I have a question about photo eyepiece, specifically for a 4x5 microscope camera with roll film backs. This is used on an episcopic compound microscope.
1. Does the photo eyepiece limit the image circle. I have seen recommendations for x2.5 eyepieces for 35mm and x5 eyepieces for 4x5. Is this simply for image scale?
2. How does this affect optimum resolving power. Obviously I cannot enlarge the image indifinately - x100 eyepieces do not exist. What would the best balance be to optimize resolving power and image scale? Is there a large difference between using a 10x objective and 5x photo eyepiece compared to a 20x objective and a 2.5x photo eyepiece? (I am assuming magnification is calculated by multiply the factors.) Is there a good reason for having photo eyepieces of different magnifications?
I hope the questions are not too rambling. I'm new to this. Thanx.
Photo eyepieces and magnification
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Charles Krebs
- Posts: 1200
- Joined: Tue Jul 13, 2004 10:50 am
- Location: Issaquah, WA USA
Will.... welcome!
I'll tackle your second question first (because I'm more sure of my answer ...
)
It will almost always be preferable, from an image quality standpoint (and certainly resolution), to use a higher power objective and a lower power photo-eyepiece. Your resolution is determined by the numerical aperture (na) of the system. Even though the magnification is the same, in the example you gave consider the following:
A "typical" 10X has a na of about 0.25, while a "typical" 20X will be about 0.40. The 20X objective is capable of delivering significantly higher resolution in this case. (The eyepiece has no effect on the resolution of the primary image... it can only take that image, and "distribute" it in different ways to the eye, film, or sensor).
I've not used larger formats, so I'll be a bit more vague on your first question. My understanding is that you want to use a photo-eyepiece that takes in most of the primary image formed by the microscope objective, and then projects or "spreads" that image to cover the format used. Use too high a power in a photo-eyepiece and you are using only a small portion of the primary image on your film/sensor.... and as mentioned above... you would be far better served, from a resolution standpoint, to use a higher power objective with less magnification in the photo-eyepiece. Use too low a photoeyepiece and you may not get an image to "fill" your format.
I'll tackle your second question first (because I'm more sure of my answer ...
)It will almost always be preferable, from an image quality standpoint (and certainly resolution), to use a higher power objective and a lower power photo-eyepiece. Your resolution is determined by the numerical aperture (na) of the system. Even though the magnification is the same, in the example you gave consider the following:
A "typical" 10X has a na of about 0.25, while a "typical" 20X will be about 0.40. The 20X objective is capable of delivering significantly higher resolution in this case. (The eyepiece has no effect on the resolution of the primary image... it can only take that image, and "distribute" it in different ways to the eye, film, or sensor).
I've not used larger formats, so I'll be a bit more vague on your first question. My understanding is that you want to use a photo-eyepiece that takes in most of the primary image formed by the microscope objective, and then projects or "spreads" that image to cover the format used. Use too high a power in a photo-eyepiece and you are using only a small portion of the primary image on your film/sensor.... and as mentioned above... you would be far better served, from a resolution standpoint, to use a higher power objective with less magnification in the photo-eyepiece. Use too low a photoeyepiece and you may not get an image to "fill" your format.
Thank you Charles. I have been looking for something on this topic on the web and have found very little. I agree that the photo eyepiece should be as low a magnification as possible as it is only magnifying what the objective is sending it. But since the film area is larger, it can handle a loss of resolving power a little better because the film image itself is not enlarged as much. I imagine there must be an optimal balance between the photo eyepiece magnification and the film format.
It seems that large-format microscope cameras are a thing of the past and the use of medium format was non-existant (the photomicrography version of APS or Disk). I recently bought an Olympus microscope with a 4x5 camera (PM-10M), but the photo eyepiece is missing - I just get a small round image in a large black field in the focusing telescope. So now I need to get an eyepiece and I am wonder what would be the best. I need an image circle of 80mm (6x6) and 125mm (6x12).
That is, of course, that I have diagnosed the problem correctly. I did set up Kohler illumination correctly, but I only get a tiny image in the center of the focusing telescope - about the size of the center cross hairs. There is no eyepiece between the microscope and camera and I believe there should be - a system chart shows one. BTW, this is an old Vanox Universal Research Microscope. Very much like this one, but a slightly later model - http://micro.magnet.fsu.edu/primer/muse ... vanox.html
And thanks for your welcome. I am very happy I found this site.
It seems that large-format microscope cameras are a thing of the past and the use of medium format was non-existant (the photomicrography version of APS or Disk). I recently bought an Olympus microscope with a 4x5 camera (PM-10M), but the photo eyepiece is missing - I just get a small round image in a large black field in the focusing telescope. So now I need to get an eyepiece and I am wonder what would be the best. I need an image circle of 80mm (6x6) and 125mm (6x12).
That is, of course, that I have diagnosed the problem correctly. I did set up Kohler illumination correctly, but I only get a tiny image in the center of the focusing telescope - about the size of the center cross hairs. There is no eyepiece between the microscope and camera and I believe there should be - a system chart shows one. BTW, this is an old Vanox Universal Research Microscope. Very much like this one, but a slightly later model - http://micro.magnet.fsu.edu/primer/muse ... vanox.html
And thanks for your welcome. I am very happy I found this site.
Will