This is an outstanding quality lens! Extremely sharp and full of contrast. This is one of the best lens I've ever used from a quality standpoint on FF. This is like an Otus lens with AF. The only con is the size and weight.

I have the 35 and the 50 art, and friends have let me borrow other art lenses. This lens is better than all of them. It is Zeiss like in quality, and it is unlikely you will find a sharper lens. In addition, bokeh seems to be very nice, and the lens has a pop often associated with Zeiss lenses. The downside of course is the size and weight. It is big, it is heavy, but there is really nothing better, and so you have a choice to make. If you want the best, you will have to deal with the size and weight. The odd focal length is fine for me, yet I understand 40mm might be strange for others.

Phenomenal sharpness and great colors across the frame. Autofocus is fast enough, and bokeh is beautiful. Heavy for the focal length, but the results are worth it. 40mm can work like both 35mm and 50mm, a really convenient length for general use.

I have a $5,000 Canon lens that is not as sharp as this Sigma lens. This is easily the best lens for the money on B&H. Paired with my Canon C300 Mark IV, this Sigma lens makes documentary-style interviews look amazing. Thanks to Sigma for the glass and B&H for the deal! Cheers! W. Oliver

I have wanted to get this lens for 2 years. I finally could afford it when B&H offered a lower price for one day in the DealZone. I do landscape photography and family photos with a Nikon D850 and a Nikon Z6. It is everything I had hoped and expected it to be: very sharp on the focus plane across the frame with a smooth transition to the out of focus areas. One caution: if you use this on a DSLR and plan to use it wide open then get the Sigma USB Dock and perform the autofocus fine tuning to ensure accurate focus. After that the focus has been very consistent on my D850.

I own most of the Sigma Art prime lenses.  When I buy a new lens, I test it for sharpness using a test chart.  The Nikon D850 camera body is theoretically capable of resolving about 115 lines per mm (lpm).  Having already owned the Sigma 35mm and 55mm Art lenses, I questioned my need for a 40mm lens.  But after seeing Sigmas published MTF curves, which appear better than those of the other 2 lenses, I bought the 40mm lens, and Im glad I did.  My lens resolution target goes from 100 lpm to 120 lpm. so 100 lpm is my limit for the D850.  At f1.4, my Sigma 40mm Art lens resolved 90 lpm center, 90 edge, and 80 corner.  At f2.8, it resolved 100 lpm center, 100 edge, and 90 corner, an amazing result.  Because the depth of field at these wide apertures is so shallow, I found critical focus with the D850 is best done by manually focusing in Live View with an external magnifier in order to obtain the peak maximum of resolution.  This applies to even after adjusting the AFFT with the Sigma dock.  Chromatic abberation and distortion are also extremely well-controlled with this lens.  My only negative is that, for a 40mm lens, it is big and heavy.  It would be nice if Sigma would come out with Art quality lenses at smaller apertures to reduce their size and weight.  I have found this 40mm lens to be comparable in sharpness to the 55mm Zeiss Otis lens, but the Otis lens is manual focus and I will be able to use this Sigma lens for focus stacking with the D850.

Having a D850 and a few other Sigma lenses I wanted something a bit different. Let’s be honest, for the most part 40mm isn’t a “go to” lens for most. Having seen other reviews and watched a ton of YouTube videos I went for it. Absolutely worth it, the sharpness and detail this lens has is incredible. While it is a little heavier, it’s worth the extra weight in your camera bag for the results. Wide open it delivers stunning images, at f4 the results are stellar. It will be a mainstay in my backpack, while it is a bit expensive and the 40mm may seem a little obscure once you see the results it will become one of your favorite lenses.

A picture paints a thousand words. I will let you be the judge of the qualities of this Sigma 40mm, f1.4 lens.

A reminder that hope is on the horizon and that Spring is in the air. This morning after cleaning the leaves from the pool I noticed the beautiful blossoms on one of my pink geraniums. Enjoy them with me.

Sony A7Rii, Sigma 40mm, f1.4 prime lens @ f4.0, 1/60, ISO 200
www.leephotostudio.com

Got this wonderful lens at a five hundred dollar discount, and am very happy I pulled the trigger. If I were on the Sony platform, probably would have opted for the Sigma 35mm f1.2, but since I'm on Canon, this optic was my closest choice.
Extremely high acutance and micro contrast from corner to corner, even wide open, becoming perfect when stopped down to f4 and f5.6. See 100 percent crop from full frame image, both attached to my review, both minimally sharpened (setting 2) in Canon Digital Photo Professional.
Focuses quickly and accurately on my Canon R5, but exhibits poor, inaccurate focus from wide open to f4 on my 5D IV.
Longitudinal chromatic aberrations are well controlled; compared to the Sigma 35mm f1.2, bokeh and focus fall-off are very good but not quite as nice, while focus speed is pretty good but again not quite up to the 35mm f1.2 level.
All in all, a spectacular optic, suitably for environmental portraits, focus stacking, panorama stitching, and general use. Heavy and large, but totally worth it.

I must admit I was impressed by the reviews and opinions I have read about this lens. All I can say is that it might be even better. Wide open at f/1.4 it is sharp corner to corner. Backgrounds are outstanding for a 40mm lens. It is truly a multi-use top notch lens for both wide apertures and landscape apertures. The weight could be a problem for some, but very manageable I would think for most. On my DSLRs it needed a general (same) sigma dock adjustment at all distances. With the adjustment all results were stellar with minor in camera adjustments on my D850 and no adjustment on my D810 and D5. Results are also stellar on my Z6 with the FTZ adapter, and as good as the Z 50mm 1.8 lens is, the sigma has much better backgrounds with comparable or better sharpness, and of course more weight. Stellar image quality still comes at a price. Overall highly recommended!