Jump to content

Circles of genuine confusion


james_lindsey

Recommended Posts

<p>I'd guess that you used a lens (or lenses) that projected an image circle smaller than the film. However, I'm also puzzled by the decreased contrast in the center of the photo. It would help immensely if you would specify the camera and lens you used (including the lens for the two photos that were o.k.).</p>
Link to comment
Share on other sites

<p>Thank you for the responses. I realized after I posted the query I should have given more info. The camera is an Mamiya RB67 Pro S and I was using a 120 6x7 back. The camera body was a spare that I was using for the first time. I am pretty sure it had the 90mm lens attached at the time. The only lens I have where I have to be careful of vignetting is my 50mm lens. it will even show vignetting with a UV filter in on.<br>

I cannot be sure that I did change the lens for the last two pix. At the time I only had two lenses, the standard Mamiya 90mm, and the 50mm, but 8 out of 10 of the pix were looking like the above, and I wondered what was causing that problem if it was not vignetting. I must admit it certainly looks like vignetting. If I did change the lens for the last two frames I am betting I would have put the 50mm 0n. Perhaps I should put another roll through it paying particular attention to the lenses I use and get back to the forum again. The film had been in the camera for some time through some hot weather which may account for the degradation of the film.</p>

Link to comment
Share on other sites

<p>Thank you for the responses. I realized after I posted the query I should have given more info. The camera is an Mamiya RB67 Pro S and I was using a 120 6x7 back. The camera body was a spare that I was using for the first time. I am pretty sure it had the 90mm lens attached at the time. The only lens I have where I have to be careful of vignetting is my 50mm lens. it will even show vignetting with a UV filter in on.<br>

I cannot be sure that I did change the lens for the last two pix. At the time I only had two lenses, the standard Mamiya 90mm, and the 50mm, but 8 out of 10 of the pix were looking like the above, and I wondered what was causing that problem if it was not vignetting. I must admit it certainly looks like vignetting. If I did change the lens for the last two frames I am betting I would have put the 50mm 0n. Perhaps I should put another roll through it paying particular attention to the lenses I use and get back to the forum again. The film had been in the camera for some time through some hot weather which may account for the degradation of the film.</p>

Link to comment
Share on other sites

<p>James -</p>

<p>Was any of this visible in the viewfinder when you shot the film?<br>

My 50mm & RB67 ProS or SD don't do this, albeit the corners do show a about one stop less exposure under some circumstances, but no such 'distinct' edge . It surely looks to me like a lens hood issue to intrude that far into the frame.<br>

Jim M.</p>

Link to comment
Share on other sites

<p>I love a good mystery!</p>

<p>James, that doesn't look like a 90mm lens "perspective" to me. The angle-of-view looks too wide. So if it really was taken with the 90mm lens, are you sure that a bit hasn't fallen off it?</p>

<p>I also find it hard to believe that such strong vignetting wouldn't be seen through the viewfinder, and that would narrow it down to some sort of circular obstruction in the camera - highly unlikely. So my only advice would be to check the condition of that 90mm lens and make sure the back half hasn't come unscrewed.</p>

Link to comment
Share on other sites

<p>Heavens, we do get some good advice here. First Andrew it <em>would</em> have been a nice pix, it was Springs first yellow flowering of beautiful trees whose name escapes me, common on the Darling Downs in Queensland 2000 ft above sea level, thank you for the kind comment.<br>

I would have had the filter on the lens but in any case the vignetting, <strong><em>IF</em></strong> it was indeed vignetting was so bad I would have definitely seen it in the viewfinder, but would have not picked up the anomaly in the operation of the lens in the viewfinder as the shutter operated in a fraction of a second.<br>

I suspect Rodeo Joe you may be on the right track. I agree the perspective of the picture looks too wide to be a taken with a 90mm lens, and the last two pix on the roll were quite ok where I suspect I used the 90mm lens.<br>

I had collected a few RB spares enough to make up another unit which I had just given my daughter after I processed the film. This 50mm lens I bought on EBay and on closer examination looked in quite bad condition and I suggested to her she gets it checked over and cleaned before use. Rodeo Joe, going by your advice I now suspect it could be a mechanical problem with this 50mm lens. Thanks everyone for your help.</p>

Link to comment
Share on other sites

<p>I seem to remember the rubber hood I had for my Mamiya 180mm lens could be folded back a bit and used with the 90mm. Could it be that you used this hood and forgot to fold it back? The perspective looks correct to me, the 90mm is about the same as a 35mm lens in 35mm terms. I also had the 50mm, which was about the same as a 24mm in 35mm terms. The 180 was like the 90mm in 35mm terms, a terrific portrait lens.</p>
Link to comment
Share on other sites

<p>Let's not forget there appear to be two issues with this photo: the very obvious "vignetting" on the perimeter, and also the decreased IQ in the center of the photo. I'd be looking for some grand unifying theory here and a single causal explanation.</p>
Link to comment
Share on other sites

<p>Dave. Actually a 90mm lens on 6x7 gives the equivalent horizontal angle-of-view to a 48mm lens on the 135 format, while the vertical A-o-V is roughly the same as a 38mm lens. A 50mm lens gives roughly the equivalent of a 27mm horizontal and 21mm vertical A-o-V. There is no single focal length comparator since the aspect ratios of the two formats are completely different.</p>

<p>So I still think the photo shown appears to be too wide to have been taken with a 90mm lens.</p>

Link to comment
Share on other sites

<p>As to the vignetting, i'd guess a hood for the 90mm placed on the 50mm and the exposures made afterward. As to the flare in the middle of the frame i'd ask about the age/quality of the film(?), something wrong internally with the lens(?), maybe a light leak(?).</p>
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...