Question about bokeh for S-M-C Tak 50mm 1.4

DrGeaux · Joined: 25 Feb 2013 Posts: 5

Hi everyone,

I recently acquired a S-M-C Tak 50mm 1.4 and have a question about the bokeh. I've uploaded a sample image, showing what string lights look like out of focus. There appears to be a ring inside of the bokeh spheres and I was wondering if this is normal for this lens?

Thanks.[/img]

RSalles · Posted: Mon Feb 25, 2013 1:02 am Post subject:

Hello,

The image is not visible here,

Renato

fermy · Joined: 17 Feb 2012 Posts: 1974

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

I don't recall seeing anything like that with any of my Tak 50's
I have seen something like it when rain drops land on the front element, shine a flashlight through the lens and look at the elements for something.

David · Expire: 2013-01-25

Can you replicate it? If not, it may have been the type of lights in the background.

tromboads · Expire: 2015-10-01

The rings inside the light?.. that would be part of the light surely?

DrGeaux · Joined: 25 Feb 2013 Posts: 5

Thanks for the replies everyone.

Lightshow: I've used a flashlight to look through the lens and don't see anything that looks obviously wrong. Just a few specs of dust inside, which I think is normal.

David: Yes, I am able to replicate it. Below is another example (although these are the same lights in a tree). I see the same problem with small point sources of light when I've done test shots at home though. I also used a small LED flashlight (with about 5 LEDs inside) and don't notice the problem much. The LED flashlight is much brighter though and I think it was slightly overexposed, which may have hid the problem. I'll try again to see if I can replicate it with a lower exposure.

visualopsins · Expire: 2025-04-11

Not normal...

Those are reflections of the inside of the lens, lit by stray light bouncing around in there. The stray light could be leaking in from the edge of lens element(s) -- check edges of elements are blackened -- wait a minute! -- after looking again, I'm changing my mind here. Smile

I think those are what leds look like! Especially when properly exposed. That dark central ring... So, yes, normal photos of (lit) leds...

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

Try a different light source.

dnas · Joined: 14 Nov 2008 Posts: 488 Location: Japan

LEDs have a central silicon chip, with a reflector around it, so that is probably consistent with that.....

kuuan · Expire: 2014-12-26

DrGeaux · Joined: 25 Feb 2013 Posts: 5

Thanks for the replies everyone. I think I may have confused people by mentioning LED lights. The images I previously posted were from non-LED christmas tree lights. I've posted a pic below that shows 3 images: the first shows the string lights in focus so you can see what type of lights these are (they are the old style string lights), the second shows the same shot out of focus and stopped down a bit, and the final one is wide open, showing the rings within the bokeh.

The final image shows the out of focus area of another shot with different types of lights. The yellowish spheres on the right are reflections from an overhead CFL in the room and the green sphere in the center is a small LED light. It's not as noticeable as it is in some of the other shots, but I can still see rings here as well.

Thanks again for the help.

visualopsins · Expire: 2025-04-11

(Resembles an) Airy Disk (effect?):

Airy Disk (wikipedia)

In first photo of latest reply I see a dark ring around the top of the uppermost lamp where glass is tapered & pinched, but that doesn't explain the dark ring from fluorescent lamp in third photo...

Could be light leakage inside lens body from unblackened edge of element(s).

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

DrGeaux · Joined: 25 Feb 2013 Posts: 5

MacTak · Joined: 15 Jun 2011 Posts: 108

This is a bit of a puzzler. I've seen this before, perhaps to the same or more likely to a slightly lesser degree, in some lenses that have an aspherical element. My personal suspicion is that your Tak has an (unintentional) aspherical element--that one or more of the elements was ground improperly (it could be an interaction) so that it is not spherical. Another option (I would suppose, maybe I'm wrong) is an issue in the homogeneity of the glass (vertically) of one or more of the elements, such that a portion of it has a slightly different index of refraction.

tromboads · Expire: 2015-10-01

Seriously tho... how are those 200% crops going to affect the actual subjects you focus on. I.e The thing worth taking a photo off? Unless of course you like round glowing balls in that case might i direct you to MS Paint. It has this wonderful circle tool where one can literally draw as many as one chooses. And better yet. They scale wonderfully at any zoom level!

Just take the Photos man. Wink

DrGeaux · Joined: 25 Feb 2013 Posts: 5