Raynox 5320

[Andy Davies]

I have two Thorlabs SM3 tubes connected to a helicoid connected to the Raynox 5320. I have tried to adjust the focus by aiming at a house several miles away but couldn't really make a good judgement as to whether to focus was changing very much.

The distance from the camera flange to the end of the 5320 on my system is currently 209.38mm and the flange distance for the Nikon to sensor is 46.5mm.

I'm concerned that I may be way out and hence am not able to determine sharp focus!

Many thanks

Andy

[rjlittlefield]

I assume this refers to the Raynox DCR-5320PRO with both parts mounted.

If so, then the numbers look about right based on the specs, but I've never had one in hand to test.

I am puzzled by your uncertainty in any case. I've tested a lot of tube lenses, and while the wide-open image quality varies wildly, I've never been in doubt about whether a lens was focused.

Can you describe in more detail why you can't tell about focus? Is the image so blurred that you can't tell whether more or less extension is better?

--Rik

[Andy Davies]

Yes, the DCR-5320PRO.

I was adjusting focus using the helicoid so the change is very slow and I was zoomed in on the LCD on the back of my D810 so it was quite hard to tell if it was sharp or not or how sharp the image should be.

How far away should the object ideally be?

[rjlittlefield]

Anything beyond a couple of hundred feet will be fine.

Let me suggest restarting this discussion from first principles.

When used behind a 10X NA 0.25 objective, the DCR-5320PRO will be acting just like a 200 mm telephoto lens that is stopped down to f/20 by the exit pupil of the objective.

For setup and testing purposes, you can replace the objective with a simple aperture, such as a piece of opaque cardboard with a 10 mm hole cut in it.

When that aperture is centered over the front of the 5320, the 5320 has to be capable of producing a sharp image. If it is not, then it won't make a sharp image in combination with the objective either.

Further, because the aperture just stops down the 5320 to effective f/20, the resulting depth of focus, back at the sensor, becomes just what any other f/20 lens would have. A focus error of 1 mm in total extension will result in catastrophic loss of fine detail.

So, a total 2 mm change in extension, centered on correct focus, will take you from pixel-level junk, to a good image, then back to pixel-level junk. If there is any ambiguity in this process then something has gone seriously wrong.

--Rik

[Andy Davies]

Many thanks Rik, I'll try again tomorrow.

What do I need to do to use the 10X Mitty at different mag? I assumed that I would need to change the tube length but from this discussion it appears that there is only one position where the image is in focus?

[rjlittlefield]

Background info.... Having the tube lens be focused at infinity puts the objective into its as-designed focus position. When the tube lens is focused not at infinity, you can still get an image that is well focused, by changing the objective-to-subject distance. However, even though the image will be well focused, its quality will degrade due to aberrations that are introduced by dragging the objective away its design point. The amount of degradation depends strongly on the NA of the objective. Using the 10X NA 0.28, you can maybe drag it away enough to change the magnification by +-30% and still have OK images. This depends on your criteria for "OK", of course. And it's not an approach that I have measured very carefully, so take the +-30% with a grain of salt.

The ideal way to run the 10X Mitty at a different magnification is to use a different length tube lens, still focused at infinity. For example using a Raynox DCR-250, at 125 mm focal length, will make the combo run at nominally 10*(125/200) = 6.25X.

This approach just changes the size of the image and does not introduce any aberrations. By packing the same amount of image detail into a smaller area, it makes the image appear sharper. On the subject side, the objective retains its original NA, but the system's overall resolution on subject may drop because of sensor limitations.

In my own kit, on APS-C sensor, my sharpest 10X combo is actually a 20X Mitty on a 100 mm tube lens (Canon Macro 100 mm f/2.8L IS USM). That combo nets out to be 10X NA 0.42. Similarly my sharpest 5X is a 10X Mitty on the same tube lens, netting out at 5X NA 0.28.

--Rik

[rjlittlefield]

By the way, if you have a bellows and a convenient way to mount the Raynox on it, then using that would typically be the most convenient way to determine the extension needed for infinity focus. Combining fixed tubes and helicoids is a bit fiddly in comparison.

--Rik

[Andy Davies]

The 5320 is made of a +2 and +3 diopter lenses. Could either of these be used as a useful shorter length tube lens?

[Chris S.]

The 5320 is made of a +2 and +3 diopter lenses. Could either of these be used as a useful shorter length tube lens?

Unfortunately, no. The focal lengths of these lenses would be 500mm and 333mm, respectively. (Focal length=1000mm/diopter.)

A bit counterintuitive, isn't it?

--Chris S.

[Pau]

333mm

...I could have a good use for it, did anyone try it as tube lens? Is possible to get it alone?

[Andy Davies]

The info on the Raynox site gives:

+2 diopter 486mm
+3 diopter 311mm
+5 diopter 170mm

where these distances are from the top of the lens to the surface of the object when the lens is set at infinity.

So what should the distance be from the D810's sensor to the front of the 5320 couplet?

They also suggest adding even more lenses to give diopters up to 10. Would this be the best way to get different mags from the 10x Mitty?

[mawyatt]

Andy,

Many, myself included, use the Raynox 150 & 250 (4.8 and 8 for 208mm and 125mm FL) with the various inf. Mitty's. Also use the old Vivitar or Zeiss 135mm f3.5 for a 135mm tube lens. The old Nikon 200mm F4 "Q" lens works well too for a 200mm tube lens.

These respectively allow 208/200, 125/200, 135/200 & 200/200 change of the Mitty magnification.

eBay is a good source for the Viviar (Komine version), Zeiss Zena "MC" version and Nikon. The Raynox 150 and 250 are available many places like B&H and Amazon. All are very reasonable price-wise.

I see some slight vignetting on DX format, more so on FX when using the Raynox 250, Vivitar or Zeiss 135.

Hope this helps,

Mike

[Andy Davies]

Hi Mike

Yes, I have the Raynox 150 and 250 as well but there is big difference in size of glass between these and the 5320 which really feels like a quality lens.

Nathan's review also prompted me to go for the 5320. Looks like a good option to use a combination of the x2 and x3 diopters to get different tube lengths.

[Andy Davies]

Should the 5320 be reversed and then the distance from the back of the Raynox to the sensor should then be 170mm as per the example given on this page where the distance from the front of the Raynox to the subject is 170mm?

http://www.raynox.co.jp/english/dcr/dcr ... /index.htm

I've tried Rik's suggestion and placed a 10mm aperture over the front of the Raynox on a house about 500m away and came up with a distance of 193mm from the back of the Raynox to the sensor. I'm still not convinced of this as again it was difficult so see much change in sharpness when turning the helicoid.

There wasn't much light around on a grey day in Wales today

[rjlittlefield]

How much range of extension does that helicoid give?

--Rik