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 Replies: 23 / Views: 3,818 |
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Valued Member
United States
359 Posts |
The observations in this post were gathered using the equipment in the $400 setup thread. I have a Canon T2i body. I was looking for a consistent method to calculate the extension tube length required to fill 90% of the camera's sensor height. After some tips from rmpsrpms, I can't take all the credit, I was able to develop the spreadsheet shown below. In the spreadsheet there is a constants section for you to enter your setup specifications such as camera sensor height, sensor to the front of the camera length, etc. There are lines (12 to 19) for 8 common coin diameters, and as you walk from left to right across the table the calculations compile and ultimately give you a required extension length (column L) for your setup at 90% of the image sensor height. By setting this extension length, when the camera is set to the proper height from the coin, you will be able to achieve proper focus of the coin at approximately 90% of the sensor height being filled. In live view I have 20 grid lines in the height, so I aim to have one full grid line empty at the top and bottom. Coin should fill the rest, achieving your 90% height fill. Columns N to R are useful if you have the manual extensions specified in the $400 setup thread. The length options are 28mm, 14mm and 7mm. These qty of each length has to be inputted manually. Your goal is to have the number in the delta column to be as close to 0 as possible. I typically choose a negative number if you can only go so close to the target value. On the far right are the setup parameters I used for each coin size. Lens to surface height, column "T" shows the physical distance from the front of the El-Nikkor lens to the surface you have the coin on. Hope this helps anyone working on their setup. Let me know if you have any questions. Thanks! Here is the screenshot of the file. PM me if you want the file.  Edited by ngs428
03/25/2018 08:09 am
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Pillar of the Community
United States
1375 Posts |
ngs428, Some really useful information for the folks using this setup  , but I don't believe you meant to say that 90% of the sensor is filled when the coin is filling 90% of the sensor height. The coin would only fill a bit less than 43% of the sensor. It's just the round peg in a rectangular hole thing  Edited by BadDog
03/25/2018 2:26 pm
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Valued Member
 United States
359 Posts |
Yes, just filling 90% of the height. Leaving room for a nice crop. The overall % of the sensor covered is much less than 90%. I edited my post for clarification about 90% referring to the height only. Below is an updated image:  Edited by ngs428
03/25/2018 09:11 am
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Pillar of the Community
Canada
9163 Posts |
Sorry but I have to disagree with some of your #'s. But first I'm NOT a techy person and a lot of your #'s went over my head.
In the manual ext. needed for .01 - 14mm ; .05 -14mm ; .10 - 7mm and 14mm ; .25 - 14mm ; .50 and 1.00 - no ext. is what I use.
The lens is a 80mm and is 25mm in length.
For the dimes which I'm doing now the coin is 172mm from the lens.
But in the end it is what works for each person.
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Valued Member
United States
359 Posts |
Yes, sounds like you have a different lens than what is specified in the $400 setup thread. I use the extension lengths and coin distances shown and it works well. You would need to have the exact same items as specified in the $400 setup thread for this to work. Camera sensor size, etc will all have an impact. That is why I have a spot to enter these for each setup on the spreadsheet.
If your works for you, by all means keep using it.
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Pillar of the Community
 United States
4038 Posts |
Very nice job! I would suggest a small diagram showing the lens dimensions to make it easier to change to different lenses. The assumption is that the physical center of the lens is used to measure the required extension rather than the mounting plane. This is not always accurate, and will vary a bit from lens to len, but gives a better result than using the lens mounting plane.
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Valued Member
Russian Federation
172 Posts |
As for me that $400 is strange setup. With small lenghts of helicoid 17-31mm there need to use different setup of various extension rings. Instead of using just one helicoid 35-90mm without extension rings at all for any size of coins and without reassembling optical system each time for different coin size.
Edited by Justwalking
04/02/2018 11:13 am
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Valued Member
United States
359 Posts |
@justwalking- good question. Not sure why, maybe Ray can chime in with his thoughts. It may have something to do with the quality of the cheaper ones in that range. That range would cover all that I calculated from dimes to silver eagles.
Thanks Ray. I will see if I can add that.
Edited by ngs428
04/02/2018 8:11 pm
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Pillar of the Community
United States
9395 Posts |
Quote:
As for me that $400 is strange setup. With small lenghts of helicoid 17-31mm there need to use different setup of various extension rings. Instead of using just one helicoid 35-90mm without extension rings at all for any size of coins and without reassembling optical system each time for different coin size. If you want to cover a wider range of coin sizes without re-assembling everything, just use a bellows rather than extension tubes. A Bellows might be more expensive, though. |
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Valued Member
Russian Federation
172 Posts |
I'm no need anything from $400 anyway )). I can get FoV from several mm to several meters with one microscope lens and one helicoid. Just wondering of using extension rings for $400 setup.
35-90mm can cover any size coin from the table above. Even less expensive 25-55mm helicoid with two constant rings 7 and 14 mm can do it.
Edited by Justwalking
04/02/2018 10:58 pm
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Pillar of the Community
United States
4038 Posts |
The original recommendation of 17-31mm was made at a time when the longer helicoids were much more expensive. You can of course choose the longer helicoid, and minimize the changes required. The 17-31mm are still the least expensive.
I'm curious to hear what microscope lens can provide decent optical coverage from several mm to several meters. That would be an optical miracle!
Contact me for photographic equipment or visit my home page at: http://macrocoins.com |
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Valued Member
Russian Federation
172 Posts |
Edited by Justwalking
04/03/2018 10:00 am
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Valued Member
United States
359 Posts |
Edited by ngs428
04/03/2018 10:44 am
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Valued Member
Russian Federation
172 Posts |
Yes. It's $6.34 more. But you paid also for 3 rings to complete short helicoid.
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Valued Member
United States
359 Posts |
Correct.
I bought the helicoid for $20.78 and 2 sets of 3 extension tubes at $7.99 each, so $36.76 total. $9.64 more than the 35-90 helicoid. So, yes the 35-90 is cheaper and easier to use, so I am going that route for the ease of use part.
Edited by ngs428
04/03/2018 12:18 pm
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Valued Member
Russian Federation
172 Posts |
@ngs428, I'm sorry that with my suggestion your calculator will be useless. ))
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Replies: 23 / Views: 3,818 |
Posted 03/25/2018 08:02 am
