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Possible alternative to barlows/teleconverters (1 Viewer)

Good idea, I may bid for a few as well, i have quite a few ext tubes spare that could be housings.

Ones I'm looking at on ebay are ones where the photos shows the inside of the lens like this one on the link. This is a Miranda lens but you can see the telenegative housing looks very similar to the photo of the Vivitar one I posted earlier. Could even be a rebranded Vivitar.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280566849614&ssPageName=STRK:MEWAX:IT

Paul.
 
Hi folks ive been using a Astro scope for a couple of years now one of the Skywatcher Maksutov types,ive got some decent results with with what is basically a 1300 mm mirror lens f13,can I just clarify if what im reading is right,if I add an extension tube between the camera body and scope I can increase the focal length without loss of light,or am I off the mark here..and also Paul how easy is it to take apart these cheap lenses as described,,
 
Hi folks ive been using a Astro scope for a couple of years now one of the Skywatcher Maksutov types,ive got some decent results with with what is basically a 1300 mm mirror lens f13,can I just clarify if what im reading is right,if I add an extension tube between the camera body and scope I can increase the focal length without loss of light,or am I off the mark here..and also Paul how easy is it to take apart these cheap lenses as described,,

Welcome Sparrowbirder.

To get the extra magnification by adding in the extension tube there also has to be something like a teleconverter between the scope and camera. Putting the teleconverter in obviously adds some extra magnification without the extra extension tube. When you put the extension between the teleconverter and the camera it increases the magnification of the teleconverter further which in turn affects the overall magnification.

The lenses are fairly easy to get apart. To get the front element off I usually stick a big lump of Blu-Tac to the front of the lens and give it a good twist anti-clockwise. That's usually enough to loosen the glass and the retaining ring etc. Then I use the same method to get the internal lenses out if they appear to be screwed in. Generally just a big lump of Blu-Tac and some screw drivers gets the job done.

Paul.
 
if I add an extension tube between the camera body and scope I can increase the focal length without loss of light,or am I off the mark here

Basically if a
1/ 1.4X tc is place directly to the camera body, you get (obviuosly) 1.4 magnification with the usual 1 stop of light loss.

2/ But if you place a 23mm (as in my example) extension tube between the body and TC, you get 2x magnification BUT with only 1.5 stops loss.

3/ if you put a 2xTC directly to the camera body you also get (obviously) 2X magnification BUT with light loss of 2 stops

So for 2x mag, example 2 is better than example 3.

Hope this clears it up.
 
Problem is my TC doesnt seem to work when I use it with my astro scope,I think its a light issue but keep getting an error code and "try cleaning the contacts " message,it works fine with my Sigma lens though,would a Barlow lens increase the focal length and is their any light loss,a 2x Barlow would give me a mag of 2600 mm,reason I asked about the lens Paul is because ive got a spare 18-55mm Canon kit lens just not sure how to get it apart (or even if it would be any good)
 
Problem is my TC doesnt seem to work when I use it with my astro scope,I think its a light issue but keep getting an error code and "try cleaning the contacts " message,it works fine with my Sigma lens though...
Have you tried manual mode? I'm guessing the camera is looking for a cpu in the scope and not finding one, hence the error message.
 
Yes, always use manual mode with the astro,ive got the Kenko 1.4 x,the light was quite poor today but I have tried to use it in better light and get the same thing,my Kenko wont couple at all with my 18-55 mm lens,its almost as if its a different thread its weird, not sure if anybody else has had this problem,anyway I suppose you just need to know the limits of the equipment,im thinking of changing over to one of the celestron F ED scopes suppose to be excellent,and they take astro eyepieces as well,so i could use a Barlow lens with one..my Maksutov can be softly focussed unless the light is perfect


MY WEBSITE http://www.flickr.com/photos/apbirdman
 
Yes, always use manual mode with the astro,ive got the Kenko 1.4 x,the light was quite poor today but I have tried to use it in better light and get the same thing,my Kenko wont couple at all with my 18-55 mm lens,its almost as if its a different thread its weird, not sure if anybody else has had this problem,anyway I suppose you just need to know the limits of the equipment,im thinking of changing over to one of the celestron F ED scopes suppose to be excellent,and they take astro eyepieces as well,so i could use a Barlow lens with one..my Maksutov can be softly focussed unless the light is perfect

You need to put some tape over the metal contacts on the back of the teleconverter. The camera reports an error because there is no camera lens attached to the teleconverter. Putting tape over the pins will stop the camera seeing the teleconverter and this will solve the error issues.

The Kenko 1.4X is in the old EOS mount while your 18-55mm lens is in the newer EF-S mount and that is why they wont couple together. The camera body can take both mounts however. EOS mounts have the red spot and EF-S have the white spots for lining up the bayonet fittings. You can't put a white spot with a red spot.

Probably better to sell the spare Canon 18-55mm, they generally fetch over £40 on ebay. Use the money to buy a cheap zoom to take apart and be left with £30 in your pocket.

Paul.
 
Saw this Cosina 70-210mm lens (see photo) on ebay and that's definitely a rebrand of the Vivitar that I have. You can clearly see the telenegative part just behind the front element and it's just the same as the Vivitar.

On ebay on Saturday I won a 28-70mm Vivitar zoom to try out next week. Just want to see how the telenegative group from a low power zoom compares to one from a higher power lens.

Paul.
 

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A photo of Jupiter I took a few nights ago with the Vivitar lens. Not bad for a single frame. Would need to take a few hundred frames and stack them in registax before it improved though.

Paul.
 

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Good grief !!

Magnificent. That would make me try the stacking technique. You should end up with, going by that one single shot, a rather incredible pic of Jupiter
 
Paul, now you got the ball rolling again...LOL. Suddenly, more oldies got snap up mysteriously on ebay...ha.... Just got myself an Vivitar 70-210 though a different one from yours but what the heck, it's about trying out. I am also bidding for this Cosina http://cgi.ebay.co.uk/Cosina-70-210...esFilters_JN&hash=item3a5f3c1dbd#ht_500wt_943 from UK ebay. So guys, watch out. I try not to bid for anything someone is already bidding, lest we bid each other out.
 
So far I've won a Miranda 75-300mm and a Vivitar 28-70mm and both should arrive mid week onwards. Total outlay is less than £15 but that was because one of them was £6 postage. Trying to keep to £5 total per lens.

Paul.
 
Won the DOI TC for £4.99 inc post, won the Sigma 75-210 for £5.99 posted.

Have taken the glass element out of the DOI, looks like the V2 one. I could simply epoxy glue it to a bayonet mount from one of my ext tube sets along with a AF confirm chip (which I have a spare one) and it woud be ready to go.
 
I found the DOI had problems with CA when I used it, especially on high contrast areas like Egrets. I just got an APO Barlow so I'm going to try that soon.

Won the DOI TC for £4.99 inc post, won the Sigma 75-210 for £5.99 posted.

Have taken the glass element out of the DOI, looks like the V2 one. I could simply epoxy glue it to a bayonet mount from one of my ext tube sets along with a AF confirm chip (which I have a spare one) and it woud be ready to go.
 
I got the other series of Vivitar 70-210 but will take a while to get here. No luck with my 2 2X DOI TC. Both turn out glary picture and worst than without TC + cropping. CA still under control though. Will try again later with improved mounting.
 
I got the other series of Vivitar 70-210 but will take a while to get here. No luck with my 2 2X DOI TC. Both turn out glary picture and worst than without TC + cropping. CA still under control though. Will try again later with improved mounting.

If it's glary or washed out with poor contrast then stray light will be the problem. Make sure everything in the tubes is at least matt black or better still flocked with black flock material.

With any teleconverter/barlow the contrast can be improved considerably by trying different methods to ensure the insides of the tubes are as black as possible. Try making some extra baffles too and put them in the 2" camera adapter as that helps I find too.

Paul.
 
If it's glary or washed out with poor contrast then stray light will be the problem. Make sure everything in the tubes is at least matt black or better still flocked with black flock material.

With any teleconverter/barlow the contrast can be improved considerably by trying different methods to ensure the insides of the tubes are as black as possible. Try making some extra baffles too and put them in the 2" camera adapter as that helps I find too.

Paul.

Paul, I think there is something wrong with my TCs. I baffled them all up, hold the camera up to prevent the focuser sagging, use two tripods to stop any pitching but still the same results. I attached all 4 shots for viewing. I found cropping as giving better results than TC.
 

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I don't see any problem with the photos. You will get a much shallower depth of field with the 2X TC but the thin depth of field where it is sharp it looks fine.

What is it that you find wrong with the TC images?

Paul.
 
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