Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-05-2020, 02:31 PM - 4 Likes   #1
Pentaxian
swanlefitte's Avatar

Join Date: May 2015
Location: New Orleans
Photos: Gallery
Posts: 3,220
The 55-300 PLM +1.4x tc aw testing extreme detail

I have been meaning to do this for awhile. Many surprises.
I measured off 40 feet or about 12.2 meters and couldn't find text I couldn't resolve. I had to search until I found text close to 0.5mm tall.It is able to resolve 1/2000 of the distance. That is like meter high leters at 2 kilometers!
I photographed indoors under a plant light on tripod with 2 second delay. Each shot once in zoomed liveview on the 'g' in 'Amygdalu' after spending time to get the best I could.
I copied just the part of each together and also transformed the smaller ones to compare same size.

So I believe the tc helped.
I also found that I could not get the lens and tc to hit 300mm I believe it DOESN"T. 294 or 322mmn, 210 x1.4 or 230x1.4. I believe there is no continuum, only discrete steps.
Next, 294mm is larger than the 300mm. I suspect focus breathing at 300 is greater than at 210mm but this could have to do with steps from 210-230.

The bottom was an after thought to show the size, not focused. No resizing is done to the original 3, only to copies for uniform viewing. Basically all the excess photo was taken away and what was left is a composite of the relevant data.

Attached Images
 
08-06-2020, 01:28 PM - 1 Like   #2
Pentaxian
swanlefitte's Avatar

Join Date: May 2015
Location: New Orleans
Photos: Gallery
Posts: 3,220
Original Poster
The question came up as to when the af will struggle. The first problem(?) was that pentax af works so well in low light even my worst lens was focusing well after my light meter couldn't function! The sigma 18-35 f/1.8 actually struggled the most.I had to find something with less contrast. I wish I had some standard to go by. In good light some things like a painted wall still won't focus until the light rakes enough to show contrast. I pulled out a black bag that holds my tripods. Then I slowly added light until I could get focus when the lens aperture was f/6.3 where the lens is about to go to f/8. (With the plm and 1.4x tc this is wide open so the camera is focusing with this aperture.) I spun the focus and when it consistently hit focus I kept that light. Next I zoomed in until the aperture switched to f/8. It could not focus even with many tries it couldn't. from full focus without hunting to zero focus came at this point.
The combo in the low contrast scene will focus in light at f/6.7 3 seconds and completely fails at f/8 3 seconds. The grain of a wood door was enough contrast that I couldn't reach failure. The paint next to the door was low enough contrast that with ample light I couldn't get success.
again as above the lens between f/6.3 and f/8 jumped from 135 and 150 in discreet steps without continuum (189, 210 with the 1.4x). I didn't test for this though.
Attached Images
 

Last edited by swanlefitte; 08-06-2020 at 01:54 PM.
08-06-2020, 02:24 PM   #3
Site Supporter
Site Supporter




Join Date: Nov 2012
Location: North Wales
Photos: Gallery | Albums
Posts: 2,306
Interesting test. Which camera?
08-06-2020, 02:30 PM - 1 Like   #4
Pentaxian
swanlefitte's Avatar

Join Date: May 2015
Location: New Orleans
Photos: Gallery
Posts: 3,220
Original Poster
This was all on the ks-2. I should have noted that. Thanks.

08-06-2020, 09:29 PM   #5
Senior Member




Join Date: Apr 2019
Location: Tomsk, Russia
Posts: 114
Interesting that 210mm + TC is sharper than 300mm.
08-07-2020, 12:29 PM - 1 Like   #6
Pentaxian
swanlefitte's Avatar

Join Date: May 2015
Location: New Orleans
Photos: Gallery
Posts: 3,220
Original Poster
Today I tried corner sharpness. Lining up for the corner is somewhat guess work because they are all different sizes. This is with focus on the corner not center focus.
294 on the left, 420 center 300 on the right.

The corner sharpness from 200 to 300 falls sharply on this lens so one would expect the 294 or 210mm to be sharpest and it still is. what is interesting is that the tc+lens is now worse than the lens alone. Their are 2 possible reasons I can see. 1 is the quality of the tc is also much better in the center. 2 is that there is a sharpness threshold where the tc enhances or diminishes a lens. You can see the plm sharpness measurements here. Pentax HD Pentax-DA 55-300mm f/4.5-6.3 ED PLM WR RE Review | ePHOTOzine keep in mind this is from one copy on a certain sensor with a certain resolution.

To check this one could test on a k3ii for a lens that scores over 1750 and under 1750 and see if the higher score gets better with a tc and the lower score gets worse.
Attached Images
 
08-09-2020, 04:41 PM   #7
Pentaxian
swanlefitte's Avatar

Join Date: May 2015
Location: New Orleans
Photos: Gallery
Posts: 3,220
Original Poster
Next test is testing the tc. Is is better in the center or is it that it only helps lenses above a critical sharpness?
I used my sharpest lens, the Sigma 70 macro. Being a macro it is also sharp in the corners, more than the 55-300 plm in the center.
I found 20 feet or about 6 meters gave me the "just barley" zone.
You can see the tc+70 on the far left is the sharpest, this was focused in the center. The tc +70 on the far right is next sharpest. the 70 alone focused on the center (left center) and the 70 focused on the corner (right center) are about the same. Enlarged versions between.
This confirms my suspicion that a critical sharpness is needed for the tc to help with detail. It also shows that the tc is better in the corners than I suspected. This doesn't really help since most lenses are much weaker on the edges. It could be a tool to make blur even more pronounced in unfocused areas.

last the sigma 70 is sharp at the corners but it does have fall off. The fact that this test doesn't show much difference in the center to corner is probably because the area of the test is so small there simply are not enough pixels on it. This lens is so sharp that at 20 feet it resolved what the 55-300 plm was resolving at 40 feet. If you assume the focus breathing at 300mm bringing the plm down to 210mm, that is still 3x the 70 and the 70 could resolve this at only 2x.

This research is bringing me to another goldilocks zone. Where is it better to have one great lens and crop vs multiple cheap lenses. Will my sigma 18-35 at 20 and cropped beat my kit 18-50 at 50? Will my sigma 70 cropped, beat my takumar 135? This might be coming next.
Attached Images
 
08-10-2020, 02:57 PM   #8
Pentaxian
swanlefitte's Avatar

Join Date: May 2015
Location: New Orleans
Photos: Gallery
Posts: 3,220
Original Poster
so today I tested my Sigma 18-35 art at 18mm f/6.7 vs my dal 18-50 at 50mm at f/6.7 to see the distance relation. They line up with the 18 at 52" to about the 50 at 109" 52/109=.477 and the 18/50=.36
In theory the 50mm should be able to capture what the 18mm does at 52" at 52/.36=144.45". In reality it needs to be much closer. 18/.477=37.7.
so with my k-s2 I am better off with an excellent 18mm than a just good >38mm. extrapolating more. my 18-35 is better than an average 18-73. This is center sharpness so if the like in the case of the 18-50, that the edge sharpness drops considerably the 18 might be better still and replace a good lens up to >50mm

another surprise found during this test is the focus by wire is discrete steps.it is easy to know when your best focus is achieved because the step is noticeable at such precise levels. Autofocus often stopped one step before best focus. This also means that moving or out slightly when best focus is achieved can create better focus if you are not at an exact distance as a focus step requires.

I guess the main take away here is if you have a great shorter lens, don't bring an average lens to cover every distance. A great wide and a great normal prime is better than an average zoom in terms of resolving power. If I have my 70mm I won't change to my good telephoto until its about twice as far away as I would like to get and even farthur away if I need corner detail. If I had the 100 macro I wouldn't bother with a <200mm unless it was very good.

The other takeaway is that my sigma 18-35 and a 1.4x tc is probably better than an good 18-100.

Thats my thoughts. sigma on the left with it enlarged in the middle at 52" vs dal 50mmm at 109"

Attached Images
 
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, k-mount, pentax lens, plm 1.4x tc, size, slr lens, steps, tc, text
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Da* 300mm f4 or 55-300 PLM with 1.4x teleconverter maciekpruski Pentax SLR Lens Discussion 20 04-23-2020 07:15 PM
55-300 PLM and 1.4x aw rear converter metering incorrect Bernie Troubleshooting and Beginner Help 10 06-01-2019 07:06 AM
55-200, 55-200 WR, 55-300, 55-300 PLM, etc, which telezoom I should get? Bui Pentax SLR Lens Discussion 67 06-25-2018 08:15 PM
55-300 PLM or non-PLM version to K-1? Vignetting etc? HankVonHeaven Pentax SLR Lens Discussion 7 01-29-2017 09:54 AM
1.4x TC + 55-300 versus 1.7x TC + 55-300 versus 55-300mm + cropping. Pentaxor Pentax SLR Lens Discussion 9 09-05-2009 02:41 PM



All times are GMT -7. The time now is 01:45 PM. | 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