Goniometers...

[Craig Gerard]

I also have the same rotation stage as you... so I'd probably also want to draw up designs for an adapter.

The Newport 30 Rotary Adapter works well for that purpose with the 481-A Series rotation stage:
http://www.ebay.com/itm/360429015099


Craig

[Rylee Isitt]

Craig,

Nifty! Problem is there is only one available to Canada, with $50 shipping - I've asked the seller for other shipping options, so we'll see.

The one you linked to won't ship to Canada, and I can't contact the seller either. Apparently he's refusing contact, because when I go through the normal process, I get this message "Unfortunately, this seller is not able to respond to your question. We suggest reviewing the item again to see if your answer is in the seller's listing."

[rjlittlefield]

Chris,

Of course you're correct about the "dead giveaway", except that it's a bit more subtle than just looking at the arcs. I did consider the curvatures. The unfortunate answer was "can't tell" because of the angle the photo was shot from. So I went with interpreting the seller's description. Clearly a mistake, in retrospect. Perhaps it can serve as an educational example for other people.

The presence of the ribbed pulleys did not escape my attention. The seller did not know what equipment the pair had come from. But a good argument can be made that in a thoroughly integrated and motor-driven system you don't need concentric rotation built into the hardware. Given an XY stage with the ability to tip, it's simple enough to program a virtual center of rotation anywhere you like -- even smack on the surface of a subject that happens to not be mounted exactly at the natural center of the goniometers. It was only a passing thought, of course.

--Rik

[Craig Gerard]

The one you linked to won't ship to Canada, and I can't contact the seller either. Apparently he's refusing contact, because when I go through the normal process, I get this message "Unfortunately, this seller is not able to respond to your question. We suggest reviewing the item again to see if your answer is in the seller's listing."

Rylee,

There is a way around that hurdle but it doesn't guarantee the seller will respond. It needs to be done via a completed item.

I've sent you a PM outlining the process. Some sellers may not appreciate circumventing their question related settings, but I haven't found a 'grumpy' one yet on those few occasions when I have used the method outlined in the PM.


Craig

[Rylee Isitt]

Craig,

Thanks for the PM. Seems odd to have to go to those lengths but I'm sure there's some cryptic reason...

[AndrewC]

Andrew, we need to be careful what we wish for, don't we? As I recall, it was you who encouraged me to come out of the dark about goniometers. ...

[Craig Gerard]

This is a question I'd like to expand and publicly ask of the more experienced goniometer users. Does the degree of apparent, usable shift increase at higher magnifications? I

need to think about this some more but wanted to introduce it into this discussion...

Craig

Not sure I fully understand the question but if you are completely centred the rotation doesn't change with magnification - little circles and big circles are still 360deg. If you are off centre you add a linear movement in xyz so magnification does change the amount of apparent movement. Odds are you are never completely centred so you have to mix both types of motion. As an aside, people often forget that (depending on your set up) you may have an extra degree of motion by rotating your camera body around the optical axis. Easy if you've got a collared lens or bellows with rotatable standards.

Goniometers are just as useful vertical as horizontal - a vertical setup is just a horizontal setup standing up I've been building a stage for a while (got distracted by building a 3D printer) which is designed to rotate the camera around the subject so it can be at any angle between horizontal and vertical. There are certain times when you want gravity to work in a certain direction but your POV needs to be neither horizontal nor vertical. Haven't quite mastered black holes yet so decided to move the camera angle.

So far as prices / brands are concerned - it doesn't really matter what brand for amateur work. Prices have never recovered since Chris first posted his pair of Thor Labs

Andrew,

Thanks for the information, all very helpful and reassuring, particularly the reminder related to camera orientation around the optical axis.

My question regarding magnification was of a more fundamental nature and an attempt to address an earlier enquiry regarding goniometers with a small range of movement compared to a set with a larger range of movement, for e.g. if using a 20X objective would an adjustment to either 'arc' translate to a larger visible displacement within the FOV as opposed to the same adjustment when using a 2X objective? The answer would appear to be obvious but I wanted to clarify.

...snip... if you are completely centred the rotation doesn't change with magnification - little circles and big circles are still 360deg

When referring to 360 degree rotation are we talking about three- dimensional rotation via a matched pair of goniometers or in combination with an auxillary rotational base?


Craig

[rjlittlefield]

My question regarding magnification was of a more fundamental nature and an attempt to address an earlier enquiry regarding goniometers with a small range of movement compared to a set with a larger range of movement, for e.g. if using a 20X objective would an adjustment to either 'arc' translate to a larger visible displacement within the FOV as opposed to the same adjustment when using a 2X objective? The answer would appear to be obvious but I wanted to clarify.

I'm still not sure I understand the question, but let me try several answers.

1. Maybe the question relates to undesired lateral motion that is caused by not having the subject exactly at center.
In this case the lateral motion as measured in mm is
1) proportional to the subject distance above or below center, and
2) proportional to the angle, and
3) independent of the size or range of the goniometer.
As a fraction of field width, the lateral motion is also proportional to the magnification, so visually it will be 10 times as bad at 20X as it is at 2X.

2. Maybe the question relates to the effect of angle on stack depth. That is, if a 5 degree shift doubles the depth of a stack at 2X, what does it do at 20X? The answer here is that it's about the same at both magnifications, doubling the depth at 20X also. The change in depth measured in mm will change less at 20X because of the smaller FOV, but it will be the same as a fraction of FOV.

Does something in here answer your question?

--Rik

[DQE]

Is there any benefit from using this as a camera mount for these types of studio macro systems? Or, is the camera typically fixed other than initial focus?

http://www.bhphotovideo.com/c/product/6 ... _Head.html

[Craig Gerard]

Does something in here answer your question?

Yes...this part:

...snip... As a fraction of field width, the lateral motion is also proportional to the magnification

Some of the other potential answers address matters which had not occurred to me

Craig

[Craig Gerard]

A matched pair (dual axis) goniometer combined with a rotational platform will be very useful for this purpose. Such devices are a pleasure to use. We've seen them used in horizontal setups, but I can envision them as being just as useful with a vertical arrangement.....something more for me to contemplate and explore.
Craig

Something like this? It has been a very useful combination, although it has suffered from neglect for the past few months, as you can probably tell by the accumulation of dust
Regards,
David

David,

Thanks for uploading the example image.

I can appreciate how the precision adjustments provided by the goniometric stages would be beneficial when used in the manner you've illustrated, both for technical and compositional purposes.


Craig

[elf]

Is there any benefit from using this as a camera mount for these types of studio macro systems? Or, is the camera typically fixed other than initial focus?

http://www.bhphotovideo.com/c/product/6 ... _Head.html

This won't rotate around the entrance pupil (unless you make a custom mount), so any adjustment of the cube would require a corresponding adjustment of the subject. I think it would be better in the field where you need to adjust the camera to the (usually immovable) subject.