Coastal 60/4 Apo Hotspotting at close focus

[brianc1959]

Andrea recently brought this to my attention, and today I was able to confirm her findings.  The 60 UV-VIS-IR Apo apparently does have a hotspotting issue for small apertures at the closest focus settings.  I found that at f/45 there is a noticeable hotspot from 1:1.5 magnification out to about 1:3.  From 1:4 through 1:infinity there is no hotspot at any aperture, including f/45.  At f/8 the hotspot does not become apparent until approximately 1:2.5.  At f/4 I was unable to see a hotspot at any magnification.

I was able to avoid the above hotspotting behaviour by using extension tubes to achieve magnifications greater than 1:4.

All of the above was checked with a Nikon D200 modified with a transparent replacement filter.

Needless to say I'll be doing everything I can to get to the bottom of this issue.

[nfoto]

Disturbing news of course for us all, but I'd like to put this in a perspective. I've been using this lens extensively since late 2007, and had not encountered the problem at all. Perhaps because I always use extension tube (PK-13, CPU-modified) to get close with the 60 APO. Also, when I use the lens in a reversed position, it is necessary to set the lens to infinity in order for the working distance be acceptable. Both scenarios avoid the situation Brian describes.

Nevertheless, I sincerely hope Brian solves this issue so we can see a Mk.II later of this already legendary lens.

[brianc1959]

Disturbing news of course for us all, but I'd like to put this in a perspective. I've been using this lens extensively since late 2007, and had not encountered the problem at all. Perhaps because I always use extension tube (PK-13, CPU-modified) to get close with the 60 APO. Also, when I use the lens in a reversed position, it is necessary to set the lens to infinity in order for the working distance be acceptable. Both scenarios avoid the situation Brian describes.

Nevertheless, I sincerely hope Brian solves this issue so we can see a Mk.II later of this already legendary lens.

Thanks,Bjørn.

Aside from a short working distance, I am curious whether you encounter any issues when reversing the lens and using the maximum (1:1.5) magnification setting?

[nfoto]

There is hardly any free distance in practice to manipulate the filter(s) and lighting the setup becomes difficult. This in turn means it's very easy to bump or jar the subject so it goes out of critical focus. Otherwise, if no displacement occurs, image quality seems just fine.

Setting the lens to infinity focus adds a few precious cm to the free distance.

Because of the zero focus shift of the CoastalOpt 60 (UV-Vis)), it is my preferred favourite lens for doing close-ups. It does slightly better than the UV 105 Nikkor in my experience and is of course unsurpassed for IR close-ups where the UV 105 shows substantial focus shift.

I have spent the last hours browsing my archive for hundreds and hundreds of close-ups done with the 60 APO in the range of magnification reported to give issues with hot spots, and have found nothing.

[Vivek]

Brian, I had mentioned this possibility to Andrea and Bob.

I do not own this lens but my deduction was based one report of Bjorn (maxmax filters).

I have an idea why this is so.  I will make long report when I find time.

[brianc1959]

Brian, I had mentioned this possibility to Andrea and Bob.

I do not own this lens but my deduction was based one report of Bjorn (maxmax filters).

I have an idea why this is so.  I will make long report when I find time.

Vivek:
The MaxMax filter phenomenon is completely unrelated to pupil image hotspotting, and is caused by angular sensitivity of the filters themselves, in common with all dichroic filters.  In fact, the MaxMax filters work perfectly well with the Coastal 60mm lens at closer object distances because the field of view is less.

[Vivek]

Brian,  I do not think so.  If this is the case, use of any UV/IR cut filters on a lens like 60/4 (or any other of similar focal length) on a modified camera like D200 UV-IR to capture visible light images at or near infinity would be a problem.

I do not find any such problems with even cheap 28mm lenses and UV/IR cut dichroic filters on such "naked" cameras.

[brianc1959]

Brian,  I do not think so.  If this is the case, use of any UV/IR cut filters on a lens like 60/4 (or any other of similar focal length) on a modified camera like D200 UV-IR to capture visible light images at or near infinity would be a problem.

I do not find any such problems with even cheap 28mm lenses and UV/IR cut dichroic filters on such "naked" cameras.

Any dichroic filter will have angular dependence, including your UV/IR cut filter.  You should be able to verify this simply by looking through it while tilting at various angles.  Tomorrow I'll try to post a couple of shots using the actual MaxMax filters in question to illustrate the point I made above.

[Vivek]

Any dichroic filter will have angular dependence, including your UV/IR cut filter.  You should be able to verify this simply by looking through it while tilting at various angles. 

I know.  But the question is if it impacts the image.  IME, even with cheap 28mm lenses (on 2X and 1.5X crop sensors) it does not.

[annedi]

I'm still getting hotspots with a 12mm extension tube.
I guess I will try another length.

Added from later post-----
for the record:
CO 60/4 hotspots in all of Ultraviolet, Visible and Infrared wavelengths
in magnification range 1:1.5 to 1:3.5
for apertures f5.6 - f45.
(...not that anyone really uses f/45...)

[nfoto]

Try PK-13. it's 27.5mm and I don't see any hot spots with it.

shot lots of close-ups with my 60 today, no issues. but following the f/45 recipe given by Brian a hot spot occurred.

writing this in the middle of nowhere using 3G broadband with my small eeePC. darkness is mitigated by reflections off the snowpack encircling me. have to spend the night sleeping in the car, no civilised lodging available for miles around . but this might net me an IR sunrise

[annedi]

I wouldn't really care if the CO 60/4 had hotspots just at f/45 or even f/32.
But to have hotspots at between 10.5" - 14" at all apertures
between f/5.6 - f/22 where I would regularly shoot ?? This is not so good.
Somewhat disappointing, actually.

[annedi]

.....and, yes, bring us all an IR sunrise !!!!!

[annedi]

Are there any bears where you are 'camping out'

[RKPhotog]

I don't own this lens (yet) but am puzzled by this discussion. I don't know the pupillary magnification factor but have to wonder why one would shoot at indicated f45. At 2:1 wouldn't that be shooting at something like effective  f90?!
Bob K

[annedi]

In the course of testing the CO 60/4 for hotspots, I ran it through all "magnifications" and all apertures
in order to determine precisely where the hotspots occur.
That included shooting at the really stopped down apertures from f/22 thru f/45
so as to have a complete record.
 
I really do not shoot at those apertures ever because diffraction pretty much begins
to destroy detail past f/16, as is well known to all of us.

Why I had to be the one to discover these darned hotspots I'll never know
as this lens has been through reviews by Lloyd Chambers ("diglloyd"), Bjørn R. and others.
I'm supposed to be the non-technical, non gear-head shooter.....

I've now tried a Kenko 20mm extension tube, but still no improvement.
I need to try the PN-11 next.
But I don't really want to rely on extension tubes to rectify hotspots in an expensive lens.

Added from later post ------
for the record:
CO 60/4 hotspots in all of Ultraviolet, Visible and Infrared wavelengths
in magnification range 1:1.5 to 1:3.5
for apertures f5.6 - f45.
(...not that anyone really uses f/45...)

[nfoto]

As I already have stated several times, I have yet to see a hot spot of my own for my shooting with the 60 APO. This excludes the test I did yesterday when I strictly followed the recipe for getting one at f/45 as outlined by Brian. However ,for all my shooting with the 60 AP over a period of nearly 20 months, no hot spot ever occurred. And I use the magnification range said to be conducive for the development of this issue. My working procedure differs from Andrea's (always lens shade, typically adding an extension ring to get magnifications 1:2 and higher), and that could at least partly explain why I didn't observe what she found.

I checked my image archive for hot spot indication in pictures taken by the 60 AP and after hours of browsing came out with a negative observation.

As far as I can understand, we don't know yet whether Andrea's copy of the 60 APO was an outlier in terms of its performance (assembly or coating issues). Lemon samples always may occur in any mass production item, no matter how high the price is (I've seen examples from several well-known makers including the 2 big companies of Japanese cameras, plus one German maker that claims their stuff is above everything else). But one would not like the incidence rate to be high (understatement). However ,we also have been informed by the designer of this lens that there is a potential hot-spotting issue in its design. Hence the lens design is in need of being modified to cater for this contingency. I trust Brian will do his utmost to track down what causes the hot spots in the first place and redesign to mitigate the problem as far as possible. With the stellar reputation the Coastal 60 APO already has gained, neither designer nor manufacturer can live with the now well-established issue even though its frequency of field occurrence is unknown and may be fairly low.

The real food for thought and the basic lesson for all parties is again the fact that positive/negative, absence/presence, are not symmetric entities. Not finding an issue does not entail its absence, only that it has not - yet - been detected. On the other hand, once something is observed, it also is confirmed to exist. Thus, the binary classification we employ is asymmetric and the ramifications of that are profound for all testers of photographic gear.


PS: I'm truly sorry that Andrea was the one to stumble upon this issue. When she first showed me test shots I could not understand at all what caused this - after all, the 60 APO has been a work horse for me for nearly 2 years  -and I'm afraid I wasn't as helpful as I should have been in following up what the underlying cause was. My apologies.

On the other hand, I had loved to detect something like this myself.

DS.
 

[annedi]

For the record, absence or presence of a lens hood plays no role in the Coastal hotspot problem
as I tested both with and without lens hoods.

Today I will try wider extension tubes as the 12mm and 20mm provided no cure for the hotspots.
I have a Nikon PN-11 and a Kenko 36mm that I haven't tried yet.
I don't have the PK-13, but it's just an hour away up at B&H if I need/want to get one.

I don't know what to do about returning the lens.
I'm just kind of depressed right now because it was kind of expensive.
I'm just dreading picking up the phone and calling Coastal about returning a second copy
as I had to already return the first one for a metal flaw in the lens barrel.

[Vivek]

However ,we also have been informed by the designer of this lens that there is a potential hot-spotting issue in its design. Hence the lens design is in need of being modified to cater for this contingency.

What would that be in the design?  I did not get that from this thread.

[nfoto]

Well, Brian is the designer and has been quite outspoken about where the problem resides (rear group).