Cheap tube lens

morfa · Post by **morfa** » Fri Jan 14, 2011 4:43 pm

While casually browsing around among the items at surplushed.com I came across one that, by it's physical appearance, reminded me of the Nikon CF tube lens shown in this post: http://www.photomacrography.net/forum/v ... 708ea090c7 The dimensions also seemed to check out a bit too well to keep my fingers from the buy button...

I received it yesterday and thought I'd share some initial impressions.

Here it is:

It's quite light weight and appear to be only one or two lens elements. I didn't have high hopes for it but I was pleasantly surprised when I saw the performance in combination with the Nikon CFI 10x 0.25 via live view on a 5DmkII. So I proceeded with some test stacking.

Uncropped test stack, 5DmkII, Nikon CFI 10x 0.25:

12MP version: http://farm6.static.flickr.com/5122/535 ... 9bcb_o.jpg

My two days of experience with this objective tells me that the CFI performs well almost regardless of which prime you hook it up to (within reason). So what was more pleasing to me was how well this tube lens performed in the corners on FF with a Mitutoyo M Plan Apo 10x 0.28.

5DmkII, Mitutoyo 10x 0.28

12MP version: http://farm6.static.flickr.com/5290/535 ... 3d29_o.jpg

The subject and framing is obviously similar to the CFI stack but the lighting is quite different so I would advice against excessive comparative pixel peeping (any differences seen could just as well be attributed to different lighting conditions). (Yes, David Miller could teach me a thing or two about getting consistent test conditions http://www.photomacrography.net/forum/v ... hp?t=11993)

During the last weeks I've tried a large number of lenses in a fairly wide range of focal lengths as tube lenses with the Mitutoyo 10x 0.28. I can say with some certainty that this is by far the best edge/corner performance I've seen from this objective on a full frame sensor.

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In combination with the CFI 10x 0.25 this tube lens yields a horizontal FOV of 3.7mm on a full frame sensor. In my setup the tube lens wasn't focused quite to infinity (more like 2-3m). This suggests to me that the focal length of this thing is very close to 200mm.

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I'm not saying this is the ultimate tube lens (lots of testing ahead) but it seems to have at least some desirable properties. One such property is the price: $9.

http://www.surplusshed.com/pages/item/l3712.html (they just told me they have 100 of these in stock)

ChrisR · Post by **ChrisR** » Fri Jan 14, 2011 5:25 pm

Well done John.
It looks like the Nikon shows a bit less well in the corners as we would expect, but still, I would have thought, good enough for many subjects.

While playing around with different lenses, I've got the impression that the "tube" lens quality matters more if you go short. At about 200mm I haven't seen a difference to speak of - though my wing scales aren't as sharp as yours!

I had to smile when seeing this potential tube lens at the Surplus Shed - at least the darned thing shouldn't clip the corners off... http://www.surplusshed.com/detail.cfm?ID=L13001 I wonder how it would fare as a 5 dioptre close-up lens for a 400mm f/2.8, or...
edit - thanks Craig

Craig Gerard · Post by **Craig Gerard** » Fri Jan 14, 2011 7:50 pm

John,

I had wondered about that lense at SurplusShed:
http://www.surplusshed.com/pages/item/l3712.html

Thanks for uploading the details of your exercise.

Craig

AndrewC · Post by **AndrewC** » Sat Jan 15, 2011 12:55 am

You are a demon for finding good stuff

So how are you mounting this ? 200mm from objective shoulder to tube lens and then another 150mm to the sensor ?

morfa · Post by **morfa** » Sat Jan 15, 2011 2:01 am

AndrewC wrote:So how are you mounting this? 200mm from objective shoulder to tube lens and then another 150mm to the sensor ?

I took Mitutoyos word for it that a closer distance between objective and tube lens does not affect image quality in a negative way. The distance is probably 20mm from objective shoulder to the front element of the tube lens.

Some quick phone snaps:

As you can see I used the "One adapter to rule them all" for the tube lens and it proved to be perfect for the job. I use PN-11 (52.5mm) to attach the rig to the stand since it has a nice rotating tripod collar. Other than that I have two 27.5mm tubes (Nikon PK-13 and Nikon M2) and one 14mm (Nikon E2) tube closest to the camera body.

AndrewC · Post by **AndrewC** » Sat Jan 15, 2011 3:21 am

PN-11 tubes are really useful - shame they don't transfer AF etc for "normal" use but in setups like this they are really useful. It's a shame they didn't make them just a little bit longer to avoid having to add a spacer between the tube and body.

If anyone knows of a T-mount tube with a tripod collar that would be a great find. As soon as I setup (and work out how to use ! ) my new mini lathe I'll try making my own but that might take a little while.

Meanwhile I've got a Nikonised Olympus 65-115mm zoom extension tube for longer lengths and a PN-11 I use with my finite objectives.

Edit: just had a thought, and took 2mins to check it. With a D5000 body you don't need the spacer between the PN-11 body and camera and D5000/PN-11/Nikon-to-T/Beljian cone gives 160mm objective to sensor for us "finite" people.

ChrisR · Post by **ChrisR** » Sat Jan 15, 2011 3:51 am

Was alignment fiddly? Your Ace adapter wouldn't be the best possible in that regard, I wouldn't have thought?

morfa · Post by **morfa** » Sat Jan 15, 2011 4:09 am

ChrisR wrote:Was alignment fiddly? Your Ace adapter wouldn't be the best possible in that regard, I wouldn't have thought?

On the contrary – I spent less than a minute on alignment of the tube lens. The rear end of the tube lens happened to line up perfectly with a rim inside the adapter so in terms of angular alignment it was pretty automatic. It's possible that it's not 100% centered but if there is a shift it's less than 0.5mm.

dmillard · Post by **dmillard** » Sat Jan 15, 2011 9:52 am

John,

Thanks for the information - I just ordered one of the lenses from Surplus Shed to play with (they listed the focal length as 172mm). I especially like
your versatile lens mount!

Regards,
David

ChrisR · Post by **ChrisR** » Sat Jan 15, 2011 10:01 am

they listed the focal length as 172mm

Most of their lenses are singles, so perhaps they just measure focused distance. I believe the proper tube lenses were reported here as being "slightly telephoto".

morfa · Post by **morfa** » Sat Jan 15, 2011 10:24 am

dmillard wrote: (they listed the focal length as 172mm)

Yes, but they seem to have their own view on focal lengths. None of the handful of unmarked lenses I've ordered from them during the years have turned out to have the exact focal length they've stated in their description (there is often a 25-30% discrepancy).

I've now tried the tube lens with the Nikon CF Plan 50x 0.55 EPI ELWD ∞/-described here: http://www.photomacrography.net/forum/v ... hp?t=11654

I'm very happy with the results.

5DmkII, Nikon CF Plan 50x 0.55 EPI ELWD ∞/-, $9 tube lens, Zerene PMAX, 1% xy alignment (scaling and rotation off)

12MP version: http://farm6.static.flickr.com/5282/535 ... 3e31_o.jpg

It's uncropped but has had a round of postprocessing in PS: Curves adjustment, high pass sharpening, dust spot removal, simple non-local desaturation of the magenta channel to get rid of a tiny amount of magenta CA around harsh highlights.

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Here I've used a different setup (sorry for the terrible phone snaps):

The tube lens is simply sitting on top of the Microscope (held in place by gravity) and the "tower" of extension tubes is built up around it (attached to the microscope frame via a dovetail->filter thread adapter). In terms of vibration this is MUCH more solid. Can't do it with the Mitutoyo though since it's too large and has too long working distance to fit between the nosepiece and xy-stage. In this configuration the distance between objective shoulder and tube lens is 45mm

elf · Post by **elf** » Sat Jan 15, 2011 12:14 pm

AndrewC wrote:As soon as I setup (and work out how to use ! ) my new mini lathe I'll try making my own but that might take a little while.

The biggest thing I learned the hard way was to turn the lathe by hand when cutting threads. Here's a link that has several versions of a hand crank: http://www.toolsandmods.com/ralph-patterson.html

Here's a link to a toolbit sharpening jig: http://www.gadgetbuilder.com/ThreadingTools.html

I can safely say my mini-mill and mini-lathe have paid for themselves many times over just making stuff for my cameras.

dmillard · Post by **dmillard** » Sat Jan 15, 2011 4:01 pm

John,

That last shot with the 50/0.55 objective is astonishing, especially considering that degree of magnification!

David

Pau · Post by **Pau** » Sat Jan 15, 2011 4:48 pm

John, thanks for posting your test and links.
I think they answer the questions about the full frame coverage of the tested objectives. I'm also very surprised about the 50X 0.55
When I receive this tube lens I plan to test it mounted in the microscope frame like in your second picture, another thing in my long and growing to do list

soldevilla · Post by **soldevilla** » Sun Jan 16, 2011 10:31 am

Another inexpensive option for use with infinite microscope objectives is to use it in front of a lens of binoculars. They are very cheap, with a 8x30 is enough and binoculars have two ... plus some eye and prisms for other inventions.