Center Filters -- skiing off piste with the S-K APO Digitar 35mm f/5.6 XL

[rdeloe]

Quick question: has anyone had any luck using the "wrong" center filter with the Schneider-Kreuznach APO Digitar 35mm f/5.6 XL? The "correct" options are the IIf (M52.5x0.75 thread, with M72x0.75mm front thread, 4x) and the customized IIg, I believe for the Alpa version (M67x0.75mm thread and M72x0.75mm front thread, 4x).

The "correct" CF is rather rare. They're all rare, but is there any other CF that works well, e.g., the II for the APO Digitar 47mm f/5.6 XL)?

 

[Paul Spinnler]

Its hit or miss as gradation on the filter can be different despite similar density factors and thread sizes on paper, but vonalpen was happy with a II ... (he sold the Alpa recently here)

 

[kinglang]

4X IIf or 4X IId fit 35XL, CF II only 3X

 

[Paul Spinnler]

Gradation patterns on the filters differs (ie when the density starts and stops and how the transition between the “starting” and “max” point of density is. You can see from above that the density patch varies.

That's sometimes a difference between CFs of the same type beyond the thread size.

Worst case you have overlapping parts of under correction followed by overcorrection or vice versa. I have an alternative for the the 43 in a Rosenstock variant, it helps but then it also is not correcting 100% the right way….

Vonalpen said the II worked well so it’s hit or miss.

 

[rdeloe]

4X IIf or 4X IId fit 35XL, CF II only 3X

The IId will fit the 35 XL, but what I'm wondering is how does it perform? My concerns relate to the points Paul made about the coverage of the gradation.

So far everyone has been polite and avoided saying, "Rob, just buy the IIf and don't worry about it." But before anyone does that, I have other lenses with strong light falloff and it doesn't bother me. The 35 XL would be the strongest, but it could be that a filter like the II that only reduced but did not eliminate the falloff would be just fine -- and 1.5 stops is easier to work with than 2 stops.

 

[rdeloe]

Gradation patterns on the filters differs (ie when the density starts and stops and how the transition between the “starting” and “max” point of density is. You can see from above that the density patch varies.

That's sometimes a difference between CFs of the same type beyond the thread size.

Worst case you have overlapping parts of under correction followed by overcorrection or vice versa. I have an alternative for the the 43 in a Rosenstock variant, it helps but then it also is not correcting 100% the right way….

Vonalpen said the II worked well so it’s hit or miss.

Good to know. I will check in with @vonalpen

 

[Shoe]

Since it hasn't been mentioned already, Alpa initially recommended the IIa for their version of this lens (36mm Apo-Switar).
This was the center filter for the 38mm Super Angulon XL.

 

[rdeloe]

Since it hasn't been mentioned already, Alpa initially recommended the IIa for their version of this lens (36mm Apo-Switar).
This was the center filter for the 38mm Super Angulon XL.

That's interesting. The IIA has an M72x0.75mm filter thread on the lens side, which would require a huge step-up ring. There's one for sale now for $799 USD. Ugh!

 

[Paul Spinnler]

If you work with step up or step down rings you also get into trouble as there might be hard vignetting. I had a marked decrease in useable IC with the 43 when using the 60 XL CF with adapter rings.

Alpa specific variant lenses have different front threads and as soon as you need to work with in between rings you will have a vignetting effect potentially. On the 43 it reduced the utility.

 

[rdeloe]

If you work with step up or step down rings you also get into trouble as there might be hard vignetting. I had a marked decrease in useable IC with the 43 when using the 60 XL CF with adapter rings.

Alpa specific variant lenses have different front threads and as soon as you need to work with in between rings you will have a vignetting effect potentially. On the 43 it reduced the utility.

Another issue with step rings that might be a problem is they will locate the filter farther away from where it's supposed to be. That could change how the gradient affects exposure.

When my copy shows up, hopefully in a few days, all mysteries about performance will be resolved. This thread is already helpful just in case I do need a CF. However, I might be OK.

This is the light falloff performance for the 35 XL. It's quite dramatic, and doesn't get a lot better at f/8 and f/11 compared to wide open.



Here's the light falloff chart for my Mamiya N 43mm f/4.5 L. It's much better, but there is a lot of light falloff with this lens. I have never used a center filter with it, or thought I needed one. Interestingly, the amount of light falloff is about the same for the edges of an unshifted 33mm x 44mm image: around 50% for the S-K and the Mamiya. It gets worse faster when shifting for the SK, but I can only shift it 8mm anyway so maybe I'll be OK.... I will definitely report back!

 

[vonalpen]

Rob has sent me a PM concerning the CF II which I used on my SK 35mm XL (with my IQ4 150 on the ALPA).
I tought I could show the corrected and the uncorrected LCC file here for a comparison.
When I bought the lens, the CF IIf wasn't available anywhere, so I got the CF II instead.
The correction ist just 1,5 stops instead of 2 stops, but C1 has no problems cleaning it up nicely.
The SK 35mm XL is a very comapct Iens with practically zero distortion.
But because I hardly used it anymore I have now sold it.

Best regards

Jost