Forum: Pentax SLR Lens Discussion
04-17-2018, 10:02 AM
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Numerous reasons.
The 60-250 is shorter, narrower, lignter, WR, has silent AF, has in-camera corrections (not valid for FF, of course), has an easily removable foot, is optically better (the Tamron even things out at approximately F5.6 or F8 depending on the focal length). The 60-250 has more reach (that extra 10mm at the wide end really makes a difference), the build quality is better, switching to MF on the lens is much easier, it is much more comfortable to carry on a strap or camera mounting clip (like Peak Design's Capture clip). There is no way I'd ever walk around with the Tamron on a clip, much too cumbersome. I prefer the Pentax's general rendering (bokeh, colours, etc).
The two flaws of the 60-250 when compared to the Tamron 70-200 are that it extends when zooming (that can be a problem or not) and that at close distances and long focal lengths, it shows some focus breathing (the effective focal length changes). Walking one step to the front or the back solves this. Of course there's the one stop of aperture difference, it might be a deal breaker for some. I can use the FA77 or DFA 100 macro WR if I ever need a faster short tele, or crank up the ISO.
I hope I have answered the question. Others might put more emphasis on some perks or flaws, I've explained my point of view.
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Forum: Pentax SLR Lens Discussion
11-20-2017, 01:53 PM
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YMMV, but having used both extensively, there is no way the Tamron could replace the 60-250 for me. Especially now that I've modified the 60-250 for full frame. It's a much better lens in my opinion.
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Forum: Pentax SLR Lens Discussion
11-20-2017, 05:59 AM
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You got good answers, I'll simply confirm that the 16-50 and 50-135 cannot be modified for full frame. The 55, 200, 300 and 560 are already compatible. Some DA lenses such as the 40 can work also without corrections, but the camera has no profiles for it.
I'd be tempted to use a much faster lens for this, such as the 77 or 100 macr WR. Or maybe the 50-135 but its AF is slow.
F4 might be enough regarding light, but performers more all the time, so you might not be able to freeze the movements so much.
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Forum: Pentax SLR Lens Discussion
06-28-2017, 04:46 AM
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Sorry to hear that. I hope you're getting better.
I'm thinking dropbox or Google Drive (or Microsoft's Onedrive?) would probably be simplest.
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Forum: Pentax SLR Lens Discussion
06-26-2017, 05:33 AM
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Forum: Pentax SLR Lens Discussion
05-29-2017, 10:10 AM
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I thought your solution let you completely replace the original tube, baffle, etc with the new ones?
There was no "before" shot.
That's impressive. It certainly is not a problem in general use. Wow.
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Forum: Pentax SLR Lens Discussion
05-29-2017, 04:46 AM
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The best test would be to shoot either a blank wall or a blue sky, with each of the baffles, at F4. Ideally at 60, 135, 250mm. Then a proper comparison could be done. I'd be happy to make actual vignetting calculations with these images.
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Forum: Pentax SLR Lens Discussion
05-26-2017, 04:44 AM
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That is a very clever idea. Based on the reports by others I'm pretty confident that the one without the cutout will work. Regarding the one WITH the cutout, please share your results!
If it works, would you be willing to share the 3D printing file? I have a colleague who owns a printer, maybe he could print one version for me.
Thanks.
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Forum: Pentax SLR Lens Discussion
04-12-2017, 01:01 PM
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You mean you'd sell the whole lens so someone could Frankenstein the baffle out of it? If you'd consider selling only the baffle, I'd be interested.
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Forum: Pentax SLR Lens Discussion
01-30-2017, 06:01 AM
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Well, performances are certainly impressive regarding vignetting. Even better than I would have thought.
do you notice any decrease in sharpness for regular shooting? That's my main concern as an optical designer, I worry that the baffle was there for a valid reason.
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Forum: Pentax SLR Lens Discussion
01-09-2017, 05:47 AM
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Nearly? Other posters suggest there is no difference.
I can't wait to see your comparison, that looks impressive!
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Forum: Pentax SLR Lens Discussion
01-03-2017, 12:15 PM
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I wouldn't mind doing it for others. I haven't done my lens yet, but after reading what others have posted, I don't foresee any problem. I modified a Vivitar series 1 70-210 in the past (the aperture tab protection was too large for DSLRs).
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Forum: Pentax SLR Lens Discussion
11-02-2016, 12:39 PM
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Can I suggest taking a before/after picture in a controlled environment? For instance, set your tripod somewhere, take an interesting subject, and repeat after the test? Make sure the light doesn't change, if at all possible, and take pictures wide open, at 60, 135 and 250mm.
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Forum: Pentax SLR Lens Discussion
09-29-2016, 05:29 AM
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Just to be clear, there are two options for this mod:
1-separate the baffle and tube from the rest of the assembly, and replace the tube by something else (cardboard in this case).
2-grind the baffle and put the tube back in place.
Option 1 is reversible but might add dust to the inside of the lens (from the cardboard), plus the cardboard might not protect some internal elements as well.
Option 2 is permanent (unless you purchase back the tube and baffle, at apparently 25$ USD) but retains the original tube.
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Forum: Pentax SLR Lens Discussion
09-28-2016, 04:59 AM
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The calculation I made was in order to fit the largest rectangle possible inside the circle. Using composition adjustment (if at all possible with the modified lens) would not be influenced by removing more, if there's a problem it will come from the corners anyway.
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Forum: Pentax SLR Lens Discussion
09-20-2016, 04:56 AM
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I calculated the maximum rectangle that should fit into the circle. Just so interested people can build themselves a jig to remove only what's needed.
I might be overthinking, that's entirely possible. A part of me is worried at hacking away part of a 1000$+ lens. And being an optical designer myself, I appreciate that we rarely include useless components into our designs. So before modifying my lens, I want to know as much as possible about the consequences.
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Forum: Pentax SLR Lens Discussion
09-19-2016, 12:56 PM
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For those interested, I've gone ahead and made the calculations as to what's needed to cut a rectangular window. The long axis of the rectangle needs to be 2.83cm in length (I went all in on significant digits...) and the short axis needs to be 1.89cm. If you can cut this shape, aligning it correctly with the flange (maybe using the foot and plane surface as a reference) then there's no need to remove the whole flange.
Note : the opening won't look like a rectangle at all, but like a circle with triangles protruding from it...
I'm still undecided on this. If anyone wants to tackle the proposed test I wrote above, let me know!
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Forum: Pentax SLR Lens Discussion
09-14-2016, 01:06 PM
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Here's an idea for testing the amount of vignetting. We can use an unmodified lens and shoot it on APS-C (or use Photozone's data, which is usually very reliable). Next someone who made the modification could take images wide open at 60, 135 and 250mm, shooting a blank wall or pure sky. It would be easy to calculate the vignetting (in %) and see how the values compare. We'd see if, regarding vignetting, we get results comparable to what the lens gives on APS-C without the modification.
Regarding general IQ, flare and ghosting could be tested by shooting a bright source at a slight angle, at varying apertures and 60mm.
I'm willing to analyse results if someone who made the modifications is willing to provide test images.
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Forum: Pentax SLR Lens Discussion
09-12-2016, 09:14 AM
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The metal is pretty thick for cutters, I'd worry about warping the rest of the part.
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Forum: Pentax SLR Lens Discussion
09-12-2016, 06:53 AM
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I've been thinking about a way to do that. Resting the lens on its foot, with the notch properly aligned, and using a straight angle guide might do the trick (if placed on a regular surface). The more I think about it, the more I like it. I'm not sure I have the right tools for my Dremel, however. I might begin with the rotating grinder and finish with a file for the corner.
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Forum: Pentax SLR Lens Discussion
09-09-2016, 12:34 PM
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Good. Have you tried it on an APS-C body?
I wouldn't call it slow, but definitely slower than the newest lenses. I use mainly the 60-250 and the 16-85 and I find that they mostly give me comparable expectations. A wider lens will always focus faster, if only because user movements are less of a problem.
The things that bothers me the most nowadays is using a screw-drive lens ;)
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Forum: Pentax SLR Lens Discussion
09-09-2016, 12:25 PM
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That would be nice, a bit like lenses that have a rectangular opening at the back. However, properly aligning the corners would be a real challenge.
I have no problem using a Dremel, and I also have a colleague who owns a machine shop... I may ask him.
I'll look closely at the few "before-after" samples that we have, and decide what I want to do. Having a FF 60-250 F4 sounds like a dream, but not at the risk of degrading the optical performances of the lens.
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Forum: Pentax SLR Lens Discussion
09-09-2016, 08:08 AM
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I'm trying to understand this, as I'm really not comfortable inserting paper or cardboard inside a lens. I'd rather dremel out a small part of the lens, but I want to understand the process beforehand.
I took the images from jatrax's wonderful post (thanks, at last a visual explanation) and added red on the part that I think I must grind. If anyone can confirm that this is correct, I'd be a happy camper (and I can decide if I want to make the modification or not).
Thanks!
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Forum: Pentax SLR Lens Discussion
09-18-2015, 11:39 AM
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Even without that mod, the 60-250 works pretty well at many focal lengths.
I'm guessing that baffle serves to
1-make the lens more telecentric
2-reduce coma
3-reduce internal reflections, flare, etc
4-act as an internal hood of sorts
Pick one (or more). Without having access to the exact lens design it's hard to do better than educated guesses.
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