Infinity objective on low-end zoom telephoto works fine

[Waltermarkfish]

The nikon zoom lens looks about 1mm longer than the canon lens protrusion into the body
So risk is high
I will not connect
I will ether buy a bellows or canon 200 mm zoom for my 10x objective to sit on
Now I have to wait no more cash

Thanks for advice
Walter

[nmz787]

How would I best use an infinity-corrected lens with a webcam or cell phone type camera, with a small lens fixed in place (which can be a pinhole or mechanical or autofocus with a voice coil)?

[rjlittlefield]

How would I best use an infinity-corrected lens with a webcam or cell phone type camera, with a small lens fixed in place (which can be a pinhole or mechanical or autofocus with a voice coil)?

Sorry, that's not going to work very well. Those cameras have short lenses with a wide field of view. When you pair them directly with a microscope objective, what you get is a small circle of image in the middle of a black field, and the image that you do get is not much higher magnification than the camera alone will do.

It is certainly possible to add yet more optics between the objective and the webcam or cell phone that will make everything play nicely together. But then you end up with what is essentially an entire microscope, with the small camera looking into the microscope's eyepiece.

--Rik

[Yousef Alhabshi]

I tried using an objective on my Nikon 70-200 F4 but got a strong huge vignette.. is this normal?
I'm using a FF cam.. but even though with a crop sensor body I'm getting almost the same results!

[rjlittlefield]

I tried using an objective on my Nikon 70-200 F4 but got a strong huge vignette.. is this normal?
I'm using a FF cam.. but even though with a crop sensor body I'm getting almost the same results!

I haven't seen much data on this. There is some discussion at http://www.photomacrography.net/forum/v ... 333#138333. Any further information you can provide will be much appreciated.

--Rik

[Blame]

We tried a few 135mm primes on FF too. I think the answer is that for FF with camera lenses vignetting is to be expected - even with primes let alone zooms.

At that focal length an enlarger lens worked best although I am not encouraged by the MFT curves of longer focal length enlarger lenses.

[Pau]

I tried using an objective on my Nikon 70-200 F4 but got a strong huge vignette.. is this normal?
I'm using a FF cam.. but even though with a crop sensor body I'm getting almost the same results!

This must very dependant of the lens desing (in particular of the diaphragm position). I do fine with the Canon EF 70-200 f4 L USM and a Nikon 10X objective with APSC from 200 to 140mm without vignette on APSC. Not yet tried with FF but I think it would work OK at 200mm.

[ChrisR]

I didn't even realise they made a 70-200 f/4, until I just looked! The old 70-210 f/4, a completely different design, was useless as a tube lens on FF, I don't think I ever tried it on APS-C.

[rjlittlefield]

This must very dependant of the lens desing (in particular of the diaphragm position).

Yes. A related issue is how much the corners darken at wide open even when the lens is used by itself, with no objective added.

Let me step through a calculation to show why.

A 200 mm f/4 lens must accept a bundle of input rays that is 50 mm in diameter (because 200/4=50). Clearly this bundle of rays has to fit through the filter thread. According to the equipment review I see, the Nikon 70-200 f/4 has a front filter thread that is only 67mm. If a full 50mm bundle were to enter the front element, it would include no less than a circle of diameter 33 mm centered on the front element (because 50-(67/2)=16.5 and 2*16.5=33). That is far larger than the roughly 12 mm hole in the rear of a microscope objective.

So, if the lens is truly f/4 even in the corners, then it's not going to vignette when an objective is added close to its front element. (Sure, stick the objective on an extension and it can vignette like crazy.)

Instead, you'll see vignetting with the objective when the lens is not really f/4 in the corners of its field. That would be the case, for example, with the lens I diagrammed at http://www.photomacrography.net/forum/v ... 667#131667. The lens diagrammed there has a large front element, so the corner vignetting is not very bad until the microscope objective is added. But with a small front element, the corner vignetting without added objective must be much worse. Assuming hard vignetting with a 10 mm hole at the rear of the objective, the clear aperture of the 67mm diameter lens could extend no more than 28.5 mm from the filter ring toward the center of the lens (67/2-5=28.5). That would imply a loss of around 1 f-stop in the corners, courtesy roughly half the aperture being blocked by the edge of the lens.

Interestingly, when I went looking for information about the Nikon 70-200mm f/4, one of the things I found was an illustration of corner darkening, HERE, in the section labeled "Falloff". Copying here a snippet of the whole illustration:

I'm not sure that this is the same lens that's being discussed, but in any case it seems to illustrate the problem. This amount of corner darkening at wide open by itself is not encouraging that the lens will work well in combo with a microscope objective.

--Rik

[Yousef Alhabshi]

Somehow I didn't get any notifications on my email with the new replies.. so apology for my late reply.

I haven't seen much data on this. There is some discussion at http://www.photomacrography.net/forum/v ... 333#138333. Any further information you can provide will be much appreciated.

I'll post some smaples today using the Nikon 70-200 F4 with different aperture setting just to see if there are any differences. does it matter which objective i'm using here?

I didn't even realise they made a 70-200 f/4, until I just looked!

I really like the performance of this lens.. it overperforms even its older sister the Nikon 70-200 VRII F2.8!
It does has VRiii technology.. I tried to shoot some pictures @1/25sec @200mm handheld & it was razor sharp (although I found a strange glow in the mid of the picture once the VR is activated.. but I won't confirm anything at this stage).

One of the reason I purchase it for.. was to use it as a medium for my infinity objectives & to be compared against the bellows+Morfanon combination.

I'm not sure that this is the same lens that's being discussed, but in any case it seems to illustrate the problem. This amount of corner darkening at wide open by itself is not encouraging that the lens will work well in combo with a microscope objective.

I believe it's the same lens since they do have only one version of 70-200 F4. So in theory, will it matter if I use the lens at smaller aperture? I mean as affecting the sharpness? (I'll try to pixelpeep the results today)

This must very dependant of the lens desing (in particular of the diaphragm position). I do fine with the Canon EF 70-200 f4 L USM and a Nikon 10X objective with APSC from 200 to 140mm without vignette on APSC. Not yet tried with FF but I think it would work OK at 200mm.

I start to doubt that the results with this lens might be somehow different than with what Canon lens can produce!

[rjlittlefield]

The rear lens (the 200 mm in this case) should always be set to its widest possible aperture to minimize vignetting.

The microscope objective will stop down the entire system to around effective f/20. The formula is effective f-number = magnification/(2*NA), so for example at 10X NA 0.25 it is 10/(2*0.25) = 20.

There may be slight differences depending on which objective you use, but since all objectives have about the same diameter hole at about the same place, I would not expect major differences.

--Rik

[Blame]

rjlittlefield has the right of it.

If a camera lens vignettes seriously wide open then it MUST kill the corners used as a tube lens.

If the front lens element is seriously wider than (focal length)/(maximum aperture) then even total lack of vignetting is not proof of suitability as a tube lens.

Assuming best case of (set aperture) = (focal length)/(front lens diameter) then the the objective MUST vignette by about a stop where wide open vignetting reaches roughly about a stop and a half. After that vignetting becomes total rapidly.

That also makes the assumption that there is zero distance between the optical center of the objective and the surface of the camera lens. Not a reasonable assumption from what I have seen. I wouldn't have much faith over 1 stop vignetting wide open.

The point being that from published data alone one could dismiss a fair number of camera lenses as viable tube lenses.

[marceppy]

Rik,

Do you think this would work with the Canon EF 100-400mm tele zoom?

Marc

[rjlittlefield]

Do you think this would work with the Canon EF 100-400mm tele zoom?

At 400 mm I expect it would, but that's only guessing from experiences reported with other Canon lenses. At 200 mm, I would expect vignetting, again only from extrapolation.

If you have such a lens, then you can test it without an objective by sticking a mask in where the objective would go. If you don't have such a lens, then I would strongly recommend not getting one in anticipation that it would work OK at much less than full length.

--Rik

Edit: fix misleading typo, "full aperture" --> "full length".

[marceppy]

Yes, I have the 100-400mm IS lens. Will give the mask idea a try. I just sold an EF 180mm macro & replaced with EF 100mm IS macro.

Tks, Marc