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rjlittlefield
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 Posted: Sun Jan 21, 2018 4:12 pm Post subject: |
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Big difference, but very confusing.
In the upper right corner, the 50 is much sharper and with less CA. In the lower left corner, the 50 still has less CA but the sharpness is reversed: 10 much sharper than 50. In the lower right corner the 50 has less CA and the sharpness is about the same. (There's nothing in the upper left corner to look at.)
At center, oddly, the 10 is noticeably sharper than the 50. The reason I say "oddly" is that at the center, changing separation should have no effect. If everything is properly aligned and all aberrations are radially symmetric, the same bundle of rays from the objective will go through the same part of the tube lens at the same angles, so you end up with the same image on the sensor.
Since they're not the same, it seems that something is in play besides separation. The 50 looks like it might be a bit motion blurred in an up/down direction. All the lines are sharp on one side, blurred on the other. Either that or you have some asymmetric aberrations in play, so the rotational angles of the lenses matter.
If these were my results, my next step would be to get a target with detail everywhere in the frame, and run another set of tests to see what parts of these results are even repeatable.
By the way, how are you illuminating these? In your earlier results, I noticed that the mid-to-dark grays have quite a bit of pixel noise. Lens tests are best shot at lowest ISO and with flash, to kill noise and vibration as much as possible.
--Rik |
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Adalbert
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ChrisR
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Adalbert
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| Posted: Mon Jan 22, 2018 6:50 am Post subject: |
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Hi Chris,
I have already seen that, you found. It is not bad :-)
But what about a square (1mm*1mm) with two diagonals (printed by the laser printer) for the LU Plan 20x ?
BR, ADi |
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rjlittlefield
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| Posted: Mon Jan 22, 2018 9:33 am Post subject: |
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| Adalbert wrote: | BTW, my current setup:
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Perhaps there is some distortion in the photo, but as shown, I have some concerns about possible misalignment:
Bellows are very convenient, but they are not very good at maintaining precise parallelism between the front and back standards. I would check with machinist's calipers to be sure.
The apparent misalignment between objective and tubes is more puzzling. For that I would check by rolling the tubes + objective on a flat surface and seeing if the objective wobbles.
| Quote: | | what about a square (1mm*1mm) with two diagonals (printed by the laser printer) for the LU Plan 20x ? |
A rectangle with 3:2 aspect ratio would be better, since that could hit all four corners.
But I suggest considering less highly structured solutions. in my own targets, the most useful part has turned out to be the "light gray" background, which the printer and photocopier have turned into a well distributed array of toner dots. See Tube lens tests on D800E full frame for illustration. An even more dense and uniform array of dots would be better, but that will give you the idea.
--Rik |
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Adalbert
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ChrisR
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| Posted: Mon Jan 22, 2018 5:13 pm Post subject: |
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They look very close to me. Good test, thanks Adi.
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Chris R |
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lonepal
Joined: 28 Jan 2017
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Chris S.
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| Posted: Mon Jan 22, 2018 11:25 pm Post subject: |
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Omer, the above represents a widespread misunderstanding of Mitutoyo literature. What Mitutoyo meant was that for optimal results, the objective should be placed within 76.5mm of the tube lens. Not at 76.5mm of the tube lens. If I recall correctly, Mitutoyo also provided a formula to help users who wanted more space than this estimate vignetting. They did not mean to imply that distances less than 76.5mm were sub-optimal. This misinformation seems to be based on an unfortunately-brief word choice in a Mitutoyo diagram or two, the need to dig into small print to understand what was really meant, and a writer at Edmund Optics who got it wrong. (Edmund Optics is a generally excellent source of information--this was unusual for them.)
Mitutoyo has expressly stated that shorter distances are just as good as 76.5mm. I can confirm this based on personal experience with a Mitutoyo tube lens and many Mitutoyo objectives.
Cheers,
--Chris S. |
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lonepal
Joined: 28 Jan 2017
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Location: Turkey
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| Posted: Mon Jan 22, 2018 11:38 pm Post subject: |
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Thanks for explaining Chris!
But it also says ''If the distance is too short, it may cause vignetting; if it is too long it causes dim image and dark images.''
Then what is the minimum distance?
I also used the Mitty 5X on a raynox as close as possible but there was no vignetting (APSC).
There is no clear information about this.
Bytheway I have no problem about the distance but this matter should be clarified I think 
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Omer |
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rjlittlefield
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| Posted: Tue Jan 23, 2018 12:09 am Post subject: |
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| Adalbert wrote: | Hello Rik,
I have tried to print a rectangle :-)
Tested with the LU Plan 10x / 0.30
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The new target is very nice.
The results are still troubling.
Upper left, quite similar.
Lower left, much sharper at 10 mm.
Lower right, much sharper at 50 mm.
Upper right, much sharper at 50 mm.
Center quite similar.
The bit about 50 being sharper in upper right but 10 sharper in lower left is the same as in your earlier tests.
The lower right corner is not consistent with earlier test, where the sharpness was about the same with the two extensions.
At this moment, my feeling is that quibbling over 10 mm versus 50 mm is maybe a bit pointless, given that the answer seems to depend on where and when you look.
For that same reason, I would be not at all inclined to generalize these results to anybody else's system.
--Rik |
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rjlittlefield
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| Posted: Tue Jan 23, 2018 12:15 am Post subject: |
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| lonepal wrote: | But it also says ''If the distance is too short, it may cause vignetting;''
...
Then what is the minimum distance? |
There is no such minimum distance. The person who wrote those words was apparently confused, because the statement is simply wrong. In this sort of system, vignetting is caused by making the distance too long, not too short.
(In other optical systems, for example coupling a camera to a microscope eyepiece, having not enough distance can indeed cause vignetting. It is a matter of matching the exit pupil of one lens with the entrance pupil of the next. With a microscope objective and a tube lens, the pupils are matched best at short distances; increasing the distance makes the mismatch worse, until finally it becomes bad enough to cause vignetting.)
--Rik |
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Chris S.
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| Posted: Tue Jan 23, 2018 12:30 am Post subject: |
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Omer,
I'd respond to your query, but Rik has done a splendid job already. I completely agree with him. 
--Chris S. |
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lonepal
Joined: 28 Jan 2017
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Location: Turkey
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| Posted: Tue Jan 23, 2018 1:29 am Post subject: |
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Rik and Chris;
Thanks for the explanations, that makes sense.
I understand the distance does not matter unless it is too long to cause vignetting.
For the optimal distance, we need Adi's test to finish
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Omer |
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Adalbert
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(more than 200mm between the camera and the lens)