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Diffraction correction with IQ4 150

I'm trying to figure the best way to get the most depth of field without using focus stacking. I'm trying to stay around f8 to limit diffraction but sometimes I have to stop down a bit. Other times I cheat and back the camera up and crop into the image. It would be helpful to know other peoples' best practices.

Do you use the diffraction correction in C1 with the IQ4 150 on apertures greater than f9? How about the Luminance Noise Tool, do you leave it on the default or turn it off?


Greg Haag

Well-known member
Weldon, I shoot with the IQ4 150 on a Cambo 1600 with Rodenstock 32, 90T/S & 180T/S. My eye is probably not critical enough nor are my prints large enough, but I have never actually been able to see diffraction in my printed images. That being said, I have never printed over 5' or shot beyond about f16. I am certain you will get some fantastic feedback from people that are much more knowledgeable and technical in short order, I look forward to learning.

Bill Caulfeild-Browne

Well-known member
Greg is right - it's almost impossible to detect diffraction issues in print. I do use the C1 diffraction tool and find it quite effective at f16 and even f22. The "blurring" can be seen on screen at 100%- but not in print. I generally print 24 by 36 inches more and diffraction cannot be seen - at least by my eye.

I photographed one of my bookcases with my XT and 32mm Rodie at apertures f4 to f22. There is no detectable difference between f4 and f8, very little difference at f11. F16 and f22 are noticeably degraded by diffraction on screen - but when I printed each file at 36 inches, no difference could be seen. In fact, if I hadn't printed the file number on each print, I couldn't tell which was which except for DOF.


Well-known member
Couple things. First, like Greg and Bill, I think diffraction effects have been a bit over emphasized, especially their effects on printed images. Second, C1 diffraction correction seems to work very well. Third, backing up and cropping the image doesn’t actually help you. If you work out the math it comes out the same depth of field.

I’ve been shooting to f/16 without worry. I don’t think it is noticeable after diffraction correction and printing out to 120 inches.


Well-known member
Ditto - what Greg, Bill and Dave said. If your goal is a print and not pixel-peeping at 100%, f/22 can be your friend (and even your best friend after C1 diffraction correction).


P. Chong

Well-known member
I routinely shoot at f/22 on my Hasselblad H3D-39, which has a larger sensor pitch than the IQ4 150. As noted by other learned posters here, nobody knows better when printed or in web sized images.
Thank you for your insights. Perhaps a better question is what kind of sharpening is the C1 diffraction correction? It's no fun without seeing some images. Here are some from a recent project I've been working on. IQ4 150 Achromatic with 50mm f10 0.2 sec Top two have C1 diffraction correction on and lower one does not. Check out the "Unit 2" word. I'm going to make some prints tomorrow to compare as well.
Etiwanda May 12th 2021 156.jpg
Etiwanda May 12th 2021 156-DC.jpg
Etiwanda May 12th 2021 156-No DC.jpg


Active member
While peak sharpness for a sensor with pixel pitch of the IQ4-150 is around f/9, in practice I share the experience of others here that especially with modern sharpening techniques, it would be virtually impossible to detect in even a large print diffraction until you pass f/11 or smaller, in my opinion.


Well-known member

I make 40" to 60" prints from images shot at f/16 and the file easily out-resolves the print. Diffraction is simply not an issue and having sharpening tools in post makes it even less of one. Basically, I use the aperture that gives me the DoF I need. The rest is really not very significant. One thing is certain, I can control the effects of diffraction in post, but I can't change the DoF.