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  1. #1
    osprey48's Avatar
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    Difference in focus aids

    I've discovered that my large focus aid focuses at a different level than my small one.When a neg is in focus using the big one, with the enlarger head high up, the small one is quite a way out. I can't check if this is still the case with the head low down, as I can't get the big one under the lens to see it, but when the small one was the only one I had, I never noticed that my prints were out of focus. Both focus aids have been adjusted so their metal wires are in sharp focus, but there is a big difference in their focus levels. Is there an explanation for this, or is it just that the small one is faulty but I never noticed?

  2. #2

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    Barry Thornton wrote about this in his book "Edge of Darkness". He found that none of his focusing aids shows the same focus point, but prints from them is identical in sharpness. So I think it's fairly safe to think that the small focusing aid you use isn't faulty and you can use whichever you want.

    Main reason of this issue is something about UV wavelength, but I'm not the expert. You can look at the "Post Exposure" from Ctein, there is technical chapter in it if I remember correctly.

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    Neil Souch's Avatar
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    I assume you are talking about the Paterson range? They are adequate, but not the best, and I used them for a number of years. If you want the best there is, as professionals would use, you just can't beat a Peak. Luckily I managed to pick one up s/h some years ago and the difference is staggering. You focus purely on the grain and it is easy to see and quick to focus on giving spot on focus every time. The only down side is they are expensive and hardly ever come up on the s/h market these days.

    Neil.

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    I has the same issue with a Paterson major and micro focuser but it was only a very marginal difference between them. The explanation that was offered to me was that the metal wires were both focused but not quite to the same point. I must admit that when focusing on the wires there does seem to be a margin for error i.e. the wires are the kind that are not clearly in or out of focus, there does seem to be a margin for error.

    If the difference in grain sharpness is large and both wires appear to be sharp then this would seem to rule out my explanation as valid but it might be instructive to see how much movement in the adjustment is possible without it altering the wire's sharpness. If there is any such movement then it may be that the explanation offered to me is correct.

    pentaxuser

  5. #5
    osprey48's Avatar
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    Thank you for the info. Yes, there doesn't seem to be a precise focus point for the wires, so its impossible to know where the correct focus is. The proof is in the finished print I suppose, so I'll pay particular attention to that next time I print.

  6. #6

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    Quote Originally Posted by osprey48 View Post
    Thank you for the info. Yes, there doesn't seem to be a precise focus point for the wires, so its impossible to know where the correct focus is. The proof is in the finished print I suppose, so I'll pay particular attention to that next time I print.
    Surely the test is to raise your enlarger head to max height, which could mean as much as 20 x 16 " on the baseboard, open lens right up for minimum depth of field, print a section from the middle on say 7 x 5 paper after focussing as accurately as you can with each focus aid, and see which print shows sharpest grain.
    That is what I do anyway, and my Focoblitz is the most accurate. In case you don't know what that is, it has a focussing electronic sensor on the baseboard which produces an electronic image of the grain on a cathode ray tube mini-TV. Saves struggling crouched over an eye-piece trying to adjust a knob at arm's length above your head. Scoponet, Patersons, Peak 3 are all pretty good but all suffer from the neck cricking drawback when focussing with the head at the top of the column. I am an autofocus fan so have a Leitz V35, a Leitz Focomat 11c, and a Durst DA 900. I check autofocus is still true about once every 6 months and these machines are amazing, they are always spot on.
    Focoblitzes go for about 50GBP currently - I have just bought a back up, it will be on eBay UK completed listings if you want to look at what it looks like.
    Drawback is the CRT screen which glows for quite a while after switching off, theoretically could fog paper. Hasn't been a problem for me, but if you used the Focoblitz every time you focussed it would certainly be an annoyance.
    I use 2 easels, one up to 10 x 8" and the other up to 20 x 16", identical height above baseboard, though as we know a mm or 2 out baseboard height is nether here nor there, it's adjustment of the negative stage that's critical. So no need to focus on a piece of scrap paper - it's thickness is immaterial
    YoungRichard

  7. #7
    osprey48's Avatar
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    I've just tried doing that, testing both focus aids with the head as far up as it will go, and they give the same result, which is a bit odd when they are different at a lower height.
    Last edited by osprey48; 11-17-2013 at 06:27 PM. Click to view previous post history.

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    Quote Originally Posted by BugraK View Post
    Barry Thornton wrote about this in his book "Edge of Darkness". He found that none of his focusing aids shows the same focus point, but prints from them is identical in sharpness. So I think it's fairly safe to think that the small focusing aid you use isn't faulty and you can use whichever you want.

    Main reason of this issue is something about UV wavelength, but I'm not the expert. You can look at the "Post Exposure" from Ctein, there is technical chapter in it if I remember correctly.
    in my tests, i verified that the depth of field in enlarging can be severa; cm.consequently,two grain focusers can diffwe from each other by quite a bitwhile both are producing 'in-focus prints ; also focusing iis best done in unfiltered white light to avoid focusingerrors due to chromatic abberation in human eyes.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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    Quality makes a difference. You can't realistically expect something that costs twenty bucks to be equal to something that costs several hundred. These
    devices have to be correctly shimmed and distanced, and there's no guarantee that any of them are unless you do testing. But a good easel magnifier will
    not only have better optics, making it easier to use, but in the case of the best ones, you will be able to use them well into the corners of a large
    projected image and not only in the center. This allows you to check for specific focus, alignment, etc - things well beyond simple general focus. So they
    can be a useful investment if you need to do critical work.

  10. #10

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    Quote Originally Posted by DREW WILEY View Post
    Quality makes a difference. You can't realistically expect something that costs twenty bucks to be equal to something that costs several hundred.
    Accepting what you say about the other benefits of the likes of a Peak focuser, I wonder if the above statement is true when and if all you require is to focus accurately on the grain, given what others including Ralph had said about the DoF.

    Anyone here with both a Paterson and a Peak tried focussing with the former and then the latter to see if both focus at the same point and more crucially even if there is a slight difference in where each grain focuser tells you to move the enlarger bellows to, does this make any difference to the sharpness of the print?

    Thanks

    pentaxuser

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