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09-18-2015, 10:44 AM - 8 Likes   #1
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DA* 60-250 mod for FF

I guess everyone has seen the samples where DA* 60-250 "almost" covers FF with some dark corners.

But Pentax has a patent for a FF 60-250 lens so I thought maybe it is just the baffle at the back causing the dark corners.

So I finally got some time and disassembled mine to remove the baffle - and tested it on sony a7r. The results are pretty good! Dark corners were gone at all focal lengths.
I've noticed some light vingeting on some focal lengths wide open but no more than what I expect from any lens.
Resolution outside the APS-C zone is good as well, except maybe at 250 (but generally mine is somewhat worse at 250 than for example at 200 even on aps-c).

It is a pretty easy mod to do - just unscrew the mount (and make sure you dont loose those spring-loaded contact pins). The baffle is just a black tube that is glued (!?) with some spots of white glue to the back of the mount.
(I find it litte weird that the baffle is just glued that way - almost like it was not part of the original design and they just figured a way do add it later.)

Apparently the glue is not strong so you should be able to easily pry it out of the mount and re-assemble the lens without it. - And you'll have your FF lens ready.

Mod is fully reversible, as you can just glue the baffle back in its place. I guess it's purpose is to reduce internal reflections but I did notice any problems in that regard while testing.
I tested without the hood but I guess it should be fine at least in the 90-250 range.

Anyway, it looks like the FF camera is delayed again but I thought someone might find this information useful.

09-18-2015, 11:04 AM   #2
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That is quite interesting. I wonder what the purpose of the baffle is and how this negatively (if at all) impacts things.
09-18-2015, 11:18 AM   #3
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Interesting...
I was thinking to sell my 60-250 but...it's worth to wait and see how yours is working on upcoming FF (I believe you are buying it that's why you did this mod?).
09-18-2015, 11:39 AM   #4
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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.

09-18-2015, 11:52 AM   #5
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QuoteOriginally posted by UncleVanya Quote
That is quite interesting. I wonder what the purpose of the baffle is and how this negatively (if at all) impacts things.
To my knowledge they put them to prevent reflections form the sensor and other shiny metal parts inside the lens and camera bodies (In a way, similar to what the lens hood is used for on the other side).
Proper solution would be to replace the baffle with one with a larger diameter - which sould be easy as it is basically a short tube with a little ring to glue it to the mount. But so far I did not notice any problems with reflections.
09-18-2015, 12:59 PM   #6
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That's amazing, such an amazing lens will be usable immediately on the new FF.

Not that it matters to my poor self but hey
02-27-2016, 12:06 PM   #7
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Hey npc, thanks for taking the time to post this.

Are you still liking your modded 60-250? Any chance you could post some photos from the A7r?
05-11-2016, 03:50 AM - 3 Likes   #8
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QuoteOriginally posted by npc Quote
I guess everyone has seen the samples where DA* 60-250 "almost" covers FF with some dark corners.

But Pentax has a patent for a FF 60-250 lens so I thought maybe it is just the baffle at the back causing the dark corners.

So I finally got some time and disassembled mine to remove the baffle - and tested it on sony a7r. The results are pretty good! Dark corners were gone at all focal lengths.
I've noticed some light vingeting on some focal lengths wide open but no more than what I expect from any lens.
Resolution outside the APS-C zone is good as well, except maybe at 250 (but generally mine is somewhat worse at 250 than for example at 200 even on aps-c).

It is a pretty easy mod to do - just unscrew the mount (and make sure you dont loose those spring-loaded contact pins). The baffle is just a black tube that is glued (!?) with some spots of white glue to the back of the mount.
(I find it litte weird that the baffle is just glued that way - almost like it was not part of the original design and they just figured a way do add it later.)

Apparently the glue is not strong so you should be able to easily pry it out of the mount and re-assemble the lens without it. - And you'll have your FF lens ready.

Mod is fully reversible, as you can just glue the baffle back in its place. I guess it's purpose is to reduce internal reflections but I did notice any problems in that regard while testing.
I tested without the hood but I guess it should be fine at least in the 90-250 range.

Anyway, it looks like the FF camera is delayed again but I thought someone might find this information useful.
Hallo - I can confirm this text!

I'm from Sweden and phoned the official Pentax rapair-place.

I ordered the part (tube plus part for the SDM-contact glued at it as described above)

For heavens blueberries do not unscrew the whole bayonet. Just remove the SDM - contact thing (two black screws) and the three chrome screws
around on the bayonet itself - symmetrically placed in circle 180 degrees from each other - leave the other (one) screw sitting there.


OK - that's done - lift out the tube together with the "SDM-part". Loosen the glue - and you have the tube in your hands.

Now what I did - I took the tube and "dremmeled" (Search for "Dremmel" - grinder?) away the baffle from inside and out - in order to keep the full length of the tube - cleaned it with compressed air etc - and dropped it back after painting the grinded surface with matte black. Fits perfect! Now I did put on the "SDM-contact holder" and fitted it in. The three screws back on the chrome bayonet holding it - and last I did put back SDM-contact itself. Take care - it forks in to the SDM-bayonet contacts and you must be sure that the tabs fits the forks on the bayonet. Back with the two black screws.

(Before starting buy yourself a professional philips screwdriver set and make sure the screwdriver has "full fit")

Voila!

How it is on my K1 - just as it is the described by the thread starter!!!!! Wonderfull!!!!

If you want back the APC-feeling - just put on the Pentax 1.4-TC.

I'll look in here to see if you have any problems not understanding my explanation - as I'm not English native speaking.

By the way - what happened to my ordered parts from Pentax? They are still in the box - if I want to revert the above work and make it true original again.

Man - What a lens!!!!!!!
Now I love it even more!

I'll keep my K3 for serious tele-photoing, birdings etc
The K5 IIs is now for sale - cheap - anyone???

05-11-2016, 04:45 AM   #9
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QuoteOriginally posted by Gutta Perka Quote
How it is on my K1 - just as it is the described by the thread starter!!!!! Wonderfull!!!!
Good to read that you obtained the results you expected.
Some pictures of the procedure (or parts you used) might help others interested in making the same adjustment in future.
05-11-2016, 05:01 AM   #10
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QuoteOriginally posted by Gutta Perka Quote
Before starting buy yourself a professional philips screwdriver set and make sure the screwdriver has "full fit")
Are the screws Philips (PH) or JIS? Using a PH in a JIS screw can damage the screw as the PH screwdriver cams out of the slot.
05-11-2016, 05:31 AM - 1 Like   #11
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QuoteOriginally posted by p38arover Quote
Are the screws Philips (PH) or JIS? Using a PH in a JIS screw can damage the screw as the PH screwdriver cams out of the slot.
PH was used by me!

---------- Post added 05-11-16 at 02:43 PM ----------

QuoteOriginally posted by rawr Quote
Good to read that you obtained the results you expected.
Some pictures of the procedure (or parts you used) might help others interested in making the same adjustment in future.
I assure You that when You have loosen the tube part - it's self exemplary.
Just take it easy slow and study the parts carefully - you can test yourself by mounting/unmounting the unworked parts.
No springs flying around and so.

But DO NOT UNMOUNT THE WHOLE BAYONET - then you will have springs all over the place.
The thread starter must have had a hell putting back those contact springs connecting to the camera house.
He managed I think because he had unmounted the whole tube and not just grinded away the baffle so he could reach
the contact springs from inside. That doesn't work with my simpler method.

Anyway - I thank the "inventor"!
05-11-2016, 07:33 AM   #12
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This is fantastic. How much did you cut off of the tube? Can you post a pic taken wide open at 250?
05-11-2016, 11:59 AM   #13
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QuoteOriginally posted by ChatMechant Quote
This is fantastic. How much did you cut off of the tube? Can you post a pic taken wide open at 250?
All the baffle out to the tube wall - that is - do not shorten the tube!

No pics needed - You will love it!
05-11-2016, 01:59 PM   #14
npc
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I finally got my K-1 yestarday and the lens works great on it! (Just remember to set the crop mode to FF not auto ).

Looks like Gutta Perka's approach to the mod is much safer/easier to do - I didn't know how the internals are back then so I removed the whole mount but then I had some hard time putting it back together with all the little pins and springs.
05-11-2016, 07:40 PM - 1 Like   #15
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Sounds like Pentax could easily modify the lens design and reissue it as FF. They could offer it at a lower price point for those of us who cannot afford the DFA 70-200mm. Why lose sales to Tamron and Sigma when the lens has already recouped their R&D costs?
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