IQ180 and 8x10 assessment

[Will Frostmill]

Hi Tim,

I second Frank Petrino's suggestions above, particularly reducing the number of cameras. If I was going to add a third camera to the mix, I'd pick an inexpensive 4x5 with an inexpensive lens. Like a Calumet CC-400 with a bog-standard 150mm Caltar, on a Tiltall. Just to demonstrate how big (or small!) the gap is between 'ordinary' equipment and extraordinary equipment and technique.

Will

[Nathan Potter]

I'd be inclined to place a resolution target in the center of the field of view for all the images. This would provide a target from which analytical data can be gathered directly from the final print. The black and white EV values can be measured with the densities recorded on film for an assessment of processing consistency for the film and - well I'm not sure how you would assess the digital exposure consistency - have to think about that a bit.

Simply print out a copy of the US Air Force 1951 target at the appropriate size. Seems if you're shooting at 100 meters or so and using a 240 mm lens the demagnification factor is about 40X so to produce a 10 um line on film would require a 400 um line on paper at 100 meters. All very doable. For consistency using different focal lengths you would scale the size of the target to end up with about a 10 um line at the image plane. Hopefully you would cover at least the 5 um to say 200 um linewidth sizes at the film and sensor plane using the USAF or equivalent resolution target .

Indeed, stability of the setup is quite crucial. Think about the laser pointer being reflected off part of the white target at 100 meters for a critical assessment of vibration.

Nate Potter, Austin TX.

Well of course I missed the demagnification factor by 10X. So at 100 meters a 10 um line at the image would be about .160 inch (4064 um). Using a USAF target indoors as others have suggested is difficult due to the small linewidths required at the target.

Nate Potter, Austin TX.

[timparkin]

1) When testing outdoors, changes in lighting can introduce unwelcome variables, and force us to make different exposures. Having to adjust things in haste can also make us error-prone. So if you can test indoors, you can banish those issues.

Probably not really possible unless we can hire a church hall or something similar. Daylight would be useful too. We will have multiple people there to fire off all cameras at the same time.

2) Some lenses are corrected for infinity (Nikkor M), while others are corrected for 1:5 (Fujinon A) or other ratios, like 1:10 for the Sironar S. These influences don't affect normal prints made by typical shooters, but if you're using a Microscope and scanning at many thousands of SPI, you might want to test each lens at close range and at infinity.

It's not a lens test as such and unless someone can give me an idea that this will introduce a significant error, I think shooting at 1:10 - 1:30 ratios would correlate with most real world usage? I'll keep it in mind though, thanks.

3) Some lenses exhibit focus shift when they are stopped down. It might be helpful to use a strong loupe and focus the image at the actual taking aperture, rather than wide open.

Good point! Hard to work out point of focus when stopped down though - I'm worried this may introduce further errors. Is this likely with Sironar S lenses?

Tim

[timparkin]

Assuming you're not using adhesive or vacuum film holders, unfortunately, you should should do multiples of each film test - at least three - to get some sense of how much variation is introduced by slop in the film holders (or frame-to-frame flatness variation in the rollfilm camera).

Will a bit of thin double sided affect focus? Quite happy to add some if it makes sense. I shall probably use the Chamonix holder as it seems a snugger construction than my fidelitys (again, unless there is a noted issue with Chamonix holders). Will probably focus bracket three shots anyway.

You should check beforehand to assure that the GG is properly aligned in the specific view cameras you're going to use, and that the RF is properly aligned in the Mamiya 7 if you use that. With the Mamiya, during the tests, you might run a focus bracket to be sure. Given the limitations of the sort-of-live-view in the IQ and the absence of it in the P45+, you may want to run a focus bracket on the digital captures as well.

Difficult to check the alignment but I know I've shot 8000dpi capable images on my 45SU and 4000 capable on the Toyo 810M (see the photograph at the botton of this post).

"Infinity" is tricky when comparing systems with such disparate "format" sizes and focal lengths. I would suggest something at studio range as well as something at middling distance outdoors, taking into account Ken's caveat re changing conditions outdoors.

Agreed.. about infinity - will keep away from that one.

Before making the test exposures, perch a laser pointer or other sensitive vibration indicator on top of each camera/lens/tripod setup and make sure that there is no detectable camera shake induced by the cable release or other shutter release action.

Great idea..

[timparkin]

shoot both cameras at the same time to avoid different lighting conditions.

Agreed

[timparkin]

I really hate to ask this because you have obviously thought long and hard on this project. But Why? What are you trying to prove? Are'nt all those cameras built square? Why not make a contact print to evaluate the results?

I'm afraid I don't understand the general flow of those questions and where they are heading but..

1) "What am I trying to prove?" - nothing, just making a comparison
2) "aren't all cameras built square?" - Typically yes, apart from roundshot ones :-)
3) "Why not contact print to evalulate?" - You can't contact print an IQ180 file

Introducing digital scanning brings a new factor that I do not feel was designed into the taking lens in the first place. Just curious. I tested dozen of lenses in the 80s and found I could get a great print from lenses that had the worst reputation. Example: 10-18-24 Turner Reich. They have huge focus shift. The instructions tell you that. refocus and they are nearly Artar sharp. again just curious. I photograph trains and old farm equipment, what do you shoot?

Scanning is the only way I know of to digitise a transparency and I don't think most lenses were designed with enlargement in mind as well. They were typically designed to get the best results on film. Some old ones were designed to get the best results on metal. If the transparency or negative produced a sharp result for printing, it will produce a sharp result for scanning I would imagine (unless there is some interaction between taking lens and enlarging lens I didn't know about).

I shoot Ghurkas and trees mostly with the occasional niece...

[timparkin]

This sounds like a lot of work! Thank you, Tim, for pursuing this irrespective of whatever the results may be.

Ta! :-)

[timparkin]

Can you try some ASA100 B&W film such as Ilford Delta 100 or Kodak TMX? I would back a 210 Sironar S on 5x7 to get very close to the best an 8x10 can do. Flatter film.
I can donate a box of Delta 100 if you want it (ordered from Harman Direct).

That would be greatly appreciated and I agree Delta 100 might be a good idea. Is that a good sharp film to use (I have not don't much black and white at all)?

I don't have a 5x7 camera but will be testing on 4x5 too just to see what the lenses will put onto film (using a 150 Sironar S which should match a 210 I would imagine - we could scale up the results and give a good guess for 5x7 results I imagine)

Tim

[timparkin]

Wow, looks like an awesome test. Good luck with everything.

Can you try some Provia 100F and the new Kodak 160 neg as well?

Just throwing that out there.

Thanks Robert.. I think Velvia 50 has the greater on film resolution to make sure we get a good result. Surprisingly for many people, Velvia has a very similiar dynamic range to provia, it's just very difficult to get at because of the dmax. I have some Portra 400 I can use for the test which is supposedly sharper than Portra 160 (although I might try one Portra 160 just to compare as I love the stuff and would like a box of 8x10).

[timparkin]

Great! Will follow with anticipation.

But do you have the best lenses? How did you make your choice for the 8x10?

Asher

I'm hoping to use Sironar S lenses as from my experience and from the MTF's I've seen they are exceedingly sharp and contrasty. Does anybody have any other non-esoteric suggestions? I may be able to borrow from a UK supplier.. The choice of lens focal length was just through looking at the standardised format small dimension to ensure a similar aspect ratio (i.e. pretend we are cropping everything square and then compare dimensions).