Sigma SD1 Merrill instead of 6D or 5D mark III Locked

Started Jan 31, 2014 | Discussions thread
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Jay Ell Regular Member • Posts: 256
Re: Actually, you have a number of issues with optical understanding yourself...

Lin Evans wrote:

Just a few here: first, you can't "fix" AA blur with sharpening.

Yes you can. I did not say that you could restore details with it. But you increase the local contrast, thus reduce or elimiante the blur.

Sharpening, other than deconvolution, is essentially edge contrast enhancement.

Indeed - this removes the slight blur caused by the AA-fitler. Deconvolution could of course tried to be used to restore the actual detail, but since the point spread function is not perfectly known, the results are never optimal, plus it's time consuming.

Push it to the degree where you try to make a conventional CFA sensor with AA filtering look like an equivalent Foveon capture and you introduce serious aliasing.

First: D7r and D800E have no AA-filtering.

I am not sure you know what aliasing is - unsharp mask does not create aliasing. It can create halos (as that's the way USM works), but there are alternative sharpening methods.

Second, DOF with smaller sensors is much greater than DOF with full frame sensors simply because to equate to the FOV of a small sensor you must use a much longer focal length lens.

False. 50/2.8 on full frame equals 33,3mm f/1.87 on DX-crop (1.5x crop).
18,6666. It is a matter of optics - there are no optical advantages in smaller formats (other than smaller lenses are possible to make).

Typical small senors on digicams may have a 6x crop factor so that a 50mm actual focal length optic gives a 300mm FOV vis a so called full frame camera. Conversely, to equate to the FOV of a full frame sensor a much wider angle lens must be used on a crop factor sensor.

No. If you want to have the same FOV, you need to have the same angle of view. You mean shorter focal lenght must be used on crop.

The formula to use is easy - to equal the crop cameras parameters on FF: f*crop_factor = focal length needed, f-number*crop_factor = f-stop needed to equal DOF and diffraction.

There are no free lunches for small formats. Even on Pentax Q (crop 5.6 if I recall right) you might want to stop down to f/2.8 to make a deep landscape shot, but on FF you only need to use f/15,7 to have the same DOF if the field of view is the same. Even this is equally in the zone where diffraction reduces image quality more than lens flaws, so stopping down more is usually not too good idea.

Wider angle lens produce greater DOF with identical apertures. Don't even start with me on "equivalent" apertures. It's been beaten to death.

With identical aperture numbers, but not with identical apertures. Equvalancy as a physical fact if by that you meant what for example Great Bustard has wrote the essey he often links to. If you do not believe in that, why not test it?

This is how to do it easily: Take two pictures with your camera, one where you crop the image 50% on both axis and then another with a lens with twice the focal length without cropping so that the field of view in the two images is the same. In both cases focus to very same point. See for yourself that if you use twice the aperture number on the uncropped longer lens picture, the DOF is identical.

This has been proven in this forum many times, both with math and physics, as well as examples.

Your problem appears that you read a lot and have minimal or zero experience using Sigma cameras.

Sigma cameras do not beat physics any more than any other cameras.

It's best not to give advice about things you have little practical experience with.

It's not best to talk about optics if one does not understand them. (Now, I am sure this is considered flamebate by the mod, but your comment is not).

It's rather like reading about formula one racing and giving advice to someone who drives formula one vehicles in competition.


The majority of people on this forum understand Sigma cameras very well,

Most people on any DPR-forums understand their cameras either badly or very badly. Sigma users are not exception to that. The same applies to basic optics - you have proven the point above.

and many of us use and have used conventional equipment commercially side by side and have done so for many, many years. You are not going to convince us with theoretical arguments which often have little relevance to actual photographic experience.

Who is this "us" you talk about? Are you a chosen Sigma spokesperson on this forum?

There are several factually accurate issues with Sigma cameras no matter if you like that or not. There are issues with conventional cameras too, but in general the issues in Foveon are significant. You're free to disagree, but if your level of discussion is discrediting others because you as a Sigma shooter with Sigma experience know better, then it might be better to now have a discussion at all.

I'm not saying you can't be happy with Sigma or that Sigma can't be used to take good photos - I've seen excellent shots taken with Sigmas, like I am sure you have too. But there are reasons why Sigma cameras are not popular among for example professional photographers of pretty mych any field and why no other manufacturer offers anything similar and why Sigma managed to buy this technology for pennies.

Sorry, but you are just not credible as an expert on Sigma and Foveon technology.

Why are you sorry? I am not sorry when I notice you have understanding problems regarding optics.

What about Foveon I've said which according to you is false? I can quite easily dig some links to for example papers of colour (in)accuracy and noise.

Anyhow, I don't even pretend to be an expert on Sigma/Foveon technology as I'm not. But I am quie well informed layman on the sensor technology as well as basic optics. It interests me.

I have nothing against Sigma - heck they make nice bang for buck lenses and one of my all time favorite lenses was a Sigma. I even like the fact that Foveon exists - it's different. I wish it were better than it is, but the basic limitations of this kind technology are unfortunate.

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