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Betlog
Tinkerer
Username: Betlog
Post Number: 1
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 06, 2011 - 07:56 am: | 
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Seeking schematic/mechanical diagram for the Sigma 600mm f8 mirror.
Or anyone who can tell me how the small mirror mounted in the middle of the front element is removed.
Looking at it from the inside it appears to be glued or screwed into it's metal housing in the center of the front element, but I do not want to touch it at all until I have some idea of how, or if, it comes out.
Thanks |
Glenn
Tinkerer
Username: Glenn
Post Number: 949
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 06, 2011 - 12:32 pm: |
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Leave well alone or you risk damaging the mirror - there is no need to remove this mirror anyway, so why risk it? |
Betlog
Tinkerer
Username: Betlog
Post Number: 2
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 08, 2011 - 09:29 am: |
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Because this:
http://oh-hi.info/tech/600mm%20mirror%20damage%2020110203%20IMGP2867a-1024px.jpg
is what looks like a lubricant bleed onto the inside of this lens/mirror assembly.
I have taken the lens apart and inspected it fairly closely, I can't be positive looking at it from 100mm away and from only one direction, and i am reticent to remove the entire front element and mirror assembly for a better look, but it looks very much like something I could rectify with a simple wipe.
In the right situation; yes it effects image quality, quite badly.
I realize that the front mirror alignment is critical, but if i could remove the smaller lens that is over the mirror I would be able to better ascertain if it's what I think it is or not.
In any case, i would like to obtain schematics for all of my older (simpler) lenses, partly as a collector thing, and because eventually I need to partly disassemble them for cleaning. |
Old_school
Tinkerer
Username: Old_school
Post Number: 124
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 08, 2011 - 07:03 pm: |
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Betlog: The image posted looks more like a cement separation, not an oil slick or migration. The pattern looks more characteristic of like a heat generated element separation or glue failure. Check on line for some sites on telescope servicing procedures. You might find a hobbyest that wil give some assistance on composition & structural configurations. I am sure you will have to remove the entire front element with the center lens (mirror) attached. This would give you the view you are looking for, but what you do after that is a good question.
I would guess at this point you have nothing to loose & look into it. Good Luck! Give some feed back as to what you come up with on this as I am curious.
The Best Mike.... |
Betlog
Tinkerer
Username: Betlog
Post Number: 3
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 09, 2011 - 04:02 am: |
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Right, thats what I thought too when i photographed it (heavily magnified) through the lens, but after splitting the lens in half and looking at it with the naked eye I am not so sure any more. There does appear to be some fluid present, but it may just be that the mirror & lens is cemented in, and thereby lends itself to a liquid appearance.. however given what you said I am also prepared to go back to assuming its a case of the previous 'professional cleaning' being responsible for pulling/twisting the assembly and thereby causing the damage to the aluminimized element.. which is likely cemented direct to the lens to guarantee alignment.
I would post a better shot, but it's dark now, I'll consider splitting it open again if it's sunny tomorrow, sunlight is the easiest way to see this thing.
TL;DR: I think you are right.
Are lens technical diagrams usually difficult to obtain? I have been looking for a few of my lenses diagrams and usually find nothing. |
Old_school
Tinkerer
Username: Old_school
Post Number: 125
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 09, 2011 - 06:34 pm: |
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Betlog: Check out this site pp 46
Care of Astronomical Telescopes and Accessories
http://www.scribd.com/doc/6722817/Care-of-Astronomical-Telescopes-and-Accessorie s
I just gave it a quick view & it will help explain how your lens is configured. There are a lot of people who build their own telescopes from scratch, maybe more than we want to know about, but they are a wealth of information & several site to look through & get information from & use.
The Best Mike.... |
Old_school
Tinkerer
Username: Old_school
Post Number: 126
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 10, 2011 - 12:59 pm: |
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B: There is one for sale on this site:
http://www.shopgoodwill.com/viewItem.asp?ItemID=8531970
Currently @ $72 |
Betlog
Tinkerer
Username: Betlog
Post Number: 4
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 11, 2011 - 05:52 pm: |
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Thanks. I am familiar with the basic configuration, it's the specifics of how sigma attach this element that I really want to know about. Trial and error to find out if its friction, glued, or threaded in is what damaged it in the first place. Unlike the 'professional repairer' caused this blemish I would prefer to know before applying any force 
The lens type frequently appears on ebay etc, unfortunately most of them are in the US, where a lot of sellers refuse international freight, and with photos that are usually poor. Even the ones that show inside the lens are usually focused only on the front element... and when there's 600mm of elements to look at this makes it very hard to tell if the lens is clean or not. Then there is shipping costs to consider.
The mount doesn't really need to be pentax-k, as i can transplant my mount section of the lens easily enough, but I think that unless I can source one locally (Australia) I will end up spending the money to buy a 'used-mint' condition one from Japan. However for now mine works fairly well. It's just flare/bloom that is sometimes an issue, but editing a bit of that, and a few more useless shots seem better than outlaying cash for something I already have. I have been using my 1000mm a lot lately, but after cleaning the 600mm a bit i remembered how small and light it is. A pleasure to use. |
