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Objective Differences - need advice

 
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mcelli



Joined: 22 May 2006
Posts: 8

PostPosted: Mon May 22, 2006 1:42 pm    Post subject: Objective Differences - need advice Reply with quote

Hi All,

I am planning on purchasing a Motic BA300 and want to add an additional objective (20x). My question is the BA300 has infinity corrected objectives and I have heard varying opinions about using non-infinity objectives on this scope. It seems tpo me there wpould be no problem other than a difference in focusing and maybe paracentricity.

Any and all opinions would be great.

Thanks,

mike
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Ken Ramos
Site Admin


Joined: 04 May 2004
Posts: 4809
Location: Western North Carolina

PostPosted: Mon May 22, 2006 2:54 pm    Post subject: Reply with quote

First of all welcome to the forums Mike! Very Happy Second, I have not heard of one being able to switch IC objectives with standard 160's. I have a Zeiss Axiostar with ICS optics and just to settle my own curiosity I screwed in a standard 160 DIN objective to see how it would work. It would not even focus no matter how far down or up I moved the stage.

This is not to say that they, the 160 objectives, would not work with a Motic scope of course, it is just that they will not work with an Axiostar.

By the way, does that Motic BA300 have a 1.3 or a 2 mega pixel digital camera installed? If so, a word of advice. Motics Windows Programs for that camera will give you a fit when you try to install the software. They do not have the MS Digital Signature required to make them compatable with Windows 96/ XP/2000 Pro etc. but they will work and be a pain in the rear in so doing. You will have to go into Tools, click on Internet Options, click on Advanced Settings, and then scroll down to Allow Unsigned Drivers and place a check mark there. Then hold your breath and load the program. Rolling Eyes

Getting back to the objectives, I would advise sticking with IC optics and if you have not purchased the Motic, I would really look at something else. Motic has a number of issues that can be a real headace, such as the seals failing in oil immersion objectives. Smile

Now all of that may have been resolved by Motic and I maybe unaware of that fact but I would check just to make sure, if you really want that particular scope. Wink
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mcelli



Joined: 22 May 2006
Posts: 8

PostPosted: Mon May 22, 2006 11:06 pm    Post subject: Reply with quote

Thanks for the info! I will be using a Canon 20D connected to a ac Laptop and 23" Cinema Display. Also, thanks for te heads up on the Motic. Anyonr rldr out there have word on the BA300? Any and all opinions are greatly appreciated.mike
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Tue May 23, 2006 7:31 am    Post subject: Reply with quote

Mike,

Infinity optical systems and finite systems have fundamental differences. You may get by with a finite objective, but there is a good chance the image quality will be compromised. In "infinity" systems some manufacturers (Zeiss, Leica) make additional optical correction in the tube lens. Nikon and Olympus make all their corrections in the objective. I don't know what Motic does in this regard, but it is another area that could cause image defects. If you can "try-before-you-buy" give it a shot... you never know! But I would not spend money on a finite objective expecting it to work OK on an infinity scope.


The quote below goes right to your question. It is from the Nikon microscopy site, on the page referenced.

http://www.microscopyu.com/articles/optics/cfintro.html
Quote:
It should be noted that objectives designed for infinity-corrected microscopes are usually not interchangeable with those intended for a finite (160 or 170 millimeter) optical tube length microscope and vise versa. Infinity lenses suffer from enhanced spherical aberration when used on a finite microscope system due to lack of a tube lens. In some circumstances it is possible, however, to utilize finite objectives on infinity-corrected microscopes, but with some drawbacks. The numerical aperture of finite objectives is compromised when they are used with infinity systems, which leads to reduced resolution. Also, parfocality is lost between finite and infinity objectives when used in the same system. The working distance and magnification of finite objectives will also be decreased when they are used with a microscope having a tube lens.
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mcelli



Joined: 22 May 2006
Posts: 8

PostPosted: Tue May 23, 2006 8:46 am    Post subject: Reply with quote

Well. Thanks Again!

I think I understand now. I will stick to infinity corrected objectives.

Now I can ask my next question! I want to purchase a used photo eyepiiece. New is 170 and I am already was overbudget...damn expensive hobbies..why couldnt I collect stamps or maybe get into scrapbooking! Anyway, I want to purchase a used eyepiece but once again I am not sure about compatibility.

Are photo tubes universal? will any eyepiece fit? I am pretty sure I want a 2.5x. My goal is to be as parfocal to the binocular head as possible. I will be monitoring the camera view on an external 23" monitor, however, it would still be nice to have a what you see (through the binoculars) is what you get set-up. Also, does anyone know of a good resource for used photo eyepieces? ....besides ebay I am always a little paranoid about buying optics from ebay.

Thanks for all your help! This is a great forum and I'm sure it is going to be invaluable to me as I get set-up.

mike
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Tue May 23, 2006 11:21 am    Post subject: Reply with quote

"... I am already overbudget..." Smile
"... expensive hobbies..." Smile Wink

Yup!

Photo tubes (I assume you are talking about the trinocular head as opposed to using one of the viewing eyepiece tubes) should have the diameter as the regular eyepieces.

A 2.5X photo-eyepiece was the "power" that worked best with the full frame 35mm format. On a Canon 20D you will record a "field" that is about 11mm diagonally. Through the eyepieces (10X) you will see a field that is about 20mm in diameter. So you will record about 1/2 (in diameter) what you see. Many people using "reduced frame" DSLR's would prefer a photo-eyepiece of about 1.7X but there's only one I know of (Olympus NFK 1.67X), they are hard to find, and would not be exactly appropriate for your optics. (They had additional chromatic correction designed to be used with a specific series of Olympus objectives).

One advantage of the newer "infinity" optical systems is that whatever eyepiece or photo-eyepiece you use, it will not have to provide (and should not!) a compensating chromatic correction. (Since I use "finite" objectives, I am really not familiar with what might be out there in terms of non-compensating photo-relays between 1.5X and 2.5X. You should look around... there may be more than I know). In photomicrography, the optical link between microscope and camera is critical. If I were you I would consider the 2.5X made by the manufacturer of your scope and optics. ($170 doen't seem unreasonable. Dust off another credit card Wink ). If you look for a used one, try to find a Nikon CF 2.5X. They are good quality and have no chromatic compensation built in.

Also, I don't know how you intend to support the camera, but attaching any SLR directly to a microscope should be done with the understanding that mirror and/or shutter vibration can cause problems. There are some "operational" ways to minimize the problems. (Some also prefer the solution of mounting the camera on a stand over the trinocular tube with no "hard" contact at all).
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mcelli



Joined: 22 May 2006
Posts: 8

PostPosted: Tue May 23, 2006 12:23 pm    Post subject: Reply with quote

Hi Charlie,

Thanks for the reply. I have seen your article detailing your setups. I like the copy stand idea, but might be pressed for space. I particularly like your flash illumination mod. I will be l;ooking for some kind of mod to incorporate my strobe a little later down the line. BTW, I've also checked out your website, your images are fantastic, really great work.

My business partner, who has been shooting plankton for years, is taking the plunge with me and is getting a new scope. He brought up the question of why use a projectipon eyepiece at all. He has used his cameras without one for years and says his pictures are very sharp. Does a projection eyepiece only provide magnification? It seems that the less glass in the way of the chip will yield higher resolution, but I'm wondering if the magnification difference is going to drive me crazy. If I am composing through the binocular head, and I have a severe mag difference then whats the ppoint of composing a shot through the head? You mentioned that a 2.5 is only going to yield about half the field? Would I be better off with a higher mag to get closer to a what I see is what I get solution?

I really appreciate the feedback!

Thanks,

Mike
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mcelli



Joined: 22 May 2006
Posts: 8

PostPosted: Tue May 23, 2006 1:09 pm    Post subject: Reply with quote

sorry, I meant lower mag to get more of the field
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Tue May 23, 2006 8:48 pm    Post subject: Reply with quote

Mike,

Yes indeed, you could use "direct projection" as long as the trinocular tube is short enough that you can get the camera sensor plane down to the plane of the intermediate image (the image that the eyepieces "pick up"). Sometimes this can be done, in other cases the camera can't be mounted low enough to have the objective's image recorded directly onto the sensor. If it is possible, then you should also realize that your camera sensor (20D) has a diagonal of about 27mm. Chances are the intermediate image will not be that large, so you will record an image with circular dark corners, and need to crop the image (unless you like that look). But you'll get everything you see with 10X eyepieces! (Keep in mind that when you get out near the very edges of the image circle it's not unusual for image quality to drop off somewhat).

Backtracking a little... your camera has a sensor with a diagonal of 27mm. The microscope objective (and tube lens) will form an intermediate image that has a "useful" diagonal of about 20mm. (That is the "field number" of Motic 10X eyepieces as well). So your sensor is larger than the image made by the microscope. If you can "direct project" (or use a 1X relay) you will therefore get an image that will have dark circular corners. If you "enlarge" the intermediate image (using some sort of eyepiece or optical connection with a magnification greater than 1) you will eliminate the dark corners. But if you magnify too much, you then have the situation where you are recording smaller and smaller portions of the view seen through the eyepieces.

Peoples preferences vary, but most would be pretty comfortable recording 15-18mm of the intermedite image onto the camera sensor. With a Canon 20D (or digital rebel or 30D) that about 1.6X relay magnification. So with "direct projection" the magnification will seem too low, with a 2.5X it might seem a bit too high.

Another option we have not discussed would be to use a 10X viewing eyepiece in the trinocular tube, and use a "normal" camera lens on the 20D. (Although like you have mentioned... my philosophy is to use the least "glass" necessary). But at least this way you have a little control over the total relay magnification. A rough guide would be as follows (FL is the focal length in mm of the camera lens):

Total Relay Mag= (FL/250)*(Eyepiece Magnification)

Depending on the eyepiece and camera lens, it may be difficult to avoid some vignetting with this approach.
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