Close up filter/lens question.....

Astro-Baby · 07-21-2020, 01:38 PM

A few weeks back I bought a supposed UV filter off eBay with a chrome ring. Been looking for a vintage UV with chrome filter ring for ages......

Unfortunately when it got here it turns out to be some kind of close up filter of uncertain diopter value. The lens/filter has a clear mensicus shape when viewed side on but it scarcely changes the focal range of any lens its put on. A 50mm will not focus to infinity and its out by a small measure. A test on a table top with a ruler shows that the closest focus point moves inwards but only by about 2”

Never having used one of these in my life before ( at least as far as I can recall ) can anyone advise how to find its diopter factor as I will sell it on and would like to be able to give some kind of accurate description. If the glass was removable I would take the lens out and replace with a UV for its chrome ring but the glass seems glued to the ring.

I did a bit if reading up on this but cant really find a simple method to calcualte diopter values and the change in foval length seems miniscule.

photoptimist · 07-21-2020, 01:56 PM - **1 Like**

The easy way is to check the focal length with the sun.

Hold a piece of paper in one hand facing the sun,
hold the close-up filter in the other hand in front of the paper,
steadily increase the distance and watch the diameter of the sunlight in the paper contract to a point (and burn a hole in the paper!!!!)
note the distance between the paper and lens
The distance between the paper and lens is the focal length.
The diopter value is 1000/focal length.

(Note: don't worry too much about accurately measuring the distance. Chances are the filter is either a +1, +2, or +4 diopter filter which have very obviously distinct focal lengths of 250, 500, and 1000mm.)

35mmfilmfan · 07-21-2020, 02:09 PM - **2 Likes**

Originally posted by photoptimist

The easy way is to check the focal length with the sun.

[*]steadily increase the distance and watch the diameter of the sunlight in the paper contract to a point (and burn a hole in the paper!!!!)

(Note: don't worry too much about accurately measuring the distance. Chances are the filter is either a +1, +2, or +4 diopter filter which have very obviously distinct focal lengths of 250, 500, and 1000mm.)

This can be great fun if you do it to someone reading a newspaper - news literally 'Hot off the press !'

Did this to a teacher using a magnifying glass over 60 years ago. 100 lines and six stripes. Worth it.

**UncleVanya** · 07-21-2020, 06:01 PM

A short lens like the 50mm won't show much change. Try a longer lens if you have one. I'm very curious.

Astro-Baby · 07-21-2020, 11:22 PM

Thanks guys....I’ll give it a go. My options on a long lens are limited as yhis dilter is a 55mm fit and most of my long glass has a wider dilter fit but. I will have to have a look, think I may have an old Paragon boxes up thats 135mm with a 55mm fit.

**UncleVanya** · 07-22-2020, 07:57 AM

Originally posted by Astro-Baby

Thanks guys....I’ll give it a go. My options on a long lens are limited as yhis dilter is a 55mm fit and most of my long glass has a wider dilter fit but. I will have to have a look, think I may have an old Paragon boxes up thats 135mm with a 55mm fit.

If you have a step ring it should work also. I've used a 62mm on a DA* 200 with a 62 to 72mm ring without noticable vignetting (the image is magnified so it doesn't require the full width. )

If you use a tripod you could even hold the "filter" in front of the lens for a quick test.

Astro-Baby · 07-22-2020, 10:31 AM

I do have step ups ( of course, I am a retro nutter

) but typically nothing for 55mm thats any help at all. I tried the sun test and it was inconclusive at best. Lens/filter wont come to a sharp point it produces a weird helix looking effect or nothing at all. Tried it on a 135mm and it does shorten the minimum focus distance by about 30cm. Which would seem a bit pointless to me. Who knows maybe macro folk have withered legs and cant move 12” closer to a target.

What I did notice though is the DOF ‘seems’ much shallower with this thing on the lens. I cant scientifically prove that right now. I would need to make up a test target and that seems a bit mad and a rigamarole.

Putting it over printed material seems to produce not much in the way of magnification.

Think I will just throw it up on ebay for 99p and see if anyone wants it. Misc camera stuff with no known application.

**Sakura** · 07-22-2020, 10:30 PM

It also could be a "Ghostles" filter

Look also at this link

Die Cast Pro - Asahi Pentax Filters

Astro-Baby · 07-22-2020, 11:32 PM

Ghostless ? i had a look but it isnst one of those. The glass isnt a doublet, what was really odd was when the lens was put up to the sun rather than producing a spot at focus its produced an infinity symbol ( a figure 8 on its side ), come in closer than an inch and the figure collapses to nothing. Further away and the figure just expands a little and then disappears.

I was wondering of its some kind of close field lens but will have to run some tests on its DoF and see.

photoptimist · 07-23-2020, 05:59 AM

Originally posted by Astro-Baby

Ghostless ? i had a look but it isnst one of those. The glass isnt a doublet, what was really odd was when the lens was put up to the sun rather than producing a spot at focus its produced an infinity symbol ( a figure 8 on its side ), come in closer than an inch and the figure collapses to nothing. Further away and the figure just expands a little and then disappears.

I was wondering of its some kind of close field lens but will have to run some tests on its DoF and see.

Strange!

I wonder if the lens has more than one focal length like a "progressive" lens for "no-line" bifocal eye glasses.

If you point a camera and lens at a brick wall or book shelf so that the entire wall is in focus corner-to-corner and then add this filter, what happens? Does the entire wall stay in focus?... shift focus uniformly?.. Or does only a part of the wall go out of focus (but can be refocused)?

07-21-2020, 01:38 PM	#1
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764	Close up filter/lens question..... A few weeks back I bought a supposed UV filter off eBay with a chrome ring. Been looking for a vintage UV with chrome filter ring for ages...... Unfortunately when it got here it turns out to be some kind of close up filter of uncertain diopter value. The lens/filter has a clear mensicus shape when viewed side on but it scarcely changes the focal range of any lens its put on. A 50mm will not focus to infinity and its out by a small measure. A test on a table top with a ruler shows that the closest focus point moves inwards but only by about 2” Never having used one of these in my life before ( at least as far as I can recall ) can anyone advise how to find its diopter factor as I will sell it on and would like to be able to give some kind of accurate description. If the glass was removable I would take the lens out and replace with a UV for its chrome ring but the glass seems glued to the ring. I did a bit if reading up on this but cant really find a simple method to calcualte diopter values and the change in foval length seems miniscule.

07-21-2020, 01:56 PM - 1 Like	#2
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,126	The easy way is to check the focal length with the sun. Hold a piece of paper in one hand facing the sun, hold the close-up filter in the other hand in front of the paper, steadily increase the distance and watch the diameter of the sunlight in the paper contract to a point (and burn a hole in the paper!!!!) note the distance between the paper and lens The distance between the paper and lens is the focal length. The diopter value is 1000/focal length. (Note: don't worry too much about accurately measuring the distance. Chances are the filter is either a +1, +2, or +4 diopter filter which have very obviously distinct focal lengths of 250, 500, and 1000mm.)

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07-21-2020, 02:09 PM - 2 Likes	#3
35mmfilmfan Pentaxian Join Date: Oct 2016 Location: Norfolk, UK Posts: 4,329	Originally posted by photoptimist The easy way is to check the focal length with the sun. [*]steadily increase the distance and watch the diameter of the sunlight in the paper contract to a point (and burn a hole in the paper!!!!) (Note: don't worry too much about accurately measuring the distance. Chances are the filter is either a +1, +2, or +4 diopter filter which have very obviously distinct focal lengths of 250, 500, and 1000mm.) This can be great fun if you do it to someone reading a newspaper - news literally 'Hot off the press !' Did this to a teacher using a magnifying glass over 60 years ago. 100 lines and six stripes. Worth it.

07-21-2020, 06:01 PM	#4
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,406	A short lens like the 50mm won't show much change. Try a longer lens if you have one. I'm very curious.

07-21-2020, 11:22 PM	#5
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764 Original Poster	Thanks guys....I’ll give it a go. My options on a long lens are limited as yhis dilter is a 55mm fit and most of my long glass has a wider dilter fit but. I will have to have a look, think I may have an old Paragon boxes up thats 135mm with a 55mm fit.

07-22-2020, 07:57 AM	#6
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,406	Originally posted by Astro-Baby Thanks guys....I’ll give it a go. My options on a long lens are limited as yhis dilter is a 55mm fit and most of my long glass has a wider dilter fit but. I will have to have a look, think I may have an old Paragon boxes up thats 135mm with a 55mm fit. If you have a step ring it should work also. I've used a 62mm on a DA* 200 with a 62 to 72mm ring without noticable vignetting (the image is magnified so it doesn't require the full width. ) If you use a tripod you could even hold the "filter" in front of the lens for a quick test.

07-22-2020, 10:31 AM	#7
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764 Original Poster	I do have step ups ( of course, I am a retro nutter ) but typically nothing for 55mm thats any help at all. I tried the sun test and it was inconclusive at best. Lens/filter wont come to a sharp point it produces a weird helix looking effect or nothing at all. Tried it on a 135mm and it does shorten the minimum focus distance by about 30cm. Which would seem a bit pointless to me. Who knows maybe macro folk have withered legs and cant move 12” closer to a target. What I did notice though is the DOF ‘seems’ much shallower with this thing on the lens. I cant scientifically prove that right now. I would need to make up a test target and that seems a bit mad and a rigamarole. Putting it over printed material seems to produce not much in the way of magnification. Think I will just throw it up on ebay for 99p and see if anyone wants it. Misc camera stuff with no known application.

07-22-2020, 10:30 PM	#8
Sakura Site Supporter Join Date: Jan 2010 Location: Netherlands Photos: Gallery Posts: 438	It also could be a "Ghostles" filter Look also at this link Die Cast Pro - Asahi Pentax Filters

07-22-2020, 11:32 PM	#9
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764 Original Poster	Ghostless ? i had a look but it isnst one of those. The glass isnt a doublet, what was really odd was when the lens was put up to the sun rather than producing a spot at focus its produced an infinity symbol ( a figure 8 on its side ), come in closer than an inch and the figure collapses to nothing. Further away and the figure just expands a little and then disappears. I was wondering of its some kind of close field lens but will have to run some tests on its DoF and see.

07-23-2020, 05:59 AM	#10
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,126	Originally posted by Astro-Baby Ghostless ? i had a look but it isnst one of those. The glass isnt a doublet, what was really odd was when the lens was put up to the sun rather than producing a spot at focus its produced an infinity symbol ( a figure 8 on its side ), come in closer than an inch and the figure collapses to nothing. Further away and the figure just expands a little and then disappears. I was wondering of its some kind of close field lens but will have to run some tests on its DoF and see. Strange! I wonder if the lens has more than one focal length like a "progressive" lens for "no-line" bifocal eye glasses. If you point a camera and lens at a brick wall or book shelf so that the entire wall is in focus corner-to-corner and then add this filter, what happens? Does the entire wall stay in focus?... shift focus uniformly?.. Or does only a part of the wall go out of focus (but can be refocused)?