keepcoding wrote:
I think you are mixing different terms:
spherochromatism = chromatic aberrations (CA)
purple fringing (PF) = magenta ghosting (mostly LoCA)
axial CA = longitudinal CA (LoCA)
lateral CA (LaCA)
And yes, the strength of APO is the correction of LoCA, not LaCA.
Some of what you say is correct, and what I was saying; of course axial and longitudinal CA are different terms for the same thing. I explicitly pointed out that LaCA is easy to fix, and that PF is a form of Axial/Longitudinal aberration.
But spherochromatism is not a generic term for CA.
Rather it's a *form* of longitudinal (axial) CA.
Quoting from Rudolf Kingslake, R. Barry Johnson *Lens Design Fundamentals* (Second Edition), 2010
"(a form of) of longitudinal spherical aberration for various colors of light, which was mentioned already, spherochromatism"
But regardless of the term one chooses to use, it's important to distinguish two different presentations of
axial colour aberrations.
One of course is PF
But the other is an *axial* aberration where elements behind the plane of best focus are green fringed, may have magenta cores (conversely in front of the plane of best focus).
Of course this is axial, because it occurs outside the plane of best focus. Lateral aberrations are caused by different magnfictions or distortions of the different colour channels *in the plane of best focus*
This second kind of axial CA is the one I think is caused by spherochromatism, and is harder to correct than PF (the first kind of axial CA. Regardless of the exact optical cause of the two aberrations, they present differently photographically.
DavidBM wrote:
An extension tube is just a tube, but some of the cheapest ones have mechanisms which can jam potentially damage contacts. So it’s probably worth getting the kenko ones, which are also flocked which is handy, and saves you flocking them yourself.
Thanks for your reply David - I will check out the Kenko ones.
My question to Fred was more along the lines of: which length of tube he uses? has he tried multiple lengths and found one to be the 'best' overall compromise in performance? and why he thinks an extension tube is better than an achromat close-up lens in the case of the Voigt 50mm f2?
Petegh wrote:
Thanks for your reply David - I will check out the Kenko ones.
My question to Fred was more along the lines of: which length of tube he uses? has he tried multiple lengths and found one to be the 'best' overall compromise in performance? and why he thinks an extension tube is better than an achromat close-up lens in the case of the Voigt 50mm f2?
I can tell you why I agree with him (which may or maynot be the same as the reasons Fred has!)
First I doubt there is an overall best compromise. What magnification do you want or need? You use what you have to use for the image you want to make. They normally come in a pair of 10 and 16mm tubes and your can use either or both.
The more extension, the more the magnification, the worse the quality, in a pretty linear fashion.
Second in general achromats work better as a lens gets longer, and less well as the lens gets shorter. In two different responds: the first respect is that magnification is higher for a given achromat (or indeed non achromatic diopter) the longer the lens. Pretty simple reason: the diopter fixes the focussing distance. So if it's fixed to, say, 50cm that's quite a bit of magnification on a long lens, but pretty much the usual MFD on a fifty. But they also seem to work better in terms of peripheral IQ on longer lenses.
Third, what works best depends in part on how good the lens already is at MFD; with a lens that is struggling at MFD (like the excellent CV 1.2/40) adding extension will only make it worse still. Adding a diopter, despite the optical compromises that involves, works better, because then the lens can be set to a focussing range in which it works better. But if the lens is already excellent at MFD like the 2/50 CV, then the slight degradation by making it focus closer with tubes is probably less degradation than adding diopters.
That's the theory anyway. I think @Fred Miranda has actual images that show the theory matters in practice...
The thing that bothers me most with extension tubes and close-up lenses is that I cannot use IBIS with those methods (needs to be turned off, unless I am missing something).
I am back to macro lenses.
Petegh wrote:
Thanks for your reply David - I will check out the Kenko ones.
My question to Fred was more along the lines of: which length of tube he uses? has he tried multiple lengths and found one to be the 'best' overall compromise in performance? and why he thinks an extension tube is better than an achromat close-up lens in the case of the Voigt 50mm f2?
I think that close-up lenses are more practical with telephoto lenses. With wide angle and normal lenses, extension tube(s) make more sense as you don't need that much extension to get high magnification.
In the case of a 50mm lens native 0.15x magnification, one would need a very strong 5+ diopter to get to half-life size (1:2) while a short 16mm extension already gets you there. It depends on how strong a lens performs at MFD but in general terms, we should strive for the shortest tube or weaker diopter to achieve the highest IQ for equal magnification.
Feb 01, 2020 at 12:06 PM
Steve Spencer Offline • • • • • • • Upload & Sell: On
keepcoding wrote:
The thing that bothers me most with extension tubes and close-up lenses is that I cannot use IBIS with those methods (needs to be turned off, unless I am missing something).
I am back to macro lenses.
You can always get IBIS with a close-up lens. The camera doesn't even know it is there, but it won't be all that effective. Depending on which tubes you use you can get IBIS with tubes as well. For IBIS you are probably better off with a tube without electronic contacts and then you can set the focal length to the optimum focal length for IBIS like you do for an adapted lens without contacts. Either way, however, don't expect much effectiveness for IBIS. I find even for macro lenses, IBIS for closeup focussing is not very effective. If you use it a tripod is definitely the way to go. So in terms of stabilization close-up lens/tubes < macro lens <<< any lens on a tripod. IBIS just isn't very effective for close-up photography, but you can get a small benefit even with a close-up lens or tubes.
So someone asked for comparison between the CV 50/2 and CV 65/2. Here's my attempt. Note, it serves no artistic purpose and is basically just trying to tease out aberrations. I'm throwing in the FE 55/1.8 as a freebie. All shot on the a7R III, focusing on the same twig on one of the branches. I processed these through PhotoNinja to make sure that there wasn't some flag on the RAW turning on corrections. (PN doesn't support that feature.) No added sharpening, minimum adjustments.
All those jumping all over the 50, I'm not seeing it being substantially different than the 65. The 65 isn't perfect either (a lens that isn't perfect....news at 11.) Both are noticeably better than 55.
Steve Spencer wrote:
You can always get IBIS with a close-up lens. The camera doesn't even know it is there, but it won't be all that effective. Depending on which tubes you use you can get IBIS with tubes as well. For IBIS you are probably better off with a tube without electronic contacts and then you can set the focal length to the optimum focal length for IBIS like you do for an adapted lens without contacts. Either way, however, don't expect much effectiveness for IBIS. I find even for macro lenses, IBIS for closeup focussing is not very effective. If you use it a tripod is definitely the way to go. So in terms of stabilization close-up lens/tubes < macro lens <<< any lens on a tripod. IBIS just isn't very effective for close-up photography, but you can get a small benefit even with a close-up lens or tubes....Show more →
Yes, the camera doesn't know it is there, and that is exactly the problem. It still assumes the focus distance hasn't changed, therefore cannot counteract camera shake correctly. It is probably safer to turn IBIS off.
The point of a close-up lens or tube for me is to get a little closer when I don't have a macro lens or tripod with me. So it is either handheld or macro lens + tripod.
So someone asked for comparison between the CV 50/2 and CV 65/2. Here's my attempt. Note, it serves no artistic purpose and is basically just trying to tease out aberrations. I'm throwing in the FE 50/2 as a freebie. All shot on the a7R III. I processed these through PhotoNinja to make sure that there wasn't some flag on the RAW turning on corrections. (PN doesn't support that feature.)
All those jumping all over the 50, I'm not seeing it being substantially different than the 65. The 65 isn't perfect either (a lens that isn't perfect....news at 11.) Both are noticeably better than 55.
So someone asked for comparison between the CV 50/2 and CV 65/2. Here's my attempt. Note, it serves no artistic purpose and is basically just trying to tease out aberrations. I'm throwing in the FE 50/2 as a freebie. All shot on the a7R III. I processed these through PhotoNinja to make sure that there wasn't some flag on the RAW turning on corrections. (PN doesn't support that feature.) No added sharpening, minimum adjustments.
All those jumping all over the 50, I'm not seeing it being substantially different than the 65. The 65 isn't perfect either (a lens that isn't perfect....news at 11.) Both are noticeably better than 55.
Thanks Fred, I'm glad they came out okay. I finally got out to do this, and it started to spritz a little. By the time I was back to my car it was a drizzle.
tsdevine wrote:
Thanks Fred, I'm glad they came out okay. I finally got out to do this, and it started to spritz a little. By the time I was back to my car it was a drizzle.
-Tim
The 55/1.8's axial CA is the one that bothers me the most when shooting wide open. Axial CA and purple fringing are very obvious.
On the other hand, I rarely see color error in CV 65/2 APO images. The CV 50/2 is not as well corrected but it's not easy to spot axial CA. Perhaps in extreme conditions only.
So someone asked for comparison between the CV 50/2 and CV 65/2. Here's my attempt. Note, it serves no artistic purpose and is basically just trying to tease out aberrations. I'm throwing in the FE 55/1.8 as a freebie. All shot on the a7R III, focusing on the same twig on one of the branches. I processed these through PhotoNinja to make sure that there wasn't some flag on the RAW turning on corrections. (PN doesn't support that feature.) No added sharpening, minimum adjustments.
All those jumping all over the 50, I'm not seeing it being substantially different than the 65. The 65 isn't perfect either (a lens that isn't perfect....news at 11.) Both are noticeably better than 55.
Guys I have not been following this lens. Been busy moving and such but I know I want this and just have a nice CV 21,CV 50 travel kit. I'm on this downsizing kick. House 2700 to 1500 yea drastic but I'm loving it.
GMPhotography wrote:
Guys I have not been following this lens. Been busy moving and such but I know I want this and just have a nice CV 21,CV 50 travel kit. I'm on this downsizing kick. House 2700 to 1500 yea drastic but I'm loving it.
GMPhotography wrote:
Guys I have not been following this lens. Been busy moving and such but I know I want this and just have a nice CV 21,CV 50 travel kit. I'm on this downsizing kick. House 2700 to 1500 yea drastic but I'm loving it.
What prompted the move, Guy? If you don't have kids at home any more 1500 is a much more manageable and pleasant size to live in than bigger, IMHO.
All shot on the a7R III, focusing on the same twig on one of the branches. I processed these through PhotoNinja to make sure that there wasn't some flag on the RAW turning on corrections. (PN doesn't support that feature.) No added sharpening, minimum adjustments.
