Nikon CF N Plan 4x's comparison -images added

[NikonUser]

Just received the APO version of this lens (new from China at considerably less cost than the recent USA ebay price).

Of course, I had to compare it with my ACHRO version.

Initially I compared the central areas and saw very little difference (ouch!) with perhaps the APO slightly better resolution, but it was a tough call.

However, edge detail was no real contest!

4mm long Lauxaniidae fly

41 frames at 0.03mm; ZS PMax

Untouched images straight out of ZS.

Full frame (ex APO), 4288 px wide reduced to 1000px wide; and 500 actual pixels selections.


NU10034 & NU10035

[rjlittlefield]

Great comparison -- thanks for posting.

Refresh my memory, please. What are the NA's of these two objectives?

And what exactly does "new from China" mean?

--Rik

[NikonUser]

0.13 and 0.20

'new from China'? simply means that the lens was advertised as being "New" and I purchased it on ebay as a BIN (Buy It Now) from a dealer in China with shipping costs (air mail) of about 50% of what most Americans charge to send a lens to Canada.

The lens arrived in a hard plastic objective vial and indeed does look new and unused.

[ChrisR]

Centrally they're both perhaps beating your sensor. They'll resolve a couple of microns, x4 = a couple of pixels , if yours are 5 microns-ish.
I'll bet a groat you'd see a difference if you used a teleconverter? Wider image circle of course too .

[ChrisR]

I remembered doing a test a little while back, which I don't think shows the centre/edge difference you're seeing.
Rather a different subject, and at a higher magnification.
Maybe my technique just made them equally fuzzy all over

http://www.photomacrography.net/forum/v ... 6012#56012
(click the pic)

[NikonUser]

Chris:
I was surprised to see how poor the fly's wing tip was with the 4x Achro. Thinking that the stacking software may have been confused (apologies to Rik) by the large number of OOF wing tips (41 frames @ 0.30 mm, most of which would be OOF for the wing tip) I ran a stack using just the frames that showed the wing tip in its best focus.

Happened to be 9 frames.

You can see the sharpness disappear as you move from the wing base (close to center of frames) to the wing tip.

4x Achro, 9 frames @ 0.03 mm, Wing sharpened for this image.

NU10037

[rjlittlefield]

Thinking that the stacking software may have been confused (apologies to Rik)

No apologies needed for that! Software gets confused sometimes. I'd rather find out when it does, so I can fix it.

The big problem in this case would be if the software was getting confused between multiple nearly-focused versions. Or, if you had inadvertently turned off Scale as an alignment option, then some amount of radial smearing would be the expected result. Restricting the stack to these 9 frames would not reveal this problem -- even the shortened stack would still be smeared. And even with the same settings, the two lenses could produce different results if their entrance pupils are enough different to affect scale change between slices.

Have you looked at the individual frames to see if they are crisp?

--Rik

[NikonUser]

Rik: individual frames are soft.

I believe I have found the cause of the soft wing tip for the 4x ACHRO; but am now surprised that the 4x APO worked as well as it did.

In order to get the entire fly into the frame (23.6mm wide sensor) I had to use minimum extension, about 120 mm, and tilt the fly. Wing tip ended up in a corner.

The lens is designed for 160 mm TL and thus the 120 mm I used covered too much real estate

It seemed logical, then, that using a TL of more than 160 mm would cover less real estate and use only the more central part of the lens where it has the best resolution.

Original fly has dried out so I used a black fly wing for the following comparison. Tip of wing orientated into a corner of the FOV.

The mm data are the extensions used, some sharpening.

Conclusion: 4x ACHRO at 160 mm TL has weak resolution in corners, at 220 mm TL (and possibly greater TL) corner resolution is much better. But for critical work, get the APO!


NU10038

[ChrisR]

That's better!
On 24x36 there are quite marked transitions from sharp to unsharp.
In the 7x pic I referenced earlier, it doesn't show but it's in the extreme corners of the 24 x 36 frame, radius about 20mm.
Even inside that the Oly 20 is beating them though.
I didn't measure the extension but presumably it would have been about 160/5 x7, = 224mm

[Chris S.]

NU, thanks for taking the time to conduct and post this test. Very illuminating.

Two thoughts: First, I'm glad the apo seems to be worth the extra cost, as I have one and am glad I don't have to slap myself in the forehead and yell "Doh."

Second, stand back, boys. NU has shown he can make wonderful images with any old piece of glass he happens upon--I think he could use the broken bottem of a Coke bottle. With these optics, watch out.

Cheers,

--Chris

edited to fix a typo

[ChrisR]

I like the apo a lot because it's really good for looking at things. It's noticeably brighter and crisper than the 0.13 . That's with a 10x eyepiece of course.

[lothman]

Conclusion: 4x ACHRO at 160 mm TL has weak resolution in corners, at 220 mm TL (and possibly greater TL) corner resolution is much better. But for critical work, get the APO!

Sorry if this is a silly question, is at 220mm TL the center of the pic still OK. And if yes how can this be undestood that the corners gain so much resolution at a greater Tube lenght? Is this because then only the better center of the lens is used?

[ChrisR]

Well, Loth, on my pics, where you can look at 8 micron pixels, in the referenced post it's on a par with the Oly 20mm F2, which is at least a "very good" lens. Whether you'd see a difference with smaller pixels - dunno, ask me later!

Lenses apparently are designed with distance and angle of coverage as parameters. The angle of coverage doesn't have to change to give more area of coverage at the greater distance. That's the "Expanding the middle" part. The centre resolution is holding up, so you'd expect the corners to improve.

[NikonUser]

Sorry if this is a silly question, is at 220mm TL the center of the pic still OK. And if yes how can this be undestood that the corners gain so much resolution at a greater Tube lenght? Is this because then only the better center of the lens is used?

Hi Lothman:
At 220 mm ext. the center still has better resolution than the corners. I guess because only the best part of the lens is being used and a long TL has no effect on the center.

The 4X ACHRO performs very well across the entire FOV on my 23.6 mm sensor from 220 mm extension (and possibly less) up to at least 300 mm for a 7.8X magnification.

TAKE A LOOK HERE

[Blame]

When you mentioned 120mm minimum extension, were you referring to total distance from sensor to seat of objective?

By rights 160mm total extension should have given you a field of view of 5.9X4mm - big enough for your fly.

160mm is the designed for distance and should give 4X, but others are increasing the magnification to 6X or 7X with the nikon 4X apo 0.2. In part I think because the objective out performs the sensor at 4X. Convention wisdom would require a pixel size of 2.8um or less for optimal resolution (< resolving power of lens X magnification/2. 1.4X4/2 um).

However optimal quality of picture will be achieved with the lowest magnification that gives good corners. optimal quality would be 5.6um or more (> resolving power of lens X magnification. 1.4X4 um).

You camera probably has pixel size somewhere in between 2.8um and 5.6um - probably closer to 5.6, but given the way pixels are shrinking it is good to plan ahead. The relatively economical canon 550D is down to 4.3um.

Bottom line - you should be getting most of the resolution that you paid for in your camera and most the resolution that you paid for in your objective. Cool.

At what total magnification are the corners sharp for you?