Starting my focus calibration of V850 using resolution target

[faberryman]

Sorry if this is a dumb question but: Does the Table imply that setting DPI at approximately 3200 is the most "efficient" way to maximize the resolution of one's negative for an Epson 750. i.e., most resolution for file size?

Yes, but why sacrifice resolution for file size. We are not talking about large files to begin with. The better efficiency argument is time. It takes less time to scan at 3200 than 6400.

[Steven Ruttenberg]

True, but again what I am observing is tge higher the dpi, the clenervthe scan and greter I can enlarge file. At 3200, file was not nearly as good as at 4200 which is what I currently scan at. And this is from practical application not svience stuff. Rarely does practical emulate science and vice versa. My image of Aspens I recently posted us at my current focus setting and at 4200dpi. If we followed all the science that image would look like crap.

[Steven Ruttenberg]

Here is the link to the dropbox folder

https://www.dropbox.com/sh/smrtz36k7...SBB9RNuWa?dl=0

[Steven Ruttenberg]

So I compared scans and found 6300 dpi scan was best. I then tweaked focus and found I was out To high by 0.0078in or 0.198mm. Not too bad at all. Bit that small adjustment made a difference.

After adjustment, I used fingernail polish to lock fasteners in place by applying a torque stripe to fasteners and holder.

I also have been thinking that we focus too much on dpi capabilities, etc. Instead we should be focuses on how well a scanner resolves an image. If film has say 65lpm capability andbthe scanner can equal that or better, then dpi only matters as in having enough to print at desired size. While it plays a role in how well a scanner resolves, things like pixel size/pitch, etc, play a part. If scanner can do better than film at given dpi then whatever that pixel count is, it is. Using more will give better scan to a point. What I am saying I guess is who cares about effective dpi vs dpi setting, etc if you get a quality scan of your image. I am more interested in resolving power in lpm than I am in number of effective pixels v

So for me anything at or above 4200dpi scanner setting is good. 6300 will give a huge file, but there is a technique for Photoshop that you can use to keep working file small and apply everything to final full size file.

Here is pic of torque stripes.

[Pere Casals]

Pere,

Sorry if this is a dumb question but: Does the Table imply that setting DPI at approximately 3200 is the most "efficient" way to maximize the resolution of one's negative for an Epson 750. i.e., most resolution for file size?

It's matter of diminishing returns, with the V850, from 3200 you get nothing more in the vertical axis, but you can get a 20% more in the horizontal axis. Beyond 4800 you get near nothing else.

But working with an oversampled image allows a better conservation of the image quality over the edition (if computer performance vs file size allows it...). For example rotation, sharpening and downsizing algorithms may take advantage of it.

As Frank Berryman noted a problem can be the additional scanning time, more than file size.

[Steven Ruttenberg]

Here is an example of binning.

These images show the final setting for focus with Betterscanning Variable height film holder, ANR glass and wet mounted target. Final height is 0.2035 in from scan glass to top of ANR glass. Film mounted on bottom of ANR glass (side facing scan glass)

The three images are as follows
1. Full 6300dpi
2. 2x2 binning using Vuescan Tiff size reduction
3. 3x3 binning using Vuescan Tiff size reduction

Note: 2x2 results in a 50% reduction in pixel dimensions. While a 3x3 in a factor of 3 reduction in pixel dimensions.

Also of interest is the file size for 2x2 is a factor of 4 reduction and 3x3 is a factor of 9 reduction.

I did not see any loss of edge sharpness in the reductions (some loss in fine detail, may have happened. I do not know about any effects on gradients, etc that will come next; an actual image.

Also note that no sharpening was applied at anytime, only white balance was set.

Next I am going to scan a density target with a Dmax of 3.05 in 1/3 stop increments (31 total) to see how scanner does. I may get one that goes to 4.05 next, they are relatively inexpensive. I am also going to do this test for some bw film, Across 100, Tmax100 and 400, Ilford D100 and HP5-400 using my Chamonix 45H-1 and my 75mm f/4.5 Nikkor, 90 f/5.6 Scneider Super Angulon and the 210 Grandagon I may buy. Also for my digital camera 5DMKIII. Why? Why not? Plus I can see if I need to adjust my development process and even see what different developers can do. Either I have been infected with the testing bug or I a bored!

https://www.flickr.com/photos/157376...57673789470327

[Steven Ruttenberg]

You do lose resolution with binning but not bad though.

[faberryman]

What I am saying I guess is who cares about effective dpi vs dpi setting, etc if you get a quality scan of your image. I am more interested in resolving power in lpm than I am in number of effective pixels.

I believe the effective resolution in dpi is just a mathematical calculation based on lpm. Most testing sites use the test target.

[Steven Ruttenberg]

I agree with this statement, but so many sites and people get wrapped around the axles on "effective" pixels, etc. You should judge your scanner on the best resolution it can resolve and what dpi setting that is on your scanner. Basically, what is the line par minimum your scanner can resolve? Who cares about effective pixels. Use scanner setting that meets your requirements for resolution. As long as it can match or exceed film capability which is around 65-80 lpm, then your good to go.

For number of stops the V850 is good for?

Well, I calculate that my V850 can do max D = 2.15 based on the step wedge I used from Stouffer. This equates to 7 1/3 stop dynamic range. This is scanning in 16 bit gray scale and outputing in 16 bit gray scale. Of course now, many should come out and say I did something wrong, or don't know what I am doing, etc. I assure you, the readings are correct.

[Pere Casals]

Well, I calculate that my V850 can do max D = 2.15 based on the step wedge I used from Stouffer. This equates to 7 1/3 stop dynamic range. This is scanning in 16 bit gray scale and outputing in 16 bit gray scale. Of course now, many should come out and say I did something wrong, or don't know what I am doing, etc. I assure you, the readings are correct.

Steven, something wrong is there, V700 exceeds 3.0D. Silverfast claims than V700 is improved from 3.1D to 3.38D by using multiexposure feature: https://www.silverfast.com/highlight...posure/en.html

V850 may even perform slightly better because coatings in the lenses.

I found that consistent with my personal tests.

Check that you are manually setting the DR end points on the histogram, that you are scanning 16 bits per channel, and that you save the scan in TIFF format. If you save it in jpg or bmp you only save 8 bits.

Also mask the area around the wedge to see ultimate performance by avoiding flare.

As long as it can match or exceed film capability which is around 65-80 lpm, then your good to go.

Capability of TMX is approaching 200 lp/mm (line pairs per mm) for high contrast (1:1000) and 1/4 of that for low contrast (1:1.6), see TMX datasheet.

"Lines per mm" and "line pairs per mm" can be confused, and there is a x2 factor for the conversion.

IMHO it's better to speak in "line pairs" and noting it with lp/mm or lppmm, because these are the usual units used by lens and film manufacturers.

The V850 is not able to retrieve all Image Quality a sharp negative may potentially have, for that you may need a drum working at high dpi, or scanning strips at high res (cezanne) and joining (stitching) the strips in Ps.

One of the reasons to go to high effective dpi is portraying well the grain structure, this is mostly intersting for roll film.