• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Fernando - your Cosina 100-300 (1 Viewer)

Musoman

PETE - Nikon/Sony Shooter
United Kingdom
Hi Fernando - decided to experiment with the same lens that you tried as an ext. tube, the Cosina 100-300. They're cheap enough if i dont like it as this one was only £5.50

How far down did you strip yours ? Obviously the glass elements were removed. I can see that getting the rear element off and the mount ring ( MD/Minolta ) would be easy enough, but how do you remove the front element and how do you attach a tube to the front that goes into the focus end of the scope ??

Also, did yours " zoom creep " if held at an angle ( pointing up or down ) I'm wondering if there is a way to tighten the zoom action so it stays firm at any length
 

Attachments

  • cosina.jpg
    cosina.jpg
    180.8 KB · Views: 152
  • cosina2.jpg
    cosina2.jpg
    161.6 KB · Views: 120
  • cosina3.jpg
    cosina3.jpg
    152.3 KB · Views: 108
Well, first that is not the same lens I used, mine was a newer version, this one:
http://www.amazon.co.uk/Cosina-100-300mm-F5-6-6-7-Af-D-Nikon/dp/B00006H1X2

I took as much as I could, glass were all removed, and the parts holding the glass too, so were all the mechanical parts. I also removed the barrel the extends while zooming. What I keep was the chassis where that barrel is supported (where are the rails for the zooming), and I also kept all the covers and zoom rubber ring for aesthetics.
On my version of the lens that chassis is made of aluminum, and has exactly 2", all I need to do there was get a orion extension tube and cut with the exact measure needed to use all the focuser movement. Then I hold the tube to the chassis with three bolts, the zoom ring rubber, also covered the exact measure of the scope focuser, so this lens was a perfect fit ;)

On other thing, don't lose those front elements, if they're anything like mine, they make for a perfect double element close up filter, with about 6 diopter, very nice for macros ;)
 
This might be an interesting project for later, I presume, Fernando, that as yours is a AF-D Nikon fit that you left the CPU contacts in - do you still get AF confirm and metering through the lens ?

how does the aperture linkage work, did you leave the aperture curtain in so you could still control the aperture size.

I am researching a solution to meter with a SW80ED/Nikon D90 setup, there are chips I could buy such ass this:

http://filmprocess.ru/nikon_spec_en.html

But dont know the price, however with many cheaap 2nd hand lenses available on ebay, a lens conversion may be an alternative.
 
Last edited:
how does the aperture linkage work, did you leave the aperture curtain in so you could still control the aperture size.

Reducing the aperture works best at the front of the scope than at the back. If you do it at the back you soon run into problems with vignetting. The 80ED comes with a lens cover that has a removable part which reveals a 50mm hole. This reduces the scope from 80mm aperture to 50mm or f12. Depth of field is increased which alters the appearance of bokeh, there's some loss of light which reduces shutter speed but photos appear a little more contrasty which is nice.

Paul.
 
At this point for nikon, the Dandelion chips are your best bet, just glue them on the Tring and you're good to go.
The only upside of using the lens is the fit and looks, the way I built my lens fit far better than extender tubes+Tadapter+tring, instead of three connection points you’ll only have one. And it looks much better too, at least IMO. That said at this point I’d go for the dandelion, specially because I’m not using the lens body anymore, I machined a new adapter from scratch.

About the aperture linkage, like Paul said you can’t use it in the back so it’s useless so I took it off.
If you want to control the aperture on the scope you’ll have to put an iris at least before the focuser, but it must be a big iris with at least 50mm clear aperture (more depending on the final position).
I made some tests about that and the iris would work perfectly if mounted right where the last baffle is, with an iris there aperture could be controlled from wide open to F/16 perfectly. I wouldn’t bother with that for the ED80 but I was considering a faster scope at some point so I gave that some though.
 
Thats interesting (Paul, you are just too full of info, you should charge consultancy fees !!)

Could you explain 'bokeh' (is it pronounced similar to 'boquet' of flowers)

Cheers
 
Bokeh is pronounced bock as in dock and ke sounds like the ke in Kent. It's a word to describe the soft out of focus background in photos. Putting the lens cap on the 80D and revealing the 50mm hole takes it to f12 and this makes the out of focus background appear more in focus. Also having slightly more depth of field will get more of the subject in focus at closer range. Depth of field increases at longer range so it's not really a problem in this respect.

Paul.
 
Well, first that is not the same lens I used, mine was a newer version, this one:
http://www.amazon.co.uk/Cosina-100-300mm-F5-6-6-7-Af-D-Nikon/dp/B00006H1X2

I took as much as I could, glass were all removed, and the parts holding the glass too, so were all the mechanical parts. I also removed the barrel the extends while zooming. What I keep was the chassis where that barrel is supported (where are the rails for the zooming), and I also kept all the covers and zoom rubber ring for aesthetics.
On my version of the lens that chassis is made of aluminum, and has exactly 2", all I need to do there was get a orion extension tube and cut with the exact measure needed to use all the focuser movement. Then I hold the tube to the chassis with three bolts, the zoom ring rubber, also covered the exact measure of the scope focuser, so this lens was a perfect fit ;)

On other thing, don't lose those front elements, if they're anything like mine, they make for a perfect double element close up filter, with about 6 diopter, very nice for macros ;)



Thanks Fernando ! ;)
 
Well here it it, and with this, i have focus down to 15ft ( from camera body , or 13 ft from scope front ) at full extension, and at the moment, distance focus to at least 100 metres. I cant fully check that for sure, until i go out with the scope and check beyond that distance.

The above is without any Barlow

Pics show the Cosina EXT tube fully retracted and fully zoomed. The mount for my 40D is an M42 > EOS Focus Confirm Chipped adapter, which works fine

One thing i will need to change in the future is the focus mech. on the scope. I find this mediocre. With the weight of the 40D + Tube mounted, the focuser dips down and makes it a bit rough to use
 

Attachments

  • Cosina EXT.jpg
    Cosina EXT.jpg
    229.9 KB · Views: 154
  • Cosina EXT2.jpg
    Cosina EXT2.jpg
    180.1 KB · Views: 156
  • Cosina EXT3.jpg
    Cosina EXT3.jpg
    259.1 KB · Views: 155
  • Cosina EXT4.jpg
    Cosina EXT4.jpg
    228.4 KB · Views: 134
Last edited:
Looks good but it's on the long side for using with a barlow, but would be ok with a teleconverter. To use a barlow you would need at least another 60mm of extension in the back of the scope just to allow the barlow to focus which would make for a lot of length stuck in the back of the scope.

Paul.
 
I plan to keep this part of the setup as 600mm only, Paul..or maybe with 1.5x TC, as you say.

I have the Barlow in another complete tube set with the correct extensions. I got fed up changing the ext tubes in and out ( threaded ones ) every time i wanted to photo a bird at distance, and then unscrewing it again to take a shot that was much closer. AS you know, that means removing the entire thing from the camera and scope, unscrewing ( or screw in ) the appropriate extra tube.

This way, i can focus on anything from 15ft to at least 100m, and possibly further ( not tested yet ) or simply remove the whole tube, and mount the other set with the barlow already screwed in. Just as quick as changing a lens....ok, add a couple of seconds for securing the tubeset into the scope :)
 
You kept the zoom mechanism? I though of that but really wanted my setup as solid as possible, so I took that off too, but the 15ft closest focus is a nice feature to have ;)

If you're thinking on upgrading the focuser, just an opinion... I have a William Optics on mine, very solid, rotary type, dual speed, beautiful to look at...but too expensive for what it is.
A friend of mine bought a knock off (don't remember where but I think it was in UK), about half the price and quite frankly better, a better fit (didn't need shimming), focus is smoother and just as solid and good looking. Both are very heavy though so keep that in mind, a decent focuser will put you an extra Kg on your scope. But a worthy Kg IMO.
 
Sounds good, do you know the name of the focuser ? I could do with upgrading mine for sure.

I kept only the zoom part of the lens - the twist to focus portion i removed. It doesnt twist anymore, just the zoom works so i can change the adapter length to suit the subject
 
Cheers Paul - I had a good look at those

Fernando reckons the cheap UK WO copy is half the price of the genuine WO focuser

Your 2nd link is the genuine WO model @ £193 - so i guess the WO UK copy would be less than £100, which is another £30 cheaper than the cheapest in your links.

Just need the name ;)
 
I very much doubt you will find a focuser for under £100, I've certainly never seen one. £130 is going to be about the minimum. The WO one used to be more expensive in the past which is probably where the discrepancy is.

Found this GSO Crayford Focuser which again is in the £130 bracket, mainly because of shipping from the States. Only weighs 1.8lbs which isn't bad for a dual speed focuser.

http://cgi.ebay.co.uk/GSO-Dual-Speed-Crayford-Focuser-Refractors-96mm-/110548160237?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item19bd2f0eed

Paul.
 
Last edited:
Well, I guess I could explain that better, his focuser was half the price than mine because I bought mine two or three years ago, and back then they costed 280€ at telescopeservice (and everywhere else), now they cost much less. My friends focuser costed about 140€, the same model as Paul linked in his post. Sorry for the mistake.

Paul, one thing about this focuser:
http://www.teleskop-express.de/shop/product_info.php/language/en/info/p775.html
It does look good for the money, but it's not rotational, I guess it depends on your shooting style but for me is a big issue, that was the thing making spend all that money on the WO, it was the only rotational option at the time and I use it a lot really, it's a great feature to have.
 
A couple more links. The first link is the WO copy for £125 and second link is an Antares/GSO unit for £116. From what I read elsewhere the Antares/GSO goes straight into the 80ED witout an adapter plate and then goes into bigger scopes via an adapter plate but you would need to check as the info on the link isn't 100% correct. At £116 this is the cheapest dual speed, 360° rotating focuser I have found. A lot of these focuser also have shorter travel than the stock unit, only around 1/2" to 1" but it's something to keep in mind.

http://www.rothervalleyoptics.co.uk/skywatcher-dual-speed-2-quot-1-25-quot-crayford-focuser_d2988.html


http://www.scopesnskies.com/prod/antares-telescope-accessories/crayford-focusor/refractor.htm


Paul.
 
Last edited:
That's a great price, I didn't know the Antares would rotate. I appears the same as the TS focuser, and when I bought my WO focuser telescopeservice.de informed me the TS didn't rotate...maybe they add that by now. In that case the TS rotates too.
 
Warning! This thread is more than 14 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Users who are viewing this thread

Back
Top