Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-03-2012, 08:06 AM   #16
New Member
prsjnb's Avatar

Join Date: Jun 2010
Location: Wiltshire
Photos: Gallery | Albums
Posts: 24
QuoteOriginally posted by Marc Sabatella Quote
I'd be willing to wager that a 2X TC on the DFA 100 - which would turn it effectively into a 200/5.6 - would yield IQ no better than the DA50-200 at 200 and f/5.6. Which is to say, better than some give it credit for, but if the DA50-200 does the job more cheaply and easily, what would be the point of the TC? Except, as noted, that it will increase magnification at the macro end, and the DA50-200 would not focus that closely.
+1 in every respect, Mark - and, just to prove the point, here are some images captured with said 'kit' lens.

[/url] [url=http://www.flickr.com/photos/garrulusapis/5889304080/]Malachite (Siproeta stelenes) - wings closed[/url] by [url=http://www.flickr.com/people/garrulusapis/]Dr 'B '[/url], on Flickr" target="_blank">

[/url] [url=http://www.flickr.com/photos/garrulusapis/5889305350/]Blue Morpho (Morpho peleides) - wings closed[/url] by [url=http://www.flickr.com/people/garrulusapis/]Dr 'B '[/url], on Flickr" target="_blank">

[/url] [url=http://www.flickr.com/photos/garrulusapis/5888735381/]Blue Morpho (Morpho peleides) - wings open[/url] by [url=http://www.flickr.com/people/garrulusapis/]Dr 'B '[/url], on Flickr" target="_blank">

Jon


Last edited by prsjnb; 06-03-2012 at 08:07 AM. Reason: grammar
06-03-2012, 10:19 AM   #17
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,720
And just to unproved a point, here are some images captured with a Tammy 90 and a Pentax 1.7 converter.















This isn't my best of collection, this is going out in the back yard to capture a few shots and coming back in. No retakes.

Lots more images here.

The disadvantages are the hassle it is putting on, getting the lens focused, you have to manually focus and then let the lens auto-focus, but the IQ? I don't think so.

You can't use the TC on a lens that isn't sharp, it'll just magnify the un-sharpness, but a nice sharp lens like the 100 or the Tammy 90, it shouldn't be a problem.

Last edited by normhead; 06-03-2012 at 10:57 AM.
06-03-2012, 12:53 PM   #18
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
We still don't know WHY the OP wants a TC for a macro lens. But we're having fun suggesting stuff, eh?
06-03-2012, 01:05 PM   #19
Pentaxian
Mike.P®'s Avatar

Join Date: Mar 2008
Location: South Coast .. UK
Photos: Gallery
Posts: 1,734
I use a Pentax 1.7x on the 100mm macro for more working length and extra magnification. Works well most of the time.













06-03-2012, 03:15 PM   #20
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
What the posted images suggest is that *either* the DFA100 + TC *or* the DA50-200 are capable of producing images that reproduce well at web sizes. The question is, would one produce results that are significantly *better* than the other? We'd need a controlled comparison and 100% crops to say for sure. I suspect it would be too close to call, and expect that some would see that as exoneration of TC's, and others as exoneration of the DA50-200 :-)
06-03-2012, 05:38 PM   #21
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,720
I can do it for the Tammy 90, but I don't own a DA 100 WR, if someone could care to send me one? I do have a DA* 60-250 for the comparison. As far as I can tell the Tammy and the 100 are very close. However, the 60-250 is not a macro, and I find the TC does not do as well at distance as it does on close ups. We feel that at distance the Tammy is very slightly superior to the 60-250, I'm willing to bet that won't be the case with a 1.7 x on, but I can take the shots.

A couple more Tammy 90 plus 1.7 images one 100% crop



06-03-2012, 07:37 PM   #22
Site Supporter




Join Date: Jul 2009
Location: Los Angeles, CA USA
Photos: Gallery | Albums
Posts: 621
It is very simple. If the focal length changes, the effective aperature changes by that ratio.


drougge ,

Simply apply the definition AA gives on page 36 of Camera and Lens. You know the focal length and the diameter of the ap. The math is easy. Regardless if the front mounted tele construction is of one element or more, it still changes the focal length. It can also reduce the t/stop value by even a greater amount, but that is another point.

Try checking pages 36-37 of the US Navy Photography training course manual, Volume 1.
Try checking The Kodak Professional Photoguide pagees 40 -41.

As far as resolution goes, I am happy that your mf lens/tele makes you happy. A 2X tele will reduce the resolution by 50% and a 1.4 tele will reduce resolution to of what it was.71%
06-04-2012, 06:34 AM   #23
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,720
QuoteQuote:
A 2X tele will reduce the resolution by 50% and a 1.4 tele will reduce resolution to of what it was.71%
I'm not sure that a one size fits all where every TC ever made is lumped into the same numbers ever works. The Pentax 1.7 is a 5 element TC. Others are as low as 2. It would seem a little simplistic that the same numbers would apply to both of them. Some lenses have as many as 13 elements. Do lenses with fewer elements have more resolution? I guess the question would be does the 2x converter work as if it were just a few additional elements added to the lens. I don't know the answer to these things. I'm just guessing that neither the Navy nor Kodak test every TC ever made, to make sure they were giving you the correct numbers. They probably tested the TC's available at the time, for their equipment.

06-04-2012, 07:40 AM   #24
Site Supporter
Stone G.'s Avatar

Join Date: Jun 2010
Location: North Zealand, Denmark
Photos: Gallery | Albums
Posts: 1,508
QuoteOriginally posted by Marc Sabatella Quote
What the posted images suggest is that *either* the DFA100 + TC *or* the DA50-200 are capable of producing images that reproduce well at web sizes. The question is, would one produce results that are significantly *better* than the other? We'd need a controlled comparison and 100% crops to say for sure. I suspect it would be too close to call, and expect that some would see that as exoneration of TC's, and others as exoneration of the DA50-200 :-)
I don't know, if you will accept my pictures and 100% crops linked to below as being "well controlled"?

TC or not TC

To me, it is fairly simple: The solution isn't alwas "buy another lens". It all depends on one's needs (and budget). A lens has a limited resolution due to its limited entrance pupil and a sensor has a limited resolution due to its finite sensing element (pixel) sizes and you may sometimes need some extra focal length (typically inlunar/planetary- and macro photography) to get your object decently resolved. A lens may "out-resolve" the sensor and due to the finite pixel size, cropping is NOT always the proper solution here.

Obviously, one may always go and buy yet another (costly) lens with a largeraperture and a longer focal length. But given the lens(es) that one have, teleconverters may just provide that extra focal length required to optimize resolution in a given situation. You give your system a chance, so to speak, to exploit the resolving power of your optics.

Last edited by Stone G.; 06-04-2012 at 07:55 AM.
06-04-2012, 09:11 AM   #25
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,720
Just from some fooling around this morning.

The whole image


Three images 1.1 crops
Sigma 70-300


Tamron 90 with 1.7


Pentax DA* 60-250


Best of six images for each lens. The Sigma 70-300 was as usual very strong, it is from 200-300 mm it has problems, The DA* produced arguably the best image although the Sigma has better contrast and the DA* contrast is bumped a bit more. So without further PP I'd venture the Sigma is is the best image. I just think I can get more out of the DA* if I work on it. The Tamron with the 1.7 is the weakest image and has some purple fringing. My light is weak today and I'm shooting at 5.6. So I can't say this is typical of my preferred shooting conditions, but in a similar test, testing all three lenses at 90mm (in other words the Tamron without the TC) the Tamron was judged best of the bunch. There may be conditions where the TC would have done better, i.e. closer to the subject. The subject was shot at about 75 feet away, but at distance, at least in this test, not so good. This is pretty much in line with my work in the field shooting with the TC. The shot I've yet to test is shooting the 250 at full reach and then adding the TC. Is the TC version better than the non-TC version blown up to the same size. SInce I only want the TC for magnification on macros, or extending my reach, that's the other question.

The other question is how much do I have to spend to beat the 60-250 with the TC? I bought and returned a Sigma 120-400, but the IQ and purple fringing were worse than the 60-250 with the TC.

An image shot with the 60-250 with the TC.



Not great, but as I said, better than the Sigma 120-400 would have done. Interestingly enough, the Sigma 120-400 was very similar to using the Tamron with a TC, good enough up close, not so good at a distance.

Another shot taken with the TC. Closer in, much better result. (75 feet instead of maybe 120-150.)



You can get great results with a TC, but you have to understand when to use it. You can't just put it on and pretend like it's a normal lens.

Last edited by normhead; 06-04-2012 at 10:38 AM.
06-04-2012, 11:25 AM   #26
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by Stone G. Quote
I don't know, if you will accept my pictures and 100% crops linked to below as being "well controlled"?

TC or not TC
Nice comparison, but that's somewhat different - comparing TC to cropping, using completely different lenses than the ones being discussed here. That one is already known to give a win for cropping with most consumer lenses, a win for the TC with the "right" lenses. Or in the case of the last comparison, looking at two different lens/combos than the ones being discussed here. I am specifically wondering how the DFA100 + 2X TC compares to the DA50-200. And of course, to what extent the specific TC used affects this.

That said, I'm surprised the TC-versus-cropping comparison came out so clearly in favor of the TC in your first test. I don't know the lens in question, nor the TC, but that wasn't a combination I expected to see come out that way. Definitely shows one should actually perform the experiments (or find someone else who has) rather than assume.

Last edited by Marc Sabatella; 06-06-2012 at 12:20 PM.
06-04-2012, 02:23 PM   #27
Site Supporter
Stone G.'s Avatar

Join Date: Jun 2010
Location: North Zealand, Denmark
Photos: Gallery | Albums
Posts: 1,508
QuoteOriginally posted by Marc Sabatella Quote
-----

That said, I'm surprised the TC-versus-cropping comparison came out so clearly in favor of the TC in your first test. I don't know the lens in question, nor the TC, but that wasn't a combination I expected to see come out that way. Definitely shows one should actually perform the experiments (or find someone else who has) rather than assume.
Well, it is perhaps a bit surprising - but here's what adaptall-2.org has to say about this lens plus TC:

.........Only the similar Nikkor performs better, but not by very much. Macro performance across the central two thirds of the film plane stands up very well against dedicated macro lenses. Amazingly, this lens yields very good macro performance across the entire film plane when used with Tamron's SP 2X tele-converter...........

And I very much appreciate your conclusion about testing rather than merely assuming. That was also, what I hoped to demonstrate.
06-04-2012, 10:28 PM   #28
Site Supporter




Join Date: Jul 2009
Location: Los Angeles, CA USA
Photos: Gallery | Albums
Posts: 621
Normhead,

Some TCs are better than others. Some work better with some prime lenses than others.

The math is simple. The resolution of the tc/lens complex is the result of dividing the resolution of the prime lens by the TC magnification. If the prime lens can resolve/print 100 lines in one millimeter at best, magnifying that result by two will only show half as many lines. For a 2X TC the reduction is by 50%. A 1.4X TC will reduce the resolution to 71%.

If the resolution approaches that of the medium (film, sensor), thatn there will be no noticable reduction of resolution. Of course all lenses and TCs degrade the image to a greater or lesser degree.

The references to the books that I made are about calulation of f/stop values, not resolution.
06-05-2012, 11:28 AM   #29
Loyal Site Supporter
drougge's Avatar

Join Date: Jan 2010
Location: Malmö
Photos: Gallery
Posts: 787
QuoteOriginally posted by lmd91343 Quote
It is very simple. If the focal length changes, the effective aperature changes by that ratio.
If, and only if, the actual aperture doesn't change size.

QuoteOriginally posted by lmd91343 Quote
Simply apply the definition AA gives on page 36 of Camera and Lens. You know the focal length and the diameter of the ap. The math is easy. Regardless if the front mounted tele construction is of one element or more, it still changes the focal length. It can also reduce the t/stop value by even a greater amount, but that is another point.

Try checking pages 36-37 of the US Navy Photography training course manual, Volume 1.
Try checking The Kodak Professional Photoguide pagees 40 -41.
I don't have those books, but I'm pretty sure of my point anyway. On a simple lens the aperture and the front (only) element is the same thing. On camera lenses this is no longer the case, but the aperture can still be no larger than the front element. I'm pretty sure you agree so far.

Now the bit you're missing: When mounting a front tele converter you now have a completely different, possibly larger, front element. This is the new maximum aperture, and the size of the old front element no more limits the f-stop than does any other internal element.
06-05-2012, 11:49 AM   #30
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,720
hmmmm... the more I read stuff the more confusing it gets. That's why in the end, I always just go take some pictures.
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!
dfa, k-mount, lens, macro, pentax, pentax lens, pentax smc dfa, quality, slr lens, smc, teleconverter, teleconverter for pentax
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax FA135 or DFA 100 Macro vsl3-e Pentax SLR Lens Discussion 6 03-03-2012 02:10 PM
For Sale - Sold: Pentax 100/2.8 Macro WR (DFA-SMC) benroy Sold Items 2 02-14-2012 11:30 AM
For Sale - Sold: Samsung D-Xenon Macro 100 2.8 (same as DFA 100 2.8 Non-WR) icywindow Sold Items 4 12-07-2011 10:35 AM
Macro: Viv S1 105 vs Pentax DFA 100 WR mtngal Pentax SLR Lens Discussion 17 08-28-2011 03:29 PM



All times are GMT -7. The time now is 11:38 PM. | See also: NikonForums.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