reflection in center of FOV

[janvangastel]

I have a reflection in the center of the FOV. I don't see it when looking through the eyepieces but I see it when looking through the camera and in photographs and video's. It is most prominent on dark objects, like the hair in the picture below (100x oil objective). No matter how good I defocus the light while Kohlering and no matter how opened or closed the field iris and the condensor iris are, it's always there. I use a camera without a lens and take photographs without any eyepiece. I hope someone knows what causes it.

relection.jpg (230.2 KiB) Viewed 14689 times

[75RR]

I use a camera without a lens and take photographs without any eyepiece.

Can you explain in more detail what you are doing? I would have expected a 'Direct Projection' setup to use a projection lens.

As to the reflection (assuming it has nothing to do with the lack of a projection lens) is probably due to 'flare' caused by a shiny section either in the phototube or somewhere on the camera.

[einman]

Try covering the eyepieces when using the camera. If the light is not diverted 100% to the camera it can enter via the eyepieces and cause this effect. That is why you don't see it through the eyepieces because you are blocking it with your head.. I turn off the lights in the room when photographing for this reason when using a scope that allows light into the eyepieces.

[MichaelG.]

I use a camera without a lens and take photographs without any eyepiece.

Can you explain in more detail what you are doing? I would have expected a 'Direct Projection' setup to use a projection lens.

If this is the case [and, like you 75RR, that's how I read it], Jan's microscope objective is being used as a 'macro lens' and all bets are off.

Please, Jan ... tell us, or show us, exactly what your set-up looks like.

MichaelG.

[ChrisR]

Jan your earlier pictures didn't show it, so is this the fist time you've tried "direct projection"?
As a technique, it should work very well unless you need CA correction in your eyepiece - Leitz, so you might need a Periplan.

If it's this eyepiece tube:
viewtopic.php?f=28&t=6900&p=61518#p61518
there's plenty of internal reflection visible there to show a "fogged" spot like that. You really have to hide all reflective surfaces, especially adapters.
Often black paper is ok, but you can of course buy special materials like Protostar. They can be hard to get.

I exxpect your Orthoplan is better, but in an Olympus CH30 I have, the inside of part of the tube is chrome plated!.
It has had a tube of black paper down it for longer than I can remember, it seems to work.

[janvangastel]

Can you explain in more detail what you are doing? I would have expected a 'Direct Projection' setup to use a projection lens.

I take the camera lens off the camera and in its place I mount an adapter. The adapter does not contain a lens. The adapter fits into the 23 mm camera tube, so not in one of the two eyepiece tubes. The light falls directly on the camera sensor, without any kind of lens, neither in the camera tube on te microscope, nor in the camera adapter.

Jan your earlier pictures didn't show it, so is this the fist time you've tried "direct projection"?

No this is not the first time. I have seen the reflection before, on dark objects.

If it's this eyepiece tube:viewtopic.php?f=28&t=6900&p=61518#p61518

No, this is not the eyepiece tube I use for attaching the camera to the microscope. I use the tube on top of the microscope, so not one of the two eyepiece tubes for visual observing.

If not clear, I can place some photographs tomorrow. Thanks for all the help.

[jimur]

Stray light in the room via the binocular eye pieces? Try turning the room lights off or covering the bino. eye pieces. Just a silly thought from a novice.

[MichaelG.]

... Jan's microscope objective is being used as a 'macro lens' and all bets are off.

I have seen your clarification, Jan, and can only repeat what I posted earlier ^^^

Objectives for the compound microscope are generally not computed to produce a decent image when used as a 'simple microscope' [macro system].

What objective are you using ?

MichaelG.

[Hobbyst46]

Is this really due to reflection? could it not be a sort of "hot spot"?

[ChrisR]

Why do you say that Michael? Is it about uncorrected chromatic aberrations which require correction in an eyepiece?

Otherwise, there's no reason at all why an objective can't be used as, if you like, a "macro lens". It's very popular.
With more recent lens designs (starting with Nikon CF objectives) you don't need the eyepiece correction so direct projection is absolutely fine. I and a load of others have been doing it for years. You can use infinite or finite arrangements, without any eyepiece; projective or otherwise.
See here, there are dozens of setups shown.
A central hotspot isn't a problem you get, doing that per se. You should initially have the tube length correct ( the intermediate focal plane in a microscope is usually 10mm from the eyepiece, so you focus a "160mm" obective with 150mm between the mounting flange of the objective, and the sensor.) but I've never heard of it causing hotspots.
At photomacrography,net you'll quite often see beginners using direct projection, and getting internal reflections. Usually there are tubes or something involved, which aren't as non-reflective as they look. That Oly microscope head I referred to did it, with the camera on a short tube (to make 150mm) on top of the dovetail, untill I inserted the tube of black paper.

Jan one way to see any reflections is to put your eye where the sensor would be, and look towards the objective. It might hurt your eye if the light is too bright, but you'll see reflections, OR light leaks.
As you say, the lighting coming from below is the first place to suspect for hot spots, but it sounds like you have that covered.

[MichaelG.]

Why do you say that Michael? Is it about uncorrected chromatic aberrations which require correction in an eyepiece?

Not specifically, Chris

On this occasion I was thinking more about reflections from the surfaces of lens elements:

You are obviously a photographer ... Do you recall the problems that Asahi Pentax had, which prompted their development of the 'ghostless' filters ?

I am perfectly happy to be wrong [which is why I wrote 'all bets are off'] ... the probability depends on the optical design of the particular objective that Jan is using.

MichaelG.

[ChrisR]

I found a thread which shows an objective + "tube" lens, focusing on a sensor via empty tubes, and what happens if there are reflections:
http://www.photomacrography.net/forum/v ... hp?t=35350

[MichaelG.]

Thanks for that, Chris

You will note that I edited my previous post, for clarity.

MichaelG.

[75RR]

I take the camera lens off the camera and in its place I mount an adapter. The adapter does not contain a lens. The adapter fits into the 23 mm camera tube, so not in one of the two eyepiece tubes. The light falls directly on the camera sensor, without any kind of lens, neither in the camera tube on te microscope, nor in the camera adapter.

This quote below is from the The Leitz Orthoplan and Ortholux II Research Microscopes pdf on Micscape (see page 12):
https://www.microscopy-uk.org.uk/mag/ar ... _Ver_4.pdf

"The Ortholux II and Orthoplan can be equipped with a viewing head providing a 38mm ISO port. Both microscopes require compensating photo eyepieces to fully correct the image prior to projection onto the image sensor."

Does your adapter have room for a Periplan?

[janvangastel]

No, my adapter has no room for a periplan. A friend of mine could 3D print an adapter for me, but I will first have to find a suitable periplan.
There are some on ebay, but I really would not know which one to buy.

When I look into the adapter tube if it is mounted on the microscope without the camera, I can clearly see reflections coming from the inside wall of the tube. When I remove the adapter and look into the tube I also see reflections, coming from the wall of the part if the tube that is between the top and bottom cover of the eyepiece house. That tube part is well baffeled, but generates reflections nevertheless. So in any case two reflecting surfaces. I have lots of flocking paper, so I could line the inside of reflecting surfaces with it, but then - I think - I will have even more vignetting then I have already.

Below another photograph. At the top/righ, best visible in the black part of the image, rays of light are visible. Possibly originating at the wall of the tube. Or spreading out from the central reflection.

reflections_2.jpg (260.74 KiB) Viewed 14566 times

[75RR]

This should help with the Periplan: https://www.photomacrography.net/forum/ ... t=periplan

[MichaelG.]

... What objective are you using ?

Please

[MichaelG.]

Is this really due to reflection? could it not be a sort of "hot spot"?

It could be almost anything

Hence my earlier comment ... 'all bets are off'
MichaelG.

[janvangastel]

What objective are you using ?

The photographs are made with the 100x oil objective. But when I use the 40x dry it is also visible.

[MichaelG.]

What objective are you using ?

The photographs are made with the 100x oil objective. But when I use the 40x dry it is also visible.

Thanks for that
I was actually hoping for a little more detail, so that we might try to find a picture of the optical formulation ... but, even based on those numbers, I am not really surprised that you are having some difficulties.

Next question: Is the camera image parfocal with the visual image ??
... probably not ... so how far adrift is it ?

MichaelG.

[janvangastel]

Yes, it is parfocal and needs only a little tuning. But I have difficulty to find perfect focus with a camera. Not only with this objective but with all of my objectives.

I found out the problem is reflection. I found this article about the same problem https://www.dpreview.com/forums/thread/2982994?page=3. Then I placed some felt in the adapter tube and the problem was gone or almost gone. See image below (did not try to find best focus). But now I can see the felt. I will place another piece of felt that fits better, but it will not be invisible.

baffeling.jpg (270.17 KiB) Viewed 14534 times

[MichaelG.]

... I found this article about the same problem https://www.dpreview.com/forums/thread/2982994?page=3.

Some excellent information there ... thanks for the link.

MichaelG.

[einman]

Very good. I had that same issue on an Olympus scope. I painted the inside of the tube flat black. On a Leitz scope I had to cover the eyepieces when using the camera, or depending on where the overhead light was positioned, it resulted in glare on the specimen.

[MichaelG.]

We need to find a reasonably priced source of this:
https://en.m.wikipedia.org/wiki/Vantablack

MichaelG.

[viktor j nilsson]

I use Doodlebug Design Crushed Velvet cardstock from scrapbook.com - highly recommended. Better than protostar. Never seen vantablack, but black 2.0, seems to have been a bit of marketing hyperbole.

[75RR]

Yes, it is parfocal and needs only a little tuning. But I have difficulty to find perfect focus with a camera. Not only with this objective but with all of my objectives.

Adding a Periplan projecting lens should help with that as I don't think your camera sensor is in the exact position it needs to be in your present setup.

[janvangastel]

Should I buy a periplan eyepiece like this https://www.ebay.nl/itm/Microscope-Micr ... :rk:3:pf:0? Or should it be a special photography periplan eyepiece, for instance like this https://www.ebay.nl/itm/Leitz-Periplan- ... :rk:2:pf:0 or this https://www.ebay.nl/itm/Leitz-Wetzlar-M ... :rk:3:pf:0 , but then, in my case, for a 170 mm instead of 160.

[mrsonchus]

Hi Jan, yes you 'should' ideally use a periplan (to achieve to matching correction) photo-eyepiece (projection eyepiece and with the red dot). However, the one in your link has 18 on it, which tells you that it's for the 160mm TL. The 170mm ones do not have 18 on them.

This is my one, without the 18, and used for 170mmTL systems as the Orthoplan has in brightfield,

ws_adapter 2.jpg (38.55 KiB) Viewed 14416 times

Having said that I also have a 'normal' periplan eyepiece that works perfectly also. I place a (in my case plastic) 'spacer' around it to hold it about 5mm up out of the tube, which makes it parfocal and a projection-objective - works perfectly and of course supplies the 'periplan' correction. The black adapter is to go from the 30mm to 23mm size, and the improvised plastic collar is just a piece cut from a tube-cap - anything will do, even a layer of tape, just to raise the normal eyepiece about 5mm....

ws_DSCN9986.jpg (61.21 KiB) Viewed 14416 times

Here next to the proper Leitz adapter, as you can see it has a 5mm-ish collar atop..

ws_DSCN9987.jpg (52.56 KiB) Viewed 14416 times

To get the same height just slip the plastic spacer over the normal p-plan eyepiece,

ws_DSCN9988.jpg (46.81 KiB) Viewed 14416 times

Or put the eyepiece into the 'proper' adapter that will raise it for you....

ws_DSCN9985.jpg (39.79 KiB) Viewed 14416 times

So, short-answer - yes the normal eyepiece (again with no 18 on it - those are for 160mm systems not 170mm) raised 5mm will work just fine. Without the 5mm spacer it isn't quite parfocal with the eyepieces, but still works perfectly and gives the exact-same GFOV and quality as the eyepieces.

Hope that helps a little Jan.

John B.

[janvangastel]

Hello John,

Thanks for your information and photographs. So I could go with the normal periplan eyepeice and keep looking for a photo periplan eyepiece. I found a 10x in the UK that has no 18 on it: https://www.ebay.nl/itm/Microscope-Micr ... :rk:3:pf:0. Can I assume this is the right one? I can ask a friend of mine to 3D print an adapter.

Jan.

[mrsonchus]

Yes that one looks the same as mine - just a simple spacer - 5mm should be right. I wouldn't go to the trouble of 3D-printing my friend, just build up with a little tape!

John B.