Accutance comparisons

[Alan Johnson]

Would not the 0.1 mm edge effect cause maximum resolution in a print to be 5 lines/mm or less? What happens to picket fences and the like when the edge effects meet in the middle?

I think one edge effect line,from light to dark,and one pixel radius sharpening both count as a complete cycle equivalent to one line-pair,in this case 0.1mm wide,10 line-pairs/mm,but I'm not absolutely sure.
The relative lightness of the lines from different films and from stand/normal developing can really only be assessed from prints.To do the test again I would make bigger (20x) enlargements of the edge.
I think it is true that edge effects would reduce the resolution of eg picket fences.

 

[fhovie]

It (my 30"x40" grainless print) was an FP4+ at ASA80 4x5 negative on Ilford Multigrade iv RC paper (roll) It was semi-stand processed in Pyrocat-P 1:1:150 for 55 minutes at 70F with 4 short agitations evenly spaced. It has a DR of 1.35. The SBR was about 7 stops. I used a condenser enlarger that I recently laser aligned (both carrier plane and lens plane) I focused it with a grain focus aid and developed it in PC-TEA. The sky is a zone 9 (just off the white) there are large areas of zone 5 -7 of bright rock that you can see small pebbles and sand on) - And it is grainless - I think an hour in pyro, stain likely masks any grain on the VC paper - I used a Grade 2 filter. I look at it every morning in the small room where I have it - ahem.

I have to say, I have never had FP4+ enlarged 8 times to 40" without visible grain, but then again that depends on distance. I can see the grain on Fp4+ on 24" print where theyere are sky or medium light tones with pyrocat HD, D76 etc. I guess we all have a different idea of what visible grain is. I find FP4+ is defintely showing a break in tonality at 20" if developed in D76 1+1 and subtle Z5-7s are present and my 10x8 colour head is as diffuse as they get!

 

[Tom Stanworth]

It (my 30"x40" grainless print) was an FP4+ at ASA80 4x5 negative on Ilford Multigrade iv RC paper (roll) It was semi-stand processed in Pyrocat-P 1:1:150 for 55 minutes at 70F with 4 short agitations evenly spaced. It has a DR of 1.35. The SBR was about 7 stops. I used a condenser enlarger that I recently laser aligned (both carrier plane and lens plane) I focused it with a grain focus aid and developed it in PC-TEA. The sky is a zone 9 (just off the white) there are large areas of zone 5 -7 of bright rock that you can see small pebbles and sand on) - And it is grainless - I think an hour in pyro, stain likely masks any grain on the VC paper - I used a Grade 2 filter. I look at it every morning in the small room where I have it - ahem.

I too find that one can do huge grainless enlargements if there are textures present (such as the rocks you speak of). The Z9 sky wont show grain because it does not have the density on the print. I suspect that were the sky gently shifting Z5-7, such as ocercast, but interesting cloud variation, you would find plenty of grain at that size. I remember doing an exactol Lux test where I found utterly grainless skies"with the very high values and a seconds test sheet of a woodland scene wwas super sharp. Then I went to print my image Demise of teh Harvest Capella (if you look in my gallery youll see teh values I am talking about) and it wont go above 20"without break up in the delicate greys in the sky. That was processed with normal agitation too!

Early riser- I totally agree and think that most people here test for mottling and all the usal demons and come up with a technique that works before comitting important film. I find that with smoothies like Acros, that an acutance dev is the only way to get decent acutance and get some visual bite back. I am going to experiement with agitation every 2-3 mins for films like this. I remember comparing acros in DiXactol to that developed in ID11 and the DiXactol (which has very agressive acutance) produced a much more 3d image. For me, whatever I do has to be simple and reliable. I dont have the patience to wait 40 mins for some film! 20 mins tops! Using Pyrocat HD and agitating every second minute still introduces way more bite than regular devs and is no trouble at all apart from a slightly increased dev time.

 

[argus]

Edge effects are a common side effect from stand development, that gives the illusion of greater acutance.

I think this is a good example of possible edge effects.
There is a distinctive glow, noticeable in the around the darkest poles in the attached image.

TriX 320 developed in Rodinal 1+150 for 50'. First 30" agitation, another 30" agitation at 15' (straight negative scan)

Greetings,
G

 

[Mahler_one]

Interesting....thanks for taking the time and effort to post the scan.

Edwin

 

[aldevo]

Thornton's "Edge of Darkness" is full of objective test data about sharpness accutance and resolution which are not all the same thing. Sharpness (increased accutance) IS A DISTORTION. It is an artificially produced line using chemistry that manipulates silver grains and or the penetration of developer into the emulsion surface by tanning. Using a resolution test, this will reduce the resolution but make the image appear sharper. The greatest resolution film I ever used was Tech Pan. It did not look that sharp. It takes grain to make an image look sharp. All this is well documented in Thornton's book.

One thing I know about the folks on APUG is that when several of them report that something works, that is to me as good an objective proof as I need. The end result is not going to be someone looking at a photo on a wall with a microscope but instead it will be the emotion generated by the subject matter and how well the image conveys that subject. That is why I don't really care about what the negative looks like under a microscope. I care about what the enlargement looks like (not withstanding the effect of negative stain on the print) - You can get an image that is too sharp as well. The finest minds in photography are here (and I am not counting myself) and I count most of my modest success at photography from taking their word for it.

Excellent post. Edge effects are a distortion and actually LOWER resolution where they occur. For scientific applications, such as metalography, developers were always used that were reformulated (e.g. D-76c) in the interest of suppressing edge effects.