pentax macro 100 2.8 onto ist digital any good?

Hi,
i saw some 100 2.8 macro lenses which where quite cheap now.

what's the quality aspect when put onto a digital ist camera? Do you need the D variant or not?

Willie Jan

The quality on digital is superb. I know several of these lenses have come onto the used market in the States, and I can't understand why.

There was one report that somebody experienced some CA with this lens on a DSLR, but I haven't observed this.

I see no reason for it to perform differently on different DSLR bodies.

Mine's not for sale!

G

Hi George,

Today's dumb question - what's CA?

I've got a few guesses but would rather know for sure as I have a Macro lens and want to know everything about it.

Thank's as always,

Chromatic aberration. Noticed as a purplish fringe. Common with non-Pentax lenses!

G

I ask this because i see on the pentax product page:

The PENTAX smc P-D FA 100mm F2.8 macro is designed specifically for digital cameras. It utilizes curvature and positioning of optical elements to virtually eliminate flare and ghosting for clear, high-quality images particularly important to digital photography. This versatile lens can also be used a telephoto lens and features our acclaimed multi-layer coating to lower surface reflection, reduce ultraviolet rays, and deliver clear, high-contrast images.

Is the 1.5 factor (making it a 150 lens) a benefit? Does the DOF stay the same?

Thanks.

The DOF stays the same providing the magnification stays the same, but the lens will have to be moved further away to get all the subject in. That holds true for using, say, either a 50mm or changing to a 100mm macro.

When you use the 100mm on a DSLR you also gain DOF because of the smaller sensor size (format) and it's too early to think about that!

Hmmm. Can't agree... sorry

Take for example, 100mm, f2.8, subject at 30cm, the DOF is:
35mm = 1mm
*ist-D = 0.7mm

at 1m subject:
35mm = 1.5cm
*ist-D = 1.0cm

So, actually the DOF is shallower with the digital. Why?
Because the "circle of confusion" is different. (We've been here before )

http://www.dofmaster.com/dofjs.html
and
http://tangentsoft.net/fcalc/help/CoC.htm


Actually, in practise, it doesn't matter
And with digital you can just check the LCD for the actual DOF after shooting, or rattle off a few at different apertures and delete later. The joys of digital

The 100mm macro f2.8 performs wonderfully on the *ist-D. It was me who experienced some CA - but only on a very extreme example where I had bright summer sun.
As a macro lens it is superb. As a portrait lens it's excellent (although renders all the subject's imperfections too!) Very, very sharp, and beautiful colour.
Definitely recommended
Matt

I know there is some disagreement over this generally, and I also know that the definition of the circle of confusion can be changed, and so the difinition of DOF will change.

Bur look at it this way. If we have a standard lens on a large format, medium format and 35mm camera all showing the same image, then there will be more DOF the smaller the format gets. This is because a 50mm lens behaves like a 50mm lens, has more DOF than a 80mm, etc.

So at the smallest extreme, a Minox uses a 15mm lens and has so much DOF nothing is out of focus.

In each of these cases the circle of confusion will be defined differently, but that isn't an issue.

The digital format is smaller than 35mm, so fitting its standard lens (a 31mm?) into the scheme of things, this will have more DOF than the 35mm camera standard lens. It can't be any other way. And we know that small digital compacts with tiny format sensors and very short focal length lenses get just about everything in focus, which fits very well into this argument IMHO.

However, the question was about macro. Let's stick to 35mm and as long as the image is kept to the same magnification, the DOF with a 50mm or 100mm macro will be the same, as long as the 100mm is moved further away from the subject to get the same field of view.

Now the sensor or the film won't directly affect DOF, or we would be arguing that a 25 ISO film had more or less DOF than a 400 ISO one. That can't be true, so the sensor resolution equally shouldn't be a factor.

I've seen this written both ways round in magazines and text books, so lots of people are confused, but I'll stick to the above and invite being corrected!

Completely in agreement there John When you are talking about comparing equivalent angles of view then yes you are right the smaller the sensor the larger the DoF.

But we were discussing a 100mm lens taken from 35mm and placed on digital. The angle of view is different, and because the APS sized CCD requires more enlargement (because it's effectively a crop of the full 35mm frame), the circle of confusion is different (check out the CoC defn). Net result is shallower depth of field, for the same focal length (but the angle of view is completely different).

So, for the 100mm f2.8 the DoF will actually be shallower on digital and you need very careful focussing

Just hope WJ Bons can follow these posts! LOL!

Matt

That's an important point for the Online Depth of Field calculator linked above. Enter the actual focal length, and not the effective focal length. i.e. Enter 100mm for the macro lens under discussion, irrespective of body type.

Just hope WJ Bons can follow these posts! LOL!

No problem!

What i want to do is not buying a lens that just fits the aps size, where after two years a full frame sensor comes out and you can sell your D-lenses.
So when i can live some time with this, until a full frame is there....

besides that i sometimes use a 645 120macro with an adapter on my mz-s, (manual). Nice quality but not usable for quick moving insects...

You'll do fine with the FA 1:2.8 100mm macro. Incidentally, it is a very well-made lens - construction quality is superb.

G

Just to chime in.....I own this lens and can confirm it works well with the *ist D, sharpness is great and CA is almost non-existent. Remember that with digital it is the equivalent of a 150 mm lens. Also it is worth noting that the lens is very heavy.