Why am I getting multiple whiskers?

[tom in mpls]

I am shooting a Contax 645 with P30+ shot at 35mm, f/8, 1/60 sec, ISO 800. Here is a resized full frame:

And here is a 100% crop of the whiskers. Why are there 3 distinct lines for each whisker? I understand that there may have been movement of the whiskers during the exposure, but I would expect to see just a blur instead. By the way, he really does have "bent" whiskers; it's his breed.

 

[LJL]

Tom,
Just offhand, I would say that looks like motion blur on the whiskers. At your shutter speed, that would not be unlikely in this case. My reasoning for suggesting this, is that the "multiples" look more pronounced at the end of the one whisker you have highlighted, while there appears to be less motion closer to the cat's face on that same whisker. Just my first observation. Things like that do have more motion than we think, and your rig is clearly catching it.

LJ

 

[Maggie O]

I'd say motion blur, combined with the translucent nature of the whiskers.

Oh, and awesome cat!!!

 

[LJL]

Tom,
The only other thing that comes to mind with this motion blur is what the bit-depth settings may be. In other words, the more distinct lines for the whiskers could be related to the number of exposures taken with the CCD to get a higher color bit depth. I am not sure how this is handled/resolved on these backs, but it might be a contributing factor.

LJ

P.S. One last thought....the P30+ and P21+ backs are the only ones that have microlenses. I am wondering if there was some sort of prismatic effect from how the microlens handled that bright line movement during the exposure. I am just fishing here, but do not know of other possible explanations on how you would get distinct lines of the whisker versus the smoother blur one might expect with motion. There have to be some separate, but very closely spaced exposure captures (bit depth idea), or some very distinct prismatic effect that delivers separate lines (microlens idea). There could be something else at work, but I am clueless as to what that might be.

 

[David K]

Tom,
I'll go with LJ and say motion blur. Simple to test, take another shot with lights and kick up the shutter speed.

David

 

[tom in mpls]

Tom,
I'll go with LJ and say motion blur. Simple to test, take another shot with lights and kick up the shutter speed.

David

I'm certain it is motion blur. It came as a surprise to me that it appears as rather distinct lines rather than a "smear".

 

[gogopix]

I've long since stopped worrying about the optics (and I am a trained physicist!) and just acknowledge that artifacts come in.
Ever close you eyes after and see a residual image? Note is doesnt 'smear'
well the man is good at processing out in the brain. Not so dsensors; there is the bayer matrix, scanning overlap, sharpening algorithms etc. Note that the 'non vibrating whisker at top also has '3 lines'

It likely can be explained, but the bottom line is that it is not a problem

as tyhe doc says, when you say "Ity hurts when I xxx..."
he says
"Don't XXX...!

Tell the cat not to shake its whiskers the next time you want a portrait!

Regards
Victor

 

[tom in mpls]

It doesn't worry me, but it does pique my curiosity.


BTW it is easily visible on the print as well.


I will ask Joey to sit more quietly next time, I'm sure he will be cooperative!

 

[gogopix]

"...A cat has about twenty-four movable whiskers, twelve on each side of its nose (some cat's may have more). Whiskers are more than twice as thick as ordinary hairs, and their roots are set three times deeper than hairs in a cat's tissue. Richly supplied with nerve endings, whiskers give cats extraordinarily detailed information about air movements, air pressure and anything they touch.

The scientific word for whiskers is vibrissae, a name that suggests their exquisite sensitivity to vibrations in air currents. As air swirls and eddies around objects, whiskers vibrate too. Cats use messages in these vibrations to sense the presence, size, and shape of obstacles without seeing or touching them. Whiskers are also good hunting tools. A cat whose whiskers have been damaged may bite the wrong part of a mouse it's attacking, indicating that signals from these delicate structures provide cats with vital information about the shape and activity of its prey - interestingly, whiskers also help cats smell odours..."

Looks like you are looking into the structure. The center may actually be a cavity with nerves

Victor

Ps have you seen this site

http://www.catswhiskersphotography.co.uk/shape.htm

 

[LJL]

All very interesting, but it still does not explain why the image shows the distinct recording of the vibration or whatever the cat is doing. That motion has been captured by the sensor. Is it from multiple exposures by the CCD for color bit depth? Is it diffraction of some sort? (Looks too distinct for that.) Is it the result of something with the microlenses? I did not think these sensors had much in the way of AA filters, so could it just be refraction/reflection off the cover glass? Why not the entire wisker? Whatever is going on, it was caught three times within the 1/60s exposure, and it is most visible at the distal end of the whisker that would have the most movement.

Would be nice to know what has caused this.

LJ

 

[Jack]

Tom: a possibility... Maybe some fluorescent lights were on nearby which often cycle faster than normal hhld current? The best are up around 20K Hz, so they wouldn't strobe the moving whiskers into three over 1/60th sec, but lesser ones fire at more like 120 or 240 and might cause this very effect... (A white Ott style viewing light also strobes faster than hhld...)

 

[irakly]

jack, i would agree except it really looks like natural light coming from a large glass patio door or something. check the catchlights. i am inclined to think that this is motion blur caused by natural vibration of whiskers.

 

[Maggie O]

Maybe it's motion combined with double-line bokeh?

 

[irakly]

Maybe it's motion combined with double-line bokeh?

double-line bokeh with a 35mm distagon? not possible besides, whiskers are in the plane of focus.

 

[Maggie O]

Why is that not possible?

 

[tom in mpls]

Tom: a possibility... Maybe some fluorescent lights were on nearby which often cycle faster than normal hhld current? The best are up around 20K Hz, so they wouldn't strobe the moving whiskers into three over 1/60th sec, but lesser ones fire at more like 120 or 240 and might cause this very effect... (A white Ott style viewing light also strobes faster than hhld...)

Excellent suggestion, Jack, but this was natural light from the window as irakly correctly noted.

 

[irakly]

Why is that not possible?

because this lens never does anything of this kind. i use it almost every day.

 

[Maggie O]

because this lens never does anything of this kind. i use it almost every day.

So it's a lens that renders everything in focus, all the time?

 

[irakly]

maggie, please

 

[tom in mpls]

Maybe it's motion combined with double-line bokeh?

Maggie, I don't know what double line bokeh is, but in this case it would need to be triple line bokeh. I see three distinct images of each whisker.