My cat, SD1M and 17-50 2.8

PanoMax said:

Do you, perchance have an image of your furry feline friend captured with a catadioptric lens? Just asking. My Questar is such a device.

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The Questar

Back to comparisons with other lens and camera.

Here I found a cat captured by the APO Telyt 180:



Clearly not as good as the Sigma combination.

George_pix said:

My cat on Dpreview.

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PanoMax said:

Do you, perchance have an image of your furry feline friend captured with a catadioptric lens? Just asking. My Questar is such a device.

Click to expand...

You read my mind. In past days I was looking for a short CATadioptric. Short because APSC and the risk of motion blur.

After studying the situation I believe that most Sigma lenses are better and they are also stabilized. No catadioptric for the moment, I am not a paparazzo.

I have the 17-50 2.8 os and the 105 macro 2.8 os. Both have shown resolution higher than SD1 pixel pitch and almost no CA.

There are even better modern lenses around but the SD1 will not gain any advantage (except for a possible larger aperture and less DOF...) You can se in my cat pictures that the DOF is really thin at 5.6. So a longer focal length could be a problem regarding DOF.

Awww, kitties.

George_pix said:

I have the 17-50 2.8 os and the 105 macro 2.8 os. Both have shown resolution higher than SD1 pixel pitch and almost no CA.

There are even better modern lenses around but the SD1 will not gain any advantage (except for a possible larger aperture and less DOF...) You can see in my cat pictures that the DOF is really thin at 5.6. So a longer focal length could be a problem regarding DOF.

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That might be back-asswards, George.

I have a spread-sheet for macro work that takes an input of magnification, based on object size and how much of the sensor it occupies. For instance, it tells me for 300mm, 20mm at f/5.6:

f-length: distance, DOF

50mm: 800mm, 75mm

105mm: 1792mm, 157mm

Where distance is an output from the calculation, not an entered value.

Which confirms that, for equal framing, the 105mm has to step back to 1.8m from the object, thereby doubling the DOF - not lessening it.

The DOF values above are based on my monitor viewed at about 450mm; on-line calculators are based on other criteria, so please don't tell me how wrong my numbers are. I have put them up only to illustrate that DOF grows with shooting distance for equal framing.

--
Ted

For a given aperture and magnification the DOF does not depend on focal length as described after the first image here:


DOF is not symmetric respect to the in focus object, video here:


It seems that the end result of the theory is that macro wide angle can keep the subject and the background reasonably in focus, or less blurred: the background is less enlarged. This is an example taken from a lens manufacturer: