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07-16-2019, 10:34 PM   #1
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Is anyone using extension tubes with K-1 that don't vignette ~200mm lenses

As I mentioned in another thread, the Kenko 25mm Uniplus tube vignettes on the Pentax 200 macro. The macro needs a short tube to allow rotating to vertical on the K-1. An extension tube with electrical contacts is preferred. Don't need AF screw drive capability.

Also need a tube to allow mounting K-1 to a Pentax K bellows. Electrical contacts aren't needed. So did Pentax or some other company ever manufacture k mount auto extension tubes?
Thanks,
barondla

07-17-2019, 03:48 AM   #2
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Yes, Pentax and I believe Vivitar made auto extension tubes (lever, no contacts, no screw drive). Since the bellows K has no lever on the camera mount side you don't need tubes with a lever either. You may need to have a conductive surface over the pins on the camera mount to get stop-down metering to work.

PENTAX Auto Extension Tube K 100mm reviews - Pentax Camera Accessory Review Database
PENTAX Auto Extension Tube K 50mm reviews - Pentax Camera Accessory Review Database
PENTAX Auto Extension Tube Set K reviews - Pentax Camera Accessory Review Database

These tubes usually go for premium prices due to supply and demand. There's a way over priced set on eBay in the $300-400 USD range. They show up on the Market Place ever so often.

Murry O'neill's excellent Pentax Bellows eBook is recommended reading:
The Pentax Bellows eBook - Articles and Tips | PentaxForums.com

Note: the Vivitar tubes are their Auto Extension Tubes AT-22 (K-mount)
https://www.keh.com/shop/pentax-35-manual-focus-auto-extension-tube-set-12-20-36-696508.html

Last edited by Not a Number; 07-17-2019 at 04:01 AM.
07-17-2019, 03:49 AM   #3
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Yes: I had the same problem rotating my 200mm macro to vertical on a digital going way back (K1 after K3 after K5 after K20 after K10). I have a set of Kenko tubes that have electrical contacts but no AF connection. The shortest one does the job. For the bellows obviously any plain-Jane* K-mount tube will serve. Both genuine Pentax and aftermarket (Vivitar etc.) K-mount tubes are usually available on EBAY, although not the rare 50mm and 100mm tubes from the LX era.

*Am I allowed to use that old phrase, or should it be "plain-John"

ADDENDUM: If you want to see what the Kenko tubes look like, GOOGLE "K-mount Kenko auto tubes" and/or go to KEH and search for same. They don't have any on hand, but they do have an image with a "not currently available" apology

DISCOVERY: Go on EBAY and search for: Movo MT-P56

Last edited by WPRESTO; 07-17-2019 at 05:03 AM.
07-17-2019, 07:34 AM   #4
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QuoteOriginally posted by WPRESTO Quote
Yes: I had the same problem rotating my 200mm macro to vertical on a digital going way back (K1 after K3 after K5 after K20 after K10). I have a set of Kenko tubes that have electrical contacts but no AF connection. The shortest one does the job. For the bellows obviously any plain-Jane* K-mount tube will serve. Both genuine Pentax and aftermarket (Vivitar etc.) K-mount tubes are usually available on EBAY, although not the rare 50mm and 100mm tubes from the LX era.

*Am I allowed to use that old phrase, or should it be "plain-John"

ADDENDUM: If you want to see what the Kenko tubes look like, GOOGLE "K-mount Kenko auto tubes" and/or go to KEH and search for same. They don't have any on hand, but they do have an image with a "not currently available" apology

DISCOVERY: Go on EBAY and search for: Movo MT-P56

Thanks for the info WPRESTO. Checked out the Movo tubes. It's exciting they make them for Pentax. Unfortunately, found this little warning in their description: "(Important Note: Cropping will occur on full-frame cameras) ". Bummer. Surprised someone produces tubes that only work 100℅ with crop cameras. The number of complaints from film and ff digital users must be high. Now I know care must be taken to find tubes for Pentax full frame. Guess older film tubes are the way to proceed. Off to check out other options presented in this thread.

Yes, the bellows and A*200 macro were a pain with the K10/20D. The Kenko Uniplus solved that. Then the K-7 and K-01 lost the overhang and were a joy. Now the overhang is back and the old solution doesn't work.

Thanks for all the info & help,
barondla

---------- Post added 07-17-19 at 09:48 AM ----------

QuoteOriginally posted by Not a Number Quote
Yes, Pentax and I believe Vivitar made auto extension tubes (lever, no contacts, no screw drive). Since the bellows K has no lever on the camera mount side you don't need tubes with a lever either. You may need to have a conductive surface over the pins on the camera mount to get stop-down metering to work.

PENTAX Auto Extension Tube K 100mm reviews - Pentax Camera Accessory Review Database
PENTAX Auto Extension Tube K 50mm reviews - Pentax Camera Accessory Review Database
PENTAX Auto Extension Tube Set K reviews - Pentax Camera Accessory Review Database

These tubes usually go for premium prices due to supply and demand. There's a way over priced set on eBay in the $300-400 USD range. They show up on the Market Place ever so often.

Murry O'neill's excellent Pentax Bellows eBook is recommended reading:
The Pentax Bellows eBook - Articles and Tips | PentaxForums.com

Note: the Vivitar tubes are their Auto Extension Tubes AT-22 (K-mount)
Vivitar Auto Extension Tube Set 12,20,36mm, for Pentax K Mount at KEH Camera
Thanks Not A Number for all the info. Will study it as time permits. Hadn't heard of the ebook on bellows.
Thanks,
barondla

07-17-2019, 09:39 AM   #5
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How interesting. Does the optical patterns or the size of the glass in the macro 200's cause the vignetting?
I don't have either of the 200mm macros but have used a de-glassed Takumar-A TC on the M200/4 without any vignetting (also the helicoid K). The TC is about 26mm long.
Found it at a photo store close out already de-glassed and they let me have it for pennies. Bought it mainly for the K bellows because of the mount issue on the K1. No need for the A contact but it is there.
07-17-2019, 10:54 AM   #6
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QuoteOriginally posted by pcrichmond Quote
How interesting. Does the optical patterns or the size of the glass in the macro 200's cause the vignetting?
I don't have either of the 200mm macros but have used a de-glassed Takumar-A TC on the M200/4 without any vignetting (also the helicoid K). The TC is about 26mm long.
Found it at a photo store close out already de-glassed and they let me have it for pennies. Bought it mainly for the K bellows because of the mount issue on the K1. No need for the A contact but it is there.
Don't think it is the optical design alone. A 50mm El-Nikkor enlarging lens reversed on the Pentax K bellows also vignettes when using the Kenko Uni-Plus 25mm extension tube. Why use an extension tube on a bellows? It's the only way to mount the K-1. The big body and prism overhang interfere with the bellows.

I'm eyeing an old teleconverter now for possible deglassification. Also looking at modifying the Kenko extension tube.

Thanks,
barondla
07-17-2019, 11:04 AM   #7
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Will be very curious to see what you find.
Never tried the 50 El-Nikkor when I had it but the 90 and 105 Rodagons don't seem to have an issue on the bellows or reverse mount on the M200.
Was looking for a single 12mm tube to mount on the bellows just because of the overhang but when the TC came around for next to nothing, decided to try that instead.
Just means I'm starting out with a bit more extension to begin with.
How would you modify the Kenko to eliminate vignetting?

Last edited by pcrichmond; 07-17-2019 at 11:06 AM. Reason: more text
07-17-2019, 11:39 AM   #8
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QuoteOriginally posted by pcrichmond Quote
Will be very curious to see what you find.
Never tried the 50 El-Nikkor when I had it but the 90 and 105 Rodagons don't seem to have an issue on the bellows or reverse mount on the M200.
Was looking for a single 12mm tube to mount on the bellows just because of the overhang but when the TC came around for next to nothing, decided to try that instead.
Just means I'm starting out with a bit more extension to begin with.
How would you modify the Kenko to eliminate vignetting?
About midway thru the Kenko there's a plastic light baffle that has a smaller opening than the rest of the tube. It is plastic so should be removable with ingenuity and patience. That's a last resort. The Kenko is important to my APS-c work and difficult to replace. The cheap teleconverters, on the other hand, are expendable.

Thing is, not even sure ff macro is a benefit to things I shoot. May use the K-01, K-7, orK-1 in crop mode. Will keep everyone updated.
Thanks,
barondla

07-17-2019, 12:00 PM   #9
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I would have never thought of a baffle in a tube. Will keep an eye on this thread to see what you come up with.
07-17-2019, 03:16 PM   #10
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As for extension tubes without baffles...it is not unusual to have shallow round baffle flush with the mount opening, but that should not vignette except with a fixed rear element at the extremes for diameter and even then only if the exit pupil is at or proximal to the lens flange. All that being said, some physical vignette is not unusual wide-open with longer lenses particularly if the front element is deeply set or if a hood is attached.

That last in mind, I mounted my Pentax-M 200/4 on my Ricoh XR-2s 35mm film SLR and evaluated for vignette at the image frame through the rear, no hood attached. Here is what I saw:
  • Lens alone -- Mild physical vignette at infinity* wide open at lens filter ring that resolves at f/5.6
  • Lens with 14mm Soligor extension -- same as lens alone
  • Lens with 24mm Soligor extension -- same as lens alone
  • Lens with 32mm Soligor extension -- same as lens alone
  • Lens with full stack Soligor extension -- same as lens alone
There was no interference at the exit pupil** from the tube's built-in baffle.

I then did the same test with my Dine' 100/2.8 Macro, a lens having a rear element of near maximum diameter fitted fixed with a few millimeter protrusion into the mirror box face. The Dine' also has its front element shallow to the lens front and filter ring.
  • Lens alone -- Physical vignette at infinity wide open at lens filter ring that resolves at f/4.0 or extension of the lens to 1:2 magnification mark on lens barrel
  • Lens with 14mm Soligor extension -- same as lens alone except resolution at 1:3 magnification mark
  • Lens with 24mm Soligor extension -- same as lens alone except resolution at halfway between 1:10 and 1:3 magnification mark
  • Lens with 32mm Soligor extension -- same as lens alone except resolution at 1:10 magnification mark
  • Lens with full stack Soligor extension -- no vignette
Again, there was no interference at the exit pupil from the tube's built-in baffle.

While these results are not directly applicable to the Pentax A* 200/4.0 Macro on the K-1, a similar test using a 35mm film body might help determine if the vignette is due to the Kenko extension tubes and if the baffle is the point of interference. After all, any vignette would be present regardless of whether the body is film or digital.


Steve

* Vignette was the same at infinity and MFD with that lens.

** Giving this some thought, this behavior is strongly expected since the exit pupil is typically distal to the mount flange on other than retrofocus lenses.

Last edited by stevebrot; 07-17-2019 at 10:38 PM. Reason: Edited for the correct 200/4.0 Macro model
07-17-2019, 08:30 PM   #11
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Thanks @stevebrot, always nice to learn something. Even though I picked up on the baffle having an effect behind the lens my mind kept the focus of the vignette coming from the way the light was entering the front or directing in the optic formula. Brain wasn't putting the rear element into play - half of an equation will always leave one guessing. I'll have to pull out the old 1000 and do some testing myself.
07-17-2019, 10:37 PM   #12
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QuoteOriginally posted by pcrichmond Quote
Thanks @stevebrot, always nice to learn something. Even though I picked up on the baffle having an effect behind the lens my mind kept the focus of the vignette coming from the way the light was entering the front or directing in the optic formula. Brain wasn't putting the rear element into play - half of an equation will always leave one guessing. I'll have to pull out the old 1000 and do some testing myself.
This sort of thing is hard to figure out without the camera, extension tube, and lens in hand. It may be that a less sophisticated tube may help here, but it is hard to tell.


Steve
08-31-2019, 05:47 AM   #13
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the pentax extension tubes should work the best... no electrical contacts, but they have aperture linkage so you can set the aperture on the aperture ring and still see what you're doing through the ovf. using extension tubes on long lenses doesn't get you as much magnification gain like a 50mm or 70mm. good luck!
09-02-2019, 12:35 AM   #14
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With my DA* 200mm F2.8 the Uniplus 25 only vignettes a little bit, it can be easily corrected...
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