Nikon 105mm f/1.8 ai-s and 105mm f/2.5 ai comparison

[Tristin]

The f/1.8 is sharper and has more contrast, but I noticed that the copy of the f/1.8 I picked up is soft on the left hand side, so I didn't bother including a comparison of the left hand side as it seems to be a defect in this individual lens.  All images shot in raw at the same exposures and converted with no adjustments or sharpening

Center


Right Edge


The f/1.8 has much more noticeable ghosts than the f/2.5, but also handles flare better.  The f/1.8 produces more rays that are also more tightly contained than the f/2.5 does.  The f/2.5 can produce more focused rays but it requires stopping down to f/22 or f/32 (which is apparently only on pre-Ai converted with the factory kit to Ai).


I was concerned about how short the f/1.8's hood is, but it worked perfectly at blocking ghosts I produced by aiming near the sun.  So that was nice.  With hoods out the f/1.8 is shorter, while with hoods off the f/2.5 is shorter.  The HS-4 for the f/2.5 sure is irritating, though I wouldn't hold that against the lens itself. The aperature ring is a bit easier to access with the f/2.5.

Assuming I can get a copy of the f/1.8 that is not soft on the left side, I can't see where the f/2.5 would outperform it except in ghosting.  The bokeh on both were so similar that I did not bother including a comparison.  The f/1.8 is virtually vignette free at f/2.8, where-as the f/2.5 reaches vignette free at f/4.

[Øivind Tøien]

As to edge performance, keep in mind that de-centering sometimes brings the sharpness towards the "non-affected" side.

Could the difference in star bursts be due to the more rounded diaphragm on the 105/2.5 AI,  vs the 105/1.8 AIS that has straight blades? (May that matters less at f.11?)
Here is a sample from the 105/2.5 AIS stopped down to f/6.3 only; it is a crop to <1/2 of the frames length. It does not show the diffuse tips of the star bursts as in your example from the AI version:



NIKON D5100, f/6.3 @ 105 mm, 4s, ISO 100

[Roland Vink]

The f/1.8 has much more noticeable ghosts than the f/2.5, but also handles flare better.

Comparing the two night shots at f/11, I'm not sure that is flare, the overall exposure with the 105/2.5 seems a shade brighter? It would also pay to ensure that all filters are removed and the lens surfaces are spotless, and check for internal haze or dust, which could easily affect the results here.

The f/1.8 produces more rays that are also more tightly contained than the f/2.5 does.  The f/2.5 can produce more focused rays but it requires stopping down to f/22 or f/32 (which is apparently only on pre-Ai converted with the factory kit to Ai).

The f/1.8 has straight edge aperture blades, which will give nice sharp rays. The AI and earlier f/2.5 has curved aperture blades so the rays will be slightly spread out and diffuse (a perfectly round opening won't produce star rays at all). As you stop down the curvature becomes less relative to the size of the opening so the rays are more defined - also diffraction is greater at small apertures so the rays are larger. If you want a 105/2.5 to produce nice tight star rays, the AIS version is better since it has straight edge aperture blades.

And yes you are correct, an Ai converted 105/2.5 (gauss/black barrel version) stops down to f/32. For some strange reason the AI conversion ring retains the f/32 stop from the pre-AI lens, while the native AI lens only goes to f/22.

[Tristin]

No filters were used and the lens were cleaned before testing.  I thought the same on the flaring at night but multiple tests showed the f/2.5 to exbibit this behavior.  Looking at the two at full resolution the f/1.8 images show the same details, but it looks darker because the contrast is much higher.  The f/1.8 does have a slighter higher transmission, but the contrast drop on the f/2.5 was much too drastic to be attributa le to that.

I should add that the f/2.5 had consistent edge to edge performance right from f2.5 where-as the f/1.8 took until f/4 to achieve the same consistency edge to edge.  At f/2.8, the f/1.8 was noticeably sharper and contrastier in most of the frame, at f/4 it was better everywhere.  I find the lack of corner performance at f/2.8 a non-issue as I would normally use that aperature, or lower, for portraiture.  So the corners don't matter at that point for me.  If I want all over sharpness, I generally want more DoF, so stopping down to f/4 would be routine even if the lens had sharp corners at wider aperatures.  The f/2.5s consistency wide open is certainly phenomenal, but I wouldn't shoot that wide an aperature on a 105mm for landscaping, etc.

You are definitely correct on the curved/straight blades.  Unless the Ai-s version doesn't have contrast issues when presented with light sources at night though, I wouldn't find more refined rays to be much help.

[Bjørn Rørslett]

The f/1.8 has a bit of veiling flare at the widest apertures as you already have discovered.  Already at f/2.8 this is nearly gone. In direct comparison with landscapes I could not detect any significant difference between the f/1.8 and f/2.5 (AI) by f/5.6 and smaller.

The star burst appearance depends on the actual model of the f/2.5, as Roland already has elaborated. My overall preference is for the AI (or AI-modified mid '70s P.C/K versions), but optically speaking little differentiates the models after the change from the 'Sonnar' to the 'Gauss' in the early '70s. The better bokeh and handling are my main reasons for preferring these versions, but no doubt the latest AIS has newer coatings to give slightly more contrast. Each to their own. There are plenty of the various 105 models floating around and price is no stumbling block to get alternative samples.

The best hood for the f/2.5 is an HN-8. For the f/1.8 I'm using a no-name 62 mm screw-in type of the same build, but shorter. The slide-out hood is annoying.

[Øivind Tøien]

"....and check for internal haze or dust, which could easily affect the results here."

My copy of my 105/2.5 AIS used for the image above is what I would almost call "horribly dusty" inside. I was able to compare it to a much less dusty sample of the same vintage with controlled torture tests of an LED flashlight shining into the lens at some distance etc., and if anything my copy caused less flare. So just do not look into these lenses, and everything is fine. 

(Haze/very fine dust particles would be an entirely different matter though).

[Bjørn Rørslett]

Some internal dust inside contributes surprisingly little in terms of degrading the image and contrast. However, the grey film deposited on element surfaces as happens in a smoker's environment certainly makes image quality take a nosedive.

[John Geerts]

However, the grey film deposited on element surfaces as happens in a smoker's environment certainly makes image quality take a nosedive.

When does that occur? Does it imply leaving the lens unprotected in a smoker's room for several hours, days or months?

[Bjørn Rørslett]

All lenses I have examined that originate from smoker's home have had this grey film sheen over the inner glass surfaces (and presumably, front and rear surfaces but here cleaned off). I am not going into smoking^* practice to study how long it takes for the problem to develop, but assume this problem gets worse over time.

^* quit smoking 35 years ago, a decision for which I am very grateful today

[Akira]

All lenses I have examined that originate from smoker's home have had this grey film sheen over the inner glass surfaces

I haven't noticed that, but that's not really surprising at all.  There ARE holes and slits in the lenses through which tiny particles of the smoke can invade and settle on the internal coating.

[Bjørn Rørslett]

Obviously a lens isn't hermetically sealed (unless made for submerged use). I had a nice demonstration of this fact  when I recently operated one of my 50 mm f/0.75 lenses to remove a hatched small bug on its inside. The speck of the dead bug was big enough to be visible in the photos. I just considered it being some ordinary dust until looking closer and found it was indeed a bug with feet and antennae and all ... including dried excrements around it.... No idea how it got there or what it fed off inside the lens must have been there for years though.

[John Geerts]

It does imply careless treatment of your gear. I think it's normal to keep all the photo-equipment in a smoke-free room and in a  dust-free cabinet.

[Bjørn Rørslett]

I keep my photo equipment in a smoke-free and reasonably dust-free house

Compared to fungus attacks, inside bugs do far less damage.... The bug probably accompanied the lens when I purchased it (from the Netherlands) and hatched later

[Thomas Stellwag]

I keep my photo equipment in a smoke-free and reasonably dust-free house

good to know that Peugeot is building clean rooms

[John Geerts]

Gasfree?