some good lens info

SONYNUT · Post by **SONYNUT** » Fri Jul 01, 2011 12:32 am

http://www.coinimaging.com/Lens_tests.html

Craig Gerard · Post by **Craig Gerard** » Fri Jul 01, 2011 1:01 am

SONYNUT,

Good find.

An interesting compilation written by forum member (mgoodm3)

Craig

canonian · Post by **canonian** » Fri Jul 01, 2011 6:19 am

Valuable info! Thanks!

mgoodm3 · Post by **mgoodm3** » Fri Jul 01, 2011 4:43 pm

I haven't added any tests in a few weeks. haven't had a lot of time lately. Hopefully I will get a new one up sometime soon.

Doing numerical testing has taught me a lot over the last couple years.

Chris S. · Post by **Chris S.** » Fri Jul 01, 2011 6:03 pm

Good information--thanks, Mark! This sort of testing and presentation must take forever.

I do have a question. In your review of the Nikon 135mm f/4 bellows lens, my monitor shows prominent magenta fringing on some portions of the example image, while your findings indicate: "Chromatic Aberration: This lens show minimal color fringing in the center (about 0.25 pixel) and minimal on the periphery (0.10 - 0.20 pixels)."

Subjectively, on my monitor, the sample images show what I'd consider severe magenta color fringing. Am I actually seeing something else? Is the perception of fringing increased in reducing these images for the Web?

Best regards,
--Chris

mgoodm3 · Post by **mgoodm3** » Fri Jul 01, 2011 7:23 pm

Interesting observation. I guess that there are two choices for the fringe on that image:

1: longitudinal CA: since the focus plain is higher on the relief of the coin, the fields are significantly behind the plane of focus. That opens the door for longCA. When you measure the CA with a target at the focus plane, this CA won't be as obvious.

2: It's actually a "purple fringe" caused by the detector mocrolenses. caused by the strong reflection off of the fields at the edge of the relief. Although the color looks a bit off to me for a purple fringe.

I will have to look into this. Maybe this will change the way that I rate CA. I may need to take images of my target tilted to the lens to see how much LongCA actually shows up in real life DOF.

Craig Gerard · Post by **Craig Gerard** » Fri Jul 01, 2011 8:34 pm

Mark,

I can see the fringing also; but I must say, that is a gorgeous coin!

http://www.coinimaging.com/images/nikon_135bel_2to5.jpg

Craig

Harold Gough · Post by **Harold Gough** » Fri Jul 01, 2011 10:35 pm

It seems that f4 is more useful than often reported, usually by inference when insisting on f2.8, in this forum, if you don't need corner sharpness, often not an issue for macro:

http://www.coinimaging.com/oly_38-28.html

Harold

rjlittlefield · Post by **rjlittlefield** » Fri Jul 01, 2011 10:55 pm

Harold Gough wrote:It seems that f4 is more useful than often reported, usually by inference when insisting on f2.8, in this forum, if you don't need corner sharpness, often not an issue for macro:

http://www.coinimaging.com/oly_38-28.html

I just checked through my records. Almost all my Olympus 38 mm shots are at f/4 or f/5.6, some at f/8 if sharpness is not critical, only one or two at f/2.8. My standard reference HERE, panel 2, agrees with Mark's results that f/2.8 is no sharper than f/4, while giving up substantial depth of field. I don't think I ever ran the 38mm at f/2.8 after doing those tests.

By the way, at http://www.coinimaging.com/oly_38-28.html and similar pages, it's important to note that in the graph of "Corner Sharpness vs Aperture", higher is worse not better. This is a graph of loss, not retention. The lens is far better in the corners at f/4 than it is at f/2.8.

--Rik

Harold Gough · Post by **Harold Gough** » Sat Jul 02, 2011 12:09 am

Thanks, Rik.

That's reassuring, as I have used the 38mm for a lot of shots with film, probably mostly at f5.6 or f8. I must try it with digital. That lens on the telescopic tube is a lot lighter than the X-pan plus Marumi.

I missed that higher is worse, the other way round being more intuitive, at least before breakfast.

Harold

lauriek · Post by **lauriek** » Sat Jul 02, 2011 4:52 am

rjlittlefield wrote:
Harold Gough wrote:It seems that f4 is more useful than often reported, usually by inference when insisting on f2.8, in this forum, if you don't need corner sharpness, often not an issue for macro:

http://www.coinimaging.com/oly_38-28.html
I just checked through my records. Almost all my Olympus 38 mm shots are at f/4 or f/5.6, some at f/8 if sharpness is not critical, only one or two at f/2.8. My standard reference HERE, panel 2, agrees with Mark's results that f/2.8 is no sharper than f/4, while giving up substantial depth of field. I don't think I ever ran the 38mm at f/2.8 after doing those tests.
--Rik

I have to mention this depends on sensor size, from my tests - nothing scientific I hasten to add - my OM38/2.8 is sharper at f2.8 on a 4/3 sensor and reasonable extension, I can see it going noticeably softer over the whole frame at f4, I assume diffraction softening.

(Of course I'm stacking so the small dof caused by lots of extension and wide aperture aren't a problem)

ETA - I wish I kept records!

Harold Gough · Post by **Harold Gough** » Sat Jul 02, 2011 5:03 am

lauriek wrote:I have to mention this depends on sensor size, from my tests - nothing scientific I hasten to add - my OM38/2.8 is sharper at f2.8 on a 4/3 sensor and reasonable extension

Good news for my micro 4/3. Of course, I have used it for several years on ISO 100 film.

Harold

seta666 · Post by **seta666** » Sat Jul 02, 2011 5:04 am

First of all thank you Sonynut for the links and mgoodm3 for those nice test (Any posibility to see a test on the JML 21mm

)

rjlittlefield wrote:
Harold Gough wrote:It seems that f4 is more useful than often reported, usually by inference when insisting on f2.8, in this forum, if you don't need corner sharpness, often not an issue for macro:

http://www.coinimaging.com/oly_38-28.html
I just checked through my records. Almost all my Olympus 38 mm shots are at f/4 or f/5.6, some at f/8 if sharpness is not critical, only one or two at f/2.8. My standard reference HERE, panel 2, agrees with Mark's results that f/2.8 is no sharper than f/4, while giving up substantial depth of field. I don't think I ever ran the 38mm at f/2.8 after doing those tests.

By the way, at http://www.coinimaging.com/oly_38-28.html and similar pages, it's important to note that in the graph of "Corner Sharpness vs Aperture", higher is worse not better. This is a graph of loss, not retention. The lens is far better in the corners at f/4 than it is at f/2.8.

--Rik

I have used the Olympus for a few weeks now and I have to say I am very satisfied with this lens; however, having it a pupil ratio of 0.85 does not mean that it actually works at f4.7? please, correct me if I am wrong

I can understan lauriek when he says the lens is sharper with good extension at f2.8, I have used it now at f4 up to 4-5X, going above that I would use it at f2.8 (because of diffraction, also corner sharpness would be quite even at that magnification)

I plan to run a test against JML, I think they are pretty similar

Harold Gough · Post by **Harold Gough** » Sat Jul 02, 2011 5:15 am

seta666 wrote: I can understan lauriek when he says the lens is sharper with good extension

It was my understanding at the time that lenses of that era, some three decades ago, and pre-aspherical design, were significantly sharper towards the centre. As you increase extension an increasing proportion of the images is from the centre or thereabouts. This is not specific to macro lenses but applies right up to super-telephotos. With the latter a teleconverter is more likely to be used and might negate some of the increase in resolution.

Harold

seta666 · Post by **seta666** » Sat Jul 02, 2011 5:33 am

Harold Gough wrote: It was my understanding at the time that lenses of that era, some three decades ago, and pre-aspherical design, were significantly sharper towards the centre. As you increase extension an increasing proportion of the images is from the centre or thereabouts. This is not specific to macro lenses but applies right up to super-telephotos. With the latter a teleconverter is more likely to be used and might negate some of the increase in resolution.

Harold

I agree with that, but I was meaning being sharper at f2.8 than at f4
I have also used teleconverter with microscope lenses with very good results
Regards