days, I think its probably related to room temperature or possibly developer exhaustion (I use a shared community college darkroom)
dev_time.jpeg


Split grade printing: Here is a really interesting result from trying to see the result of split grade printing. I've seen it quoted that split grade isn't different than using regular contrast filters other than you can go in-between grades (And dodge/burn different grades). But I don't think that's necessarily true based on this graph. You can see that the highlights remain basically unaffected by the grade 5 exposure until it approaches 50% of the total time. This coincides with my experience that I can use a short grade 5 exposure on a print to bring my dark grays all the way to black without affecting any of the other tones.
split_grades.jpeg


Contrast Grades: This needs some more work to align the exposures, but just pulling from the data I already have, this is kind of interesting to see the relative slopes of different contrast grades. Note that in the case of the split grade print, it does quite closely resemble a grade 2 exposure in this case.
grades.jpeg


Cyanotype: This was super interesting to me! Before I got access to my community college darkroom, I had been making tons of Cyanotypes and even upgraded to the "New Cyanotype" formula. This is a comparison of New Cyanotype to Multigrade paper. It really blows me away how incredible these "modern" materials are. A couple interesting aspects of the cyanotype curve; the elbow shape with a low-contrast toe and then a short, high contrast, section leading right into the shoulder has been something that is really annoying me about cyanotypes because its so hard to get clean highlights and dark shadows at the same time. I had to start creating really high contrast negatives by giving N+2 development to make them look okay. Cool to see that vindicated in the data. Also the slight upwards hump at the end is a real thing. The cyanotype process reverses pretty significantly with over exposure and starts creating "Prussian White" instead of Prussian Blue. This oxidizes back to blue but never quite as dark as sections that weren't over exposed.
cyanotype_v_silver.jpeg


Cyanotype contrast: One thing I noticed a while back is that the amount of acid mixed into the sensitizer had an effect on contrast. Its more subtle than with multigrade papers but noticeable in prints and here in the data.
cyanotype_acid.jpeg


Acknowledgements: I'd like to thank my thesis advisor Sage for her watchful nonchalance
20220828_222751.jpg
 
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jonmon6691

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Mods let me know if this is allowed in the analog only section, the media was analog only, but I don't want to blow anyones fuse by showing some data analysis from a computer rather than hand-made on graph paper :tongue:

Otherwise please discuss! I'm currently working on testing my sheet film next, I made a zone X exposure of the test strip on FP4+ rated at 125 and gave N+1 development. I'm just working on my density measurement methods so I can determine my "true ISO" and development time.
 

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You are welcome to use all sorts of digital tools - all we ask is that if you are discussing various types of photography, put those discussions in the parts of the site that are appropriate for them.
 

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These are very nice tests, @jonmon6691. I'm sure they'll spark quite some debate - and in any case the plots are a joy to look at. I like this sort of thing, which of course helps. Props for going through the moves of getting all this onto (digital) paper! I like the way you did the measurements; looks like you automated the hell out of it once the scanning was done, which I think is a nice way to leverage the technology we have available these days. Very nice.

Concerning your development time: paper developer can be temperamental, I guess. I know, because I run a replenished regime mostly, and that sometimes goes awry, with similar results to your one-minute test. That's a good sign I need to kick the chemistry back in line. Perhaps I missed it, but what kind of developer are you using?
I've noticed this gap get smaller or go away on some days

That's odd, unless you mean that the gap closes due to the 2 minute patches becoming less dense. In that case, yeah, probably a temperature and/or aerial oxidation effect. You have to push developer pretty darn hard to get it to exhaust just by doing its work; in my experience, the air gets to it far sooner than the paper does.

I've seen it quoted that split grade isn't different than using regular contrast filters other than you can go in-between grades (And dodge/burn different grades). But I don't think that's necessarily true based on this graph.

Can you tell us what it is in your graph that would refute this claim? IMO for that you'd have to do a split grade chart as well as a single-exposure print that approximates the split grade curve as closely as you can. I don't see this in the present chart. I do see the plain grade 0 exposure, but it's kind of evident that this would be shaped differently from your split grade scales. As far as I can tell, your chart pretty much proves the opposite of what your claim: that split grade exposures work out the same as single grade exposures. Of course, split grade has the distinct advantage of the burn/dodge thing.

this is kind of interesting to see the relative slopes of different contrast grades.

Check out the datasheets of Ilford Multigrade and Foma's Fomabrom papers. They match your results pretty closely, I think.

It really blows me away how incredible these "modern" materials are.

You might want to pick up carbon printing :wink: In all seriousness though, a lot has to do with surface texture and quality. We generally print cyanotypes onto matte paper with the sensitizer soaking into the paper. A perfectly matte surface will always be more reflective (unless coated in Vantablack or something like that) due to light scattering. You might be surprised if you took a cyanotype and then overlayed a heavy layer of gloss over it, for instance a heavy gelatin topcoat or even an acrylic one. Heck, even waxing your prints goes a long way; it's always been a fairly popular practice for a reason.

I had to start creating really high contrast negatives by giving N+2 development to make them look okay.

Yes, New Cyanotypes ask for crazy long-scaled negatives. I see people underestimating this all the time; the same for salt prints BTW.

The cyanotype process reverses pretty significantly with over exposure and starts creating "Prussian White" instead of Prussian Blue.

With silver processes and in particular Van Dyke Brown this is also a common issue. It tends to be fixed by gold toning. It also has to do with how heavy your sensitizer is laid down. If you try backing it off a little, the problem might be reduced somewhat without affecting dmax.

One thing I noticed a while back is that the amount of acid mixed into the sensitizer had an effect on contrast.

Sure does, as with other processes. Notice also the highlight degradation; that's the price you pay. There's a balance there that can be difficult to hit sometimes. But it's been a long time since I did any New Cyano's.

Keep up the good work, I'm very much looking forward to further measurements and analyses. Fun stuff!
 

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Clever, the X-Axis makes sense because the steps are plain as day, and they're 0.15 apart (nominal).

Looks like fun.
 

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Nice study. Good advisor helps.

Wondering how you measured the densities - are these based on scans? You have some sort of software that can slice the data along a line and spit out the pixel values.

Regarding cyanotype, were the strips 'aged" before measurements or done fairly soon after drying. If so, perhaps that bump at the end might heal with time. Or doing a peroxide treatment might do the same. Or perhaps it is permanent in the New cyanotype. In classic cyanotype, which has been my only experience, I have not seen this reversal to any appreciable degree - I do my drying at elevated temperature (around 50-60 C) and it seems to achieve maximum density relatively quickly in, a matter of hours.

:Niranjan.
 
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jonmon6691

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These are very nice tests, @jonmon6691. I'm sure they'll spark quite some debate - and in any case the plots are a joy to look at. I like this sort of thing, which of course helps. Props for going through the moves of getting all this onto (digital) paper! I like the way you did the measurements; looks like you automated the hell out of it once the scanning was done, which I think is a nice way to leverage the technology we have available these days. Very nice.

Thanks yeah I have a janky python script which uses OpenCV to work with the raw tif file from Silverfast 9. Basically it just displays the image in a window and I can just click a start and end point of each wedge and it will draw a line and at the end write all the pixel values along the line out to a csv file. It was a fun little mini project to learn how to make the script. Its been a decade since I had to use an Affine transformation :tongue:

Concerning your development time: paper developer can be temperamental, I guess. I know, because I run a replenished regime mostly, and that sometimes goes awry, with similar results to your one-minute test. That's a good sign I need to kick the chemistry back in line. Perhaps I missed it, but what kind of developer are you using?


That's odd, unless you mean that the gap closes due to the 2 minute patches becoming less dense. In that case, yeah, probably a temperature and/or aerial oxidation effect. You have to push developer pretty darn hard to get it to exhaust just by doing its work; in my experience, the air gets to it far sooner than the paper does.

I actually don't know what the developer is. I asked once but didn't get a clear answer... I'll bet its temperature, its been a heck of a summer up here and the AC struggles to keep up on the 95+ days. I'll probably settle on 90 seconds in the soup just to be on the safe side. One thing I haven't noticed which kind of surprised me, is that it seems like its hard to over-developer the paper. It seems to kind of just stop when its done which doesn't really match with my experience on films. Not sure I understand why though

Can you tell us what it is in your graph that would refute this claim? IMO for that you'd have to do a split grade chart as well as a single-exposure print that approximates the split grade curve as closely as you can. I don't see this in the present chart. I do see the plain grade 0 exposure, but it's kind of evident that this would be shaped differently from your split grade scales. As far as I can tell, your chart pretty much proves the opposite of what your claim: that split grade exposures work out the same as single grade exposures. Of course, split grade has the distinct advantage of the burn/dodge thing.
For me its the fact that the highlights show basically the same separation as they do with the straight grade 0 exposure. Where I'd expect the tonal separation to expand more or less evenly across the whole range of tones for a straight grade print. But I don't have any clean data to back that up. That goes along with my comment for the grades plot, I'd like to get some more controlled examples of each grade

You might want to pick up carbon printing :wink: In all seriousness though, a lot has to do with surface texture and quality. We generally print cyanotypes onto matte paper with the sensitizer soaking into the paper. A perfectly matte surface will always be more reflective (unless coated in Vantablack or something like that) due to light scattering. You might be surprised if you took a cyanotype and then overlayed a heavy layer of gloss over it, for instance a heavy gelatin topcoat or even an acrylic one. Heck, even waxing your prints goes a long way; it's always been a fairly popular practice for a reason.
Interesting... yeah I'm using Hahnemuhle Platinum Rag for the blueprints which is definitely a delicate matte finish. I'd be interested to read more about coating. I guess that's pretty much a standard last step for daguerrotypes so I'm sure there's some pretty solid methods/materials to try out.

Yes, New Cyanotypes ask for crazy long-scaled negatives. I see people underestimating this all the time; the same for salt prints BTW.

With silver processes and in particular Van Dyke Brown this is also a common issue. It tends to be fixed by gold toning. It also has to do with how heavy your sensitizer is laid down. If you try backing it off a little, the problem might be reduced somewhat without affecting dmax.

Sure does, as with other processes. Notice also the highlight degradation; that's the price you pay. There's a balance there that can be difficult to hit sometimes. But it's been a long time since I did any New Cyano's.

Keep up the good work, I'm very much looking forward to further measurements and analyses. Fun stuff!
Cyanotypes are a helluva gateway drug to alt process :wink:

Nice study. Good advisor helps.

Wondering how you measured the densities - are these based on scans? You have some sort of software that can slice the data along a line and spit out the pixel values.
I wish I understood a little better how a real densitometer/reflectance meter worked so I could have an idea if I'm doing this right. Basically I'm taking the raw pixel value from a 16bit monochrome scan, dividing that by the darkest value to get a sort of dimensionless reflectance scale that goes from 1x up to however many times brighter the brightest spot is, then taking the log (base 10) of that number. I'm using Silverfast 9 scanning using its "HDR raw" which normally I'd run through their separate Silverfast HDR program. The HDR program applies an appropriate gamma curve for pictorial contrast so that makes me think the intermediate raw file is likely to be free of any arbitrary adjustments or mapping curves, but I don't really know that for sure. I guess I could scan the step wedge itself, I hadn't thought of that till now...

Regarding cyanotype, were the strips 'aged" before measurements or done fairly soon after drying. If so, perhaps that bump at the end might heal with time. Or doing a peroxide treatment might do the same. Or perhaps it is permanent in the New cyanotype. In classic cyanotype, which has been my only experience, I have not seen this reversal to any appreciable degree - I do my drying at elevated temperature (around 50-60 C) and it seems to achieve maximum density relatively quickly in, a matter of hours.

:Niranjan.

I always hit my prints with peroxide in between washing steps. I know its not necessary but its too damn satisfying to skip :wink:

With my sensitizer I get really intense reversal during the exposure which pretty much goes away after oxidization, but doesn't quite go as dark as dmax which is a little odd

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jonmon6691

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Took a stab at using this scanner method to analyze a sheet of FP4+ that I gave a Zone X exposure to with the step wedge taped on top of. In theory that should place the clear section of the step wedge on zone 10, then as the step wedge gets denser, we move back down the tone curve with step 21 corresponding to 11 stops less aka zone zero.

I'm still not quite sure I'm calculating density correctly since the densities I'm getting seem way too high compared to what I'd expect based on the targets that are in Ansel Adams "The Negative". Basically I'm taking the scanner value for unexposed film (high number because lots of light passes through) and calling that my film-base-plus-fog-raw (FBFR) level. Then I'm taking each pixel value and calculating log(FBFR / pixel_value). This seems to create an H&D curve that looks right in that it starts near zero then has a toe, then zooms up with a relatively flat section, but the values near the end seem too high. I threw in horizontal lines for the density targets from the book for reference. I'd expect with N-1 development that I wouldn't 2 stops denser at zone VIII than expected.

Screen Shot 2022-08-30 at 10.06.47 PM.png

Does anyone know if I can corroborate this using a light meter? I'm not sure how to get proper density numbers with that method either
 
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@jonmon6691 - this has been discussed at length in several densitometry/sensitometry threads, IIRC @radiant has applied a scanner as a densitometer with good success.

Briefly, using the transmission step wedge, you can calibrate your scanner's output pixel values to OD and then relate that to an unknown sample's density readings from the scan. Ideally, you can scan the step wedge together with your 'unknown' film strip and relate the RGB or K values in the uninverted scan.

If your Stoffer wedge is calibrated, your results should be, in absolute terms, quite accurate. If it is not, you have to make the assumption that each step is OD 0.15 away from the next.

I think the same can be applied to reflection density measurements, using a calibrated reflection tablet, in order to bypass whatever transfer function the digitizing steps apply.
 

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For reflection density, if you can back out L*ab data from the scans - you can calculate D from L* using the method described here:


:Niranjan
 

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Development time: This was the most surprising result, but with my setup, I'm getting much more range from my RC paper by developing for another minute longer than Ilford's recommended time of 1m.
Thanks for sharing your dedication and nerdery! The development time surprise is fascinating and now I'm wondering if someone can replicate the result. I just follow Ilford's 1 minute recommendation but perhaps that time needs revisiting by Ilford?
 

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I'll bet its temperature, its been a heck of a summer up here and the AC struggles to keep up on the 95+ days.

I'm confused; this would suggest that your developer warms during the course of a session. That would make it more active, hence resulting in a shorter required development time. Perhaps you could shed clarity on this?

It seems to kind of just stop when its done which doesn't really match with my experience on films. Not sure I understand why though

Paper is generally developed to completion. For that reason a somewhat longer development time doesn't hurt and doesn't make all that much of a difference. At some point high values (low densities) will suffer and develop a bit further, reducing contrast, so don't overdo it.

For me its the fact that the highlights show basically the same separation as they do with the straight grade 0 exposure. Where I'd expect the tonal separation to expand more or less evenly across the whole range of tones for a straight grade print.

Weeellll...the issue is that some of those curves show rather fancy shapes if you look closely and I'd be tempted to make let's say 5 strips for each exposure combination and then average those out. The chances that you're looking at idiosyncracies here are, well, present. Also, paper doesn't always behave as you'd intuitively expect it. For instance, I was testing with some paper (I think it was Adox MCP) at some point, exposing it at different grades and particularly looking at shadow separation. Turns out that there was very little difference in separation of the deepest shadows across the various grades. Old paper, bad testing, developer issues? I don't know, but it was remarkable. Part of the problem is that with your kind of testing, you're entering terrain where good control over all variables becomes important. That makes it a chore, which is one of the reasons I don't spend much time on this kind of testing. You really need to lock yourself up in a darkroom for a couple of days to get some good results in, which also involves a lot of (tedious) rework.

The development time surprise is fascinating

Depends a bit on what's happening exactly...see my comment above on the developer issue. Anyway, I'm not too surprised if there's something odd going on with a developer in a community darkroom that nobody can apparently identify. There might be all sorts of things going on here; different dilutions on different days, different rates of exhaustion/aerial oxidation depending on how much traffic the darkroom has seen...personally I'd be tempted to bring my own bottle of developer and use it for my own session and then discard. In any case, I'd hardly see a reason for Ilford to revise their recommendations based on what is in the end a rather shaky observation at best.

that I gave a Zone X exposure

How? Maybe you just overexposed massively. If you used an enlarger to expose the film, how did you figure out how much light to actually throw onto the film to equate with an in-camera exposure? Just guessing here, but this is an obvious faux-pas that could have happened. You wouldn't be the first to mistake a measurement of baseboard illumination as equal to an in-camera light flux level while in reality there's a massive difference. The story doesn't hold if you took a sheet film holder and taped the step wedge to a piece of sheet film and exposed the thing in an actual camera.

I guess that's pretty much a standard last step for daguerrotypes

And tintypes, and orotypes probably, and many more I guess. But we're talking prints on paper here, and those have different kinds of finishes; the list would be too long to sum up, but some examples include a gelatin (or albumen) top coat, renaissance wax etc. I've used cheap furniture polish, which worked quite well although it reeked of petroleum to high heaven. Probably not very 'archival'.


I always hit my prints with peroxide in between washing steps.

I've read, and my own experience seems to corroborate it, that if you skip the peroxide, dmax turns out just a tad higher if you just let it develop over time the natural way. The peroxide trick is pretty addictive though.
 

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If you can aim the light meter so that you read the patch, a one stop change in reading is an 0.30 density difference.

Your reading of very light and very dark will not be very accurate, but you can adjust the scale of your graphs by some gray results.
 
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jonmon6691

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@jonmon6691 - this has been discussed at length in several densitometry/sensitometry threads, IIRC @radiant has applied a scanner as a densitometer with good success.

Briefly, using the transmission step wedge, you can calibrate your scanner's output pixel values to OD and then relate that to an unknown sample's density readings from the scan. Ideally, you can scan the step wedge together with your 'unknown' film strip and relate the RGB or K values in the uninverted scan.

If your Stoffer wedge is calibrated, your results should be, in absolute terms, quite accurate. If it is not, you have to make the assumption that each step is OD 0.15 away from the next.

I think the same can be applied to reflection density measurements, using a calibrated reflection tablet, in order to bypass whatever transfer function the digitizing steps apply.
For reflection density, if you can back out L*ab data from the scans - you can calculate D from L* using the method described here:


:Niranjan
Thanks for the input! @nmp I read that page, it seems like the L*ab calculation is based on having L values from the calibration target which need to be converted to densities to check the scanner values. When it comes to calculating density from the scan file, they say to do basically the same thing I already did, which is super reassuring in a way! But the only difference was that for the L0 value, they used 2^16 where I used the actual value of by film-base-plus-fog. The only difference this value makes though is shifting the whole graph up and down, it doesn't squeeze it to better fit the density range expectation of 0.1-1.3
If you can aim the light meter so that you read the patch, a one stop change in reading is an 0.30 density difference.

Your reading of very light and very dark will not be very accurate, but you can adjust the scale of your graphs by some gray results.
I just got this amazing analog light meter, the SEI Exposure photometer, I'll give it a shot to try and at least get a range measurement between 100% transparent and the max density

Thanks for sharing your dedication and nerdery! The development time surprise is fascinating and now I'm wondering if someone can replicate the result. I just follow Ilford's 1 minute recommendation but perhaps that time needs revisiting by Ilford?
I should say that as @koraks very wisely pointed out, take this is a boulder-sized grain of salt in terms of concrete predictions of what you should expect in your darkroom. My experience here just informs what variables I now know I should question when using an unknown developer/conditions for the first time

I'm confused; this would suggest that your developer warms during the course of a session. That would make it more active, hence resulting in a shorter required development time. Perhaps you could shed clarity on this?

Paper is generally developed to completion. For that reason a somewhat longer development time doesn't hurt and doesn't make all that much of a difference. At some point high values (low densities) will suffer and develop a bit further, reducing contrast, so don't overdo it.
I guess my thought was that on warmer days the gap would close and the 1m development would "reach completion" and the extra 60 seconds wouldn't show a big gap. But dilution, oxidation, etc especially in a darkroom shared by newbies like me where who knows if stop bath tongs are being dipped or something like that... Could all have some effect that varies. The joys of living in a society :smile:

Weeellll...the issue is that some of those curves show rather fancy shapes if you look closely and I'd be tempted to make let's say 5 strips for each exposure combination and then average those out. The chances that you're looking at idiosyncracies here are, well, present. Also, paper doesn't always behave as you'd intuitively expect it. For instance, I was testing with some paper (I think it was Adox MCP) at some point, exposing it at different grades and particularly looking at shadow separation. Turns out that there was very little difference in separation of the deepest shadows across the various grades. Old paper, bad testing, developer issues? I don't know, but it was remarkable. Part of the problem is that with your kind of testing, you're entering terrain where good control over all variables becomes important. That makes it a chore, which is one of the reasons I don't spend much time on this kind of testing. You really need to lock yourself up in a darkroom for a couple of days to get some good results in, which also involves a lot of (tedious) rework.
Don't threaten me with a good time! Isn't it funny how answers always just lead to more questions. I'm definitely going to follow up with more controlled contrast strips, but I'm not going to try and chase absolutes, my main goal is just to gain an understanding of the knobs and how sensitive they are in general compared to other knobs.

How? Maybe you just overexposed massively. If you used an enlarger to expose the film, how did you figure out how much light to actually throw onto the film to equate with an in-camera exposure? Just guessing here, but this is an obvious faux-pas that could have happened. You wouldn't be the first to mistake a measurement of baseboard illumination as equal to an in-camera light flux level while in reality there's a massive difference. The story doesn't hold if you took a sheet film holder and taped the step wedge to a piece of sheet film and exposed the thing in an actual camera.
20220827_200742_small.jpg

This first go-around was mostly just to get a feel for the methods. The exposure was in-camera, and I kept adding light until I was outside of reciprocity failure region of the film. But as you can see it was different temperatures so its not the greatest conditions. But the light was less than a third of a stop away from flat along the white card so the shape of the curve should be okay.

And tintypes, and orotypes probably, and many more I guess. But we're talking prints on paper here, and those have different kinds of finishes; the list would be too long to sum up, but some examples include a gelatin (or albumen) top coat, renaissance wax etc. I've used cheap furniture polish, which worked quite well although it reeked of petroleum to high heaven. Probably not very 'archival'.

I've read, and my own experience seems to corroborate it, that if you skip the peroxide, dmax turns out just a tad higher if you just let it develop over time the natural way. The peroxide trick is pretty addictive though.
Really appreciate the input, seriously!
 

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I should say that as @koraks very wisely pointed out, take this is a boulder-sized grain of salt in terms of concrete predictions of what you should expect in your darkroom. My experience here just informs what variables I now know I should question when using an unknown developer/conditions for the first time
Not to worry, I don't change anything unless Ilford or my own experience warrants it. Thanks again!
 

Bill Burk

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With the SE I photometer, the top scale is (relative) density. Each line is 0.10.

So pull the front lens out as far as possible and get as close as you can to the Stouffer scale on a light source. You know the “nominal” density of each step from the envelope it came in (or you can figure it out and write it there if it doesn’t already say).

Every other step will be 3 marks different (0.15 x 2 = 0.30)

You’ll quickly see how you can judge densities, probably to 0.05 precision by judging between the lines.

You got this!
 
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