Rollei IR 400 film vs Tmax, Delta 100

[herb]

A good deal of my efforts have been IR landscapes, using The Rollei film with a 720nm filter. Good results, got into two shows.
Only lately have i used it for regular b/w work, and find that it gives quite different results from the other panchromatic films- only Rollei says it is panchromatic.
Speciifcally, the rendering of fine detail and particularly shadow detail is several orders of magnitude greater than the other two.
There has to be some explanation. The only thing I can think of is that the film base in 4x5 is the same thickness as the roll film, unusual in my experience, and VERY thin. This does not compute, however, so I am now asking the wise ones if there is some formulation in this film that is not covered in the Rollei data sheet.

I develop it in xtol stock 9 minutes, and the other two at 6 min, also xtol stock replenished.

 

[AllenBaxter]

Herb:
I am new to IR film photography and noticed your thread. I plan on using the Rollei 400 IR film with a Hoya R72 filter. If I may ask I am confused about exposing for the IR. I have read that this film should be exposed at ISO 25 for approximately 1/2 sec at f16. My question is how do you best determine the proper exposure? Do you use the ISO 25 value and then meter without the filter and adjust for a certain number of F stops. I have read that the Hoya R72 accounts for about 6 - 8 f stops. I would appreciate any recommendations. Thanks Allen.

 

[Athiril]

Rollei IR 400 like 400S, 80S and ATP are superpanchromatic, not panchromatic unfiltered.

 

[herb]

To Rollei IR

I find one half sec at f11 more likely, but you are. Close at f 16
Differences in water might make the difference.
Super panchromatic??

 

[herb]

Rollei "superpanchromatic"

Ok, Digital truth says the term 'Superpanchromatic" refers to the fact that the film also has sensitivity to the IR spectrum as well as the regular panchromatic spectrums.

That still does not explain the sharpness/detail comparison.
I asked them to fill me in on that.

 

[Athiril]

Superpan has extended red sensitivity, more than regular pan, as well as IR (albeit at much lower sensitivity, hence EI 25 for IR filter), different objects reflect the same in some parts of the spectrum and differently in others.

So some things may have contrastier edges at transitions, and simply more contrast and local contrast, as well as greater overall reflectivity, hence more exposure to a dark area.

 

[ath]

TMAX and Delta have a straight density curve while IR400 has an s-shaped one. This means more contrast in the mid tones which makes IR400 look sharper. Shadows and lights will look different because of the additional sensitivity to IR.

 

[Marco B]

TMAX and Delta have a straight density curve while IR400 has an s-shaped one. This means more contrast in the mid tones which makes IR400 look sharper. Shadows and lights will look different because of the additional sensitivity to IR.

Doesn't this potentially also mean that herb is potentially developing or exposing his TMax and Delta 100 sub-optimally, not making maximum use of the available exposure latitude? If anything in your description is true, IR400 should have less shadow separation caused by the toe, which is contrary to what herb observes?? :confused:

 

[Athiril]

You could also look at it as the T-Max having higher contrast shadows at a certain exposure, and dropping out to black (thin), while the Rollei may at a certain exposure have open low contrast shadows that roll off slowly.