65mm +1.4x ext. tube same as 90mm lens?

[chris77]

well, what would be the actual difference (fow etc).
obviously loosing speed, but the increased sharpness of the excellent 65 l-a sekor z, could it be worth it?

 

[wiltw]

photozone.de used to test the Canon 70-200mm zooms and measure MTF for lens alone, then also with the Canon 1.4x teleconvertor attached. They generally found about -10% loss in MTF in using the Canon teleconvertor with various incarnations of the Canon 70-200L zooms (f/2.8, f/4, IS, non-IS). So unless your 65mm is at least 10% better in MTF to begin with than the 90mm, the teleconvertor+lens combination will not win.

I am not familiar with the 65mm lens, but if it were designed for macro distances while the 90mm is not, the macro designed lens will indeed perform better at very close focus distance and for flat field correction, while the conventional (non-macro) lens will not perform as well.

OTOH, in doing a bit of web searching, it seems the 65mm is not a 'macro' design but merely a wide angle lens for the Mamiya. And teleconvertors are NOT designed to perform will with 'retrofocus' optical designs, they are designed to be used with 'telephoto' optical designs. So that points to the 90mm signficantly outperforming the WA+telecon combination!

 

[chris77]

photozone.de used to test the Canon 70-200mm zooms and measure MTF for lens alone, then also with the Canon 1.4x teleconvertor attached. They generally found about -10% loss in MTF in using the Canon teleconvertor with various incarnations of the Canon 70-200L zooms (f/2.8, f/4, IS, non-IS). So unless your 65mm is at least 10% better in MTF to begin with than the 90mm, the teleconvertor+lens combination will not win.

I am not familiar with the 65mm lens, but if it were designed for macro distances while the 90mm is not, the macro designed lens will indeed perform better at very close focus distance and for flat field correction, while the conventional (non-macro) lens will not perform as well.

OTOH, in doing a bit of web searching, it seems the 65mm is not a 'macro' design but merely a wide angle lens for the Mamiya. And teleconvertors are NOT designed to perform will with 'retrofocus' optical designs, they are designed to be used with 'telephoto' optical designs. So that points to the 90mm signficantly outperforming the WA+telecon combination!

very good information.. thanks!!

 

[Dan Fromm]

I just reread the original post, realized that although the poster wrote "extension tube" it meant "teleconverter." The two are not at all the same.

Whether or not using a TC behind a wide angle lens is wise, it can be done. OP, if you have the lens and TC, try the combination out.

 

[RalphLambrecht]

well, what would be the actual difference (fow etc).
obviously loosing speed, but the increased sharpness of the excellent 65 l-a sekor z, could it be worth it?

lens plus teleconverter will never be as good as original lens but if the converter is of great design, it may be good enough for you;example: I use a Carl Zeiss 250mmf/5.6 plus a Carl Zeiss 2x converter;it's not as good as the 50mm Carl Zeiss, which I can't afford but, the images are quire decent.I just use 400ISO film instead of 100 ISO film to compensate for the light loss and take images ,I otherwise couldn't.

 

[tedr1]

not as good as the 50mm ? perhaps this is 500mm?

 

[chris77]

lens plus teleconverter will never be as good as original lens but if the converter is of great design, it may be good enough for you;example: I use a Carl Zeiss 250mmf/5.6 plus a Carl Zeiss 2x converter;it's not as good as the 50mm Carl Zeiss, which I can't afford but, the images are quire decent.I just use 400ISO film instead of 100 ISO film to compensate for the light loss and take images ,I otherwise couldn't.

i am talking about an extension tube. its just a ring.
are we talking about the same thing here?

 

[pentaxuser]

I am so confused now that I need to go back to the B&H ship/no ship thread for a bit of restorative therapy

pentaxuser

 

[markbarendt]

i am talking about an extension tube. its just a ring.
are we talking about the same thing here?

An extension tube's whole job is to allow focusing on subjects that are closer to the camera. It reduces the minimum focus distance.

The change in f number is purely based on the distance from the aperture to the film, not a change in optical characteristics.

65 with extension is not equal to 90.

 

[MattKing]

65 with extension is not equal to 90

This is correct.
What you get is a 65mm lens that only focuses close.
In the case of the RB or RZ 65mm lenses, a range between close, and really close.
Where did you get a reference to a "1.4" extension tube? They are usually described in terms of how much extension they add in millimeters.

 

[chris77]

An extension tube's whole job is to allow focusing on subjects that are closer to the camera. It reduces the minimum focus distance.

The change in f number is purely based on the distance from the aperture to the film, not a change in optical characteristics.

65 with extension is not equal to 90.

thanks for pointing it out!

 

[jeffreyg]

+1 for what Mark says. The confusion is calling the ring 1.4x. The extension tubes are usually designated in millimeters and do not have lenses. Teleconverters are ie 1.4x and 2x and have a lens and extend the focal length of the lens they are coupled with with your example making your 65mm a 91mm. I have the Hasselblad 2x and find images made with it and several of my lenses to be very sharp. I too use it with 400 speed film and a sturdy tripod.

http://www.jeffreyglasser.com/

 

[chris77]

This is correct.
What you get is a 65mm lens that only focuses close.
In the case of the RB or RZ 65mm lenses, a range between close, and really close.
Where did you get a reference to a "1.4" extension tube? They are usually described in terms of how much extension they add in millimeters.

ok. i see that i made a mess here....
my mistake. i dont really know how i come up with 1.4 extension...
well.. nevermind then!
and tx everybody!

 

[Leigh B]

An extension tube is just a rigid, inflexible bellows. It's not an optical component or system.

It has a defined length, which cannot be changed. If you want a variable length, use a bellows.

- Leigh

 

[markbarendt]

ok. i see that i made a mess here....
my mistake. i dont really know how i come up with 1.4 extension...
well.. nevermind then!
and tx everybody!

No need to apologize, no mess. You just learned 2 things instead of one.