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conkar
Joined: 18 Dec 2010
Posts: 200
Location: Sweden
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 Posted: Sun Mar 18, 2012 5:20 am Post subject: |
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| ChrisR wrote: | Sorry, my mistake, then , there's something else going on??
I took them both into photoshop, and put one on a layer above the other.
Setting the upper blending mode to "difference" and the entire picture looks black.
They are different on closer inspection, but the RGB values are all under about 10.
Have you used some software to align the images and match the colours, or something?
I always find it hard to compare images because of minor lighting, dimensional or colour diffrences, so I'm intrigued to know how you did it! |
The illumination used for these pictures was 4 IKEA jansjö LED-lights WB 3000 kelvin.
Zerene Stacker Pmax was used to stack the images.
I liked to treat the images equivalent so I let photoshop handle most of that by it's auto functions.
- Auto tone,- Auto contrast, - Auto color, Auto levels and 100% unsharp mask.
I then finally cropped out the stacking artifacts from the lower and right border by my eyes.
Regards,
Conny |
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conkar
Joined: 18 Dec 2010
Posts: 200
Location: Sweden
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| Posted: Sun Mar 18, 2012 5:25 am Post subject: |
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| ChrisR wrote: | | Just to be clear, I'm not accusing you of cheating! |
I did not think that was the case. 
| naturephoto1 wrote: | | ChrisR wrote: | | Just to be clear, I'm not accusing you of cheating! |
Hi Chris,
I do not think that what Conny was suggesting at all. I think what he meant was that this was supposed to provide blind test results, but that there are ways to "cheat" to figure out which lens was which.
Rich |
You are right Rich, it's what I meant and it was a hint to to those who could not wait until I revealed how the images belonged to a particular objective.
Update: Now I have updated the images and labeled the pictures with the objectives as they related to.
Regards,
Conny |
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BugEZ
Joined: 26 Mar 2011
Posts: 796
Location: Loves Park Illinois
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| Posted: Fri Mar 23, 2012 8:18 pm Post subject: |
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I purchased one of these lenses and I am pleased with the results on my Pentax *ist (small sensor). I have used it mounted in front of a 200mm telephoto. Previously I have used a 20X Olympus lens on extension tubes. I don't own the proper tube lens to pair with the OLY and so it has not produced good images. The color aberration with the JML + 200mm tele is much less and the sharpness is very good. The working distance is satisfactory. I like the narrow profile as it provides access for lighting the subject from the front.
In the net this was an inexpensive upgrade to my equipment.
Kind regards,
Keith |
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Craig Gerard
Joined: 01 May 2010
Posts: 2877
Location: Australia
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| Posted: Fri Mar 23, 2012 9:43 pm Post subject: |
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Keith,
Do you have an image taken with the JML 20X that you would consider uploading?
Craig
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To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!" |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 20250
Location: Richland, Washington State, USA
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| Posted: Sat Mar 24, 2012 2:23 am Post subject: |
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My copy of the JML 20X came yesterday. Here's what I see.
1. The JML 20X does not conform to any standard that I know. When used on a 200 mm tube lens, it delivers 17.3X. I can get 20X by using it finite, on 222mm total extension from sensor to shoulder of mounting threads.
2. The working distance is about 12 mm.
3. At 20X and finite, on an APS-C sensor, the image quality is about the same as my Nikon CF M Plan 20X NA 0.40 ELWD 210/0, except that the JML has significant lateral CA easily visible as color fringes in the corners. This CA can be almost completely canceled by a Photoshop lens correction filter with "Fix Red/Cyan Fringe" pushed clear left.
Sample moth wings (almost the same area) can be seen here:
JML on 222 mm extension
Nikon CF M Plan 20X NA 0.40 ELWD on 200 mm extension
Flash exposure for the Nikon lens was about 2/3 stop less than the JML. I don't know whether this reflects a smaller aperture in the JML, some difference in the way the light reached the subject, or a difference in transmission of the lenses. Given the smaller diameter of the JML, I would have expected it to go the other way if light were being blocked, but I did not investigate carefully. [Update: It's due to a smaller aperture. The JML measures NA 0.30. See HERE later in this same thread.]
The JML lens seems like a good buy at current prices ($55 plus shipping) but I don't believe it would come close to a Mitutoyo 20X when viewed at actual pixels.
--Rik
Last edited by rjlittlefield on Thu Apr 26, 2012 1:38 am; edited 1 time in total |
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BugEZ
Joined: 26 Mar 2011
Posts: 796
Location: Loves Park Illinois
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| Posted: Sat Mar 24, 2012 6:01 am Post subject: |
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Craig Gerard wrote:
| Quote: | Do you have an image taken with the JML 20X that you would consider uploading?
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I posted several shots of a weevil here
http://www.photomacrography.net/forum/viewtopic.php?t=16462
The last photo is with the JML.
I think Rik's posting above where the lens is compared to another lens is quite helpful for contrasting the JML's strengths and weaknesses.
Keith |
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BugEZ
Joined: 26 Mar 2011
Posts: 796
Location: Loves Park Illinois
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| Posted: Sun Mar 25, 2012 10:19 am Post subject: |
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Rik wrote:
| Quote: | | the JML has significant lateral CA easily visible as color fringes in the corners. This CA can be almost completely canceled by a Photoshop lens correction filter with "Fix Red/Cyan Fringe" pushed clear left. |
I don't own Photo Shop but I do have the ability to adjust for color aberration (CA) in the software that was shipped with my camera. This software is what I use for RAW to JPG conversion.
I found a single image that contained a well focused CA artifact near the edge of the frame. I played around with the CA settings (separate adjustments for red and blue) till I found the right "formula" to reduce the CA in the converted images. Finally I used the new settings and re-converted the RAW stack and combined them with Zarene.
The CA is substantially reduced and the sharpness at the boundaries is somewhat improved.
This has moved my impression of JML from the "glag I bought it" catagory to "very glad I bought it".  Thanks for the tip!
I particularly like the CA artifact illustrated as it also makes a smiley face!
Keith |
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g4lab
Joined: 23 May 2008
Posts: 1434
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| Posted: Sun Mar 25, 2012 10:23 am Post subject: |
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| There is a finite tube length standard for metallurgical scopes that has a tube length of 210 or 215mm I have some Nikon 210s and Leitz used 215 and I think others did too. |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 20250
Location: Richland, Washington State, USA
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| Posted: Sun Mar 25, 2012 11:33 am Post subject: |
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| g4lab wrote: | | There is a finite tube length standard for metallurgical scopes that has a tube length of 210 or 215mm I have some Nikon 210s and Leitz used 215 and I think others did too. |
True, but those are physical tube length. The total extension from shoulder to sensor is about 10 mm less due to the image being formed that far down inside the tube. The Nikon 210's deliver rated magnification at 200 mm extension, but the JML "20X" is more like 18X in that configuration.
--Rik |
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seta666
Joined: 19 Mar 2010
Posts: 867
Location: Castellon, Spain
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| Posted: Sat Mar 31, 2012 3:03 am Post subject: |
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| rjlittlefield wrote: | | Flash exposure for the Nikon lens was about 2/3 stop less than the JML. I don't know whether this reflects a smaller aperture in the JML, some difference in the way the light reached the subject, or a difference in transmission of the lenses. Given the smaller diameter of the JML, I would have expected it to go the other way if light were being blocked, but I did not investigate carefully. |
Could this lens be a 20/0.30 then? I remember seeing a JML 20/0.30 in their catalogue but I could not find it anymore.
NA 0.30 around f1.6 NA 0.40 around f1.2, 2/3 EV difference
Regards
Javier
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 20250
Location: Richland, Washington State, USA
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| Posted: Sun Apr 01, 2012 12:49 pm Post subject: |
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| seta666 wrote: | | Could this lens be a 20/0.30 then? |
Could be. I measure the front element as 9 mm diameter = 4.5 mm radius. Combined with working distance of 12 mm, this implies NA of 0.35 or less. (0.35 = sin(atan(4.5/12))
--Rik |
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seta666
Joined: 19 Mar 2010
Posts: 867
Location: Castellon, Spain
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| Posted: Sun Apr 01, 2012 3:08 pm Post subject: |
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| rjlittlefield wrote: | | seta666 wrote: | | Could this lens be a 20/0.30 then? |
Could be. I measure the front element as 9 mm diameter = 4.5 mm radius. Combined with working distance of 12 mm, this implies NA of 0.35 or less. (0.35 = sin(atan(4.5/12))
--Rik |
nikon 20X SLWD has NA 0.35 but 20mm WD, still a NA of 0.35 for a lens with a WD of 12mm seems pretty good.
However exposure difference should be around 1/3 of a stop, unless lens light transmission is very different
A couple of single shots with a continiuos light source would tell you for sure the difference ( just if you want to give it a try it ;-)
Regards
Javier
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 20250
Location: Richland, Washington State, USA
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| Posted: Sun Apr 01, 2012 4:26 pm Post subject: |
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| rjlittlefield wrote: | | I measure the front element as 9 mm diameter ... this implies NA of 0.35 or less |
As with most lenses, the entrance cone does not utilize the whole diameter of the front element.
Running light backwards through the lens, I measure the cone of light as 7.8 mm diameter at 12.2 mm distance from focus. That calculates to NA 0.304, within measurement error of 0.30 but not 0.35.
--Rik |
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naturephoto1
Joined: 13 Nov 2011
Posts: 509
Location: Breinigsville, PA
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naturephoto1
Joined: 13 Nov 2011
Posts: 509
Location: Breinigsville, PA
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