How do I test and compare lenses

Archived from groups: rec.photo.digital (More info?)

Isn't there a mount to be removed from some lenses before it is fixed to the
adaptor? I'm not suggesting that you immediately start dismantling your
lens, but I seem remember having to do that once a long time ago with an M42
screw lens on a Russian camera, NOT a Pentax.

Archived from groups: rec.photo.digital (More info?)

"teflon" <teflon@bluebottlefly.com> wrote in message
news:BDEDA277.EF1F%teflon@bluebottlefly.com...
> Isn't there a mount to be removed from some lenses before it is fixed to
the
> adaptor? I'm not suggesting that you immediately start dismantling your
> lens, but I seem remember having to do that once a long time ago with an
M42
> screw lens on a Russian camera, NOT a Pentax.
>
That was probably a T-mount lens. They had a threaded adapter that was
similar in size, but a slightly different thread pitch.

Archived from groups: rec.photo.digital (More info?)

"Siddhartha Jain" <losttoy2000@yahoo.co.uk> wrote in message
news:1103618869.666764.215070@f14g2000cwb.googlegroups.com...
>
>
> Suggestions/pointers appreciated.
>

1: There is always the possibility that the adapter that you bought may be
throwing things off. If you could get your hands on an Asahi Pentax screw
mount camera, and conduct the tests using that, you might obtain improved
results, in which case I would recommend that you obtain a genuine Asahi
adapter, rather than an aftermarket one.

2: Your lens might be defective. Takumar lenses are well known for their
sharpness, contrast and build quality. See:
http://www.luminous-landscape.com/ [...] 1-24.shtml

3: SMC Takumar lenses were tested by Popular Photography Magazine, and the
Takumars tested sharper than the Leica lenses. Your test results are
clearly out of line with the conventional wisdom regarding Takumar lenses.

See: http://medfmt.8k.com/mf/rangefinder.html#keppler

I really question the wisdom of testing a screwmount lens on a camera that
uses another lens mount. If anything, your tests just might reveal that the
use of aftermarket adapters may adversely affect lens sharpness.

Archived from groups: rec.photo.digital (More info?)

Scott Schuckert wrote:
>Just how bad ARE your results?

http://www.geocities.com/losttoy20 [...] esize.html

http://www.geocities.com/losttoy20 [...] -crop.html

Unfortunately, I seem to have hit the data transfer limit on geocities


Well, the horrible results are at f/1.4 only and not at other
apertures, so could something still be wrong with the lens?

Funnily, in the f/1.4 image, the part around the centre is a bit more
sharper than the centre itself!!
I am more inclined to think that I goofed up somewhere.

- Siddhartha

Archived from groups: rec.photo.digital (More info?)

Siddhartha Jain wrote:
> Siddhartha Jain wrote:
>> Unfortunately, I seem to have hit the data transfer limit on
>> geocities
>
> Fixed. Now at fortunecity as well.
>
> http://members.fortunecity.com/los [...] esize.html

The f/1.4 seems more focussed on the mug than the text. Do bear in mind
that even the best lenses, when working at large apertures, will only
focus on a plane parallel to the sensor. Take great care to ensure that
your test target is completely flat and parallel with the sensor.

All but the best macro lenses are likely to have a curved "plane" of
focus.

Cheers,
David

Archived from groups: rec.photo.digital (More info?)

"Siddhartha Jain" <losttoy2000@yahoo.co.uk> wrote in
news:1103649121.175680.131530@c13g2000cwb.googlegroups.com:

> http://members.fortunecity.com/los [...] esize.html
>

I think it looks like what I'd expect. The 1/4 makes the foreground and the
background out of focus, and the focus plane (with the water bottle) is in
focus, but a little soft at large aperatures.

Bob

Archived from groups: rec.photo.digital (More info?)

Siddhartha Jain wrote:
> Hello,
>
> Yesterday, after a long wait (US to India by regular mail), I received
> my M42-to-EOS adapter that I had ordered for $12.95 from eBay.
>
> I immiediately set upon comparing the kit lens (Canon 18-55mm) with the
> Pentax Super Takumar 50mm f/1.4 on my Canon 300D.
>
> First, I mounted the camera on a tripod, secured all the screws, set
> the camera to "M" mode and went about shooting a fixed subject indoors.
> Once I set the focus, all I did was change aperture values for each
> successive test shot to compare the difference between various f-stops
> of the lens. I also used timer and MLU.
>
> The images at 1.4 are horribly unsharp. Sharpness started picking up at
> f4, was best at f5.6-f10 and was reasonable at f16.
>
> I compared the kit lens at 50mm f/5.6 to the Pentax 50mm at f/5.6.
> Results were not very different.
>
> But somehow the horrible unsharpness at f/1.4 and the little difference
> in results between the kit lens and the Pentax 50mm left me thinking if
> I've been doing something wrong in the testing.
>
> Other than that the Pentax's focussing ring is damn smooth. Once I went
> back to the kit lens I was *shocked* by the jerky and wobbly focus
> ring. Metering wasn't tough either with the Pentax. In "M" mode, I just
> made sure than the adjustments to the shutter speed kept the exposure
> indicator at "0".
>
> Suggestions/pointers appreciated.
>
> - Siddhartha
>

You did the test right except you should use a FLAT sheet of paper with
fine text as the subject.
All f-16 lenses have optimum sharpness in the 5.6-11.0 range.
This is what you observed.
As the aperture increases, DOF decreases.
f 1.4 will have a very narrow DOF at the distance you took this picture.
The Aquafina bottle is in quite sharp focus at f 1.4
The text which you are using for comparison is out of focus because of
DOF considerations.
Next time use a page from a high quality magazine at about 6 ft. away to
avoid DOF problems and be sure you focus VERY critically at each f-stop.
Whenever I do lens tests with 35 mm SLRs, I use flash illumination (one
on each side at 45° from the subject)to minimize any effects from mirror
bounce or shutter slam. I dont know if the 300D has a mirror or a focal
plane shutter like 35mm, but flash will negate any tripod unsteadiness.
Bob Williams

Archived from groups: rec.photo.digital (More info?)

Colin D wrote:
> There seem to be artifacts around the letters in these shots. What
image
> setting were they shot at? (large/fine probably. You should do this
kind
> of test using RAW to avoid compression artifacts in the image).

These were shot at the highest JPEG setting, don't recall whats it
called.

I realise I will have to switch to RAW soon but I am shooting in JPEG
till I get used to the camera and get to know how to use it optimally.
Other than that I hate to sit on the computer to do post-processing,
but I reckon I will have to learn the dark art of PS processing
- Siddhartha