[jeremy_c]

I bought a 16-50 DA* today and took a snap of a magazine page using the FA 50mm f/1.4 prime, 18-55mm 3.5-5.6 AL II kit lens and the new 16-50mm DA*. I was in Av @ 5.6, ISO 100. I did add +1EV for the 18-55mm kit lens because it's always -1ev or more on my camera for some reason. Other than that, I made no other corrections. The word in the center, "also" was my focus point. This is a 100% crop on the center of the image.

18-55mm AL II


16-50mm DA*


50mm prime


Now, I do not know what this test really proves, but I did find a few things interesting.

#1... The 16-50mm set to 50mm produces a wider image than my 50mm prime.
#2... The prime was brighter, washing out the image a bit
#3... The 16-50mm is a big step from the kit lens (obviously)

Now, I have 10 days for a complete refund and 30 days to exchange. How can I test my lens to make sure it's a good batch? My serial number is 9029841. I paid a higher price from a local retailer so that I could easily return, get another if necessary and I want to take advantage of that, if necessary. I don't want to go searching high and low to find a fault, but if my lens has a common problem and could/should be better, I would like it to be and think I paid for a good one :-)

Thanks for any input,

Jeremy

[Marc Sabatella]

#1... The 16-50mm set to 50mm produces a wider image than my 50mm prime.

It's very typical with zooms that they only achieve their stated focal length when focuses at infinity. The closer in you focus, the wider the angle of view becomes even when leaving it at the same focal length setting.

BTW, if your kit lens produced an image that dark with +1EV, something would seem seriously wrong...

[arbutusq]

A better wayto do the test is to set the camera up in manual mode, using the same Av and Tv. The 18-55 will be a bit darker than other lenses even with manual for some reason. I did a test about that a year ago and posted the results on the forum. The test I posted was with the 16-45 but I have tested it with other lenses as well.

[Douglas_of_Sweden]

A better wayto do the test is to set the camera up in manual mode, using the same Av and Tv. The 18-55 will be a bit darker than other lenses even with manual for some reason. I did a test about that a year ago and posted the results on the forum. The test I posted was with the 16-45 but I have tested it with other lenses as well.

He has got the same aperture and ISO and almost the same exposure time, so I'd say it is good enough comparison.

And it does look like the DA*16-50 is sharper than the A50/1.4! I must get one.
Could you post similar shots at f2.8? These are at f5.6.

Thanks for posting!

[jeremy_c]

A better wayto do the test is to set the camera up in manual mode, using the same Av and Tv. The 18-55 will be a bit darker than other lenses even with manual for some reason. I did a test about that a year ago and posted the results on the forum. The test I posted was with the 16-45 but I have tested it with other lenses as well.

One of my complaints with the 18-55 was I always had to do +1EV at least when in any program mode (Sv, Av, Tv, TAv, P, or Green). I was wanting to test how the camera handled each lens in a manner I would normally shoot. For instance, I have taken quite a few shots w/my prime, then put on my 18-55 and forgot to add the +1EV and shot away. I am sure I'll be doing plenty more of that.

Now, with the 16-50, seems I don't have to remember to do a +1EV at all on it because the camera handles the lighting just fine. As for the 18-55, I'll probably put it back in it's original box and store it incase my other lens needs to go back for repair or something. I'm pretty sure I will not get anything reasonable out of a kit lens on the used market.

Jeremy

[jeremy_c]

BTW, if your kit lens produced an image that dark with +1EV, something would seem seriously wrong...

I agree. I did post on the forum asking a question about it before but the general consensis was that the kit lens did produce darker lenses. It was suggested that I get a new focus screen. Here is the original thread about my +1EV requirement:

https://www.pentaxforums.com/forums/general-pentax-photography/42619-50mm-pri...pose-same.html

Jeremy

[jeremy_c]

And it does look like the DA*16-50 is sharper than the A50/1.4! I must get one. Could you post similar shots at f2.8? These are at f5.6.

I want to play a bit with my 50mm prime. I did a few focus tests (Home) and it seems that my 50mm prime is front focusing quite heavily. I need to redo the tests to make sure. After I get that sorted out, I'll do a similar test at 2.8.

Jeremy

[ghelary]

2 different lenses of the same focal lenth and at the same aperture won't expose the same.

The reason that the light transmitted on the sensor is not only function of the diameter of the front element of the lense (which determine aperture) but also function of the absortion of the glass elements of the lense.

So if you compare a zoom and a prime, at same focal lense and same aperture, with all other elements equal in manual mode, the image for a zoom will be significantly darker due to a higher number of elements (as compared to the prime)

For that reason, movie technicians speaks about T-stops (for transmission) and not f-stops.

regards,
Guillaume

[audiobomber]

And it does look like the DA*16-50 is sharper than the A50/1.4! I must get one.

In the quick in-store testing I did, the 50mm F1.4 was sharper at 2.8 than the 16-50 was at F4.

My 18-55mm underexposes by .7EV.

[kristoffon]

Without fixing the exposures this comparison is useless... If you can't get well exposed photos from the camera then please do shoot RAW, ISO 280, and fix it there.

[jeremy_c]

Without fixing the exposures this comparison is useless... If you can't get well exposed photos from the camera then please do shoot RAW, ISO 280, and fix it there.

A great deal of my test was to see how the camera was able to expose them. I don't want to have to go into manual mode all the time or tweak my settings. So, if the 18-55 does not expose correctly all by itself, that's a major problem to me. Likewise, if the 50mm prime I have over exposes all the time, that seems to be a problem to me as well.

I wanted to test the whole package, not simply the lens.

Jeremy

[kristoffon]

A great deal of my test was to see how the camera was able to expose them. I don't want to have to go into manual mode all the time or tweak my settings. So, if the 18-55 does not expose correctly all by itself, that's a major problem to me. Likewise, if the 50mm prime I have over exposes all the time, that seems to be a problem to me as well.

I wanted to test the whole package, not simply the lens.

Jeremy

I´m sorry but there must be something wrong with your lenses or camera. I have the FA 50 and the 18-55 kit lens, plus very many others, and would certainly have noticed if there were such a huge problem exposing my pictures. My 50mm prime doesn´t overexpose and my kit lens doesn´t underexpose.

[kibipod]

may be you need to do the focus calibration again to get rid off ff. 16-50mm did nice job.

[jeremy_c]

may be you need to do the focus calibration again to get rid off ff. 16-50mm did nice job.

I have not done a focus calibration on it. I do have a chart from pentaxdslrs.com and I'll give that a go.

Jeremy

[jeremy_c]

may be you need to do the focus calibration again to get rid off ff. 16-50mm did nice job.

Ok, I did fix the focus issue. The prime needed a +5 :-/ Attached are center crops of the new test. The wider view is the 16-50mm (set at 50mm). I used manual mode in this case. ISO 100, f/8, 3sec exposure. You can view full sized images at:

http://jeremy.cowgar.com/files/1650DA-STAR-full-cereal.jpg
http://jeremy.cowgar.com/files/FA50-f1_4-full-cereal.jpg

Jeremy