Out, out ##### spots!

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dhmiller
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Out, out ##### spots!

Post by dhmiller »

I'm trying to figure out the source of some spots on one of my objectives. Here is a photo from the 200mm f/4 manual focus Nikon tube lens I am using both normal (all white) and inverted (the big blank space ;-)) that shows there is no dust on the sensor nor in the barrel of the lens. These were taken at f/32 on a smooth and clear white card, one is out of focus and the other is in focus. And here also is a shot with the objective attached that show spots in several places (outer edges, most notably) as well as a shot in situ, though the spots therein don't line up with the ones in the white image. Any suggestions/advice would be appreciated.
tube lens alone inv.jpg
Objective on white 1.JPG
tube lens alone.JPG
spots.jpg

Chris S.
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Re: Out, out ##### spots!

Post by Chris S. »

My guess is that it's sensor dust. You didn't mention which objective you're seeing this with, but I know that you have objectives that are effectively f/71 (Mitutoyo 100/0.70) and f/45 (Mitutoyo 50/0.55). These are ruthlessly revealing of sensor dust.

I clean camera sensors under a stereo microscope--a sensor loupe, at least in my hands, is not powerful enough.

BTW, it gives me pause when our list of disallowed words censors your quotation from Shakespeare.

--Chris S.

dhmiller
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Re: Out, out ##### spots!

Post by dhmiller »

Thanks, Chris. (I've also got the 20x ;-))
I took several shots of the white card with the tube lens alone using the common technique for finding spots and I see absolutely nothing. An inverted shot reveals sensor spots even better and that also showed nothing. Been using the same technique for years, so not sure about it being a sensor issue... I can give it a wipe, but hate to do the for no reason.

lothman
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Re: Out, out ##### spots!

Post by lothman »

do the spots rotate with the lens? or stay in place?

dhmiller
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Re: Out, out ##### spots!

Post by dhmiller »

I'll have to check... Rotating would mean they are in the objective, I would assume.

Lou Jost
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Re: Out, out ##### spots!

Post by Lou Jost »

I took several shots of the white card with the tube lens alone using the common technique for finding spots and I see absolutely nothing.
This is NOT an adequate test for sensor dirt. Sensor dirt visibility depends strongly on the aperture of the lens. When using a high-mag objective, the system is stopped down far more than when using the tube lens by itself (especially if you left the tube lens at f/4). It is common to see dirt problems with such objectives, even if everything looked fine with less powerful objectives or with the tube lens.

At the very least, you should stop the tube lens down to its smallest aperture if you want to use this test. [Edit- I see you did do that.] Even that will not be enough though.

I have absolutely no doubt (well, maybe 0.01% doubt) that you are seeing sensor dirt.
Last edited by Lou Jost on Fri Oct 23, 2020 7:14 pm, edited 1 time in total.

Chris S.
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Re: Out, out ##### spots!

Post by Chris S. »

dhmiller wrote:
Fri Oct 23, 2020 1:01 pm
Thanks, Chris. (I've also got the 20x ;-))
Dennis, I didn't mention your 20x, because a 20/0.42 equates to f/24--revealing of dust, but not so ruthlessly as your 50x(f/45) or 100x (f/71). It's those tiny effective apertures that make dust appear in focus on your sensor. In modern, regular photography, nobody uses anything like f/71, so dust too small for regular photographers to notice becomes very noticeable to us.

I like Lothar's suggestion to rotate something. I also agree with Lou that this is exactly what sensor dust looks like.

Harold Edgerton, the great pioneer of photographic flash, learned that he could photograph bacteria without a microscope or even a lens. He simply put a solution containing bacteria on a piece of film* in a big, dark room, and placed his flash far enough away to make it resemble a point light source. When he enlarged the film, the bacteria were nicely imaged. You're doing something rather similar, every time you put a high-magnification objective in front of your camera.

--Chris S.

*It was a long time ago when I heard Edgerton tell this story, and in my recollection, he said "photographic paper," not "film." I wrote "film" above because paper doesn't make sense to me just now.

dhmiller
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Re: Out, out ##### spots!

Post by dhmiller »

OK, thanks for the comments. Guess the white card is irrelevant then. I do clean my sensor whenever I see something suspect and have it set to Clean every time the camera starts and stops. But will give it another look.
Btw, can I use my normal camera lens cleaning fluid and lens tissue (PecPad) on an objective? Good enough for my 600mm, but maybe that's not relevant either. ;-)

rjlittlefield
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Re: Out, out ##### spots!

Post by rjlittlefield »

If that last image is a whole frame, shrunk to fit the forum, then I'm going out on a limb and suggest that maybe it's dust on the rear element of the 200 mm telephoto. I'd expect anything on the sensor to look a lot sharper under that condition.

It's very unlikely to be anywhere on or in the objective, because anything there will be totally OOF, spread across the whole image plane.

--Rik

Chris S.
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Re: Out, out ##### spots!

Post by Chris S. »

dhmiller wrote:
Fri Oct 23, 2020 6:01 pm
Btw, can I use my normal camera lens cleaning fluid and lens tissue (PecPad) on an objective? Good enough for my 600mm, but maybe that's not relevant either. ;-)
I don't know what's in your normal lens cleaning fluid. I use ethyl or isopropyl alcohol for cleaning lenses, or if a lens is very grungy, then a bit of ROR. Your objectives are Mitutoyo, and I've cleaned quite a few such with these solvents. Some other manufacturers specify different solvents. No problem using a PEC-PAD. I know you're used to caring for expensive optics, so you don't need additional advice in that department. So feel free to skip the following paragraph that I can't stop myself from writing. :D

The cleaning fluid goes on the PEC-PAD, not on the glass--and just use a little bit. The PEC-PAD is used only after blowing the objective with air to remove anything lose. And the PEC-PAD is not pressed directly against the glass if this can be avoided, but folded so as to billow out a bit, and this billow is what ideally contacts the glass.

--Chris S.

lothman
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Re: Out, out ##### spots!

Post by lothman »

Chris S. wrote:
Fri Oct 23, 2020 8:43 pm

I don't know what's in your normal lens cleaning fluid. I use ethyl or isopropyl alcohol for cleaning lenses, or if a lens is very grungy, then a bit of ROR.

--Chris S.
what is ROR?

dhmiller
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Re: Out, out ##### spots!

Post by dhmiller »

Rik - thanks for the suggestion. Didn't;t check the back of the 200, so will give that a look, Just cleaned my camera's sensor and still getting spots, so maybe that's the ticket,
]
Chris - Thanks, much. Yes, many, many cleaning sessions under the belt (a single day on safari alone requires a few ;-))
But as noted, not likely the Mitu... (PM coming to you).

Chris S.
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Re: Out, out ##### spots!

Post by Chris S. »

ROR is a commercial product for cleaning lenses and other things. ROR is an acronym for "Residual Oil Remover."

Rounding off the numbers in the MSDS, ROR consists of:
  • Distilled Water 85%
  • Liquid Soap 9%
  • Isopropyl Alcohol 4%
  • Sodium Chloride 1%
  • Ammonia 1%
The official ROR website hails the product with refulgent hype, but ROR is basically soapy water with a bit of alcohol and dashes of salt and ammonia. Still, the stuff works well if a lens has oil or other stubborn gunk on it. It comes in a small spray bottle, and my bottle has lasted me for years. It's not my primary cleaner, but the cleaner I resort to if alcohol hasn't worked.

--Chris S.

viktor j nilsson
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Re: Out, out ##### spots!

Post by viktor j nilsson »

I find that ROR is terrible if that's all you use. It evaporates very slowly and does not dry cleanly. I can't really see anyone using it as their only cleaning fluid.

But it is pretty good at getting off stubborn gunk. Like Chris, I use it for tough jobs. But I always finish off with petroleum ether or isopropyl alcohol.

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