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troubles building a Raynox DCR-150 tube assembly
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All Ex



Joined: 20 Jul 2015
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Location: Greece Thessaloniki

PostPosted: Fri Feb 02, 2018 1:54 am    Post subject: troubles building a Raynox DCR-150 tube assembly Reply with quote

(Admit edit, RJL. This posting and subsequent replies originally appeared at the end of Raynox DCR-150 tube assembly with flocking. They have been split to a separate thread here to help simplify the original thread.)

Hello to everyone, I`ve built the thing:


I have a slight question :

What is the equal focal length of the tube? You see, instead of the extension tubes I placed a focusing helicoid and even when I extended it all the way, I`m not taking the full power of the objective, I attache in the front of it.
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rjlittlefield
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PostPosted: Fri Feb 02, 2018 12:13 pm    Post subject: Reply with quote

All Ex wrote:
What is the equal focal length of the tube?

The tube itself has no focal length. It's just an empty tube. The focal length is provided by the lens that you stick on the front. For the Raynox DCR-150, that is nominally 208.33 mm, probably a little different from one lens to another.

As for the length of the tube, you should adjust that so that the Raynox will focus at infinity, with no objective stuck in front of it. The total length of the tube needed to do this is usually someplace around 160-165 mm, depending on type of camera and slight variations between lenses.

Quote:
You see, instead of the extension tubes I placed a focusing helicoid and even when I extended it all the way, I`m not taking the full power of the objective, I attache in the front of it.

I'm not sure what you mean: "not taking the full power of the objective".

If that means you have measured the magnification, and it is less than what is printed on the side of the objective, then I can think of several possibilities:
a) You may be using a tube lens whose focal length is shorter than what the objective expects.
b) The tube lens may not be focused at infinity.
c) The measurement of magnification may be wrong.

--Rik
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All Ex



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PostPosted: Sat Feb 03, 2018 1:11 am    Post subject: Reply with quote

First of all Rik I thank you for the answer you gave me.
a) & c) are not apply b) (the tube lens is not focused properly at infinity) must be the answer I`m seeking.
Being confined in my bed {sitting on it) for 15 years isn`t helping to focus the tube at infinity since my room does not help at all (5X3,5 meters).
I hope my friend this afternoon will understand the concept and do the focusing for me.
The first thing I did was to adjust the length of the tube to be in distance of 208.33 mm between the Raynox and my sensor but the measurement of my caliper could not be so precise.
Thank`s

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rjlittlefield
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PostPosted: Sat Feb 03, 2018 10:37 am    Post subject: Reply with quote

Quote:
The first thing I did was to adjust the length of the tube to be in distance of 208.33 mm between the Raynox and my sensor but the measurement of my caliper could not be so precise.

That should get you close. The measurement does not need to be very precise. Even if you are off by 10 mm, the change in magnification will be only about 5%. For a lens with focal length 208 mm, a 10 mm difference in length is about the difference between focusing at infinity and focusing at 4 meters. Focusing at 4 meters will make the tube longer than focusing at infinity, which will give more magnification.

What objective are you using, what magnification are you measuring, and how are you making the measurement?

--Rik
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All Ex



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PostPosted: Sat Feb 03, 2018 2:06 pm    Post subject: Reply with quote

Today I tried with a friend of mine to focus the tube at infinity and I failed.
I was making the measurement with a Mitutoyo 5X and it sowed me 4X.
I`m making the calculation by the function:
magnification = sensor width/ frame width I use for the calculation of the frame width a ruler which has lines every half of a mm.
I`m thinking that the distance between my sensor and the Raynox should be (for f=200) 210 mm, calculating the 10mm of the eyepiece.
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PostPosted: Sun Feb 04, 2018 12:02 am    Post subject: Reply with quote

All Ex wrote:
I`m thinking that the distance between my sensor and the Raynox should be (for f=200) 210 mm, calculating the 10mm of the eyepiece.

Your thinking is confused. The Raynox DCR-150 is nominal 208.33 mm, not 200, and nothing in the calculation should involve an eyepiece. The 10 mm that you are thinking about is only for finite objectives, not infinite.

But in the end your number is not far off. At infinity focus, my reversed Raynox DCR-150 measures 200.8 mm from the rim of the lens to the sensor. The length of just the tubes would be 156.8 mm, equal to 200.8 mm minus the flange focal distance for your camera.

Note that this is for a Raynox DCR-150.

I notice that in a lot of your old postings you speak of a Raynox DCR-250, and I don't see that you have ever written about a 150.

So I have to ask, in the setup that you are having trouble with, are you using a DCR-150 or -250?

--Rik
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All Ex



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PostPosted: Sun Feb 04, 2018 12:49 am    Post subject: Reply with quote

The mod with the Raynox 250 DCR is working as expected, I`ve maid this one with the DCR-150, I` ll go on with the caliper once again in case that I`ve made somewhere a false measurement (in extending the focusing helicoid).
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All Ex



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PostPosted: Wed Feb 07, 2018 7:54 am    Post subject: Reply with quote

I can`t believe it is happening, what am I missing here? Here are the facts:
I have made this



My flange focal distance is 46.5mm. Therefore when I place in front of it an objective I would normally take closely the magnification of it.
I measure the magnification with the formula :
Magnification=sensor width/frame width
Since I`m using an FX camera when I gave it a 5X Mitutoyo it gave me this:



The small lines are half a mm away from the bigger ones.
What am I doing wrong?
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ChrisR
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PostPosted: Wed Feb 07, 2018 8:50 am    Post subject: Reply with quote

The magnification looks just close -
36/((208/200)x5)
should give 6.92mm.

the blur looks like movement, I think.
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PostPosted: Wed Feb 07, 2018 9:40 am    Post subject: Reply with quote

All Ex wrote:
What am I doing wrong?

My best guess is that you've somehow messed up in calculating the magnification.

In the image that you've posted, I measure 911 pixels in 6 mm. The full image width is 1024 pixels, so the frame width is 6*(1024/911) = 6.74 mm. Then 36/6.74 = 5.338X.

Expected magnification with all nominal specifications would be 5*208.33/200 = 5.208X.

The discrepancy is only 2.5% (5.338/5.208 = 1.025).

This does not look like a problem to me.

What have I missed?

--Rik
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All Ex



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PostPosted: Wed Feb 07, 2018 9:58 am    Post subject: Reply with quote

After Riik`s post, everything is clear to me.
The blur ChrisR is indeed a movement, I just didn`t connect the cable and I shat the trigger by hand.
Thank you, both.

Smile
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All Ex



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PostPosted: Thu Feb 08, 2018 4:27 am    Post subject: Reply with quote

Rik wrote:

In the image that you've posted, I measure 911 pixels in 6 mm

Till morning I`m trying to get to that number photoshop is telling that the width of that image is 7360 pixels when the resolution is 300 pixels/inch, can you please tell me the logic behind that estimation?

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enricosavazzi



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PostPosted: Thu Feb 08, 2018 7:13 am    Post subject: Reply with quote

All Ex wrote:
Rik wrote:

In the image that you've posted, I measure 911 pixels in 6 mm

Till morning I`m trying to get to that number photoshop is telling that the width of that image is 7360 pixels when the resolution is 300 pixels/inch, can you please tell me the logic behind that estimation?

I guess what Photoshop is telling you is that the image resolution as set in the file header is 300 pixels/inch. This setting can be arbitrarily changed, means nothing useful to us, and has nothing to do with the image magnification relative to the subject. I believe it is a largely legacy setting used in the printing industry for preparing a digital image for color separation and rastering.
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PostPosted: Thu Feb 08, 2018 7:37 am    Post subject: Reply with quote

Alex, to check it's "OK", you don't need to go counting pixels. In the method I used above, the width of the Field Of View, multiplied by Magnification, is the width of your sensor (36mm). (Yours is 35.9mm!)

Your magnification is 5x with a 200mm tube lens, but the raynox is about 208mm, which gives 5 x 1.04 = 5.2
So you would expect a frame width of 36/5.2 = 6.9mm

As you can see by looking at the image of the ruler, it's OK.

To be super accurate you'd need a flat, aligned subject all in focus, but we know that for quality purposes, a small percentage "out" is OK. Otherwise, in-lens focus bracketing wouldn't work,
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PostPosted: Thu Feb 08, 2018 8:37 am    Post subject: Reply with quote

I couldn`t agree more with you ChrisR that "a small percentage "out" is OK" and enricosavazzi`s explanation looks and seems to be right.
I made several thoughts on the issue, like that the size of the sensor particles is not the same in a 12 MP sensor as in a 36 MP one. I tried several calculations with no result and no lack.
That Rik`s calculation just got me very curious. Besides all the literature it was very accurate.

And another irrelevant thing:
for moments in the URL`s window appears the site marked as "not safe" at other times just has the circle with the "i" inside it.
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