K7 with SMC 1.7X AF adaptor underexposing?

Junah · 07-19-2012, 12:52 PM

When I take pictures with my K7, 1.7X adaptor and DAL 55-300 the images appear a little too dark. Should I be compensating to correct this? or should the TTL metering recognise this and set the correct aperture/speed, I usually shoot on fully automatic.
is this normal?

**jatrax** · 07-19-2012, 03:32 PM

Too dark on the LCD or too dark when printed or viewed on computer? What does the histogram say? Jpeg or RAW? There are lots of variables including maybe your monitor is not calibrated correctly. But if the external variables have all been eliminated then that points to the camera, or camera / lens combination.

I have the k-5 and it seems to underexpose on some lenses, particularly on older ones (F or FA series). I just dial in a 1/2 stop or so of compensation. You can fix it in PP but the compensation adjustment is there to correct exactly this situation so best to use it and get things right in the camera.

audiobomber · 07-19-2012, 05:50 PM

Originally posted by Junah

When I take pictures with my K7, 1.7X adaptor and DAL 55-300 the images appear a little too dark. Should I be compensating to correct this? or should the TTL metering recognise this and set the correct aperture/speed, I usually shoot on fully automatic.
is this normal?

At 300mm wide open, you have an aperture of f/9.86. Maybe you just don't have enough light to make the picture.

It's possible that the lens combo is simply underexposing, or maybe there's something else going on. We can speculate all day, but we won't know until you post samples with exif intact.

Lowell Goudge · 07-19-2012, 07:26 PM

i use the 1.7x adapter quite a lot, but never on a variable aperture lens. does the aperture change, when you zoom as far as what the camera recognizes?

It may be an issue that the under exposure is at the long end only because the camera does not know the true aperture. remember this adapter does not feed through the lens data pin, because this is used to control the AF in the adapter.

**jatrax** · 07-20-2012, 04:34 PM

Originally posted by Lowell Goudge

does not feed through the lens data pin, because this is used to control the AF in the adapter.

Lowell, you confused me on this. I just received my 1.7x, have not used it yet. So the data pin controls the AF on this?

Lowell Goudge · 07-20-2012, 05:08 PM

Originally posted by jatrax

Lowell, you confused me on this. I just received my 1.7x, have not used it yet. So the data pin controls the AF on this?

Yes. The adaptor feeds aperture data through the first 6 pins counting from the lens locking pin, but it is not a direct feed through, there is electronics that converts the aperture information so that the camera actually knows the aperture as modified by the 1.5 stops of light loss for the TC. The 7th pin is used by the AF system to control the moveable elements in the TC that perform the focusing. Note that when using this adapter, the lens's own AF is not used, only the moveable elements of the adapter

**jatrax** · 07-20-2012, 07:38 PM

Originally posted by Lowell Goudge

Note that when using this adapter, the lens's own AF is not used, only the moveable elements of the adapter

Yeah, I understand that, I think this was made originally to work with A lenses, right? So on an A lens set at f/2.8 the camera will read f/4.5?

But I assumed the screwdrive slot would move the focusing elements.

Lowell Goudge · 07-21-2012, 04:17 AM

Originally posted by jatrax

Yeah, I understand that, I think this was made originally to work with A lenses, right? So on an A lens set at f/2.8 the camera will read f/4.5?

But I assumed the screwdrive slot would move the focusing elements.

Nope. You manually focus close to what you need and the adapter does the rest. On a short lens that covers just about the whole focus range but on a tele only a portion,

**jatrax** · 07-21-2012, 12:53 PM

Originally posted by Lowell Goudge

You manually focus close to what you need and the adapter does the rest

Ok, played around with this a little last night and I understand you need to manually focus close first, I used an A 135 f/2.8 that was handy and you had to get fairly close manually and then the adapter would finish it by locking in. But there is a screw drive socket on the adapter which does not pass through to the lens, so if the 7th pin is used to drive the focusing elements of the adapter then what is the screw drive for?

Lowell Goudge · 07-21-2012, 04:22 PM

Originally posted by jatrax

Ok, played around with this a little last night and I understand you need to manually focus close first, I used an A 135 f/2.8 that was handy and you had to get fairly close manually and then the adapter would finish it by locking in. But there is a screw drive socket on the adapter which does not pass through to the lens, so if the 7th pin is used to drive the focusing elements of the adapter then what is the screw drive for?

The screw drive in the adapter drives the elements in the teleconverter. ThenAF process uses the 7th pin to send focus distance adjustment to the camera body, same as a lens.

07-19-2012, 12:52 PM	#1
Junah Junior Member Join Date: Apr 2011 Posts: 27	K7 with SMC 1.7X AF adaptor underexposing? When I take pictures with my K7, 1.7X adaptor and DAL 55-300 the images appear a little too dark. Should I be compensating to correct this? or should the TTL metering recognise this and set the correct aperture/speed, I usually shoot on fully automatic. is this normal?

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07-19-2012, 03:32 PM	#2
jatrax Site Supporter Join Date: May 2010 Location: Oregon Photos: Gallery \| Albums Posts: 10,770	Too dark on the LCD or too dark when printed or viewed on computer? What does the histogram say? Jpeg or RAW? There are lots of variables including maybe your monitor is not calibrated correctly. But if the external variables have all been eliminated then that points to the camera, or camera / lens combination. I have the k-5 and it seems to underexpose on some lenses, particularly on older ones (F or FA series). I just dial in a 1/2 stop or so of compensation. You can fix it in PP but the compensation adjustment is there to correct exactly this situation so best to use it and get things right in the camera.

07-19-2012, 05:50 PM	#3
audiobomber Pentaxian Join Date: May 2008 Location: Sudbury, Ontario Photos: Albums Posts: 6,684	Originally posted by Junah When I take pictures with my K7, 1.7X adaptor and DAL 55-300 the images appear a little too dark. Should I be compensating to correct this? or should the TTL metering recognise this and set the correct aperture/speed, I usually shoot on fully automatic. is this normal? At 300mm wide open, you have an aperture of f/9.86. Maybe you just don't have enough light to make the picture. It's possible that the lens combo is simply underexposing, or maybe there's something else going on. We can speculate all day, but we won't know until you post samples with exif intact.

07-19-2012, 07:26 PM	#4
Lowell Goudge Pentaxian Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 15,400	i use the 1.7x adapter quite a lot, but never on a variable aperture lens. does the aperture change, when you zoom as far as what the camera recognizes? It may be an issue that the under exposure is at the long end only because the camera does not know the true aperture. remember this adapter does not feed through the lens data pin, because this is used to control the AF in the adapter.

07-20-2012, 04:34 PM	#5
jatrax Site Supporter Join Date: May 2010 Location: Oregon Photos: Gallery \| Albums Posts: 10,770	Originally posted by Lowell Goudge does not feed through the lens data pin, because this is used to control the AF in the adapter. Lowell, you confused me on this. I just received my 1.7x, have not used it yet. So the data pin controls the AF on this?

07-20-2012, 05:08 PM	#6
Lowell Goudge Pentaxian Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 15,400	Originally posted by jatrax Lowell, you confused me on this. I just received my 1.7x, have not used it yet. So the data pin controls the AF on this? Yes. The adaptor feeds aperture data through the first 6 pins counting from the lens locking pin, but it is not a direct feed through, there is electronics that converts the aperture information so that the camera actually knows the aperture as modified by the 1.5 stops of light loss for the TC. The 7th pin is used by the AF system to control the moveable elements in the TC that perform the focusing. Note that when using this adapter, the lens's own AF is not used, only the moveable elements of the adapter

07-20-2012, 07:38 PM	#7
jatrax Site Supporter Join Date: May 2010 Location: Oregon Photos: Gallery \| Albums Posts: 10,770	Originally posted by Lowell Goudge Note that when using this adapter, the lens's own AF is not used, only the moveable elements of the adapter Yeah, I understand that, I think this was made originally to work with A lenses, right? So on an A lens set at f/2.8 the camera will read f/4.5? But I assumed the screwdrive slot would move the focusing elements.

07-21-2012, 04:17 AM	#8
Lowell Goudge Pentaxian Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 15,400	Originally posted by jatrax Yeah, I understand that, I think this was made originally to work with A lenses, right? So on an A lens set at f/2.8 the camera will read f/4.5? But I assumed the screwdrive slot would move the focusing elements. Nope. You manually focus close to what you need and the adapter does the rest. On a short lens that covers just about the whole focus range but on a tele only a portion,

07-21-2012, 12:53 PM	#9
jatrax Site Supporter Join Date: May 2010 Location: Oregon Photos: Gallery \| Albums Posts: 10,770	Originally posted by Lowell Goudge You manually focus close to what you need and the adapter does the rest Ok, played around with this a little last night and I understand you need to manually focus close first, I used an A 135 f/2.8 that was handy and you had to get fairly close manually and then the adapter would finish it by locking in. But there is a screw drive socket on the adapter which does not pass through to the lens, so if the 7th pin is used to drive the focusing elements of the adapter then what is the screw drive for?

07-21-2012, 04:22 PM	#10
Lowell Goudge Pentaxian Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 15,400	Originally posted by jatrax Ok, played around with this a little last night and I understand you need to manually focus close first, I used an A 135 f/2.8 that was handy and you had to get fairly close manually and then the adapter would finish it by locking in. But there is a screw drive socket on the adapter which does not pass through to the lens, so if the 7th pin is used to drive the focusing elements of the adapter then what is the screw drive for? The screw drive in the adapter drives the elements in the teleconverter. ThenAF process uses the 7th pin to send focus distance adjustment to the camera body, same as a lens.