JML 21mm f/3.5 manufacturers' specs

[Bob^3]

In case this was missed at the end of Charles’ first JML post, here it is again (see last lens in list):








If this is the lens (they said they were 99% sure), it appears to be optimized for 12x (nominal reduction ratio?), with a resolution of 200 DPI (dots per inch). I did not ask why they spec. this series in DPI, instead of the usual LPM. I normally associate DPI with printer resolution or (more rarely) monitor resolution. Regardless, considering the tests done so far, 200 DPI would seem to be very low value for this lens. However, if that resolution refers to the performance at 12x magnification, that may indeed be the case, E.F = (12+1)3.5 = f45.5 (if the lens is symmetrical).

I’m also not sure what is meant by the 21-degree “half angle” spec. Is this half the more typically used ‘angle of view’ which relates the effective focal length to the image format (i.e. image circle) when forming an image of an object at infinity?

Rik, HELP!

[elf]

What strategy shall we employ to get some B-series lens to test?

[rjlittlefield]

Bob, I had missed the end of Charles' thread. Thank you for the repost and the reference.

I assume you sent JML a picture of your lens, or pointed them to one.

Regardless, it would be good to point out that our copies do not look exactly like the illustrations for either A or B Series, and inquire whether it does match the mount for their part # WFL20414. I can easily imagine that different lenses in the series have somewhat different mounts, but it would be nice to have them say that it appears to be an exact match to that particular lens.

I confirm that the lens I have is 27.0 mm OD and 28.9 mm in length, so at least the dimensions match.

I have no idea why JML specified these lenses as "dots per inch". It makes no sense to me in terms of the nominal reduction ratio, since the ratio for some lenses is specified as "infinity".

Perhaps they have a ready answer for that question, if asked.

I tried putting WFL20414 into their web site's Search box. It matches the format they specify for part number, but nothing is found.

I would be curious to know if that lens is still being made, and if so how can they be purchased and at what price. Likewise for the higher quality B Series lenses, as elf suggests.

Regarding "half angle", I would interpret that as you did except for the part about "object at infinity". The usual formulas for relating angle of view to focal length and sensor size do depend on infinity focus, but to my understanding the key measurement really is the angles of rays as they pass through the lens. Extending a symmetric lens to give 1:1 reduces its angle of view to about half, but in exchange the diameter of its image circle about doubles. The maximum angles through the lens remain constant.

I hope this helps. Thanks for tracking down all this info. I look forward to seeing what else turns up.

BTW, I notice that morfa's lens has a long axial scratch extending from the "L" of JML to the end of the lens barrel. Mine does too. Do other people's?

--Rik

[seed]

Mine does not.

[Bob^3]

What strategy shall we employ to get some B-series lens to test?

Hmmm...good point, elf. If their B-series (400DPI) lenses have the same chromatic optical qualities as the A-series (200DPI), with twice the resolution…

Here is my last email to the “Director -Catalog Division”.

2nd email:
I thank you very much for the information. It will help with the intended application for this lens, which is to form well-corrected, high-resolution images on CMOS sensors with image circles between 24 mm and 43 mm at on-sensor magnifications from 4x to 9x. Preliminary tests show excellent correction for chromatic aberration and very good resolution across the field at 4x to 6x magnification. In fact, it seems to out perform many traditional dedicated macro lenses in this role. Also, the resolution would appear to be considerably better than your specification states, at magnifications below 12x.

I was simply curious regarding the intended applications for this lens. The test results made me wonder whether this might be one of your many custom tailored lens designs.

3rd email:
Actually, I will add that there are a number of other folks, with considerably more experience and knowledge of optics than I, currently testing this lens. Many of them including me were previously unfamiliar with JML Optical.

While I cannot guaranty any new sales for this lens, I can perhaps offer a bit of well deserved visibility for your company. Depending on the final test results and your price point for small quantities, you may receive some additional sales.
Regards,

He has a Confidentiality Notice in his signature, so I will not quote his responses here.

I did not fully disclose the intended purpose for this lens or mention the existence of this forum (of course, they may find it by Googling their name). Obviously, some companies might take a dim view of their products being discussed in this manner, especially considering the lenses were acquired on eBay for $10 each! On the other hand, some companies might welcome it as free publicity. I suspect there are many in this forum that, like me, use optical components in their profession. So they might be OK with the concept.

Maybe we could make a group buy, which might justify a B-series sample?

[Bob^3]

I assume you sent JML a picture of your lens, or pointed them to one.

Yep...four images from all angles and all dimensions (the same as yours, BTW - and both of mine have scratches).

I would be curious to know if that lens is still being made, and if so how can they be purchased and at what price. Likewise for the higher quality B Series lenses, as elf suggests.

Yes, he indicated these were standard catalog products and asked if I needed more.

OK I'll write him back. He seemed very cooperative and I truely do have a professional (as well as hobby) interest in their lenses, for process inspection systems I work with.

Do you think it would be wise to send him a link to this forum? From my personal point of view, I generally feel it's best to be completely open regarding intentions---beside, he might just be a photographer himself and get a kick out of it!

[rjlittlefield]

Do you think it would be wise to send him a link to this forum? From my personal point of view, I generally feel it's best to be completely open regarding intentions---beside, he might just be a photographer himself and get a kick out of it!

Sure, send him some links. Be sure to include a couple of topics that include the intended sort of photos, like Charles Krebs' and morfa's.

You know, one of the odd features of this field (macro photography) is that most of the best lenses are from days gone by. Aside from microscope objectives and the MP-E 65, I cannot offhand think of any lens that shoots for optimum performance in the 1-10X range using modern design and manufacturing techniques. Perhaps there's an opportunity here.

--Rik

[enricosavazzi]

BTW, I notice that morfa's lens has a long axial scratch extending from the "L" of JML to the end of the lens barrel. Mine does too. Do other people's?

--Rik

Mine does have the scratch. I have seen internal lens barrels with comparable scratches, as well as optical elements with comparable pencil marks on their girdles. I believe these marks are made while centering a lens element and/or to indicate the proper relative orientation of two elements/groups/subassemblies.

[morfa]

Very interesting – thanks for pursuing the investigation Bob!

About the scratches: I got three of these lenses (to justify the shipping) and two of them are scratched on the barrel. I thought I made them when opening the package!

[shrek]

Hi
I am new on the forum , and I found It wonderfull
I Find the price of Objective , and I am surprised with the diffence 10 dollars VS 300!


21 4 20 21 22 6 18x WFL20415 / 100 300,00 $


best regard

jean pierre

[Bob^3]

Well, I did ask some additional questions of the JML rep. Once again, due to his Confidentiality Note, I will not quote his direct answers. However, since none of this appears to be in any way proprietary, I'll just rephrase the answers.

I have some further interest in both these series of Wide Field lenses. Upon review, I have a few additional questions regarding the identification and stated specifications of 21mm f/3.5 lens, as well as more general questions.

I noticed that the part number you reference is for an A-Series lens. However, the overall physical form (barrel shape) more closely matches the B-Series diagram (there is no extension on the actual lens, as shown in the A-Series diagram), even though the measured length and diameter of part # WFL20414/100 do closely match the actual lens. Is it possible this is a B-Series lens, optically; or are there cases where A-Series optics are installed in B-Series barrels? Is it possible to verify whether or not the lens is an exact match for part # WFL20414/100?

Ans: All 21mm f/3.5 lenses are A-series the diagrams are for illustration only. There is a difference in resolution between the A and B series. Still 99% sure that the lens is WFL20414/100.

I do not fully understand the use of dots per inch (dpi) callout for resolution in this context---instead of the more usual lines per mm (lpm or lp/mm) used with most of your other lens specifications (e.g. here http://jmloptical.com/downloads/MultiElementListing.pdf). I normally see dpi resolution in reference to output devices such as printers and (sometimes) monitors. Further, I do not know how to mathematically relate dpi to lpm for lenses. Could you please explain the criteria used to determine these values?

Ans: Best translation he can offer, 200 dpi is equivalent to 2 lpm in the object plane, 400 dpi is equivalent to 4 lpm. However for WFL20414/100 at 12x reduction ratio, that would be 12x2 lpm in the image plane. The lens is designed for 12x reduction ratio, but other reductions or magnifications will work.

Are all of the A-Series lenses rated at the same resolution (200 dpi) and the B-Series (400 dpi) - other than ones stated below the chart?

no specific answer

Do you perhaps have lpm or lp/mm values for the 21mm f3.5 and for both the A- and B- lens series---along with MTF data or charts?

see above---no answer WRT MTF data

Are the lenses listed available off-the-shelf, especially the 21mm f/3.5? If so, what are the current prices of the ones not listed (like the WFL20414/100) in your pricing here:
http://jmloptical.com/product/Wide%20Fi ... 20DPI.aspx
and here:
http://jmloptical.com/product/Wide%20Fi ... 20DPI.aspx
Entering WFL20414/100 or WFL20414 in the JML search box shows no matches.

Ans: Currently 2pcs in stock at $300/ea

The scratches on the lens barrels mark the best "focal plane" for resolution for document scanning and imaging applications.

In my next email, I will provide links to appropriate threads in this forum and propose Rik’s idea of the possibility of JML supplying state-of-the-art lenses designed specifically for photomacrography, or at least of testing more of their off-the-shelf parts for this purpose. Who knows, it might just become a nice niche business for them---not to mention the possibility of raising the bar in macro photography! I have absolutely no idea what the worldwide market might be for true macro lenses. Perhaps the admins here have some estimate based on number of hits on this site? Or we could do an eBay history search.

Is it OK to ask them if they might be willing to participate in a forum discussion on this, so all the members can have input?

BTW, I ordered 3 more of these before Charles and John (morfa) posted their great images which instantly increased the vapor pressure of the remaining lenses, causing them to evaporate!

p.s. Actually, perhaps it would be better if we write a joint email to JML on the forum prior to sending, so we can have a member consensus?
Regards,

[Bob^3]

I just cross referenced the stock number (61580) given by the JML rep for part # WFL20414/100 to the full pdf stock list on their site, which I think gives more interesting data than the catalog list (highlighted):




This indicates it's an f/3.1 lens with a limiting resolution of 180 lpm.

I'd like to get my hands on stock # 67300...smaller angle of view, but faster f/2.8 and much higher resolution.

[PaulFurman]

Bob, I found an excel sheet there with the same data:
www.jmloptical.com/downloads/MultiElementListing.xls

Also, searching 'wide field' on their site gives:
http://www.jmloptical.com/products/Wide ... es%20.aspx
Where the prices are all around $300 to $400 for similar spec'ed lenses, and the 21/3.5 is not included... of course they're out now so...

I suspect the scratches might mean they were rejects from some specific project. Mine has other dings on the mounting lip area as well and the long scratches could only mark rotation, which shouldn't matter for whatever use.

Still, that's not a bad price for a great 35mm macro lens. There's a 35mm f/2.8 for $400 rated for 5x and the same 'half angle' of 19 as this (if that means image circle), and similarly, the excel data doesn't quite have a match but shows a 35.3mm f/2.8 for 7x with half angle of 14.7 (close) and double the mtf.

If I weed out lenses with less than the resolution of the 21/3.8 and half angles lenss than 12, apertures less than f/3, I get this list:

INDEX OF JML LENS SYSTEMS
(mm) ANGLE MTF AXIS MTF EDGE LIMITING
STOCK # EFL F/# MAGNIFICATION HALF RESOLUTION RESOLUTION RESOLUTION
(degrees) ( lp/mm – contrast) ( lp/mm – contrast)
29300 4.8 2.0 0.0X 41.5 125-.70 125-.50 200 lp/mm
29300 5.1 2.0 0.0X 41.5 125-.70 125-.50 200 lp/mm
54230 11.2 2.2 65.9X 15.5 150-.24 150-.18 200 lp/mm
51990 11.4 2.8 72.0X 16.2 160-.53 160-.48 400 lp/mm
51150 11.5 2.5 48.0X 19.0 170-.21 144-.21 300 lp/mm
54960 13.1 1.1 25.5X 14.5 80-.58 50-.62 180 lp/mm
53150 14.0 2.5 21.7X 14.3 60-.78 60-.68 400 lp/mm
69350 14.2 2.2 48.0X 14.5 140-.70 140-.34 220 lp/mm
54160 15.4 2.5 45.0X 16.7 180-.48 180-.32 400 lp/mm
55080 15.5 2.8 42.0X 18.4 160-.45 150-.20 240 lp/mm
59140 16.5 2.8 42.0X 29.1 120-.42 120-.22 180 lp/mm
60590 16.5 2.8 42.0X 29.1 100-.28 100-.22 180 lp/mm
24100 17.0 2.8 0.0X 13.2 55-.74 55-.52 200 lp/mm
53900 17.2 2.8 48.0X 16.1 140-.55 140-.43 300 lp/mm
54810 17.4 2.8 44.2X 15.0 120-.38 120-.31 200 lp/mm
55060 17.5 2.8 37.0X 18.4 160-.24 150-.26 240 lp/mm
60320 19.2 2.5 24.0X 17.8 120-.62 120-.25 220 lp/mm
54430 19.7 2.8 42.0X 14.2 160-.60 160-.26 240 lp/mm
53970 19.9 2.8 32.0X 15.1 120-.51 120-.52 300 lp/mm
51090 19.9 2.8 36.9X 16.0 120-.52 120-.48 340 lp/mm
55040 20.4 2.8 31.5X 18.5 142-.28 125-.20 200 lp/mm
50560 21.9 2.3 42.0X 18.3 100-.58 100-.25 200 lp/mm
50580 22.0 2.8 42.0X 18.3 120-.22 100-.15 200 lp/mm
50790 23.2 2.8 42.0X 15.2 144-.42 144-.42 220 lp/mm
50620 23.5 2.3 39.0X 18.1 120-.34 120-.18 200 lp/mm
70124 25.3 2.8 24.0X 15.6 100-.55 100-.43 300 lp/mm
55020 26.2 2.8 24.0X 18.6 120-.22 108-.20 180 lp/mm
51190 29.0 2.8 24.0X 17.4 140-.55 140-.23 240 lp/mm
58850 29.7 2.9 22.9X 16.9 80-.74 80-.56 220 lp/mm
62901 29.7 3.0 24.0X 18.6 200-.20 120-.20 220 lp/mm
76990 35.3 2.8 7.0X 14.7 90-.48 90-.36 300 lp/mm
54670 37.0 2.8 24.0X 13.3 170-.28 150-.26 240 lp/mm
54250 90.0 3.0 24.0X 16.6 80-.26 80-.26 200 lp/mm

One thing that's odd is the resolutions should not be possible due to diffraction at the given magnification for many of these, so I don't think we're interpreting quite right. I haven't worked the numbers but someone said 5x at f.3.5 max, not the 12x design spec for 180lp/mm mtf. Don't quote me on all that but it seems in the ballpark. Last one on the list is a 90mm f/3 for 24x which doesn't sound possible given the amount of extension you'd need for 24x with a 90mm lens.

[Bob^3]

I suspect the scratches might mean they were rejects from some specific project. Mine has other dings on the mounting lip area as well and the long scratches could only mark rotation, which shouldn't matter for whatever use.

The JML rep did say that the scribe mark (linear scratch) on the lens is to allow certain customers to rotationally align the lens for optimum “focus plane” for flat line copy (type) imaging and printing applications. So, there is likely some asymmetry to the plane of focus. It may just be simple field curvature that will be fully mitigated by stacking methods; or it could be a more significant form of aberration (such as coma) that will not allow proper focus toward the outside of the frame. It might be good for each member to test their copies to determine what effect the oreintation of the scribe line might have on their particular subjects of interest.

Also, I am seeing some copy to copy variation in my five JML lenses. Nothing major and I can’t scientifically quantify it yet---but my first copy seems to be somewhat less sharp in the corners below 6x on the Nikon D700, even as I rack through focus. The other four copies are better. Two look really good in 4x to 5x range. I haven’t tried to measure changes in field curvature at different magnifications, yet.

Regards,

[PaulFurman]

My mount is actually a rubber piece that snugs into a reversing adapter, so that allowed me to try tilts and it seems to hold up to quite a bit of tilting with still no vignetting. This suggests the image circle is quite large.