Help - Wrong mount?


cubicon

New Member
Jul 8, 2006
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Choa Chu Kang
#1
Hi guys, bought a cheapo extension tube from ebay. says its for pentax k mount.

I can mount the lenses on one end, but to the body end i just cant get it to rotate and sit in. Did i get the wrong mount or i do not know how to mount a tube ? please help. pic as below

i tried to browse a few other tube in ebay and they look the same.



:)
 

detritus

Senior Member
Sep 12, 2009
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shootingbugs.blogspot.com
#3
ok... judging by the looks of it, that's the "100% manual" type of extension tube, with no mechanical coupler, whatsoever.

generally, it should mounts on the camera just like any k-mount lens - red dot to red dot, slot in, turn.

if the ebay ad u bought from states PK mount but it doesn't fit, then u better revert and tell them.

if u want, can meet me somewhere between yishun and woodlands. i can a set of tubes u can use to compare against the ones u have to determine if there's really something wrong.
 

edutilos-

Senior Member
Dec 28, 2010
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#4
Is it just me or is the dot slightly off?





The 2 images of K-mount I could find show the dot within the boundaries of the arc, rather than outside. But it could be parallax error.

Btw, TS, which part of the mounting process can't you achieve? Can you slot the tube onto the body, but can't turn, or?
 

cubicon

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Jul 8, 2006
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Choa Chu Kang
#5
i can mount to it the body but just cannot turn it in. i will take a better shot later and post it up.

my 2nd purchase for a reverse mount just reach as well, no problem turning it in ...
 

detritus

Senior Member
Sep 12, 2009
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shootingbugs.blogspot.com
#6
i can mount to it the body but just cannot turn it in. i will take a better shot later and post it up.

my 2nd purchase for a reverse mount just reach as well, no problem turning it in ...
u mean it mounts onto the body but it doesn't lock when u turn it is it?
 

cubicon

New Member
Jul 8, 2006
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Choa Chu Kang
#7
your tube's body end seems to have this raise part instead of being flat across?
anyway here is the picture, looks align to me ...

 

edutilos-

Senior Member
Dec 28, 2010
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#9
Ah, I thoguht it was parallex error.

Try to check with the seller? Sometimes the QC is not so good, might be some misalignment or not made well.
 

detritus

Senior Member
Sep 12, 2009
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shootingbugs.blogspot.com
#10
i cannot even turn it, the resistance is very obvious
that sounds like its very poorly made! better don't force it! it may damage the mount on your camera.

seriously, if i receive goods of this quality, i will inform the ebay seller. sounds like the dimensions are off by a few mm.
 

detritus

Senior Member
Sep 12, 2009
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shootingbugs.blogspot.com
#12
yeah, just email the seller, hope he gives a replacement piece
if the seller is willing, suggest u either work towards a partial or full refund. forget the replacement.

this type of manual tube is very hard to use. because there's no "auto aperture" mechanism, the VF becomes very dark when u step down.

to use this kind of tubes, u have to manual focus wide open, step down after achieving desired focus distance, then press shutter to take the photo. needless to say, u'll get a lot of misses.

look for a set of vivitar "auto" tubes instead (or if u can get PK-A ones, even better).
 

cubicon

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Jul 8, 2006
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Choa Chu Kang
#13
i was just buying these to mess around with the macro, thats why i got the reverse mount as well.

also, there is a thing i dun quite understand with tubes. it is mentioned in quite a lot of sites. when using tube, the F-stops gets affected.

Does it means i have to step down F2.8 -> F4.8

OR

does it means the image will look like it stepped down x-stops ?
 

edutilos-

Senior Member
Dec 28, 2010
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#14
i was just buying these to mess around with the macro, thats why i got the reverse mount as well.

also, there is a thing i dun quite understand with tubes. it is mentioned in quite a lot of sites. when using tube, the F-stops gets affected.

Does it means i have to step down F2.8 -> F4.8

OR

does it means the image will look like it stepped down x-stops ?
Neither, I think...?

On the other hand, the extension moves the lens aperture farther away from the film, and so by the inverse-square law of light falloff, the image on the film is fainter. This leads to longer exposure times, which is sometimes a pain. If I'm shooting a flower and there are puffs of wind, I may lose the shot if I try using an extension tube. For example, when shooting life-size macro using lens extension, you lose two full stops of light. If you have TTL metering, your camera meter sees this dimmer light and automatically gives you the correct exposure to use. But if you are using a separate light meter, you have to figure out how much exposure to add by means of a calculation.
Timothy Edberg Photo Tip: Macro Photography Methods

2. There is light fall off when using any extension tube, sometimes the equivalent of 3 f-stops of light is lost when using multiple extension tubes together. This light lost can affect the camera's ability to auto focus. Manual focusing is recommended should the lens begin to "hunt" (not lock onto the subject).
THK Photo Products, Inc.

Depth of field is a function of magnification and magnification alone. Doesn't matter if you have a macro lens, a lens on extension tubes, a lens with closeup filters or whatever. DOF is exactly the same and at high magnification there isn't much of it!

DOF is based on the actual working aperture, so it's the marked aperture modified by the reduction due to the added extension.
70-200 f/4 with 36mm extension tube - depth of field? - Photo.net Canon EOS Forum
 

detritus

Senior Member
Sep 12, 2009
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shootingbugs.blogspot.com
#15
i was just buying these to mess around with the macro, thats why i got the reverse mount as well.

also, there is a thing i dun quite understand with tubes. it is mentioned in quite a lot of sites. when using tube, the F-stops gets affected.

Does it means i have to step down F2.8 -> F4.8

OR

does it means the image will look like it stepped down x-stops ?
if u can post the original article, it'll be better so pple can respond to the exact context :)

frankly, these tubes makes macro painful! there are much easier ways to achieve magnification.
 

cubicon

New Member
Jul 8, 2006
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Choa Chu Kang
#16
if u can post the original article, it'll be better so pple can respond to the exact context :)

frankly, these tubes makes macro painful! there are much easier ways to achieve magnification.
such as a reverse mount ? :D

exact article ... most prob cant find it anymore. it's those random websites on photography that i surf when i am bored
 

detritus

Senior Member
Sep 12, 2009
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shootingbugs.blogspot.com
#17
cubicon said:
such as a reverse mount ? :D

exact article ... most prob cant find it anymore. it's those random websites on photography that i surf when i am bored
Such as using the 18-55 kit lens, which can focus close and magnify up to 0.25. (Free)

Such as getting a raynox 250. (100+)

I never liked reverse lens. Feels very "messy". Very hard to handle also. Too close.

Anyway for macro, its common to step down to f8 and beyond cos dof is very shallow.
 

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