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Old 01-04-2010, 08:02 PM
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Another cheap lens test

I simply could not resist recent ebay item on sale..
It was Tamron Popular 400mm F6.3, from '70-ies last century... for $30.
When it arrived, I found moisture on the rear glass element, inside.. no idea how the water get in ?? But it was easy to loose retaining ring and clean the element with soft tissue. Assembled again, it looked very good.

The reports on this lens (and most of others) on the web were useless, of course: lots of "poetic" descriptions, lots of images of flowers and birds, but none in terms of MTF or some high-contrast objects images that would indicate the true quality of the lens.

So, tonight I did the usual thing: star field at full aperture, 10sec exposure time, couple of shots only because mosquitoes were unbelievable hungry... So I run inside as soon as I could.

Some bad news: lens suffers from significant astigmatism, visible on the Beta Cruci image (attached, 100% crop from centre of the frame).

Good news: very similar distortion in corners. It seems the glass (front element, it will be the major contributor to the problem) is probably just "pinched". If this is true, relaxing the retaining ring will help here.
Further indication that this may be true is, none of the astigmatism is visible at f11.. so the central part of the front element is not "potatoid", only the edges are deformed.

So, after relaxing the glass, I may have another decent lens for photometry (aperture being 62mm diameter, not bad for the purpose). Or, it will be good as finder or guide scope.
I will certainly post the results of the procedure when I have them.
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Last edited by bojan; 01-04-2010 at 08:44 PM.
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  #2  
Old 01-04-2010, 08:47 PM
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will be interesting to see how the results come out.
Ritchie
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Old 01-04-2010, 09:50 PM
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mithrandir (Andrew)
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I have a 1970s Vivitar Series 1 70-210 constant aperture f3.5 with a Minolta XE series mount. Any chance of attaching this to a QHY8 for some "wide" field work?
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Old 01-04-2010, 10:18 PM
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jjjnettie (Jeanette)
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I wish you could have had better results. But for a cheapy lens, I guess you can't expect much more.
Hope you get do get some improvement.
Keep us posted.
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Old 01-04-2010, 10:48 PM
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astroron (Ron)
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Hi Bojan , I have a 300mm F/5.6 Tamron lens that I used on my 35mm Minolta SRT 101 film camera, I cannot use it on my DSLR, what other astronomical uses can I use it for I have plenty of finder scopes
I bought it in Singapore in the 1960's
Cheers
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Old 02-04-2010, 07:49 AM
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I had one Tamron 200mm lens with Minolta mount converted to M42 (and then to EOS), have a look here:
http://www.iceinspace.com.au/forum/s...hlight=minolta

It seems Minolta cameras are quite deep, so at the end, after removing the locking mechanism from the lens and attaching M42 flange (removed from one old and faulty Hanimex M42 lens, and with a little help of my friend in his machine shop) I have another 3.11mm extra focus mechanism movement after reaching focus with 400D (via M42-EOS adapter).
The optical results (when used with external aperture at f4 - f5.6) were quite good, it is actually better than much more expensive Canon 200mm F2.8 (also stopped down with external aperture), and I am going to use it much more often in the future (especially after discovering that I can get rid of mild residual lateral CA in final image with Gimp plugin (freeware, of course)

For manual lenses in general, there are plenty of information available on internet..
One of the web pages I used a lot for initial information is here:
http://photonotes.org/articles/eos-manual-lenses/
There, only non-invasive procedures are discussed, but as I am an "invasive" person, I go for a lot and cut, glue, chip off.. until it fits

I am not sure how QHY8 is mounted, it seems it is M42 or some kind of T-mount?
But what ever it is, I am sure it is quite possible to fit Minolta lens on it.
However, be aware that zoom lenses are not as good as primes in general.

Last edited by bojan; 02-04-2010 at 09:14 AM.
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Old 02-04-2010, 10:02 AM
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Interesting thread here Bojan. I have to test my $5.50 135/2.8 yet.
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Old 02-04-2010, 10:06 AM
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Quote:
Originally Posted by DavidU View Post
Interesting thread here Bojan. I have to test my $5.50 135/2.8 yet.
Do you have it on your camera already?
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Old 02-04-2010, 10:15 AM
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Not yet, I'm waiting for a 300D I am borrowing from a friend.
May be I could show it to you?
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Do you have it on your camera already?
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Old 02-04-2010, 10:25 AM
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No worries, just say when and where :-)
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Old 02-04-2010, 10:27 AM
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Tamron 400mm F6.3 dismantled..

Now this is going to be tough..
I have the front group out out the tube (it seems it is just an ordinary achromatic doublet, ~300mm FL. The rest of optics in the system is rear group of two elements, functioning as a field flattener), but I can't unscrew the retaining ring of the cell, it is too tight..
I will have to make a special tool to pull it apart, and this will take some time...
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Old 04-04-2010, 06:20 PM
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After relaxing the very tight retaining ring, not much has changed in terms of astigmatism.
It seems this lens will be useful as guider only... or perhaps for Solar eclipse, since it is very sharp at f11 and beyond.
Well, it's been $30 only.. not bad after all :-)
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