What made this?

ChrisR · Post by **ChrisR** » Wed May 29, 2013 4:52 pm

A mini equipment quiz for a change.
Sensor is 24 x 36 12.1MP
Millimeter graph paper - sorry it's twisted, and some strips of 600 grit SiC paper.
What optics were used?
Full frame, then Centre/Mid/Edge at 100%.

[edit to show crop areas]

rjlittlefield · Post by **rjlittlefield** » Wed May 29, 2013 6:05 pm

Binoculars in reverse?

--Rik

ChrisR · Post by **ChrisR** » Wed May 29, 2013 9:39 pm

Hmm no I'll have to try that - got some stabilised ones.

Much more commonly mentioned stuff for the forum.
Rik you could have done this with what you have (ok , wouldn't have bothered) but I'm surprised it came out like this.

Cactusdave · Post by **Cactusdave** » Thu May 30, 2013 12:59 am

Reversed microscope eyepiece?

Craig Gerard · Post by **Craig Gerard** » Thu May 30, 2013 2:12 am

Chris,

The mm graph would indicate you are at approximately 1:1. Have you pushed a 2X down to 1X?

The initial image displays non-uniform vignetting. I recently experienced a similar result when using FF, a 2X infinity-corrected Mitutoyo objective and a bellows. Swapping out tube lenses had no positive impact on the distribution of vignetting. After further troubleshooting I found the problem, previously suspected, to be related to a misaligned front standard of the bellows which was causing a degree or two of tilt (on a non T/S bellows) ....long story, currently being rectified, so I won't digress into specific details.

Craig

Guido · Post by **Guido** » Thu May 30, 2013 2:21 am

First sight i was thinking about a flatbed scan but that is impossible because the vignetting

ChrisR · Post by **ChrisR** » Thu May 30, 2013 6:02 am

Craig's close, but not there yet.

curt0909 · Post by **curt0909** » Thu May 30, 2013 9:12 am

Infinity objective tube lens?

ChrisR · Post by **ChrisR** » Thu May 30, 2013 1:30 pm

Not quite... I was just curious to see how far a Nikon 4x NA 0.1 BE objective could be pushed. This is on a 50mm f/1.8 standard camera lens.
It seems that on DX/APS, you could use it right down to 1:1.

The asymmetry came from having to hold the objective close, almost inside the lens, to get this much image circle.

curt0909 · Post by **curt0909** » Thu May 30, 2013 2:40 pm

That's unbelievable. So you have a 2x 0.1 NA objective for <$100. I'm going to have to pick one of these up. Thanks for the info

ChrisR · Post by **ChrisR** » Thu May 30, 2013 3:27 pm

I was surprised, too.
I believe it should be a just a 50mm f/4 really, but the hole isn't 12.5mm...

It was about $55 direct from Nikon. They had a few orders after it was praised on this forum.
Other folk have ordered them and received the 4x "E", which (probably) has a "CFI" thread, whereas this one's rms.

I do have 4x NA 0.1 "genuine" CFI, which is quite different.

I wonder how another standard 50mm camera lens, reversed, would compare. They should be "ok" at f/4. I could probably find one or two, or 6.

rjlittlefield · Post by **rjlittlefield** » Thu May 30, 2013 5:44 pm

ChrisR wrote:I believe it should be a just a 50mm f/4 really, but the hole isn't 12.5mm...

I think I can explain that.

The lens is a 50 mm f/5 (5=1/(2*0.1)). The front principal plane is located 5 mm "above" the shoulder of the mounting threads. That's 50 mm away from the DIN parfocal point at 45 mm "below" the shoulder of the threads. Measured at the principal plane, the entrance cone will be 10 mm wide (=50/5), but at the location of the front lens element it's quite a lot smaller, more like 7 mm in fact. See discussion HERE regarding placement of the entrance pupil etc.

I suspect the difference between my f/5 and your f/4 is a bit of confusion about how to calculate an "equivalent" f-number. It's finite versus infinite that makes the difference between equivalent f/4 versus f/5. If you grab say a 50 mm enlarging lens and just extend it to provide 4X, then indeed that lens will have to be f/4 to provide NA 0.10 on the subject side and effective f/20 on the camera size. But if you stick that 50 mm enlarging lens in front of a 200 mm used as a tube lens, then in that configuration the 50 mm only needs to be set on f/5 to provide the same NA 0.10 and effective f/20.

I hope this helps.

--Rik

dolmadis · Post by **dolmadis** » Thu May 30, 2013 10:37 pm

The asymmetry came from having to hold the objective close, almost inside the lens, to get this much image circle.

As a beginner I am having trouble visualizing what the arrangement is between the objective and the lens.

Learning Curve !!

Any chance of a photo or a diag please?

Thanks

John

ChrisR · Post by **ChrisR** » Fri May 31, 2013 1:16 am

You can use an infinity corrected scope objective on a camera lens as a "tube" lens. (200mm gives you the designed magnification of the objective).
Later infinity objectives are mostly not rms threaded, but this one is.

So a flat, disc-with-hole adapter, male filter thread on the outside and female objective thread on the inside, does the job, with caveats.
My "rms" adapter goes to M42 so needs a M42-52mm filter adapter as well, which means the objective is a little further out.
The glass on the standard lens is recessed, about 10mm.
The objective looks/behaves somewhat like a 7mm hole in a lens cap. The "tube" lens has to enlarge the objective's field of vision enough to cover the sensor, wthout the insides of either lens getting in the way. The further you move the objective from the camera lens, the more it's likely to vignette.

See Rik's link for a piccy of the objective.
I put it inside the adapters, hanging through the threaded hole. Not an arrangement to be recommended, though it did place it very near the lens.

To cover APS (approx 22 x 15) you can afford some vignetting, so don't need it that close. It's actually asking for trouble, with reflections between the glass and metal surfaces.

I suspect it might "work" on the front of an 85mm "standard zoom" camera lens to give 85/50* = 1.7x magnification, = about 13mm on the long side. Quite useful for your bryos.

* the objective is actually about 50mm FL. (200/4 = 50)

dolmadis · Post by **dolmadis** » Fri May 31, 2013 1:33 am

@ChrisR

Thank you for explaining your novel change to the conventional tube lens/infinite objective arrangement.

John