Optical tube length and flange focal distance

[4odonates]

What is the difference between mechanical tube length vs. optical tube length for an AmScope 4x microscope objective? How does flange focal distance (FFD) factor into determining optical tube length? I know the mechanical tube length of my 4x microscope objective is 160 mm, and I know the FFD of Fujifilm X-Series mirrorless cameras is 17.7 mm. Beyond that, I'm not sure of the correct distance to mount the objective from the camera sensor.

Related question(s): Let's say I want to use extension tubes to mount the microscope objective at the correct distance from the camera sensor. What's the best/least expensive way to do this on a Fujifilm X-Series mirrorless camera?

Thanks for sharing your expertise!
Walter

[rjlittlefield]

Walter, welcome aboard!

I suggest first to read through our "FAQ: How can I hook a microscope objective to my camera?", at https://www.photomacrography.net/forum/ ... 29&t=12147 .

Very briefly, you need to subtract 10 mm from the objective's mechanical tube length (160 mm) to get the optical tube length (150 mm), then from that you need to subtract the FFD of 17.7 mm, to get a new mechanical tube length of nominally 132.3 mm, measured from the shoulder of the mounting threads of the objective to the face of the camera bayonet. The exact length is not critical for such a low power objective.

"Best" depends on what capabilities you want to have in the end. The most flexible approach is to use bellows, which also plays nicely with using reversed enlarger lenses and to get intermediate magnifications. The cheapest approach is probably to get a basic X-mount to M42 adapter like https://www.amazon.com/Fotodiox-Lens-Mo ... B008BBI7D2 , then M42 tubes to get the required total length, and finally an M42-to-RMS adapter like https://www.amazon.com/Pixco-Adapter-Ro ... B07K435N4M (flat) or https://www.amazon.com/Thread-Microscop ... B07PP7N4X7 (cone).

eBay often has adapters at lower prices, if you don't mind waiting for delivery from China.

--Rik

[4odonates]

Sincere thanks for welcoming me to the group, Rik, and thanks for the detailed reply!

After thinking about your answers I experienced an epiphany last night. Among other things, I realized I have the right equipment on hand in order to cobble together a rig that fits the specifications you described. After limited testing, I’m pleased to report it seems to work well.

I wonder whether anyone would be curious to see photos of my Rube Goldberg rig for Fujifilm X-Series cameras.

Thanks again,
Walter

[rjlittlefield]

I wonder whether anyone would be curious to see photos of my Rube Goldberg rig for Fujifilm X-Series cameras.

Yes, of course! In my world, Rube Goldberg is a respected source of design ideas.

--Rik

[4odonates]

I'm working on a blog post related to the 4x magnification macro rig I cobbled together. I expect to publish the post on Friday, 04 November 2022.

May I have permission to use one of the photos in the FAQ article that you referenced, Rik? Of course a source credit will be included in my blog post. Is there a preferred citation format that I should use?

Walter

[rjlittlefield]

If the photo is one of mine, then I grant permission. If the photo is by someone else, then they would have to do that.

The preferred format is anything that leads directly to the original work. For a post at photomacrography.net, that should include the URL of the post and should look something like https://www.photomacrography.net/forum/viewtopic.php?p=76195#p76195 . In this example, ?p=76195 specifies which post and #p76195 causes the browser to scroll directly to that post, if possible.

Such a URL can be obtained by clicking on the little "document" icon just below the post title, at the left side of the window:

--Rik

[4odonates]

This is the photo. Is it yours?

http://janrik.net/MiscSubj/2011/FAQ-How ... hromat.jpg

Thanks!
Walter

[rjlittlefield]

Yep, that's one of mine.

Again, the proper link is to the posting at photomacrography.net which talks about that image. The url that you've provided just points to an array of pixels, with no context.

--Rik

[4odonates]

As promised, here’s the link to a blog post I created that describes/shows the macro rig I created by following your guidance, Rik. Thanks again for your help!

https://waltersanford.wordpress.com/202 ... -practice/

Walter

[rjlittlefield]

Thanks for the link.

On quick read, that all looks great except for a glitch in one sentence:

featuring a mechanical tube length of 160 mm minus 10 mm for the objective itself.

This would be better as "10 mm for the microscope's eyepiece".

The reason it's 10 mm is because that's the distance between the eyepiece's shoulder (at the end of the mechanical tube) and the location of the focused image (10 mm inside the tube).

--Rik

[4odonates]

Thanks, Rik! I edited my blog post to include your suggestion, verbatim. Truth be told, I wasn’t sure about what I wrote but didn’t know where to look for fact checking. Now I understand.

Thanks again!
Walter

[4odonates]

I thought it would be a good idea to update my blog post to include your recommendations for gear that can be used to mount a microscope objective on Fujifilm X Series cameras. So I did. Also added an annotated image that illustrates FFD.

https://waltersanford.wordpress.com/202 ... -practice/

Related questions.

1. What if there isn't a combination of tubes that equals the optical tube length (in my case, 132.3 mm)? Is that when you need to add a helicoid to the rig?

2. Does a helicoid feature a lock to fix its length? Otherwise, the microscope objective might shift position when using a macro rig with a helicoid.

Thanks for your advice!
Walter

[lothman]

Well done Walter.

But just one idea. If someone has the possibility to 3D-print the tube adapter the you could modify this part by adding some struts in order to bolt on an Arca plate (similar to the suggestion by Adalbert). Later you adapt this combo at the tube adapter and no longer at the camera. This would wobble much less and give you automatically an alignment between slider and optical axis.