Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-01-2010, 01:59 AM   #1
Veteran Member
milesy's Avatar

Join Date: Jan 2009
Location: Melbourne
Photos: Gallery
Posts: 379
300mm Lens

HI all

i have 2 lenses that reach 300mm one is the Sigma 28-300 and the other a Vivitar 70-300.

I have been playing with both of them (with the k-7) and zoomed out to 300mm on either lens i am not exactly happy with the result that i get - the pictures seem to be extremely soft.

I didnt have the vivitar at the time, but when i hade the IST i didnt seem to have this problem.

any ideas on why i would be seeing the issue now?

I know this is an open question and not that easy to answer but an responses would be well received

thanks

11-01-2010, 02:14 AM   #2
Inactive Account




Join Date: Aug 2008
Location: Michigan, USA
Photos: Gallery | Albums
Posts: 7,484
The camera is out resolving the lens. At least that's the excuse I've read most. My Tamron 70-300 is a little soft at the 300mm end as well.

11-01-2010, 02:50 AM   #3
Veteran Member
milesy's Avatar

Join Date: Jan 2009
Location: Melbourne
Photos: Gallery
Posts: 379
Original Poster
but what does this mean exactly (if that is the reason)
11-01-2010, 05:16 AM   #4
Loyal Site Supporter
dcmsox2004's Avatar

Join Date: Apr 2008
Location: rhode island
Photos: Gallery | Albums
Posts: 7,331
hi milesy....... as a long time shooter, i've had the tamron, and too found that at 300mm, about f8 or so, the images were a wee bit soft and also suffered from purple fringing around the subject in bright conditions.... the 28-300 type of lens is a good all around lens.. but it does not yield those really great, sharp photos that a 300mm prime can, or a better quality zoom lens is able to achieve... unfortunately, to get those sharp shots, better glass is really the answer....
i'd suggest the pentax da 55-300mm lens.... gets very good reviews, reasonably affordable, either new or used..... i'd used mine (sold it to buy more expensive lenses) for quite a while and found it to be quite competent from the wide end of 55mm thru the end at 300mm... (f8 ususally).... if money is no object, the 1st generation sigma 70-200mm f2.8 non macro, the sigma 100-300mm f4 are superb lenses which offer some zoom range capability (over a prime)..... check out the forum lens reviews ... great resource....
best of luck !! dave m

11-01-2010, 05:38 AM   #5
Loyal Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,409
Milesy, are you saying that the lenses don't perform as well on the K-7 as they do on other bodies? If that's the case, it may be something that can be addressed by focus adjustment. In general though (although I'm not familiar with either of those lenses), you can only expect so much in terms of resolution at the extreme end of a zoom.
11-01-2010, 05:58 AM   #6
Senior Member




Join Date: Jun 2009
Location: LAKE PLACID,FL
Photos: Albums
Posts: 110
The resolving power of a lens

A circular opening is similar to the single slit just discussed, except that it exists in two dimensions instead of one. It causes its own form of diffraction pattern. In optical systems, any lens or mirror (e.g. a camera lens or the lens in the human eye) will make an image in which light from each point in the object is spread out over a certain region surrounding the point that is supposed to be (according to geometric optics) its image point. This causes a certain amount of blurring in the image.

Mathematically, the angular resolution of any lens is thus diffraction limited by the following relation.



where D is the diameter of the lens and l is the wavelength. The factor 1.22 is a tradition based on a detailed calcultion of the exact position of the first dark ring in the diffraction pattern. In applications, the relevant angles are very small, so one can replace sinq by q, provided that q is measured in radians

The diffraction limit is a fundamental limitation on the quality of the image, which applies no matter how well the lens is designed or manufactured. It implies that lenses or mirrors used to see very fine details must have relatively large diameters. In the case of microscopes, some people use "oil immersion" lenses: having a layer of oil in contact with the lens reduces the wavelength of the light due to its index of refraction, and thus allows for better resolution with a given diameter D. To see even finer detail, one can use a smaller wavelength by using an electron beam instead of light. (The wave effects of electrons will be studied later in the Quantum Mechanics portion of the course

Mike
11-01-2010, 06:10 AM   #7
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
i am inclined to think the real issue is that with a higher MP image the OP is starting to see detail that was non existant before because he has 2 times the resolution in the sensor.

While many 50/70mm -300mm zooms are reported soft at 300mm and a prime would be better, I suspect the "disappointment" is really just the result of pixel peeping.
11-01-2010, 02:00 PM   #8
Site Supporter
Nowhere Matt's Avatar

Join Date: Nov 2007
Location: Nowhere Land
Photos: Gallery | Albums
Posts: 2,318
I have the Sigma 28-300, K-7 and K10 and noticed this weekend in harsh, bright light at 300mm that it can be a bit soft. I have not yet compared it's sharpness at 300 to my Pentax F 100-300 and it may not matter much to me in any event. I still like how the lens performs for me in many situations.

11-01-2010, 02:03 PM   #9
Veteran Member
milesy's Avatar

Join Date: Jan 2009
Location: Melbourne
Photos: Gallery
Posts: 379
Original Poster
thanks for all your replies guys - its appreciated.

Lowell Goudge - unfortunatley the dissapointment isnt from pixel peeping - in fact its very noticable without zooming at all......i have some photos taken with the same lens a few years back with the 6Mp camera and at first glance they look much better - but its then when you start looking at the detail that i think the issue was there also but was hidden by the lower resolution.

Dadipentak - i tried a quick and dirty focus adjustment on the lens starting at 0 adjustment then going -10 then -5 then +5 then +10..and to be honest the most detail when zoomed in at 100% in photoshop was at the 0 setting - so im figuring that this isnt going to help

As for the 55-300 is t here a massive difference between the DA and the DA L version?? because its looking like i need to buy a new lens.
11-01-2010, 04:49 PM   #10
Pentaxian
Transit's Avatar

Join Date: Aug 2007
Location: Whanganui NZ
Photos: Gallery | Albums
Posts: 4,075
QuoteOriginally posted by milesy Quote

As for the 55-300 is t here a massive difference between the DA and the DA L version?? because its looking like i need to buy a new lens.
L has no quick focus , no hood and a plastic mount.
Picture quality said to be the same.
I just took delivery of DA-L yesterday ($us285 inc 7 day delivery from somewhere in Asia)
I am really really happy with the sharpness wide open at 300mm
Pete
11-01-2010, 05:40 PM   #11
Senior Member




Join Date: Mar 2008
Posts: 102
QuoteOriginally posted by milesy Quote
thanks for all your replies guys - its appreciated.

Lowell Goudge - unfortunatley the dissapointment isnt from pixel peeping - in fact its very noticable without zooming at all......i have some photos taken with the same lens a few years back with the 6Mp camera and at first glance they look much better - but its then when you start looking at the detail that i think the issue was there also but was hidden by the lower resolution.

Dadipentak - i tried a quick and dirty focus adjustment on the lens starting at 0 adjustment then going -10 then -5 then +5 then +10..and to be honest the most detail when zoomed in at 100% in photoshop was at the 0 setting - so im figuring that this isnt going to help

As for the 55-300 is t here a massive difference between the DA and the DA L version?? because its looking like i need to buy a new lens.
I'd recommend grabbing one of the many focus charts to find out exactly how much, if any, front or back focus the lens has. Then you can be sure you're getting the most out of what you've got.

And if you need some temptation, I had the Tamron 70-300 and I recently got the DA* 300mm f/4. There's a whole world of difference in every aspect from lens build quality to focusing to sharpness and PF/CA.
11-01-2010, 06:36 PM   #12
Loyal Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,409
QuoteOriginally posted by milesy Quote
i have some photos taken with the same lens a few years back with the 6Mp camera and at first glance they look much better
I guess it's worth asking if you're making an "apples to apples" comparison--jpeg prints to jpeg prints or jpeg print to computer monitor?
11-01-2010, 10:02 PM   #13
Veteran Member
milesy's Avatar

Join Date: Jan 2009
Location: Melbourne
Photos: Gallery
Posts: 379
Original Poster
for comparison i am looking at monitor to monitor.......i guess the final print if i were to do one may well be different .

here ill put up an example.


both taken at the same F stop and ISO one with the Ist and one with the K-7

both resized for 1000 pixels on the long side

this one with the K-7



this one with the Ist

11-02-2010, 01:21 AM   #14
Veteran Member




Join Date: Oct 2007
Location: France
Photos: Albums
Posts: 804
Hi,
this is a general trend for tele zooms to be softer on the long side; it is a flaw induced by the design of these lenses, a divergent element increase magnification the same way as a TC would do.
If you really want top image quality the DA*300 is the good choice. I own one and this lens outresolves the sensor of the K20D. Already very good at f4 it is stellar at f5.6. It is a recent lens design, state of art, and is completely free of CA and purple fringing, which is very useful in birding. Only issue is that the sdm is a bit slow and there is no focus limited, which would be useful as the lens focus down to 1?5 m (it can be used as a macro lens !)
This is my recommandation
Regards
11-02-2010, 06:23 AM   #15
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by milesy Quote
for comparison i am looking at monitor to monitor.......i guess the final print if i were to do one may well be different .

here ill put up an example.


both taken at the same F stop and ISO one with the Ist and one with the K-7

both resized for 1000 pixels on the long side

this one with the K-7



this one with the Ist
Certainly the K-7 photo appears softer.

Do you mean that both full sized (un-cropped) photos taken with the same lens were re-sampled to 1000 pixels wide; ie, IST 3008 -> 1000; K-7 4672 -> 1000?

If so, some of this is focus, some may be contrast, some may be camera software, but I don't believe it can be because the K-7 sensor pixel density is higher. I think this is true because in both cases about the same fraction of the sensor's width contributed to each photo.

There are clearly focusing problems with the first photo: the blonde hair under the girl's eye is out of focus; it is 4-5 display pixels wide. The woman has a couple individual hairs above her forehead only a 2-3 pixels wide.

Dave
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
300mm, didnt, k-mount, lens, pentax lens, slr lens, vivitar
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Landscape New lens (DA 55-300mm) vs Quantaray 70-300mm charliezap Post Your Photos! 5 08-31-2010 01:19 PM
For Sale - Sold: k100d,pentax 18-55 lens, quantary 70-300mm lens..carying bag and more suzook Sold Items 4 06-23-2010 09:03 AM
K-x: 55-200mm kit lens vs Sigma 70-300mm APO lens ChopperCharles Troubleshooting and Beginner Help 9 01-19-2010 10:16 PM
For Sale - Sold: Pentax k-2000 + kit lens (18-55) + sigma zoom lens 70-300mm dexmus Sold Items 6 11-09-2009 05:25 PM
Best budget tripod for a K20D kit lens and a Tamron 70-300mm lens. shaolin95 Pentax Camera and Field Accessories 13 08-29-2009 11:53 AM



All times are GMT -7. The time now is 02:48 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top