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Old 19th April 2012, 09:15 AM
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Default Acceptable Sharpness

As I said in the thread on cameras I am using a converted Zeiss Nettar with a 0.3 mm pinhole. I measured the distance from the film plane to the pinhole and it is 69 mm. Using online resources and the Eric Renner book these say that a 0.3 mm pinhole is the size to use.

However my images when compared to other examples I have seen are very soft. I know I am not going to achieve absolute sharpness, that is what lenses are for, but is there an accepted standard or is it all up to the individual and the amount of creativity that one wishes to achieve. I am basing my question having seen the exhibition by Steve Gosling, images on the net and comparison with images made by BobRob. BobRob uses a pinhole slightly smaller than the recommended but still achieves good results, definitely sharper than mine.

I am using the camera on a Manfrotto carbon fibre tripod with a home made sliding plate as a shutter. Film has been 400 ISO either HP5 Plus or Rollei RPX 400. I have yet to make any prints but will do next session to post for comment.

Any thoughts would be appreciated.

Bill
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Old 19th April 2012, 11:31 AM
paulc paulc is offline
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Pop the pinhole on the neg carrier and wind the enlarger up. Project on to the baseboard with a 50mm lens, and once focused, you should be able to see just how round the hole is.

I made a pinhole a while back in a piece of shim stock using a high speed drill - The edges were very ragged and took a while to clean up with the aid of a polished sewing needle.
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Old 19th April 2012, 12:36 PM
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My photo tutor told me the best pinholes were made from gold leaf. Extremely thin, difficult to make and very easy to destroy.
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Old 19th April 2012, 02:05 PM
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Originally Posted by paulc View Post
Pop the pinhole on the neg carrier and wind the enlarger up. Project on to the baseboard with a 50mm lens, and once focused, you should be able to see just how round the hole is.

I made a pinhole a while back in a piece of shim stock using a high speed drill - The edges were very ragged and took a while to clean up with the aid of a polished sewing needle.
Thanks Paul. The 0.3 mm pinhole is a commercially made item and I had it in the enlarger the other day. I am happy that it is round and has no burrs. I also checked the size at the same time.

I have some brass shim material so I intend to use that for the next one but I will bear your note in mind when I make it.

Bill
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Old 19th April 2012, 04:56 PM
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A few things spring to mind, just suggestions though... I would try using a slower film and longer exposures, resting the camera nearer the ground perhaps to include some foreground which will look sharper. Although just a pinhole you still need to keep the camera very steady. Heavier tripod maybe.
Try out the pinhole on bigger formats and see if it looks different.
Try mounting the pinhole closer to the film plane... how did you adapt the nettar, does it still have the bellows? There may be an optimum focal length too.
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Old 19th April 2012, 07:46 PM
Paulographic Paulographic is offline
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Pinholes in the past were often made with sewing needles the guage of the needle dependent on the neg size and distance from the film. Tables for this can sometimes be found in old books.
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Old 19th April 2012, 10:27 PM
paulc paulc is offline
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Quote:
Originally Posted by Argentum View Post
My photo tutor told me the best pinholes were made from gold leaf. Extremely thin, difficult to make and very easy to destroy.
Gold leaf is indeed extremely thin, typically 0.0001mm to 0.000125mm. So thin, it is translucent in places when held up to the light. I have a few books of the stuff here.

Perhaps your tutor was referring to foil which is much thicker and considerably more expensive ?
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Old 20th April 2012, 07:09 AM
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Quote:
Originally Posted by Xpres View Post
A few things spring to mind, just suggestions though... I would try using a slower film and longer exposures, resting the camera nearer the ground perhaps to include some foreground which will look sharper. Although just a pinhole you still need to keep the camera very steady. Heavier tripod maybe.
Try out the pinhole on bigger formats and see if it looks different.
Try mounting the pinhole closer to the film plane... how did you adapt the nettar, does it still have the bellows? There may be an optimum focal length too.
Allowing for reciprocity I was using an exposure time of about 45 seconds in sunshine. I have found though that for the Rollei film this is too long. It would appear that this film has better reciprocity characteristics than others. There is no mention of reciprocity correction in the data sheet.

Interesting that you mention nearer being sharper as somewhere I'm sure I read that a pinhole has an optimum focus distance and that there is a depth of field effect. Can't find where I read that now though.

The Nettar does still have it's bellows and that is what gives me the focal length of 70 mm. Using various tables on the Internet and in the Eric Renner book they all appear to give a 0.3 mm hole. Lots of calculations seem to indicate the hole size is the square root of the focal length divided by 25. However if you work this back for a Zero Image camera they divide the square root by 35. That would require a hole of 0.23 mm for 70 mm focal length. Later today I am going out with my Wista and a roll film back and am going to try a series of shots at say 10 mm intervals from 70 mm up to see if there is a point at which the hole works best.

Thanks for the reply

Bill
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Old 20th April 2012, 07:11 AM
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Pinholes in the past were often made with sewing needles the guage of the needle dependent on the neg size and distance from the film. Tables for this can sometimes be found in old books.
I have found plenty of tables of recommended needle sizes, the problem is finding somewhere that sells the needles. Most shops these days don't seem to go down to as fine a needle as the tables suggest.

Bill
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Old 20th April 2012, 07:40 AM
Niall Bell Niall Bell is offline
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I bought a few needles and using a set of vernier calipers measured their diameters. [I've also tagged each with tape on which is written the diameter- [I'm lovingly told that this indicates OCD, but there you go.]

From the known diameters and using table in Renner, I made camera with focal length to suit needle.

Results still were not brilliant. I posted a picture on this forum sometime last year.

Interestingly, over breakfast this morning I was reading a booklet on pinholes I'd picked up by Fabbri, in which it says that pinholes should be able to produce images comparable with those from digital cameras!

Mine aren't.

Niall
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