relay lens: to use or not to use

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Pau
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Post by Pau »

iconoclastica wrote:How do I determine the tube factor?
Take a picture of a ruler or micrometer slide (depending of magnification).
The relationship between the image size on the sensor and the object size is the total magnification.
Divide it by the objective magnification and you have it.
- Do it at the right focusing point, the position where changing objectives the system is parfocal
- If you use direct projection you will have the head magnification factor, if you use a relay lens you need to take it in the account.

If you want to know the tube factor with the eyepieces the procedure is the same but taking the eyepiece field diameter ("field number") as reference in place of the sensor size.
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Pau
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Post by Pau »

Does the black Zeiss photo tube fit well at the female Nikon dovetail? I'm surprised to see this hybrid.
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iconoclastica
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Post by iconoclastica »

First a correction to what I wrote before: the vignetting at the very corners has straight edges, so must be the field aperture. Opening the field aperture a little more removes the black corners.

I get 0.91mm over the width of the Camera's display in live view. The EOS 7D sensor's witdh is 22.30mm, so the magnification would be 20.3x if the given width of the sensor is also the effective width (used from edge to edge). The objective used is the Nikon 20x 0.4 160/0.17 full metal (122604).

So far so good, but for a double check I added 44mm to the tube length (the EOS-EF flange distance), and laid a tracing paper screen on top for direct measurement:


Image

For 20x magnification the projection ought to be 20mm long, but it really is 25mm...
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iconoclastica
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Post by iconoclastica »

Pau wrote:Does the black Zeiss photo tube fit well at the female Nikon dovetail? I'm surprised to see this hybrid.
The diameter of the dovetail is 47.7mm, that of the Nikon's head 48.8mm. It's slightly off centre, therefore. Should I continue with this tube, I's either fine 0.5mm offset strips, or make a new dovetail disk in the 3D printer. The latter is neater, but the printed plastic may not be strong enough.
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Ichthyophthirius
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Post by Ichthyophthirius »

iconoclastica wrote:I get 0.91mm over the width of the Camera's display in live view. The EOS 7D sensor's witdh is 22.30mm, so the magnification would be 20.3x if the given width of the sensor is also the effective width (used from edge to edge). The objective used is the Nikon 20x 0.4 160/0.17 full metal (122604).

So far so good, but for a double check I added 44mm to the tube length (the EOS-EF flange distance), and laid a tracing paper screen on top for direct measurement:

For 20x magnification the projection ought to be 20mm long, but it really is 25mm...
Hi,

I can't quite follow. Which is it? It's the right way to determine the tube factor (compare sensor size and image of the micrometer)!

As far as I know, the intermediate image in this microscope is located 105 mm above the upper edge of the dovetail. That's where the sensor should be.

Regards, Ichty

iconoclastica
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Post by iconoclastica »

I don't understand it either. By measurement, I found a 109mm distance, but that couldn't explain such a difference.

So, unless I made a mistake and extended the total tube length too much by 25% (4cm!), the tracing paper is in the position of the sensor and the size should be 20mm. However, from the existing tube I removed 1mm (the adapter ring) and added 45.3mm extra extension tubes. That should have added th 44mm flange distance to the sensor.

I'll retry the same thing tomorrow stressing exact measurements. Meanwhile, the camera method says tube factor is 1x.
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iconoclastica
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Post by iconoclastica »

OK, this is what I do:

Image

With the image focus as sharp as I can get it, I adjust the height of the photo tube until I see in magnified live-view the image maximally focused too. The resulting photo is this:

Image

Visible is 0.915mm on a sensor with documented width of 22.3mm, so magnified 24.37x

The length of this tube, measured from the top of the flange downto the bottom of the head is 123mm. Add to this 44mm flange distance, then the sensor is 167 above the reference point, i.e. the base of the head.

Then I extended the tube and finetuned it with the helicoid until the top was 167mm above my reference point. On top of it I placed a slide with a piece of scotch magic on the down side and a transparent ruler. This looked like this:

Image

Here one mm projected measures 24.3mm.

So, both measurements are in agreement with eachother, and also with yesterday's. But my calculation of the in camera magnification was not. I had a bad rhinoviral attack yesterday, therefore I divided 22.3 by the reciproke of 0.91mm, as you
might have noticed :wink:
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rjlittlefield
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Post by rjlittlefield »

iconoclastica wrote:therefore I divided 22.3 by the reciproke of 0.91mm, as you might have noticed :wink:
Always a simple mistake to make. Good that you caught it by running the double-check. Thanks for the illustrated explanation!

--Rik

iconoclastica
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Post by iconoclastica »

Now there seems to be a tube factor of about 1.25x, I wonder where does it come from? My photo tube can still be put in place when I remove the head altogether. Down there, there's only the polarisation analyzer. Beyond that, it seems I am looking straight into the objective. Indeed, with no head between the revolver and the photo tube, the in-camera magnification is very near 20x.

So, the discussion head introduces the tube factor? Yes, it does and it does so before the beam splitter. With the second binocular head in place, both fields of view are identical. With the second binocular head mounted without the discussion head, I see a wider field and the field aperture around its perimeter.

Thinking that such a factor ought to be indicated somewhere on the discussion head, I turn it around in my hands for a marker and indeed it's there: right in front of my eye is a little sticker 1.25... (You can even see it if not read it in the photos above).
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Ichthyophthirius
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Post by Ichthyophthirius »

Hi,

So this head seems to have a 1.25x tube factor. It's also writen on this teaching head: http://www.prc68.com/I/Labophot.html#Dual_View_Teaching (great website!) and I now realise that the same "1.25" sticker is on your microscope as well.

That's actually working to your advantage as it magnifies the intermediate image a bit. You therefore get mainly the high-quality centre area of the image onto your sensor!

I think that's the best-possible camera setup you can get.

Regards, Ichty

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Post by ChrisR »

Chris R

iconoclastica
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Post by iconoclastica »

ChrisR wrote:
Hey, VERY useful. :smt023
Exceedingly useful! It's he accesorie-catalogue I have been dearly missing.

Thanks evereyone, for your comments.

Wim
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