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iangreenhalgh1
Joined: 18 Mar 2011 Posts: 15679
Expire: 2014-01-07
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Posted: Sun Sep 13, 2015 7:44 am Post subject: Mirror lens diameter |
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iangreenhalgh1 wrote:
Hi folks
I have a project that requires a large diameter helicoid. So I thought a cheap mirror lens would be the place to find such a thing.
So, what I need to know is - what is the approx diameter of the helicoid on the typical cheap 500mm mirror lens? _________________ I don't care who designed it, who made it or what country it comes from - I just enjoy using it! |
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dan_
Joined: 05 Dec 2012 Posts: 1058 Location: Romania
Expire: 2016-12-19
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Posted: Sun Sep 13, 2015 11:27 am Post subject: |
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dan_ wrote:
What diameter you need it to be, Ian?
You may look at Bronica or Pentax 6X7 helicoids, too. Or at old Russian or German 300mm/4 or bigger broken lenses, as well.
Finding a very large diameter helicoid may be not so easy.
I needed a greater than 80mm (inner diameter) helicoid for my TT&H 12 Inch/4 aerial lens and I could only find a proper one after ~3 years of monitoring ebay.
Last edited by dan_ on Sun Sep 13, 2015 2:11 pm; edited 1 time in total |
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fuzzywuzzy
Joined: 18 Dec 2010 Posts: 1258 Location: Down East, Canada, eh?
Expire: 2013-11-30
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Posted: Sun Sep 13, 2015 1:08 pm Post subject: Re: Mirror lens diameter |
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fuzzywuzzy wrote:
iangreenhalgh1 wrote: |
Hi folks
I have a project that requires a large diameter helicoid. So I thought a cheap mirror lens would be the place to find such a thing.
So, what I need to know is - what is the approx diameter of the helicoid on the typical cheap 500mm mirror lens? |
I don't know if this is typical, but my 3m-5a extends in a very limited range, from infinity to MFD the extension is only 4-5mm, not sure if that would be useful in your application.
3m-5a's filter size 77mm btw to give an idea of helicoid size. _________________ I welcome C&C, editing my pics and reposting them on the forum is fine.
NEX-F3
~~~~~~~~~
CZJ Sonnar 135/4, Biotar 58/2, Pancolar 50/2, Tessar 50/2.8, Flek 35/2.8, Flek 25/4
Super Takumar 135/2.5, 135/3.5, 100/4 bellows, 50/1.4, 28/3.5
Helios 58/2, 3M-5A 500/8, Mir 20M
Vivitar Series 1 70-210 - - - - - - - - Nikkor 200/4
Rikenon 28/2.8 - - - - - - - - Zeiss 50/1.7 Planar
PB 50/2.4, 135/2.8
Yashica 50/1.9, 28/2.8, 135/2.8
Hexanon 28/3.5, 50/1.4 |
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calvin83
Joined: 12 Apr 2009 Posts: 7555 Location: Hong Kong
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Posted: Sun Sep 13, 2015 2:00 pm Post subject: |
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calvin83 wrote:
Samyang 500mm f/6.3 if you can find one cheap. It takes 95 mm filter. _________________ https://lensfever.com/
https://www.instagram.com/_lens_fever/
The best lens is the one you have with you. |
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iangreenhalgh1
Joined: 18 Mar 2011 Posts: 15679
Expire: 2014-01-07
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Posted: Sun Sep 13, 2015 2:03 pm Post subject: |
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iangreenhalgh1 wrote:
Thanks guys.
I need one that is 77mm diameter or bigger.
4-5mm of extension sounds like much too little. _________________ I don't care who designed it, who made it or what country it comes from - I just enjoy using it! |
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dan_
Joined: 05 Dec 2012 Posts: 1058 Location: Romania
Expire: 2016-12-19
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Posted: Sun Sep 13, 2015 2:33 pm Post subject: |
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dan_ wrote:
Before finding the big helicoid I've used an adapted Pentacon 6 macro bellows for focusing the big lens. It can be adapted for larger threads, it's pretty solid and it's not very big. It is relatively cheap, too. You can use one as a good temporary solution till you find a proper helicoid.
Pentacon 300/4 has the smallest outer diameter = 82mm (but I don't know its inner diameter...). |
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calvin83
Joined: 12 Apr 2009 Posts: 7555 Location: Hong Kong
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Posted: Sun Sep 13, 2015 3:55 pm Post subject: |
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calvin83 wrote:
If the the weight of the optical block is not too heavy and the distance of the rear element to the sensor is not very limited, you may consider adding a hood to the front of a lens/helicoid to make more room to hold the optical block... _________________ https://lensfever.com/
https://www.instagram.com/_lens_fever/
The best lens is the one you have with you. |
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iangreenhalgh1
Joined: 18 Mar 2011 Posts: 15679
Expire: 2014-01-07
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Posted: Sun Sep 13, 2015 6:01 pm Post subject: |
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iangreenhalgh1 wrote:
Good suggestions, thanks. I've employed a set of P6 bellows to adapt my mamiya rz67 lenses to my a850.
The optics are quite heavy, I'm using the front cemented doublet from a broken Fujinon TV broadcast grade lens which is about 75mm in diameter and a Fujinon broadcast grade 0.8x converter which has 82mm threads. I want to vary the distance between them, hence the helicoid. _________________ I don't care who designed it, who made it or what country it comes from - I just enjoy using it! |
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