Remedy for vibrations

[Pau]

Here you have excellent oscilloscope graphs illustrating the flash duration:

viewtopic.php?p=183328#p183328

https://secure.flickr.com/photos/980361 ... 12/detail/

[Guppy]

In macro or microphotography it is crucial among other factors to work with very short exposure times.
I use the term “t0.5” as a measure for the burning time of a flash. That is the time taken from the 50% maximum until the value has dropped down to 50%.

Less convenient are photo-transistors for measuring, since its rise time and decrease times are approximately 5-15 micro seconds. Phototransistors have to be connected to an independent power supply unit.

More useful is a photo diode which rise and decay time is approximately 5 nano- seconds. The Photodiode in parallel can be connected, with a 10 Ohm resistance to the microphone plug of a sound card on a computer and thus the curve can be visualized and measured in a audio program (e.g. the freeware audacity).
It must be pointed out that the flash is not placed to close to the photodiode; a distance of
2- 4 m is recommendable. In case of a too close position the diode is going to be overdriven and the curve shows a flat maximum; in addition, besides the light time also the voltage is
measured. The entry level of the microphone should be set to approximately 80% to avoid an overdrive as well. Furthermore, one has to keep in mind that the sound card and the software digitalize the analogues signal with a sampling frequency of 96 kHz and have to be appropriately adjusted.
A correctly measured curve, at full power, is characteristic, showing a fast rise to maximum, a roundish top and a slow decrease in an e-function manner.

Using reduced power, the curve shows after some time a sudden drop and if the power of the flash is even more reduced the drop in the curve occurs before the maximum output is reached (voltage and light intensity).
This method allows measuring and comparing different flashes.

This method of measuring the flash burning time is simple and cheap. However, it is to keep in mind that the measurement is not absolutely precise! But it is an appropriate way to compare flashes in comparable circumstances. The time measuring point of t0.5 (half voltage or -6db) can only be found roughly, since the curve (of the photodiode, the sound card and the software) is not absolutely linear in its amplitude.

The photodiode I am using is:
SIEMENS Silicium-PIN-Photodiode with short circuit time SFH 203.
The approximate price is 1 euro.

Studio flashes possess a high guidenumber (e.g. 55), however, the burning time usually is about the same over all power levels (full to 1/32 power), typically the burning time is approximately 1/200s to 1/1'000 s, due to long flash bulbs. The power reduction is regulated by the light intensity and therefore studio flashes are not suitable for macro photography.

A flash curve with Audacity


Kurt

[Big Pete]

"Remove the second rail, you can adjust the distance by sliding the Stackshot rail along the tilt head'sclamp.
Mount the monitor onto the board rather than from the same plate, it looks wobbly".
I did remove the second rail (NiSi) but kept the the Siri head for up and down movement.
The monitor sits beside the rig board for now.
I am also using gravel in a smaller container where my lab lift sits on top. As i mention before my photography is about orchids and they grow in pots from an inch across to 6-8 inches and the plants vary in height from 2"-10."
The suggested flashes looks good but my pocket book is to thin at the moment so I have to make due with my Visico studio flash for now. The other problem with a smaller flash is the charging of the batteries on a daily basis.
Is it important to have the objekts on the same board as the camera?
Lots of questions and I am a slow learner at the age of 72!

[Big Pete]

I also noticed that the objekt moves up and down, from side to side when I go trough the stack. Is that normal or is something out of wack on my stackshoot?

[JKT]

I suspect the threaded shaft is not quite straight. At least my newer one has that problem. Offset between the end bearing and thread center would cause similar effect.

[Big Pete]

JKT, what to do about the shaft that is not quite straight?

[Big Pete]

Big Pete, thanks for sharing pictures of your setup. They are a big help.

I agree with the comment that your monitor should come be removed from your macro rig's base. Having that much mass on a long arm is asking for vibration that might take a long time to dissipate.

From the partial image of your studio flash, it appears that the brand is Visico. I don't know which model, but just now looked at data for one model, the Visico Studio Flash VCHH. The company lists flash duration as "1/800th~1/1200th" (of a second, presumably). By flash standards, this is pretty slow--small flashes can easily attain durations of 1/50,000 second or faster. I'm skeptical that enough vibration elimination can be expected from your type of flash.

Also, flash manufacturers should disclose their metric for measuring flash duration. I don't see this stated for Visico. One common standard is t.5, meaning that stated flash duration is declared at a point where 50 percent of the flash's light has been emitted. This still leaves lots of light coming out after flash duration has officially ended, and some flash's outputs have long "tails." Here is a link for a fuller discussion of this.

So it is possible that your studio flashes may not be capable of freezing out vibration for macro photography.

An approach you might try is to turn on live view on your camera, and zoom in as far as you can. Do you see any movement on the monitor? Take a step or two with your feet. Is movement transferred from the floor to your rig, as evidenced by movement on the monitor? Slew your StackShot forward or backward--do you see any unwanted movement? Try tapping on the baseplate of your rig and noting the magnitude and direction of any movement. Try tapping other parts of the rig, including the lens.

In each case, what sort of movement do you induce, and how long does this movement take to dissipate?

Such a process is unlikely to give you a quick answer, but it will help you understand your rig's vibrational characteristics. Once understood, these characteristics are easier to deal with.

The idea of adding weight to your rig is often a good one. But I'd urge you to characterize your rig's vibration before and after doing so. An aspect of increasing your rig's mass is that you'll be changing its resonant frequency (probably lowering it). While this is generally a good thing, it can be a bad thing if you happen to be tuning the resonant frequency to match some energy input your rig is facing. (As an example, I once put my rig on top of some small, barely-inflated inner tubes. This isolated it very well from the vibration of my furnace. Then I noticed that the rig was moving rhythmically in exact match to my heartbeat. I was standing on a concrete basement floor, with my wrist resting lightly on the heavy slate pool table that held my rig 80-pound rig. I was surprised that such a tiny input of energy could move so much mass, but it did. I had apparently tuned things to pick up on the vibrational frequency of about 70 beats/minute.

--Chris S.

Here are three new pictures of my macro rig as of today: https://www.flickr.com/photos/organize/ ... 0296179195

[rjlittlefield]

Here are tre new pictures of my macro rig as of today: https://www.flickr.com/photos/organize/?start_tab=one_set72177720296179195

That link asks me to organize my own photos. It probably works for you, but we need a link into your account, preferably to the exact photos you want to show.

--Rik

[ray_parkhurst]

I also noticed that the objekt moves up and down, from side to side when I go trough the stack. Is that normal or is something out of wack on my stackshoot?

I suspect your system is moving up/down/side-side due to vibrations, and the flash is capturing it at different points in the movement as it goes through the stack.

[Big Pete]

Sorry, my bad! here is the proper link: https://www.flickr.com/photos/125705582 ... 0296179195
https://flic.kr/p/2mZdaKa
https://flic.kr/p/2mZbif1
I will try my smaller flashes and check for any difference in vibrations as well!

[Macro_Cosmos]

I have discovered that in certain cases, mounting via the camera will induce a lot of vibrations. It seems to be a better idea to mount via the lens tube, which of course is sometimes impossible.
I'll show an example tonight.

[Big Pete]

Today I have tested with three smaller flashes and can state that it is a lot about the duration of the flashes! A short stack shows a lot better sharpness even thou some smaller vibrations remains.

Thank you all for your valuable help for now!

[Big Pete]

One more question, would Godox AD100 pro or Godox V1s work out for me to avoid small vibrations? Is the flash duration time fast enough to nail the objekt compared with my Visico 400Ws studio flash?

[physicsmajor]

I also noticed that the objekt moves up and down, from side to side when I go trough the stack. Is that normal or is something out of wack on my stackshoot?

Most people are focused on the system and mechanical vibration, but there's been less discussion about the subject itself. Because of this comment I'd like to go the other direction - I've done some macro photos of orchids (none quite this small) and flowers. The smaller the flower, the finer the stem it tends to arise from and these often - literally - wave in the breeze, or from a stray breath!

My setup can be triggered over Wifi from a different room, so after setting up these subjects I've had improved results by closing off the room, disabling the home HVAC, waiting 5-10 minutes and then triggering the stack.

Beyond swaying due to air movement, live plants can move and adapt to changing lighting conditions within the duration of a stack. They seem immobile but are not. This can be quite a challenge when they start folding up in the dark (flash) or try to turn toward your continuous light source! Your description of the object moving around the frame could be due to similar effects. Flash certainly helps individual image sharpness, but remember the plant itself can bob, weave, or rotate during the stack.

[Big Pete]

physicsmajor, with mini orchids and super thin stems I always try to support with tooth sticks to avoid any movement. That helps a lot as my own breath will disturb the shot.

But I like to get a good fast flash with a very short "burning time" or duration so that can freeze the image. Also I am sick and tired of changing the four AA batteries in my Mets 54MZ-3 and need a better capacity for longer stacks.
That i s the reason I ask for input on the two Godox flash alternatives.