Scott Schroeder
28-Feb-2005, 08:06
I was hoping for a little help with a problem I am having with my Fuji 12.5/450 C mounted on an extension tube for my toho http://tinyurl.com/68mkr
I have taken about five different photos in different lighting situations and I am quite sure I have a problem with reduced contrast from interna reflections as described below from Kerry's review of the TOHO:
"Originally, I had two concerns about using such a long extender. The first was mechanical vignetting when using movements. I had Steve Grimes make the diameter of the spacers as large as possible to prevent this problem. Testing with the maximum extender length indicates there is absolutely no mechanical vignetting when employing the maximum rise the Toho is capable of achieving, even with the lens wide open. In other words, experimental testing has proven that mechanical vignetting is not an issue. The second concern was reduced contrast due to internal reflections. The 450mm Fujinon C has a HUGE image circle, and that means there is a lot of excess, non-image light bouncing around inside the extender. Due to their mechanical and physical properties, camera bellows do a good job absorbing most of this non-image light. So, on a camera with longer bellows (and no extender) this is rarely an issue. The extender is both smaller in diameter and lacks the geometric advantage of the pleated bellows in absorbing this light. For that reason, I have initially been using a lens shade to help limit the excess light entering the camera. I have also taken a few images without using a shade. So far, I have not noticed any reduction in contrast or other ill effects that could be attributed to internal reflections within the extender. However, before I am ready to declare this a total non-issue, further testing is definitely in order. In the end, it is possible that the use of the extender could cause a very slight reduction in contrast in some lighting situations. In these extreme cases, proper lens shading techniques (always a good idea anyway) might alleviate any problems. Once I have had a chance to further test the extender under a wider variety of lighting conditions, I will post an update. Due to the physical geometry involved, this is absolutely not an issue with the extender in its shortest configuration (as used with the 14" L.D. Artar and the 360mm Fujinon A)."
I am pretty sure it isn't the lens itself b/c I have heard this is a very sharp lens. unfortunately the toho is the only camera I own, so I can't test it without an extender.
My question is how can I reduce the reflections?
I have considered just linind the extender with black cloth. any reasons why not?
Also, the image appears sharp on the GG (albeit less than my other lenses) but I am shocked by lack thereof on the negs.....any reason for this?
Thanks for any help and opinions
I have taken about five different photos in different lighting situations and I am quite sure I have a problem with reduced contrast from interna reflections as described below from Kerry's review of the TOHO:
"Originally, I had two concerns about using such a long extender. The first was mechanical vignetting when using movements. I had Steve Grimes make the diameter of the spacers as large as possible to prevent this problem. Testing with the maximum extender length indicates there is absolutely no mechanical vignetting when employing the maximum rise the Toho is capable of achieving, even with the lens wide open. In other words, experimental testing has proven that mechanical vignetting is not an issue. The second concern was reduced contrast due to internal reflections. The 450mm Fujinon C has a HUGE image circle, and that means there is a lot of excess, non-image light bouncing around inside the extender. Due to their mechanical and physical properties, camera bellows do a good job absorbing most of this non-image light. So, on a camera with longer bellows (and no extender) this is rarely an issue. The extender is both smaller in diameter and lacks the geometric advantage of the pleated bellows in absorbing this light. For that reason, I have initially been using a lens shade to help limit the excess light entering the camera. I have also taken a few images without using a shade. So far, I have not noticed any reduction in contrast or other ill effects that could be attributed to internal reflections within the extender. However, before I am ready to declare this a total non-issue, further testing is definitely in order. In the end, it is possible that the use of the extender could cause a very slight reduction in contrast in some lighting situations. In these extreme cases, proper lens shading techniques (always a good idea anyway) might alleviate any problems. Once I have had a chance to further test the extender under a wider variety of lighting conditions, I will post an update. Due to the physical geometry involved, this is absolutely not an issue with the extender in its shortest configuration (as used with the 14" L.D. Artar and the 360mm Fujinon A)."
I am pretty sure it isn't the lens itself b/c I have heard this is a very sharp lens. unfortunately the toho is the only camera I own, so I can't test it without an extender.
My question is how can I reduce the reflections?
I have considered just linind the extender with black cloth. any reasons why not?
Also, the image appears sharp on the GG (albeit less than my other lenses) but I am shocked by lack thereof on the negs.....any reason for this?
Thanks for any help and opinions