Question about DIY bellows

Started 6 months ago | Questions thread
ProfHankD
ProfHankD Veteran Member • Posts: 6,165
Re: Question about DIY bellows

khunpapa wrote:

ProfHankD wrote:

khunpapa wrote:

In film era, there're lots of bellow on the market. By its nature, the flexible film is more prone to the air pressure than the solid sensor. But you won't see this hypothetical vacuum effect at all.

You will see turbulent air flow that stirs dust, hence way more dust.

I have minolta bellow & olympus bellow for years. Never see such turbulent. How to observe it (and the dust)?

Stop down. The 4mm cover glass means the dust spots will be many times more diffuse than on, for example, a typical Sony mirrorless.

BTW, the E-M5 never fears dust. ;-D

Yeah, that's why 4mm of cover glass... so the dust spots are way less obtrusive. Unfortunately, it also causes CA on all lenses not designed for it.

Hrrrmmm. While noticing ugly CA from Oly 12/2, I rarely see CA from the old MF lenses too.

BTW, if there were dust spot, even it's less obtrusive, it'd be there. But out of 60,000 shots from my (now broken) E-M5, I see less than 100 images. Most of them occur because I change lens at the dusty environment and forget to activate the SSWD after that.

The cleaning cycle works pretty well, but it's not magic either. Catch is, you have to stop down quite a bit for typical dust to be visible -- probably around f/22, which is well past the diffraction limit for MFT. The thicker cover glass is actually a very smart move for new lenses because it hides dust so well, but the Fuji GFX actually does it one better: Fuji has a thin cover glass with a large air gap behind it, making dust less visible without making the cover glass a significant optical element.

..

Talk about 4mm thickness and CA from "all lenses not designed for it", I think that's unjustified.

It's a fact. Again, how severe it is can vary, but 4mm of glass with something like 1.5 index and typical dispersion behind the lens is a significant optical element with MFT pixel sizes. Metabones MFT focal reducers actually correct for it and the creator of those Speed Boosters has commented on this issue here many times....

If I put m4/3 lens on A7 body, I'll get severe vignette, right? Does this because of the A7's sensor have faulty design? Using the famous Oly 12/2 on some Pana m4/3 body will create lot of very ugly CA, despite the lens is designed for the m4/3 sensor and conform to m4/3 spec. Invest many Sigma lenses to FF dSLR, you may need the focal calibrator despite Sigma design their lens to be used on FF sensor.

Huh? Yeah, lenses are designed for specific coverage and many lenses suffer bad CA. Transverse CA is especially severe in various modern lenses, because it is easy to correct digitally, so lens designs will trade allowing more (correctable) CA for improving other properties that aren't as easy to correct in software (e.g., less curvature of field).

Today camera techs are more and more propriety system. The era of puting lens A into hole B without problemis fading away .

That is true. Lenses are now being designed as part of a camera system, counting on various aspects of the sensor, sensor stack, and computational processing.

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