Crop factor effect on front element lens scratch

[stephen_schoof1]

<p>I think I know the answer to this, but...I basically want to use a D80 to test the image quality of a 24mm f2.8D that has a slight scratch dead center on the front element. However, I will be mainly using this lens on a 35mm film body - I just want an immediate answer as to whether the scratch is going to be a problem, and a crop-sensor body is all I have available for digital.</p>

<p>At first I thought testing on the D80 would be invalid, because it's one of those tiny scratches that I know would be inconsequential on a telephoto but will probably show up in certain situations at wider focal lengths. I was afraid the 36mm equivalent on the D80 would not give an accurate idea of the severity of the scratch when the lens 'goes back to being' a 24mm on a film body. Then it dawned on me that the crop-sensor is really just eliminating the edges of the image area, and the D80 will see exactly what a full-frame would see in the center of the image. So my question boils down to, am I correct in thinking this way, and if my 24mm looks fine in the center on a D80 I won't have a more obvious defect appearing in the center of my full-frame film?</p>

[Two23]

<p>From my own experience, the lens will focus right through the scratch. The only time it might be a factor is if you are shooting into bright light, where it might cause flare. In the old days photographers would paint the scratch with black India ink.</p>

<p>Kent in SD</p>

[michael_bradtke]

<p>Listen to what Kent says. Small scratches will hardly ever be noticeable.<br>

If you are interested you might want to read this</p>

<p>http://www.lensrentals.com/blog/2008/10/front-element-scratches</p>

 

[Rick Helmke]

<p>The scratch shouldn't be an issue but you are correct in your thinking.</p>

<p>Rick H.</p>

[thomas_k.]

<p>Also if you are planning to shoot landscapes with this lens and use apertures f16 or smaller it may blur/soften image on both DX and full frame.</p>

[michael_bradtke]

<p>" A slight scratch dead center on the front element"<br>

As long as it does not flare it will have no effect on the image. Especially if you are using the lens on film where you have so many more limiting factors like film grain and film flatness.</p>

[mike_halliwell]

<p>Might be worth making sure you've got a good lens hood for it.</p>

[ShunCheung]

<p>If you are buying that lens, this kind of scratch is a great excuse to bargain down the price, but should you want to re-sell it in the future, that argument will work against you.</p>

<p>If the scratch is small, it is a minor issue. The bigger issue is that the 24mm/f2.8 AF-D has the same optical design as the 1977 24mm/f2.8 AI. I have owned both versions; it was great in 1977 but it is no longer the best 24mm lens now in 2014, but those limitations are a lot more obvious on today's high-pixel DSLRs. 35mm film is a lot more forgiving. The 24mm/f2.8 AF-D also uses a very shallow hood, but that is expected for a wide angle.</p>

[JDMvW]

<p>Try it and see. Depends on the lens, internal reflections in the same, and on how light is entering the lens in a particular shot.</p>

<p>In the old days, people found that real India ink (what we used to call "Higgin's Infernal" actually "Eternal") would help cut down flare (fill the scratch and wipe off ink outside the scratch), but this will not work nearly so well, if at all, if you use a Sharpie type ink.<br>

I personally preferred Pelikan inks.</p>

[stephen_schoof1]

<p>Thanks for the advice. I've tried it on the D80 and it seems undetectable except in the most extreme rare circumstances (slight glare if the scratch is positioned on the boundary of a dark shadow and bright light source shot at f16 or 22, with the bright light several stops overexposed - it'll still produce a nice clean silhouette in normal shooting). This is actually my own most-used lens - I just noticed the scratch and wanted to make sure it wouldn't be an issue on an upcoming trip. It's possible it's been there for years...</p>

[glen_h]

<p>I don't know about scratches, but I one time was surprised to see that my Panasonic camcorder, in wide angle zoom, could focus on dust on the skylight filter. <br>

For normal distances and apertures, and, as noted, when there isn't a bright light source, it should be fine.</p>