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Photomicrography question

 
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augusthouse



Joined: 16 Sep 2006
Posts: 1195
Location: New South Wales Australia

PostPosted: Sun Sep 28, 2008 1:06 am    Post subject: Photomicrography question Reply with quote

I had a question from a Chinese photomicrographer and need to pass it on to more experienced members. Direct quote of message received below.

Quote:
"I can see a very clear and sharp image from the eyepiece, but the image which I took by my Digital Camera--Olympus E330 with the relay lens of the microscope (DDR Zeiss), is never as clear and sharp as that I observed via eyepiece. The microscope's light source is powered by a AC transformer,Should I try a DC power for the light source? Or,Could you please offer me some suggestion?"


Need some help with possible suggestions on this one.

Is it something to do with parfocal? The photographer in question has a rather extensive collection and knowledge of microscopes; so I am assuming the scope, eyepiece, objectives and relay-lens are all in sync; but the DSLR is not in sync with the relay-lens?

I am also assuming that the "DDR Zeiss" referred to is possibly a GFL trinocular or similar (waiting for confirmation on this).

Craig
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Charles Krebs



Joined: 01 Aug 2006
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PostPosted: Mon Sep 29, 2008 1:16 am    Post subject: Reply with quote

Really need more info on this one. Is it a trinocular scope? What "relay optics" are being used and how is the camera mounted? How is in-camera focus being determined? What measures have been taken to deal with SLR vibration issues?

"AC transformer" or "DC power" should have nothing to do with it.
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Harold Gough



Joined: 09 Mar 2008
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PostPosted: Mon Sep 29, 2008 2:23 am    Post subject: Reply with quote

Possibly something as simple as a dirty mirror/prism?

Harold
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augusthouse



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PostPosted: Wed Oct 01, 2008 8:12 pm    Post subject: Reply with quote

Thanks. I have forwarded your comments and suggestions.

Craig
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augusthouse



Joined: 16 Sep 2006
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PostPosted: Fri Oct 03, 2008 4:48 am    Post subject: Reply with quote

I have received some more information in regard to this matter, so have included below as received. (some slight modifications in translation)

For the record, this man is a true gentleman.

Quote:
About the problem of taking photos with my microscope. It is hard to describe it clearly with my poor English; so, I attach some photos to show you my equipment and partial paper of the DDR zeiss Peraval----it is my favourest microscope; the relay lens I used is K4:1. In the attachment is an example of what I taken with my E330,it is obviously not as clear and sharp as I observed with eyepiece.

I would make time to read the article on the website which you offered me.


* The articles referred to in the quote are two articles on Charlie's website.

The following images were attached to the email I received.






Your help and suggestions would be greatly appreciated.

Craig
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Charles Krebs



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PostPosted: Fri Oct 03, 2008 2:38 pm    Post subject: Reply with quote

Craig,

The first two things I would want to examine are the method used to set focus in the camera, and what is being done to avoid vibration problems.

It appears the camera is mounted directly to the microscope. This can make vibration problematic. One way to "eliminate" it as a problem is to put neutral density over the light source and use exposures of about 3 seconds or so. Any methods the camera provides to reduce vibration, such as mirror lock-up, should be used. (I don't know too much about this camera, but generally it's really tough to use a SLR directly on a microscope if it doesn't have -at least!- provision for avoiding mirror vibration).

As to focus... naturally it is very critical. Many are not aware that it is not a good idea to focus the camera image by changing the microscope focus to the point it is no longer in focus through the microscope eyepieces. When this is done, you "upset" the objective-to-subject distance for which the objective design was calculated. (In truth this is not a big issue with low mag/low NA ...numerical aperture... objectives, but it is not a good practice). When people use a manufacturers dedicated camera system that was designed to be used with their microscopes this is not an issue since it the camera is made to be par-focal with the eyepieces (or extremely close to that ideal). When you "adapt" a camera such as a SLR, it's always a good idea to try to make the attachment in a way that the camera can be adjusted up/down so that it can be made par-focal with the eyepieces.

An absolutely vital piece is the "low-power, projection eyepiece" used in the trinocular head. Your acquaintance says that he used the "K4:1". The "K" part is important, because that means it is properly "corrective" for the microscopes objectives used. (Most microscope objectives from this era were designed so that final color corrections were made via an eyepiece... either a "visual" one or a "photo" one. These are usually marked with a "K" or "C"). One red flag I see is the magnification. A 4X relay magnification is really too much for a 4/3 sensor. An appropriate relay magnification for a 4/3 sensor (format diagonal of 21.6mm) would be in the range of 1.25X to 1.5X. A relay magnification of 2X would be "usable", but at 4X you are recording a highly magnified section of the center of image formed by the objective. (The recorded image would be only about a 5mm diameter section of the 20mm diameter image formed by the objective). An analogy --not perfect-- would be to consider the image quality you might obtain if you put two 2X "teleconverters" on a regular camera lens. You'll get a "bigger" (more magnified) image, but I would not expect too much in terms of resolution or image quality. With a microscope image it's even worse, because the physics of light (i.e. "diffraction") causes the resolution you are starting with to be already fairly limited (low). Enlarging this too much results in what is commonly referred to as "empty magnification".

I can't really offer a good solution to this. When these microscopes were made, 35mm was about the smallest format to consider (24x36mm with a diagonal of 43.3mm). The typical "low-power, projection eyepiece" made to be used with the 35mm format was between 2.5X-3.3X. (And again, the 4/3 sensor has a diameter that is only half that of the 35mm format). Lower power relays can be purchased from third party manufacturers, but they are very expensive and would not have the proper corrective capabilities. One thing that can be tried is to "raise" the photo-eyepiece in the trinocular tube. That will reduce the magnification it provides. The camera will need to be moved to make things parfocal again. This is not that difficult, but it does require some custom work.

Another option would be to compare image quality using an "afocal" technique. This is where a "normal" 10X eyepiece is used in the trinocular tube and a lens is used on the camera. I remember an article by Ted Clarke that outlined how he approached this... and I seem to remember that he was also using a Olympus E330. I'll check to see if I can locate it after I post this.

So your acquaintance might be troubled by any one of these things, or a combination of them.

It could also be something entirely different, but assuming things are clean and in good optical condition, and his technique is otherwise OK, these are the things I would look at.

Charlie
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Charles Krebs



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PostPosted: Fri Oct 03, 2008 2:40 pm    Post subject: Reply with quote

I found that "afocal"reference right away....

http://www.microscopy-uk.org.uk/mag/imgfeb07/E330Microscope.pdf
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augusthouse



Joined: 16 Sep 2006
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PostPosted: Fri Oct 03, 2008 3:14 pm    Post subject: Reply with quote

Charlie,

Thankyou for the detailed information and the additional link to Ted Clarke's article.

With the information provided in your post, combined with the articles on your website and the Ted Clarke article I am certain my friend in China will reach his destination.

I will send through your response word-for-word and followup with him to make sure he has been able to fully understand and apply the wealth of information contained therein.

Again, thankyou. Most appreciated.

Craig
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