Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-31-2017, 01:41 PM   #1
Loyal Site Supporter
Loyal Site Supporter
ivanvernon's Avatar

Join Date: Oct 2012
Location: Medina, OH
Photos: Albums
Posts: 5,940
Hazy center vignette when using 645 lens on K-1/K-5ii

I am using Chinese Pentax 645-to-K-mount adapter to fit Pentax 645 lenses on to my Pentax K-1 and K-5ii cameras. There is no glass in the adapter. I am unimpressed with image quality in terms of sharpness, though otherwise acceptable. Based on my experience to date, there is not much point to the adapter exercise.

However, I have noticed one curious behavior that I am unable to explain. A light blur/vignette appears near the center of many of the images. I have noticed this using both the K-1 and K-5ii cameras, and both the Pentax 645-A 55mm f 2.8 and the Pentax 645-A 80-160mm. I am attaching a few photos where this effect appears. I will appreciate any explanations or theories on why this effect occurs.

Thank you.

Attached Images
View Picture EXIF
PENTAX K-5 II  Photo 
View Picture EXIF
PENTAX K-5 II  Photo 
View Picture EXIF
PENTAX K-5 II  Photo 
05-31-2017, 01:46 PM   #2
amateur dirt farmer
Loyal Site Supporter
pepperberry farm's Avatar

Join Date: Dec 2014
Location: probably out in a field somewhere...
Photos: Gallery | Albums
Posts: 26,213
just a WAG, but could the adapter be allowing light into the mirror box?
05-31-2017, 01:57 PM   #3
Pentaxian
35mmfilmfan's Avatar

Join Date: Oct 2016
Location: Norfolk, UK
Posts: 2,192
Or could it be internal reflections within the body of the adapter ? Or, indeed, the adapter not fitting snugly to either the lens or the body ?
05-31-2017, 02:20 PM   #4
Pentaxian
photoptimist's Avatar

Join Date: Jul 2016
Photos: Albums
Posts: 4,636
The image circle of a 645 lens is quite large compared to the sensors on the K-1 and K-5 and all that collected light has to go somewhere. If the inside of the adapter is shiny (even if it is black), you'll get this kind of center fogging (what 35mmfilmfan mentions).

The best solution is an aggressive lens hood to cut down light entering the lens.

05-31-2017, 02:58 PM   #5
Loyal Site Supporter
Loyal Site Supporter




Join Date: Aug 2011
Photos: Albums
Posts: 2,039
QuoteOriginally posted by ivanvernon Quote
A light blur/vignette appears near the center of many of the images
I think it is the reflection from the sensor bounced back to sensor by the rear element, since the rear element is not coated to reduce reflection from that direction.
reflection from the inner side of the adapter might cause more defused haze, not that center-weighted.
05-31-2017, 04:00 PM   #6
Veteran Member
RAART's Avatar

Join Date: Apr 2013
Location: Oakville, ON
Photos: Gallery
Posts: 1,095
It is the internal reflections bouncing back same as on some older regular lenses, just google blue dot lens reflections... however that does not have nothing to do with 645 lenses. I also suggest that you invest in really good quality 645 to K adaptor.

I use 645 Mamiya 210mm F4 lens on K-3 and I love it... remember that K-3 has higher pixel per inch ratio as K-1 and it will be very critical in terms of sharpness.

Here is example of the lens resolution.
06-01-2017, 06:49 AM   #7
Loyal Site Supporter
Loyal Site Supporter
ivanvernon's Avatar

Join Date: Oct 2012
Location: Medina, OH
Photos: Albums
Posts: 5,940
Original Poster
Thanks for comments

Thanks for all the helpful comments. I will experiment accordingly and report progress or lack thereof.

06-01-2017, 07:31 AM   #8
Pentaxian
mattb123's Avatar

Join Date: Apr 2010
Location: Colorado High Country
Photos: Gallery
Posts: 10,076
If the inner surfaces of the adapter are shiny, you can black them out with a flat black enamel pen for very little money. I did this with a cheap shiny 67/645 adapter and it helped.
06-01-2017, 08:18 AM   #9
Loyal Site Supporter
Loyal Site Supporter
ivanvernon's Avatar

Join Date: Oct 2012
Location: Medina, OH
Photos: Albums
Posts: 5,940
Original Poster
Thanks for comments

Thanks for all the helpful comments. I used black construction paper to fashion a lengthy hood, same diameter as lens exterior measurements, and shortened it to about 6 inches, just less than the length that produced vignetting. I taped the hood onto the lens and made numerous test shots. The photos produced were mosly too poor to display because of the bright midday sun. However, I was unable to reproduce the center area vignetting, although a better test will be made in less bright light later today.

I am attaching a few other shots to illustrate the lens's characteristics as used on the Pentax K-3 camera. These seem to me to be of reasonable sharpness and quality. However, I will greatly appreciate any comments anyone may be able to offer on these shots--not from an artistic standpoint, just from the standpoint of lens performance,.

Many thanks to all who take the time to respond.
Attached Images
View Picture EXIF
PENTAX K-3  Photo 
View Picture EXIF
PENTAX K-3  Photo 
View Picture EXIF
PENTAX K-3  Photo 
View Picture EXIF
PENTAX K-3  Photo 
View Picture EXIF
PENTAX K-3  Photo 
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
645-a, adapter, camera, cameras, center, center vignette, effect, k-1, k-5ii, pentax, pentax help, photography, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
vignette pykeyuk Pentax K-1 & K-1 II 13 12-10-2016 11:49 PM
28-45mm Vignette w/ filters Gunner Pentax Medium Format 8 08-05-2016 12:38 PM
Landscape photos corner sharpness and lightroom vignette raider Digital Processing, Software, and Printing 13 06-26-2015 04:24 AM
K-5II & AK-TTL, (K-5II stabilization error) FECOmp Troubleshooting and Beginner Help 7 02-08-2014 09:23 AM
Will filter and lens hood vignette on 18-55mm? sandstone Troubleshooting and Beginner Help 3 03-02-2012 08:00 PM



All times are GMT -7. The time now is 03:23 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top