Telecentric Lenses and IQ

mawyatt · Post by **mawyatt** » Fri Feb 17, 2017 6:43 am

I have been reading about telecentric lenses and believe I’ll need to use them under 5X for my stack and stitching chip imaging efforts coming up.

I have Mitutoyo 5, 10 & 20X which I understand from Rik & Peter are close to telecentricity (if that's a proper word) by themselves. I often use the Mitty 5X with Raynox 250 and this gives me 3.125X which if the 5X is close to telecentric, then it should be at 3.125X also.

The usual assortment of Nikon lenses collected over many years; 50 f1.4 & 1.8, 85 f1.8, 105 f2.8 & 300 f4, 16-35 f4, 24-70 f2.8 and 70-200 f2.8. Also a 1.4 teleconverter, a Rokinon 135 f2, Kenko extensions tubes and a 42mm Iris, that I could employ to help cover the lower magnification ranges.

IQ is extremely important to me with the chip images, so achieving telecentricity & IQ at the lower magnification ranges (1~5) may prove to be very difficult, at least for me, thus my request for some guidance.

What would the community recommend for creating telecentric lenses covering the 1~5X range with the basic lenses I have, believe I have 3X covered with the Mitty and Raynox 250. IQ is very important, maybe more so than absolute telecentricity.

I'll probably use a Nikon DX (D500) format camera, although I do have an FX (D800E) I could also use.

Any advice is greatly appreciated.

Best,

Mike

austrokiwi1 · Post by **austrokiwi1** » Fri Feb 17, 2017 12:05 pm

The SK 210/5.6 has good resolution but suffers from CA so I think that lens would be a non-starter for you. From my discussions with Lou Jost I believe ( but have not confirmed) that the SK APO Componon 150mm HM might be an option. The front element of the 150mm is around 43mm in diametre, it is not as good as the 210's 70mm front element but it still is a usable diameter. I would anticipate the resolution would be better and the CA near non existent with the 150mm

mawyatt · Post by **mawyatt** » Sun Apr 23, 2017 8:30 am

Thanks austrokiwi1.

I should mention I have the Nikon PB6 bellows also. I use it with the Raynox 250 reversed and Mitutoyo 5X with good results at 3.125X.

I've tried the Rokinon 135 with reversed Nikon 50mm F1.8 and IQ was pretty good but not as good as the Rayonx 250 and Mitutoyo 5X. I had a Mitutoyo 2X but it wasn't very good with Raynox 150 IMO, thus I don't have it anymore.

I also have a Nikon 105 F2.8 VR which with Kenko extensions and 1.4 Teleconverter can cover 1~2X, but not sure the IQ can't be improved with another lens combo.

Any advice from you and the other lens experts is greatly appreciated.

Best,

Mike

Lou Jost · Post by **Lou Jost** » Sun Apr 23, 2017 9:17 am

If you reverse a lens on your Rokinon, you could put a telecentric stop in the front focal plane of the reversed lens. You can accurately place the aperture using step up and step down rings threaded into the insides of step-down rings mounted on the lens front. For low m you might consider reversing the 70mm Sigma macro lens, or the 50mm Oly f/2.0 macro lens. Both are among the best macro lenses ever, and the Oly is also one of the fastest, giving you more room to stop down a couple of stops to eliminate aberrations without getting diffraction. It also has a very convenient front focal plane location-- an aperture sitting directly on the lens front makes it very close to telecentric.

If you wait a while I will be testing a very similar set-up soon. I bought the new Sigma Art 135mm f/1.8, which is sharper (even at f/1.8) than the Zeiss 135 Apo Sonnar and your Rokinon, but your Rokinon has less CA. I will test the two macro lenses I just mentioned, and the Oly 90mm f/2 macro, reversed with telecentric stops. I'll report them here.

mawyatt · Post by **mawyatt** » Sun Apr 23, 2017 9:46 am

Lou,

The Nikon 50 F1.8 was reversed on the 135, gave very good results but not as good as the Mitty 5X with the Raynox 250 reversed. I found the best results @ f5.6 on the reversed 50mm F1.8.

Yes, the new Sigma Art lenses are some of the best optics available, and the 135 reviews has been stellar. When I got the Rokinon last year and did some tests, it showed sharpness across the full FX frame like I had never seen, stunningly sharp...and your new Sigma Art is even better (not to mention the AF which the Rokinon doesn't have, but doesn't matter for our macro use).

Last year I went to Lens Compare to "see" how the Rokinon compared to the Zeiss, that's when I placed my order!! I figured it might make a good "tube" lens for my Mitty's, unfortunately it does not!!

Anyway, looking forward to your test and evaluations.

If this doesn't work out well, you can always just hand draw the images

Were those drawings for the cataloging of the new species?

Best,

Mike

Lou Jost · Post by **Lou Jost** » Sun Apr 23, 2017 10:18 am

Mike, your Rokinon is actually better than the Zeiss and Sigma in terms of chromatic aberrations. I am curious, what was wrong with your pictures when you used it as a tube lens? I would have expected it to be excellent.

Yes, those drawings are the most important part of botanical publications that officially describe new species. So a lot of my macro photography is just an intermediate step in the making of these drawings (or sometimes color paintings) of my new species.

mawyatt · Post by **mawyatt** » Sun Apr 23, 2017 11:03 am

Lou,

It (Rokinon 135) just wasn't nearly as sharp as with the Raynox 250 reversed when using the Mitty 5X. It did perform well with a reversed Nikon 50mm F1.8, just not quite as good.

I think someone (Beasty ?) got a Rokinon 135 after I posted how intrinsically sharp it was last year and found the same result with it as a tube lens.

Believe it may be due to the way the image plane is created for the sensor. With the Rokinon it must be highly corrected to give such sharpness across the lens at full frame, thus a very flat plane and maybe highly sensitive. With the objective in front so close this must seriously disturb the correction I'm guessing.

Anyway, I'm not an optics type, just a semiconductor/electronics type, so what do I know

Looking forward to your tests.

I found a Sigma 50mm F2.8 Macro at KEH for $109 + shipping. Wonder if this would make a good combo with the Rokinon 135?

Best,

Mike

rjlittlefield · Post by **rjlittlefield** » Sun Apr 23, 2017 11:23 am

Mike, be sure to take a look at http://www.photomacrography.net/forum/v ... hp?t=18323 ("Telecentric combo at 0.8X to 1.69X"). Something like that may work with some of the lenses that you have. I don't have any experience with the lenses in your kit, so I don't know whether it will work or not.

--Rik

Lou Jost · Post by **Lou Jost** » Sun Apr 23, 2017 11:53 am

Mike, the 70mm macro is MUCH better, and so is the 50 Oly. But then again, as you note, sharpness in normal use doesn't seem to transfer to sharpness in our unconventional uses. I really don't understand it-- the Raynox is so unsharp compared to your Rokinon.

Yes, I remember Beatsy had the same experience with it as a tube lens. I wonder if the Sigma 135 will be any better. My very cheap Vivitar 135 (sometimes less than $100 on eBay) does an excellent job. I'll be very disappointed if the expensive Sigma does worse.

mawyatt · Post by **mawyatt** » Sun Apr 23, 2017 7:59 pm

Rik,

Thanks for the pointer. I took a quick look and will need some time to digest all the good stuff on this thread. I sure hope the Nikon 105 F2.8 works as well as your Canon with the Raynox out front. How would you rate the IQ of that configuration?

Thanks for all the help,

Best,

Mike

mawyatt · Post by **mawyatt** » Sun Apr 23, 2017 8:18 pm

Lou,

I see a few Vivitar 135mm F2.8 on eBay, what is the version you use and have good results with?

Best,

Mike

Lou Jost · Post by **Lou Jost** » Sun Apr 23, 2017 8:40 pm

I have several since they are cheap. The best are the ones made by Komine, with serial numbers starting with 28.

Also, to add to the list of known-good telecentric macro lens+ Raynox combos, I've had good results with my Tokina 90mm macro + Raynox.

rjlittlefield · Post by **rjlittlefield** » Mon Apr 24, 2017 3:00 pm

mawyatt wrote:How would you rate the IQ of that configuration?

Sorry, I don't have any more information than presented in that thread, now almost 5 years old. Generally I think of telecentric as being a tool for stack-and-stitch, so my criterion for IQ would have been to compare corners with center. In the areas that I described as "high quality", that would have meant pretty sharp at actual pixels on 15 megapixel APS-C, even into the corners of those areas.

--Rik

mawyatt · Post by **mawyatt** » Fri Apr 28, 2017 3:43 pm

rjlittlefield wrote:Mike, be sure to take a look at http://www.photomacrography.net/forum/v ... hp?t=18323 ("Telecentric combo at 0.8X to 1.69X"). Something like that may work with some of the lenses that you have. I don't have any experience with the lenses in your kit, so I don't know whether it will work or not.

--Rik

Rik,

I finally got a few moments to try your suggestion, sorry for being so late (voice coil thread is driving me nuts, well my wife will tell you I got there long ago

).

The Nikon 105mm F2.8 VR Macro has a recessed front element from the front threads, so suspect I can't get the Raynox as close as you can with the Canon. Since I don't have a 62mm to 43mm ring, I had to use a 62 to 52, then 52 to 43 to get they Raynox 250 connected up to the Nikon 105mm. So that pushes me a little further out.

I used the technique of looking backwards at a bright source (my monitor) with my long glasses thru the front Raynox element with the 105mm aperture set to f32 and the eyepiece shutter opened. I tried to focus the aperture as best I could.

I found that the Nikon 105mm focus setting was about 1.5 feet on the lens scale, this gave me about a 1.17X by hand holding and measuring a ruler.

I suspect I could get slightly higher magnification if I could get the Raynox closer. The focus distance from the Raynox front flange is about 75mm.

If I set the 105mm to closest focus distance (55mm from the Raynox front flange) I get about 2.19X, but looking at the aperture it's quite out of focus. So my guess far away from telecentric.

I may try a stack (when I get some time) around 2X to see what the results look like, which is an magnification about where I would like to try some stitching for starters.

Anyway, thanks for the idea and keeping us non-optical folks informed.

Best,

Mike

Lou Jost · Post by **Lou Jost** » Fri Apr 28, 2017 3:50 pm

With my 90mm lens the correct placement of the Raynox was quite far in front of the front element. But I was looking at lower m, like 0.5 if I recall. Not sure what would have happened if I had tried to focus on something closer.

I found it best to keep the lens + camera fixed , at fixed focus, and move the Raynox to find the appropriate distance to make the aperture appear sharp through binoculars that were focused at infinity, per Rik's suggestion.