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help with lighting and diffusion particularly with objective

 
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Koorosh



Joined: 20 Jun 2014
Posts: 215
Location: London

PostPosted: Sat Jul 25, 2015 11:37 am    Post subject: help with lighting and diffusion particularly with objective Reply with quote

Hi everyone,
I have been looking around for a while on the subject with little help. I've seen you guys using janjso lights- I have two plus another much stronger light with colder light. I have had to push iso to 300+ currently with 1/160 or lower, and still not getting satisfying lighting. I use a ping pong ball hemisphere over the end of the objective and feel both diffusion and intensity probably more so are difficult.
If you can steer me to good links or inform me of your techniques and tricks?
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 17696
Location: Richland, Washington State, USA

PostPosted: Sat Jul 25, 2015 11:53 am    Post subject: Reply with quote

"still not getting satisfying lighting"

Please tell us more about what this means. Is the light not bright enough? Is the color wrong? Are you getting not enough diffusion? Too much? And so on.

If you have some sample images that illustrate the problems, then showing or linking to those might help too.

inform me of your techniques and tricks?

I generally just make a "light tent" of Kleenex tissue paper all around my subject, and fly lights around the outside of the tent until I like what I see through the objective. I used to use ping pong balls more often, but because of their small size it's harder to control the light distribution than it is with a larger tent.

--Rik
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Koorosh



Joined: 20 Jun 2014
Posts: 215
Location: London

PostPosted: Sat Jul 25, 2015 1:05 pm    Post subject: Reply with quote

It's generally the intensity of light that is bad really. What kind of ISO settings etc are you using?
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rjlittlefield
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Joined: 01 Aug 2006
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PostPosted: Sat Jul 25, 2015 2:18 pm    Post subject: Reply with quote

Koorosh wrote:
What kind of ISO settings etc are you using?

Generally ISO 100, sometimes ISO 200.

My last set of stacks, at http://www.photomacrography.net/forum/viewtopic.php?t=28177, were at ISO 100 and used exposure times of 0.4, 0.5, or 1.0 second, depending on magnification. Those were Kleenex light tents.

The cherry maggot stacks at http://www.photomacrography.net/forum/viewtopic.php?t=27702 used more directional lighting as shown at http://www.photomacrography.net/forum/viewtopic.php?t=27714, with just fingertips of latex gloves stretched over the Jansjö heads. Those were ISO 200 at 1/15 and ISO 100 at 1/10. I don't recall why I used ISO 200 for some of those.

--Rik


Last edited by rjlittlefield on Sat Jul 25, 2015 2:22 pm; edited 1 time in total
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Chris S.
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Joined: 05 Apr 2009
Posts: 2699
Location: Ohio, USA

PostPosted: Sat Jul 25, 2015 2:20 pm    Post subject: Re: help with lighting and diffusion particularly with objec Reply with quote

Koorosh wrote:
I have had to push iso to 300+ currently with 1/160 or lower, and still not getting satisfying lighting.

Do you mean you are using shutter speeds of 1/160 second? That strikes me as a very brief exposure--perhaps the source of your problem.

I've never used--or even seen--a Janjso light, but it would have to be very bright indeed to permit a 1/160 second shutter speed with, say, a 10x microscope objective. Higher-magnification objectives require even more light. And if you are diffusing the Jansjo (which you almost certainly should), you'll lose a lot of light.

Have you tried much longer shutter speeds?

Personally, I always shoot studio macro at my camera's base ISO (so 100 or 200, depending on the body). With my light sources (very, very different from Jansjos), I use a shutter speed of 8 seconds, and vary the intensity the light source to create the proper exposure.

I'd suggest that you run a series of tests, doubling the exposure time until you get into the ballpark. So 1/125, 1/60, 1/30, 1/15 second, and so on. When you get close, experiment with 1/3 f-stop increments. Then report back--preferably, with example shots.

Longer shutter speeds bring problems of their own, which can be discussed later.

--Chris

--Chris
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Koorosh



Joined: 20 Jun 2014
Posts: 215
Location: London

PostPosted: Sat Jul 25, 2015 5:57 pm    Post subject: Reply with quote

Ah, that was the problem then! I am used to exposure times with a flash on an MPE-65, and in my mind was thinking that was pretty standard even with continuous. I've shifted the shutter speed to take longer exposures and it seems to have made the effect.

Wow Chris, that is a long exposure! I don't know if this is a common thing in cameras, but mine actually adjusts the image brightness as you change the shutter speed, ISO and or aperture without taking an image. It's helpful in any case!

Quote:
Those were Kleenex light tents.

Might sound stupid, but do you have an image of the tent construction? I have just rolled a cylinder of tissue, but it is a bit fiddly putting the specimen into place and then getting it over it, while avoiding the lens simultaneously, although do-able.

Those maggot stacks are incredible Rik! Very impressed- looking forward to getting better at this game.

I know I was supposed to post an image on the other post as well but I've not been around to do so, and I'm intent on getting some more stacks done because so far I've only done one but had the kit for a fortnight now. Been an uphill struggle, but I'm getting there, and thank you Smile
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Chris S.
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PostPosted: Sat Jul 25, 2015 7:17 pm    Post subject: Reply with quote

Koorosh wrote:
Ah, that was the problem then! I am used to exposure times with a flash on an MPE-65, and in my mind was thinking that was pretty standard even with continuous. I've shifted the shutter speed to take longer exposures and it seems to have made the effect.

Great to hear! Very Happy

I don't know what objective you're working with, but remember that a 10x/0.25 has an effective f-stop of f/20; a 10x/0.30 lets in a bit more light at f/17. These are probably much smaller than the f-stops you were using on your MP-E 65.

Also, when working with a flash, you typically want a shutter speed that produces a black image with ambient light, making an exposure only if the flash goes off, to prevent ghosting. So it's not too surprising that this shutter speed would underexpose with continuous lighting.

Quote:
Wow Chris, that is a long exposure!

With my lights, I could place plenty of light on the sensor for much shorter exposures, but I dial back the light for another reason. The Nikon camera bodies I prefer lack electronic first shutter curtain. I work around this by using exposures long enough that the fraction of a second at the beginning, when shutter vibration is dissipating, contributes insignificantly to the image. Through testing, I've found that this requires more than four seconds on my rig, at the magnifications I shoot (up to 100x). My illuminators have shutters, and I keep meaning to build a controller to sync them to my StackShot controller--but this has never made it to the top of the to-do list. If it does, I'll be able to block the light during the vibration-dissipation periods, and use much shorter exposures.

Quote:
I don't know if this is a common thing in cameras, but mine actually adjusts the image brightness as you change the shutter speed, ISO and or aperture without taking an image. It's helpful in any case!

If I understand it right, you're referring to the liveview image on the back of your camera? (Or on your computer screen, if you tether.)

In my (Nikon) experience, liveview also changes as one adjusts camera settings--but not in a particularly accurate way. Even the liveview histogram isn't especially accurate. So I take a test shot, check the histogram, adjust the lights, and repeat as needed. If you don't already happen to be good friends with your histogram and ETTR (Exposure To The Right), this is a good time to become well acquainted. Very Happy

Cheers,

--Chris
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rjlittlefield
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Joined: 01 Aug 2006
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PostPosted: Sat Jul 25, 2015 8:19 pm    Post subject: Reply with quote

Quote:
rjlittlefield' wrote:
Those were Kleenex light tents.

Might sound stupid, but do you have an image of the tent construction?

I did not, but since that glass of epoxy filler is still set up, I just now shot a couple of snapshots for you.

Light tent about 1/3 constructed:



Finished, ready to add lamps:



Right, there's a certain, um, "informality" to it. A lot of my lighting setups have that character. Draped tissue, held in place with blue painter's tape. The tissue is disposable; the tape comes off clean.

--Rik
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Koorosh



Joined: 20 Jun 2014
Posts: 215
Location: London

PostPosted: Sun Jul 26, 2015 6:37 am    Post subject: Reply with quote

Quote:
I've found that this requires more than four seconds on my rig, at the magnifications I shoot (up to 100x).


Wow, that's a long time for a shot! Are you taking images of Protozoa?

After you saying about the flash and shutter settings, it makes sense really and I don't know why I thought I might achieve similar exposures with continuous. I'm concerned about vibration really. I have the rig on sorbothane hemispheres, and the rig itself weighs in excess of 10 kilos, so maybe I shouldn't worry so much? Certainly since adding the hemispheres, the rig on top of it is actually far more wobbly, but when it comes to taking images, I can't see any shake at all while it stacks, and up until my last attempt at stacking last night, I was only waiting for a second in between shots.

Quote:
I don't know what objective you're working with, but remember that a 10x/0.25 has an effective f-stop of f/20; a 10x/0.30 lets in a bit more light at f/17. These are probably much smaller than the f-stops you were using on your MP-E 65.


Yes, I'm using the BE 10x infinity objective with a Raynox DCR 150 as the tube lens. Shocked by the detail it picks up, although it is a pain to use I have to admit. The mounting side of my rig is very poor currently... I have a piece of foam to take the pins of specimens, and I've wedged that into a sewing reel..

Ah, which brings me to my next question: I'm using 5um step sizes for use with that objective, and 15um for the 4x version. Are they ok as step sizes?

Quote:
In my (Nikon) experience, liveview also changes as one adjusts camera settings--but not in a particularly accurate way


I think you're right about that- just remembered my confusion when I was taking images outside one day and the live-view/ actual images not adding up Smile Just read up on ETTR! What about when, say, an image is just one solid colour for much of the frame and it appears that there is little signal other than that? When I was stacking at the NHM, Chris Raper taught me about the histogram, which I understand at least a little bit. I found that in a lot of images however (e.g. small wasp not filling much of the frame at 5x surrounding by flat grey background) that the histogram seemed a bit meaningless, and I just had to expose and sort the image by eye. Any thoughts?

Quote:
Right, there's a certain, um, "informality" to it.


Hey, I've seen your stacks. If it works it works Smile My sewing reel is quite pitiful as a mount and is obviously very frail, but I ran out of money. Not sure where to go from here. Was thinking maybe going for one of those insect balls used to manipulate the angle of them under stereo microscopes, although I don't expect that they would be very sturdy bases.
[/quote]
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ChrisR
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PostPosted: Sun Jul 26, 2015 9:17 am    Post subject: Reply with quote

These "Helping Hands" are quite cheap on eBay and have enough mass not to wobble in the breeze, though they aren't "finely" made:

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Charles Krebs



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Location: Issaquah, WA USA

PostPosted: Sun Jul 26, 2015 2:57 pm    Post subject: Reply with quote

Quote:
I'm concerned about vibration really.


Quote:
Ah, which brings me to my next question: I'm using 5um step sizes for use with that objective, and 15um for the 4x version. Are they ok as step sizes?



In your A6000, check into your "Custom Settings" (gear wheel icon). Be sure that the one to use "e-Front Curtain Shut." is set to on. This should avoid any camera vibration in your exposure. You should allow a little "settle" time after touching things to move to the next step (and the camera "re-sets"). The sorbothane hemispheres under a base of high mass is primarily to avoid or minimize external "environmental" sources of vibration that might have an effect on your set-up.

For a 10/0.25 you can figure 6-10 micron (depending on how much pixel peeping you do), so you are quite safe with 5 micron.

For a 4/0.10 you can figure about 40 micron per step
For a 4/0.13 about 30 microns.

If you are using 15 microns with a 4X now you are probably acquiring far more images than you really need. if you have a stack acquired at 15 micron steps try stacking it using every other frame. (Options>Preferences>Input/Output>Preprocessing>"Stack every N'th frame" . Compare it to a stack using all frames. I doubt you will see any difference.)
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