Trying to determine total magnification with full-frame DSLR

adauphin · Post by **adauphin** » Sat Mar 14, 2020 10:13 pm

I searched and couldn't accurately figure my total magnification on the sensor.

I'm using an Olympus brightfield/darkfield metallurgical scope with a Nikon D810 on the trinocular tube. The 810 is attached with a Meiji MA150-50 with a 2.5X photo eyepiece.

Not sure if this measurement is needed but from the top of the photo eyepiece I have about 100mm to the sensor. Some sites stated the size of the display matters but I wasn't aware it matters if I'm saving to a SD card.

Any input is appreciated.

Scarodactyl · Post by **Scarodactyl** » Sat Mar 14, 2020 11:05 pm

Put bluntly, the "size of display" stuff is just garbage used by makers of digital microscopes to lie about what magnification they actually deliver. You can buy a bigger monitor and display the picture at a larger size but who cares, that's not a metric that matters at all.

You can easily measure the field of view by photographing a ruler or micrometer or whatever. Then you can either calculate the on-sensor magnification (since you know how wide the image is, and how wide the camera sensor is) or better yet just report the FoV since it's the only really translatable metric.

adauphin · Post by **adauphin** » Sat Mar 14, 2020 11:22 pm

Ok, thanks, I hear you about the "size of display". I did also see the older post with the ruler, and thinking about it, if I see the same image at 100X through the eyepiece as what I see in the display then it's a safe bet what I have....I will try that.

I was thinking there was a simple math equation but looks to be more involved. I will definitely try the ruler.

Scarodactyl · Post by **Scarodactyl** » Sat Mar 14, 2020 11:42 pm

It gets harder to calculate when you mix components across optical systems. 2.5x on a Meiji might not be 2.5x on an Olympus.

adauphin · Post by **adauphin** » Sun Mar 15, 2020 12:47 am

Sorry I don't have an actual pic, but with a metric ruler, this is what I have in my field of view with the 10X objective.

The red vertical lines are in the FOV, please note what edge of the hash mark the line rests on.

So this would be just slightly under 2X?

Edit to add: 2MM through eyepiece, and just over 1MM in the D810.

Scarodactyl · Post by **Scarodactyl** » Sun Mar 15, 2020 1:02 am

That would be one way to view it, though it can get even more complex since eyepiece FoV is also variable. 10x/20mm eyepieces are giving a different FoV vs. 10x/26.5mm ultra widefield ones, though both are 10x. It's easier and more broadly applicable to calculate the on-sensor magnification. The width of the d810 sensor is 35.9mm, so if we call it 1.1mm it would be about 32x on sensor, or about 3x vs the nominal 10x mag. I have a feeling you could get a wider FoV without cropping under ideal circumstances but ai am not sure. Have you considered trying an Olympus pe 2.5x? They cost less than thr Meiji you have.

adauphin · Post by **adauphin** » Sun Mar 15, 2020 1:21 am

I appreciate all this. Brief history, I bought this scope along with a Motic BA400 mainly for the kids and their schoolwork about a year ago, but I will likely use the Olympus more...both are just now getting a camera mount.

What you are saying is making more sense now and I'm understanding it better. I went with the Meiji for the kit, but I'm surely open for suggestions.

I do want to cover the entire sensor and assume that comes down to tube length? Or both the tube and adapter?

Thanks again.

Scarodactyl · Post by **Scarodactyl** » Sun Mar 15, 2020 10:30 am

The camera should be positioned over the photo eyepiece so that it is in focus at the same time as the eyepieces. There are ways to adjust the magnification, either by moving the position of the eyepiece or the position of the camera, but you'll get an image that is either degraded or not parfocal that way (or both). Of course the Meiji eyepiece is probably not quite ideally positioned by default, since it is designed for a different optical system, but it is probably not too far off.

Alan Wood · Post by **Alan Wood** » Mon Mar 16, 2020 2:12 am

Scarodactyl wrote:

Have you considered trying an Olympus pe 2.5x? They cost less than thr Meiji you have.

The Olympus PE photo eyepieces do NOT fit into standard eyepiece tubes. The lower part of their body is about 24.8 mm wide.

The Olympus FK and NFK photo eyepieces are standard size, but they are designed to correct residual aberrations in Olympus objectives.

Alan Wood

Scarodactyl · Post by **Scarodactyl** » Mon Mar 16, 2020 11:23 am

Alan Wood wrote:Scarodactyl wrote:

Have you considered trying an Olympus pe 2.5x? They cost less than thr Meiji you have.
The Olympus PE photo eyepieces do NOT fit into standard eyepiece tubes. The lower part of their body is about 24.8 mm wide.

The Olympus FK and NFK photo eyepieces are standard size, but they are designed to correct residual aberrations in Olympus objectives.

Alan Wood

Ah. That makes sense--so if he's able to fit a Meiji it must be set up for 23mm eyepieces. I was assuming an infinity scope for some reason but this would probably imply a finite setup. If that's the case then you'll definitely get a benefit from an fk or nfk correcting residual abberations, depending on the objectives.