HDR B&W negative scanning

[alanselk]

I am getting very inconsistent results scanning in HDR mode in silverfast 6 Ai for B&W negatives. I set the negfix to the appropriate film type (Tmax or Delta) and bring it into HDR. At times I`m getting very dark scans. To dark to work with in HDR even with exposers set at max. My negatives are well exposed (I use the zone system) but I`ve just about gave up on HDR scanning unless I can correct this.
I get better results scanning in normal mode in 6 Ai (non-HDR) in 16 bit: making adjustments before I do the scan (but no sharpening) then bringing it into HDR as a positive and fine tuning from there (all in 16 bit mode) I have a Microtek 120tf so I scan close to 4000dpi. Then I can resize to what I want to print.
Am I missing something in the HDR scans for B&W negatives that I`m getting these mixed results.

Alan

[degrub]

Are you setting "gamma for HDR" to something other than 1 ?

Frank

[alanselk]

Well... yes. I have been setting gamma at 1.8 for both 6Ai and HDR. That`s the normal setting for a Mac. Now; I have heard someplace that when scanning raw that the gamma setting may change, but I admit I don`t have the expertise to know what to change it to. I`m assuming from your question that I should be using ?1? as the gamma setting. (and do I check the box ?for HDR output??) Also; would I set the gamma to one in 6Ai (does it have any affect when scanning raw?) HDR, or both?

[degrub]

THere is a special setting in the options, General tab, "gamma gradation" that you need to have set to something other than 1 (usually 1.8 to 2.x), otherwise the HDR image will be too dark when you open it in HDR. Also you must check the "for HDR output" check box to have it take effect. Have a look at Ian Lyon's HDR tutorials:

http://www.computer-darkroom.com/hdr_tutorial/hdr_1.htm

Otherwise you may have to use the negafix expert panel to adjust the curves for those film types.

http://www.computer-darkroom.com/sf5-ne ... egafix.htm

Frank

[alanselk]

Okay, that`s looking better. I haven`t worked out all the details yet. (I`ve downloaded the tutorial and gone through the part on gamma settings, I`ll go through the rest as time permits) The logic of it seems to be (correct me if I`m wrong) : raw scans tend to be dark (just the nature of the beast) so I scan at 1.8 gamma, yet I tell HDR that the incoming scan is 1. Therefore it it raises the value, so in the end it comes out something close to normal. That`s as near as I can figure. Whatever it is it`s working.

Thanks much
Alan Selk