If the pixel size is identical ...

[Oren Grad]

I think that process lenses in general are probably sharpest wide open.

In general this is not true of process lenses from the film era.

 

[Rob de Loe]

Which lenses, out of curiosity, are best wide open?

Of the lenses that I have, the Rodenstock 105 macro Digaron HR, the Rodie 180 HR, my SK macro lenses. That’s a few off the top of my head.

It's not common though. Those are some superb lenses you have.

I had to double-check the Rodenstock HR Digaron-S 180/5.6 MTF charts because I was skeptical. Sure enough, look at that 80 lp/mm line at f/5.6. It drops down a bit at f/8. Coarser details improve a tiny bit at f/8, but wow, this is an impressive lens. Image quality is excellent right across the frame. Shift would be a treat with this one.


Compilation from the Rodenstock data sheets

Such consistent image quality right across the frame from wide open is not commonplace. It's much more common for wide open to be better only in the centre of the frame, but decline towards the edge. For example, I just added the sibling of your 180mm lens to my lineup -- the HR Digaron-S 60mm f/4 in its Linos inspec.X L 60mm f/4 variant. The 80 lp/mm line for my 60mm starts higher wide open than at f/8, but it takes a nose dive as you move outwards. Good image quality across the whole image circle needs f/8. This is quite typical in my experience.


Compilation from Rodenstock data sheets

 

[Erik Kaffehr]

deednets wrote

With some interest about the GFX100RF I tried to figure out whether this could be a camera for me, as I had been using all 3 versions of the RX1, the Q, Q2 and the X100F ... so in short: I am kind of used to the concept of a fixed lens camera.

From reading Jim's blog :

https://blog.kasson.com/the-last-word/format-size-and-image-quality/

It's easier to design build a terrific f/4 lens than a faster lens;

It's easier to design build a terrific lens for a larger sensor than for a smaller sensor.

I wouldn't agree fully with your interpretation of what Jim states.

Lens designs are scalable. Basically, a lens is designed to cover an angle of view with some angular resolution. The maximum aperture is part of that design.

So, when a lens is used for a given format, it is asigned a focal length that covers that format. If a lens design covers 4/3" at 25 mm, it will cover 24x36 mm at 50 and 33x44 mm at 64 mm.

If we consider a high end f/1.4 lens like the Otus 50/1.4 it is pretty big scaling it up to cover 33x44 would double the weight.

But, equivalence comes to rescue here. To yield similar DoF at full aperture the 33x44 mm lens would need f/1.8 and designing an f/1.8 lens will take less effort and result in less weight.

Now, stopping subject motion would need still need the same shutter speed, so we would need to raise ISO on the 33x44 mm sensor to compensate for the smaller aperture. We could use ISO 170 instead of ISO 100 and still get away with the same noise and DR.

On the other hand, photographers like me seldom never shoot full aperture but rather use medium apertures in the lower range. So, I am doing fine f/2 or f/2.8 lenses on 24x36.

Would lens designs be perfect, a lens at f/4 would outperform a lens at f/5.6. But lens designs are not perfect although they may be close to optical for their intended purpose.

Combining these two then could in theory make Gfx100Rf f/4 a superior image generator than Rx1 versions, Q, Q2, X100F.

Very clearly, the 102 MP can deliver more detail than the 61 MP of the Leica Q3 or Sony A7rIV.

Most good lenses will deliver detail at the pixel level over a large part of the sensor when shooting at optimal apertures.

Best regards

Erik

 

[Ketan G]

... how is it that so much is being read into the image quality?

With some interest about the GFX100RF I tried to figure out whether this could be a camera for me, as I had been using all 3 versions of the RX1, the Q, Q2 and the X100F ... so in short: I am kind of used to the concept of a fixed lens camera.

What bugs me though are the relatively slow maximum aperture and the lack of IBIS. If what the rumour mill is correct that is? And then there s the pixel size:

• Fuji X-Pro3 3.76µm
• SONY A7RV 3.76µm
• Leica Q3 3.76µm
• Fuji GFX100 3.76µm

Isn't the APS-C, the FF just a crop of the MF camera? And if that is the case, how is it that MF would then have better quality, provided you look at your image at 100% rather than down-sampling an image?

Ignoring for a moment that the GFX has a different aspect ratio, if the pixels are the same, would that not mean there is only something to be gained if you down-sample an image, as any crop would be roughly the same?

Dunno but is there maybe also some other factor at play that I am not seeing?

Thanks

Deed

P.S.: Sorry if this has been asked gazillions of times before!

I shoot extensively with both the A7RV and GFX 100S II and I find the A7RV noisier than the GFX in the shadows, despite them having the same pixel pitch. I cannot explain this on a technical level and perhaps Jim's responses have done that. My conclusion is based on usage, but I also took the DPReview test chart raw files for the A7RV and GFX 100/S, selected ISO 100 low light options, then downloaded, boosted the exposure and shadows by the same amount. There are probably some variables with that approach that I can't control for, but the difference at a pixel level looks large enough that those variables wouldn't account for the difference on their own. The two crops below are 900x900 pixels and taken from the same part of the frame. A7RV first, then GFX:


A7RV


GFX

In addition to this difference, I can use ISO 80 on the GFX and it's even cleaner, slightly, than ISO 100. In conclusion, for my eyes the differences between the two sensor sizes are visible even at the pixel level.

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http://www.ketangajria.com