Using Pentax-F on K10D

kroal · 08-31-2015, 05:24 AM

Hi guys. Few days ago I became a happy owner of Pentax -F 50/1.7. But yesterday I found few issues that I've never met before. It was a sunny day so I started using built-in flash in slow sync mode. The general mode of using camera was Av (lens in Auto position). After few shots with aperture set to 2 I found a huge exposure miss. Almost the same situation taking a shots without flash with very light background. While using kit lense (18-55) gives normal results. What is my mistake? It is my first time of using F-lenses. Here under you can find to images made by kit and 50mm lens with slow sync flash.

Attached Images

View Picture EXIF

View Picture EXIF

**eonb** · 08-31-2015, 05:59 AM - **1 Like**

The aperture in the second image is open more, even though the exif info reads the same. Look at the Eiffel tower in the background for the clue in this. I've not got any F lenses to try. Did you try the shot in manual as well? I reckon the lens was at f1.7 as the picture looks about 2 stops and a bit over exposed.

**UncleVanya** · 08-31-2015, 06:13 AM

Flash can be tricky with close subjects and large ( open ) apertures. Post some of the non flash misses.

On the shots posted, it looks like the flash shoot was taken from closer than the other, is that true? That could account for the differences in depth of field.

If you dismount the lens and manually flip the aperture control arm mouth the ring is set to A does the lens stop down evenly and rapidly?

kroal · 08-31-2015, 06:17 AM

Originally posted by eonb

The aperture in the second image is open more, even though the exif info reads the same. Look at the Eiffel tower in the background for the clue in this. I've not got any F lenses to try. Did you try the shot in manual as well? I reckon the lens was at f1.7 as the picture looks about 2 stops and a bit over exposed.

No. I didn't try manual mode because shutter speed couldn't be above than 1/90 (while using built-in flash). So I couldn't shot in this mode with small apertures. To the point - this is the open question for me when I use manual settings.

**UncleVanya** · 08-31-2015, 06:52 AM

Originally posted by kroal

No. I didn't try manual mode because shutter speed couldn't be above than 1/90 (while using built-in flash). So I couldn't shot in this mode with small apertures. To the point - this is the open question for me when I use manual settings.

So which mode were you in?

**Just1MoreDave** · 08-31-2015, 07:21 AM

The EXIF says spot metering was used. The camera would have to be using the exact same "spot" for these shots to meter the same. I think that's at least a contributor.

kroal · 08-31-2015, 08:27 AM

Originally posted by UncleVanya

Flash can be tricky with close subjects and large ( open ) apertures. Post some of the non flash misses.

On the shots posted, it looks like the flash shoot was taken from closer than the other, is that true? That could account for the differences in depth of field.

If you dismount the lens and manually flip the aperture control arm mouth the ring is set to A does the lens stop down evenly and rapidly?

OMG. You were right. There is some issue with aperture blades. They stuck at 1.7 and works a bit tight. So aperture was always 1.7. Do anyone has exp. in repairing such problem?

**UncleVanya** · 08-31-2015, 08:35 AM

Originally posted by kroal

OMG. You were right. There is some issue with aperture blades. They stuck at 1.7 and works a bit tight. So aperture was always 1.7. Do anyone has exp. in repairing such problem?

Dcshooter

Not a Number · 08-31-2015, 10:39 AM

I don't think shipping from Ukraine to Dcshooter is going to be all that inexpensive.

**UncleVanya** · 08-31-2015, 10:50 AM

Originally posted by Not a Number

I don't think shipping from Ukraine to Dcshooter is going to be all that inexpensive.

True - but he may be willing to share some wisdom on how to approach fixing it.

kroal · 08-31-2015, 10:51 AM

Originally posted by Not a Number

I don't think shipping from Ukraine to Dcshooter is going to be all that inexpensive.

Yeah. Definitely. So, repairing is a new challenge for me. That is why I just need an advice (materials, manuals, etc...).

link81 · 08-31-2015, 12:48 PM

how mechanical are you?

I've taken my F 50 apart a couple times, and it works fine now. But i would not recommend someone doing it unless you have mechanical skills, and patience. The Correct screwdrivers and fine tweezers are a must.

stevebrot · 08-31-2015, 02:44 PM

Originally posted by link81

Correct screwdrivers and fine tweezers are a must.

Add very good eyesight and/or a workbench magnifier.

Steve

Not a Number · 08-31-2015, 06:17 PM

Originally posted by stevebrot

Add very good eyesight and/or a workbench magnifier.

Steve

An infinite amount of patience helps enormously too.

**Just1MoreDave** · 09-03-2015, 02:51 PM

I have seen some of these for sale with oil on the aperture blades which would be consistent with the symptoms. You can access the aperture blades by unscrewing the beveled trim ring around the front element. Some kind of friction tool, like a sink drain stopper, should grip the thing well enough. Then you'll see a brass colored ring with three tiny screws in it. My Moody's JIS #000 fits these. They were a bit tight. The ring holds on the front lens group so don't tip the lens to let the screws fall out without holding the group in. Once the group is removed you can see the top side of the aperture blades. I have had reasonable luck carefully wiping them down with mineral spirits or naptha, then drying them off, several times, using the aperture lever to move them and distribute the solvent. The blades are thin metal so you can't press on them. When the solvent is dry, try the aperture lever again and see if the blades snap closed properly. You should check the inner lens surfaces of rear and front groups to see if either has oil or solvent on them, and clean that before reassembly.

Sometimes I have to remove the rear lens group to clean the other side of the blades. The oil migrates everywhere so the ideal repair is to remove the blades, wash them and the area in solvent and reassemble. That usually means a lot of disassembly since the aperture mechanism is right at the heart of the lens.

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08-31-2015, 05:59 AM - 1 Like	#2
eonb Site Supporter Join Date: Oct 2012 Location: North-East England Posts: 73	The aperture in the second image is open more, even though the exif info reads the same. Look at the Eiffel tower in the background for the clue in this. I've not got any F lenses to try. Did you try the shot in manual as well? I reckon the lens was at f1.7 as the picture looks about 2 stops and a bit over exposed.

08-31-2015, 06:13 AM	#3
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Flash can be tricky with close subjects and large ( open ) apertures. Post some of the non flash misses. On the shots posted, it looks like the flash shoot was taken from closer than the other, is that true? That could account for the differences in depth of field. If you dismount the lens and manually flip the aperture control arm mouth the ring is set to A does the lens stop down evenly and rapidly?

08-31-2015, 06:17 AM	#4
kroal New Member Join Date: Jun 2011 Location: Poltava Photos: Albums Posts: 20 Original Poster	Originally posted by eonb The aperture in the second image is open more, even though the exif info reads the same. Look at the Eiffel tower in the background for the clue in this. I've not got any F lenses to try. Did you try the shot in manual as well? I reckon the lens was at f1.7 as the picture looks about 2 stops and a bit over exposed. No. I didn't try manual mode because shutter speed couldn't be above than 1/90 (while using built-in flash). So I couldn't shot in this mode with small apertures. To the point - this is the open question for me when I use manual settings.

08-31-2015, 06:52 AM	#5
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by kroal No. I didn't try manual mode because shutter speed couldn't be above than 1/90 (while using built-in flash). So I couldn't shot in this mode with small apertures. To the point - this is the open question for me when I use manual settings. So which mode were you in?

08-31-2015, 07:21 AM	#6
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	The EXIF says spot metering was used. The camera would have to be using the exact same "spot" for these shots to meter the same. I think that's at least a contributor.

08-31-2015, 08:27 AM	#7
kroal New Member Join Date: Jun 2011 Location: Poltava Photos: Albums Posts: 20 Original Poster	Originally posted by UncleVanya Flash can be tricky with close subjects and large ( open ) apertures. Post some of the non flash misses. On the shots posted, it looks like the flash shoot was taken from closer than the other, is that true? That could account for the differences in depth of field. If you dismount the lens and manually flip the aperture control arm mouth the ring is set to A does the lens stop down evenly and rapidly? OMG. You were right. There is some issue with aperture blades. They stuck at 1.7 and works a bit tight. So aperture was always 1.7. Do anyone has exp. in repairing such problem?

08-31-2015, 08:35 AM	#8
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by kroal OMG. You were right. There is some issue with aperture blades. They stuck at 1.7 and works a bit tight. So aperture was always 1.7. Do anyone has exp. in repairing such problem? Dcshooter

08-31-2015, 10:39 AM	#9
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	I don't think shipping from Ukraine to Dcshooter is going to be all that inexpensive.

08-31-2015, 10:50 AM	#10
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by Not a Number I don't think shipping from Ukraine to Dcshooter is going to be all that inexpensive. True - but he may be willing to share some wisdom on how to approach fixing it.

08-31-2015, 10:51 AM	#11
kroal New Member Join Date: Jun 2011 Location: Poltava Photos: Albums Posts: 20 Original Poster	Originally posted by Not a Number I don't think shipping from Ukraine to Dcshooter is going to be all that inexpensive. Yeah. Definitely. So, repairing is a new challenge for me. That is why I just need an advice (materials, manuals, etc...).

08-31-2015, 12:48 PM	#12
link81 Veteran Member Join Date: Jan 2011 Location: 12822 Photos: Albums Posts: 459	how mechanical are you? I've taken my F 50 apart a couple times, and it works fine now. But i would not recommend someone doing it unless you have mechanical skills, and patience. The Correct screwdrivers and fine tweezers are a must.

08-31-2015, 02:44 PM	#13
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by link81 Correct screwdrivers and fine tweezers are a must. Add very good eyesight and/or a workbench magnifier. Steve

08-31-2015, 06:17 PM	#14
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Originally posted by stevebrot Add very good eyesight and/or a workbench magnifier. Steve An infinite amount of patience helps enormously too.

09-03-2015, 02:51 PM	#15
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	I have seen some of these for sale with oil on the aperture blades which would be consistent with the symptoms. You can access the aperture blades by unscrewing the beveled trim ring around the front element. Some kind of friction tool, like a sink drain stopper, should grip the thing well enough. Then you'll see a brass colored ring with three tiny screws in it. My Moody's JIS #000 fits these. They were a bit tight. The ring holds on the front lens group so don't tip the lens to let the screws fall out without holding the group in. Once the group is removed you can see the top side of the aperture blades. I have had reasonable luck carefully wiping them down with mineral spirits or naptha, then drying them off, several times, using the aperture lever to move them and distribute the solvent. The blades are thin metal so you can't press on them. When the solvent is dry, try the aperture lever again and see if the blades snap closed properly. You should check the inner lens surfaces of rear and front groups to see if either has oil or solvent on them, and clean that before reassembly. Sometimes I have to remove the rear lens group to clean the other side of the blades. The oil migrates everywhere so the ideal repair is to remove the blades, wash them and the area in solvent and reassemble. That usually means a lot of disassembly since the aperture mechanism is right at the heart of the lens.