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ofarcis
Joined: 27 Jan 2013
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Location: Madrid - Spain
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Blame
Joined: 14 May 2010
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 Posted: Fri Mar 07, 2014 7:37 am Post subject: |
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The Mitutoyo 5x NA 0.14 is an excellent lens but it does need a good tube lens to do its best.
Usually you will get best results with a fixed focal length lens rather than zoom. If you must use a zoom it usually has to be at its longest focal length to avoid vignetting.
Given that you are using the cropped sensor Canon 600D I would suggest a focal length of between 135mm and 160mm would be about right to get maximum center sharpness without loosing too much in the corners. That is about 3.5 to 4x. A lens will give the crispest pictures when used at an optimal magnification.
Options for a tube lens include the some camera lenses like the CZJ 135/3.5 and various 135/5.6 enlarger lenses. |
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jazzper
Joined: 29 Mar 2013
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Location: Copenhagen, Denmark
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| Posted: Fri Mar 07, 2014 8:02 am Post subject: |
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| Blame wrote: |
Given that you are using the cropped sensor Canon 600D I would suggest a focal length of between 135mm and 160mm would be about right to get maximum center sharpness without loosing too much in the corners. That is about 3.5 to 4x. A lens will give the crispest pictures when used at an optimal magnification.
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Isn't 5x the optimal magnification for a 5x objective? I mean, it must be the magnification on the sensor that counts, regardless of the crop factor, or have I missed something? 
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ofarcis
Joined: 27 Jan 2013
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| Posted: Fri Mar 07, 2014 8:19 am Post subject: |
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The sensor factor of 600D is 1,6x. If divide the 200mm (for this objective) / 1,6 = 125mm. Not really is exactly and can be from 120 to 140mm aprox.
Ok, i think is better to use 5x and not 3-4x.
The problem that Blame explain is the zoom lens can be crop the image. You see black rings in the corners.
Is a good idea to use enlarger lenses. Someone are use one for this propused? I have some Componon-S, Componan, Rodagon, etc. But only 50mm.
Someone that have an mitutoyo similar to mine, what lens use?
I have one friend that use Tamron 55-200 DI II Aspherical but i can't compare with my Canon Zoom Lens EF 70-210 because they live in Luxemburg and I live in Spain.
Regards, Oscar.
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jazzper
Joined: 29 Mar 2013
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| Posted: Fri Mar 07, 2014 9:01 am Post subject: |
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Yes, I have the same Mitu, and I use old Olympus lenses from the OM range: 100mm, 135mm and 200mm.
I just got a little bit thrown off by the crop talk, and I still don't get it, but that's another story 
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ChrisR
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| Posted: Fri Mar 07, 2014 9:04 am Post subject: |
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| Quote: | | Isn't 5x the optimal magnification for a 5x objective?... have I missed something? |
Yes  . A 5x infinite objective is only 5x when it's used with the intended "tube" lens, which for Nikon and Mitutoyo is 200mm (Olympus 180mm iirc).
One way of looking at it:
The "tube" lens is making the objective's image circle suit the eyepiece, sensor or whatever's downstream. If you make the good quality part of the image circle "just" fit your sensor, that's better than enlarging the middle and losing peripheral information.
It happens that many infinite objectives will cover an aps-C or DX sensor just about right, with a "tube" lens about 135mm. That gives
magnification = 5 *135/200 = 3.375x , with a "5x" objective.
You're right in your suggestion that magnification is only really useful if you know the sensor size. If you use a larger sensor, you'd need a longer "tube" lens to cover it all, which would apparently increase the magnification (say to 5x, with a 200mm "tube" lens) . But you still have the same subject size, filling the sensor in both cases.
So scratch "5x" off your Mitty and write "Quarter inch field" on there instead! |
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jazzper
Joined: 29 Mar 2013
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| Posted: Fri Mar 07, 2014 9:46 am Post subject: |
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| ChrisR wrote: | | Quote: | | Isn't 5x the optimal magnification for a 5x objective?... have I missed something? |
Yes . A 5x infinite objective is only 5x when it's used with the intended "tube" lens, which for Nikon and Mitutoyo is 200mm (Olympus 180mm iirc).
One way of looking at it:
The "tube" lens is making the objective's image circle suit the eyepiece, sensor or whatever's downstream. If you make the good quality part of the image circle "just" fit your sensor, that's better than enlarging the middle and losing peripheral information.
It happens that many infinite objectives will cover an aps-C or DX sensor just about right, with a "tube" lens about 135mm. That gives
magnification = 5 *135/200 = 3.375x , with a "5x" objective.
You're right in your suggestion that magnification is only really useful if you know the sensor size. If you use a larger sensor, you'd need a longer "tube" lens to cover it all, which would apparently increase the magnification (say to 5x, with a 200mm "tube" lens) . But you still have the same subject size, filling the sensor in both cases.
So scratch "5x" off your Mitty and write "Quarter inch field" on there instead! |
Sorry to say Chris, that didn't help me much!
I am fully aware that I need a 200mm for my Mitu to get 5x. I was just under the impression that Blame says that 5x isn't the optimal magnification for a 5x objective, which sounds strange to me.
Regarding the crop talk, I don't think about that at all: 5x on the sensor is 5x no matter how big the sensor is! I'm not talking about filling any odd sized sensor with a given subject.
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ChrisR
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| Posted: Fri Mar 07, 2014 9:51 am Post subject: |
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| EErrm, well it's NOT optimal if it fills MORE than the sensor. Yes? |
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jazzper
Joined: 29 Mar 2013
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| Posted: Fri Mar 07, 2014 9:56 am Post subject: |
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| ChrisR wrote: | | EErrm, well it's NOT optimal if it fills MORE than the sensor. Yes? |
That's another story.
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rjlittlefield
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| Posted: Fri Mar 07, 2014 11:28 am Post subject: |
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| jazzper wrote: | | I was just under the impression that Blame says that 5x isn't the optimal magnification for a 5x objective, which sounds strange to me. |
Let me try.
Each objective has an optimal distance from subject. That distance is determined by the objective's design; it serves to minimize aberrations.
At that distance, the objective covers a certain size circle on the subject with a high quality image.
After that, what's "optimal" depends on what you mean by that word.
Assuming that you do not have a particular subject in mind, then optimal usually means making the sharpest image.
Making the sharpest image is accomplished by adjusting the image size so that the circle of high quality just fills the sensor. If you make the image bigger than that, then you crop off detail around the edges without picking up correspondingly more in the middle. If you make the image smaller than that, then the corners go bad.
So no, 5X is very often not the optimal magnification for a 5X objective. The optimal magnification depends on the sensor size.
ChrisR's suggestion to "scratch "5x" off your Mitty and write "Quarter inch field" on there instead!" is a brilliant way of capturing the concept. If a particular objective covers a quarter inch field with high quality image, then its optimum magnification is whatever spreads that quarter inch across the whole sensor.
--Rik |
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ofarcis
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rjlittlefield
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| Posted: Fri Mar 07, 2014 11:51 am Post subject: Re: Mitutoyo M Plan APO 5x + Canon EF 70-210mm |
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I am confused by your conclusion. Here are crops from center and edge, shown at 200% to make the differences obvious.
Center:
Edge:
To my eye, the Mitutoyo is noticeably sharper in both areas, with strikingly less CA on the edge.
The main advantage of the Mitutoyo will probably be in chromatic aberration, not sharpness -- especially at image center. This difference is more obvious with some subjects than others. If you photographed a halogen light bulb filament, I expect you would see big differences in the amount of false color.
--Rik |
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rjlittlefield
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| Posted: Fri Mar 07, 2014 12:09 pm Post subject: |
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| ofarcis wrote: | | There is some mathematical formula to calculate what the proper magnification for optimum sharpness and details or otherwise it is necessary to test until it is? |
You have to test, to determine how big is the circle of high quality image.
Once you have that number, it is a simple division to determine the appropriate magnification: sensor diagonal divided by field diameter.
In quick testing just now (live view only), my Mitutoyo 5X seems to have a high quality circle that is about 11mm diameter on subject. That is, the corners look pretty good on my Canon T1i (22.3 x 14.9 mm) when used at 2.5X on a Canon 100mm f/2.8 L IS USM focused at infinity.
One thing to watch out for: center quality is pretty tolerant of focus changes in the rear lens, but corner quality may change much more. For best results, test what rear lens focus gives you the best corners. If you don't have time or inclination to test, then infinity focus is your best bet.
--Rik |
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Blame
Joined: 14 May 2010
Posts: 342
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| Posted: Fri Mar 07, 2014 12:23 pm Post subject: |
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| ofarcis wrote: | Ok, Rik.
There is some mathematical formula to calculate what the proper magnification for optimum sharpness and details or otherwise it is necessary to test until it is?
For example, in my case the sensor size is 22,3x14,9mm.
Regards, Oscar. |
Well not exactly. More experience and rule of thumb. The mitutoyo 5x is supposed to have a field of view of a 4,8mm circle. That is the manufactures specification.
In practice it can deliver about a 6.3mm circle without significant degradation and, with the right tube lens, up to 12mm with blurred corners.
22.3/6.3=3.54 so you need something like 3.5x magnification to keep sharp sides with slight loss of resolution in the corners. A fair compromise. As a 135mm tube lens gives 3,4x and it is a common length for lenses it will do. Tube lens focal length doesn't need to be exact. You can fine tune by adjusting tube length. |
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