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  #1  
Old 2nd May 2010, 08:00 PM
jamesrickard jamesrickard is offline
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Default Enlarger lens aperture.

I was wondering about something that I read in one of those very useful printing articles in Black and White photography.
A printer. I forget who, did a test print on on Ilford MG resin coated.
Having done the test he did a further test print on Ilford FB warmtone.
He used the time for the RC print and added a stop for the FB.saying that in his experience WT was a stop slower than the RC. He used the same time and opened up the aperture one stop.
I realise that it is an obvious way to adjust exposure but I have to say all I have ever done is stop my lens down two stops and never change it.
I have no idea why I do it this way but I have never really give aperture much thought when enlarging unless exposure times are really short or long. So my question's are.
1. Is this a good way of exposure control or is it a no no.
2. Is it possible to use an rc paper for test strips.If so is a stop a good estimate for Ilford MG RC and WTFB.
3. How many stops is optimal for an enlarger lens I have a leitz focotar 40mm and a Nikon f2.8. If that makes any differance why is that aperture optimum.
Thanks.
James
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  #2  
Old 2nd May 2010, 08:14 PM
Dave miller Dave miller is offline
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I do my initial test prints on R/C paper because it’s cheaper. I know the approximate difference in speed between the various papers that I have because I have tested them. This enables me to know the approximate change to speed or aperture that I need to make when I change papers, but I will normally still make a test strip with the new paper to fine tune my exposure. Whatever method you use, you need to have tested and verified that it works for you, on your equipment.

Normally I adjust exposure by changing time rather than aperture, but the aperture is selected to get me into the 10 to 30 second exposure range that I prefer.

You will only find the optimum lens apertures by testing. Stopping down two stops is a rule of thumb guide that is usually about right, but print the same enlargement at all apertures and see which is best. Testing a lens may be a bit of a drag, but it only has to be done once.
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Old 2nd May 2010, 09:23 PM
Mike O'Pray Mike O'Pray is online now
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Let us know what you find, James. Conventional wisdom says that for a f2.8 lens the best resolution occurs in the mid range so for a f2.8 to f16 lens it is by convention f8 or f11 or maybe if two stops is the best rule of thumb then f5.6.

I normally go to f8 as any bigger gives me very short exposure especially with Kentmere which is a stop faster than Ilford.

If I may make an observation which I hope doesn't get this post off topic. I have noted that with my El Nikkor 50mm lens and leaving the analyser probe on exactly the same spot and if I get a reading of say 8 secs at f8 then opening up to f5.6 doesn't give me 4 secs exactly. It is close but always slightly more than 4 secs.

I can only think that in reality my f5.6 doesn't quite have a linear relationship with f8. In other words I am assuming that my f5.6 is not quite double the aperture of f8.

Could there be another explanation?

Mike
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Old 3rd May 2010, 06:13 AM
Dave miller Dave miller is offline
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Quote:
Originally Posted by Mike O'Pray View Post
SNIP

If I may make an observation which I hope doesn't get this post off topic. I have noted that with my El Nikkor 50mm lens and leaving the analyser probe on exactly the same spot and if I get a reading of say 8 secs at f8 then opening up to f5.6 doesn't give me 4 secs exactly. It is close but always slightly more than 4 secs.

I can only think that in reality my f5.6 doesn't quite have a linear relationship with f8. In other words I am assuming that my f5.6 is not quite double the aperture of f8.

Could there be another explanation?

Mike

The lens aperture control is a mechanical device built with an allowable tolerance; therefore the steps must be regarded as approximate until tested and proven. In addition older lens may have aperture cams worn to the extent that an appreciable difference may be found in reaching a setting in an upwards direction to that reached when closing the lens down.
Time control on the other hand (if made by an electronic timer) should be much more accurate and repeatable, hence my preference for relying on the timer rather than aperture for exposure control.
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Old 3rd May 2010, 08:01 AM
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RH Designs RH Designs is offline
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On my Nikkor 80mm, there is only about 2/3 stop between wide open (5.6) and one stop down.

Using an Analyser or ZoneMaster, density is a more reliable means of checking than exposure time because the meters include reciprocity failure compensation. In fact Mike I'd expect slightly less than 4 seconds when opening up one stop from an 8 sec exposure. Use the densitometer readings though, when there should be a difference of 0.30 log.D per stop.
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Old 3rd May 2010, 04:51 PM
Mike O'Pray Mike O'Pray is online now
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Thanks both. I do always rely on my analyser for exposure. I don't have a RH Designs model as you may know from my footswitch thread. It is a Philips PDT2020 and has no densitometer facility.

Richard, I must check out which way the reading goes when opening up a stop

Mike

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Old 3rd May 2010, 05:09 PM
Alan Clark Alan Clark is offline
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James,
I too have a Leitz Focotar . Mine is 50mm. At one stop down it reaches its maximum sharpness, but only at the centre. At two stops down max. sharpness extends right to the corners. How do I know? I did a simple test! As a result I only use it at 2 stops down.

Regarding doing a test strip on RC paper then extrapolating an exposure for fibre paper I have to say that I don't think this makes sense. It might if you only wanted to find the corect printing time. But test strips are also used to discover what the print will look like. RC and Fibre paper look different. You wouldn't drink a pint of Boddingtons to find out what Black Sheep bitter tastes like, would you?
I prefer to keep life simple. If I intend making a print on , say, Ilford Warmtone fibre paper, then I use this paper for all preliminary test prints. Another point. Contrast can vary from packet to packet, For this reason I do all my tests, and the final print, with paper from the same packet. Keeps things simple and is a lot less hassle in the long run.

Alan
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Old 4th May 2010, 07:43 AM
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Quote:
Originally Posted by Mike O'Pray View Post
I do always rely on my analyser for exposure. I don't have a RH Designs model as you may know from my footswitch thread.
I have a terrible memory, and I should have spotted the difference between "analyser" and "Analyser"!
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  #9  
Old 4th May 2010, 03:12 PM
jamesrickard jamesrickard is offline
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Thank you all for the advice.
I accept that using FB paper for tests is right. However the ease of getting a good RC test print and then just adding a stop had an appeal to a lazy streak in me, so easy to dry and so forth, and much cheaper to work out burn and dodge times.
So my lesson today is dont be cheap and lazy it really is not worth it.
Also aperture adjustment are not always going to be linear, it makes a lot more sense to control time in f stops than the aperture.

Thanks everyone.
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