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Oly 45 1.8 with Pana GTC1 converter... works !!!

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Gregm61 said:
LMNCT said:
The GTC1 has no effect on the sharpness of the 45 1.8.
Click to expand...
I've seen claims like this before. When the images get posted, another truth comes out. No adapter that adds optical elements to the primary lens have no affect on image quality.
Click to expand...
Aren't you too demanding?

This converter is a cute little thing and it makes silver lens on black body less ugly. What else could one expect from lens? And yes, it takes pictures.





Whith that said, I have to disappoint OP and everybody who expected 90mm F1.8. It's not that, not even close. For $130 it's a useless toy that I will get rid of ASAP.

OP, you should have known better before talking about F1.8 aperture. Just point camera to sky or evenly lit wall and see what exposure camera measures with and without converter on 45mm F1.8 lens.

I will write more details about it in few hours, I have to do something else now.
 
micksh6,

I read your post with interest. You posted a link and then took it off (edit?). Anyways, from your post I take it that you have the tele converter and actually tried it on your own camera. Would love to hear your comments. I'm trying to figure out your comment about 'useless toy' - whether it is sarcasm or whether you really mean that.

I'll say that I have an excellent Panasonic LX3 and with the dedicated wide angel converter, I can find very little degradation - at least not visible to me. It shoots wide open with great sharpness corner to corner with the converter. So some converters can be really excellent.

Thanks,
MTMT
micksh6 said:
Gregm61 said:
LMNCT said:
The GTC1 has no effect on the sharpness of the 45 1.8.
Click to expand...
I've seen claims like this before. When the images get posted, another truth comes out. No adapter that adds optical elements to the primary lens have no affect on image quality.
Click to expand...
Aren't you too demanding?

This converter is a cute little thing and it makes silver lens on black body less ugly. What else could one expect from lens? And yes, it takes pictures.





Whith that said, I have to disappoint OP and everybody who expected 90mm F1.8. It's not that, not even close. For $130 it's a useless toy that I will get rid of ASAP.

OP, you should have known better before talking about F1.8 aperture. Just point camera to sky or evenly lit wall and see what exposure camera measures with and without converter on 45mm F1.8 lens.

I will write more details about it in few hours, I have to do something else now.
Click to expand...
 
LMNCT said:
The new Telephoto converter from Panasonic, GTC1, works very well with the 45 f1.8 and creates a very light 180 mm 1.8 lens. I prefer it on the Oly rather than on the 14-42 GX lens for which it was designed.
Click to expand...
It makes the lens a 90 / 3.6, which is equivalent to a 180 / 7.2 on FF. Big, big difference between a 90 / 3.6 and a 180 / 1.8.
 
Great Bustard said:
It makes the lens a 90 / 3.6, which is equivalent to a 180 / 7.2 on FF. Big, big difference between a 90 / 3.6 and a 180 / 1.8.
Click to expand...
As already discussed in the thread it is a front mounted teleconverter so it is not a 90/3.6 (which would be the case for a rear mounted teleconverter). It would be a 90/1.8 for a properly sized front mount teleconverter.

However, in this case it appears the front element may be undersized for a 90/1.8 so it probably isn't quite that either.
--
Ken W
See profile for equipment list
 
kenw said:
Great Bustard said:
It makes the lens a 90 / 3.6, which is equivalent to a 180 / 7.2 on FF. Big, big difference between a 90 / 3.6 and a 180 / 1.8.
Click to expand...
As already discussed in the thread it is a front mounted teleconverter so it is not a 90/3.6 (which would be the case for a rear mounted teleconverter). It would be a 90/1.8 for a properly sized front mount teleconverter.
Click to expand...
Interesting. So a front end TC changes the diameter of the entrance pupil? Makes sense, I guess, since the entrance pupil (virtual aperture) is the diameter of the iris (physical aperture) as it appears through the front element, thus it makes sense that a front mount TC changes its size.
kenw said:
However, in this case it appears the front element may be undersized for a 90/1.8 so it probably isn't quite that either.
Click to expand...
The FE would have to be 50mm to make the 45 / 1.8 into a 90 / 1.8. Even then, however, it would be equivalent to a 180 / 3.6 on FF. Still pretty good, though!
 
Great Bustard said:
kenw said:
Great Bustard said:
It makes the lens a 90 / 3.6, which is equivalent to a 180 / 7.2 on FF. Big, big difference between a 90 / 3.6 and a 180 / 1.8.
Click to expand...
As already discussed in the thread it is a front mounted teleconverter so it is not a 90/3.6 (which would be the case for a rear mounted teleconverter). It would be a 90/1.8 for a properly sized front mount teleconverter.
Click to expand...
Interesting. So a front end TC changes the diameter of the entrance pupil? Makes sense, I guess, since the entrance pupil (virtual aperture) is the diameter of the iris (physical aperture) as it appears through the front element, thus it makes sense that a front mount TC changes its size.
Great Bustard said:
However, in this case it appears the front element may be undersized for a 90/1.8 so it probably isn't quite that either.
Click to expand...
The FE would have to be 50mm to make the 45 / 1.8 into a 90 / 1.8. Even then, however, it would be equivalent to a 180 / 3.6 on FF. Still pretty good, though!
Click to expand...
Assuming the zoom pic of the GTC1 is accurate:

http://www.jr.com/panasonic/pe/PAN_DMWGTC1/

then given that the outer diameter is 53.5mm, the FE looks to be about 32mm. This, in combination with the 45 / 1.8, would make for 90 / 2.8 (90mm / 32mm = f/2.8) at best (still better than a 2x TC!), which would be equivalent to a 180 / 5.6 on FF.
 
Great Bustard said:
Interesting. So a front end TC changes the diameter of the entrance pupil? Makes sense, I guess, since the entrance pupil (virtual aperture) is the diameter of the iris (physical aperture) as it appears through the front element, thus it makes sense that a front mount TC changes its size.
Click to expand...
Yep, you got it exactly. It effectively magnifies the entrance pupil.
Great Bustard said:
The FE would have to be 50mm to make the 45 / 1.8 into a 90 / 1.8. Even then, however, it would be equivalent to a 180 / 3.6 on FF. Still pretty good, though!
Click to expand...
Yeah, and from the picture of the converter it is questionable that it is really that large. The outer diameter is 53mm and the front element significantly smaller than that. Which means it would "vignette" even on the optical axis. Though a more accurate interpretation would be that the aperture stop is now at the front element if you have the 45/1.8 wide open (the iris of the 45 is no longer actually doing anything optically). In general that means a lot of other optical parameters may now be suboptimal as well (CA, coma, field curvature, etc.) as they vary with aperture stop position.

Not surprising since it was designed for a 42/5.6 lens! Trying to use it with an entrance pupil three times larger probably won't work as intended.

EDIT: I cross posted with your addendum. Good job on the diameter estimate. So yeah, wide open the front element has definitely become the aperture stop of the optical system.
--
Ken W
See profile for equipment list
 
kenw said:
EDIT: I cross posted with your addendum. Good job on the diameter estimate. So yeah, wide open the front element has definitely become the aperture stop of the optical system.
Click to expand...
No, the aperture stop stays with the diaphragm, so the f-number stays the same with the host lens. Just think, you view the diaphragm through the front element (of the converter)

and its size is controlled by the magnification of the converter, not the size of the FE. A too small FE will give you vignetting wide open, but it won't change the f-number.
--
Bob
 
If front mounted teleconverters have little (I will use this word in conjunction with the ongoing debate) effect on F-number then why didn't we see more of them in the film SLR days where most people had a rear mounted 1.4X or 2.0X in their kit bag with the adverse effect on effective maximum aperture?

second question: would you have to remove any filter from your lens before attaching a front mounted TC?
 
MT said:
micksh6,

I read your post with interest. You posted a link and then took it off (edit?). Anyways, from your post I take it that you have the tele converter and actually tried it on your own camera. Would love to hear your comments. I'm trying to figure out your comment about 'useless toy' - whether it is sarcasm or whether you really mean that.
Click to expand...
I didn't edit my recent posts in this thread.

Sure, I got one, few hours ago. I preordered this converter long before, hoping that Panasonic would exceed design specs, but they didn't.

What kenw and Great Bustard wrote about front element size is true, but I only knew outer diameter - 53mm, this might allow close to 50mm front element. I would have liked 90mm F2.5 AF lens too, if front element was smaller. The reality is that rear element size matters too and Panasonic made it ridiculously small.

Panasonic is not to blame, they did what they promised (although IMO it's overpriced). This converter will work on any slow zoom and will provide aperture about F4.8-F5.0 at 42-45mm. Oly 45mm will allow just a bit faster aperture than F5.6, but not even F4.5. Pana X or Oly 12-42mm zooms will not reduce aperture.

The reason I called this expensive toy is that for very little more than $130 one can get Oly 40-150mm zoom. This zoom is about as fast at 90mm (F4.9) and pretty sharp. And it can go longer than 90mm, you know.

Oly 40-150mm zoom was on sale for $100 last year, I thought everyone who wanted cheap tele got it. Now it costs more, $160 refurb at Cameta, but still, IMO, way better value than this converter for $130.

This converter on Oly 45mm will have hard time beating 40-150mm zoom in image quality and it won't have wider aperture. That's the point.

Use case of this converter is probably a lady with small purse carrying GF3 with X collapsible zoom and this thing, with no room for 40-150mm. Pretty limited usage, isn't it? And this breaks IBIS on Oly (Pana OIS will probably break too, neither like being fooled about focal length).

Now, I haven't measured sharpness of this this thing. All above assumed the converter doesn't degrade sharpness in way non-pixel-peepers can see on regular cat photos, which I can trust is true.

I will shoot resolution chart in the next couple of days, and some test shots, just out of curiosity, I need to do some other tests anyway.

OP could have noticed that converter doesn't keep F1.8 aperture. Camera measures around 2.5-2.8 stops less light with it attached. It is even worse than rear-mounted 2x teleconverters. Worst part is that DOF becomes wider as well. Background blur is nonexistent, just like with 90mm F5.0 lens.

On the contrary, other, larger front mounted teleconverters, like mine TCON-17 do not require more exposure (within 1/6 stop granularity). And TCON-17 does provide more background blur, so it really makes 75mm F1.8 lens. But, TCON-17 is too big and heavy.

I guess, there can be no miracles, no cheap fast long AF lens for people. Have to wait for Oly 75mm F1.8 then.

See the rear element of this converter. The filter ring is 37mm, there is Oly lens cap for comparison. The rear element is tiny, good for F5.6, but not enough for much faster aperture.



 
bobn2 said:
kenw said:
EDIT: I cross posted with your addendum. Good job on the diameter estimate. So yeah, wide open the front element has definitely become the aperture stop of the optical system.
Click to expand...
No, the aperture stop stays with the diaphragm, so the f-number stays the same with the host lens. Just think, you view the diaphragm through the front element (of the converter)

and its size is controlled by the magnification of the converter, not the size of the FE.
Click to expand...
Only true if the entire optical system is large enough that you can still see the entire image of the iris from the front of the lens. Trivial example to explain why you are wrong - put a lens cap on a lens with a tiny hole in it. The optical system is not a vignetted F/1.8 optic anymore. It is a F/100 optic with the aperture stop in front of the lens.

In fact, you can't vignette a lens on the optical axis - that violates the definition of vignetting which is based the ratio of transmission from an off axis point to an on axis point. As the ratio of the on axis point to the on axis point is always one there is no vignetting by definition.

The fact that someone happens to put an iris somewhere in a lens does not make it an aperture stop at all. If properly designed the iris coincides with the aperture stop, however this is not always true in an improperly designed optical system.

The aperture stop is defined as the diaphragm or element which determines the diameter of the cone of energy which the optical system will accept from an axial point on the object. That could be the iris, the front element, the back element, a lens cap with a hole in it, or an improperly sized baffle, cold stop or glare stop.

In this case - 45/1.8 with the teleconverter on it - the aperture stop of the system is the front element of the teleconverter for wide apertures. At small apertures the aperture stop is in fact the iris of the 45/1.8.
bobn2 said:
A too small FE will give you vignetting wide open, but it won't change the f-number.
Click to expand...
Ah, no. See discussion above. If the front element constrains the on axis light it is by definition now the aperture stop. For more detail see "Modern Optical Engineering" chapter 9 which has an extensive discussion of aperture and field stops, pupils and baffles with good diagrams.
--
Ken W
See profile for equipment list
 
Thanks! You likely saved me some hassle. I have one on order to be shipped Monday from a NY source. I'll call and cancel tomorrow.

Essentially I had hoped for a 90mm 1.8 equivalent (180mm in 35mm equivalence) but 2.5 to 2.8 stops less light is a non starter for me. I was hoping for a poor man's solution to the upcoming 75mm 1.8 Oly prime and was willing to suffer a bit of resolution loss. But the low light loss is too much as it really, as you noted, not much better than the 40-150 zoom that I already have.

Thanks again! Your type of posts is what makes this forum great and helped me transfer from the Sony NEX system to MFT and it has been the right move for me.

MTMT
micksh6 said:
MT said:
micksh6,

I read your post with interest. You posted a link and then took it off (edit?). Anyways, from your post I take it that you have the tele converter and actually tried it on your own camera. Would love to hear your comments. I'm trying to figure out your comment about 'useless toy' - whether it is sarcasm or whether you really mean that.
Click to expand...
I didn't edit my recent posts in this thread.

Sure, I got one, few hours ago. I preordered this converter long before, hoping that Panasonic would exceed design specs, but they didn't.

What kenw and Great Bustard wrote about front element size is true, but I only knew outer diameter - 53mm, this might allow close to 50mm front element. I would have liked 90mm F2.5 AF lens too, if front element was smaller. The reality is that rear element size matters too and Panasonic made it ridiculously small.

Panasonic is not to blame, they did what they promised (although IMO it's overpriced). This converter will work on any slow zoom and will provide aperture about F4.8-F5.0 at 42-45mm. Oly 45mm will allow just a bit faster aperture than F5.6, but not even F4.5. Pana X or Oly 12-42mm zooms will not reduce aperture.

The reason I called this expensive toy is that for very little more than $130 one can get Oly 40-150mm zoom. This zoom is about as fast at 90mm (F4.9) and pretty sharp. And it can go longer than 90mm, you know.

Oly 40-150mm zoom was on sale for $100 last year, I thought everyone who wanted cheap tele got it. Now it costs more, $160 refurb at Cameta, but still, IMO, way better value than this converter for $130.

This converter on Oly 45mm will have hard time beating 40-150mm zoom in image quality and it won't have wider aperture. That's the point.

Use case of this converter is probably a lady with small purse carrying GF3 with X collapsible zoom and this thing, with no room for 40-150mm. Pretty limited usage, isn't it? And this breaks IBIS on Oly (Pana OIS will probably break too, neither like being fooled about focal length).

Now, I haven't measured sharpness of this this thing. All above assumed the converter doesn't degrade sharpness in way non-pixel-peepers can see on regular cat photos, which I can trust is true.

I will shoot resolution chart in the next couple of days, and some test shots, just out of curiosity, I need to do some other tests anyway.

OP could have noticed that converter doesn't keep F1.8 aperture. Camera measures around 2.5-2.8 stops less light with it attached. It is even worse than rear-mounted 2x teleconverters. Worst part is that DOF becomes wider as well. Background blur is nonexistent, just like with 90mm F5.0 lens.

On the contrary, other, larger front mounted teleconverters, like mine TCON-17 do not require more exposure (within 1/6 stop granularity). And TCON-17 does provide more background blur, so it really makes 75mm F1.8 lens. But, TCON-17 is too big and heavy.

I guess, there can be no miracles, no cheap fast long AF lens for people. Have to wait for Oly 75mm F1.8 then.

See the rear element of this converter. The filter ring is 37mm, there is Oly lens cap for comparison. The rear element is tiny, good for F5.6, but not enough for much faster aperture.



Click to expand...
 
OM User said:
If front mounted teleconverters have little (I will use this word in conjunction with the ongoing debate) effect on F-number then why didn't we see more of them in the film SLR days where most people had a rear mounted 1.4X or 2.0X in their kit bag with the adverse effect on effective maximum aperture?
Click to expand...
There are several reasons why they are not used so much:
  • They are larger.
  • They degrade the image more in general (or put it another way, harder to make so they don't degrade the image)
  • They need to be matched to filter size and AOV
  • Generally they are more complex and therefore expensive.
Of course, they are coomonplace for compacts and video, where IQ demands are not as high.
OM User said:
second question: would you have to remove any filter from your lens before attaching a front mounted TC?
Click to expand...
Moving the converter our would restrict its angle of view and might result in more vignetting.
--
Bob
 
kenw said:
bobn2 said:
kenw said:
EDIT: I cross posted with your addendum. Good job on the diameter estimate. So yeah, wide open the front element has definitely become the aperture stop of the optical system.
Click to expand...
No, the aperture stop stays with the diaphragm, so the f-number stays the same with the host lens. Just think, you view the diaphragm through the front element (of the converter)

and its size is controlled by the magnification of the converter, not the size of the FE.
Click to expand...
Only true if the entire optical system is large enough that you can still see the entire image of the iris from the front of the lens.
Click to expand...
Yes, you are right.
--
Bob
 
Great post!
kenw said:
kenw said:
kenw said:
EDIT: I cross posted with your addendum. Good job on the diameter estimate. So yeah, wide open the front element has definitely become the aperture stop of the optical system.
Click to expand...
No, the aperture stop stays with the diaphragm, so the f-number stays the same with the host lens. Just think, you view the diaphragm through the front element (of the converter)

and its size is controlled by the magnification of the converter, not the size of the FE.
Click to expand...
Only true if the entire optical system is large enough that you can still see the entire image of the iris from the front of the lens. Trivial example to explain why you are wrong - put a lens cap on a lens with a tiny hole in it. The optical system is not a vignetted F/1.8 optic anymore. It is a F/100 optic with the aperture stop in front of the lens.

In fact, you can't vignette a lens on the optical axis - that violates the definition of vignetting which is based the ratio of transmission from an off axis point to an on axis point. As the ratio of the on axis point to the on axis point is always one there is no vignetting by definition.

The fact that someone happens to put an iris somewhere in a lens does not make it an aperture stop at all. If properly designed the iris coincides with the aperture stop, however this is not always true in an improperly designed optical system.

The aperture stop is defined as the diaphragm or element which determines the diameter of the cone of energy which the optical system will accept from an axial point on the object. That could be the iris, the front element, the back element, a lens cap with a hole in it, or an improperly sized baffle, cold stop or glare stop.

In this case - 45/1.8 with the teleconverter on it - the aperture stop of the system is the front element of the teleconverter for wide apertures. At small apertures the aperture stop is in fact the iris of the 45/1.8.
kenw said:
A too small FE will give you vignetting wide open, but it won't change the f-number.
Click to expand...
Ah, no. See discussion above. If the front element constrains the on axis light it is by definition now the aperture stop. For more detail see "Modern Optical Engineering" chapter 9 which has an extensive discussion of aperture and field stops, pupils and baffles with good diagrams.
--
Ken W
See profile for equipment list
Click to expand...
 
I wanted to properly test sharpness of this converter (just out of curiosity) but I can't even do that. I have a setup with resolution chart but it requires 90mm lens to focus at about 8 feet. I would expect 2x teleconverter to double minimal focus distance but this converter makes it ridiculously long - 12-15 feet maybe. I haven't had such problem with TCON-17 converter.

So, I just shot a fence. First shot with Oly at F1.8 aperture and DMW-GTC1 converter, second shot is with Oly 40-150mm zoom at 89mm wide open. See shutter speed, the 40-150mm zoom is about as fast, within 1/6 stop exposure granularity, and histograms are similar, so the converter makes Oly 45mm about 90mm F4.9 lens, and it kills contrast.

And trust me, bokeh is horrible too. Worst of all 90mm lenses at F5.0 that I've ever seen. I can't spend more time with this converter, it will go back.







 
Yikes! That is pretty ugly. Low contrast and veiling glare aplenty! I suspected that various aberrations would be pretty bad - effectively moving the aperture stop to the front element of a lens rarely does an optics design any favors. Still, that contrast/glare is bad for F/5.

Well, I guess as everyone has said it was too good to be true. You want that aperture you'll need a heavy T-CON.

Thank you very much for trying it and posting the results though - that is very helpful (as was your 75/1.8 thread from before).
--
Ken W
See profile for equipment list
 
or maybe that should be bad enough. Having seen this, in particular the shutter speed settings that you need to use, I think I will give the converter a miss.
 
Why is the metering changing with a front mounted converter, this seems strange?

I used the gwc1 with the 14mm and both metered identical, wouldnt that effect metering too?








OM User said:
or maybe that should be bad enough. Having seen this, in particular the shutter speed settings that you need to use, I think I will give the converter a miss.
Click to expand...
 
micksh6 said:
Meanwhile I can post pictures taken with Oly 45mm and TCON-17 (what I called 75mm F1.8 lens last year, before Oly announced it).



Click to expand...
Bloody Hell! I've never thought of trying it yet I have got this combination (except for the body which is a GH2) at home. This highly regarded TCON-17 hasn't been out of the pouche since I tested it in front of few of the 300mm lenses I have. I wasn't very happy about the results then but now with AF on the 45mm F1.8 this is an altogether different game.

I've gotta shoot some charts tonight... which is all very exciting :P
I'll report back.

--
Duarte Bruno
 
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