Using NON DIGITAL lens on DIGITAL SLR

[sean_buerger]

Hello Camels!

To save some money I use two types of adapters on my SIGMA SD10. One is for M42 lens type the other one is for NIKKOR lens type. The link is purely mechanical and does not extend to electronic controls (AF motor, aperture control). This reduces obviously the functionality of the camera - lens combo. It does give me the opportunity to use glass that otherwise would collect dust only

When doing a rather comprehensive test with some prime lenses from Nikon, I noted a discoloration in the centre of the picture, when stopping down. I suppose that is due to reflection of the aperture blades or whatever. Fact is that the lens was not designed for reflecting CMOS sensors, rather than film.

This is what I get. Anyone note something like this before...

[sean_buerger]

Oops. Forgot the picture

[metalstorm]

Not so sure about whether a lens is designed for CMOS or not. Maybe some coatings help it. Most of the FF lens are/were designed with film in mind and they seem to work rather well on most digitals crops.

[jfrancho]

You say "stopping down," - how far down? It could be diffraction, which, for Canon sensors, usually manifests as softness, starting at f/11. I have no idea what the limit is for Sigma. There are quite a few vintage lens enthusiasts I know that use some very old glass on digital SLR cameras with excellent results. Do some experimenting with different apertures, and let know what the results are.

[bill8131]

Sean,

For what it's worth, I've been shooting straight digital for several years and don't own a "digital" lens, I've never seen anything like that.

Now, I don't don't want to start a verbal war with the Nikon gang, but, if this is only happpening with the Nikon lenses, that would explain (posssibly) why Nikon went so heavy into the "digital" lens series, not just for the ratiio difference? Just wondering.

And yes, my gear is all Canon. *I hope someone has the correct answer! it's an interesting one, that I'm sure will have a lot of opinions!

Bill

[sean_buerger]

The picture shown is stopped down to 16 (as shown in the filename).

On my 1.2/55 the 'purple spot' effect becomes visible at f=5.6 and get's more obvious from there onwards. On the 3.5/28 I can see more or less the same thing (with less intensity) starting at f=11.

However those two, are the only ones having this effect so far.

What SIGMA claims on their website, is that they have specific coating on the lens (near side camera) to prevent harmful reflections from the imager. I don't know, whether the aperture blades are a factor here.

Cheerio. Sean.

[sean_buerger]

Ok. Let me show me the test results.

I would like to add that I LUV NIKON lenses. The 1.2/55 is crisply sharp at f=2.8! The spot issue was seen also on other sets (one indoor and another outdoor at infinity). Only when stopping down, I get this...

[sean_buerger]

And more aperture settings...

[sean_buerger]

As I'm stopping down (see filename), you can see the centre of the picture gradually turn colder until the purple spot comes out.

I should add that the Nikkor 1.2/55 is really old (probably my age, haha)

Cheers.

[jfrancho]

My very rudimentary understanding of this, is that at higher aperture settings (small aperture, "stopped down") the light is too unidirectional to properly illuminate each photosite on the sensor, and therefore results in softness and discoloration. How the so called "coatings" work to mitigate that, I have no idea. I, like Bill above, use Canon, and exactly none of my lenses are "digital," or designated EF-S. In fact, I'm pretty sure my 35 f/2 is closer to 20 years old than 10, which automatically predates the digitalera for consumers.