Backfocus problems with Hasselblad

[nikita_kirilkin]

<p>Hello guys :)<br>

I've got Hasselblad 503Cx with 80 and 150mm lens and a couple of extension tubes. Usually I shoot portraits and closeup portraits using extesnion tubes. And everething works ok. But if I shoot from distance 3 and futher I usually have frontfocus..<br>

How is it possible and why I dont have frontfocus shooting closeups?</p>

 

[leicaglow]

<p>There are only three things I can think of: 1) Is your focus screen seated correctly, and in good condition. 2) Does it happen with the same back? Is the back seated correctly? 3) Is the film backing plate coming up tight to the film, ensuring a flat film plane?</p>

[nikita_kirilkin]

<p>Sorry, in the topic subject should be <em>frontfocus </em>insteafd of <em>backfocus</em>.<br>

<strong><a href="../photodb/user?user_id=1713391">Michael Axel</a></strong><br>

Yep, I've got two backs and have the same problem. Anyway I'm going to send in to service..<br>

But I wonder, if the problem with focus screen, etc.. Why do I have perfect images shooting closeups?</p>

[q.g._de_bakker]

And that (perfect close-ups) is indeed what makes this a mystery.<br>In close-ups focussing errors are magnified. So if these errors are gone in close-up, but present themselves in long range photography...<br>Now if you would guestimate focus in long range photography, using the distance scale on the lens to match your guestimate of the subject distance to set focus, instead of inspecting focus on the ground glass, while always setting focus using the ground glass in close-up... But you don't do that.<br><br>What happens when you set the lens to the infinity stop and point the camera at, say, the moon?

[ivan_murdzhev1]

<p>I've been having the same issue with a 500ELX but I've always thought it's the focusing screen - it simply doesn't have enough resolution (or magnification) for precise focus. My close-up shots are all fine but when I step back with the 80mm lens and take, for example, a medium shot with the person's whole body in frame, I often get front focus. I'm having this issue with 35mm cameras as well - when it comes down to focusing manually, I get front focus more often than back focus in medium-to-wide shots.</p>

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=282122">Q.G. de Bakker</a><br>

If focusing on infinity, it's almost ok (I looked at wedge)<br>

I cant do that, because I shoot portraits, but not landscapes.. So I need focus on eyes with opened diafragm.</p>

<p><a href="../photodb/user?user_id=2457699">Ivan Murdzhev</a><br>

Hello, colleague :)<br>

I never had this issue using 35mm.. You wrote, <em>that it simply doesn't have enough resolution.</em> But I used wedge to focus on object.</p>

 

[Rob F.]

<p>Do you stop down after focusing? Or take the shot wide open? And do you use the same aperture for the close-up as for the more distant shot? I'm looking to see if a case can be made for a shift of focus effect when stopping down.</p>

[q.g._de_bakker]

The mystery grows: so it's o.k. at close range and at infinity, but not in between?<br>Are you sure your portrait sitters do not move after focussing?

[Rob F.]

<p>Also: do you use the same extension tube at both distances? Or only use a tube for the closest shot?</p>

<p>For that matter, are you using the same lens in both cases? Or the 80 in one case and the 150 in the other? All changes in method should probably be noted, whether they appear relevant or not at the moment.</p>

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=273989">Rob F.</a><br>

You mean spherical aberration? I'm sure it's not. Cause I saw many photos, made with 2.8 aperture (80mm lens).<br>

I use ext. tubes only for closeups (ext tube won't allow you to focus far away..). I made test shots using 80 and 150.<br>

<a href="../photodb/user?user_id=282122">Q.G. de Bakker</a><br>

Yep. Last time I photoed static objects :)</p>

<div></div>

[dave_wilson1]

<p>Somewhere here, I have an article by Ansel Adams about focus shift using extension, I think there's something by John Shaw too. If anybody knows what I'm talking about, maybe they can direct you there. In the mean time as I'm going through my daily affairs, I'll try and locate it/them. Also, my first take other wise would be the alignment involving the mirror and or focus screen or both. Over the years I've used a set of five Bronica SQa bodies and four Hasselblads and have never had this, so I think it's mechanically out of alignment somewhere.</p>

[sfcole]

<p>Hi,<br>

I was told that the 500c/m has foam dots in back of the mirror that must be replaced periodically to ensure correct focus. Is that the same with the 503cx, and if so, could that be an issue? I too seem to have front-focus issues at close distance with an 80, although it could just be focus error.</p>

[dave_wilson1]

<p>Nikita, I'm not a pretender, so I'm not going to try and explain something I don't know that much about, I'm a reader, I read experts and try to understand better to suit my specific need. So I did some reading around and there are some references to focus shift with the extension tubes where once you set the aperture down after focusing wide open, your point of focus can be off, so if there's enough light to focus with the aperture stopped down that might help. Another point to consider is that of diffraction, stopping down the lens with extension at distance other than infinity and so on. If you can get your hands on John Shaw's 1987 "Closeups in Nature", he goes through this very clearly on pg 141. Ansel doesn't go into much detail, only that at smaller apertures there can result a shift, so to stop down and then refocus. In your case, if you feel your camera is working normal otherwise, I would consider studying the effects of "focus shift" and "diffraction at higher magnifications".</p>

[q.g._de_bakker]

Scott,<br><br>It's the same in the 503 CX, yes.<br>But that would not explain focus being correct at both infinity and in close-up range, but not in between.<br>I don't know what would, by the way. Focus shift due to stopping down would also not.<br>Nor would diffraction; diffraction will reduce overall resolution, never a shift in focus.

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=1947909">Scott Frindel Cole</a><br>

I tried to find them, but I didn't manage to do it..<br>

<a href="../photodb/user?user_id=70549">Dave Wilson</a><br>

Dave, I use ext. tubes only for closeups (they are designeg for this). And I dont have front/ backfocus.<br>

I doubt about focus shift, because lenses are not too fast..</p>

<div></div>

[q.g._de_bakker]

Focus shift due to stopping down really does not explain this. So really no need to think about any longer.<br><br>The trouble however is that it's hard to think of something that would explain this.

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=282122">Q.G. de Bakker</a><br>

Unfortunately yes :)<br>

May be there is a point to buy <em>FOCUSING SCREEN ADAPTER </em>and check focus?<br>

<br /></p><div></div>

[Rob F.]

<p>Also: do you use the same extension tube at both distances? Or only use a tube for the closest shot?</p>

<p>For that matter, are you using the same lens in both cases? Or the 80 in one case and the 150 in the other? All changes in method should probably be noted, whether they appear relevant or not at the moment.</p>

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=273989">Rob F.</a><br>

I can't use ext. tubes (don't ) to focus, say, at 2 metes. Nobody can. Because ext tubes are designed for decresesing focusing distance.<br>

That's why I don't use ext tubes for distance shots.<br>

Problem appears from approximately 3m and futher..</p>

[Rob F.]

<p>Nikita, somehow I thought you were taking pictures at two different distances both in the closeup range. That's why I asked if you used the extension tubes for both shots.</p>

<p>Actually in the photo you posted, it looks like the eyes are in pretty good focus, and the lips are not. Do you regard this shot as an example of the problem? Where did you focus--presumably on the eyes? I'm thinking that the lips being out could be curvature of field at this close distance, wide open. And I'm sure they are closer to the camera than the eyes are.</p>

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=273989">Rob F.</a><br>

I posted 2 photos. Closeup photo is ok and eyes are in focus.<br>

But previous photo I took from the distance about 10 meters and as you can see, the girl is not in focus</p>

[Rob F.]

<p>OK, copy that. I'll think about it some more.</p>

[Rob F.]

<p>OK let's summarize.<br /> 1. Photos taken at close range with 80mm Planar and extension tube are OK.<br /> 2. Photos taken at some distance (did you say 3 meters?) with the 150mm Sonnar are not OK, they front focus.</p>

<p>Correct so far? Some questions:<br /> A. How are photos with the 80mm and <em>no</em> extension tube, at normal (3M?) distance?<br /> B. How are photos taken with the 150 Sonnar <em>with</em> an extension tube, close to minimum distance?</p>

<p>Trying all possible combinations may help to isolate the fault.</p>

<p>Also: I see that a post I wrote on the 19th got repeated verbatim on the 20th. I don't know how that happened, and I'm sure it caused unnecessary confusion. I wish I knew how that could have happened! My mistake, or a computer thing? Sorry!</p>

[nikita_kirilkin]

<p><a href="../photodb/user?user_id=273989">Rob F.</a><br>

To avoid misunderstanding.. All closeup photos taken with 80 and 150 are ok. Almost all distant photos (from 3m) have frontfocus. That's it..<br>

Unfortunately it's not digital camera :)</p>

[Rob F.]

<p>Nikita, is there any difference in the way you view the screen when shooting closeups, vs. the more distant shots? For example, looking through bifocals vs. the distance prescription? (Do you wear bifocals?) Are you looking through the pop-up magnifier? Are you using a prism? If so, which one?</p>

<p>We may have exhausted all there is to say about tubes and lenses, so maybe it's time to take a new direction. what about viewing conditions?</p>

<p>Also are you using an original screen, or an acute-mat?</p>