Specific circle of confusion for 8x10, large prints

Jarin Blaschke · Nov 13, 2017

Hi all:

I apologize if this is covered very often, and this is a very subjective topic, but I'm missing the equation to decide upon a functioning circle of confusion for a specific set of parameters.

For larger prints, I don't fully trust my loupe when judging depth of field on a grainy ground glass that is stopped-down and dim, so for confirmation, I obtained one of the seemingly better depth of field apps for the field. In order for the app to function with any accuracy, I need to input the acceptable circle of confusion in microns. Here are my parameters:

I want to be able to enlarge 8x10" negatives to 32x40" (4x)
I want sharpness maintained at as close as 9" viewing distance (for those who care to look).
I want to resolve 8 lines/mm for those with good vision (is this a good figure?).
I shoot FP4 developed in a metol-pyro developer, and use Apo Sironar S optics between f/20 and f/45.

For 4x enlargement, I have already figured that diffraction limits me to f/45 or wider apertures. I am just missing a reliable DoF component. I will be purchasing a laser measurement tool as well to aid in wider scenes.

Thank you!
-Jarin

ic-racer · Nov 13, 2017

You can't directly measure your acceptable circle of confusion. You calculate it backwards from existing acceptable prints.

Prof_Pixel · Nov 13, 2017

Here is some interesting info for you: https://en.wikipedia.org/wiki/Circle_of_confusion

wiltw · Nov 13, 2017

Most DOF calculations and DOF scales on lenses (such as lenses for the 135 format) assume (unfortunately) the poor eyesight of 'manufacturer standard', rather than the more proper assumption that the viewer has 20/20 corrected vision! People with 20/20 vision can perceive details which are roughly 1/3 the size of those used by lens manufacturers (~0.01 in features for a 8x10 in print viewed at 1 ft)
The 'manufacturer standard' assumes 0.02501mm as the CofC for a 135 format shot at the focal plane, which is then enlarged by 8.5x to create the 8" x 10" print. Using the “Zeiss formula”, the CofC is sometimes calculated as d/1730 where d is the diagonal measure of the original image (the camera format). For full-frame 35 mm format (24 mm × 36 mm, 43 mm diagonal) this comes out to be 0.025 mm.

tedr1 · Nov 13, 2017

I have seen as a guide the use of a circle of confusion between one thousandth and one fifteen hundredth of the print diagonal.

RalphLambrecht · Nov 13, 2017

Jarin Blaschke said:
Hi all:

I apologize if this is covered very often, and this is a very subjective topic, but I'm missing the equation to decide upon a functioning circle of confusion for a specific set of parameters.

For larger prints, I don't fully trust my loupe when judging depth of field on a grainy ground glass that is stopped-down and dim, so for confirmation, I obtained one of the seemingly better depth of field apps for the field. In order for the app to function with any accuracy, I need to input the acceptable circle of confusion in microns. Here are my parameters:

I want to be able to enlarge 8x10" negatives to 32x40" (4x)
I want sharpness maintained at as close as 9" viewing distance (for those who care to look).
I want to resolve 8 lines/mm for those with good vision (is this a good figure?).
I shoot FP4 developed in a metol-pyro developer, and use Apo Sironar S optics between f/20 and f/45.

For 4x enlargement, I have already figured that diffraction limits me to f/45 or wider apertures. I am just missing a reliable DoF component. I will be purchasing a laser measurement tool as well to aid in wider scenes.

Thank you!
-Jarin

Jarin, It seems to me that you have all the required data. I don't have a full answer but like to send you a free pdf with it when you send a request to rwlambrec@gmail.com. For now, Yes,8lp/mm covers people with good vision.Even 7lp/mm would do that.
For the CoC stick to the standard of an 8x10 negative, which is(sorry have to look that up myself).

RalphLambrecht · Nov 13, 2017

ic-racer said:
You can't directly measure your acceptable circle of confusion. You calculate it backwards from existing acceptable prints.

That's correct. I should have posted this attached table earlier.

Jarin Blaschke · Nov 13, 2017

So, after perusing the Wikipedia article (if it is to be believed), it seems I should use a CoC of 40 microns / .04mm. My figuring is below, with one important question:

1.) At 25cm viewing distance, supposedly good vision can distinguish 5 line pairs/mm, which is a CoC of .2mm according to the wikipedia article. However, should this not instead be .1mm? Don't you need two CoCs to make a line pair? If you can distinguish 5 line pairs, isn't that the same as 10 lines?
2.) Anyway, for now let's go with .2mm CoC equivalent at 25cm viewing distance. I want to afford a little extra scrutiny for audiences like myself, so figured a .16 CoC which puts viewing distance at 20.83cm (8.2").
3.) I will be enlarging 4x, so .16mm on the print divided by 4 is .04mm on the film (40 microns).

...or should it really be .02mm (20 microns), since we deal in line pairs?

Unfortunately I have to save serious darkroom rentals (the 8x10 enlarger) for real printing only, and can't find this answer through extensive testing. I have to just go by a conservative formula until the first major project.

Jarin

RalphLambrecht · Nov 14, 2017

Jarin Blaschke said:
So, after perusing the Wikipedia article (if it is to be believed), it seems I should use a CoC of 40 microns / .04mm. My figuring is below, with one important question:

1.) At 25cm viewing distance, supposedly good vision can distinguish 5 line pairs/mm, which is a CoC of .2mm according to the wikipedia article. However, should this not instead be .1mm? Don't you need two CoCs to make a line pair? If you can distinguish 5 line pairs, isn't that the same as 10 lines?
2.) Anyway, for now let's go with .2mm CoC equivalent at 25cm viewing distance. I want to afford a little extra scrutiny for audiences like myself, so figured a .16 CoC which puts viewing distance at 20.83cm (8.2").
3.) I will be enlarging 4x, so .16mm on the print divided by 4 is .04mm on the film (40 microns).

...or should it really be .02mm (20 microns), since we deal in line pairs?

Unfortunately I have to save serious darkroom rentals (the 8x10 enlarger) for real printing only, and can't find this answer through extensive testing. I have to just go by a conservative formula until the first major project.

Jarin

I recommend to stick with lp/mm;hope you get something from the pdf I've sent you.

Dan Fromm · Nov 14, 2017

Hmm. 4x enlargement. >= 8 lp/mm in the final print. >= 32 lp/mm in the negative. CoC <= around 1/32 mm = 3 microns.

Format has nothing to do with it, only intended enlargement and resolution needed in the final print.

Jarin Blaschke · Nov 14, 2017

Dan: Your math makes sense, but as there are 1000 microns in a millimeter, you mean 30 microns, no?

What won't stop snagging me is how a line pair equals the equivalent CoC. Shouldn't we need a CoC to resolve a line, therefore two CoCs are needed per line pair?

Ralph: thanks for the document. I can take a focused (whoops) look later today.

Jarin

tedr1 · Nov 14, 2017

Some discussion at this thread may be relevant https://www.photrio.com/forum/threads/coc-and-depth-of-field.80816/

Dan Fromm · Nov 14, 2017

Jarin, thanks for the correction. ~ 30 microns it is. Here are two line pairs: |||. First and second lines make one pair, second and third lines make a second pair. # of line pairs = # of lines - 1. If the CoC is < the distance between the lines, they'll be resolved.

RalphLambrecht · Nov 14, 2017

Jarin Blaschke said:
Dan: Your math makes sense, but as there are 1000 microns in a millimeter, you mean 30 microns, no?

What won't stop snagging me is how a line pair equals the equivalent CoC. Shouldn't we need a CoC to resolve a line, therefore two CoCs are needed per line pair?

Ralph: thanks for the document. I can take a focused (whoops) look later today.

Jarin

Jarin google for 'point spread'function' to get your answer and search for a book called'Clarity' You'll enjoy it.

zilch0md · Nov 14, 2017

Jarin Blaschke said:
So, after perusing the Wikipedia article (if it is to be believed), it seems I should use a CoC of 40 microns / .04mm. My figuring is below, with one important question:

1.) At 25cm viewing distance, supposedly good vision can distinguish 5 line pairs/mm, which is a CoC of .2mm according to the wikipedia article. However, should this not instead be .1mm? Don't you need two CoCs to make a line pair? If you can distinguish 5 line pairs, isn't that the same as 10 lines?
2.) Anyway, for now let's go with .2mm CoC equivalent at 25cm viewing distance. I want to afford a little extra scrutiny for audiences like myself, so figured a .16 CoC which puts viewing distance at 20.83cm (8.2").
3.) I will be enlarging 4x, so .16mm on the print divided by 4 is .04mm on the film (40 microns).

...or should it really be .02mm (20 microns), since we deal in line pairs?

Unfortunately I have to save serious darkroom rentals (the 8x10 enlarger) for real printing only, and can't find this answer through extensive testing. I have to just go by a conservative formula until the first major project.

Jarin

Hi Jarin,

Going by the CoC formula in the Wikipedia article, one should input the anticipated viewing distance and enlargement factor, in addition to your personally desired print resolution, specified in lp/mm (line pairs per millimeter).

Reading the post I've quoted, above, it looks as if you're letting the formula dictate your closest anticipated viewing distance - putting the cart before the proverbial horse. Adults with healthy vision can typically focus no more closely than 25 cm (about 10 inches). That's why 25 cm has long been the so-called "standard viewing distance" when discussing resolution in terms of lp/mm (vs. angular resolution, expressed in arc-minutes, where distance is irrelevant.)

THX, the people who provide specs for theaters, both commercial and home theaters, fit their viewing distance calculations to an assumed maximum human acuity of 1.0 arc-minute, which equates to 6.88 lp/mm at a viewing distance of 25cm. Double the viewing distance and you can go to 3.44 lp/mm, yet still deliver 1.0 arc-minute of angular resolution.

Many photographic texts, however, including John B. Williams' Image Clarity: High Resolution Photography, consider 8 lp/mm to be the maximum resolution of healthy human vision at the standard viewing distance of 25cm. Of course, it varies from person to person, but I once read that eagles can resolve 24 lp/mm at 25cm, so I think it's safe to assume that most humans are limited to less than 10 lp/mm.

8 lp/mm at 25cm is equivalent to 0.86 arc-minute of angular resolution. I really suspect THX is rounding up from 0.86 to 1.0 arc-minute to make their theater calculations a little easier, but the net impact of that rounding, if indeed it was a conscious decision to round up to the nearest integer, is that they are telling people to sit a lot closer to their 1080p flatscreen TVs (and twice as close, still, to their 4k flatscreens) than they would if THX would acknowledge that we can resolve 0.86 arc-minute (8 lp/mm at 25cm) instead of only 1.0 arc-minute (6.88 lp/mm at 25cm).

Reading between the lines, it sounds as if you anticipate (or desire to support) a minimum viewing distance of 25cm (the closest distance at which healthy eyes can typically focus), a 4x enlargement factor and a desired print resolution of 5 lp/mm at 25cm.

Running the equation...

Max. permissible on-film CoC (mm) = viewing distance (cm) / desired final-image resolution (lp/mm) for a 25 cm viewing distance / enlargement / 25

CoC (mm) = 25 / 5 / 4 / 25 = 0.05 mm <--- Try this in your DoF calculations.

Note that if somebody views your print at a distance of 40 cm (15.75 inches) instead of 25 cm (9.84 inches), they will perceive a resolution equivalent to viewing an 8 lp/mm print at 25cm. It's only if they can focus more closely than 25cm and choose to do so, that they will perceive subject detail at something less than the equivalent of 5 lp/mm viewed at 25cm. And frankly, it's more likely that people will be looking at a 32x40-inch print from distances greater than 25cm. So... 5 lp/mm is probably "critical enough" for a 4x enlargement when your final print dimensions are that large.

Regarding your concern for the ratio of line pairs to CoCs, there are many references which say that a 0.2 mm CoC at the film or sensor equates to 5 lp/mm prior to enlargement. There are several texts that say CoC, prior to enlargement, is the reciprocal of the lp/mm you will record on film or at the sensor, or lp/mm is the reciprocal of the maximum CoC diameter you permit via DoF calculations and adherence to those calculations.

If, for example, you anticipate an 8x enlargement to produce 8x12-inch prints from a 35mm negative, 5 lp/mm at the print requires 40 lp/mm at the negative and thus, you must perform your DoF calculations with a maximum permissible in-camera CoC diameter of 1/40 = 0.025mm. The reciprocal of 40 lp/mm is roughly 0.03 mm. Sound familiar? Many people are disappointed with DoF calculators that use 0.03mm CoCs for 35mm format. They need to increase their desired print resolution from 5 lp/mm to 8 lp/mm, for example, and do the DoF calculations to limit on-film CoC diameters to the reciprocal of 8 lp/mm or 0.125 mm (but it's really tough to achieve 64 lp/mm on-film to deliver 8 lp/mm in an 8x enlargement, except with the likes of Tech Pan and some very good glass.

One last tip: Once you've calculated the maximum permissible CoC diameter for a specified viewing distance, enlargement factor and desired print resolution in lp/mm, you can calculate the f-Number at which diffraction will just begin to inhibit your desired print resolution as follows:

Max f-Number = CoC / 0.00135383

Warning: This formula only works if you've used the Wikipedia CoC equation (above) that takes into account your desired print resolution, viewing distance, and enlargement factor.

Thus, for an in-camera CoC diameter of 0.05 mm, you can stop down to 0.05 / 0.00135383 = 36.9, or about f/32 + 1/3 stop without concern for diffraction inhibiting your print resolution goal of 5 lp/mm in a 4x enlargement to be viewed at 25cm.

How was that constant 0.0013583 derived? Search for it on this page: http://www.faqs.org/faqs/rec-photo/lenses/tutorial/

OK, I'm rambling, but I hope that helps.

Mike

RalphLambrecht · Nov 15, 2017

zilch0md said:
Hi Jarin,

Going by the CoC formula in the Wikipedia article, one should input the anticipated viewing distance and enlargement factor, in addition to your personally desired print resolution, specified in lp/mm (line pairs per millimeter).

Reading the post I've quoted, above, it looks as if you're letting the formula dictate your closest anticipated viewing distance - putting the cart before the proverbial horse. Adults with healthy vision can typically focus no more closely than 25 cm (about 10 inches). That's why 25 cm has long been the so-called "standard viewing distance" when discussing resolution in terms of lp/mm (vs. angular resolution, expressed in arc-minutes, where distance is irrelevant.)

THX, the people who provide specs for theaters, both commercial and home theaters, fit their viewing distance calculations to an assumed maximum human acuity of 1.0 arc-minute, which equates to 6.88 lp/mm at a viewing distance of 25cm. Double the viewing distance and you can go to 3.44 lp/mm, yet still deliver 1.0 arc-minute of angular resolution.

Many photographic texts, however, including John B. Williams' Image Clarity: High Resolution Photography, consider 8 lp/mm to be the maximum resolution of healthy human vision at the standard viewing distance of 25cm. Of course, it varies from person to person, but I once read that eagles can resolve 24 lp/mm at 25cm, so I think it's safe to assume that most humans are limited to less than 10 lp/mm.

8 lp/mm at 25cm is equivalent to 0.86 arc-minute of angular resolution. I really suspect THX is rounding up from 0.86 to 1.0 arc-minute to make their theater calculations a little easier, but the net impact of that rounding, if indeed it was a conscious decision to round up to the nearest integer, is that they are telling people to sit a lot closer to their 1080p flatscreen TVs (and twice as close, still, to their 4k flatscreens) than they would if THX would acknowledge that we can resolve 0.86 arc-minute (8 lp/mm at 25cm) instead of only 1.0 arc-minute (6.88 lp/mm at 25cm).

Reading between the lines, it sounds as if you anticipate (or desire to support) a minimum viewing distance of 25cm (the closest distance at which healthy eyes can typically focus), a 4x enlargement factor and a desired print resolution of 5 lp/mm at 25cm.

Running the equation...

Max. permissible on-film CoC (mm) = viewing distance (cm) / desired final-image resolution (lp/mm) for a 25 cm viewing distance / enlargement / 25

CoC (mm) = 25 / 5 / 4 / 25 = 0.05 mm <--- Try this in your DoF calculations.

Note that if somebody views your print at a distance of 40 cm (15.75 inches) instead of 25 cm (9.84 inches), they will perceive a resolution equivalent to viewing an 8 lp/mm print at 25cm. It's only if they can focus more closely than 25cm and choose to do so, that they will perceive subject detail at something less than the equivalent of 5 lp/mm viewed at 25cm. And frankly, it's more likely that people will be looking at a 32x40-inch print from distances greater than 25cm. So... 5 lp/mm is probably "critical enough" for a 4x enlargement when your final print dimensions are that large.

Regarding your concern for the ratio of line pairs to CoCs, there are many references which say that a 0.2 mm CoC at the film or sensor equates to 5 lp/mm prior to enlargement. There are several texts that say CoC, prior to enlargement, is the reciprocal of the lp/mm you will record on film or at the sensor, or lp/mm is the reciprocal of the maximum CoC diameter you permit via DoF calculations and adherence to those calculations.

If, for example, you anticipate an 8x enlargement to produce 8x12-inch prints from a 35mm negative, 5 lp/mm at the print requires 40 lp/mm at the negative and thus, you must perform your DoF calculations with a maximum permissible in-camera CoC diameter of 1/40 = 0.025mm. The reciprocal of 40 lp/mm is roughly 0.03 mm. Sound familiar? Many people are disappointed with DoF calculators that use 0.03mm CoCs for 35mm format. They need to increase their desired print resolution from 5 lp/mm to 8 lp/mm, for example, and do the DoF calculations to limit on-film CoC diameters to the reciprocal of 8 lp/mm or 0.125 mm (but it's really tough to achieve 64 lp/mm on-film to deliver 8 lp/mm in an 8x enlargement, except with the likes of Tech Pan and some very good glass.

One last tip: Once you've calculated the maximum permissible CoC diameter for a specified viewing distance, enlargement factor and desired print resolution in lp/mm, you can calculate the f-Number at which diffraction will just begin to inhibit your desired print resolution as follows:

Max f-Number = CoC / 0.00135383

Warning: This formula only works if you've used the Wikipedia CoC equation (above) that takes into account your desired print resolution, viewing distance, and enlargement factor.

Thus, for an in-camera CoC diameter of 0.05 mm, you can stop down to 0.05 / 0.00135383 = 36.9, or about f/32 + 1/3 stop without concern for diffraction inhibiting your print resolution goal of 5 lp/mm in a 4x enlargement to be viewed at 25cm.

How was that constant 0.0013583 derived? Search for it on this page: http://www.faqs.org/faqs/rec-photo/lenses/tutorial/

OK, I'm rambling, but I hope that helps.

Mike

great reference thanks

ic-racer · Nov 15, 2017

Jarin Blaschke said:
... can't find this answer through extensive testing. I have to just go by a conservative formula until the first major project.

Jarin

You could ask someone. For my critical enlarged 8x10 work I don't stop down past F32 on the taking lens. When one is analyzing the prints for such detail, tripod stability and lack of wind, correct focal point for the focus spread, and absolute coincidence between GG and film plane are essential.

Jarin Blaschke · Nov 15, 2017

Thank you everybody! Especially Mike with his comprehensive response (how long did that take you!?) and Ralph with the very detailed document you emailed me.

I’ve settled on 8 lp/mm for 32x40 prints, which puts my CoC at .031mm (31 microns, or 32 lp/mm). From the most conservative figures I’ve seen, I have to shoot at 32 2/3 or wider to prevent degradation from diffraction.

I always walk up and lean into very big prints to see if I can relish in close details; I’d like to provide this opportunity in my own prints. Broad and close inspection are both important.

I can make contrast prints at home; I’m going to eventually test see if I can recognize a difference between 8 and 10 or 15 lp/mm when I really get close to the prints. 8x10 contacts may require a higher standard.

J

RalphLambrecht · Nov 15, 2017

Jarin Blaschke said:
Thank you everybody! Especially Mike with his comprehensive response (how long did that take you!?) and Ralph with the very detailed document you emailed me.

I’ve settled on 8 lp/mm for 32x40 prints, which puts my CoC at .031mm (31 microns, or 32 lp/mm). From the most conservative figures I’ve seen, I have to shoot at 32 2/3 or wider to prevent degradation from diffraction.

I always walk up and lean into very big prints to see if I can relish in close details; I’d like to provide this opportunity in my own prints. Broad and close inspection are both important.

I can make contrast prints at home; I’m going to eventually test see if I can recognize a difference between 8 and 10 or 15 lp/mm when I really get close to the prints. 8x10 contacts may require a higher standard.

J

be aware that there is a subjective print improvement with higher resolutionYou may not be able to resolve above 8lp/mm but,15 lp/mm may still look cleaner to your eye. I is suggested that up to 25lp/mm can be appreciated subjectively.

zilch0md · Nov 15, 2017

Jarin Blaschke said:
Thank you everybody! Especially Mike with his comprehensive response (how long did that take you!?) and Ralph with the very detailed document you emailed me.

I’ve settled on 8 lp/mm for 32x40 prints, which puts my CoC at .031mm (31 microns, or 32 lp/mm). From the most conservative figures I’ve seen, I have to shoot at 32 2/3 or wider to prevent degradation from diffraction.

I always walk up and lean into very big prints to see if I can relish in close details; I’d like to provide this opportunity in my own prints. Broad and close inspection are both important.

I can make contrast prints at home; I’m going to eventually test see if I can recognize a difference between 8 and 10 or 15 lp/mm when I really get close to the prints. 8x10 contacts may require a higher standard.

J

Wow! You're going for it - 8 lp/mm in 32x40 prints. At 4x enlargement, I think this is achievable - securing 32 lp/mm on-film, but you might find some of your lenses are not up to the task, depending on how close the corners come to the edge of your image circle. Here's hoping you have something like the Schneider Super-Symmar XL's to play with.

I've never actually shot large format, but here's a spreadsheet showing both manufacturer's specs and calculated specs that you might find interesting. I put it together 15 years ago, so you won't find some of the more modern LF lenses (Digitars, etc.)

Dead Link Removed

Links to similar spreadsheets for other LF formats can be found at the bottom of this page at my website:
Dead Link Removed

These same spreadsheets are also hosted by QT Luong at http://www.largeformatphotography.info/lenses/

Back on topic, I doubt you can find LF lenses for 8x10 that can actually secure 64 lp/mm in the corners of the frame (as would be needed to achieve 16 lp/mm in a 4x enlargement), but my understanding of LF lens performance might be dated. Still, I suspect you're going to find your goal of 8 lp/mm in 4x enlargements to be very "confining" when you get out into the field. You'll be climbing up on top of your vehicle the way Ansel Adams did, to get away from those Nears that are too Near - even with some tilt in the game. But I really admire your passion to take it on.

Mike

DREW WILEY · Nov 15, 2017

My advice : Ignore all the math, as well as terminology which is itself nothing but a circle of utter confusion. A good loupe and really knowing how to use it on the ground glass is a thousand times better. And yes, I do know how to make very sharp 30X40 prints from 8X10 film. But unless you also have some kind of precision film holder, like an adhesive one, you can't achieve a consistent focal plane anyway. It's far easier to demonstrate these techniques than chatter about them.

DREW WILEY · Nov 16, 2017

Unless you are shooting something flat in a studio, every shot presents its own challenges. That's part of the fun of it. Often you must prioritize exactly what part of the image deserves acute focus and what can yield a bit. First I compose the shot, including the relevant tilts & swings etc. Then I recheck the focus on critical areas with a 7X loupe stopped HALFWAY down to my final intended aperture, which is generally still sufficiently bright enough (or carry a laser pointer and aim it at the intended plane - that works even in a cave!). Of course, I print optically using glass carriers and a vacuum easel. Digital prints are limited in the detail they can carry. But managing detail involves esthetic as well as technical decisions. There is a lot of psychology involved too. You have to direct the viewer's eye where you want it. Good luck! 8x10 photography is great fun, but takes awhile to master. I've never used hyperfocal theory with it even once.

Jarin Blaschke · Nov 16, 2017

Mike:
I have only one lens so far, a 300mm Rodenstock Apo-Sironar S. It is the reason I have no other lenses so far : ). I work in film/movies (cinematographer), and put together a full 8x10 kit and basic contact-print darkroom after finishing a 3 1/2-month film project. I also have a daughter and other large responsibilities, and so, as before, I have to wait for substantial projects to expand the kit if I want top-quality optics and to pay for substantial photography trips. Of course, the more I shoot this format, the more I learn that I've mostly paid for wide-aperture performance with such a lens. And here I am trying to maximize deep focus, large prints! At f/32, perhaps other lenses would have performed just as well. Still, I have shot some portraits at f/8 to f/11, and have been grateful for the sharpness at these stops, although the bokeh with this lens is not the most beautiful.

I'd probably be very satisfied with 8 lp/mm at 32x40. It's only with the 8x10 contact prints that I really appreciate truly fathomless sharpness, when it really invites you to lean in and squint and still you know that it's holding much beyond what you can see and you curse your mortal eyes. I've found that quality with my early proof prints (on Lodima or Lupex), although I will soon be contact printing negs shot at f/64, f/90 and f/128 and I'll soon see if I can find much difference in a contact print versus the f/16 to f/32 negs I've printed so far. I will say, being able to see knots on barbed wire hundreds of feet from camera, in a small print, is amazing. My 'math' says f/128 delivers all the line pairs I can see, but as you said, there may be a real subjective difference (Ralph).

I'll tentatively calibrate like this:
8x10 contact: 15 lp
16x20; 10 lp
20x24: 8lp (same req. as 16x20)
30x40: 8lp

Drew:
I get where you're coming from too! This all seems masturbatory until I have some real experience in delivering these kinds of technical prints, and the kind of real-life rigor required. Nonetheless, I have a pretty good 8x loupe and a Maxwell screen, but don't expect them to adequately convey what a negative needs to render for a 32x40 print. I can't wait for experience to replace all this theory.

J

Jarin Blaschke · Nov 16, 2017

Drew:

What loupe do you use, by the way? I have an 8x, and it seems slightly too strong, and the noise of the screen slightly too great to do my best job focusing.

J

DREW WILEY · Nov 16, 2017

I must warn you that 8X10 photography is an addiction very difficult to cure! But in terms of sharpness, you're only as good as the weakest link in the entire workflow. A loupe helps you check alignment of your camera too, something you can't just take for granted. I generally use Peak 7X loupes; but the type of ground glass is important too (I hate fresnels).

Specific circle of confusion for 8x10, large prints

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