Image Circle

[rjpierrard]

<p>Hello,</p>

<p>I can't seem to find a database of lens' image circles - I'm interested in getting a shift adapter and using the lenses on some micro 4/3 body, or maybe a Nikon DX.</p>

<p>Specifically I'm interested in the:<br>

Tokina 11-16/2.8 (I know it covers FX up to 14mm)<br>

Nikon 24/2.8D<br>

Nikon 50/1.4D<br>

Nikon 85/1.8D<br>

Nikon 70-210/4</p>

<p>But since I haven't been able to find the image circle data, I don't know how much shift there is available on each lens...</p>

<p>Thanks in advance!</p>

[bebu_lamar]

<p>I have never seen image circle size published for any lenses designed for 35mm camera. But since all the lenses you mentioned must cover the full frame 35mm you can assume that the image circle is 43mm</p>

[rjpierrard]

<p>43mm is the absolute minimum diagonal image circle for a 35mm/FX format sensor.<br />I can't assume that because it makes no sense to design a lens with the absolute minimum required image circle when people care at all about light falloff and corner image quality.<br>

Also, the Tokina lens is listed as a DX lens, but when on a FX camera, it will cover up to 14mm (with an unfortunate amount of distortion).</p>

[john_tran14]

<p>Hi BeBu Lamar! Good to see you!<br>

Take the Tokina 11-16mm 2.8 for example (I don't have this lens and it seems to be a lens that got much attention lately, see another post here too):<br>

Somebody claimed he tried it on the F6, F100, F4, N75, N70 and N55 and it worked perfectly, although you'll get black corners wider than 15mm. He actually shot Velvia in the F4; it works fine at 16mm.<br>

Only that creates enough confusion because of the different claims for 14mm, 15mm, and 16mm. Is it possible that people came to those numbers based on what they see in the viewfinder? and the viewfinders of those cameras are quite different.<br>

Does it also depend on where the lens is focused on? infinity or closest distant?</p>

<p>Does it also depend on what definition of focal length that the particular lens really follow?</p>

[rjpierrard]

<p>I do actually have the Tokina 11-16/2.8; I have not used it on FX yet, but on my old Nikon FG corner vignetting is gone by 14mm. It may be that the viewfinder doesn't show 100% of the exposure, so 15mm is a safe bet. A certain unnameable person online has tested the lens on FX digital, and you can see results on his website.<br />Focus doesn't seem to affect it the image circle, at least on this lens.<br>

Unless there's a way of calculating the image circle, or a list for different lenses, I'll use these as approximants: <br />DX lenses 35mm diag.<br />FX lenses 50mm diag.<br />645 lenses 80mm diag.<br />67 lenses 100mm diag.</p>

[steve_levine]

<p>The diagonals for the formats are as follows: (35MM) FX 43.2mm,(Nikon )DX 28.2mm.</p>

[mike_halliwell]

<p>The diagonals of the CX, DX or FX format are not necessarily those of the lenses in question. They are the minimum dimension required to prevent bad vignetting.</p>

<p>There is no way of calculating the image circle, it depends on the <strong>design</strong> of the lens and not just the focal length. A normal 28mm wide angle lens and a 28mm PC Shift Lens have very different Image Circle dimensions.</p>

<p>As they're not published, just do the experiment. Mount the lens on a board, just like a large format lens board, affix a piece of translucent material (kitchen grease-proof paper works OK, as does drafting film) at the focal plane distance (lens flange > FP =46.5mm), position it in a darkened room and point it out the window, lens focused on infinity with the aperture wide open. You should see an upside-down, <em><strong>but circular</strong></em>, image of whatever's outside. That<em><strong> is</strong></em> the image circle. Measure with calipers. Simples.....</p>

<p>It's impossible to do on a normal nikon body as all the internal baffles (and the 'film gate') cut off the 'Excess Image Circle' to help prevent flair. Whether the lens itself has light baffles to prevent the maximum Image Circle is a more tricky issue.....</p>

<p>Something like a Nikon 14mm AF is designed for FX, so should have a huge amount of Shift Potential Coverage for 4/3rds or CX! Might even try it myself! Sigma do a 14mm AF lens for considerably less $$$</p>

[rodeo_joe1]

<p>Useable image circle will change with aperture too. It's not so much about vignetting as about how good the image quality is away from the centre, and this varies wildly from lens to lens. The 24mm lens is probably on the very edge at 43mm. The 50mm lens you might squeeze some more coverage from, and the 85mm should have quite a bit of spare image to play with. The zoom will probably have a limited coverage at any focal length.</p>

<p>To see the vignetting alone, you can simply focus the lenses on a bit of white paper and view the image circle.</p>

[rjpierrard]

<p>Thank you Mike, I was hoping someone here would have an answer!</p>

[craigd]

<blockquote>

<p>...on my old Nikon FG corner vignetting is gone by 14mm. It may be that the viewfinder doesn't show 100% of the exposure...</p>

</blockquote>

<p>"May be?" It's dead certain. The only Nikon film SLRs that show 100% of the image in the viewfinder are the professional models (F, F2, ... F6). I think you've just proven John Tran's point.</p>

<p>As has already been noted, image size will vary according to a number of variables. Not only is each lens model different from every other, but focus distance and aperture will affect the size of the circle, and the image circles of zoom lenses will vary by focal length (as your experience with the Tokina 11-16mm lens shows). Also, some models have a rectangular flange at the back which further limits the image projected into the camera.</p>

[bebu_lamar]

<p>So shouldn't the OP play it safe and assume the 43.2 mm as the image circle? If the lenses are to be used on the 4/3 system it's plenty of room for shifting. </p>

[mike_halliwell]

<p>Did someone on PN use the sacred <strong><em>tech</em></strong> word '<strong>ASSUME</strong>' ? and that's a big <em><strong>IF</strong></em>!....</p>

[bebu_lamar]

<p>what's wrong with the assumption? The lenses must cover at least that much and no warranty to cover any larger. Some of the lenses may cover a bit more but wouldn't it safe to assume that it will cover only the 35mm frame and use them based on that. The 4/3 is significantly smaller than teh 35mm frame and should allow for good shift and tilt. </p>

[mike_halliwell]

<p>The assumption is just fine, but I guess it's kinda stating the obvious. A lens built for 35mm film covers the FX format and will therefore easily cover any smaller format. But the OP wants to know more! </p>

<p>Yes, it covers FX, but when 'shifting', it's how much more will it do?</p>

<p>With digital, the vignetting aspect can, to some small extent, be corrected in post. The usual way of expressing fall-off is in stops and I guess with the D7000's latitude you'll get quite a lot more usable circle, but it's only going to be another couple of mm's.</p>

<p>The actual mechanics of shift adapters whilst allowing infinity focus may be your real problem here. However, I suppose with the flange>chip distance being smaller with 4/3rds or CX, there's some space to play with.</p>